Cracked blade- What went wrong?

J

JH225

Gold Member
Joined
Feb 7, 1999
Messages
1,145
OK, so I take my O-1 and grind out a 1/8" little neck knife, take it all the way through 220, heat it with my torch to non-magnetic and quench it in warmed oil. Upon taking it out of the quench, I notice that the blade is slightly warped near the middle of the edge, I put a little thumb pressure on the tip of the blade while examining it and the blade snapped right at the warped part.

What did I do wrong? Get the blade too hot? Not heat the quench enough? Anything else?

It was a real nice grind too :(
 
Where was the break?
1 uneven grinding in thickness
2 overheated during grinding
3 hot spot and stress rizer created by torch
4 nick or thin spot in blade edge
Possibly many others.
 
Maybe the blade was too thin, quench oil was too light and/or blade was beyond nonmagnetic especially in the middle where it warped. Leave the edge thicker next time? Were the lights on or was the sun bright so you couldnt see the colors? Do you have a good strong magnet? I now use a cow magnet because I couldnt feel the pull with the wifies refrigerator magnets.
 
What quenching oil were you using?

If you heat the blade more from one side than the other, uneven heat can cause warp, though generally not to this degree.

Breaking it with finger pressure indicates something very wrong. Once in a great while it could indicate a fault in the steel itself.

Just an outside chance, could water got into your oil? The oil floating on top of the water could have allowed the edge to have been quenched in water rather than oil?

There are some good trouble shtting thoughts in all the suggestions.

Don't give up the ship!
 
Did you grind to a finished edge first before quenching?if so try leaving it a little thicker.Also did you try bending it back in shape before you tempered it in the oven,That would have caused a break.I know I did that once.I had a blade warp during the quench and thought that I could straighten it by hand real quick before tempering,needless to say I learned real quick not to do that again,The Blade became two pieces of steel in my habds and I had a very sad look on my face when it happened and I believe I said some really bad words to myself at that time also..
Just some thoughts..
Bruce
 
Hey Bruce, I learned a neat trick from Kevin Cashen while at the ABS Intro class. Kevin calls it 'Quenchus Interuptus'.

Basically you do your quench just like you normally would but when quenching you pull the blade out of the oil and check it after the wild bubbles settle down. When the oil still smokes but doesn't vaporize off of the blade the steel is at around 450 F (depending on your oil). You have about a 10 second window to straighten out any bends or warps before the blades cools down too much. You do this with your hands. Don't need to chuck it up in a vice or anything. Of course you have to wear gloves for that but it really works. I seldom have any warping because I always triple normalize and usually do an edge quench. But, it's a neat trick anyway.

The reason for the 'Quenchus Interuptus' according to Kevin is to allow a more stable environment for the formation of martensite since it starts to form somewhere between 400 - 500 F. It's also referred to as 'Mar Quenching'. You just take the blade out of the quench at the right temp and let it air cool like when you're normalizing. Then go ahead with the tempering. I use that procedure on most of my blades and am real happy with the results.
 
I wonder if you could still etch the two broken pieces and see if any abnormalities show up near the break? Not sure if this would work, just a thought.
 
Guy's,

Thanks for all of the excellent thoughts. After talking it over with one of our rather knowledgeable members, I believe a combination of two things happened.

First - I think I should have left the edge a little thicker. It was to the point of one third of the pregrind thickness, but I think I will leave it a little thicker on the next try.

Second - I also believe that I did get the blade too hot on one side. I was probably in a hurry to get it done, and did not heat it evenly on both sides. The grain was rather coarse along the break instead of being very fine.

I have learned a great lesson with this screw up. "Take your time and pay attention to details".
 
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