Cracking problem
Cracking problem
(OP)
hello all, I am having a problem of cracking in 4140. I am induction hardening and tempering. I am having small crack develop along the parting line showing up under magnaflux. The draw temperature is 550 for 2 hours. Is temper embrittlement any issue? I am racking my brain on why we are seeing cracks.





RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
Regards
RE: Cracking problem
If you can, try to get your parts into the tempering step ASAP. They should still be warm, not room temp. When this is not possible they should be reheated to 375F min. ASAP after quenching.
RE: Cracking problem
You mention a "parting line". Is this part forged?
If the stock material is hot rolled or hot forged, it is standard practice to remove the outer 1/8" (or so) of hot rolled bar stock, or to 100% machine hot forged blanks. This is because the hot working process can contaminate the outer layer of material.
Also, induction hardening is usually a localized process. That is the whole part is not subject to the heating/quenching process. Personally, I would not use induction hardening (or similar processes like flame hardening) unless I was concerned about distortion during quench. The transition area between the heat treated area and the non-heat-treated area can cause problems.
Finally, trying to get a TS of over 250 ksi (Rc 50) with 4140 is really pushing the limits for that alloy. You might want to consider another material.
Good luck.
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
Take a sample and grind down the parting line and shot peen it before hardening to relieve internal stresses then see if it still cracks after tempering.
RE: Cracking problem
Fred Specht
Ajax TOCCO
847606-9462
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
RE: Cracking problem
Not grinding crack unless burning and you would see.
Leaving in temper at longer time will make no difference, need high oven temp, add 25F.This will not prevent the cracking, something else is causing.
Fred Specht
Ajax TOCCO Magnethermic
847-606-9462
RE: Cracking problem
RE: Cracking problem
last months "Forging" magazine had an article, just up your ally. "Defects in Hot forgings" by H.J. Henning. You must read @ www.forgingmagazine.com on page 21.