Speaking about Heat Treat in Auto and Aerospace industry is a serious thing. The fact that you cannot measure 100% of parts unless you use destructive testing, well it is kind of scary. That is why both industries address very strict standards for temperature measurement and control: pyrometry.
SAE AMS2750 is the most popular pyrometry spec in the aerospace industry and it helps us to answer critical questions of the process:
• How accurate is your temperature measurement?
• How much temperature variation is in the furnace?
• Was the load exposed to a consistent temperature during the process? And
• How do you know you know?
The majority of aeronautical companies (and some others like energy and medical) reference AMS2750 to assure that parts are heat treated according to the highest specifications.
The pyrometry requirements from CQI-9 are quite similar. Actually, when the Automotive Industry Action Group launched this assessment back in 2006, they referenced AMS2750 to comply the pyrometry requirements. In the third revision of the CQI-9, the group decided to write their own requirements due to the unique characteristics of the auto industry, but CQI-9 is still based on the aerospace practices, so it is yet complex
We need to have in mind that we face two complicated standards that require skilled personnel to interpret their requirements. In fact, up to 80% of the findings in Heat Treat Nadcap audits are related to pyrometry. However its proven that properly implementing either of these specs will result in a controlled process capable of preventing defects.
At the end, metrology (temperature metrology in this case) shows one more time that you can leave the plant knowing that you have managed a safe product for many generations to come.