Thread: What happens to the blade at 473 °F (245 °C)

I'm reposting my question here because I need an authoritative answer and I don't think my original message got read by the craftsmen.

I need to autoclave my razors (because I want to give traditional straight shaves, i.e., not with a disposable blade, in a barber shop). Although wet autoclaves operate at a lower temperature, they are expensive. I can get a cheaper dry-heat autoclave but it operates at 473 °F. Since this is close to tempering temperature I'm concerned that it will damage the blade. Is that true?

PS: The handle will always be steel, like a Wapi.

That is right up there with the temperatures that will soften steel.

It probably depends on the type of steel and the accuracy/precision of the autoclave. I have tempered a few of my razors at ~475-500 deg. F for 2 cycles at 1.5 hours each and the result is still very hard steel (for .9% to 1% carbon steel). So, initially, I'll say it's possible that this will work for you, but repeated tempering cycles may continue to soften the steel (slightly) even if the temperature does not increase.

If the steel is around .5% carbon but has been tempered initially at very low temperatures to retain an adequate amount of hardness, then the autoclave will likely soften it a noticeable amount. But if it's higher carbon, like .7% or more, it may be perfectly fine.

You may have to sacrifice a blade to know for sure. If you have a toaster oven or regular oven with a dedicated (and accurate) thermometer you could run a test to see what happens.

I won't claim to be the final word on the subject, but I can say that I've used those temps and had good results for my steel, others will surely add more detailed info for you. Anyone know the carbon % on a Wapi?

Tempering steel will also release and stress in the metal. With the thin ,etal of concave razors and the amount or grinding in the product do not be surprised if the blade comes out warped. You can be sure the metal will move, the question is how much. +1 on what Russel said about the metal type and Amount of carbon. 'Tempering will cause the dissolved alloying elements to precipitate, or in the case of quenched steels, improve impact strength and ductile properties.' - Wilipedia.

Here's more from Wilipedia:
Tempering is a heat treatment technique for metals and alloys. In steels, tempering is done to "toughen" the metal by transforming brittle martensite into bainite or a combination of ferrite and cementite. Precipitation hardening alloys, like many grades of aluminum and superalloys, are tempered to precipitate intermetallic particles which strengthen the metal.
The brittle martensite becomes strong and ductile after it is tempered. Carbon atoms were trapped in the austenite when it was rapidly cooled, typically by oil or water quenching, forming the martensite. The martensite becomes strong after being tempered because when reheated, the microstructure can rearrange and the carbon atoms can diffuse out of the distorted BCT structure. After the carbon diffuses, the result is nearly pure ferrite.
In metallurgy, there is always a tradeoff between ductility and brittleness. This delicate balance highlights many of the subtleties inherent to the tempering process. Precise control of time and temperature during the tempering process are critical to achieve a metal with well balanced mechanical properties.

I don't know if it would meet inspection requirements but a pressure cooker works the same way as an autoclave. You can buy an electric pressure cooker for less than $100.

It's very likely that 473 degrees will ruin the temper on most razors. The tempering range for blades is usually in the 375 to 500 F range, with 400 to 425 being more common. Any time you go over 300 F you should start to worry...

Just my 2 cents,
Josh

I will go with Josh.

Since we don't know the exact steel (but my guest will be 12c27 or similar), we can't really predict the effect on the temper, but this temperature is on the edge from "no effect" to "screw with the temper".

I can't tell you for sure it will totally ruin it, but I can't tell you for sure it won't.

Don't take a chance.




EDIT: If it's 12c27 as I think, it won't do any good to the razor...



I'm not really familiar with the HRC hardness of razors, but it must be close to knives (57-58)

Vintage razors go from 58 to 62, from what I've been told, so the temper on some would probably be affected at the low end of that range.

Josh

Here's an update for those who are interested:

I wrote to Mastro Livi and he replied that razors subjected to high heat (245 °C) will get softer and softer, losing their edge. I've continued searching and I found a dry heat autoclave that operates at 170 °C for 2 hours. I think this temperature will not be a problem. There is yet another option, which is a pressure cooker at 121 °C for 30 minutes. I think I'm going to go for the dry-heat autoclave because it is smaller and more professional than a pressure cooker, which would be out of place in a barber shop. I also don't want to be in the position of justifying a pressure cooker to the Modena health department. If I purchase 5 or 6 all-steel razors I should be good to go.

Have you looked into getting a UV sterilizing oven? I will be the first to admit that I don't know much about this area, but I have seen some UV devices being used here in the US. They may also be used to sterilize scissors and combs.

Barbers a few decades ago were concerned about safety, too, and they may have had tools that would do the job without ruining their razors.

It's cool to hear that you're looking to offer traditional straight shaves. It's sad that the practice has largely died out.

Josh

Originally Posted by JoshEarl

Have you looked into getting a UV sterilizing oven? I will be the first to admit that I don't know much about this area, but I have seen some UV devices being used here in the US. They may also be used to sterilize scissors and combs.

I'm not an expert on sterilization, but this might be ok from a material point of view.

BUT

UV have a bad effect on polymers and epoxies, so don't put micarta scales in a UV oven, I'm not sure about the celuloid, but I wouldn't take a chance.