Good day.

I have recently obtained some 440C, and I was considering making a kitchen knife from it, due to it being stainless. I've read about how difficult it can be to forge, so it will likely be a purely stock removal knife. Though I typically forge my blades, I've done a few all stock removal. Not quite as fun in my opinion, but a better option given the material. I'm concerned about the heat treat, but I would very much so like to do it myself, rather than sending it to someone.

Now... Everything I've been able to pull up on various websites about heat treating 440C is conflicting. Some say oil quench, some say air hardening, some say you can do either (which i didnt think was possible, but ive been wrong before.) and some on either sides of those spectrums talk about a cryo cycle after hardening. I've no access to liquid nitrogen to do cryo, nor do I believe I have the knowledge, setup, or skill to use it. My question is: to anybody who has worked with 440C, what is the recommended way to heat treat? Is it true it can be oil hardened or air hardened? This just seems strange to me. Is a cryo cycle necessary? What I (think I) understand about cryo is that it converts all the austenite left over from the quench into martensite, maximizing hardness before tempering. That being said, and assuming I actually understand it correctly, it would not be completely necessary, as the quench would still harden it, just not to its full potential, yes?. 

Thank you in advance for your time. 

Try dry ice and acetone it gets about -170

Thank you for the reply.

I do have acetone. Dry ice on the other hand, I do not. Any recommendations on where I could obtain some? I've read about making your own by capturing the CO2 from a fire extinguisher, so that is one option. 

So is cryo necessary? I've read that 440C can achieve an RC 60 hardness, but I assume that is only after a cryo cycle, yes?

I get dry ice from my local grocery store; they stock it for folks living in the middle of nowhere to get their frozen foods home.  I would look under Ice in the real paper yellow pages.  When I lived in New Jersey I'd get it from places that provided it for ice cream trucks.  

Thanks Thomas, I'll try to look for it around my area. I've never seen it in a grocery store, but I could have overlooked it. I'll check the yellow pages too. 

Depends on what type of grocery stores you have.  Generally you will need to ask.

That makes sense. Not necessarily the kind of thing you want right on the shelf. I'll be asking around for sure then. Thanks for the tips.

Some welding suppliers also carry dry ice.

Interesting. Perhaps my local AirGas will have it. Worth looking into. Thanks.

What would be the recommendation for hardening before the cryo? As stated, I've heard air or oil hardening. I'll likely do oil hardening if either are an option.

So after nearly constant research for the past few days, I've established a process (on paper) that I am going to try to follow to a dime.  Please, feel free to critique if anything is wrong. I would like to do it well the first time.

Normalize (twice) at °1600-°1700 

*Oil* quench at °1500-°1600 to °150

Cryo quench (dry ice and acetone) down to °-170 and allow to return to room temperature

Dual cycle temper @ °350-°375, one hour per cycle. 

 

Thoughts? Stainless is a bit foreign to me, so I would not doubt that something here is off. 

Thanks in advance. 

On 05/05/2017 at 4:19 AM, Will W. said:

Now... Everything I've been able to pull up on various websites about heat treating 440C is conflicting. Some say oil quench, some say air hardening, some say you can do either (which i didnt think was possible, but ive been wrong before.)

From what I can see, the concept of oil quenching an air hardening steel for a knife is that it give an effect similar to the use of a hamon (internally, not visually) on a plain carbon steel, with the thicker steel in the back of the blade being less hard than the thin cutting edge.