关键词: SUS410钢, 半马氏体, δ-铁素体, Cr当量/Ni当量

Abstract: SUS410 half martensitic stainless steel (0.08% ~0.15%C , 12.5%~13.5%Cr) is easy to produce inner surface defects in production of hot rolled thick-walled seamless steel tubes. The localization analysis of the crack defects at inner surface of 139.7 mm x 38.1 mm tube, the results shows that the thermoplastic decline of steel is caused by the large precipitation of δ-ferrite in steel near crack. During the deformation process, the deformation of the two-phase region is not coordinated, and finally cracks appear at the boundary between austenite and δ-ferrite. According to tlie Schaeffler phase diagram, the chemical composition of steel is redesigned, the Cr equivalent /Ni equivalent ratio decreases from 4.51 of originel defect tube to ≤ 3.0, the heating temperature of tube bloom decreases from 1200~1300℃ to 1180~1280 ℃ ,the internal surface defects are effectively solved, and the qualified rate of ultrasonic flaw detection increases to 97.9%.

Key words: SUS410 Steel, Semi-Martensitic, δ-Ferrite, Cr Equivalent/Ni Equivalent