Dear Mohd:
From an article in link.spriger.com:
Austenitic stainless steel welds which normally contain some ferrite may be exposed to high temperatures either during stress relief or service exposure. Ferrite being an unstable phase is transformed to various secondary phases during high temperature exposure.
Sigma formation is not only a function of temperature but also initial ferrite content and readily forms even at lower temperatures like 600 °C when initial ferrite content is high (FN.4 low, FN.12 high). This in contrast to the earlier studies where it was noticed that short time exposures at temperatures up to 700 °C did not show sigma formation.
-- From an article in link.spriger.com:
Austenitic stainless steel welds which normally contain some ferrite may be exposed to high temperatures either during stress relief or service exposure. Ferrite being an unstable phase is transformed to various secondary phases during high temperature exposure.
Sigma formation is not only a function of temperature but also initial ferrite content and readily forms even at lower temperatures like 600 °C when initial ferrite content is high (FN.4 low, FN.12 high). This in contrast to the earlier studies where it was noticed that short time exposures at temperatures up to 700 °C did not show sigma formation.
Regards
On Sat, Aug 31, 2013 at 10:41 PM, Octane Mac <octane.mac@gmail.com> wrote:
It has to be before PWHT otherwise heat treatment itself can cause sigma phase embrittlement or 885 F embrittlement of austenitic stainless steels; chances of which increase with higher ferrite content. Therefore, in order to perform a heat treatment without having any possible embrittlement, a prior measurement of ferrite content is necessary.Octane--On Sat, Aug 31, 2013 at 4:19 PM, mohd <mohd52100@gmail.com> wrote:
dear sir,
why ferrite measurement shall be taken before PWHT for 300-series steel.
regards,
mohd.
--
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