4340 hardening from full anneal
4340 hardening from full anneal
(OP)
I am having problems achieving full hardness from 4340 bar stock from full anneal. I can achieve full hardness from a part as machined (normalized and tempered-orinally 30 HRC) to 55 HRC. However, I then fully annealed the part (to about 10 HRC)and when I went to re-harden I could not achieve higher than 35 HRC, even after 3 tries, 2 at 30 minutes and again at 60 minutes. My hardening is at 1525F and oil quenching. Any ideas?





RE: 4340 hardening from full anneal
Also what is the purpose of softening initially and then hardening.
RE: 4340 hardening from full anneal
RE: 4340 hardening from full anneal
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: 4340 hardening from full anneal
RE: 4340 hardening from full anneal
RE: 4340 hardening from full anneal
RE: 4340 hardening from full anneal
As an alternative, modify your process. Instead of a full anneal, use a sub-critical anneal (temper at 1275 F for an hour). While perhaps not as soft as a full anneal, the toughness will be better (I'm guessing you are annealing to prevent cracking during the welding), so it should do what you want. With the sub-critical anneal, it should harden up just fine from 1525.
rp
RE: 4340 hardening from full anneal
RE: 4340 hardening from full anneal
A full anneal is not required for this material. Prior to welding, a subcritical anneal is the preferred method.
RE: 4340 hardening from full anneal
A star to you for having come back and solved the mystery. I have been thinking the whole night of this strange observation. Though I was certain about decarb theory. I discussed with ASM expert and he too was of the same opinion of decarb layer .