reference info for heat treatment size variation

Hi,
I am a novice to your site, but would like to ask a question regarding heat treatment of steels.
We currently machine high volume 12L14 & 11L17 steel components for
use in hydraulic cartidge valves. We have made these close tolerance parts for many years for our customer. Last year our customer changed its internal heat treat process by switching gases (I do not know what gas they are using).
Since the switch they appear to have had problems with substantial growth and distortion on the parts which has caused additional problems for them in their diamond honing processes. They are starting to point their finger to us saying that we have 'dull' cutting tools that are imparting stresses that are causing the problems that they encounter 'after' heat treatment. Our parts are in tolerance when received by the customer.
Do you have any sources that may refer to growth patterns when steels such as we are machining are case-hardened? I would like to do some reading on this topic before the proverbial 'sh-t' hits the fan.
Thanks in advance.
Bob Ducanis Marshall Manufacturing Corp. Cape Canaveral, FL www.marshallusa.com
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snipped-for-privacy@marshallusa.com (bob ducanis) wrote in message

Bob,
Production Gas Carburising G Parrish Pergamon Press
Case Hardening of Steel ed E Boyer ASM
ASM Metals Handbooks' vol 4 Heat Treating, vol 5 Surface Engineering.
Although I am an avid self-study myself your company's problem would best be examined by an outside laboratory familiar with heat treatment, process control and failure analysis. My first impression is that your customer has increased variation in the case depth of the free machining parts - only testing (case depth determination of several old and newly produced parts) could verify. Their explaination of "tooling stresses" causing distortion after heat treatment demonstrates their ignorance of their own process (the TRUE ROOT CAUSE). Bet ya they got rid of their metallurgist several years ago - and havn't got enough common sense to regret it!
Good Luck.
Ed Vojcak
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My best guess is: 1) they are using a different quench method or racking. Gas change alone shouldn't make any difference. 2) material is not being received stress relieved in its raw state. Your best defense is to stress relieve a ocuple of parts after machining, let them heat treat them. If they distort after this, it's proof that it's their fault.
bob ducanis wrote:

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