What’s up guys?!?!?!? Michael with Michael Talks Metal back again for the 146 th time…….. For this episode we will delve into some of the finer points of chemical composition in steels.
Any alloy we name has a chemical composition associated with it. Common grade designations or complicated specifications have requirements for elements and are our starting point. You know how I am about specifications.
The chemical composition we see on the typical test report refers to the “batch” melted at one time…. called a heat. The final chemical analysis from the melt must conform to requirements. All requirements of the alloy and / or specification need to have reported values to show conformance.
Another type of analysis, called a check analysis can be performed to verify conformance of material or parts. Check analysis follows different rules and recognizes that additional variations in chemistry can occur that affect results.
An ADDITIONAL allowance is made to the required heat chemistry requirements ………… both under the minimum and over the maximum for each element.
Let’s take a simple example: Suppose we have an aerospace part made from
4340 alloy and the end customer performs a verification test. In reviewing the reported results, the Chromium value is shown as 0.92%. 4340 heat chemistry is required to have 0.70 to 0.90 % Chromium. Check analysis limits for Chromium allow .03% variation under the minimum or over the maximum, so any result from 0.67 to 0.93% would be acceptable.
The variation allowed increases with the amount of the element required, so a verification test performed on a 304 stainless steel part would have an additional variation of 0.20 % Chromium to the required Chromium range.
Variation in an element is not permitted to be above and below in the same heat.
Permitted variations for check analysis vary by product as well as by the amount of elements present. Way too much for us to show you in a short video.
AMS has great references….
AMS 2259 Check Analysis Limits for Carbon and Low Alloy Steel
AMS 2248 Check Analysis Limits for Corrosion and Heat Resistant Steels
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Specifications and part requirements can alter what we have shown you today. ..
So for the 146th time …CHECK THE SPECS!!!!! TWICE
This is Michael with Michael Talks Metal. Thank you for watching. Need more info about steel and metal, check the website for more info: www.michlinmetals.com. Still here and haven’t subscribed, click here. Missed last weeks, right here. Thanks for watching, see you next Thursday same time, same place, 10am YouTube. I’m out!