Research on Microstructure and Mechanical Properties Control of Small Diameter S32750 Super Duplex Stainless Steel Tubes

Effects of different solid solution temperatures on the microstructure and mechanical properties of S32750 super duplex stainless steel tubes were investigated by means of tensile test, hardness test, scanning electron microscope and metallographic microscope. The results show that, when the solid solution temperature is 1020 ℃ or below, there are precipitated phases in S32750 duplex stainless steel. When the solution temperature is 1060 ℃, no precipitation phase can be observed in the matrix, but the grain boundaries are wider. When the solution temperature is 1100 ℃, the grain boundaries return to normal. At this time, the comprehensive mechanical properties of S32750 duplex stainless steel are better. The tensile strength and yield strength are 906 MPa and 610 MPa, respectively, the elongation is 34%, and the ratio of ferrite and austenite is close to 1∶1. With the increase of the solid solution temperature, the grain growth shows a trend of fast first, then slow and fast, and the austenite in the matrix gradually decomposes and transforms into ferrite. The temperature range is 980-1140℃,and the holding time is 5 min, and the influence on the strength of S32750 super duplex stainless steel from large to small is:precipitated phase＞ferrite＞grain size.