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Participant

Join Date: May 2010
Location: Mumbai, India
Posts: 4

Sigma Phase and Surface Cracks in 317LM Grade

03/23/2011 5:16 AM

Dear all ,

we are prearing 317LM grade with chemistry in the range of standerd chemistry from scrap by EOF --> convertor ---> VD/VOD --> CC process in 240X 280 mm billets.We roll them to 125Ø. then we peel it to 121mm in 2 stages. The surface is showing cracks after peeling, sometimes throughout the lenght of bars.Also, we have found the problem of sigma phase in the microstructure. Its around 10%. We were not able to remove it completely after heat treatment of 1200°C for 6 Hrs on a sample.

Can u please tell me about the possible reason for sigma phase formation ???

ANy ways to remove it from microstructure ???

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Participant

Join Date: Apr 2011
Posts: 1
#1

Re: Sigma Phase and Surface Cracks in 317LM Grade

04/12/2011 6:37 AM

How do you confirm that Its Sigma Phase?

Please let me know the following test results

1. IGC Test as per ASTM A262 Practice "C" - Corrosion rate

2. Composition of Sigma Phase - EDS Analysis Results

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Participant

Join Date: May 2010
Location: Mumbai, India
Posts: 4
#2
In reply to #1

Re: Sigma Phase and Surface Cracks in 317LM Grade

04/13/2011 4:00 AM

Sir ,

The sample has passed the ASTM A262 practice C.

THe EDEX analysis shows its phase rich in Mo with other elements more or less same as the base metal.

The hardness at the the phase is around 350 BHN and above while that at the base metal is around 175 BHN.

The literature shows that small amount of sigma will be present in Mo grades irrespective of cares taken, but homiginisation at around 1200° will control it

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