I just read another thread, and it got me to thinking :eek: Ok, how much better would it be to use nitre blue salts for tempering, rather than the standby toaster oven? In other words, is it worth the expense and time, to build up one of these systems (the Brownells niter blue salts go from 300 - 900 degrees according to the thread) just for tempering? As Ed Caffrey pointed out in the thread, this system would also be good for bluing if desired.
So, would I benefit a lot from having a salt tempering system, vs. the oven style method of tempering? Your thoughts.
Thank you
Robert

I find salts so far above and beyond what just an oven (even really good ones) can do in tempering, that I shudder when thinking of going back to anything else. Since I have yet to do comparisons of salts designed for bluing vs. salts designed for quenching I will remain cautiously dubious of Nitre Blue for quenching, but I see no reason why they would not work wonderfully for tempering.

When working in open air ovens, you spend 1/2 to 3/4 of the time you thought you were tempering just getting the piece up to temperature, not so with salts. I start my tempering at 1/2 hour intervals until I zero in on the HRC desired and then go for a 1 hour temper to nail it. Ovens require much more time just to move the HRC a bit. Ovens are prone to cool spots and being much hotter near the elements, the salts are a great equalizer giving a very uniform temper. This is not to knock ovens, many a great knife is being made in well regulated and controlled kilns, but a toaster oven...? I say treat yourself to an entirely different world and use the toaster oven to make yourself a good hot bagel while you watch your blade tempering in the salts ;) .

Kevin, what type salts would you recommend and where would a person obtain them. I'm wanting to try some experimenting on bainite so I'm wanting them for the higher holding quench tempertures.

Thanks Robert for asking this over here.

Bill

Now you have me in a corner. The assitant fire chief on our dept. has a saying-" if all you have is a complaint with no solution to offer, all you are doing is bitching." I am just really picky about using stuff that was designed for the intended purpose, mostly because I am too lazy to research and test everything before making substitutions. I would recommend checking with the various heat treat suppliers and see what they offer, and if you can get it in reasonable quantities (I realize that this can be a challenge) . I use HeatBath (Park) Thermo-quench salts, I am sure there are many similar products being made out there. I believe Heatbath also makes other low temp salts such as Marquench- B and others. I would shop around myself before accepting somebody elses word that I cannot get it in my area.

Thank you Kevin, good info. Bill, didn't mean to hijack the thread from one forum to another, but I wanted to focus in on just the tempering aspect. Brownells also sells a high temp salt, but I don't know anything about it. I have used the nitre blue, just for that, bluing, but am now going to build up a temper system. Later on I may sneak into the world of hi-temp salts, but for now the Evenheat is getting the job done (hopefully).

I didn't mean to back anyone into a corner, just figured if a person( whomever)knew the salts I'minterested in for a particular purpose,it wouldn't be a problem. I don't take anyones advise or suggestions as the gospel, sometimes it just gives me a little better place to start my quest for the answers I'm looking for, other then what I already have.

Thanks I'll check with some heat treating supply companies.

Bill

Not at all Bill, the corner I was in was the one where I need to admit that I don't have all the answers ;) .

Kevin, help me understand this: Instead of putting the blade in a conventional "air" type oven for 2 hours, two or three times, you just put the blade into the salts at say 375, pull it out after 1/2 hour and check it on your Rockwell meter, and if it's not quite there yet, you add or subtract a few degrees and back into the salts it goes. When you get to where you want it (say 61 HRC), back into the salts it goes for another hour. Is that right? I'm sure (Im positive) that there's a chart somewhere listing the ideal HRC's for a given steel/purpose, but I don't have it saved anywhere. Can anyone point me in the right direction please? I appreciate all of this info guys, I find it facinating.

When using a container for salts, is there a difference in temperature between the upper and lower levels of the liquid?....the reason I ask, is that I was experimenting with a 10inch high pot of peanut oil trying to get a stable temperature but I was getting as much as 30 F difference between top and bottom..........(my burner is at the bottom)..not good for a point first quench.

I want to experiment with low temperature salts hence my interest in this thread :) .

Thanks.

Kevin

Kevin, help me understand this:...

You have pretty much summed it up there. The darned thing about those specs and charts is that I have never had my temps vs. HRC match the books :confused: . All of the other temperatures have worked the way they should but tempering temps are always slightly different in blades in the real world. Enough so that I just do not trust them and verify every temper myself. I have learned a lot about what happens in tempering by doing this, I have also learned that even though you may have the same steel type, each blade will temper differently at certain times. Years ago, in the oven, I used to just do everything at 400F. for 2 hours and then call it good. Then I got my salts and a hardness tester and things got a lot more interesting. Tempering is a very complex process that still wrinkles my brow a bit more than all the others.