Duplex stainless steels (DSSs) used in subsea structures and desalination industries require high corrosion and erosion resistance as well as excellent mechanical properties. The newly introduced cast duplex grade ASTM A890 7A has a unique composition and is expected to have a much better resistance to corrosion and erosion compared with the super-duplex grades 5A and 6A. This work is a comparative study of the mechanical properties, corrosion, and erosion-corrosion resistance of super-duplex grades 5A and 6A and the hyper-duplex grade 7A. The three DSSs exhibited equiaxial austenite islands in the ferrite matrix and balanced phase ratios. The hardness of the grade 7A was nearly 15% higher than those of the super-duplex grades, which is attributed to the effect of the higher contents of W and Mn in 7A. The impact toughness of grade 7A was found to be lower than those of the super-duplex grades due to the carbide precipitation resulting from the partial substitution of Mo with W. The oxide layer strengthening effect of rare earth elements and the higher pitting resistance equivalent number (PREN) of grade 7A resulted in higher corrosion resistance. The harder and more passive grade 7A showed a 35% lower material loss during erosion-corrosion.

用于海底结构和海水淡化行业的双相不锈钢（DSS）要求具有高耐腐蚀性和侵蚀性以及出色的机械性能。新推出的铸造双相牌号ASTM A890 7A具有独特的成分，与超双相牌号5A和6A相比，有望具有更好的耐腐蚀性。这项工作是对5A和6A超双相钢和7A超双相钢的机械性能，耐腐蚀和抗腐蚀腐蚀性能的比较研究。这三个DSS在铁素体基体中显示出等轴奥氏体岛，并且具有平衡的相比。7A级的硬度比超双相不锈钢高近15％，这归因于7A中W和Mn含量较高的影响。由于Mo部分被W部分取代而导致碳化物沉淀，发现7A级的冲击韧性低于超级双相级。稀土元素的氧化层强化作用和更高的抗点蚀当量数（PREN）等级7A导致更高的耐腐蚀性。硬度更高，更被动的7A级材料在腐蚀腐蚀过程中的材料损失降低了35％。