Cracked blade

[DANA HOLMAN]

Well it was bound to happen sooner or later. I was working on a blade, took it to 600 grit with sananite for hamon, heat treated as I normaly do, resanded before tempering. I did not see any crack, but after tempering I had a 5/16 crack about 1 inch from the recosso. This is the first one for me.
So can anyone tell me if they think it happened during heat treating or tempering, I would think during heating. It's a shame because the hamon was very good
Thanks for any help
Dana

[Lin Rhea]

Dana,
           Can you tell a little about your situation? What steel, temperature your quenching at, type of forge, etc. ?

     I will say that it's VERY hard to know what happened or when from a distance, but we might can narrow it down a little.

       You said that you finish the blade to 600. I assume you are talking about the sides and top, but in what condition is the cutting edge? Is it finished? If not, which way are the scratches, length ways or accross the edge? Is the edge ground square or does it have a radius in it? Lin

[DANA HOLMAN]

Lin
I think the steel is close to 5160 it is the old buggy spring, I've made 3-4 from this steel. Heated to nonmagnetic and quench in veg oil, tempered @ 400 for 2 hr.
The reason I take my blades to 400-600 grit is I think it's easier to sand them when the steel is anealed. Just my thinking, after the tempering I have very little hand sanding to do. All the sanding is length ways and I some what sand edges. The cutting edge is about the weight the size of a dime or smaller
Hope this helps
Dana

[Lin Rhea]

Dana,
       I would have to see the blade to get some idea of what may have happened. If I was watching you go through the process , I MIGHT be able to see what happened, but right now we're guessing a little more than I am comfortable with.
         I suspect the blade may be a little thin on the edge, or may have some cross ways scratches right where it cracked.

[DANA HOLMAN]

Lin I will forge another one and take some pictures then maybe you can tell me where I went wrong
thanks
Dana

[tomh]

how much time elapsed between quench and temper? I have heard of some people having trouble with cracks if it is a long time.

[Lin Rhea]

That is true.

[DANA HOLMAN]

Tom
most of the time it's only 10-15 min, I let it cool just enough to handle it and then sand it and in the oven. I'm still scratching my head
Dana

[Lin Rhea]

I take it straight to the oven as soon as I can hold it with gloves.

I also look it over while on the way to the oven. Usually I have some inkling of a crack if there is one. Not always, but most of the time, I hear or feel it crack.

[DANA HOLMAN]

Lin
I stop to take the scale off, so I can see the color. Should I stop and go stright to the oven?
Dana

[Lin Rhea]

Yes, but you should have an idea of what steel it is and have the oven set accordingly. If it is an unknown steel you are shootin in the dark unless you know how to work it up the charts. The colors verify what you know about the steel, but that is just a start. The real test is the actual hardness, which you test by files, chopping etc.

[DANA HOLMAN]

Yes Sir, file and chop test, this is really unknown steel, but I've made 3-4 knives from this steel, and no problems, would it be wise to break the blade? Just to see the inside, I did anneal it, because I thought I would grind it to make a smaller, but I would end up with about a 7/8" blade, so I won't  regrind
thanks Dana