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Broken WIP kitchen knives. Who is to blame?

I broke the test blade I heat treated the other night. Measured 60-61rc after 2 tempers. There is a very thin decarb/oxide skin which is almost impossible to avoid with any type of gas shielding. This is why we grind spots onto our blades to hardness test. It gives us a unaform finish and gets us through the skin.

I’m doing 2 more tests with more abd less gas shielding to see if we can get different results. I did see some very shallow fishers which would of been removed when grinding the blade. Thy are dark so I’m almost thinking thy where there before the heat treat. Also a crack from heat treating shows up perpendicular to the edge or spine. These run parallel to the edge/spine which is the direction the steel was rolled in. So if there was an inconsistency in the steel surface it would be stretched out lengthwise just like this. But other than that the grain unde high magnification is fantastic.

I’m posting all of my results as I want people to know we have full transparency in trying to figure out what caused his blades to crack. Abd if it’s something we did then we want to know as it is our mission to provide the best knife heat treating on the market.

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I also tested the thermocouple to make sure it was still within spec, which it was. Here is a video of me testing it.

 
JTknives JTknives totally respect you and seriously doubt this issue is your doing.

Highly discounted product due to irregularities should be a lesson learned.
 
Update, we are doing a second test with an adjusted gas mixture and smidge hotter temp. Will keep you all updated. The blade came out super clean so I’m very optimistic with the results. This issue has caused us to really dig in and see if we can make our AEBL heat treating even better. IMG_4354.jpeg
 
I did one more break on a knife at a point where I saw a small crack and this one had clear dark spots. I didn't see these dark spots on any of the other breaks.
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So, I have heard that when you see marks like that in the crack they are indicative of a crack that existed before heat treat.
Anyone have any more info on that topic?
 
Here is the results of our latest AEBL test. The issue the OP brought up got me really wanting to drill down and look at our processes with a macro lens. What I have discovered I believe is a better heat treat then our previously offered AEBL offering. This in no way means what we were providing was not good but quite the opposite. Ask anyone who has had our AEBL heat treat service and thy all live it. That’s why this issue really got under my skin and bothered me. So I did some testing and research with our current shielding gas and established a baseline standard. You seen this standard above with the break test I showed above.

Our new process involved getting a 2nd cylinder of gas and mixing the gasses on the fly befor it enters the oven. I also played with the austenite temp. The result is quite amazing as the blade is extremely tough and the gas shielding skin has all but been removed. The below pictures and video is done on an aebl blade that was identical to the last blade tested.

The blade in the end came out at 61-62rc after the 2 identical tempers the last blade received. Looking at the cross sections under the microscope revealed an extremely fine grain with basically zero surface skin from gas shielding. Also those little microscopic vertical fissures are gone. I do not know what caused those but both these blades where cut from the exact same sheet if AEBL.

The blade was extremely hard to snap in the vise and while doing it I didn’t think I was going to be able to get it to snap. This result is quite a-bit tougher than the last test by probably a factor of 2. And this blade also came out harder than the last one which can be explained by the adjust austenite temp. When testing the oxide skin depth it was found to be practically nonexistent. As is it was measuring 60-61 and after grinding a spot and re testing it jumped to 61-62.

Here are the test pictures. Also the first blade snapped into 3 sections and this on only snapped at the tang junction. Both blades where snapped the exact same way in the open jaws of a vice and then as you will see I grab the tang with one hand and flex it twords me. I find an open jaw to give better results as once the snap happens the blade can fling forward free of restriction. I hope our transparency to our testing shows how much we actually care about your blades. We might not be the fastest out there (just my wife and I and 2 kids) but we try and be the best.

PS that dark spot is just a tiny spec of dust on the lens.

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And here is the video of me actually snapping the blade and how far it went and how much force it took.
 
I hope you were wearing eye protection!
 
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