anneling vs stabilization heat treatement

[ionutamartei]

hi everyone,
Could someone tell me if I will do annealing heat treatment to stainless steel is done also a stabilization? If Yes why in SA-312 stabilization heat treatment is a supplementary requirement?
Extras:“Subsequent to the solution anneal required in 6.2,
Grades TP309HCb, TP310HCb, TP321, TP321H, TP347,
TP347H, TP348, and TP348H shall be given a stabilization
heat treatment at a temperature lower than that used for
the initial solution annealing heat treatment.”

 

[metengr]

The stabilization treatment is most effective in reducing intergranular sensitization for stabilized grades of austenitic stainless steel, like those with Cb or Ti additions. Testing has shown that austenitic stainless steels with higher Ti/C ratios exhibit reduced sensitivity to sensitization.

The reason for being a supplementary requirement is that not all applications require a stabilization treatment.

 

[ionutamartei]

Thanks for response
But my question was: if I do annealing heat treatment is done also a stabilization of the materials?
Stabilization usually is done to 843 to 899°C,and the purpose is dissolve the precipitated chromium carbides.
Annealing heat treatment is done to 928 to 1093°C the primary purpose is to obtain softness and high ductility
What is the difference of these heat treatments? Maybe holding time?

 

[EdStainless]

In the solution annealed material there must be no carbides at all, or else they screwed up the anneal.
The material will be soft and single phase.
When you stabilize you deliberately form carbides (Ti or Cb) and don't form Cr carbides. This ties up all of the C in the alloy.
This prevents future formation (in service) or Cr carbides and the resulting susceptibility to intergranular corrosion.
If your service is at 850-900C then skip the pre-treatment.
Anything less than 1000C is not an anneal.

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P.E. Metallurgy, Plymouth Tube

 

[ionutamartei]

What is the holding time for anneling? but for stabilization?

 

[EdStainless]

It depends.
If I am reannealing something after cold work that has no carbides then I am looking at a few minutes at temperature.
If I am dissolving carbides then it depends on how coarse they are, anywhere from 10 min to 1.5 hrs.
It also depends on temperature, 1 hr at 1000 is roughly equal to a few min at 1100.
Everything that we make is thinner than 6mm. We anneal most 3xx alloys at 1065 for times from 5 to 10 min.

Stabilization takes a bit of time because the temperatures are lower and reactions and diffusion are slower.
The time will depend on the alloy and composition.

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P.E. Metallurgy, Plymouth Tube

 

[ionutamartei]

I had an experience in Kazakhstan where the beneficiary ask us to perform stabilization PWHT even if the materials (pipe and fittings) where not stabilized by heat treatment. The materials was came only with annealing heat treatment so from my point of view is not correct. The materials should be delivered with annealing + stabilization heat treatment. Am I right?
in ASME code stabilization heat treatment is a supplementary requirement

 

[EdStainless]

I know of many applications where the start-up procedure is designed to hold the material in the stabilization region for 12-24 hours.
As for doing it to welds, they should have required it be done before the welding, even if they just did it localized. Not there is any real harm in doing it afterwards as the alloys are designed to stabilize when welded. It is just redundant.

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P.E. Metallurgy, Plymouth Tube