color case hardening/blueing

[OconeeDan]

OK, I know Karl (KBA forge) likes to hot blue parts in some of his knives, I have seen them myself and they are very nice.
I have always liked the appearance of bone/charcol color case hardening on gun receivers, and think it would look awesome on a knife blade.
My question...is this a feasable thing to do with a blade, or will the temper be ruined?  Or can it be "incorporated" into the tempering process?
Thanks, Dan

[Lin Rhea]

Dan,
  I responded to your question a couple of days ago, but it's gone now. I cant figure that one out.

  I do think it will ruin your heat treat. The temperatures required to case harden are pretty high compared to the drawback temps. I'm no expert on case hardening though. I'd like to hear some more input.
                               Lin

[OconeeDan]

Thanks Lin.  I have read it used to be used for knives and swords.  But we have learned a lot about metallurgy in the past century.
Maybe a call to a company that does this for other products is in order.
Dan

[Lin Rhea]

Dan,
    Case hardening is a hardening of the surface layer, but not very deep. It would be better than no hardening at all, but not enough for a seviceable knife, IMO.
     For a nice look that is similar to CH, you might try some of the mustard type patinas mentioned here somewhere in the past.
                            Lin

[Leftieshot]

I tried the mustard patina and wasn't impressed.  But I'm not sure I did it right.  I then tried soaking the blade in white vinegar and wow what an odd looking affect.  It looks tarnished and dull.

[OconeeDan]

Thanks for your imput.  
The damascus I have seen that was heat blued, I thought looked nice.  But I think the temper is compromised in the heat blueing.  So I was thinking that maybe color case hardening may be an alternative.  
But I guess you don't get something for free.
Dan

[Jeremy]

Most of the hot bluing only needs to be heated to just below the boiling point.  That's lower than the typical draw temps for steel and shouldn't change the temper on a knife. You can also cold blue.  

Like Lin said, the temps for case hardening are very high and it's normally done on mild not high carbon steel.  You pack the steel tightly with a high carbon content material (bone, ash, etc), heat it all to above critical and wait for the carbon to migrate into the mild steel.  Try it with a high carbon steel and you may actually decrease the carbon content of the steel (depending on what you pack it in).

The color effects you get by doing it are just oxides forming based on impurities in the packing material.  You can get a similar effect by combining a bunch of different patina methods.  Start off with spreading a little mustard and let it sit.  Then go cut up some meat and/or veggies, then blue it.

I did a few trade points awhile back where after I did the final grind I put it through another tempering cycle to give them the straw yellow color, then etched 'em in my normal FeCl:water mix without first degreasing the point.  Gave a nice mottled look to it.  Bluing them after that likely would have made it look pretty close to being case hardened.

[OconeeDan]

Jeremy, thanks for that explaination.  That is what I needed.
Dan

[Lin Rhea]

I was thinking that you could have several small jars of Ferric Cloride. "Contaminate" each one with a different non ferrous metal, brass, copper, etc. Experiment with a blank piece till you like it or decide it wont work. I would think you'd have to develope a patchwork look with overlapping colors.

I have not tried this, so I am only brainstorming. OK, maybe a light drizzle. Lin

[skullworks]

Here are some carbon blades I used lemon juice on. Not sure how well you can see them.