Heat treat gone wrong?

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Wowndeye

Joined
Apr 15, 2014
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Okay... So I'm finally dialing in my first knife here and have just begun to encounter a huge disappointment. As I've filed/sanded the bevel down to it's final edge and it's become a "razors edge", I've had a couple small chips in the edge due to what I can best describe as the edge feeling like tin foil out toward the final 1/8" of the blade. It's so weak and bends with the press of a finger from one side to the other. I don't know if my angle is just too thin (probably combined angle of 5 degrees before putting a 10 degrees for honed edge) or if my heat treat was a failure! :( I'm using 1/8" 1080 and I thought my hardening/tempering went off without a hitch. Brought the steel up to temp, quenched in quart of olive oil preheated to 130, ran a file across it w/ no scratching after it air cooled, stuck it in the oven at 400 for two consecutive cycles for two hours allowing to air cool to room temp in between.

I've made many mistakes along the way on this knife and learned from every one of them and thought I was finally in the home stretch, but this one is seriously depressing because all my work thus far looks to have resulted in a useless item!

While I'm at it, what approach do others use to hone their final edge and what angle is common for a Drop Point Hunter style blade? Did some searching but didn't find much.

Any thoughts?
 
It could be the edge is too thin, I would go 15 -20 on each side, 15 more of a slicer, 20 for hard work you can flatten the edge and put a new bevel on it, typically you want about 0.015 to 0.020 thickness then do your bevel.
 
First, flatten the edge back until it is a barely visible flat line. About .005" for a hunter is good. Then sharpen it at 15 degrees per side to get the sharp edge. This should take care of the problem.

Now, that is all assuming that the HT was good. You mention filing and sanding the edge down to a foil edge. After HT, it should be too hard to file, and can only be taken down with sandpaper or stones. If a file will take metal off, I am sorry to say the knife is not hardened.
 
Grrrrrrr..... Okay, not what I was hoping to hear, but needed to! I have been using a file at the end here. Not sure what I did wrong but I'll refire it and see what happens. Before firing, I'll file down the profile of the blade and hope it isn't too much but I think I'll just be taking off maybe a hair over a 1/32" then take it to 15 degrees each side following!

Here's hoping! ;)

Thank you for the help! :)
 
If you can press your finger behind the edge and easily see it bulge it is probably too thin.

Don't file the edge back, just run the knife edge down for a few passes over sandpaper. That should quickly take a thin edge down.
 
Will do Daniel! :)

@Stacy, my plan was to heat to 1500F then quench in quart of olive oil I have (preheated to 130 degrees) for about a minute then temper at 400 degrees for two hours, 2x letting it cool to room temp in between. Sound like a plan?

This is what I did last time and I thought the color of the metal looked good for 1500 degrees and it was non magnetic when I did the quench, so I'm really not sure where I went wrong. Any help would be appreciated for sure! :)
 
Keep in mind that it can take a while to get the temperature part down. I have probably heat treated 500 knives and I just get the color temperature thing. (I use a digital reading to go by) Good on the magnet but there are still a lot of variables to deal with. You are working with what you have and that is good!

A 400 degree temper for 1080 may be too low. Once you feel edge geometry is correct (if you are still having problems) you might want to bump the temper up to 425 and do a few edge tests. With a lower soak temp you may be OK at 400 though, testing is everything at this point.

You can water cool the knife between tempers. Keep your heat treat going in one quick continuous motion with little wait time... once it is cool in the hand it goes right into temper, then right into cool water, then right back into the temper oven, etc.
 
One quart of olive oil for 1 minute may not be enough. Use a gallon, and cool until it can be held comfortably in your hand.
 
I'm guessing one quart won't cool fast enough because of the knife heating the oil? I'd read that Canola oil or vegetable grade mineral oil from a feed store (if I recall) would be good?

@Daniel, how do you get a digital reading on the temp? Yeah, I'm working with what I've got but hope to get better equipment slowly but surely here!

Won't raising the tempering temp make it less hard in the end?

Thanks again!
 
Another question, so even after hardening AND tempering, a file should not be able to shave a blade? Just rolling those thoughts around in my head and it made sense after hardening, but despite the tempering knocking down the hardness a few numbers it should be still hard enough to resist work by any files?

I'm finally about to work on the knife and clean it up before reheating and am just worried It may warp.
 
Remember to remove any decarb by grinding before checking with a file. A used file will skate off the blade. The file test can be tough to judge a knife by. I'd cut stuff. :D

I'd try a higher temper cycle or change the edge geometry before heat treating it over again. Take your edge back to "dime thick" if you want to harden/quench again.

I use a kiln but like I said, that is good to work with what you have.

Yes, more oil will go a long ways.

Twisting your tip into a 2x4 (lightly at first! ) after heat treat will tell you a lot. A hunting knife or general EDC should be able to take that unless you are going for a very thin tip. Next, stab a piece of plywood and pry the tip out... (maybe not with this one yet :) ) Shave some wood, etc. Well heat treated 10xx will take quite a lot.
 
The tempering temp is to balance hardness with toughness. Too hard, and the edge will chip. Too soft and the edge will roll and not hold an edge. With 1080, you will want to be at Rc59/60 for edge holding, or 58/59 to prevent chipping. If the hardening works right, 425f is a good place to start, but you may need to go a bit hotter depending on geometry. 1080 and 1084 are almost the same thing. Aldo's 1084 has a few extras that make it great for knives compared to industry standards. These steels are euctoid, so they are nearly identical in heat treat, and very forgiving.

Yes, too little oil results in the blade heating the oil, losing the quench ability. I use 5 gallons, which is overkill, but I like to be on the safe side, especially with 13" or 14" blades.

http://www.cashenblades.com/steel/1084.html
 
Wowndeye said:
@Stacy, my plan was to heat to 1500F then quench in quart of olive oil I have (preheated to 130 degrees) for about a minute then temper at 400 degrees for two hours, 2x letting it cool to room temp in between. Sound like a plan?

This is what I did last time and I thought the color of the metal looked good for 1500 degrees and it was non magnetic when I did the quench, so I'm really not sure where I went wrong. Any help would be appreciated for sure! :)
Click to expand...

One quart will not do it. One gallon is the minimum.

The quenchant has be fast enough to remove the heat from the blade in the time needed to make martensite. It has to have enough mass to extract that heat, or it won't drop the temperature fast enough. 1080 needs a fast quench.

Olive oil works, but canola is cheaper and as good or better. Get a gallon and put it in a tall metal container.

When the blade is non-magnetic plus about 100°F quench immediately in the warm oil. The blade should go from forge to oil in one smooth and quick movement. Have everything ready and practice the quench a few times with the blade cold....then do it one time at 1500°F.

I agree with Willie that 425°F or 450°F may be needed to get a balance of hardness vs. toughness for 1080. Test the edge and see how it holds up, and re-temper at 15-25° higher if needed.
 
@Daniel, for the knife tip test, do you mean immediately after hardening or after hardening and tempering? And for the twist test, what am I evaluating? Whether it gets bent or breaks off or chews up the wood?

@Everyone, so I went out yesterday and purchased TWO gallons of Canola oil and will be getting a container today! ;) If everything goes smooth, I'll be re-heat treating tonight.

Fixing my mistakes has forced me into changing my blade design because of how much material I had to take off the edge, but I think I've been able to salvage it and actually am liking how it's turning out so I'm hoping I get it right this time! :) After realizing how much I had screwed it up I was so depressed because of how much time I had already put into it I almost threw it away, but am really glad I didn't!

I'm a perfectionist and am determined to successfully execute each step of the process, even though it's my first and I want it done now and have been tempted many times to compromise quality! I knew mistakes were going to be a given due to this being the most I'd ever worked with steel before as well as the first time I'd ever made a knife but a couple were temporarily demoralizing... Things are starting to look up now though! :)

I'll follow up soon so you can see the fruit of your input! Thanks again!
 
Wowndeye said:
@Daniel, for the knife tip test, do you mean immediately after hardening or after hardening and tempering? And for the twist test, what am I evaluating? Whether it gets bent or breaks off or chews up the wood?
Click to expand...

Test after tempering. You should be going right into temper. The knife shouldn't be sharpened during heat treat either. If you were to do the test before tempering the tip would would snap off like glass.

Twist test - (not for a light duty knife like a kitchen knife) lightly twist the tip into the side grain of a 2x4 - if it chips/snaps it is too hard and if it bends and keeps the bend it is probably too soft. Don't "try" to break the tip off. (maybe later!)

I'd save a tough test like this until late into testing, you should feel confident that it will take it. If you are going for super thin geometry and high hardness this test might not tell you much as the tip should probably break! On the other hand a .030" thick edge at 59 RC should be able to do this with ease even with force.
 
Okay, that's what I figured. I'll have pictures when done, but I think the tip is pretty hardy and if done right, should do okay going into a 2x4, but like you said, I'll save that one for last! :)
 
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