Bevel grinding in the context of tempering

[smartanimal]

Hello all. I'm wondering if I might be able to get some tips from anyone about tempering. Or what I can do in this situation pictured above. I mentioned it in another thread of Mine but since it's a different blade I figured I'd give it its own thread so as not to derail the other one.

Basically i accidentally got mixed up with my tempering times and got the above pictured result. As I understand it, it's the spine that should be blue / purple and the rest of the knife that should be straw colored.

I originally wanted to do a Scandi grind at 30 degrees inclusive. I ended up putting the bevel on the slack part of the belt to get a convex primary bevel although I was thinking of just putting a secondary bevel on it anyway.

I got a basically sharp edge that I then ground back to a little less than a millimeter in width to avoid warping.

I then heated the blade in a charcoal fire until the whole knife was non magnetic and then quenched in canola oil until cool to the touch, sanded, then put in the oven at 425 for 2 cycles of 2 hours (in retrospect I have no idea where I got the two hours from).

Is there a way I can re harden / quench and try tempering again or is my edge too thin? Shod I get it professionally done?
Using o1 steel btw.

 

[coldsteelburns]

You can't always trust the oxidation colors from tempering, there can be a number of factors that give the blade different colors at different spots, such as oil from your hands etc. Also, there is nothing wrong with two 2 hour tempering cycles, that can actually better than one hour in some cases, as long as you don't heat it above your aimed temperature.

Also, you can pretty much always re-heat treat carbon/ tool steels (I don't really know much about stainless steels since I don't use them) at least a couple of times as long as you still have enough "meat" in the blade so it doesn't warp like a pringle. Of course you will end up with a slightly smaller profile each time it's re-heat treated due to the extra grinding down of the edge to give some thickness to it before hardnening, etc. However, before going about trying to re-heat treat it, first put an edge on it, and do some testing with it, it may very well be just where you want it.

One exapmle of testing would be to try the "brass rod test." You can do a quick search on it, but basically you drag the edge back across a 1/4" or so piece of brass round stock (doesn't really "have" to be brass though, it's just that brass a bit softer than say, stainless steel or mild steel round / pin stock) as if you were stopping the edge, while putting slight pressure on it (enough for it to slightly deform around the rod, but not too much) and watch the edge closely. Ideally you will see the edge "flex" a bit over the rod and then return to straight while passing over the rest of the edge. If you indeed got it too hot during the tempering cycles, the edge with be too soft and it will "roll", or stay bent over, which means it needs to be re-heat treated.. If the edge chips, if means you didn't temper it at a high enough temperature so as to "take away" the brittleness, which means all you have to do is put it through another tempering cycle, about 15-20 degrees hotter that your last one, and each successive temper until the edge stops chipping. Of course there are other factors than can cause the edge to chip, such as the grain being too coarse due to getting it too hot in the forge, but I'm just trying to give a simplified version here.

Hope that helps ya out a bit. And I'm sure ther guys will chime in who know more than myself. :thumbup:

~Paul

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[coldsteelburns]

BTW, this thread just reminded me of a very cool picture of a "collage WIP" that Ryan Weeks posted a few years ago. Check out the colors on the blade in the "HT & Temper" photo, it has some pretty crazy colors to it! And this was only tempered in an oven (not drawn back on the spine with a torch or anything), showing that even with the entire blade at the same temperature, you can still get different colors.

~Paul

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