Multiple heat treatments

K

Knife Outlet

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Jan 4, 1999
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Is there any advantage (or disadvantage) to heat treating steel more than once? What effect would repeated heating and quenching have on blade steel? Thanks.
 
From my reading, this is my understanding. If your HT is 100% flawless, more HT will not help, but in this imperfect world, things are rarely 100% flawless. Sometimes, especially with more complex steels like 52100, after one 99% flawless HT not all of the steel might have turned to austinite and some of the carbon might be trapped in carbides. In that case a double or triple HT will fix it. The parts of the steel that HTed properly the first time will have the carbon fairly evenly distributed and hopefully be small grained, so it'll convert more easily the second and third time, while the parts that didn't work right will get caught in the second or third, hopefully leaving you with the equivilent of one flawless HT.
 
Normalizing at least twice and maybe three times will reduce the grain size of the steel so that you can get the most from a single heat treat. What ever way you want to go about it is up to you. I know some that will anneal first ( to make it soft for threading and drilling) and then when almost competed with the gringding, will normalize 3 times and then harden once before tempering. I normalize twice and then anneal after forging. I grind bare handed so as to be able to tell when the steel starts to get hot, then quench to keep cool. After I finish the grinding, drilling, or threading, I will harden once and temper twice. I use the 52100 and have been extremly successful with it in cutting contests, JS performance test for the ABS, and used with 15N20 to make damascus for my MS performance test.
After reading several popular knifemakers heat treats, the one thing that is common is that the grain is reduced to the smallest size sometime before the hardening part of the heat treat.
Maybe even if you don't do anything to it but heat treat it 3 times, it will still reduce the grain so that by the time you have run it through the heating process multiple times, the grain is reduced.
This is just my theory and I guess every one has one.
 
A good number of years ago, Congress proposed closing the patent office because they felt science had invented everything that was of any value.

This relates to this topic because there are two decidedly different points of view here. Those that look at the world through a slide rule and say Multiple quenches do not help...and those of us that do believe in Santa who think it does.

Take your pick! :D
 
Raker, thanks. Now I just need to know what normalizing is. I understand annealing, quenching and tempering but normalizing isn't in my vocabulary yet. Take care.
 
My understanding of normalizing is to bring the steel up to just above critical (nonmagnetic point) and then allow to air cool back to black. After a few times of this, the grain is pretty well refined.
I also believe in Santa and do the soft shoe and chant while swinging the hot blade in the north and south direction from the tang using a special set of normalizing tongs. These tongs are kept in a special wooden box so that the magnetic field of the earth will constantly re-energize them. :)
You just can't afford to take chances when your doing the best you can.
 
Mete,
Good basic summary of heat treatment, thank you for taking the time to creat the site page.

One point I disagree upon is the Cryogenics statement, if you use liquid nitrogen at -100 F, yes it is not very effective except for retained austenite. Most if not all bearing manufacturers who use 52100 will use the liquid nitrogen process. If you use the -300 F cryo treatment it will give improved physical properties. Data supports the deep -300F cryo treatment over many years of real world applications.

Multi temper does give increased properties however, the knife making applications may not be beneficial. We find that with D2 and similar alloys, a triple temper will give much longer life (increased spall resistance) in many service applications. Warren Cutlery found that with their wood carving knives made from 1095, a double temper greatly increased toughness and edge holding.

Retained Austenite will change over time (long time, not tempering time) if the steel temperature is elevated to approx. 250F-300F, as you know the steel will grow in size due to crystaline structure of Martensite vs. Austenite. At room temperature there just is not enough energy for the transformation.

The hardening process is essentially a time-temperature-transformation process, which is illustrated in the T-T-T curve, which I am certain you have examined in your research.

Regards,
FK
 
FK, reading your comments - do you understand that I am a metallurgist ? I have made many comments about cryogenics and stand by my statements that most of cryo is hype .Reading through cryo websites you will find lots of nonsense , unproven theories ,scientifically incorrect, etc.
 
If I do three quenches because the first one might not be correct will I be more likely to learn by always doing three quenches - just in case - or would I be more likely to learn by doing only one quench? Generally, one quench is all it takes if done properly.

Mete is our resident metallurgist. When he tells me cryogenics benefits hardened steel by transforming retained austenite to untempered martensite I take it to the bank. Mete has taught me more about properly heat treating steel than I would have learned on my own in ten more years.

RL
 
...and I can vouch that Roger's HTing is some of the best there is. I recently had two ATS-34 blades HT'ed and cryoed by Roger, and they've performed fabulously!
 
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