A question on warp straightening and hamon formation

David Stifle

David Stifle

Joined
Nov 20, 2008
Messages
10,188
Hi Guys,

I've been clamping my blades to straight flatstock during tempering to straighten them, and it works fine except when I do it with a clayed blade. On my last two clayed blades, when I took them out of the oven and started sanding them down to reveal the hamon, I discovered that the side of the blade which was clamped to the flatstock has a muddled, indistinct hamon, really just a big smear. The other side of the blade had a perfectly formed hamon.Since it's happened to me twice, I'm assuming the act of clamping it to another piece of metal during the temper is what ruined the hamon. Can anyone help me understand what's going on here?

Thanks,

Dave
 
Interesting, I've not gotten that problem, at least with W2. I've had a couple chef knives that needed significant clamping to a straightedge during tempering- they went through several cycles each and the hamon didn't suffer.

I did have a few times when I was unable to remove warpage in hamon blades by clamping during tempering. That's frustrating.
 
More of a question, but could you clamp it along the spine but above the hamon so it wouldn't touch the line?
 
Salem. these blades were W2 also. The only thing I can think of, as strange as it sounds, is that I barely wiped the quench oil off the blades before I clamped then down and put them in the tempering oven. But still, isn't the hamon hard wired once the steel has been quenched? so why would the side that is clamped down disfigure the hamon so bad?

Msgysthath, These were not flat ground blades, so it would have been impossible to clamp them by the spine only. That could also leave the
uclamped portion of the blade to twist.

Dave
 
Tempering temperature and time can certainly dull the hamon. The shorter the time in the oven the better.
Never heard of this one sided effect though. Thanks for the warning.
I guess it would be best to clamp over a pin rather than to a flat surface that has full contact. Come to think of it, I once clamped a blade and the disk of the "C" clamp touching the blade left a mark that stayed for a long time through the finish grinding stage...
 
David,
If you took the hot blade right out of the oil, wiped it off, clamped it up, and placed in the temper oven, it may well not have affected the rate of conversion to martensite in the area with the heat sinking of the clamp metal. This area would be much less defined since the conversion was spread out over a larger area. On the un-clamped side, the place where the pearlite meets the martensite would still be a distinct line.

The pearlite nose for W2 is less than one second, but the drop to Mf is as much as one minute or more.

Let the blade cool to room temperature COMPLETELY before clamping and tempering.

I had a new maker say that he was not getting hard blades and was following all the advise I gave him on HT. Upon closer evaluation, I found that he was pulling his blade right from the quench after 10 seconds, wiping them off, and sticking them in a pre-heated temper oven at 450F. .......They never converted to martensite.
At best he got a bainite/pearlite mix.
After changing his procedure to having the blades cool completely, washing them off in cool water, and then putting them in the oven, the hardness suddenly jumped to where it should have been. What he had over-done was my comment stating, "Place the blade in the temper oven as soon as possible."
 
Stacy, thanks! I was doing exactly as you described. Next time I'll make sure to let the blade cool before clamping. I understand now that I was doing wrong.

Dave
 
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