color change after heating the metal?

[andypo]

I guess this would be a simple question for a metallurgical engineer,
We have a sprocket made of 4140 HTSR steel that gets heated to be pressed onto a shaft. The oven is set to a 180-190 deg. C. 2 of the sprockets were left in the oven for a longer time (maybe 1-2 hr) and the color changed to a dark yellow.
Geometry hasn't been effected. Now I have to determine if it's OK to use these sprockets, but I can't say if there were any changes to metal itself.

Thanks.

 

[redpicker]

Without knowing the hardness of the material, or its specific heat treatment, it is kind of hard to state for certian that nothing has happened to the material. But, in general, exposure to 180-190 C for an hour or so will turn freshly machined steel a straw yellow color and exposure to these temperatures should have very little effect on the properties of the steel.

I think your're fine.

rp

 

[TVP]

I agree with redpicker, it is likely that the properties have not been affected by an extra 1-2 hours at a 180-190 C.

 

[unclesyd]

4140 parts are baked out at this temperature or slightly higher for hours to alleviate H2 Embrittlement. Your color is just the beginnings of an oxide formation. You probably have some good fingerprints on the parts.

We operate 4140 parts at 283C for days on days with no problems.

 

[andypo]

Thank you all.