Author Topic: Heat treatment FAQ thingy - LOOOOONG post - 4 parts  (Read 15596 times)

GuyFawkes

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Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« on: May 27, 2006, 01:39:24 AM »
Gonna put this here, this is info from 1924, but it still holds true


Hardening

Critical Temperatures. -- The "critical points" of carbon tool steel are the temperatures at which certain changes in the chemical composition of the steel take place, during both heating and cooling. Steel at normal temperatures has its carbon (which is the chief hardening element) in a certain form called pearlite carbon, and if the steel is heated to a certain temperature, a change occurs and the pearlite becomes martensite or hardening carbon. If the steel is allowed to cool slowly, the hardening carbon changes back to pearlite. The points at which these changes occur are the decalescence and recalescence or critical points, and the effect of these molecular changes is as follows: When a piece of steel is heated to a certain point, it continues to absorb heat without appreciably rising in temperature, although its immediate surroundings may be hotter than the steel. This is the decalescence point. Similarly, steel cooling slowly from a high heat will, at a certain temperature, actually increase in temperature, although its surroundings may be colder. This takes place at the recalescence point. The recalescence point is lower than the decalescence point by anywhere from 85 to 215 degrees F., and the lower of these points does not manifest itself unless the higher one has first been fully passed. These critical points have a direct relation to the hardening of steel. Unless a temperature sufficient to reach the decalescence point is obtained, so that the pearlite carbon is changed into a hardening carbon, no hardening action can take place; and unless the steel is cooled suddenly before it reaches the recalescence point, thus preventing the changing back again from hardening to pearlite carbon, no hardening can take place. The critical points vary for different kinds of steel and must be determined by tests in each case. It is the variation in the critical points that makes it necessary to heat different steels to different temperatures when hardening.

Determining Hardening Temperatures. -- The temperatures at which decalescence occurs vary with the amount of carbon in the steel, and are also higher for high-speed steel than for ordinary crucible steel. The decalescence point of any steel marks the correct hardening temperature, and the steel should be removed from the source of heat as soon as is has been heated uniformly to this temperature. Heating the piece slightly above this point may be desirable, either to insure the structural change being complete throughout, or to allow for any slight loss of heat which may occur in transferring the work from the furnace to the quenching bath. When steel is heated above the temperature of decalescence, it is non-magnetic. If steel is heated to a bright red, it will have no attraction for a magnet or magnetic needle, but at about a "cherry-red," it regains its magnetic property. This phenomenon is sometimes taken advantage of for determining the correct hardening temperature, and the use of a magnet is to be recommended if a pyrometer is not available. The only point requiring judgment is the length of time the steel should remain in the furnace after it has become non-magnetic, as the time varies with the size of the piece. When applying the magnetic needle test, be sure that the needle is not being attracted by the tongs.

The correct hardening temperature for any carbon steel can be determined accurately by the use of a pyrometer. A form of apparatus often used for testing specimens of steel consists of a small electric furnace in which to heat the specimen, and a special thermo-couple pyrometer (see "Pyrometers") for indicating the range of temperatures through which the steel passes. The pyrometer consists of a thermo-couple, connecting leads and an indicating meter. The thermo-couple is of small wire so as to respond readily to any slight temperature variation. When testing a piece of steel with this apparatus, the temperature indicated by the meter rises uniformly until the decalescence point is reached. At this temperature, the indicating pointer of the meter remains stationary, the added heat being consumed by internal changes. When these changes are completed, the temperature again rises, the length of the elapsed period depending upon the speed of heating. The temperature at which this pause in the motion of the indicating pointer occurs should be carefully noted. To obtain the lower critical point, the temperature is first raised about 100 degrees F. above the decalescence point; the steel is then removed from the furnace and is allowed to cool. The decrease of temperature is immediately shown by the fall of the meter pointer, and, at a temperature somewhat below the decalescence point, there is again a noticeable lag in the movement of the pointer. The temperature at which the movement ceases entirely is the recalescence point. Immediately following, there may occur a slight rising movement of the pointer. During these intervals of temperature lag, both during heating and cooling, there may occur a small fluctuation in temperature; hence, a definite point in each of these intervals should be considered when a test is made, both critical temperatures being taken at the time the pointer first becomes stationary.

While it is possible to harden steel within a temperature range of about 200 degrees and obtain what might seem to be good results, the best results are obtained within a very narrow range of temperatures which are close to the decalescence point. The hardening temperature for both low tungsten and carbon steel can be located with accuracy, and the complete change from soft to hard occurs within a range of 10 degrees F. or less. After the temperature has been increased more than from 35 to 55 degrees F. above the hardening point, the hardness of steel is lessened by a higher temperature, provided the heating is sufficiently prolonged for the steel to be thoroughly heated.

Hardening or Quenching Baths. -- When steel heated above the critical point is plunged into a cooling bath, the rapidity with which the heat is absorbed by the bath affects the degree of hardness; hence, baths of various kinds are used for different classes of work. Clear cold water is commonly employed and brine is sometimes substituted to increase the degree of hardness. Sperm [whale oil] and lard oil baths are used for hardening springs, and raw linseed oil is excellent for cutters and other small tools. The effect of a bath upon steel depends upon its composition, temperature, and volume. The bath should be amply large to dissipate the heat rapidly, and the temperature should be kept about constant, so that successive pieces will be cooled at the same rate. Greater hardness is obtained from quenching in salt brine, and less in oil, than is obtained by the use of water. This is due to the difference in the heat-dissipating qualities of these substances. When water is used, it should be "soft," as unsatisfactory results will be obtained with "hard" water. If thin pieces are plunged into brine, there is danger of cracking, owing to the suddenness of the cooling.

The temperature of the hardening bath has a great deal to do with the hardness obtained. In certain experiments a bar quenched at 41 degrees F. showed a scleroscopic hardness of 101. A piece from the same bar quenched at 75 degrees F. had a hardness of 96, while, when the temperature of the water was raised to 124 degrees F., the bar was decidedly soft, having a hardness of only 83. The higher the temperature of the quenching water, the more nearly does its effect approach that of oil, and if boiling water is used for quenching, it will have an effect even more gentle than that of oil; in fact, it would leave the steel nearly soft. With oil baths, the temperature changes have little effect on the degree of hardness. Parts of irregular shape are sometimes quenched in a water bath that has been warmed somewhat to prevent sudden cooling and cracking. A water bath having one or two inches of oil on top is sometimes employed to advantage for tools made of high-carbon steel, as the oil through which the work first passes reduces the sudden action of the water.

Irregularly shaped parts should be immersed so that the heaviest of thickest section enters the bath first. After immersion, the part to be hardened should be agitated in the bath; the agitation reduces the tendency of the formation of a vapor coating on certain surfaces, and a more uniform rate of cooling is obtained. The work should never be dropped to the bottom of the bath until quite cool. High-speed steel is cooled for hardening either by means of an air blast or an oil bath. Both fresh and salt water are also used, although, as a general rule, water should not be used for high-speed steel. Various oils, such as cotton-seed, linseed, lard, whale oil, kerosene, etc., are also employed; many prefer cotton-seed oil. Linseed has the objection of becoming gummy, and lard oil has a tendency to become rancid. Whale oil or fish oil give satisfactory results, but have offensive odors, although this can be overcome by the addition of about three per cent of heavy "tempering" oil.

A quenching solution of a 3 per cent sulphuric acid and 97 per cent of water will make hardened carbon steel tools come out of the quenching bath bright and clean. This bath is sometimes used for drills and reamers which are not to be polished in the flutes after hardening. Another method of cleaning drills and similar tools after hardening is to pickle them in a solution of 1 part hydrochloric acid and 9 parts water. Still another method is to use a heating bath consisting of 2 parts barium chloride and 3 parts potassium chloride. This method is satisfactory for reamers and tools which are not to be polished in the flutes after hardening.

Oil Quenching Baths. -- Oil is used very extensively as a quenching medium as it gives the best proportion between hardness, toughness and warpage for standard steels. Special compounded oils of the soluble type are now used in many plants instead of such oils as fish oil, linseed oil, cotton-seed oil, etc. The soluble properties enable the oil to make an emulsion with water. A good quenching oil should possess a flash and fire point sufficiently high to be safe under the conditions used and 350 degrees F. should be about the minimum point. The specific heat of the oil regulates the hardness and toughness of the quenched steel, and the greater the specific heat, the harder the steel will be. Specific heats of quenching oils vary from 0.20 to 0.75, the specific heats of fish, animal, and vegetable oils usually being from 0.2 to 0.4, and of soluble and mineral oils, from 0.5 to 0.7. The oil should not contain water, gum when used, have a disagreeable odor or become rancid. A great many concerns use paraffin and mineral oils for quenching, while a few use crude fuel oils. The quantity of steel that can be quenched per gallon of oil depends on the fluidity of the oil, or its draining qualities. The so-called "refrigerating qualities" are really the capacity of the oil to remove the heat from the steel at a fast rate and then radiate its own heat to the atmosphere.

Tanks for Quenching Baths. -- The main point to be considered in a quenching bath is to keep it at a uniform temperature, so that each successive piece quenched will be subjected to the same heat. The next consideration is to keep the bath agitated, so that it will not be of different temperatures in different places; if thoroughly agitated and kept in motion, as is the case with the bath shown in Fig. 1, it is not even necessary to keep the pieces in motion in the bath, as steam will not be likely to form around the pieces quenched. Experience has proved that if a piece is held still in a thoroughly agitated bath, it will come out much straighter than if it has been moved around in an unagitated bath. This is an important consideration, especially when hardening long pieces. It is, besides, no easy matter to keep heavy and long pieces in motion unless it be done by mechanical means.

In Fig. 1 is shown a water or brine tank for quenching baths. Water is forced by a pump or other means through the supply tube into the intermediate space between the outer and inner tank. From the intermediate space it is forced into the inner tank through holes as indicated. The water returns to the storage tank by overflowing from the inner tank into the outer one and then through the overflow pipe as indicated. In Fig. 3 is shown another water or brine tank of a more common type. In this case the water or brine is pumped from the storage tank and continuously returned to it. If the storage tank contains a large volume of water, there is no need of a special means for cooling. Otherwise, arrangements must be made for cooling the water after it has passed through the tank. The bath is agitated by the force with which the water is pumped into it. The holes at A are drilled at an angle, so as to throw the water toward the center of the tank. In Fig. 2 is shown an oil quenching tank in which water is circulated in an outer surrounding tank for keeping the oil bath cool. Air is forced into the oil bath to keep it agitated. Fig. 6 shows a water and oil tank combined. The oil is kept cool by a coil passing through it in which water is circulated, which later passes into the water tank. The water and oil baths in this case are not agitated.

Hardening High-speed Steel. -- High-speed steel must be heated to a much higher temperature than carbon steel. A temperature of from 1400 degrees to 1600 degrees F. is sufficient for carbon steel; high-speed steel requires from 1800 degrees to 2200 degrees F. The usual method of hardening a high-speed steel tool, such as a turning or planing tool, is to heat the cutting end slowly to a temperature of about 1800 degrees F., and then more rapidly to about 2200 degrees F., or until the end is at a dazzling white heat and shows signs of melting down. The tool point is then cooled either by plunging it in a bath of oil (such as linseed or cotton-seed) or by placing the end in a blast of dry air. When an oil quenching bath is used, its temperature is varied from the room temperature to 350 degrees F., according to the steel used. The exact treatment varies for different steels and it is advisable to follow the directions given by the steel makers. High-speed steel parts that would be injured by a temperature high enough to melt the edges are hardened by heating slowly to as high a degree as possible and then cooling, as described. Formerly, the air blast was recommended by most steel makers, but oil is now extensively used. Care should be taken to quench the heated steel rapidly after removing from the source of heat. The barium-chloride bath has been used quite extensively for heating machine-finished, high-speed steel tools preparatory to hardening. The barium-chloride forms a thin coating on the steel, which is thus protected from oxidation while being transferred from the heating bath to the cooling bath. Tests have demonstrated, however, that barium-chloride baths have certain disadvantages for heating high-speed steel preparatory to hardening, because if the steel is heated to the required temperature, the surface of the tool is softened to some extent. These tests indicate that whenever this salt is used as a heating bath, the temperature should not be raised above 2050 degrees F. When about 0.010 inch is ground from the cutting edges of the tools, the influence of heating in barium chloride may be negligible. (See "Disadvantages of Barium-chloride Bath".)

Very satisfactory results in hardening high-speed steel tools, such as cutters, drills, etc., have been obtained by the following method: First pre-heat in an oven-type gas furnace to from 1300 degrees to 1500 degrees F.; then transfer the steel to another gas furnace having a temperature varying from about 2000 degrees to 2200 degrees F.; when the steel has attained this temperature, quench in a metallic salt bath having a temperature varying from 600 degrees to 1200 degrees F., depending on the kind of high-speed steel used. The piece to be hardened should be stirred vigorously in the bath until it has obtained the temperature of the bath; then it is cooled, preferably in the air, and requires no further tempering; or it may be put directly into the tempering oil, which should be at a temperature anywhere between 100 and 600 degrees F. The tempering bath is then gradually raised to the heat required for tempering. The salt bath used for quenching should be calcium chloride, sodium chloride and potassium ferro-cyanide, in proportions depending upon the required heat. Various kinds of steel require different temperatures for the metallic salt bath. After the temper of the tool has been drawn in the oil, the work is dipped in a tank of caustic soda, and then in hot water. This will remove all oil which might adhere to the tools, and is a method that applies to all tools after being tempered.

The Taylor-White Process. -- This process of hardening high-speed steel is, in brief, as follows: The first method, commonly known as the "high-heat treatment," is effected by heating the tool slowly to 1500 degrees F., and then rapidly from that temperature to just below the melting point, after which the tool is quickly cooled below 1550 degrees. At this point, the cooling is continued either fast or slow to the temperature of the air. It is important to avoid any increase of temperature during the cooling period. The second or "low-heat treatment" consists in re-heating a tool which has had the high-heat treatment to a temperature between 700 and 1240 degrees F., preferably in a lead bath, for a period of five minutes. The tool is then cooled to the temperature of the air either rapidly or slowly.

Heat-Treatment of Spring Steel. -- A number of experiments were made at the Baldwin Locomotive Works, to determine the effect of different heat-treatments on the transverse elastic limit and the modulus of elasticity of steels commonly used for locomotive springs. The points investigated were the effect of annealing, the comparative effect of quenching in water or oil, and the effect of re-heating the steel to various temperatures after complete cooling in water or oil. The steel used for the tests was basic open-hearth spring steel of the following composition: Carbon, 1.01 per cent; manganese, 0.38 per cent; phosphorus, 0.032 per cent; sulphur, 0.032 per cent; silicon, 0.13 per cent. This steel was found to reach its decalescence point at 1360 degrees F. Previous experiments had shown that, for annealing, it should be heated 40 degrees or 50 degrees above this temperature, and for hardening, from 50 degrees to 100 degrees above the point of decalescence. For the experiments, the following temperatures were used: For annealing, 1400 degrees F.; for quenching in oil, 1450 degrees F.; for quenching in water, 1425 degrees F. The results obtained are given in the table, "Results of Tests on Spring Steel".
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GuyFawkes

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Re: Heat treatment FAQ thingy - LOOOOONG post - 3 parts
« Reply #1 on: May 27, 2006, 01:40:23 AM »

Heat-Treatment of Spring Steel. -- A number of experiments were made at the Baldwin Locomotive Works, to determine the effect of different heat-treatments on the transverse elastic limit and the modulus of elasticity of steels commonly used for locomotive springs. The points investigated were the effect of annealing, the comparative effect of quenching in water or oil, and the effect of re-heating the steel to various temperatures after complete cooling in water or oil. The steel used for the tests was basic open-hearth spring steel of the following composition: Carbon, 1.01 per cent; manganese, 0.38 per cent; phosphorus, 0.032 per cent; sulphur, 0.032 per cent; silicon, 0.13 per cent. This steel was found to reach its decalescence point at 1360 degrees F. Previous experiments had shown that, for annealing, it should be heated 40 degrees or 50 degrees above this temperature, and for hardening, from 50 degrees to 100 degrees above the point of decalescence. For the experiments, the following temperatures were used: For annealing, 1400 degrees F.; for quenching in oil, 1450 degrees F.; for quenching in water, 1425 degrees F. The results obtained are given in the table, "Results of Tests on Spring Steel".

As the table shows, the highest elastic limit obtainable, when heating to 1450 degrees and quenching in oil, was 187,400 pounds per square inch, which was obtained when the temper was not drawn after quenching. The higher the tempering temperature, the lower the elastic limit fell. When the steel was quenched at 1425 degrees F. in water, and the temper was not drawn, it was brittle and broke when deflected 0.175 inch. Drawing the temper to 600 degrees F., after hardening in water, gave an elastic limit of 219,800 pounds. When the temper was drawn to 1050 degrees F., the elastic limit dropped to 180,700 pounds, but the test piece did not break at 1.1 inch deflection. The tests show that the modulus of elasticity is practically constant, and apparently independent of heat-treatment. The conclusions are that steel of 1 per cent carbon, when quenched in cold water at its critical temperature or slightly above, is usually too hard and brittle for making springs or tools. The tests also show that the elastic limit of 1 per cent carbon steel can be made to vary from 78,500 to 240,800 pounds per square inch, by changes in the heat-treatment, and that very small changes in temperature when drawing the temper are sufficient to affect the elastic limit of the steel. Hence, to obtain good results, it is necessary to have means of heating the steel uniformly to the proper temperature, as well as cooling at the desired rate in a medium, the temperature and heat conductivity of which can be kept reasonably constant.

Local Hardening. -- One method of hardening locally is to cover the part that is to remain soft with a thin metal shield, so that it prevents the surface from being suddenly cooled by the direct action of the cooling medium. The steam or vapor which forms beneath the cover prevents the cooling medium from entering until the work has cooled sufficiently to prevent hardening; hence, a rather loose-fitting shield is desirable. The shield should be made of sheet iron or steel of about No. 29 gage (0.014 inch), for ordinary work. It is composed of one or more pieces, depending on the shape of the part, and, when several pieces are required, they can be bound together with wires or rivets. Of course, the surfaces to be hardened are left exposed. The heating should be done in a furnace or open-forge fire. A lead bath should not be used, because the hot lead beneath the shield will cause an explosion when the part is cooled. The quenching bath can be the same as when the shield is not used.

Local hardening is also effected by the application of a compound called "Enamelite" to the parts which are to remain soft. This compound, for tool steel, is in the form of a powder which is mixed with hot water to form a paste. It has the property of clinging to the steel and liberating hydrogen (the greatest known non-conductor) when the heated steel is plunged into the water. This causes the steel to retain its heat long enough to escape the chill, so that it remains soft where the enamelite has been applied.

Defects in Hardening. -- Uneven heating is the cause of most of the defects in hardening. Cracks of a circular form, from the corners or edges of a tool, indicate uneven heating in hardening. Cracks of a vertical nature and dark-colored fissures indicate that the steel has been burned and should be put on the scrap heap. Tools which have hard and soft places have been either unevenly heated, unevenly cooled, or "soaked", a term used to indicate prolonged heating. A tool not thoroughly moved about in the hardening fluid will show hard and soft places, and have a tendency to crack. Tools which are hardened simply by dropping them to the bottom of the tank, sometimes have soft places, owing to contact with the floor or sides of the tank. They should be thoroughly quenched before dropping. when a tool appears soft and will not harden, it probably has been decarbonized on the surface by too much heat or by soaking too long. The surface must be removed before the tool will harden properly. Tools are sometimes soft because the cooling bath is not large enough for the tools being hardened, and becomes too warm after a few pieces have been quenched.

Overheated Steel. -- Overheated steel that is not actually burned can be partly restored by heating to the proper heat, and allowing it to cool slowly in hot ashes or sand; when cold, the steel is hardened again at the proper hardening heat. Tools treated in this way are not as good as when treated at the proper heat throughout, but they are partially restored, and if the overheating originally took place in forging, the risk of cracking in hardening will be lessened by adopting the process mentioned. Care should be taken that the tuyere of the forge is well covered when heating tool steel; a tool coming in direct contact with the air blast will become surface burned, show soft places in hardening and wear badly in use.

Scale on Hardened Steel. -- The formation of scale on the surface of hardened steel is due to the contact of oxygen with the heated steel; hence, to prevent scale, the heated steel must not be exposed to the action of the air. When using an oven heating furnace, the flame should be so regulated that it is not visible in the heating chamber. The heated steel should be exposed to the air as little as possible, when transferring it from the furnace to the quenching bath. An old method of preventing scale and retaining a fine finish on dies is as follows: Fill the die impression with powdered boracic acid and place near the fire until the acid melts; then add a little more acid to insure covering all the surfaces. The die is then hardened in the usual way. If the boracic acid does not come entirely off in the quenching bath, immerse the work in boiling water. Dies hardened by this method are said to be as durable as those heated without the acid

Tempering
Tempering by the Color Method. -- Hardened steel can be tempered or made softer and less brittle by re-heating it to a certain temperature (depending on the nature of the steel and its intended use), and then cooling. When steel is tempered by the color method, the temper is gaged by the colors formed on the surface as the heat increases. First the surface is brightened to reveal the color changes, and then the steel is heated either by placing it upon a piece of red-hot metal, a gas-heated plate or in any other available way. As the temper increases, various colors appear on the brightened surface. First there is a faint yellow which blends into straw, then light brown, dark brown, purple, blue and dark blue, with various intermediate shades. The temperatures corresponding to the different colors and shades are given in the table on temperatures and colors for tempering. Turning and planing tools, chisels, etc., are commonly tempered by first heating the cutting end to a cherry-red, and then quenching the part to be hardened. When the tool is removed from the bath, the heat remaining in the unquenched part raises the temperature of the cooled cutting end until the desired color (which will show on a brightened surface) is obtained, after which the entire tool is quenched. The foregoing methods are convenient, especially when only a few tools are to be treated, but the color method of gaging temperatures is not dependable, as the color is affected, to some extent, by the composition of the metal. The modern method of tempering, especially in quantity, is to heat the hardened parts to the required temperature in a bath of molten lead, heated oil, or other liquids; the parts are then removed from the bath and quenched. The bath method makes it possible to heat the work uniformly, and to a given temperature with close limits.

High Temperatures judged by Color, and Colors for Tempering
Degrees Centi- grade   Degrees Fahren- heit    High Temperatures judged by Color   
   Degrees Centi- grade   Degrees Fahren- heit    Colors for Tempering
400   752   Red heat, visible in the dark   
   221.1   430   Very pale yellow
474   885   Red heat, visible in the twilight   
   226.7   440   Light yellow
525   975   Red heat, visible in the daylight   
   232.2   450   Pale straw-yellow
581   1077   Red heat, visible in the sunlight   
   237.8   460   Straw-yellow
700   1292   Dark red   
   243.3   470   Deep straw-yellow
800   1472   Dull cherry-red   
   248.9   480   Dark yellow
900   1652   Cherry-red   
   254.4   490   Yellow-brown
1000   1832   Bright cherry-red   
   260.0   500   Brown-yellow
1100   2012   Orange-red   
   265.6   510   Spotted red-brown
1200   2192   Orange-yellow   
   271.1   520   Brown-purple
1300   2372   Yellow-white   
   276.7   530   Light purple
1400   2552   White welding heat   
   282.2   540   Full purple
1500   2732   Brilliant white   
   287.8   550   Dark purple
1600   2912   Dazzling white (bluish-white)    
   293.3   560   Full blue
   298.9   570   Dark blue

Tempering in Oil. -- Oil baths are extensively used for tempering tools (especially in quantity), the work being immersed in oil heated to the required temperature, which is indicated by a thermometer. It is important that the oil have a uniform temperature throughout and that the work be immersed long enough to acquire this temperature. Cold steel should not be plunged into a bath heated for tempering, owing to the danger of cracking it. The steel should either be pre-heated to about 300 degrees F., before placing it in the bath, or the latter should be at a comparatively low temperature before immersing the steel, and then be heated to the required degree. A temperature of from 650 degrees to 700 degrees F. can be obtained with heavy tempering oils; for higher temperatures, a lead bath is generally used. A tempering oil which has given satisfactory results in practice has the following characteristics: Composition, mineral oil, 94 per cent; saponifiable oil, 6 per cent; specific gravity 0.920; flash point, 550 degrees F.; fire test, 625 degrees F. The foregoing figures apply to new oil. When the oil has been used long enough to be rendered practically useless, an analysis shows the following changes: Composition, mineral oil, 30 per cent; saponifiable oil, 70 per cent; specific gravity, 0.950; flash point, 475 degrees F.; fire test, 550 degrees F. The great difference in the composition of new and old oil is due to the loss of mineral oil, resulting from the high heats to which tempering oil is frequently or constantly subjected; hence, the durability of the tempering bath can be increased by occasionally adding new mineral oil.

Flash Point and Fire Test. -- The distinction between the "flash point" and the "fire test" of an oil is as follows: The flash point is the temperature at which the amount of vapor given off is sufficient to form an inflammable or explosive mixture with the air over the surface of the oil, so that the gaseous mixture ignites and burns with a momentary flash when a flame is applied. As the temperature of the oil rises, more vapor is given off, and then the production of vapor is rapid enough to maintain a continuous flame, the oil takes fire and burns. The temperature at which this occurs is called the fire test, firing point or burning point of the oil.

Tempering in a Lead Bath. -- The lead bath is commonly used for heating steel preparatory to tempering, as well as for hardening. The bath is first heated to the temperature at which the steel should be tempered; the pre-heated work is then placed in the bath long enough to acquire this temperature, after which it is removed and cooled. As the melting temperature of pure lead is 618 degrees F., tin is commonly added to it to lower the temperature sufficiently for tempering. Reductions in temperature can be obtained by varying the proportions of lead and tin,

To Prevent Lead from Sticking to Steel. -- To prevent hot lead from sticking to parts heated in it, mix common whiting with wood alcohol, and paint the part that is to be heated. Water can be used instead of alcohol, but in that case the paint must be thoroughly dry, as otherwise the moisture will cause the lead to "fly". Another method is to make a thick paste according to the following formula: Pulverized charred leather, 1 pound; fine wheat flour, 1-1/2 pound; fine table salt, 2 pounds. Coat the tool with this paste and heat slowly until dry, then proceed to harden. Still another method is to heat the work to a blue color, or about 600 degrees F., and then dip it in a strong solution of salt water, prior to heating in the lead bath. The lead is sometimes removed from parts having fine projections or teeth, by using a stiff brush just before immersing in the cooling bath. This is necessary to prevent the formation of soft spots.

Pots for Lead Baths. -- Melting pots for molten lead baths, etc., should, preferably, be made from seamless drawn steel rather than from cast iron. Experience has shown that the seamless pots will sometimes withstand six months' continuous service, whereas cast iron pots will last, on average, only a few days, under like conditions. Cast steel melting pots, if properly made, are as durable as those made of seamless drawn steel.

Tempering in Sand. -- The sand bath is used for tempering certain classes of work. One method is to deposit the sand on an iron plate which is heated by suitable means as indicated in the accompanying illustration, Fig. 9. With this method of tempering, tools such as boiler punches, etc., can be given a varying temper by placing them endwise in the sand. As the temperature of the sand bath is higher toward the bottom, a tool can be so placed that the color of the lower end will be a deep dark blue when the middle portion is a very dark straw, and the working end or top a light straw color, the hardness gradually increasing from the bottom up. Tools to be heated by this method must be polished, as the temper is judged by the color. for tempering parts in quantity, sand tempering machines have been developed. One well-known design has a horizontal revolving cylinder containing rows of perforated pockets which become filled with sand in steady streams upon the work. The drum revolves at different rates of speed for different classes or work, usually making from 3 to 10 revolutions per minute. The heat is supplied by a gas burner. The machine is equipped with a thermometer, which does not indicate the actual temperature of the sand, but a somewhat lower temperature than would be required for the same tempering color, under other conditions. The thermometer reading, therefore, is relative and not a precise indication of the tempering temperature.

Tempering Furnaces. -- In tempering furnaces the only really important consideration is to insure that the furnace is so built as to heat the bath uniformly throughout. It is doubtful if there can be found a tempering furnace on the market that will fill this requirement entirely, although many give good results in general. It is never safe, however, to let any tools being tempered rest against the bottom or sides of the tank, as no matter how scientifically the furnace may be built these parts are, in most cases, hotter than the fluid itself. It is, of course, just as important not to let the thermometer rest against any of these parts in order to insure correct readings. After the pieces tempered are taken out of the oil bath, they should immediately be dipped in a tank of caustic soda (not registering over 8 or 9), and after that in a tank of hot water. This will remove all oil which might adhere to the tools.

Fig. 7 shows an ordinary type of tempering furnace. In this the flame does not strike the walls of the tank directly. The tools to be tempered are laid in a basket which is immersed in the oil. In Fig. 8 is shown a tempering furnace in which means are provided for preventing the tools to be tempered from coming in contact with the walls or bottom of the furnace proper. The basket holding the tools is immersed in the inner perforated oil tank. The same arrangement can, of course, be applied to the furnace shown in Fig. 7.
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GuyFawkes

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Re: Heat treatment FAQ thingy - LOOOOONG post - 3 parts
« Reply #2 on: May 27, 2006, 01:41:11 AM »
In tempering, the best method is to immerse the pieces to be tempered in the oil before starting to heat the latter. They are then heated with the oil.

Tempering High-Speed Steel. -- Heavy high-speed tools having well-supported cutting edges (such as large planing or turning tools) are often used after hardening and grinding, without tempering. Tools that are comparatively weak should be toughened by tempering to suit the particular service required. The steel is generally heated in a bath of lead, oil, or salts. The tempering temperatures recommended by high-speed steel manufacturers usually vary from 400 degrees to 1000 degrees F., so that definite information should be obtained from the maker of the particular steel to be used. One well-known manufacturer recommends re-heating hardened lathe tools to 1000 degrees F., and tools such as milling cutters, taps, dies, etc., to 500 degrees or 650 degrees F. According to another manufacturer, it is desirable to temper most high-speed steel tools in order to make them more resistant to shocks, the drawing temperatures varying from 600 degrees to 1100 degrees F. Still another steel maker advises tempering lathe and similar tools to 950 degrees F. Lower temperatures varying from 400 degrees to 500 degrees F. are sometimes recommended for tools such as cutters, dies, reamers, etc.

Annealing

Annealing Steel. -- The purpose of annealing is not only to soften steel for machining, but to remove all strains incident to rolling or hammering. A common method of annealing is to pack the steel in a cast-iron box containing some material, such as powdered charcoal, charred bone, charred leather, slaked lime, sand, fireclay, etc. The box and its contents are then heated in a furnace to the proper temperature, for a length of time depending upon the size of the steel. After heating, the box and its contents should be allowed to cool at a rate slow enough to prevent any hardening. It is essential, when annealing, to exclude the air as completely as possible while the steel is hot, to prevent the outside of the steel from becoming oxidized.

The temperature required for annealing should be slightly above the critical point, which varies for different steels. Low-carbon steel should be annealed at about 1650 degrees F., and high-carbon steel at between 1400 degrees and 1500 degrees F. This temperature should be maintained just long enough to heat the entire piece evenly throughout. Care should be taken not to heat the steel much above the decalescence or hardening point. When steel is heated above this temperature, the grain assumes a definite size for that particular temperature, the coarseness increasing with an increase in temperature. Moreover, if steel that has been heated above the critical point is cooled slowly, the coarseness of the grain corresponds to the coarseness at the maximum temperature; hence, the grain of annealed steel is coarser, the higher the temperature to which it is heated above the critical point.

If only a small piece of steel or a single tool is to be annealed, this can be done by building up a firebrick box in an ordinary blacksmith's fire, placing the tool in it, covering over the top, then heating the whole, covering with coke and leaving it to cool over night. Another quick method is to heat the steel to a red heat, bury it in dry sand, sawdust, lime or hot ashes, and allow it to cool. Quick annealing can also be partially effected by heating the piece to a dull black-red and plunging it into hot water. This method is not to be recommended.

Annealing High-speed Steel. -- The following method of annealing high-speed steel is recommended by one of the largest high-speed tool steel manufacturers in America, and corresponds in all important points to the practice of most other manufacturers: Use an iron box or pipe of sufficient size to allow at least one-half inch of packing between the pieces of steel to be annealed and the sides of the box or pipe. It is not necessary that each piece be kept separate from every other piece, but only that the steel be prevented from touching the dies of the annealing pipe or box. Pack carefully with powdered charcoal, fine dry lime or mice (preferably charcoal), and cover with an air-tight cap, or lute with fireclay; heat slowly to a full red heat (about 1475 degrees or 1500 degrees F.) and keep at this heat from 2 to 8 hours, depending upon the size of the pieces to be annealed. A piece 2 by 1 by 8 inches requires about three hours. Cool slowly as possible, and do not expose to the air until cold. A good way is to allow the box or pipe to remain in the furnace until cold.

A series of experiments made to determine the proper temperature to which to heat high-speed steel for annealing, showed the following results: When the steel was heated to below 1250 degrees F. and slowly cooled, as in annealing, it retained the original hardness and brittleness imparted in forging. When heated to between 1250 degrees and 1450 degrees F., the Brinnell test indicated that the steel was soft, but impact tests proved that the steel still retained its original brittleness. However, when heated to between 1475 degrees and 1525 degrees F., the steel became very soft; it had a fine-grained fracture, and all of the initial brittleness had entirely disappeared. In carrying these tests further, to 1600 degrees, 1750 degrees, and 1850 degrees F., it was found that the steel became very soft, but there was a gradual increase in brittleness and in the size of the grain, until at 1850 degrees F. the steel again became as brittle as unannealed steel. Dried air-slaked lime was used as a packing medium in making these tests.

Casehardening
Casehardening is the process of hardening the surface of low-carbon steel or iron by carbonizing the surface. When parts must be casehardened in quantity, they should be packed in an iron box contained some carbonaceous material. The box and its contents are then heated for a certain length of time, depending upon the depth of hardened surface desired and the nature of the material. The heat for casehardening varies from 1600 degrees to 1800 degrees F., the temperature being governed, to some extent, by the requirements. The absorption of carbon begins when the steel reaches about 1300 degrees F. At the end of the carbonizing period, the box is withdrawn from the furnace and is allowed to become quite cold. The articles are then placed in a muffle furnace and are re-heated to about 1470 degrees F., after which they are quenched in cold water, tepid water or oil, the bath depending upon the purpose for which the parts are to be used. For ordinary purposes, clear cold water is satisfactory. To produce a very hard surface, use salt water. When a hard surface is not as important as a tough core, use an oil bath. The practice of allowing the box and its contents to cool, and then re-heating prior to quenching, is based on the old rule of hardening on a rising heat. This method gives more satisfactory results than that of dumping the parts into a tank of cold water at the end of the carbonizing period.

Different Methods of Casehardening. -- A committee of the American Society for Testing Materials recommended the following practice for casehardening carbon-steel parts. Four different conditions were considered, varying from the heat-treatment that would give the hardest surface and the least strength, to that which would give the greatest strength with the least hardness of surface: When a hard case is the the only requirement and lack of toughness or even brittleness is unimportant, the articles may be quenched by emptying the contents of the casehardening boxes directly into cold water or oil. In this way both the core and the case are coarsely crystallized and the strength is reduced. If the articles are allowed to cool to a temperature slightly exceeding the critical range of the casehardening, usually from 800 degrees to 825 degrees C. (1472 degrees to 1517 degrees F.), and then quenched, the core and case still remain crystalline, but the danger of distortion or cracking in the quenching bath is reduced and the strength is somewhat increased. The next recommended method is to increase the toughness and strength of the article and refine the case. The articles are allowed to cool slowly in the carbonizing pot to a temperature of about 650 degrees C. (1200 degrees F.), are then re-heated to a temperature slightly exceeding the lower critical point of the case, which usually is from 775 degrees to 825 degrees C. (1427 degrees to 1517 degrees F.) and are then quenched in water or oil. The should be removed from the quenching bath before the temperature has fallen below 100 degrees C. (212 degrees F.). By allowing them to cool slowly to a temperature of about 650 degrees C. (1200 degrees F.) and then re-heating to a temperature of about 900 degrees to 950 degrees C. (1652 to 1740 degrees F.), followed by quenching in oil, from which they are removed before they have dropped below a temperature of 100 degrees C. (212 degrees F.), then re-heating to about 800 degrees C. (1472 degrees F.) and again quenching in water or oil, both the case and the core will be thoroughly refined and their toughness greatly increased. In order to reduce the hardening stress created by quenching, the objects, as a final treatment, may be tempered by re-heating them to a temperature not exceeding 200 degrees C. (392 degrees F.).

Casehardening Packing Boxes. -- Hardening boxes are made of either cast or wrought iron. The box should not be too large, as pieces in the center may then not become sufficiently carbonized. For small articles, a box measuring 12 by 10 by 8 inches is large enough, and for such parts as bicycle axles, pedal pins, etc., the maximum size should be about 18 by 12 by 11 inches. The boxes should have a plate lid which must be luted or sealed with clay after the contents are packed.

Carbonizing Materials. -- The carbonizing materials in general use are charred leather, powdered bone, cyanide of potassium, wood and "animal" charcoal, prussiate of potash and other compositions consisting of mixtures of carbonaceous matter and certain cyanides or nitrates. For slight hardening, cyanides are often used. Charred leather gives good results, although poorly charred leather or that made from old boots, belting, etc., should not be used. A mixture preferred by some to charred leather consists of 60 parts of wood charcoal and 40 parts of barium carbonate. The casehardening compound employed at the Altoona Shops of the Pennsylvania Railroad is made in the following proportions: 11 pounds prussiate of potash; 30 pounds sal-soda; 20 pounds coarse salt; 6 bushels powdered charcoal (hickory preferred). These ingredients are mixed together, 30 quarts water being added.

Steels for Casehardening. -- The percentage of carbon in steels ordinarily used for parts to be casehardened varies, as a general rule, from 0.15 to 0.20 per cent. If the carbon exceeds 0.20 per cent, it tends to give a hard instead of a soft core. If the carbon content is too low, the steel may be difficult to machine; hence, steels containing as much as 0.20 to 0.25 per cent carbon are often used for casehardening. For general work, steel of the following composition will be found satisfactory: Carbon, 0.16 to 0.20 per cent; manganese, less than 0.35 per cent; silicon, not over 0.30 per cent. The sulphur and phosphorus should be as low as possible, not exceeding 0.1 per cent.

Degree and Depth of Hardened Surface. -- The percentage of carbon contained in the casehardened surface should vary according to requirements. A high-carbon case containing 1.1 per cent carbon gives a very hard wearing surface suitable for work that must withstand a fairly constant pressure, as shafts running bearings, etc., but for parts which must withstand repeated shocks, this amount of carbon would render them too brittle, and in such cases it is advisable not to exceed 0.90 to 1 per cent carbon. For most purposes, 0.90 per cent carbon is preferable. Recent investigations indicate that the percentage of carbon in the hardened crust varies with the depth of the latter; the deeper the penetration, the higher the carbon content. Crusts about 0.050 inch deep usually have from 0.85 to 0.90 per cent carbon on the surface. In many instances, a penetration of 0.40 inch is sufficient, but if the work is to be ground after casehardening, it is advisable to carbonize to a depth of about 1/16 inch. Too deep a carbonized case makes the work more brittle, partly because of the prolonged exposure to a high temperature and partly on account of the increase in the hardened section and the decrease in the softer and more ductile core; hence, parts to withstand bending stresses, like gear teeth, should not be carbonized too deeply. The penetration of the carbon increases with the temperature and with the time of exposure, but not in direct proportion to these two factors. Carbonization takes place rapidly until the crust is saturated with carbon, when there is a sudden diminution in the rate of carbonization, which varies according to the temperature.

Casehardening for Colors. -- For hardening and at the same time coloring such parts as wrenches, etc., the following mixture may be used: Mix 10 parts of charred bone, 6 parts of wood charcoal, 4 parts of charred leather and 1 part of powdered cyanide. The leather should be black, crisp and well pulverized, and the four ingredients well mixed. The object in charring the bone and leather is to remove all grease. The parts to be colored must be well polished and should not be handled with greasy hands. To obtain satisfactory work, these rules must be observed. If the colors obtained are too gaudy, the cyanide may be omitted, and if there is still too much color, leave out the charcoal. The parts to be colored and hardened should be packed in a piece of common gas pipe having a closed end. Pipe is preferable because the pieces can be dumped into the cooling water with little or no exposure to the air. The open end of the pipe can be places close to the surface of the water before the parts are removed, but with a box there would be more or less exposure. This class of work should be heated to a dark cherry-red and kept at that temperature for about four or five hours. If the temperature is too high, no colors will appear. The tank should be arranged with a compressed air pipe connecting with the water pipe at the bottom in such a way that a jet of air is forced upward, thus filling the tank with bubbles. There should also be a sieve or basket in the tank for receiving the work. After quenching, place the parts in boiling water for five minutes and then bury them in dry sawdust for half an hour. Another mixture recommended for coloring consists of 10 parts granulated bone, 2 parts bone black and 1 part granulated charred leather.

Gas Process of Casehardening. -- Owing to the growth of the armor plate industry, efforts were made to find a better and cheaper method of carbonizing the plate. The first method employed was to place an armor plate in a pit and cover it with a layer of charcoal; then another plate was laid onto it, after which the pit was covered and heated to a temperature high enough to cause the steel to absorb the carbon from the charcoal. The next method tried was to force a current of carbonaceous gas between the two plates, instead of using charcoal. This caused the carbon to penetrate in less time and was found to be more economical. Later the plates were heated by electricity, and the use of electricity and carbonaceous gas gave a more uniform carbon penetration. This process was followed by the development of a muffle carbonizing furnace. In this the work is placed in a revolving retort through which is forced a current of carbonaceous gas. This retort serves as a muffle and is surrounded with the flames of the heating gases. It is claimed that in this furnace small pieces can be carbonized much more quickly and at about one-half the cost, as compared with packing in iron boxes and baking. Some of the gases that have been experimented with are methane, ethylene, illuminating gas, carbon-monoxide, carbon-dioxide, and gases made from petroleum, naphtha and gasoline. Carbon-monoxide was found superior to other gaseous materials, but, while it is capable of rapid penetration, there is an oxidizing effect that might spoil small parts which cannot be ground afterwards. To overcome these bad effects of carbon-monoxide, a new process has been developed in which the work is packed with wood charcoal in a cylinder, and, when heated to the carbonizing temperature, a current of carbon-dioxide is injected into the cylinder.

To Clean Work after Casehardening. -- To clean work, especially if knurled, where dirt is likely to stick into crevices after casehardening, wash it in caustic soda (1 part soda to 10 parts water). In making this solution, the soda should be put into hot water gradually, and the mixture stirred until the soda is thoroughly dissolved. A still more effective method of cleaning is to dip the work into a mixture of 1 part sulphuric acid and 2 parts water. Leave the pieces in this mixture about three minutes; then wash them off immediately in a soda solution.
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GuyFawkes

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Re: Heat treatment FAQ thingy - LOOOOONG post - 3 parts
« Reply #3 on: May 27, 2006, 01:41:39 AM »
Pack-hardening. -- Pack-hardening, as the term is generally understood, consists in treating steel (generally tool steel) with some carbonaceous material and quenching it in oil. The terms "pack-hardening" and "casehardening" are often used interchangeably and the two processes are similar. The surface of the steel is supplied with additional carbon by the use of some carbonaceous material that will not be injurious. To do this, the steel is packed in sealed iron boxes with the carbonizing material. Bone should not be used for pack-hardening tool steel, as it contains a high percentage of phosphorus, which tends to make the steel weak and brittle. For steel that is to contain not more than 1.25 per cent carbon, charred leather is recommended. For obtaining a higher carbon content, use charred hoofs or horns or a mixture of the two. The leather, hoofs or horns can be used repeatedly by adding a quantity of new material each time. A mixture of charred leather and charcoal is also used for pack-hardening. The work should be so packed that it does not come in contact with the box. First place a layer of carbonizing material in the bottom and then a layer of work, no two pieces touching each other. When treating gages, or parts that are likely to spring, they should be so packed that there will be little liability of springing when they are drawn up through the packing material. The parts should not be dumped into the quenching bath, as it is better to handle the pieces separately. It is a good plan to attach a piece of iron wire to each part to facilitate removal from the box. If there are several layers of work, the wires should be so arranged that the various layers can be taken out in the proper order, beginning with the top row. The temperature for pack-hardening should be as low as is consistent with the desired results, and should be uniform throughout the box. To gage the heat, holes may be drilled through the cover at the center so that test wires (say, 3/16 inch in diameter) can extend to the bottom of the box. When the latter has been in the fire long enough to heat the contents to about a dull red (as near as can be judged) a wire is withdrawn; if it is red hot begin timing the heat; if not, wait and withdraw another later, the test being continued until one is withdrawn that has the desired heat. The length of time necessary for heating depends upon the depth of hardening surface desired. For ordinary snap-gages, from one and one-half to two hours after the steel is red hot is sufficient. Ordinary work requires a temperature of about 1475 degrees F. Pack-hardening minimizes the danger of cracking and warping.

Casehardening Alloy Steels. -- When nickel steels are heat-treated by casehardening, nickel seems to retard the process somewhat and the hardness of the "case" is somewhat lower than that obtainable in ordinary carbon steels. On the other hand, nickel tends to oppose the crystallization of the steel at high temperatures and to eliminate the consequent brittleness. With a 2 per cent nickel steel, the following temperatures are recommended: The steel should be quenched from a temperature of 1830 degrees F. It is then given a second heating to 1380 degrees F., and is again quenched, after cooling to about 1290 degrees F. A single quenching from 1290 degrees F. gives the greatest hardness in the case but not the greatest tenacity in the core. Quenching from 1380 degrees F. gives a somewhat higher tenacity but a slightly lower hardness in the case. A 6 per cent nickel steel should be quenched first from 1560 degrees F., and after re-heating, from 1245 degrees F. Since this high nickel percentage almost completely prevents the brittleness of the core, one quenching from about 1290 degrees F. is, in most cases, sufficient. Steels with from 1 to 1.2 per cent chromium are sometimes used when an especially hard case is required. This element aids the crystallization of the core and the double quenching is necessary. Chrome-nickel steels with a low chromium content require about the same heat treatment as pure nickel steels. A mixture of 60 parts wood charcoal and 40 parts of barium carbonate is recommended for carbonizing.

Casehardened Gears. -- There are four general classes of steel used for case-hardened gears, viz. , straight-carbon, nickel, chrome-vanadium, and chrome-nickel steel, and, in each of these classes, several modifications will be found in the market. On the whole, the steels containing chromium are preferable. Before being carbonized, the carbon content of each of the steels mentioned should be about 0.20 per cent; under no circumstances should it be more than 0.25 per cent, to avoid brittleness in the teeth. The carbon in the "case" should be increased to about 0.90 per cent, which can readily be done by using the proper carbonizing material and temperature for carbonizing. This temperature, in general, should be about 1600 degrees to 1650 degrees F. for the classes of steel mentioned. Lower temperatures do not give sufficient depth of case, unless the heating operation is much prolonged. Conversely, higher temperatures result in a case of excessive carbon content and a core of such large grain-size that it will not respond as readily to the subsequent heat-treatment. The proper heat-treatment, after case-carbonizing, is very important. The work is first allowed to cool in the box after carbonizing. It is then re-heated to 1550 degrees or 1625 degrees F. and quenched in a suitable medium to refine the core; next it is re-heated to 1350 degrees or 1425 degrees F. and is again quenched to harden the case; finally, it is drawn in oil to a temperature not over 400 degrees F., to further increase the strength and toughness of the material. The temperatures given are approximate, and more definite information concerning any particular steel should be obtained from the steel-maker. Casehardened gears have harder surfaces, as shown by the scleroscope test, than tempered gears.

Tempered Gears. -- Unlike casehardened gears, tempered gears are of uniform carbon content, and when hardened have a uniform hardness throughout the tooth section. The steels used for tempered gears are of three general classes, viz. , silico-manganese, chrome-vanadium and chrome-nickel steel, the last named, in different modifications, being the most generally used. The carbon content for the different classes varies from 0.40 to 0.60 per cent. The heat-treatment of all these steels consists simply in heating the gears slowly and uniformly to the hardening temperature, which is usually about 1500 degrees F., quenching in oil, and afterward drawing in an oil bath. Tempered alloy steel gears are preferred to casehardened gears for some purposes, especially where strength is the main consideration. They are particularly adapted for "clash gears".
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solarguy

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Re: Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« Reply #4 on: May 27, 2006, 06:38:53 PM »
Kawamba!

Such a lot of information packed into such a short article.  I'm filing both a hard copy and a digital version.

Guy, you are a treasure trove of goodies.

I would like to poke around through your library some time, were it convenient (as in, not on a different continent).

Finest regards

troy

GuyFawkes

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Re: Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« Reply #5 on: May 27, 2006, 07:19:06 PM »
for years now I've been threatening to scan my dad's old 1954 collins engineers diary... pocket sized, but an absolute goldmine on any engineering subject you care to name, from steam flanges to screw threads and anything else you can think of..
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hotater

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Re: Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« Reply #6 on: May 28, 2006, 12:35:22 AM »
All good information and timeless.  There are MANY shortcuts, kinks, tricks, and tips to simplify it all for the backyard DIYer, too

Annealing trick---  Fill a five gallon bucket with common slacked lime.  Heat the part until a magnet falls off of it and the WHOLE part is the same color as what the magnet was stuck to and plunge, quickly, the whole part into the lime and kick the bucket several times to settle the lime around the part.  Wait at least an hour, preferrably two, before removing and knocking the lime off.  Watch out, it'll still be hot.

Tempering trick--  Most spring steel is tempered at about the same temperature motor oil burns.  Put the hardened part in a pint of motor oil in a cast iron plumber's pot and heat it until the oil burns off to just above the part.  Remove the heat source and let it cool.  Test it before putting a lot of time in finishing it.  It'll be stronger after polishing than before, so if it holds up before its' finely finished the chance of it ever breaking after polishing are extremely slim.

I've repaired heat-treated parts and made sidelock springs for some of the most expensive guns in the world for forty years using those two methods and common  O-1 or 1095 tool steel stock.

Cast Iron fact--- The wearability, machineablility, and durability of cast iron depends on the composition and physical structure  more than the heat-treat.  Most heat treat on cast iron is annealing (I've seen chain conveyors of cast parts slowly inching their way through the annealing furnaces) to avoid cracking under cold or stressful conditions.

 For case-hardening mild steel--- I use a product available at big machinery supply houses called "Casenite" (sp).  One pound of it has lasted me since 1969 and I have a half a can left!  Oxy/acty torch case hardening to .020" (.5mm)deep  and Rc60 (after three cycles) can be done on 1018 and A-36 parts, but a single application gives .010 of Rc 62 and that's plenty for everything I do.  Wear glasses designed for sodium flare.  It's an intense yellow that regular glasses don't do much for.

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Re: Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« Reply #7 on: May 28, 2006, 03:10:59 AM »
Some very cool stuff here....
Seems to me if the lights ever actualy do go out we should get together and rebuild society.
I'll wined the electrical equipment and brew the beer....

Doug

On a serious note this thread just proves a point I've been making to many people when the subject of peak oil come up. There realy is nothing made by man than can't be repaired or altered in some way to work. There's a lot of clever people with the know how to keep from living in cave.



rpg52

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Re: Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« Reply #8 on: May 28, 2006, 03:26:43 AM »
Guy & Hotater

2 questions: 

Guy -

"To prevent hot lead from sticking to parts heated in it, mix common whiting with wood alcohol, and paint the part that is to be heated. Water can be used instead of alcohol, but in that case the paint must be thoroughly dry, as otherwise the moisture will cause the lead to "fly".

"Another method is to make a thick paste according to the following formula: Pulverized charred leather, 1 pound; fine wheat flour, 1-1/2 pound; fine table salt, 2 pounds. Coat the tool with this paste and heat slowly until dry, then proceed to harden."

What does it say about a culture that writes and saves such amazing detail about something as esoteric but useful as hardening various forms of iron?  How many other cultures possessed similar information, but have lost it because it wasn't saved in a form that we can still read?  (e.g., I'm thinking of Peruvian stone work, etc..)

Hotater -

From whom did you learn these tricks of the trade, and has anyone else ever written them down (until now)? 

Both -

Where should such information be stored so that it will be available in the future?

I don't necessarily expect either of you to respond to these rhetorical questions, unless you would like to.  These posts just piqued my curiosity.   :)

It must have something to do with my fascination with anthropology, this is just classic late iron age information.  Kind of like shaping arrow heads or starting a fire with flint would be in the stone age.  I personally am not likely to ever use it, but kids being taught in metal shop should have to learn about it at least.  Is someone carving this into stone (or, better yet,  casting it into iron?)

Ray

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GuyFawkes

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Re: Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« Reply #9 on: May 28, 2006, 01:45:10 PM »


Where should such information be stored so that it will be available in the future?

I don't necessarily expect either of you to respond to these rhetorical questions, unless you would like to.  These posts just piqued my curiosity.   :)

It must have something to do with my fascination with anthropology, this is just classic late iron age information.  Kind of like shaping arrow heads or starting a fire with flint would be in the stone age.  I personally am not likely to ever use it, but kids being taught in metal shop should have to learn about it at least.  Is someone carving this into stone (or, better yet,  casting it into iron?)

Ray



I'm not sure this is really on topic for here, so I've answered this in my blog, of you want to post a response to that here then that is up to you, I'll answer, if I can.

http://www.surfbaud.co.uk/blog/archives/10-The-fount-of-all-knowledge.html
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Original Lister CS 6/1 Start-o-matic 2.5 Kw (radiator conversion)
3Kw 130 VDC Dynamo to be added. (compressor + hyd pump)
Original Lister D, megasquirt multifuel project, compressor and truck alternator.
Current status - project / standby, Fuel, good old pump diesel.

hotater

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Re: Heat treatment FAQ thingy - LOOOOONG post - 4 parts
« Reply #10 on: June 02, 2006, 04:31:49 AM »
Doug---

For many years I've been a member of the American Custom Gunmakers Guild.  Charter member ,past officer, pres, etc.   The gunmakers and knifemaking crafts use many deciplines to create one object.  Both  HAVE to learn the old way of doing things to successfully do it now.
    CNC and EDM has changed some of that now, but when I was trained there was a LOT of emphasis on fitting pieces of mild steel 'light tight and finger tight' and other patiences taxing skills.

Every year in Reno the ACGG and the Firearms Engravers of America hold a joint show and business meetings and vote in new members.  Part of the show are the Monday Seminars.  I've taught several and other gunmakers and engravers have taught many hours of them.  Most of these are on video tape (side of room, single focus, but interesting enough.) and are for sale at  www.acgg.org/  and www.fega.com/

Pick up any edition of "Machinery Handbook" any time you see a copy.  MUCH of this information is there.

Another good way to pick up neat tips is hang out on interesting websites.   :D
7200 hrs on 6-1/5Kw, FuKing Listeroid,
Currently running PS-Kit 6-1/5Kw...and some MPs and Chanfas and diesel snowplows and trucks and stuff.