Case Hardening a high carbon steel?

V

Vincent Price

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Feb 28, 2020
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I am new to forging but made knives via stock removal back in my twenties. I built a Forge over the winter and plan to boost retirement with a few hand forged knives here and there. My first customer who happens to be a friend wants a Bushcraft knife but wants it case hardened. He has a thing for the case hardened look and I have to admit being a "Cowboy" myself I do also. My question is can you case harden a high carbon steel like 1075 to achieve the color he's looking for? I say 1075 because thats what I have on hand and have used mostly. Would it be less durable as a knife? I have never case hardened anything. I know they make case harden coloring treatments you can apply but he really doesnt like that idea.
 
Case hardening is for low carbon alloys that need surface hardness. The temperatures involved would make high carbon steels very brittle.
 
Bill DeShivs said:
Case hardening is for low carbon alloys that need surface hardness. The temperatures involved would make high carbon steels very brittle.
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I'm no expert on hamon or pattern welded steel, but it kind of sounds like that's what's being asked about.
 
N.W. Gean said:
I'm no expert on hamon or pattern welded steel, but it kind of sounds like that's what's being asked about.
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No
This pretty blue gold stuff is what he wants.
Even if you could do it, it would wear off

gl0g0qzso7421.jpg

Full res photo
https://preview.redd.it/46m2huzso74...bp&s=a65a9832c4ecf52c529ffadc3e211fefbba75984

46m2huzso7421.jpg
 
Yep, the guy wanting me to forge the knife for him wants the color case hardened color like the receiver of the rifle in the picture but on a 1075 steel.
 
You basically pack the parts in a mix of charcoal and bone, bake it at 1400f for an hour or so, then quench in water. Then oil be it up and leave it. You can't temper it or it'll ruin the colors.

Like Bill DeShivs Bill DeShivs said, it'll make a really brittle knife if made out of high carbon steel, and if you use mild steel, it'll make a crappy knife that won't hold an edge.

You could case harden the furniture (guards, butt caps, etc).
 
Since he's wanting just the colors you could make the knife as normal (HT'd, tempered, etc) then polish the portion of blade you want the colors on to a nice mirror finish. Now with edge in water, use a hand torch to heat the rest of blade with hand torch to bring out colors. You can get nice blues, yellowish, etc with heat. That will make somewhat of a "case hardened" look. The colors are pretty sensitive and will be damaged pretty easy, so it's more of a "display" knife.
 
What K Ken H> said... torch temper part of the spine to give the colors he wants but keep the edge cool so you don't ruin the HT/temper of the cutting edge. But those colors are still only on the surface and won't last on a real user knife.
 
Yeah heat temper colors just about wipe off with your fingers. That are not durable at all. Only color I have found that kinda holds up is that whispy blue colors from cutting a foil high temp open during heat treat of high temp steels.
 
Maybe just make the blade from mild steel and case harden it. It would or should only be for display anyway if he is wanting those colors.
 
Maybe he would be open to using mild steel bolsters on his knife so you can case harden those. I've seen a few smiths do it on their guards and maybe butt caps. From what I've heard/read over the years, there seems to be quite a bit of trial an error and quite a few factors (some subtle and some not so subtle) in pretty much every step of the process that can affect how the color turns out, and even some luck, so you may have do it a few times to get something you like.

~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)
 
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I almost forgot, a bladesmith I follow on youtube just shared a video on his case hardening process a few days ago while doing some fittings. Maybe it could be of some help to you if you happen to end up trying it out.



~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)
 
As others have mentioned, some air hardening steels (D2, A2, etc) are able to get some pretty colors. I don't know how much they hold up on his knives, but I've always though Medford's was able to get some pretty neat colors with his "Vulcan finish" (oxides from heat treating left on the blade). He may do something else to the blades to help influence the colors, like purposefully allowing some oxygen to remain in foil packet (for heat treating) or maybe putting some oil on it, but I dunno.

Anyway, from a purely aesthetic point, I think the colors on ones like these look very nice:

https://www.instagram.com/p/pcJysaMXaU/

https://www.instagram.com/p/lkP6PwMXcT/

~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)
 
Here's a recent little kiridashi I made for myself to try out some heat coloring on (with a plumbers torch). I wanted to see if the rougher surface from forged finish and/or the "ura" (hollow, fuller) on the back would help to hold the color a little better over time, although the oxides aren't on the actual blade, so the only wear it'll get will mostly be from handling it.






(Those two spots with the vibrant purples on the back are actually peacock blues, but in certain lighting and angles they look like the above)

But yea, just wanted to show some example of the ways already mentioned above to achieve some colorful oxides.

Ok, now I'm done... lol
~Paul
My Youtube Channel
... (Some older vids of some of the older knives I made)
 
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