Sigma Phase and Surface Cracks in 317LM Grade

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 ???