Thread: Need to temper again, Safest bet?

For O1, I usually temper twice for two hours at 400 for ~62 HRC.

I have a high-end toaster oven in my shop that is really accurate and has a timer and stuff on it. It works like a charm and uses very little energy compared to my gas kitchen oven. My blades are usually a brownish yellow when they come out. I cool them in still air, then put them back in for another cycle.

Question for Mike: does it matter how the steel cools between tempering cycles? I've seen it recommended to water cool 52100 between cycles, which I've had good results doing, but don't understand this metallurgically. Is it like putting cold water on spaghetti noodles?

I have another question too for the metallurgists amongst us.... I kind of LIKE the golden bronze color that results from the temper. If I placed the shave ready razor back into the oven to turn the bevel that color, will it "un-ready" the edge?

Originally Posted by PapaTony

...Question for Mike: does it matter how the steel cools between tempering cycles? I've seen it recommended to water cool 52100 between cycles, which I've had good results doing, but don't understand this metallurgically. Is it like putting cold water on spaghetti noodles?

The al dente of 52100 might crack teeth...I suppose a tomato sauce including some nitric acid would soften it up nicely!

I like the use of a still air box myself but there should be no real dynamic motion from tempering temperatures down to room temp water if you used it. For the most part rapid cooling simply reduces the time in between cycles and allows more work to get done in a shorter period.

The bronze color is an oxide formation and will not affect the edge to any degree. It's a nice looking color to my eye too. It will get erased with honing though. No surface treatment survives honing or abrasion.

Originally Posted by Mike Blue

The al dente of 52100 might crack teeth...I suppose a tomato sauce including some nitric acid would soften it up nicely!

I like the use of a still air box myself but there should be no real dynamic motion from tempering temperatures down to room temp water if you used it. For the most part rapid cooling simply reduces the time in between cycles and allows more work to get done in a shorter period.

The bronze color is an oxide formation and will not affect the edge to any degree. It's a nice looking color to my eye too. It will get erased with honing though. No surface treatment survives honing or abrasion.

Glad you liked the cooking metaphor Mike I thought it was just some more voodoo.

Everybody has to eat. Most people understand things related to food and I'll use whatever example works to get a point across. The plus side is that someone will read that and think heat treating steel requires a taste test. "Hmm, what'd you think Papa, maybe 1.48% chromium? I think the 52100 dealer shorted you on chemistry." We'll drive them all nuts! LOL

Of course, al dente 52100 may only be case hardened...

I tried making one razor from 52100, and it left a sour taste in my mouth. Maybe it (or me) just need to stew a little longer.

Imo, other than feeding into the steel fetish of the knifemaking world, a 52100 razor makes as much sense as a bookshelf made of reinforced concrete. None of the benefits of the material are useful, and the downsides are downright annoying.

52100 is really good at taking a lot of abuse and not caring about it. That's why they use it for ball bearings and propellor blades of turbo jet engines. That also means that forging it, grinding it, sanding and polishing it, and honing it, is going to be 'not fun at all'. And to what end? Its edge is not sharper than a plain O1 edge. And shaving does not impart any level of stress on the edge where the difference between O1 and 52100 would matter.

It has its uses where it shines. Razors is not one of those.
This reminds me of the guy who had a fully hardened M42 razor made against all our advice. In the end, it was almost impossible to hone, and didn't shave particularly well.

I have 52100 around which I bought because it sounded like something cool to work with. I've made a couple of knives with it, and then I lost all interest in it. It's just not the right tool for the job.