Effect Of Hot Rolling Process On Microstructure,Texture And Properties Of Sn-Containing Ferrite Stainless Steel

In this paper,the structure,texture,mechanical properties,formability,corrosion resistance and related mechanism of Sn-containing ferritic stainless steel at finish rolling temperatures of 730?,800?,870? and 940? were systematically studied.The hot rolling process is further optimized to provide a theoretical guidance for rolling,heat treatment and product application for Sn-containing ferritic stainless steel.The main conclusions are as follows:The results of metallographic examination show that with the finish rolling temperature decrease,both the storage energy of deformation and the driving force of recrystallization increase,and the homogeneity of the structure is improved.Because of the inheritance of the structure of the hot-rolled and annealed band,the fine and homogeneous structure is also obtained during the subsequent cold rolling and annealing.However,when the finish rolling temperature is 730?,the recrystallized grains are not fully grown,which reduces the homogeneity of the structure.The results of macro-texture test show that the ?-fibre texture in hot-rolled and annealed steel sheet is obviously enhanced by lowering the finish rolling temperature,and strong y-fibre texture is formed in cold-rolled and annealed steel sheet due to the inheritance of the texture in hot-rolled and annealed steel sheet.However,when the finish rolling temperature is 730?,the recrystallized grains in the cold rolled and annealed sheets are not fully grown,which reduces the homogeneity of the structure,resulting in a certain degree of decrease in the strength of the texture of the y-fiber.The test results of mechanical properties and formability show that the stress-strain curves of cold-rolled and annealed sheets at different finish rolling temperatures have obvious yield platforms.With the decrease of finish rolling temperature,the yield strength and tensile strength show an increasing trend.When the finish rolling temperature is 730?,the yield strength and tensile strength reach their maximum values,which are 339 MPa and 528 MPa,respectively.The elongation increases first and then decreases with the decrease of finish rolling temperature.The maximum elongation is obtained at the finish rolling temperature of 800?.With the decrease of finish rolling temperature,the work hardening index(n value)does not change much,but the plastic strain ratio(r value)first increases and then decreases,reaching the maximum value of 1.57 at 800?,and the earing parameters(r value)first decreases and then increases,reaching the minimum value of 0.28 at 800V.The results of wrinkle and cupping experiments show that the average wrinkle height(Ra)and maximum wrinkle height(Rt)decrease first and then increase with the decrease of finish rolling temperature.The minimum average wrinkle height(Ra)and maximum wrinkle height(Rt)are 0.723 and 3.967 ?m,respectively,when the final rolling temperature is 800?.With the decrease of finishing rolling temperature,the cup burst value first increases and then decreases,reaching a maximum of 9.83 mm at 800?.The corrosion resistance test results show that the corrosion resistance of cold-rolled and annealed sheets with different finish temperatures in the solution of 500C,30%H2SO4 at constant temperature is the lowest,the corrosion rate is the lowest and the uniform corrosion resistance is the best when finish rolling temperature is 800?.With the decrease of finish rolling temperature,the grain size in cold-rolled and annealed sheet is refined,the structure is more uniform,and the passive film on the surface is more stable,which is not conducive to pitting nucleation.When finish rolling temperature is 800?,the grain size of cold-rolled and annealed sheet mainly distributes in the range of 10-20 ?m,the grain size is moderate,the degree of homogenization is the highest,and the pitting corrosion resistance of FeCl3 solution is the best.Polarization curves are measured in 3.5%NaCl solution.With the decrease of finish rolling temperature,the self-corrosion potential and pitting potential increase first and then decrease.When the final rolling temperature is 800?,the self-corrosion potential(Ecorr)and pitting potential(Eb)are the most positive,the pitting current density(Ib)is the smallest and the electrochemical corrosion resistance is the best.