Fixing slight warping post HT on 3V

[Huntsman Knife Co. LLC.]

Hey guys,

I have a 3V utility knife that I had heat treated come back slightly bowed. The blade is almost completely finished and I just now noticed the bow

I surface grind most of my blanks before doing bevels to get everything flat and square but the chuck is strong it likely flattened out the bow in the blade while surface grinding and I didn't bother to check for straightness afterwards.

So here's the problem. There's about .050 of a bow across the entire blade and I need to get rid of it without inducing stress or harming the edge.

Whats the best method to use? This is a pretty thick blank at .21 and I've never had to straighten an air hardening steel, let alone one that tempers so high. My current plan is to shim it up in a vice, heat with MAPP gas to about 4-500 along the spine and tang and then tighten the vice and let it cool.

 

[samuraistuart]

That is very little bow, but I know how you feel!!!! I've used a couple of C clamps, a bar of scrap steel, and a small nail as a fulcrum, all placed into the oven, to take out a bow. But the warp I had was severe. Tweaking those clamps to get that small of a warpage out might prove difficult, IDK. Maybe worth a try? Clamp the bar of scrap steel to your blade, parallel, with one clamp at the tang and the other towards the tip. Place the nail between your blade and the scrap steel at the apex of your warp. Tighten one of the clamps until the blade is COUNTER bent the other way. Over-bend it just about as much as it was bent the other way, and place that whole contraption in the oven. Not sure about temps for 3V, but 400 works well for simple carbons steels. Once it is done, you can take it out and check. You may have to do this a couple of times to get it dead straight. Some have suggested dowsing the blade in water while it is cooling down while still clamped. Never have tried that approach, tho. This clamping method worked PERFECT for me to get a bow out of a 13" oal knife that was .065" thick. I hope it works for you, or someone might have a much better suggestion.

 

[Stacy E. Apelt - Bladesmith]

The three point straightening process should work fine. Do it at 400F, not at room temp. repeat as needed (400F each time0 until youget it out.

 

[Huntsman Knife Co. LLC.]

On my 4th attempt using the 3 point system I cracked the tang

didn't bend at all before cracking and is still bowed. It may not be possible to fix such a small a bow on thick steel.

Damn. Had the whole blade finished and got greedy. $100 mistakes are not ones you easily forget I suppose.

 

[mete]

That's one of the high tech steels that you can temper low [400F ] or high [900 F ] ,I prefer the low.
Thins happen at the steel mill which may add stresses that show up after HT. To prevent - before you HT sress relieve at 1200 F for two hours , then straighten if necessary. , then HT.

 

[Stacy E. Apelt - Bladesmith]

Bummer. It happens now and then, but it always hurts.

I had a tiny warp in a wakizashi a few years back. It was not much more than your warp. I went to straighten it and about the third bend it snapped in half. I made a pair of tanto....but it really was gut wrenching when it wend "SNAP!".

 

[james terrio]

On my 4th attempt using the 3 point system I cracked the tang

I'm not at all surprised that it went badly. 3V is definitely not something you want to be fooling around with post HT. "Normal" old school "rules" of warming it up and straightening it out simply do not apply... that works fairly well with simple alloys, but... This ain't your grandfather's Oldsmobile

The only way to do it right, is to do it right the first time. Having to "correct" warps and wobbles after hardening just means it wasn't right to begin with, or there's something fouled-up in your HT process.

 

[Huntsman Knife Co. LLC.]

I've noticed in my destruction testing with 3V that it will almost always break before it bends and takes a set like 52100 or similar will. I probably shouldn't be surprised with the results.

It looks like this knife was a lost cause then since I didn't catch the warpage early enough on. Live and learn

 

[Justin King]

I was told by the guys at Peters a while back that in order to straighten 3v post-HT, you have to fixture it during the heat cycle and run it at 10-15 degrees higher than the original tempering cycles. Unless it was tempered in the lower range, you're looking at 980-1000F. The hardness starts to drop drastically once you bust the 1000F mark, so without precise temp control this is pretty risky business. Even with a good oven I would expect to lose a half point or more of hardness, if everything went well. I found this info to be dead on, the one time I had to deal with this, and it took multiple cycles to take out a fairly small warp. Warped 3v is stubborn stuff.