Growth in heat treatment

[dgallup]

We have some low alloy steel components that we gaseous nitrocarburize case harden. The parts grow a little in heat treat and we have to take this into consideration in the machining so they finish up the correct size. I'm currently designing similar parts that are about 40% bigger and trying to decide if I should expect the same amount of growth or if the growth will scale proportionately with size. I'm leaning toward the same amount of growth since it's just a thin hard case and it should be about the same depth. If we were through hardening then the growth would be more nearly proportionate to size. Do I have that right or am I all wet? We will of course do some trials to prove it out either way but I like to get these things right from the start.

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[metengr]

dgallup;
Your assumption regarding the same amount of growth from nitrocarburizing is correct.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.921.3381&rep=rep1&type=pdf

 

[gearteeth]

Growth occurs at the immediate surface; it is volumetric change due to the diffusion.

Amount of growth will depend on:
• Steel chemistry
• Gas dissociation or gas ratios
• Process temperature selection
• Time at process temperature

All of the previous affect the thickness of your compound layer. If all of these variables are the same then you can expect similar growth.

 

[dgallup]

Thanks.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.