I have been away demonstrating at the ABS hammer in in Troy Ohio, so I wasn't able to include input until today. I myself use Heatbath/Park Metallurgical oils for any work that I don't just run through the salt baths. If I were doing 5160, 52100, O1, L6, 8670M and other oil hardening steels I would use Parks AAA, it is a very nice and well designed medium speed quenching oil. I don't use AAA very often because any steel that will quench well in it will also quench just fine in low temp salts, which is certainly my preference. If I have to do quenching of 1075, 1080, 1084, 1095, W2, W1 or other rather shallow hardening steels I use Parks #50 as a medium speed oil just will not get them entire over the top for full hardness. As mentioned any particular steel really needs to be matched to an appropriate speed quenchant, all you want is maximum martensite conversion, beyond this only get you unnecessary stress on the blade that you will have to deal with or experience distortion or even cracking; speed is never the single defining factor of a good quenchant.
Now that I have mentioned the Heatbath/Parks products that I am familiar with I need to deliver the bad news-
Heatbath/Parks won’t sell it to you. That company only deals with an exclusive client list that is limited to serious industry and very large scale operations only. Even if they would sell it to knifemakers you would be buying it in 55 gallon drums. You can get it on the secondary market but the cost of a 5 gallon bucket is going for prices that are too rich for my tastes.
Now let me tell you about the largest and oldest quench oil manufacturer of them all- Houghton International (
http://www.houghtonintl.com/) and the good news is that they like your business just as much as anybody else’s, and make some of the finest quenchant to boot! I would use Houghton products, and have set up friends in industry with them, if I wasn’t already completely set up with Parks oils. If you visit their website they also have some fantastic informative articles about heat treating as well. On the recommendation of a friend who is very much involved in the technical end of R&D at Houghton I would suggest Houghto-Quench 3440 for when you want to approach water quenching speeds. My friend assures me that it is just about the fastest oil you can get. Houghto-Quench 3430 is less severe and good for a wide range of alloys in blade sizes.
I have been marquenching for over 15 years and feel obligated to add a little note for the sake of public safety. Products designed to properly do martempering/marquenching are carefully engineered to handle those temps and still extract heat without becoming incendiary devices capable of death and destruction. Heating an oil to within a degree of its flash point and then adding a 1500F piece of steel to it requires a little planning. Most oils acquire more quench speed from being gently heated up to about 150F but above 200F the thermal extraction abilities start to be harmed by more heat. For these reason I have always been a huge proponent of using products that were engineered to perform that task properly and safely, and Mother Nature never really cared about martempering.
I would also like it noted that my recommendation or criticism of any particular quenchant comes from results based upon the most objective analysis I can provide of the desired properties and internal structure. What a good blade should be is determined by each individual and any attempts by me to qualify or quantify a quenchant based upon such criteria would be like chasing the wind. How one person likes a blade to cut is a feeling, not a fact I can either refute or support, how much martensite vs. pearlite that can be observed within the steel is.
Hazards from hot oil, fire, toxic vapors or smoke resulting from improvised quenchants are also not a matter of opinion and something that makes me feel obligated to say – find your own level of desired performance in both a quenchant and the resulting blade, have fun, but please be safe guys.