Experimental Research on Solidification of Duplex Stainless Steel Refined by Complex-Nucleus with TiN

摘要

In Duplex Stainless Steel (DSS), duplex refers to two phase microstructure. At present, it has been widely used in chemical industry, ocean project, and oil industry and so on. Compared with other types of stainless steel, DSS has a distinctive feature that the ferritic phase and austenitic phase took approximately equal share of the solid solution. Thus it has excellent intergranular corrosion resistance, welding performance and super plasticity etc. However the two phase microstructure at elevated temperature makes the production more difficult. DSS usually contains a higher content of N (about 0.20%), the solubility of N atom in δ-ferrite is only 0.1% which is in a saturated state. It would easily precipitate during solidification and the defects might occur under the surface. In addition, grain of 5-ferrite in casting microstructure is coarse, the segregation is severe, the formed columnar crystal zone is well developed, the two phase microstructure of α+γ is distributed unevenly along the slab cross section, hot-working property is poor, and edge crack appears easily. Therefore, improving the solubility of N in δ-ferrite and refining the grain to increase the equiaxed grain ratio, is the effective measure to improve the surface quality, thermoplasticity, low temperature strength and toughness of duplex stainless steel.