That gives you an idea of the stresses that occur in steel during their phase changes. It's the battle between the unhardenable 203 and the hardenable 1084.

What you need to do is avoid letting the thick spine area of the 1084 reaching austenite. You do not want the thick areas converting to martensite and creating stress.

Are you using your forge or an oven for austenizing?

Steel when it is hardened is lager than when annealed, the A230E will not harden so if is staying the same size through heat treating. the 1084 through hardened and grew, in thickness this is no issue, in width there is not enough change to produce much of an issue, in length how ever a great deal of strain is built up as the core gets langer and is held in place by the jacket until that strain over comes the strength of the material as a crack.

now that we understand what happened we can think of preventing it. one way is to do as Karl mentioned and only harden the thinner section of the knife one way is to temper immediately to relieve the strain, like before the blade reaches room temp or to cold hammer the cladding to expand it release the tension, or use materials that are more compatible in hardening.

MP

Had that happen once with some damascus core San Mai but never with monosteel core. Have you tried 410 for the cladding? Seems to move with the carbon steel better imo.

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one way is to do as Karl mentioned and only harden the thinner section of the knife one way is to temper immediately to relieve the strain, like before the blade reaches room temp

MP

That's just not soon enough. Most of the time it splits before you'd be able to get it back up to tempering temp. Ask me how I know. (The only person I know who has made more than me is Burt Foster.)

|quoted:

Had that happen once with some damascus core San Mai but never with monosteel core. Have you tried 410 for the cladding? Seems to move with the carbon steel better imo.

It doesn't much matter if it's 410, 420, 203E or wrought iron. That differential will kill ya'.

I have a secret....................

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It doesn't much matter if it's 410, 420, 203E or wrought iron. That differential will kill ya'.

I have a secret....................

How close do we have to lean in to hear this secret?

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How close do we have to lean in to hear this secret?

The reason the spine splits is because that's where the thickest non-hardening element is.

That's where the most expansion/non-expansion differential is going to take place.

It will also split under the choil.

How would you go about getting hot steel to NOT harden? What could you use to inhibit hardening when you quench?

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How would you go about getting hot steel to NOT harden? What could you use to inhibit hardening when you quench?

I'll venture a guess...

Maybe slap some clay on there?

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I'll venture a guess...

Maybe slap some clay on there?

Bingo!!!

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That's just not soon enough. Most of the time it splits before you'd be able to get it back up to tempering temp. Ask me how I know. (The only person I know who has made more than me is Burt Foster.)

My understanding is it needs to be back in the temper before it hits MF, so above around 450, I think I got that from Greg Cimms. it has worked for me in the past the few times I messed around with it.

MP

|quoted:

My understanding is it needs to be back in the temper before it hits MF, so above around 450, I think I got that from Greg Cimms. it has worked for me in the past the few times I messed around with it.

MP

Just don't get the super thick places hard in the first place. I've been making the SS San-mai for 11 years and have made a few mistakes early on. I would never risk trying to get it back up to temp to avoid a split. I applaud those who succeed.

I'm very much a beginner at San mai I've done 6 with A203e/ 52100 (first 2 split down the center) and one 410/26C3 and one Aeb-l/ 26C3 a simple carbon steel with 1.25% carbon and .30 chromium it took quite awhile to find that clay thing and I still haven't used it. It may be a different thing because these are kitchen knives,but I think that stress relieving cycle after profiling and really being careful (as I should always be) with my normalizing and thermal cycles has eliminated problems since the first two. I did water quench one of the two stainless blades don't think I'll do that again p 50 gets the steel plenty hard. By the way Karl you were definitely one I paid close attention to during my research.

That makes sense. Thanks for the help