A quick question for all you knife makers out there. I understand the process of heat treating and tempering but is there any time constraint between the two processes? I.e. should tempering be done as soon as is practical after the heat treat or does it not matter at all...... for example would it matter if it was delayed by a day or two?
Tempering
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The thinking is that the temper should be done shortly after hardening. The blade is under a lot of stress so the sooner you can relieve that the better.
I tend to do a first stage temper straight in my kitchen oven that's not at the full temperature I want straight after, just to features the steel. I'll then do a second temper the next day in my heat treat oven which is more accurate and has cooled after the much hotter hardening.
I tend to do a first stage temper straight in my kitchen oven that's not at the full temperature I want straight after, just to features the steel. I'll then do a second temper the next day in my heat treat oven which is more accurate and has cooled after the much hotter hardening.
it depends on the type of steel, ambient temperature, heat treating regime and geometry of the piece as to how critical time is; but as a general rule get a stress relieving temper (anything over 150C) as soon as possible. Once that first one is done, you can do your proper tempering at any time there after.
Most spring steels will be ok for hours or days (thought there is a chance of dropping it and thus breaking in the meantime), but I've watched a drawknife made from O1 bend and then snap whilst it sat on my bench waiting for the oven to come up to temperature! These days I have the tempering oven up to temperature (first tempering run at a lower than intended temperature such as 180-200C) before I even quench the blades, that way as soon as they are hard they can go in still warm
Most spring steels will be ok for hours or days (thought there is a chance of dropping it and thus breaking in the meantime), but I've watched a drawknife made from O1 bend and then snap whilst it sat on my bench waiting for the oven to come up to temperature! These days I have the tempering oven up to temperature (first tempering run at a lower than intended temperature such as 180-200C) before I even quench the blades, that way as soon as they are hard they can go in still warm
... but I've watched a drawknife made from O1 bend and then snap whilst it sat on my bench waiting for the oven to come up to temperature! These days I have the tempering oven up to temperature (first tempering run at a lower than intended temperature such as 180-200C) before I even quench the blades, that way as soon as they are hard they can go in still warm
That's very interesting! Although it's never happened to me, I have dropped one and snapped after quenching; I think I'll follow your method from now on
Cheers,
Broch
That's very interesting! Although it's never happened to me, I have dropped one and snapped after quenching; I think I'll follow your method from now on
Cheers,
Broch
yep it was an odd one. I could hear a weird creaking noise and as I looked around to see what it was, I saw the drawknife move and then half of it fell on the floor! I've had other things split as they cooled (such as laminated blades or axes) and the contracting soft sides have split the hard core steel. Also watched lots of things warp in the couple of minute straight after quenching as the martensite forms.
As already said, oven tempering just after quench I get this up to temp as I bring the forge up too, I work mainly spring steel which is very forgiving.
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