tempering times ?

[insanity]

I have noticed that some people use multiple tempering heats. Does this have an effect different than using one heat cycle for the same total length of time?

WS

 

[Matt Shade]

There's hundreds of different ways to HT and temper, you can get a lot info on it in a machinist handbook, or by experimenting. Also a lot of reading here.
It seems like for any steel, the tempering time matures at about 2 hours. After that it doesn't seem to change much, unless you let it cool and do it again.To get different levels of hardnes you use different temperatures. Thats for uniform hardness, theres also differential tempering and other things to do too.

 

[Will52100]

I'm no metalurgist, but the way I understand it is that after the first temper, as you let it cool down you get a small amount of martensite transfored that didn't completly transform in the quench, so if you don't re-temper, you have un-tempered martensite in the blade, presenting a potential weekness. A third temper just makes shure.

I think I read somewhere that some swords tested still had martensite transforming and were over 100 years old. I also have read that is the reasone for cryo treatment, the 300+below zero completes the transformation.

I don't know, it's still magic to me

 

[Epsilon]

I have noticed that some people use multiple tempering heats. Does this have an effect different than using one heat cycle for the same total length of time?

Steel type will greatly determine the need for temper styles. Carbon steels require both less time and less or no multiple tempers. They are a pretty straight shot. Something like ATS-34 commonly needs multiple tempers. Why? Well you temper after the quench to relieve 'x' amount of stresses compounded. If you retain austenite, it is usually desirable to convert that to martensite (cryo, freeze, etc helps the process along quicker). Fresh, untempered martensite forms and needs to be tempered. Thus a second temper performs this.

That's one example, many more are also valid. Tempering will depend on austenitizing temp, soak time at that temp, cooling method and speed and part size. The core ingredients.

-Jason