Possible to get Kurouchi on non-forged stainless steel?

I found a programmable kiln/oven at work today that I could do some heat treating on the weekends, woohooooo! We also have an ultracold freezer that goes to about -175F, so not quite liquid nitrogen, but much better than dry ice/alcohol slurry. So, since I have friends asking me to make knives for them but probably not as OCD about cleaning and drying them while prepping, stainless would be a good choice probably.

I would like to leave a kurouchi finish on the blades. I am doing stock removal, no forging, but for the 1084 carbon steel I'm currently using, I just backyard heat treat with torch, quench in oil, and leave the black scale on there. For stainless steel heat treat in an oven, can I just leave the blades unwrapped, without HT foil, then quench in air or between aluminum plates? Will this leave a stainless kurouchi style finish? I'm thinking AEB-L (or possibly 440c) since relatively inexpensive.

I say go for it and ask questions later.

I would not leave the steel unwrapped. I may be off here, but isn't the reason for the wrap to keep the oxygen away from the blade to minimisa decarburisation as the austenizing temperature for stainless is higher than for carbon steel?

I finally got some replies on another forum I've been frequenting and they said decarburization is a problem due to the temperature and soak time. I guess KU finish on Japanese stainless clad is leftover from forging scale? I haven't been able to find anything by google yet...

If your grinding after HT, and tweaking the profile....it really makes no difference whatsoever to the edge having a little decarb on the surface. I have done forge finish 14c28n which included the whole forging process, a full anneal cycle, then heat treatment on the steel unwrapped or coated....no issues. If you want a set Kurouchi finish though you would want to oil quench it rather than plate quench otherwise naturally you will just have dry scale.

Is decarbonizing an issue at certain temps or more so at temps needed to heat treat? Point being, i dont see people forging wrapped stainless which tells me it's either not a concern cause the temp is less or there's an expencted amount of carbon loss during forging that you dont want made worse during heat treat.

Depends on the stainless, I've forged quite a bit of 14c28n, similar to aeb-l. Stainless has a much smaller forging window than carbon, I like to keep it between 900-1100 degrees for forging. So yes there will be decarb on the surface, but it can be minimised by working in a carburising/reducing flame. After forging you have to let it cool slowly, otherwise it will of course harden, and in order to get it back to a fully annealed state you have to run a pretty long heat cycle, I usually go for a long subcritical anneal ramping down from 950 with a long soak at 750-800. That's pretty much all day in the kiln! At heat treat it's in the electric kiln again at 1080 degrees c but held only for 5 minutes at temperature. Decarb as I understand it happens only at the exposed surface, I have never experienced any carbon loss enough following this procedure to effect hardening or final hardeness. But deffinately treat each different steel with a different set of rules, I'm sure not all stainless would be so forgiving.

Thank you for all the information Will.

WillC said:

If your grinding after HT, and tweaking the profile....it really makes no difference whatsoever to the edge having a little decarb on the surface. I have done forge finish 14c28n which included the whole forging process, a full anneal cycle, then heat treatment on the steel unwrapped or coated....no issues. If you want a set Kurouchi finish though you would want to oil quench it rather than plate quench otherwise naturally you will just have dry scale.

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Will, thank you so much for the info! :doublethumbsup:

If I try oil quenching for kurouchi, would it be good to quench into vegetable oil part way then smoosh between aluminum plates? I'm wondering about how much it will warp without plate quenching. I am only doing stock removal (no forging), so I'm guessing it would be better to do all the grinding post HT to avoid warps? I will probably start with AEB-L in 2 to 3 mm thickness. This is a bit in the future for me, but trying to learn and plan things out now...

I would grind the taper, leave it at 60-80 grit or so to give the scale something to stick to, and just go for the oil quench, vegetable, rape seed oil is fine. The plates will disturb the scale, cryo for best hardness straight after quench, then double temper, 175 degrees c for full hardness. Then carefully grind the bevels trying to keep the bevels crisp and scale in tact. I did used to have some warping issues with aeb-l, Its so fine grained it can warp during temper too and sometimes grinding, but also can be carefully straightened after temper with a bending jig or fork if necessary.

Thank you Will! :doublethumbsup: