Heat treat question -different thickness cross section

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Sep 9, 2005
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Hi Guys,
quick question regarding air hardening steel.

I dont do my own HT but I have seen that when guys treat air hardening steel, they take it from the heat source and place it between 2 pieces of metal or steel, mainly to keep it straight? When this happens though, the parts of the knife that are in direct contact with the other steel will of course cool quicker than a section that was maybe thinned with grinding or filing, for instance if you grind the bevels before HT.
Will this maybe affect the hardness compared to the sections that were in contact with the other steel?

In the past I have always ground the bevels in before HT but now I am wondering if this the right approach.

Can you please advise?

Thank you,

Mike
 
I don't know the correct answer but will say I worry about the same thing so I use thin steel 1/8" or less and do not grind any bevels before heat treat.
 
So a few things. One, the parts in contact with the plates will cool faster, and the plates are mainly to help keep the blade straight. That said, the reduced thickness at the edge also causes the section to cool faster, I am not going to do the math but it's possible that the convection on the thin cross section has a higher cooling rate than the plate conduction. I would definitely say this is plausible if you remove the blade from foil, less so if you don't.

The more important thing is that even in foil with no plate contact the thin cross sections we work with will still cool fast enough to ensure a full transition to martensite, so it's not a big issue.
 
Normally, there is no problem. On a very thick blade with a very thin edge you can get some bacon curl, but it is not a common problem.

Many of us just profile the blade and harden it. After hardening we grind in the bevels. This saves work and guarantees a flat blade.
 
Hi Skinner1nc and Hi Stacy. Thanks for the replies and sorry that I am so late in acknowledging, I just didn't think of looking at the post again until now. You both have good points for me to take away from this.
Skinner1nc, very good point about with the edge being thin, the heat loss with be more rapid so I guess it balances things.
Stacy, I was just concerned about it being more difficult and time consuming to grind hardened steel and also of course, the belt wear is bound to be more. I will just have to test it and see;).
Thank you all for your replies.

Mike
 
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