4140 heat treating variation in rc
4140 heat treating variation in rc
(OP)
We had 7/8" dia bar 4140h heat treated, 41-50 rc. the vendor could not get a consistent rc reading on the outside ,30-54. Why would this be. Also we machined some parts and got 41-54 rc readings. Why would this be? The vendor has also tried re-heat treating the bars with the same result on the o.d. when trying hardness test(varies 30-52). The ht process is vacuum / gas, not oil quench. We want to finish machine the bar stock at the blueprint rockwell call-out(41-50rc). We also want to hold the rc to with-in 5 points on the lower end, for consistant machining purposes.Could you suggest a fix to get this material in this range, preferably 42-47 rc. Why would the od be so varied?
Thanks
Jim
Thanks
Jim





RE: 4140 heat treating variation in rc
1. decarburization during heat treatment OR
2. method of hardness testing
I would have a complete metallurgical analysis performed of a heat treated bar to evaluate the specific cause of hardness variability.
Hardness testing alone will not provide you with the root cause of the problem. It could be that the method of hardness testing is the cause of variability.
RE: 4140 heat treating variation in rc
Have you seen this problem before? It has us scratching our heads. We though we just send the bars out for ht get them back certified to rc and machine. Why such a problem? I also have mill certs for the mat'l.
RE: 4140 heat treating variation in rc
RE: 4140 heat treating variation in rc
I have also seen where hardness testing was done incorrectly resulting in lower hardness values. The hardness testing should be performed by a qualified lab.
You need to work directly with your vendor or heat treater to resolve this problem. They should provide you with a metallurgical analysis report or at least request one as a customer. Also, I would verify who is performing the hardness testing and their test method.
RE: 4140 heat treating variation in rc
Is there anyone who has ran across this problem? How was it resolved?
Thanks,
Jim
RE: 4140 heat treating variation in rc
RE: 4140 heat treating variation in rc
Decarb can be removed by machining which you have done.
Were hardness tests after machining performed by heat treater or others? If the hardness tests before and after heat treat were done by the same facility, it would point to localized decarb since the lower readings increased after machining.
The large variation in hardness readings after machining suggests the possibility of alloy segregation. This condition occurs during the steelmaking process and can be verified by metallurgical analysis which has already been suggested.
Jesus is THE life,
Leonard
RE: 4140 heat treating variation in rc
Jim