Water quench 8620H?

[vcz]

I am making a replica of an 1880s vintage single-shot action. I've machined the structural parts(receiver,breechblock) out of 8620H barstock. I want to "case-color" harden these parts which involves pack carburizing in bone&wood charcoal and a water quench out of the furnace. Most sections of the parts are around 1/4"thick. I plan to gas carburize for 30min. @ 1575F with an air cool and then pack carburize for 30min. @ 1475F and water quench to get the desired "case-color" surface finish. Finally I plan to temper at 450F for 1hr. I hope to obtain parts with .003-.007" thick 54-58Rc case and 32-38Rc core. Does this sound like a reasonable process to end up with tough wear resistant parts.

 

[Metalguy]

8620 is normally oil-quenched. If your parts have large or abrupt changes in thickness, you could end up cracking them.

If you have a piece of 8620 left over, you could rough-machine it to a more severe condition and attempt a water quench to see what happens.

I once cracked a fairly large 4140 forging (about 100 lb.) that was on the low side of the Cr and Mo limits, and it would not harden in oil. Rather than scrap it, I tried water, pulling it out after in had turned black. It cracked anyway, but it did harden!