# Softening spine with a torch



## Marko Tsourkan (Jul 11, 2011)

Is there a practical reason to soften a spine on a knife? Is this done with a torch while the edge of the knife is immersed in the water? Can it be done with a portable torch?


Marko


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## rockbox (Jul 11, 2011)

I assumed that differential heat treat was so you could have a super hard edge and still have some flex for strength. The same reason for san mai. What I never understood is why people do it for kitchen knives that have under 63 hrc since you can make knife with that hardness through out without any strength issues. 

I have no clue what the proper way to do it would be but I think it would be easier to put the edge between some quenching plates versus water assuming you heat treating before grinding.


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## JMJones (Jul 11, 2011)

Yes it can easily be done with any torch, even propane. My experiance is only with high carbon and not stainless steels. I dont think it would do much on a blade that was differentially hardened because the spine should already be a mixture of pearlite and martensite and much softer than the edge. However if you did a full quench on a high carbon steel, you can temper the whole blade at whatever temp you choose for the edge, then put the edge in water and bring the spine up to whatever temp you would like to temper it at. Quench plates would probably work but a pan of water allows you to keep the edge under the water and if you feel that you are getting to hot on the spine you can give it a quick dip to cool it off.


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