Stainless hardening temps

[Eli Jensen]

Hey folks, quick question. I am wanting to get into kitchen knives, and thus am investigating stainless steel. I also, however, and starting to braze my bolsters on pre-HT, which on my 1084 is not a problem as the melting temp of the fittings is a good 200-300F above critical temp.

My question is, what are some hardening temps of various stainless steels well suited for kitchen cutlery? I am hoping there might be one <1700? If not, what are my options for other steels i.e. tool steels?

[Ray Rogers]

Stainless steels will either be higher or MUCH higher than carbon steels. 440C and most of it's clones need about $1850 and the newer fancy steels like S30V need 1950 to 2100, depending on the steel in question and the exact hardening formula you're trying to follow. In addition, most any stainless will be held at these temps for at least 30 minutes, sometimes for an hour. These temps must be held very closely which makes an electric furnace or maybe salt pots the only practical way to get the job done....

[Doug Lester]

I don't have listing for much in the way of stainless steels but even 440C lists an austinizing temperature of about 1900 degrees and I think that this is what you'll find with most, if not all, stainless steels with enough carbon to make knives from. Those people who actually use stainless steels would be able to tell you better but my impression is that stainless steels need a higher austinizing temperature with longer soak at temperature, maybe a half hour, to dissolve the carbides with sometimes even a short preheating soak to prevent distortion.

I have made all the knives that I have in my kitchen, with the exception of my steak knives (another project) and they're all carbon steel. I use, wash, then dry them and under no circumstances do they get put into the dishwasher. No, they're not all shiny and bright. My worse cared for one, from before I got strict with myself in how to care for it, does have quite a bit of a patina on it, the later ones much less so but it's only a patina. It doesn't effect the knives' performance in any way. About all stainless steel will do is allow you to abuse your knives more and get away with it.

Doug

P.S. I see Ray and I were typing at the same time again.

[Ray Rogers]

Doug,

Great minds think alike! Unfortunately, that is also true of feeble minds.

Eli,

What Doug said about carbon kitchen knives is true, most of the kitchen knives I made for myself are carbon. But, I have made hundreds of kitchen knives for professionals as well and there is no way you'll be able to make knives for that crowd without using stainless. Many pros like and even prefer carbon blades but sometimes they need stainless blades anyway. Unfortunately, carbon blades can leave a slight discoloration on white vegetables and in gourmet preparation that simply is not acceptable. And, there are plenty of pros who prefer stainless blades and more than a few don't know the difference....

[Eli Jensen]

Is the story any better with tool steels? I am not going to HT air hardened steels myself. Doing research cause I don't want to send something out and have the fittings melt in their oven, or more likely they send it back and i waste time and money on shipping.

[Ray Rogers]

Tool steels are nothing but carbon steels that have certain characteristics useful in tool making (which often includes knives of various sorts). If you stay away from the tool steels that have a lot of chromium, like D2, most will HT in the same range as 1084. High chromium steels will more likely HT similar to stainless steels. That's probably not the whole story but it's probably as close as you'll get without naming a steel - and if you can name it then you can look up the HT specs for it ...

[Eli Jensen]

Do copper alloys stain food?

[Ray Rogers]

Not that I'm aware of. Copper skillets and pots have been used for decades. Of course, if you were to make a blade out of copper that would likely stain a fresh vegetable which is what I was talking about earlier. Before you start throwing copper into the mix, especially with carbon steels you should be aware that electrolysis could be an issue (just as it could be with most any two dissimilar metals). For commercial kitchen knives the safest bet is a stainless blade with stainless fittings and either some type of synthetic handle or professionally stabilized wood ....

[Eli Jensen]

what is electrolysis?

[Ray Rogers]

That's the reaction between two metals that can result in corrosion. Ever seen a hunting knife with a brass guard stored in a leather sheath and the brass and the leather turn gooey green? That's an extreme example. Less extreme examples aren't so visible. Electrolysis can eat away at the tang inside a handle or under the scales to the point where the handle falls off or the scales separate from the handle. This is one reason why we're always preaching sealing up a handle with a waterproof epoxy since the process only happens when there is some water available to support it. This is also why everything you read about soldering guards stresses that you make darned sure you have neutralized the flux. I suspect the same could be true with brazing ...

[Eli Jensen]

Does a water based flux mitigate that? And it can't happen to internal components if theres no water?

[Ray Rogers]

In a kitchen knife there is always water - it goes with the territory. We're talking about the same general process that we use to plate metals (as in gold plating), or the same as when we etch our logos on our blades (enhanced and sped up by adding electricity). Basically, we're talking about building a crude battery in your knife handle. Anything that allows ions to move around is a problem....

[Eli Jensen]

I'm always paranoid about flux between the fittings and the steel that is/can be sealed in there. I don't know much about the science behind it. I've been using a water and titanium based flux, mainly because its for prolonged heat at high temps. Surely any water evaporates fairly quickly. As far as outside areas, I always try and neutralize well with baking soda and soap, and I grind almost any surface anyhow.

[Ray Rogers]

Most guys would take those precautions. But, all it takes is a microscopic pin hole to let the moisture eek into the interior so, if there were any flux sealed inside it could get active. Or for that matter, no flux but different metals plus moisture.

I think the bottom line is that you can do anything your heart desires on your own knives or knives for your friends but commercial kitchens are a very unforgiving environment. Chefs are people too and they like shiny things and exotic metals but if any of that ever goes bad even in the slightest way it can be all that's required to sink your reputation among that crowd. Word to the wise ...

[Eli Jensen]

And I can't really blame them either. Cooking is a big liability. I'm not terribly worried about pinholes. I'll be posting new knives soon, correct me if I'm wrong and should be worried.