Annealing 316 During Heat Treatment

[metalman8357]

Hi all,

Just a quick question. I have a component that is friction stir welded 316SS and 1060 plain carbon steel. We'd like to Austemper the 1060 component, but I'm wondering if this will have any affect on the hardness/corrosion resistant properties of the 316 part? Induction hardening is not an option due to cost. The 316SS component has undergone quite a bit of cold working and is around 35HRC. I'm wondering if the austempering process will anneal the 316 component appreciably?

 

[metalman8357]

I believe the re-crystallization temperature for 316 is around 1050C, and this is higher than the austenitizing temp of 880C so I might be good here. Can anyone think of any detrimental effects to the work hardened 316 component that might come about for holding at the austenitizing temp of 880C during austempering the 1060 component? Decreased corrosion resistance? Stress induced martensite reverting back to austenite reducing the hardness?

 

[CoryPad]

The cold worked 316 likely will distort during the austempering operation. The 316 part may become sensitized during the austempering operation, reducing corrosion performance. This does not sound like a good idea.

 

[metengr]

I agree with CoryPad. Why don't you first austemper the 1060 material followed by friction welding?

 

[metalman8357]

We would like austemper the 1060 component first, but it loses it's hardness from the heat generated during the welding process (In addition to the friction welding, their is also a regular fillet welding operation). How much time at the austenitizing temperature is enough to cause sensitization? Also, is it possible that the cold worked 316 will lose some hardness, in addition to possible distortion?

 

[metengr]

In that case, I would manufacture a prototype and perform a destructive examination. It doesn't cost that much and the results will indicate which direction to proceed.

 

[weldstan]

Sensitization will occur during welding and austempering. Whether this will be a problem depends on the service environment. Metengr's recommended approach should be highly considered.

 

[EdStainless]

Make sure that you are using 316L, the C should be 0.02% or lower for ideal results.
Then you will not need to worry about sensitization.

Make a sample part.
You can test resulting weld strength, distortion of the the SS, softening of the SS (it will often).
You also need to do micros and corrosion tests of the 316 near the welds. You should be looking for sensitization and the formation of detrimental intermetallic compounds.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[kumkumvijay]

The stainless steel will undergo sensitization and will results in poor corrosion resistance and hardness drop depends on the time exposed.
Due to different thermal expansion of different material , distortion will occur. The weld med with mixed material will respond in a different way than both parent metal ( may be more metalic carbides).

 

[EdStainless]

With low carbon and short hold times there will be no sensitization of the SS.
Distortion is the biggest problem that I would worry about.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube