Made one of my first knives with S7, not sure about edge retention...

T

Texas Porcupine

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Sep 17, 2015
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This may be more of an opinion request than a recommendation, but I'd like your input all the same. A while back I aquired a piece of S7 tool steel and decided to make a bushcraft knife with it. Yes I am very much a hobbyist, so I know S7 probably isn't the best choice for a beginner project, but I got it free and I was excited to have a knife made from something other than scrap or a worn out file. I was in the Air Force and had access to an oven and help from experienced fabricators (my flight chief). I thought I had followed the heating, soaking and air quenching parameters closely, especially since when I pulled it out of the oven it warped slightly :-\

But now I'm not so sure.... it doesn't seem to hold an edge very well even though I can get it shaving sharp. Although I am a bit of a sharpness freak, so I might be a bit obsessive, even though it doesn't seem to compare in edge retention to my whittling knife I made from an old file.

Am I being too obsessive, or does it sound like a heat treat flop? It is tough to sharpen, but seems to go dull after a couple of tough cutting tasks like cutting zip ties and cardboard. Is this just the kind of performance I should expect from a knife made from S7? Is it even worth taking out as my primary bush knife or should I just start over and make something from easier metals like O-1 or 1095?

I did try the file test and it did grab a little...
 
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S7 is not noted for its edge holding, but it should be plenty serviceable for that application. Can you detail the heat treating g and sharpening procedures?
 
I don't remember exactly what we did but I believe it was 1725° with immediate air quench, no follow up tempering. For sharpening (I've reworked the edge angle) recently I've used the eze-lap diamond sharpeners from course to fine, honed with a ceramic glass honing stone, then stropped with a leather strap.
 
From what I've read, s7 has .5% carbon, which is not very good for knives. It is a shock resistant steel rather than a steel meant for cutting edges. Your file knife likely had around .95 to 1% carbon which is why it would hold an edge much better.
 
S7 was never designed for edge-holding, it's meant for stuff like jackhammers and power-hammers. If you want a knife that will take a heckuva lot of beating without cracking or breaking, it's a great choice. It's not a very good choice for a hunter, razor or chef's knife.

As I recall, Daniel Fairly uses S7 for his knives sometimes and has his HT dialed in to make the most of its edge-retention. Search for his posts or send him a message. :)
 
Ok I will look into that!

I was able to receive some additional information on the knife today, fwiw. I went to Texas Knife maker Supply and they were kind enough to do a hardness test on it for me and told me it was between RC 52-54, which they told me was adequate (barely) for regular use but would just require more frequent sharpening, which I'm ok with lol, being that I am a little obsessed with sharpening knives. I did go ahead and grab a piece of O-1 while I was there anyways! The quest for knife making knowledge continues!
 
So you didn't temper and still only got a 52-54? First, quenched steel should be tempered. Second, I think something went wrong if your hardness readings are that low.

Just to give an idea of what you could expect from reasonably treated S7, a chopper should be able to pass the ABS journeyman's test of chopping 2 2x4s and still shave your arm.
 
Did you wrap the blade in H/T foil? Was the blade preground before H/T? You may have decarbed the whole blade edge.

Stan
 
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