1st hollow grind and it cracked

rocketmann

rocketmann

Joined
Dec 24, 2005
Messages
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Well I'm not very happy right now, just quenched my 1st hollow ground knife and I noticed a small 1/4 in crack in the blade at the cutting edge:barf: . I think it must have been a stress riser that caused it. I ground it to a 220 grit and left the edge about dime thick and quenched in 120 degree oil. I guess it's back to the old drawing board, and this time I will be sure to get all of the scratches out!!! It was looking pretty good too..well I'm tempering it anyway and will break it to see how it looks inside...maybe I can learn something from this..:(
 
Well I tempered the blade once at 400 for one hour. Bent the blade in a vice 20 degrees and it snapped in half. the steel was dull grey and I could see the grain with the naked eye, It looked like very fine grey sand.. I guess 2-3 temper cycles may have helped but I didn't want to waste the time..BTW the steel is from an old round sawmill blade about 26 inches across.I am told that this is usually L6?? The blade hardended well. Does anyone know the proper way to heat treat this steel or do I have to play with it to get it right?? Thanks for any imput..:(
 
A mate of mine who forges changed the way he profiled a blade before heat treat. He use to grind along the cutting edge and have no problems. On the blade that cracked he profiled the blade at right angles to the edge, something he vows to never do it again. hope this helps.

Peter
 
Problem is that "usually L6" doesn't tell you if you blade is the usually or the unusually .Saw blades can be many steels.
 
That sucks... But this is what makes it fun! Right? Right?! :)

This is one of those times you need to experiment with several small pieces before attempting to heat treat the actual blade.

My personal opinion is that you didn't temper it long enough. 400 degrees is probably pretty good, but I'd go at least two hours. I doubt one hour was enough to actually do very much. Good luck!
 
Probably too hot at time of quench.

Did you normalize before quench?

Stress risers in simple carbon steels are usually not a problem, I've quenched blades at 80 grit finish with no probs.

Also maybe a bit thin for a hollow grind pre-heat-treat ???
 
I quench at 50 grit with no problems but I never hollow grind. Everything I do is flat grind.
 
Did you normalize?

I cracked a blade last week, the only thing I did different was I didn't normalize. Usually I normalize twice and it's all good.
 
No I didn't normalize :grumpy: I allways do on forged blades but on this stock removal knife I forgot...I also think it may have been to hot when I quenched it. As I stated in another thread I just got a pyrometer and my coffee can forge is well over 1800 degrees. I am going to switch from map gas to propane and see if that cools it down some..I know that I can quench as soon as the blade turns non-magnetic but I like to soak it for a few minutes or so..It may be getting to hot during the soak..Looks like I have some experimenting to do.........:cool:
 
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