154CM heat coloring: any changes to steel properties

zyhano

zyhano

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Hi all,

I have a 154CM steel blade that has been heat colored to a brownish color. This was a procedure done on a finished blade of a production knife. I've seen a chart indicating that that means it was heated to about 390 degrees Celcius (730F).

It is very evenly colored. I'm trying to find out how the heat coloring was done (temps, cooling etc) since I did not do it myself.

In the meantime I'm wondering if/how it might have affected the properties of the steel in terms of toughness, hardness etc. Especially toughness, since I don't want it to break upon falling.

I assume the heat applied was not for a prolonged period of time, probably in the range of minutes at most. It is a small-ish blade of around 0.14" thickness and 4" length
It seems to me this could be seen as a very short form of tempering, but tempering needs time to be executed.

see also: https://www.crucible.com/pdfs/SelectorKnifePocketRotatedCrucibleLLC.pdf

thanks for your insights!
 
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In my naive opinion, there is not enough data, really depends on how slowly and evenly it was heated and cooled down. If you are lucky, it will have gained a little toughness (at the expense of a little hardness). If it were me, I'd hand-sharpen it and see how it behaves on the bench-stone ....
 
Thanks ferider ferider . In my naive opinion, I don't think I'm able to notice the difference under regular use based on what I've read/understand :) So hopefully someone will know something more and either prove my opinion correct or incorrect.
The previous owner will get back to me on this so I'll have more information. But a couple of minutes with even heating (because coloring is even) seems like it should not affect tempering if I understand correctly. The charts for 154CM and how tempering works are beyond my knowledge.
 
In for answers. My limited understanding is that it will soften the steel.
How much? I have no idea.
 
thanks Bill DeShivs Bill DeShivs and Dirt Dirt . so here is some more information, if possible I would appreciate it if you can give an explanation on why it would be fine (or not) so my understanding of it is a little more science based than gutfeeling based, though both are fine for me ;)

"I didn't heat it nearly to 735 F. I don't have any source capable of that kind of heat. I heated it in a kitchen oven. I don't recall the exact figures, but it was somewhere around 450 F for 45 minutes. I tented it with aluminum foil. The foil didn't touch the knife, but it shielded the knife from direct exposure to the oven's heating element. Once I took it out of the oven, it cooled in the air. I didn't cool it in water or anything like that."
 
Given the info "..450F.. tented aluminum foil.." - I think, blade has a thin baked deposited(src from blade; foil; oven) coat of rust. Which should easily be remove with bar-keep-friend. Hardness should remain above 60rc (assuming decent/good ht). Whereas intrinsic surface oxidation (straw coloring) normally occurs starting around 600F to 900F - which bkf can only remove/fade some but a hint of brown remain (easily remove with sand paper).
 
First, 154CM is an air-hardening steel. These steels don't follow the same heat treat rules that carbon steel does.
 
Well, I fold. I was talking more about the ~700°f range for a period of time. I didn't even know you could color steel at that temp (450f).
 
Thanks for the response so far. Here's a picture.

The temperatures for heat coloring are indeed different for obtaining the color the blade has now as opposed to what the temp was in the oven.
Rust coating could be, inspecting with a triplet of 20x magnification doesn't make me any wiser except that the edge has a lighter color, which could be because of the different 'finish' of the edge vs the blade.

I have used 6 micron diapaste from DMT to polish part of the blade a bit with a wood backed strop, and indeed it comes off easily.
The edge indeed has a more rust-like feel over it that also comes off with stropping with 6 micron compound.

I'm not sure what barkeepers friend is, but I assume it's some sort of polishing compound. (edit: already looked it up. oxalic acid to remove rust)

overall shot, with some colors for reference.
brs-color.jpg

here's a better look at the edge. near the tip you can see the colorization there.
brs-color-edge.jpg
 
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an update!
It was rust indeed BluntCut MetalWorks BluntCut MetalWorks ! Thanks a lot for the tip.
and all others for their help :thumbsup:
I've bought some barkeepers friend and after starting on some other rusty metal, decided to give it a go.
some pictures for reference, but basically just softly polishing with the stuff on a wet cloth solved a lot. Etching is still on and looks pretty good again.

tip polished, you can see the color difference clearly
brs-barkeeper-1.jpg

pivot stuff is a little harder to get to, but used an ear cleaning stick
brs-barkeeper-2.jpg

looking good
brs-barkeeper-3.jpg

the tools of the trade
brs-barkeeper-4.jpg
 
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