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Lerch
09-02-2011, 11:59 PM
Just wondering if there needs to be some form of duration in between tempering cycles? Is it okay to cool the blades to hand temp and then place them back in the temper or do you need to allow them some duration of time to stabilize or anything? what i have been doing is placing the blade on my quenching plates until i can pick it up bare handed comfortably and then placing it back in the oven for another cycle, time duration is probably 10 minutes

just trying to make them as best i can!!

thanks
steve

scherar
09-03-2011, 07:34 AM
I remove the blade from the oven, put it on its spine on top the oven (or in a separate rack) and let cool to ambient temperature. Usually takes 15-20 minutes and then place back in oven (on spine) for the second temper.

Fred Rowe
09-13-2011, 08:01 AM
When you quench steel it does not always produce 100% hardened steel, known as martensite. Instead of martensite you have some percentage of retained austenite. Retained austenite is not stable, but will change into martensite over time. This new martensite will be untempered and brittle. You fix this by tempering a second time. The idea behind multiple tempers is that with each temper cycle, more of the retained austenite will convert to martensite.
The retained austenite will convert to martensite over time, so if you let the steel rest for a day or so after the first temper cycle it gives the austenite a chance to change to untempered martensite. What you want to produce with the whole heat treating process is tootsite which is tempered martensite.

Fred

ArtinNC
09-18-2011, 08:38 AM
But what steel we talking about???

Lerch
09-18-2011, 11:28 PM
The steel i am using is 440c stainless, CPM154 and now Elmax stainless. I am looking into doing D2 to try and do a Hamon blade but that is another subject

So I it ideal to do the temper sessions in rapid succession or to allow a resting time between each? Fred from what you said i would gather that the rapid succession is better to ensure a more uniform overall transformation to tempered Martensite steel

What i have been doing now is heat treat, hand cool to liquid nitrogen cryo for around 8hrs then temper twice

Is there a benefit to a third temper cycle with it following 2 cycles directly??

When people had stated that there blades where triple tempered it usually seemed like they did a heat treat, snap temper, cryo and then double temper

Since im not doing a snap temper is there any reason to do a third temper cycle or does 2 accomplish all that needs to happen?

thanks
steve

ArtinNC
09-19-2011, 07:44 PM
I'm using ATS34 Taking it to 1950 for 40 minutes cool in quench plates for 2 minutes then to room temp and after one hour, and then in liquid nitrogen over night and let it warn up for one hour and then two tempers first at 950 and the second at 900 both for two hours . And getting Rc 60 .

BossDog
09-19-2011, 09:35 PM
Good question. Everything I've read is to let the steel come back to room temperature between temper cycles but I've never seen any data or testing around it.

Lerch
09-19-2011, 09:51 PM
ya my question is if the duration at room temp is crucial in any way. does it need to stabilize for some period at room temp or can it be placed back in the next temper cycle as soon as it is hand cool? so far for the most part my blades have spent no more than 5-20 min at room temp between temper cycles and like everyone else i am just trying to make the best stuff i can

thanks
steve

ArtinNC
09-20-2011, 08:33 AM
I don't have any ansers , But I have allways let it cool for One hour between temper cycles. I think there is on problem about bring the blades to hand cool then right back in for the next temper cycle .

Cubane
09-21-2011, 04:42 AM
If you look at the curve on the heat treat charts the time factor essentially shows the percentage of steel converted to martinsite once you have gotten past the nose on the curve. Most of it is done very quickly say 96%. After 24 hours you might be at 99.5% or something so the first temper straight after HT is to get that 96%. I do one 24 hours later to get the next 3.5%. Looking at the curve the time taken for the rest to convert is weeks/years so it isn't worth worrying about. At least that is how it was explained to me.

Alistair
(the actual percentages probably vary depending on the steel they are just here to get the idea and are probably completely inaccurate.)