Microstructures And Properties Of Ni-Saving Casting Duplex Stainless Steel

Duplex stainless steel, which consist of about similar of ferrite phase (a) and austenite phase (y) in the solid solution organization, are designed to combine the best features of ferrite stainless steel and austenitic stainless steel. It is used in petrochemical industry, military industry, marine and power industries because of its excellent corrosion resistance and mechanical property. Ni is important element in the duplex stainless steel. It is not only rare but also expensive in our country. Therefore, the research and development excellent comprehensive performance of nickel-saving duplex stainless steel has a certain practical significance. In this paper, nickel-saving casting duplex stainless steels replaced expensive Ni with low cost manganese and nitrogen was being developed.In the paper, the nickel-saving casting duplex stainless steel Cr25Mn10Mo4Ni2N was melt by investment casting and induction furnace. The effect of solution temperature(1000℃,1020℃,1040℃,1060℃,1080℃, 1100℃,1120℃,1150℃)on microstructures and properties of nickel-saving casting duplex stainless steel were studied by means of OM, XRD, ESEM and electrochemical workstation. And also a comparative study with 2205 duplex stainless steel and 316L austenitic stainless steel were drew.The nickel-saving casting stainless steel is made up of a, y and a phases when the solution temperature is among 1000～1100℃. As the solution temperature increased, σ phase reduce. When the solution temperature is 1120℃, the a phase completely disappears. The microstructure only contains a and y phases. When the solution temperature is low, the hardness of material is relatively high. As the solution temperature increased, the hardness of material gradually decline.The electrochemical performance tests show that the material after treated at 1120℃, the steel has excellent corrosion resistance property. The material after treated at 1150℃, its corrosion resistance property is poorer. When the annealing temperature is increased from 1000℃ to 1100℃, its corrosion resistance property of the steel is improved.In artificial seawater, simulated oilfield water and simulated formation water, the nickel-saving casting duplex stainless steel has the best pitting corrosion property; the pitting corrosion property of 2205 duplex stainless steel is poorer, while the 316L austenitic stainless steel is worst. The corrosion media of simulated formation water shows the strongest aggressive corrosion, followed by the simulated oilfield water, and the last is artificial seawater.Tensile tests indicated that the specimen of 1120℃ solution treatment has the toughness fracture features of tensile fracture. Many isometric dimples are distributed in tensile fracture, which showing that those materials have good tenacity. The plastic of the steel is worse than 2205 and 316L. While the strength and hardness is best.