Influence Of Different Annealing Temperatures On The Microstructures And Properties Of Cold Rolling304L Stainless Steel

304L stainless steel (SS) is one kind of austenitic stainless steel. Due to the excellent qualities such as excellent plasticity, easily processing, good weldability and super corrosion resistance, the304L SS is extensive used in the fields of transportation industry, aerospace, petrochemical industry, food processing, health care and so on for. However, the demand for the304SS with excellent properties increases with the rapidly developed economy. Especially in auto industry, the lightweight is an important topic for the present design of car all over the world due to the fact that the lightweight of automobile has double effects on energy conservation and environment protection. Therefore, there is important significance to improve the mechanical properties of the304L stainless steel for both the development of304SS and the environmental protection.In present study, the evolution of microstructures and mechanical properties for a cold-rolled304SS with the heat-treatment conditions has been investigate by using the optical micrograph, transmission electron micrograph and tensile tests. The as-received304SS (d=-40μm) has been rolled at room temperature to a reduction of66.7%. And the steel has been kept at400℃for600s before the next pass. The microstructure of the cold-rolled steel mainly consists of the martensite laths. The partial recrystallization begins at750℃and the grains grow up to10-15μm at950℃. The cold-rolled steel exhibits a yield strength of1620MPa and a tensile strength of1700MPa with a strain of12.3%. After annealing, the stress decreases with increasing annealing temperature while the strain goes along a contrary way. For example, the yield strength and tensile strength is670MPa and875MPa for the sample annealed at770℃, respectively. However, these values decrease to345MPa and800MPa for the sample annealed at950℃. Meanwhile, the strain increases from43.8%to58%. At a strain rate of0.5m s-1, the yield stress and tensile stress is1250MPa and1880MPa, respectively, and the strain is as high as15%. With increasing strain rate up to5m s-1, these values increase to1900MPa,2330MPa and20%, indicating a positive strain rate sensitivity.The volume fraction of martensite increases with increasing strain rate. However, at the same strain rate of tension, the volume faction of martensite for the cold-rolled sample is higher than that of as-received sample. According to the SEM observations, it is suggested that the deformation process converts from the brittle fracture into ductile fracture with increasing annealing temperature. In addition, the dimple becomes deeper and bigger with increasing strain rate, closely related to the good ductility. The dislocation density and volume fraction of martensite decrease with increasing temperature, accompanying with more irregular martensite shape. The deformation process is dominated by slip, martensite transformation, twining as well as the interaction among the martensite, twin, staking fault and dislocation.