flame straightening

SHOKR

SHOKR

Well-Known Member
hi-lo!

i send my work to a HTer who can do a not-so-good job from time to time
in the past period i got back from him seriously warped blades in Sverker21 (d2) and 55Cr3(5155)

i was going to go for the heat in oven with clamps and shims but someone suggested flame straightening method, anybody tried that before? any info or tips?
i checked online but didnt find a good source of info, specially since all the sources i found were speaking about non tempered steels

thanks
 
I have never heard of flame straightening but it sounds like heating with a torch. I'm thinking if you heat with a torch you will have hard time getting the steel hot enough to straighten without ruining the heat treatment. What type of steel are you using? I have had pretty good lick clamping my warped blades straight (angle iron and c clamps) and tempering the blade another cycle in an oven (350-400 Deg range depending). I'm only using simple carbon steel (1084, 5160, 1095, etc)
 
Brad
i'm HT noob, never tried it, so what i was told before was heat below temper heat and use the fixture you just mentioned

recently two different people suggested the flame straightening, one said he learned it by heating with hair dryer (or heat gun too probably) and touching one side with wet towl (i am guessing the convexed side to shrink it)
another told me a torch (because its more contralable in heat spread than heat gun) along the center line and let it cool between heats
while reading one suggested torch and water spray bottle for cooling

as i mentioned i'm using 55Cr3 (pretty much 5155) and sverker21 (which is d2)
 
Well I would not think a heat gun would get hot enough to do anything but I have been wrong before. My method is simply another tempering cycle. For example I temper 1084 at 400deg. If I have a knife that is warped I do one cycle at 400deg for 2 hours then I clamp the blade straight or a little further then temper it again at 400deg for another 2 hours. At this point if the blade is still warped I clamp it again and do my final cycle. I do 3 tempering cycles at 400 for 2 hours sometimes I need to do another cycle to get the warp out. Another thing to try in the future is leave a little extra meat so you can true the blade up after heat treating.

I have never worked with D2 so I don't know what temp you should use.
 
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Thanks Brad

I dont know if i can do the 400F temper and still keep things right, but i guess i better try sooner than later. Got some atudying up to do!

I leave a LOT of meet, actully one of the 5155 blades that warped was aprox 8" (1/4")that wasnt even ground because i wanted to chisel grind it
Another unground D2,but was about 1/8"
 
I wouldn't use a torch to heat the blade once it's been tempered. It would be too easy to over draw the temper. I would do the oven method.

Doug
 
Another vote for the oven method. Read up on the steel you are using and find the optimal tempering temperature, a quick google search shows D2 to be in the 400-500 Fahrenheit range for 58-60 rockwell hardness which should pose no problem for an electric cooking oven (double check this temp, as I said this was from a quick search, verify!). Take note that temp controls on ovens are notoriously inaccurate, a good oven thermometer is highly advised... Clamp the already tempered blade to a straight, flat, and stout piece of metal (Doug's angle iron is an excellent choice), using random metal shims (coins work great) if needed. Temper for about 1-1 1/2 hours, take it out of the oven and quench it in water... angle iron, clamps, and blade, the whole assembly, do not unclamp it and then quench. 3 out of 4 times this will fix it, but if it does not you may need to do it again with more shims so the blade is warped/bent in the opposite direction of the warp. If it is still warped after this, ditch the clamps and angle iron and temper the blade for about an hour, then Wearing thick gloves take the knife out of the oven, quickly bend it straight by hand and then quench in water. I've only had one give me that much trouble, but I did in the end manage to get it straight, it just took a few tries.
 
Thanks a lot

Yeah i decided will go for the oven now
Give it a shot with a small 5155 which i should heat at 400 from what i understood

Queation tho, some said leave it to cool, others say quench, whats the effect of each?
 
With the blade in a vise, determine the apex of the warp. Heat that area of the spine to blue or even gray, not allowing the colors to go to the edge. Flex the blade a little beyond straight, hold that position and pour water on it until cooled. That will lock it in straight. You may need to repeat to get it just right. This was Bill Morans method and works very well in most cases.
 
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