Thermally Stabilized Stainless Steel Type 347 7

[hnaziri]

Is there such a thing as "Thermally stabilized stainless steel type 347"?

 

[SMF1964]

mcguire: My notes/documents on this indicate the following references in notes from previous investigations in my company:

- "Proposed ABB Combustion Engineering Policy Statement Regarding the Heat Treatment of Stainless Steel Bends and Welds", a Tech Service (Windsor) document received in-house 3/1993, but no date of the policy statement is given in our fax copy of that document. The document proposes stain-induced precipitation hardening in the cold bend regions as having an adverse influence on creep properties. A subsequent EEI Prime Movers Committee report (EEI Pub. No. 65-58, June 1965) does not find supporting evidence.

- A Kraftwerk Union topical report "Material Comparison of AISI 347 to KWU specifications with AISI 316 Nuclear Grade (316 NG)" shows a reduction in IGSCC with increasing Cb/C ratios (Nb/C for those on the other side of the pond).

 

[mcguire]

Nb(orCb)carbides form and dissociate at a fairly low temperatures compared to titanium. If there is a supersaturation of Nb and C after welding or heat treating or if there is some dissociateion from service temperature, then cold work would accelerate and localize any subsequent precipiation, since cold work raises diffusion rates of sunstutional solutes like Nb.

I have generally noticed that SCC is accelerated by any action which destabilizes austenite, like the removal from solution of carbon. Maybe something like that is occurring in cold worked areas.

Stabilizing anneal of 347 would allow all Nb and C to combine which would detract from creep properties, since it is Nb in solution which hinders the dislocation motion which causes creep. Nb carbides coarsen easily, so they don't help against creep.


Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[metengr]

mcguire;

Meteng
When you find that reference could you let the rest of us know, too. That's an odd phenomenon.

As promised, here are several references regarding strain induced precipitation hardening in Austenitic stainless steel containing Nb;

1. Cracking in Welded Joints of Austenitic Steel in CEGB Power Stations, Autumn Meeting 1960, Welding Technology

2. The effect of heat-treatment and microstructure on the high temperature ductility of 18%Cr-12%Ni-1 Nb steels, Journal of the Iron and Steel Institute, October 1960


3. Heat-affected zone cracking in welded high-temperature austenitic steels, Journal of the Iron and Steel Institute, October, 1960

4. Microstructural causes of heat-affected zone cracking in heavy section 18-12-Nb austenitic steel welded joints, Journal of the Iron and Steel Institute, January, 1961