Austenization temps and corrosion resistance

galadduin

galadduin

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Dec 25, 2004
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I've always wondered if the austenization temps affect the corrosion resistance of stainless or semi stainless (like D2) steels. There are many (theoretically unlimited) temperature selections of austenization, one may heat to 1020 C, one may go up to 1060 or 1070 with D2, and after subzero all different knives can be performers if done right. Is there any effect on chrome carbides and free chrome in the steel structure thus resulting different corrosion resistances???

Thanks
Emre
 
Oh man, you might need to ask this on the forum where Roman Landes hangs out.

I'll do the best I can.

The higher austenitization temperatures will free up more chrome by dissolving carbides. However there are two problems. One is RA, the other is the martensite can only hold so much carbon, so it is going to pop back out and combine with something. That something is frequently free chrome. So you went full circle.

There are a few things you can do. Quench quickly, such as a moderate oil quench or plate quench. That will prevent the carbon from forming as many chromium carbides on the way down. It still pop out, but at lower temperatures where it leaves the chrome alone. And use the lower temper temperatures, keeping the carbon in the martensite (stay away from anything resembling a secondary hardening hump).

A high austenitizing temperature will encourage RA, and the low tempering temperatures won't decompose it - so you're going to need to include cryo as a part of the quench or your RA will be out of control.

so - fast quench, and low temperature tempers.


...there, how was that?
 
Thanks Nathan, that was what I was looking for. I had a discussion on a Turkish Forum, I wrote there similar to what you have told me, but I had to be sure if I'm wrong or not.

BTW who is Roman Landes? Is my question too silly, if thats the case I'm sorry...:confused:
 
Nathan the Machinist said:
Oh man, you might need to ask this on the forum where Roman Landes hangs out.

I'll do the best I can.

The higher austenitization temperatures will free up more chrome by dissolving carbides. However there are two problems. One is RA, the other is the martensite can only hold so much carbon, so it is going to pop back out and combine with something. That something is frequently free chrome. So you went full circle.

There are a few things you can do. Quench quickly, such as a moderate oil quench or plate quench. That will prevent the carbon from forming as many chromium carbides on the way down. It still pop out, but at lower temperatures where it leaves the chrome alone. And use the lower temper temperatures, keeping the carbon in the martensite (stay away from anything resembling a secondary hardening hump).

A high austenitizing temperature will encourage RA, and the low tempering temperatures won't decompose it - so you're going to need to include cryo as a part of the quench or your RA will be out of control.

so - fast quench, and low temperature tempers.


...there, how was that?
Click to expand...

are you saying you can oil quench d-2 i always just heat it up to 1750 let it air cool and draw twice, how much better performance can i get by stress relieving and cyro. and what is the process seqence. regards
 
Emre,

Kevin Cashen started a very technical and formal forum. Roman can be found there. It might be poor form for me to link to it from here. I'll send you an email.

Machinest (sic)
Yes, you can oil quench D2. It will have improved corrosion resistance.

D2 is designed to be an abrasion resistant, dimensionally stable and relatively tough steel for stamping and drawing dies. In the industry standard HT I used to use (for dies) it has large carbides, retained austenite and carbon lean martensite. Much of the chrome is tied up in carbides. For knife blades we want better edge stability and corrosion resistance so we use a somewhat different HT.




Edit to add:

Just to be clear - D2 is going to have large carbides and a large carbide volume regardless of HT.
 
Last edited:
The idea behind the high austenization temps for high alloy steels like D-2 is to get everything dissolved and into solution so you can lock it into the structures you want with out any of the previous formations leftover in the steel to cause problems. These temperatures are always given as a range, partly because the alloying elements in a certian grade of steel are also given as a range and partly to account for the thickness of the steel being used. Generally the thicker pieces are recommended at the higher temps and the longer soaks so that everything has a chance to get into solution. Chromium and vanadium carbides are particularly tenacious and don't like to dissolve, and the more chromium or vanadium there is in the particular alloy the higher the temps you need to get them into solution. Getting more directly to your question I do know that for some high chrome steels to be stainless, they need to be heat treated. Using too low of an austenization temp may leave some structures undissolved and lead to corrosion resistance problems.

Del
 
Hmmm, I've found that D2 (in blades anyway) tends to be more prone to pitting rather than forming a more general layer of corrosion (or patina for that matter). Could this have something to do with not using high enough austenization temps/long enough soak? Such that not everything went into solution properly?
 
And don't forget the tempering temperature ! With stainless steel you usually have the option of a high [ ~ 500 C] or low [~ 250 C] temper but the low will have better corrosion resistance.
 
So if someone suggested to you that 1950 is above the boiling point of Chromium - so heat treated blades need to be ground down to find actual stainless metal - would you have a response for them?

This is not my suggestion. It was posed to me originating from someone whose HTed blades need a lot of post HT grinding. For my answer I referred to Crucible spec sheets. They reference corrosion resistance without any reference to grinding away steel post HT.

Interested in informed or more articulate answers.

Thanks

Rob!
 
Please use F or C when mentioning a temperature ,it will save confusion !!
Chromium - melting point - 3407 F, boiling temperature - 4829 F

Corrosion resistance is often due to the formation of oxides on the surface .In the case of stainless steel it's chrome oxide .If you tie up Cr with carbon that Cr is not available for corrosion resistance. Small spots of rust on stainless may mean that these are areas where Cr carbides have formed.
 
Thanks all for very informative answers. Actually I have asked a similar question a year ago or so but unfortunately I forgot that I had the same answers before from same friends (Nathan, Mete and Kevin). Delbert thanks a lot for your reply, it actually shed some light on low aus-temps also...

Nathan, that forum is an ocean, all I wanted a glass of water :D Now I dived to that sea, thanks a lot for that link...

Best regards and marry Christmas...
Emre
 
Thanks Mete. When the question statement was raised, I just kind of rolled my eyes and let it go. I guess I should have looked up the numbers myself. We haven't had any corrosion problems - just wanted to answer a question I was asked.

Oh yes - I'm 57 years old in North America. Degress F is my default. :D

Rob!
 
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