Another dumb question- Cryo Treatment

[khaos]

So its been floating around that a Wonderedge is simple a Cryo'd goldedge. And we all know that Friodur's are cryo'd. I bet the Dovo stainlesses' EISHARTNUNG (ice hardened) is cryo as well. So if I take one of my blades and let it sit a few hours in liquid nitrogen, will the same effect happen? Or does the tempering have to be doen right after forging? Does it matter whether the blade is carbon or stainless (I know they're differnt, but does cryo treating have positive effects on both?)? I know the basic idea is tranforming Austensite into Martinsite and causing the precipitation of carbides, I'm just wondering if there's a really in depth process, or if it is quite simple if you have the tools. I do in fact have liquid nitrogen available to me this weekend, so if in theory it is possible, I would like to try. I have a standard oven for heating to a controlled temp around 500 deg F, and would be willing to try heating in a cast iron furnace if more temp is needed.

[BKratchmer]

I am by no means an expert, journeyman, apprentice, or any sort of steelworker. I am at best an ambitious ignoramus. With that in mind:

I believe (smarter people will know for sure) that the cryogenic work comes after a first temper, and then another tempering cycle is run to grow/merge/organize/harden the raw martensite.

Take with a block of salt.

[khaos]

Thanks. Hopefully that second temper doesn't have to be very hot. Hopefully someone can let us in on teh exact temperatures of the various stages. Also, does it have to be immediately after first temper, or can I do it on anything?

[Mike Blue]

Cryotreatment is best applied to high alloy steels, meaning stainless in the common tongue. There is spurious evidence (at best) that this process works on low alloy steels, meaning high carbon steels when they have been properly heat treated in the first place.

The low temperature cycle is meant to convert retained austenite into martensite. Austenite is less tough and more prone to fracture and is less desirable as one of the crystalline components. The optimum time for freezing a blade is in the quench. I would suggest that to be a very dramatic experience for the ordinary blade crafter.

Given that most folks would quench in air/oil/water or other preparation and then complete the freezing cycle, there is the possibility the interruption may induce changes that are not accounted for. There was a wonderful segment of this process on the Discovery/History channel about how the steel strips for Bic type razors were made. The strip is coming out of the induction heater at a yellow color and in less than a half inch straight into a quenching system cooled by liquid nitrogen. It's moving pretty fast too.

After the freezing cycle, the steel MUST be tempered to convert the fresh martensite into tempered martensite. Ref: John Verhoeven Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel. It should be of interest that Dr. Verhoeven does not mention the cryo treatment of high carbon steels anywhere in the chapter about them, but does discuss cryo treatment in the chapter on stainless materials.

It will not likely hurt a high carbon blade that has been properly heat treated. There is the risk that the preparation for heat treatment was off a little and the cold shock could induce a significant risk of stress or fracture too. But, there will be nothing gained in the steel and the only measured change will be in the pocket of the liquid nitrogen supplier and provider of equipment, or your heart if the blade breaks.

Interestingly enough, the very people who are publishing the research that this is a process that everyone should do are the one's who have an interest in selling you the equipment. I call that a conflict of interest. It calls into question the validity and reliability of their conclusions.

If an owner-maker wants to do this to their blades, no problem with me, it's their business. I like processes that leave fewer questions to answer than I started with.

See here: and root around a little. This has been discussed before.

http://straightrazorpalace.com/razor...h-doing-2.html

[Mike Blue]

Thanks. Hopefully that second temper doesn't have to be very hot. Hopefully someone can let us in on teh exact temperatures of the various stages. Also, does it have to be immediately after first temper, or can I do it on anything?

You need to have the exact specifications of the steel type to know the answer to that. Get those and I will look up what you need in the Heat Treater's Guide.

[khaos]

Thanks so much for all the help. I was just curious mainly. Finding the steel specifications will be hard.... I've noticed some of the Solingen blades and actually my French blade have two numbers on them, one of which is 4 digits, could this be the steel? Like Boker has 1056 and stuff, and the Dovo 1516 or 1885. If so i'll keep my eyes peeled and when I find one I'll definately ask.

[Philadelph]

I've noticed some of the Solingen blades and actually my French blade have two numbers on them, one of which is 4 digits, could this be the steel? Like Boker has 1056 and stuff, and the Dovo 1516 or 1885.

Not at all. Those numbers have nothing to do with the steel type. They are only "model" numbers.

[Mike Blue]

No problem. Good luck in your search. I have seen references to INOX steel that include data that cover the entire range of 300 series austenitic stainless steels. This would be okay for kitchen furniture but not blades. Some INOX labels have been applied to chrome-vanadium alloys and those would make fine blades. I think the common use is that Inox is another way of simply saying stainless steel.

The Cr-V steels will austenitize at between 980-1060 C, are air quenched and tempered between 300-500 C. With higher hardness occurring at the higher tempering temperature because it takes a lot of heat to get carbides to precipitate in these steels. Goes to show that the alloying elements really change the equations. Generally the older books show decomposition of the retained austenite was relieved by multiple tempering cycles.

[khaos]

Philadelph- what if the razor has two numbers on it?
Mike Blue- I assume you know this but I'm not sure, INOX is "inoxidable" ie rust proof ie stainless. So you are correct. The germans like stamping things INOX or Rostfrei (rust free) rather than stainless steel. I don't know why. Just somethign I've noticed even on my three sets of kitchen knives.

[gugi]

So its been floating around that a Wonderedge is simple a Cryo'd goldedge.

the grind seems different to me and the evidence of the steel being of the same composition and going through the same heat treatment is even less than all currently made dovos being the same blade.