I found this at:
http://www.cancom.net/~hnilica/metals.html
Note the Very long soak time at high temperature for annealing: Heat to 1440 degrees F and soak for 8 hours, cool at the rate of 15 degrees F per hour to 1200 degrees F, hold at that temperature for 6 more hours, then cool in still air.
52100 BALL BEARING STEEL
Besides using ball and roller bearings, races/balls/rollers, it can be obtained in bar stock. In comparison to 5180, 50100B and O-1, it has more Carbon and more Chromium.
Carbon heightens the abrasion resistance and Chromium hardeners deeper with simpler heat treatments and makes the blade stronger. It does not take much Chromium, even 0.5% is enough.
Heat treatment recommended by Crucible Specialty Metals:
Forging: Forge at 2000 degrees F, cool in still air afterwards.
Normalizing: Temperature at 1850 - 1700 degrees F.
Annealing:
Heat to 1440 degrees F and soak for 8 hours, cool at the rate of 15 degrees F per hour to 1200 degrees F, hold at that temperature for 6 more hours, than cool in still air.
Hardening:
Oil quench from 1550 degrees F should give a hardness of 67 Rc. Water quenching is said to be risky, introducing too much stress.
Tempering:
Assuming that the blade reached full hardness in the quench, tempering temperature of:
350 degrees F...............................60 - 61 Rc
450 degrees F...............................58 - 59 Rc
500 degrees F...............................56 - 57 Rc.
The heat treatment of 52100 is different than that of many of the other alloy steels, including 5180, in that the hardening temperature controls the amount of Carbon that dissolves in the austenite - the condition of steel at high temperature where it is a solid solution of Iron and Carbon.
This gives a finished blade that has lower banite - a transformation product that forms at the lower temperature than martensite rather then tempered martensite - the hardest form of steel.
When overheated for the quench, most alloy steels simply have coarser grain, but 52100 will develop a week structure.
Triple quench / triple draw method: (as done by Ed Fowler)
-The theory behind the triple quench is that by bringing the blade rapidly up to the hardening temperature, the grain size remains smaller then when the usual soak time is used. The soak time allows all the transformations to be made within the steel, yet the grain grows with the additional time at the soak temperature. With the rapid quench the transformation is not complete, however the second and third quenches complete the necessary transformation.
-This method seems to produce the best cutting and stronger blades with more edge holding ability than a single quenched blade of the same hardness
-After proper forging, normalizing and annealing, use magnet to judge the critical temperature and quench the blade in Texaco type "A" oil heated to 180 degrees F.
Cool the blade and let sit for 24 hours. Repeat the identical process 2 more times.
Now put the blade for 8 - 10 hours into the freezer and follow by 3 tempering cycles at 375 degrees for 2 hours each.
Note: Blades hardened at 24 hour intervals cut better and demonstrate greater strength and toughness, than the blades hardened 3 times in one day.
Molten salt quench method: (as done by Al Pendray)
After forging and rough grinding, heat the blade to 1850 n-1900 degrees F, hold 3 - 5 minutes, then quench in molten salt at 500 degrees F, hold 3 minutes, then air cool.
Place back in the salt at 500 -98% degrees F and hold for 2 - 3 hours. Then heat to 1550 degrees for 30 seconds for thin blades, 60 seconds for thick blades and quench in 475 - 500 degree salt.
450 degrees F..............................60 - 61 Rc
500 degrees F..............................59 - 59 Rc
Hold the blades in the salt quench at temperature for 2 - 4 hours. The longer time produces tougher blade that is 1 - 2 points Rc softer.
Hope this helps!
Paracelsus
