SAF2507 is the third generation super duplex stainless steel, American Standard (national standard ZG 00Cr25Ni7Mo4N). Its microstructure has an ideal duplex structure with ferrite / austenite ratio of about 50 / 50. It has the characteristics of both austenite and ferritic stainless steel. Compared with austenitic stainless steel, it has higher plasticity and toughness and no room temperature brittleness, The intergranular corrosion resistance and welding performance are significantly improved, its strength and corrosion resistance are very strong, and its pitting corrosion resistance and crevice corrosion resistance are excellent. It is also a nickel saving stainless steel. Due to the high content of ferrite in the steel, the brittleness of the steel is increased, the fluidity is poor, the grain size is coarse, and the tendency of hot crack is greater. Moreover, due to the increase of nitrogen content, the probability of air hole in valve casting is greater.
Therefore, this kind of steel brings great difficulties to the design of valve casting process and the melting of liquid steel. At present, some domestic valve foundry manufacturers have always had some problems in the production of super duplex stainless steel SAF2507 large-diameter and high-pressure valve body. Pores, oxidation slag inclusion and cracks are serious in the production process, resulting in high scrap rate and large amount of welding repair. Therefore, the delay of construction period and the failure of delivery on schedule are caused.