What Happened?

This was the third knife into the quench using McMaster Carr 9 second oil pre-heated to 120 degrees, using a limiter plate and going in tip first. The first two blades had a consistent and uninterrupted quench line. This blade however came out strangely, with what appears to be an additional quench line with a corresponding transition zone behind the quench line that runs out to the edge. The quenchant was around 130+ by the time this blade was done; other than that the process was the same as usual. I was certain I had even and consistent color along the blade edge prior to quenching as well. I believe this blade must be heat treated again. Any thoughts?

I'm not sure but I would be tempted to clean it up (grind the decarb off) and give it a quick etch in ferric chloride. The etch should tell you how far up the blade got hardened.

Here are the results of that test.

Jon, what you'll want to watch is if you can still see that line after the blade is sanded to about 800 grit and etched. I've seen things like that before and most times it's okay. Like Brad said, you can't ever trust what you see right out of the quench. I always hit blades with 120 to knock of scale and decarb. Then in strong light, you can see what you've really got most of the time.

I have been surprised a time or two with a faint line that runs down to the edge when etched at a higher polish. If that happens here, it would appear you lingered a little too long before rocking the rest of the blade down to quench the heel.

From your second pic, it appears you might be okay. The higher polish and final etch will tell the definitive story.

I'm with John on this, from what I see I think you nailed it. After tempering you should be able to do a little nondestructive testing just to be sure.

Jon, I'm not telling you how to do things so I'm gonna say this just in case you aren't aware of it. Edge quenching blades will ruin your expensive quench oil in very short order. If you use some type of clay, you could do a full quench, still get a nice hamon, and not ruin your oil. I apologize if you are already aware of these facts and are willing to deal with them to get the effect you're looking for. Just wanted to give you a "heads up".

John, The line will definitely be visible upon final sanding. Does this cause a heat induced stress riser behind this line?

Darrin. Please elaborate. I do not wish to ruin my oil.

I took the blade down to 400 grit, convexed the edge and did some testing. Brass rod test is good and cuts through 1/16 brazing rod with no deformity. Most of the chopping was centered upon, and on, both sides of the area of interest with performance results equal to the rest of the blade. I think it will be fine. I will post up the finished blade when it is complete. I am still interested in understanding what potential issues this could have/may have created in the blade.

Darrin, I found Kevin's explanation on why not to edge quench in Parks, I imagine the same holds true with McMaster. I am always willing to learn something I do not already know; more importantly I am always willing to learn something I already think I know, lol. I am highly appreciative of everyone who takes the time to share their thoughts on these processes.

Yes, the same is true for all quenching oils. Hot steel above the surface of the oil will cause flames which will, in turn, cause the oil to deteriorate quickly.

Here is the mostly finished blade. From what I can tell the effect is aesthetic only.

If it passes cutting tests fine, it's probably okay.

I would re-do it if it were mine, solely because it would bother me from an aesthetic standpoint. And I wouldn't want a potential buyer to doubt it. But.........I'm not telling you what to do and again if it cuts well, that's what matters.

One thing to mention about the oil. I've edge quenched lots of smaller blades in parks without any flame up of the oil at all. If your oil doesn't flame your fine. But I do like Darren mentioned and use clay now if I want to do that and fully quench the blade whether I'm going for hamon or not.

Darrin Sanders said:

Yes, the same is true for all quenching oils. Hot steel above the surface of the oil will cause flames which will, in turn, cause the oil to deteriorate quickly.

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I not shure about this...Please can You explain in which way it "deteriorates"....only thing is it might not cool down as fast as not deteriorated?I use the same oil since 10 years and dont know what all happened to it and I never felt or have a practical evidence that it is not quenching as good as ever.

Overheating quench oil causes oxidation. Most commercial quench oils use additives to slow this process, but it will happen over a period of use. The general rule is no more than one pound of metal per gallon of oil.

Edge quenching causes severe overheating because you are reducing the surface area of oil to transfer the heat, and causing high localized heat in an area. This is why you get all the smoke and flames. The flashpoint is probably around 250-300 and the maximum working temperature around 150. Commercial quenchants come with data sheets just like the steel we use.

You don't want to overheat your steel, and you shouldn't want to overheat your quenchant either.

Darrin's advice about coating part of the blade with clay is the accepted alternative to edge quenching, and won't overheat your oil.

You ever think about what all those fumes you inhale during an edge quench do to your respiratory system?


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Jon Kelly said:

Here is the mostly finished blade. From what I can tell the effect is aesthetic only.

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I completely accept your finding that this is just aesthetic - but with a handmade knife, I would suggest aesthetics are important. Would you pull this knife out to show off to your buddies? More importantly, do you want your maker's mark on it at times when you aren't around to explain the anomaly? I have to agree with others who have suggested re-doing the HT completely. I really like everything else about this blade. :thumbup1:

What this looks like to me is a secondary quench line resulting from the timing getting off in rocking the blade on the limiter plate/platform during the edge quench, and would suspect that carefully dragging the finished knife across a sharpening stone would give a slightly different feel, or bite, in that very small edge area. I am not fan at all of edge quenching, and there are reasons for my lack of enthusiasm that relate to maintaining both the quality of the quenchant and the knife. Probably needless to say that I agree wholeheartedly with Darrin that the clay quench will not only save on the oil but will also give you a much more defined martensitic/pearlitic transition right where you want it rather than a gradient of phases; that bold and defined line is, after all, why folks do the clay thing.

Thanks everyone for the responses. I will be heat treating this blade again using clay.

Edited to add results.