Positive affirmation

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Joseph Mansfield

Joined
Dec 24, 2020
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Hey all, I'm brand new to knife making and just finished my first knife with 5160 then subsequently destroyed it. Directly after grinding off the scale from heat treat I noticed a crack in the edge that went up about a half inch towards the spine so I decided to just put a working edge on it and see if I could learn from its failure. Low and behold it snapped after being batonned through some oak logs. So what I'm wanting is some advice on how to avoid having my blade crack during the heat treat.

My intent was to make a pretty robust all around camp knife so I made it out of 1/4 material. Its blade is about 7.5 inches long and 2 inches wide. Its a full flat grind.

I did an edge quench because I want it to take a pretty good impact because I baton my knives from time to time to make firewood. I used an oxy acetylene torch to heat the edge past magnetic and I felt like it was a pretty even heat. I didn't bother flipping the knife over while heating because I felt that the heat was bleeding through pretty well but looking back this may have been the root of my problem. I quenched in about 1 quart of AAA oil heated to 200 degrees but then it had to be walked down 2 flights of stairs since the oven is on the top floor and I quench in the basement. I dipped about 2/3 of the blade in the oil and let cool for about 10 seconds then i sandwiched between 1/4 plates of steel and clamped. After it cooled to being just warm to the touch I brought it out to look at it. It had a slight warp to a small portion of the edge so ill be leaving the edge thicker on the next one but other than that it looked good so I set it down on the table of my grinder and that is when I heard the "ping". Anyway, I tempered at 450 for 4 hours and I achieved good hardness and toughness other than the crack.

So after that lengthy explanation my overall questions are:
1. Where do you think I went wrong and had that crack develop? Should I have heated both sides of the blade and that differential heating caused stress? Or is it something to do with my sandwiching method or did just setting it on the grinder table really do it?
2. Does an edge quench make sense in this role and do you have any advice on my heat treating method that I should do differently? Should the whole blade be heated then only the edge quenched or should the edge be heated and the whole blade quenched?

I've read as much information on heat treating 5160 as I could find and specifically edge quenching 5160 but there are so many opinions out there so I figured I would make my own thread with the specifics.
 
I wouldn’t personally bother doing an edge quench. These steels are tough just go ahead and through harden it. Also if you are heating then removing from heat and walking down two flights of stairs before quenching it is definitely cooling down too much you’re looking to make that transfer to quench within a few seconds. Also if you can get access to a heat treat oven or send out for HT that’s a better option than using a torch. I would think you lessen stresses by heating the whole blade evenly and then quenching the whole blade evenly.
 
imill3567 said:
I wouldn’t personally bother doing an edge quench. These steels are tough just go ahead and through harden it. Also if you are heating then removing from heat and walking down two flights of stairs before quenching it is definitely cooling down too much you’re looking to make that transfer to quench within a few seconds. Also if you can get access to a heat treat oven or send out for HT that’s a better option than using a torch. I would think you lessen stresses by heating the whole blade evenly and then quenching the whole blade evenly.
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The blade is heated and quenched in the same location within about a second. The oil is heated upstairs then a helper brings it downstairs to quench the blade. I really would like to avoid sending out for heat treatment just because I'm attempting to do everything in house. It just ads authenticity to me. I know it would be a higher quality end product but to me something about doing it yourself is really rewarding if I can get it done well. Also, I really like the way an edge quench looks after acid etch. Do you think that you're at a disadvantage performance wise with an edge quench vs full quench?
 
Joseph Mansfield said:
The blade is heated and quenched in the same location within about a second. The oil is heated upstairs then a helper brings it downstairs to quench the blade. I really would like to avoid sending out for heat treatment just because I'm attempting to do everything in house. It just ads authenticity to me. I know it would be a higher quality end product but to me something about doing it yourself is really rewarding if I can get it done well. Also, I really like the way an edge quench looks after acid etch. Do you think that you're at a disadvantage performance wise with an edge quench vs full quench?
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If it’s done with a torch then I would say yes it’s going to be hard to get an accurate temperature that would get you the best performance.
 
Where did you get the 5160? Is it new stock or a leaf spring?
 
How smooth was the finish before heat treat? Before clamping, how straight was the knife? It's possible that you had a stress riser if your finish was too coarse, or if you had a little too much of a warp after quenching, you might have stressed things too much by clamping. Where did the steel come from? It's also possible that there may have been a crack in the steel already. Pictures of the knife may help, even in its current condition.

Just a couple of other thoughts:
Your AAA quenchant is way too hot. Recommened pre-heat is about 120F to 130F for an open tank. I'd also use at least 1 gallon. I imagine that 1 quart is too small of a volume for a 1/4" thick piece of steel, even if only 7 inches long.

Even heating is very important. If you can get a few fire brick or even a small roll of kaowool to make a heat chamber, you'll have an easier time getting a good even heat. I'd focus less on edge quenching and more on just getting everything to a good even temp before quench.

The time it takes to walk from your quench tank to your tempering oven is a non issue.
 
I think it was just coarse ground at 36 grit. I wasn't aware that the smoothness of the finish could cause complication during the heat treat. What grit is typical for pre heat treat?

The steel is from Jantz supply. And I would put some pictures up except I haven't had time to figure out how to do so on this forum yet.

I am going to be using 1 gallon of quenchant next time since I moved to a larger tank and currently all I have is one gallon.

So I guess I just need to be building myself a forge then.
 
At 36 grit there could be possible stress risers that can cause the blade to crack
 
I’ve discovered that even heat application does affect how much warp a blade picks up. Steel seems to want to “walk” towards the heat source so you need to hit both sides with the torch evenly. My usual first step is to heat to blue on the spine and then start bringing up the edge to quenching temp.
 
Forget "authentic" and go for measurable quality.

At least until you get some better equipment

JT does it in singles and it's reasonable.

Forget edge quenching
If you torch heated it, it's probably overheated.
One quart of oil in a quarter inch blade camp knife is not enough oil.


Show photos, you probably have a hole or notch that promoted that crack.
 
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