Steel - linear dimension change after heating & cooling

[tomwalz]

I’m a brazing guy, definitely not a steel guy. We did some prototypes for a big company project and the prototypes work very well. However now everybody has questions before we go into production. One is about the change in dimension after brazing.

We can’t measure one but I think it is there. This is a very robust part and the machining tolerances on this part are 0.010”.

The question is:

If I heat a piece of steel to 1500 F and let it cool will there be a dimension change from the part dimension before heating compared to after cooling.

I am not talking about distortion, just growth or shrinkage.

Example: if it starts at 1,000 inches and grows to 1,010 inches will it come back to exactly 1,000 inches?

I think it changes a tiny fraction of a % and would grow or shrink depending on the chemistry and / or grain structure but would really appreciate a source.

Thanks,
Tom


Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[CoryPad]

This is an example of thermal expansion and contraction. Temperature changes induce thermal expansion strains, which are elastic. Since they are elastic, your item will contract back to its original size.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[metengr]

tomwalz;
In a perfect world (no residual stress, no oxidation, isotropic behavior, homogenous material, same heat up and cool down rate), if a piece of steel is heated from ambient temperature to some temperature (x) and cooled back to ambient temperature, it should not change dimensionally.

Considering the number of variables, I would do the experiment yourself to monitor actual dimensional change.

 

[tomwalz]

Thank you.

So that means there is absolutely no change in dimension, even just theoretical, due to the processing?

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[tomwalz]

Got both answers now - thank you gentlemen.

tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[unclesyd]

tomwalz,
What is the steel that you are heating to 1500F?

With a lot of steels you will get a phase change that will alter the dimensions slightly upon cooling and if reheated any the change in dimension will be permanent.

 

[redpicker]

As unclesyd says, it really depends on many varialbes.

If the carbon and alloy content of the steel is such that the transformation temperature is below 1500F, then there will be a dimensional change due to a volume change associated with the transformation. This change is reversable, however, and will reverse itself upon cooling. But, because the mechanical properties of the material are vastly different before and after this change, permanent dimensional changes can occur if the heating and/or cooling rates are fast enough. Then there is the effect of piro microstructure. Again, if the transformation temp is below 1500F, if the final microstructure is very different than the begining microstructure, you may also see a surprising dimensional change.

rp

 

[HgTX]

It may also depend on the conditions of restraint during heating and during cooling.

Hg

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[tomwalz]

It looks like it was residual stress in the steel and not a growth issue.

We brazed a carbide ring into a steel holder. The steel was about 6 inches across and about half an inch thick. It turns out that the rings became ovals.

The unbrazed parts measured between 6.498” and 5.000” inches in any diameter.
Afterwards they had a definite major and minor diameter. There was also a huge difference in the amount and direction of growth from part to part.

6.492 6.509
6.494 6.51
6.498 6.505
6.5 6.503
6.504 6.509
6.509 6.512


Thanks to all,
tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com