Study On Properties Of New Seawater Resistant Stainless Steel

Austenitic stainless steel were widely used in contact with the chloride solution environment,because it has excellent pitting and crevice corrosion resistance. With the development of marine engineering, the working environment of materials even worse, so corrosion hazard becoming more serious. Therefore, research and development of new stainless steel with excellent corrosion resistance and high strength are staring our in the face.In this paper, the effect of alloy composition(Mn, Cu, Si, V) and heat treatment conditions on corrosion resistance of test steel were studied and optimized by using orthogonal tests. The optimal composition and heat treatment conditions were obtained by optimization design and Verification test. The microstructure and morphology of samples were examined by XRD, EMPA and the corrosion resistant properties caused by the effect of aollys elements in test stainless steel system were investigated.A new seawater resistant stainless steel was developed and its compositions were 20%Cr,18%Ni,6%Mo,0.2%Mn,0.8%V,0.1%Si(in wt.%). The point corrosion rate and crevice corrosion rate of test steel are 0.008mm/a,0.085mm/a. The results show that the sequence of factor significance is Mn>Cu>Si>V; solution temperature>aging temperature>solution time.The effect of Mn,Cu contents on mechanical properties of test steel are researched at the same time. The results show that the effect of Mn,Cu contents on number, morphology of precipitates and grain size are significant. Appropriate amount of precipitates can significantly improve the mechanical properties of test steel. In contrast, excessive precipitates would distribute in a continuous network, which could obviously decrease its mechanical properties. When test steel contains 0.2% Mn,0.3% Cu, its mechanical properties was best.Comprehensive the results of corrosion resistance and mechanical properties, a proper heat treatment technique for the test was obtained, solutionized at1100℃for 2h and oil-quenched, then aged at 520℃for 4h and air-cooled. After heat treatment, this test steel had tensile strength (σb) of 642MPa, elongation rate (δ) of 27.1% and hardness of 93.3HRB.