Hey Glort...
I have made similar blades in the past, here's how I did it....
Materials required:
Steel section, DOUBLE the height of the blade required, cut to correct length.
2x channel iron, heavy section, at blade length
2x chain blocks
2x chains
Tack weld the channels down the long edges of the plate to bend
Hook the chain blocks to a suitable point and then to the chain, wrapping one turn of the chain around the channels/plate, then the chains to another suitable point.
Pull the chain blocks evenly, the channel stops the edges from bending, and keep going until a suitable parabolic shape is formed. (Note: the channels are on the outside edges of the bend.)
Once the initial bend has formed, remove the chain wrap and link the chains/blocks directly to the channels, much less pull is required as the curve increases...
When you have the correct curve on the blade after releasing the tension, section the parabola down its length, you then have a blade plus a spare.
Remember, a dozer blade is not a plain section of a circle in shape, it is somewhat parabolic to lift the ground to the center of the blade to transport it... The more parabolic and "flatter" at the base, the more it can shear the ground and lift for any single pass.
On the other hand, if you want a blade that can be used for levelling, lean more towards a circular section, it will not lift and carry as much ground....
Just my .00c worth....
Cheers
Ed