Growth of Material in Heat Treat

[DennisP]

Does the reduction ratio of the raw material have any bearing on the rate of growth of a part in heat treat? For example, given a single heat of steel, one bar drawn to a diameter of 1" and one bar drawn to a diameter of 1/2". The 1" bar is turned to produce a part of .45" diameter as is the 1/2" bar. Both are heat treated. Would one expect the resulting growth in heat treat to be any different for the two starting sizes of material?

 

[TVP]

There is certainly a chance that one will experience more distortion than the other. Growth is usually reserved for describing the volume expansion that occurs when a steel part is hardened (case carburized & quenched, austenitized & quenched, etc.) and there is a martensitic transformation. There will be no difference in this phenomenon as long as the treatment parameters are the same.

 

[Maui]

The relative amount of volumetric growth induced by the martensitic transformation during heat treatment should be the same for both bars. The amount of volumetric growth should be slightly less than 3%, and you can calculate what the growth in the length dimension should be based on this figure (note that it won't be 3% in one dimension).

 

[unclesyd]

As stated above the volume change rate due to change in crystal structure during heat treatment is going to be the same on both bars.
I would recommend that you get the expected expansion
from the manufacturer as different alloys have different rates, some essentially 0.0 others have a negative volume change, others quite high. To stop this growth one has to go to additional steps to to stop growing. Until the advent of LN2 we accomplished this by multiple tempers. If you are going a precision size the transformation has to be complete before finishing.

What material are you working with?

 

[tomwalz]

Some excellent replies above.

I would point out the use of terms such as "should" and "expected" indicating that real-world results may differ from theoretical.

An example we ran into a few years ago involved brazing a carbide ring into a thin steel holder about 6 inches in diameter. Because the steel holder had been machined out of rolled plate it warped a bit during brazing in reflection of its having been rolled.

This was a case where it should have grown and shrunk back to the original shape. But there were other factors at work.



Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[DennisP]

Thanks for all the valuable information. We are using 52100 and thru hardening to RKW 30N 77 Min.It's been our experience that each heat acts a little differently regarding the growth in length after heat treat, even in a well controlled heat treat process. Enough so that we need to perform a test when we change heats to insure that parts remain in spec after heat treat. We currently have the situation I described in my OP and was trying to determine whether or not we would need the test. Thanks to all.