tempering multiple times

kile

kile

Joined
Mar 19, 1999
Messages
620
I really don't know anything about heat treating, but I seem to have gotten lucky on the few blades I have made and tested using formulas I have found on BF. What I don't understand is why tempering three times is better than tempering once, and if that is true, would it be better to temper 6 or 9 times, or 100 times? Can somebody please explain this to me, or point me somewhere where i can figure it out for my self? Sorry if this has been answered before, but I couldn't find the answer anywhere.

Kyle Fuglesten
 
Kyle, it's about refining grain structure as well as reducing hardness to a useable level. After 2 or three tempering cycles, the amount of change becomes insignificant, and thus, not worth the time and effort.
 
Tempering does several things. It reduces the hardness of the steel to a usable level. It increases toughness of the blade material. Tempering also converts any retained austunite to martensite. The martensite is whats needs to be tempered. By doing multiple tempers the newley converted martensite becomes tempered. In my experiance two tempers for carbon steel are sufficient. Stainless steel however seems to respond very well to 3 tempers and a subzero quench for me.
 
Being sometimes lucky and using an HRC testing machine, sometimes you don't need to temper at all, sometimes more then 5 times.
Reason for this is simple..I use mainly spring steel, but no-one ever guaratees me this is in fact 5160. I had one once which you could waterquench easy and reach HRC 60, another one didn't wanna go over 55, and another one got about 62 after oil quench.

My basic rule is that if it's too hard, temper.. if it isn't, don't temper. Or temper once.

Sometimes the steel also get's much softer and other time it doesn't change anything.

I really should get some standard in my HT-process, but for that i need to know which steel i'm using in composition.

Basically, i'd temper once and test, if you don't like it, temper again.
Technically, if you temper enough at the right temperature, you should be able to anneal the steel.

or something... I shouldn't have replied :D
 
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