Cracks in my blade

[DANA HOLMAN]

Hey Guys its need awhile since I've been on but, I have a problem. the other day I was working on a bowie and after I heated treated it and was doing the finial grind I noticed a crack in the blade. It was almost half way down the blade. and then yesterday another one did the same thing. I'm using 5160 as I have for 3 yrs. and have done the same steps over and over again with good blades in the end. Both knives went through the chop test, could this be where the cracks started?. I broke the first blade and the core (to me) Looks very good, If I can get my picture to post I'll post them.
If any one can help, I thank you
Dana

[Lin Rhea]

I have a few questions Dana to try to narrow down the problem.

1- Did you forge or stock remove this blade?

2- Is it new steel?

3- Describe how, if at all, you heat your oil for the quench. Also, what oil do you use?

4- What are the steps you mentioned? You can probably answer all of the questions under this one, but be specific with question 3 please.

[DANA HOLMAN]

Lin, #1- I did forge the blades #2-no it was a leafspring, this may be the problem.  #3- I have a guench oil but its not parker 50. i heat the oil by heating up a bar of steel and putting in the oil and stiring. #4 After forging and annealing, i grind the blade, hand sand the blade to 320 grit, then i normalize 2 times and on the third time i quench. then ill sand alittle just so l can see the color in the oven. I'll final grind, test the edge and then finish the blade with hand sanding.
Hope this help you with my problem.

[Lin Rhea]

OK let's start at the beginning.

If you forge the steel too cold, it could form small cracks that will show up later. Just stay in the steels safe forging range, orange to bright red.

If you use old leaf springs, you will have more cracking than if you use new material, all else the same.

Here I have to ask something that may sound strange. When it comes to stirring your oil, what kind of steel are you using to heat and stir? Angle iron, rebar, etc?

Some of the words we use sometimes get mixed up and mis used. When you say normalized, what color/temperature do you mean?

Bear with me, I think we can figure it out.

[DANA HOLMAN]

Lin, i have a small pan of oil maybe a gallon of oil. the steel is just a 1/4" x 1 1/2 bar. i heat the end up about 4-5" to red and stick it in the oil and move it around until it cools off.
the normalizing I'll bring it up to orange the first time then let it cool to black. the second time I'll bring it up to a good red and let it cool to black.
Then I'll bring it up to nonmag. and quench
It kind of funny, ive forged 6 knives from this steel at the same time and 3 have broken and 3 are fine. The third one had not even been heated yet, so you may be right about forging to cold.
Hope this helps

[Lin Rhea]

Every thing is sounding good, but I want to get this point clarified. You are stirring your oil with a hot bar of steel, right? Is that bar some of your 1/4 X 1 1/2 high carbon blade steel? Or is it some non specific steel dedicated for this one and only purpose?

[DANA HOLMAN]

Lin, It's just low carbon (home depot) scrap that I've used for 3 years and that's all I use it for. Should I not be stirring the oil? I've never checked the temp. on the oil doing it this way but I will tomorrow.

[Lin Rhea]

No, Dana, that is fine to heat your oil that way.

I was afraid that you may have got some of your blade steel of that same size mixed up and used it (the blade steel) to heat and stir it. This would inadvertently harden it, which could be  later forged into blades that are very prone to cracking.

So far, it's pointing toward forging too cold.

[DANA HOLMAN]

Thanks for your help.

[tippit]

I know I learned my lesson on forging 52100 too cold.  It has to be hotter than 5160 or 1084 as it will spider crack through out if hit cold.  Once again Detective Lin to the rescue by digging up more forging info from Ray Kirk.

[Lin Rhea]

 Jeff, as you probably can guess, it comes from lots of mess ups myself.  

[beaver#1]

I had this same problem with a couple of mine a fewonths ago. And I figured either forging to cold or a bad section of steel.      ( sense like you said I also followed my regular process).   Lin, have you ever had a bad price of steel that would cause this?

[Lamey]

Ive had 1084 not crack but SEPERATE, like it was made by rolling 2 thin pieces together at the mill.... that in turn separated during forging.

This is one reason I really like to work with round bar, ive never had any issues, of any kind when using round bar be it in W2, 1086, L6 or 5160.

[Lin Rhea]

Dustin, I have indeed had a small bar of 1084 tear in odd places. It was not just a fluke, because three different guys had the same thing happen with that same bar at a forging demonstration. It's rare but it's good to know that it can happen.