quenching San Mai

Greenberg Woods

Greenberg Woods

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Dec 27, 2013
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Hey guys. Im looking to get some blue 2 and white 2 san mai, low carbon sheathing, about an 8th of an inch in total thickness. My question was, when should I heat treat it? On a post about blue and white steel Stacy mentioned that for thinner stock its best to harden first and work the steel hard, but I was wondering if the low carbon jacket would stop that from being effective, meaning I would need to quench AFTER grinding or the jacket would make it cool to slowly. Thoughts?
 
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I think the steels you are going to use are those of the shallow hardening family.
If i'm correct, the mild jacket alone would function as the clay in an hamon blade, so you may want to grind before hardening, and expect only the exposed steel to harden in the quench.
 
I haven't seen any problem with the san-mai causing insufficient hardening in thinner billets done pre-bevel. Blue steel is a bit easier to HT than white, but both are done unbeveled in thin section.
Just use a good oil and get the austenitization temp well controlled. Parks#50 at room temp works fine for me.

If you worry about it, just grind a fairly steep edge bevel to expose about 1/4" of core, then do the HT.

As for the metallurgy of the quench, the low carbon skin will loose temperature at the same rate as the core. Think about it,..... the only difference in the skin and the core is about .80% carbon...otherwise it is pretty much identical. It would be no different than quenching a solid piece of Hitachi Blue steel. The soft iron would NOT act like insulating clay.
 
I disagree, but i explain why...
i agree the outer jaket will loose heat at the same rate, nevertheless it'll add thickness to the billet; that is the only factor i'm considering.
A thin section, of shallow hardening steel will fully harden with pretty much any oil, but a thicker one of the same steel would require a pretty fast quenching.
I hope my post didn't cause any misunderstanding or confusion
 
Smiths here in Japan quench their sanmai blades all the time while still fairly thick without any problems. The soft iron jacket does not slow the quench.
 
Ok, my question is, who the hell measures inches in 18ths? OP, if you are using one of those calipers that measures in fractions, switch it to decimal. I cannot think of any good reason to make a machinist tool that reads in fractions. Now, rant ranted, we do often give steel stock in "standard" fractional measurements; i.e. 1/4, 1/8, 3/16, 5/32. Sorry to de-rail...pet peeve.

Bob
 
eh eh, in fact, i originally didn't caught the thickness, i reason in metric, but then i tought 1/18 it's very thin, that negates any quench slowing concern :)
 
eh eh...it should be easier if all of you would switch to metric....and speak italian LOL ;)
 
I have never had a problem quenching san mai in the unground profiled state- Ihave had traditional style chisel ground (ni mai? :) ) blades go completely muppetational in the quench and require some creative straightening-perhaps because mild and high carbon expand and contract at slightly different rates?
(I dunno why they would, but some of the warps I've gotten have been pretty spectacular on normalized blades)
 
Thanks Stacy, pretty thin either way.
JW, when you quench mild steel you don't have the huge expansion of the martensite transformation, but the high carbon slab would grow, iirc, 4% volume.
The effect you get is one side grows more than the other and gives a banana shape :) Some smiths pre-bend by experience, some other peen straighten (peen on the convex side) after hardening and there are still the usual straightening techniques which work well enough. But a warping on ni-mai is always to be expected.
The real problem is when you get you san mai central layer split in half lenghtwise in case you have thick mild slabs aside...that's one of the reasons why i prefer to grind before hardening san mai.
 
stezann said:
Thanks Stacy, pretty thin either way.
JW, when you quench mild steel you don't have the huge expansion of the martensite transformation, but the high carbon slab would grow, iirc, 4% volume.
Click to expand...

Its usually a fraction of a percentage not anywhere close to 4%.
 
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