heat/stress risers and tang stamps

[Alarion]

Three is fine, as long as at least the first one is really good and hot. I used to go with the prevailing ideas about low temperatures for blade steels, but now I have been doing enough metallography that I am becoming a greater proponent of using heat to move sutff around, instead of barely kicking things over Ac1 and segregating things worse. If you really want to see cracking- get a heavy carbide laden band down the center of a piece that you failed to break up and then quench just a wee too fast! It will crack along that line every damned time.

I do the first one REAL hot, let's say that's almost an anneal.
Then I do the other two progressively lower and with slooooow cooling.
Then I bring up the blade to non mag very slowly, and, if possible, just the tip and edge, then quench.

 

[Gene Martin]

Just to clarify, the blade was 1/4" 154CM. I stamped it and heat treated it. It cracked. I've done a number of other blades for the same customer, using his stamp which consistes of 3 initials. The stamp is about 1/8" tall x 1/2" long. It's a commercially made stamp.

In 14 years I've had 2 blades crack. Both cracks were the result of 60 grit marks on the cutting edge prior to heat treat. One was D2, the other ATS34. That hasn't been a problem since I started making sure the edges were smooth prior to heat treat.

The only difference between this and all the other stock removal blades I do, and there have been a lot of blades under that bridge, is the stamp. Nothing else is different. I'm really anal about following the book on heat treating, so I don't fool around there and change things. The blades are always cold before they go into the LN. The soak time is about 12 hours, although that will be shortened in the future.

The blades are warmed to ambient temp before drawing temper. I use a Paragon furnace for all heating cycles on air hardening steels.

That should answer everything as to method.

Like I said earlier, I hate problems and like to know I'm doing it right, every time. My customer is shortchanged otherwise, and that isn't an option.

Again, a very informative discussion. I won't stamp tangs on 154CM in the future because it will be a 5 day heat treat job before it's over.

Thanks and keep the ideas coming. I keep learning.

Gene

 

[Alarion]

Bufford said: I have never had a problem stamping knives in my 20 year plus of knifemaking. I work mainly with 440C. Prior to HT after all the grinding and drilling has been done, I spot heat the area on the tang that will be stamped to a cherry red with a torch. Strike once with hammer, clean it off with a quick pass on the grinder. Then move on to heat treat.

The only problem with this method is that you only have one chance with the hammer striking the stamp. The stamp better be even or it will leave an uneven impression which can be difficult to correct. With practice it gets better. Isn't that a big part of knifemaking anyways?

Uhm... dunno... You are actually hardening that part with the quick cooling the stamp causes... But I guess the subsequent heating up evens everything out.
I'd normalize, though.
Yep, maniac of normalization. I do it even if I laid a single hammer blow on the steel.

 

[Bufford]

Glad you've never had any problems but that sounds like trouble for an air hardening steel. I would bet it's not much softer heated to a red heat than in the annealed state. Have you tried it without heat? Maybe one of the metallurgists can comment on this.

I learned by trial and error, as there was little published about knifemaking back in the early part of the 1980's.

I ordered my first stamp from the Evers Stamp company somewhere in New York. Anyways I struck the stamp on cold blades and quickly found that the stamp wore down quickly after just a few knives. I worked with 01, and 440C, and both were hard on the stamp cold.

I then tried heating the tang to a dull cherry red, and have been able to use the stamp hundreds of times with no noticable wear. So this method works for me.

As for stressors being raised in the steel, good question, but not one knife has ever been returned to me for breakage from heating the tang. I guess it all works out when I heat treat and temper. My customers like the edge holding, so the heat treating must be working out properly.

Periodically it is a good idea to calibrate the heat treat oven, to make sure the thermostat is acurate. Over time mine has been out by 100 degrees.