Acceptable Heat Treatment Warpage

[CastMetal]

Recently had a 8"x8"x3" (milled down from a larger size) H-13 tool steel block with a 3"x2"x1" pocket machined out of it sent out for heat treat. It was hardened to ~40 HRC from 30 HRC. All surfaces came back out ~.005".

Question is what do you consider an acceptable amount of warpage?

With the stresses added from machining some change is expected but this is much more than a previous heat treatment shop was getting.
Next step if I wanted to correct this is to check their process but it really has little effect on the end product. More just curious what others have experienced / find acceptable.

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations

 

[Metalhead97]

castmetal,

H-13 I believe will air harden. How much warpage do you get if it's air-cooled ?

metalhead

 

[swall]

Your statement that another heat treater did not produce the same distortion tells me that you have answered the question already (i.e. .005" was not the expected level of distortion, although that is apparently acceptable for the application). You need to find out the differences in the heat treat processes. Perhaps the first shop gave the piece a 1000F salt quench to equalize the temperature, then air cooled and the second shop didn't. It would also have been beneficial to stress relieve at 1200-1245F prior to machining the pocket. Acceptable distortion is whatever amount allows the product to remain fit for usage and can be replicated during future production.

 

[CastMetal]

Swall,

Acceptable was a poor choice of wording. Perhaps "typical" or "commonly expected" results would have been better. Stress relieving prior to machining is a good suggestion if it does become an issue, thank you. Yes I have assumed the process differs from shop to shop but I was more curious what others think is a baseline/standard for good vs bad distortion control by a heat treater, yes there are many variables outside of their control such as stress relief but at a certain point, say .01" distortion per 1" of material would it be considered "poor" distortion control/ process/ temperature control?

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations