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Heat-Treating & Hardening 4140 Steel

Heat-Treating & Hardening 4140 Steel

Heat-Treating & Hardening 4140 Steel

I chose 4140 steel to be machined and hardened, RC 56-62 to a depth of 0.030” – 0.060” to achieve high strength components.

I was just told that hardening 4140 will achieve a thru-hardening instead of case-hardening.

Is this true, 4140 can’t be case-hardened? If so, what other type of high strength material can I use?

Any response will be greatly appreciated!

RE: Heat-Treating & Hardening 4140 Steel

4140 is not case hardened by carburizing but it is frequently induction hardened to the hardness and depth you desire and beyond.

If you want the core to be softer you can first normalize, or quench & temper in a furnace to the desired lower hardness level. This treatment also prepares the near surface for optimum induction hardening response.

RE: Heat-Treating & Hardening 4140 Steel

So what you’re telling me is that I can have my components Heat-Treated & Hardened to my specs?

Any response will be greatly appreciated!

RE: Heat-Treating & Hardening 4140 Steel

If you need surface hardness and the core to be tough,you can consider 8620 instead of 4140 alloy.

RE: Heat-Treating & Hardening 4140 Steel


It is not quite as simple as yes or no.  Case hardening is typically used to mean carburizing, but it is also used to describe induction hardened components.  4140 is not used for carburizing, but it can be surface hardened using induction.  Based on the feedback that you received, it sounds like your heat treater was describing the problem of 4140 and carburizing.  If you want the part carburized to your spec, then the suggestion of 8620 by arunmrao is a good one.  If you want the part induction hardened and tempered to your spec, then 4140 would be ok.  I would limit the hardness to be under 60 HRC if it is 4140, but 55-62 HRC is fine for carburized 8620.

RE: Heat-Treating & Hardening 4140 Steel

Thanks for the replies,

Using 8620 steel will require extra machining and grinding due to the extreme warping in the metal. Nitriding the part will give me the result that I am looking for using 4140 steel to a depth of 0.010 – 0.015”, without the extra machining involved.
One point that was brought up was that Nitriding will provide wear resistance and not impact resistance. Is it the same with 8620 steel?

Any response will be greatly appreciated!

RE: Heat-Treating & Hardening 4140 Steel

metal for metal, 8620 will exhibit a better resistance to impact load due to the present of nickel element.

A good design must have a balance among all aspect.

the manufacturing / heat treatment process practicality, equipment availability (in a specific region), cost, part design (geometry).

Best regards,

RE: Heat-Treating & Hardening 4140 Steel

you could also use 1045 (which would probably be cheaper due to the lower alloy content) and heat treat it. It WILL case harden but it will not through harden. hardness depth will depend on section thickness and quenchant used.

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