Carburized Soft Spots

[Tigrrr]

I'm getting softs spots on carburized parts that were machined prior to heat treat. Something is masking small spots on the surface preventing carbon penetration. Any suggestions? Anyone else encounter and solve this problem?

 

[arunmrao]

Please check the loading pattern of charge. See that all the surfaces of the components are freely exposed. Perhaps a proper fixturing suitable for the component to be heat treated needs to be designed. If you can furnsh the details I shall be able to help you in designing. Hope this helps.

 

[gdodd]

If gas carburizing soft spots can be caused by parts held too close together restricting flow of the carburizing gas to the surfaces requiring hardening during soaking. This is a common problem with flat parts that move to mask one another off after charging the furnace.

Masking can also produce a slack quench in mild steels with low hardenability so suggest you review your process.

 

[kieke]

We have noticed this problem as well at our firm, and we don't have a proper explanation yet, but we have a reason to believe that these soft spots are caused by the use of soluble oils while machining before heating. Can anyone give aproper solution?

 

We experience this problem much more often now that Big Brother won't let us use solvents to clean parts before heat treat. The problem is that water-based cleaners just don't work as good as solvents. Problems can obviously be from cutting fluids or oils, but also from leaking hydraulics on machines. We have had acceptable results with specific cleaners/oils/steels only to get soft spots when we switch to a different steel alloy. Apparently subtle reactions can take place between the material alloying elements and cutting fluids during the cutting process. This is one case where the good old days was really better.

 

[rido]

Check out if there is the right steel tipe to be carburised.
The other point is - may be you do not reach the required temperature for chemical diffusion process.

 

[Tigrrr]

arunmrao and gdodd- Thanks, the loading pattern was never a problem.

kieke - run a design of experiments with the soluble oils to see if you can turn on/off the problem. Good luck!

formulaross - exactly! The problem occurred after the ban on trichloethylene. I wish I had more research on the surface effect of cutting oils on steels. Also I agree, steel grade makes a difference.

rido - we wouldn't be in the heat treating business if we didn't use the right steel, temp, carbon pot, etc. (smile)