Heat treatment still good after machining ?

Good Morning,

New to this forum, I am a quality engineer with about 10 years of experience in the industry.

I have a question to experienced engineers here.

I have a stainless steel part that has a requirement to be heat treated AFTER machining. This supplier has found a bar that comes pre-heat-treated (to the correct parameters per our request) and they insist that after machining the heat treatment properties will still be there. This is a square bar that will be turned in the lathe at one end, to remove about 0.5 inches of material.

I understand enough about heat treatments of steels to know that this cannot be true (machining will create enough heat to change the crystalline structure of the material), but for the sake of a second opinion (and maybe I am wrong after all), can you guys please chime in and tell me if there is any way these guys are right ?

I don't think they are.

I appreciate your time, thank you for the support.

DS

Machining should NOT create enough sustained heat to un-heat treat the SS. In fact, machining heat treated SS is going to increase the manufacturing cost and manufacturing challenges.

Many times heat treat after machining is specified so the residual stress from the machining is removed. Is the heat treat a bulk or surface treatment? That can also make a huge difference.

Timelord

Needs to consult with manufacturing...

The heat treatment is a good way off engeneering process. This is a nice guidelines. Thanks.

The lathe should not generate enough heat to disrupt the properties of the steel unless you are running it at extremely high speeds and/or you are not using cutting fluid.

We regularly temper 35NCD16 steel and then machine without affecting properties. You can find tempering properties by looking at a phase diagram (for example, stainless steel:

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The lathe should not generate anywhere near this much heat.