Edge/torch quenching W1

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Posted · Report post

Hey all. I've annealed and shortened the sashimi knive i tried to make which cracked when i quenched. The one here.

I really only want about 1/8" of the edge of this blade to get hard.

So i was thinking of using a torch to heat only the edge, then quenching only the edge in water.

I was thinking of coating the whole blade with a thin wash of clay, just enough to keep it from oxydizing at all.

Does anyone think I may have sucess this way? Or might this cause the heated edge to split upon hardening?

Please keep in mind that this is a sashimi knife the will not get used very often, and only put to careful use cutting fish flesh. So I'm not interested in going for maximum toughness. I'm not worried about leaving the spine very soft or in it's annealed state.

Thanks for any advice.

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Posted · Report post

i wouldnt use a torch to heat ... hard to get even all along blade ... what type of forge are you useing?if you are useing a propane forge try putting a piece of pipe that the blade will fit in in the forge ( a knife maker friend taught me this trick) the pipe heats up and heats the blade but without the direct blast from the forge hitting the blade ... gives a more even heat with less scaleing ... as far as the edge quench that us a good idea... and that will give you your hardened edge and soft back ... you might also try oil instead of water . all the edge cracks i have ever had on knives have been because of water hardening.. I now use vegtable oil or crisco (the crisco hardenes back up for transport)...good luck!

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Posted · Report post

You can throw a couple of pieces of real charcoal in the pipe as O2 scavangers too. Works better with one end of the pipe closed and in a coal forge rotate it till the entire pipe is to heat before putting in the blade.

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Posted · Report post

Since the piece you are working with has already cracked at least once that you know of you really have nothing to lose by testing any methods that youi wish. If it were mine I wouild start with annealing it first. Try the edge quench and see what happens. Have you researched to see how the knives you are trying to duplicate were heat treated and what kinds of steels were used? Another thing to consider is that even though the knife will only be used little and you are not concerned with it having toughness, after it has been fitted and later on your needs may change. Generally speaking a knife that is not tough may be brittle. If the knife use changes in its life this may lead to failure and possible injury. Be safe as you learn...

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Posted · Report post

I was told when in doubt use oil. The few times I've quenched in water I got cracks when I was using high carbon steel. I use used diesel motor oil.

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Posted · Report post

Thanks for the comments guys. I have two knives almost ready to quench, one is the failed one, shortened to a smaller but still perfectly useable size (about a 6" blade) for a sashimi knife. The other is a 2nd sashimi knife, same as the first, about 9" newly forged.

I am worried about getting an even heat using a torch but i may try it on the shorter blade, using a map gass torch and moving it back and forth to try and heat just 1/8" or so along the edge. If thats not too dificult to evenly heat a thin area along the edge then i may try it on the longer blade.

I think i will try oil for a milder quench as well. Can anyone recommend a temperature to heat the oil to or just do it at room temp?

So... about doing this properly... sashimi knives are traditionally made by forge welding a piece of carbon steel along the edge of a larger piece of wrought iron. I have not any wrought iron, and even less of the skill necessary to forge weld a thin piece of carbon steel along another piece of anything.

So the quest towards gaining experience and practicing techniques continues... I'm still having fun at this.

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Posted · Report post

I've been told about 100 deg but I have always used room temperature without a problem. It may flame up on you. I have my oil in a metal bucket and I keep some old license plates with the buckets and when it flames up I smother the flames with the license plates.

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Posted · Report post

Thanks. I just got 5 or 6 quarts of motor oil from a friend who was cleaning out his garage. I'm going to use that.

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Posted · Report post

Thanks for the link Glenn. I hadnt considered the issues discussed in that thread.

Luckily, i have about 6 quarts of new 10w30 which had been sitting in a friends garage and he gave them to me after a recent (20year overdue) garage cleanout. Kind of an expensive quenchant, but i think this stuff had been sitting in his garage for nearly 20 years...

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