Strawing

[Wolfgang Pfeifer]

Neil,


Strawing color indicates the Hardness/Temper ratio. After carbon steel parts are hardened they are brittle as a result of sudden cooling in oil or water baths. In short, tempering (re-heating, 300-750 F range) relieves the stresses and makes the parts serviceable for their designed use and less likely to break.


Colors go from:

â??Very pale yellow 430 Fâ?� to

â??Light yellow 440 Fâ?� to

â??Pale straw-yellow 450Fâ?� to

â??Straw-yellow 460 Fâ?� to

â??Deep straw-yellow 470 Fâ?� and all the way through brown, purple blue at 640 F.


Make note of the extreme narrow range, 10 F from shade to shade. Flame annealing is imprecise, difficult and frustrating. Gradual and uniform heating is critical to success while tempering/annealing. Electric Furnaces with process control including ramp and hold settings are ideal for this process, but are expensive.


I have done the following:


Use a steam iron, secure it bottom up in a fixture. Use a quality industrial thermometer with 1/8 inch probe and run trial heats to establish temp settings. Drill a 1/8 hole in a small block of aluminum, stick in the probe thermometer and place on the iron bottom. Under-shoot by 20 F and creep up to the desired range. Record all settings. This method has worked for me when I heat treat punching, shearing and forming dies.


Good Luck