WTB a heat treating oven

[KenH]

Ken - excellent, thanks for the guidance. Do you know of a technical description of the metallurgical transformation that takes place in the cryo cycle? Say, a TTT diagram, or equivalent?

Bob, Austenite that does not transform to martensite upon quenching/tempering is called retained austenite (RA). Here is a link for more reading:

Retained Austenite Decomposition and Carbide Precipitation during Isothermal Tempering of a Medium-Carbon Low-Alloy Bainitic Steel

The effect of isothermal tempering on retained austenite decomposition and carbide precipitation were investigated in a medium-carbon low-alloy bainitic steel. High-resolution dilatometry was used to perform isothermal tempering at 350 °C, 550 ...

www.ncbi.nlm.nih.gov

Here is perhaps a better paper thats aimed more toward knifemakers:

What Happens During Tempering of Steel? - Knife Steel Nerds

Thanks to Shawn Houston and Tyler Christian for becoming Knife Steel Nerds Patreon supporters. We have reached our first goal and therefore I will be interviewing Devin Thomas and posting it as an article to the website. In a previous post I wrote about what happens during rapid quenching of...

knifesteelnerds.com

 

[fitzo]

Bob, if you look at the TTT for 1095 you'll see temps listed (lower left usually) for Ms, M50, M90, and occasionally Mf. Martensite start, 50%, 90%, finish.
The higher the alloying elements the lower the martensite finish temp is. Heck, even some 1095 TTTs suggest Mf is zero degrees. For high alloys it's off the charts low. Thus the need for cryo to get the greatest conversion of austenite to martensite. Some alloy steels can get by with dry ice temps (-78C). There are some of these crazy alloys, though, that need as low as -150C or else high temp tempering in the secondary tempering range. Then you need the LN. There is always some retained austenite in high alloy steels even after full HT with cryo. That will stabilize with time and won't budge without autenitizing temps again. That obviates the need to keep moving from furnace to quench to cryo to temper lickety split with high alloy steels.

my 2cents. worth less than that in today's market most likely. The pity for me about cryo is I have the Dewar and everything but can't find LN. Jerks at Airgas won't dispense to a Dewar and I haven't managed to find the folks Ken suggested to me who do semen storage and see where they get it. Fortunately, a local supermarket carries dry ice for fishermen coming off charters on Lake Michigan.

 

[MTBob]

Hey guys, thanks for the follow-up on cryo treatment. That's very helpful. I'm traveling right now, and need to study this in more detail.
I'll also search for other cryo postings. Perhaps I'll start a post just on Cryo Treatment, options / alternatives, etc..

 

[Gliden07]

Nothing special on using dry ice - just use a container the blade will fit into with a bit of extra space. Break up the dry ice into fairly small chunks, better actually crushed, but as fine as you can get it. Pour alcohol over the dry ice, careful it will boil over easy. Once it's mixed to a good slurry mix (perhaps 50/50?) slide the blade into the mixture. I usually put blade from quench plates to freezer for a few minutes to get the blade temp down to around 0°F, then into the dry ice mixture for the next 30 minutes or hour.

Depending on the cost of dry ice it can be fairly cheap route when doing only a few blades a month. There is some benefit to using a freezer to get to -5°F for a n hour.

Good advise! I buy my Dry-Ice from a company that makes it into pellets or as they call it "RICE" I use RMV Antifreeze for the alcohol portion. I also use the heavy Styrofoam cooler (from the mail order food places) for insulation. Best thing is after use strain the Antifreeze out and reuse it on your next batch. Another source for dry ice is to advertise for it when you want to do a heat treat I've gotten it for free a few times that way or, if you know someone ordering steaks schedule your heat treat on their delivery date.

 

[Heikki]

I'm curious, does anyone make their own dry ice with CO2? We recently needed to make some at work for freeze plugs to do a repair. I didn't know if it was cost effective to have your own tank and set up.