Help can you reheat treat S35VN

[Buster63]

I screwed up the heat treat on two blades and they came out at 57rc, is it possible to reheat treat them and how should it be done, thanks for any help

 

[Stacy E. Apelt - Bladesmith]

Just re-do it. It is now martensite, which is a good starting place.

 

[Buster63]

Just re-do it. It is now martensite, which is a good starting place.

Thanks for the help

 

[DevinT]

High alloy and stainless steels need to have a temper anneal before being rehardened.

Wrap in foil, heat to 1350’f for 6 hours and then re-heat treat.

Hoss

 

[Stacy E. Apelt - Bladesmith]

I will defer to Devin.

I was under the understanding that the existing martensitic structures would convert back to austenite at the austenitization temp. I use 1975°F and a 30-minute soak. 375°F temper. I have redone only a few blades (due to a tempering error), and they seemed fine ... but didn't do extensive testing on them.

 

[Buster63]

Thanks for everyone’s help, I messed up on the temper and was not sure if it was possible to reheat treat them.

 

[DevinT]

High alloy steels including stainless steels, are prone to fish scale grain coarsening when re-hardened. Some form of annealing is required to prevent this.

I believe Sandvik has mentioned this in some of their data sheets for cutlery grades.

Hoss

 

[Stuart Davenport Knives]

I was about to say the exact same thing as DevinT. It needs to be annealed, and I remember him correcting me a while back about the exact temper anneal temperature. I had recommended 1200°F which is for carbon steels, but Hoss corrected me and said for stainless steels it is indeed higher, 1350°F.

Some of the carbide structure was dissolved in the first austenitizing, so grain growth can be an issue when trying to just re-harden a stainless steel, and an anneal is really the best way to go about it.

 

[JoeBusic]

Doesn't it temper while heating up to austenitizing temps?
Grain refining theory says when the grains are smaller, aus temp should be lowered. If mart is start condition, then the time@aust is shorter. If the time and temp are the same, steel behaves as overheated and soaked for too long. Thus, if one re-HT's steel, he should take into account that the grains are smaller and set the time and temp accordingly to avoid grain enlargement.
Of course, when in doubt or not having experience, resetting by annealing is a wise choice.

 

[Buster63]

So once the 6 hr cycle is done should the blades be left in the oven overnight to cool or take them out to cool?

 

[DevinT]

So once the 6 hr cycle is done should the blades be left in the oven overnight to cool or take them out to cool?

Furnace cool.

 

[DevinT]

Doesn't it temper while heating up to austenitizing temps?
Grain refining theory says when the grains are smaller, aus temp should be lowered. If mart is start condition, then the time@aust is shorter. If the time and temp are the same, steel behaves as overheated and soaked for too long. Thus, if one re-HT's steel, he should take into account that the grains are smaller and set the time and temp accordingly to avoid grain enlargement.
Of course, when in doubt or not having experience, resetting by annealing is a wise choice.

Nope, it needs to cool to room temperature before re-heating.

Hoss

 

[Buster63]

Thanks