Cause and prevention of cracks in CE3MN duplex stainless steel castings

The research institution focused on the CE3MN casting super duplex stainless steel material for the valve body of the 30 "-300 Lb upper mounted ball valve. Using FactSage 8.2 thermodynamic calculation software and FSstel steel database, combined with experimental methods such as optical microscope, scanning electron microscope, energy dispersive spectrometer, and X-ray diffractometer, the cause of cracks in the CE3MN material casting when cutting the as cast riser before solution treatment was studied and analyzed. The results show that during the slow heating or slow cooling process of CE3MN castings within the sensitive temperature range of brittle phase precipitation, a large amount of harmful intermetallic compounds rich in Cr and Mo, such as the σ phase, are generated due to severe segregation of casting components. They are mainly dispersed in the ferrite matrix in the form of short rod like or fine needle like structures, or distributed at the α/γ phase boundary in the form of long chain like, strip like, coral like, (σ+γ 2) cell like, and long needle like Weibull structure. Production practice has shown that before gas cutting the riser of CE3MN castings, the blank is pre treated with solid solution treatment to eliminate the brittle σ phase in the as cast state, suppress crack formation and propagation, or cold sawing is used to cut the as cast riser before solid solution treatment, which can fundamentally avoid the temperature factor that causes cracks.