Effect Of Cold Rolling Annealing Process On Microstructure And Mevhanical Behavior Of Lean Duplex Stainless Steel

Mn-N bearing lean duplex stainless steel can be used to replace the traditional Ni-Mo duplex stainless steel.While further saving expensive Ni resources,it also leads to metastability of the austenite component phase.There is obvious phase change induced plasticity(TRIP effect)to improve its mechanical properties,showing broad application prospects in the fields of rail transit and ocean engineering cold-rolled duplex stainless steel strip is the most widely used product,and its microstructure evolution and mechanical behavior during the cold-rolling and annealing process play a very critical role in regulating the mechanical properties of economical duplex stainless steel.This article takes a Mn-N alloyed TRIP duplex stainless steel(nominal composition:Fe-19Cr-5MN-0.23Ni-0.3N)as the research object,and uses SEM,TEM,EBSD and other microscopic characterization methods to study different cold rolled annealing process and its microstructure evolution law,combined with system tensile test,analyzed the mechanical response characteristics under different process conditions,and clarified the relationship between structure and performance.The main findings are as follows:(1)During cold rolling,the metastable austenite phase(?)can transform to martensite(??)in two transformation modes,including: ??? martensite(transition phase)???,???'.As the amount of cold rolling deformation increases,the martensite content increases,the yield strength and tensile strength of the test steel also increase,and its elongation at break decrease.When the cold rolling deformation reaches 60%,the deformation-induced martensite ?' is basically saturated.(2)The martensite obtained by rolling undergoes a reverse phase transformation,so that the grains are significantly refined.The ferrite grain size has no obvious change compared with the initial state,and the two-phase structure is still distributed in interphase strips.The austenite grain refinement improves the yield strength and elongation of the test steel,and also increases the stability of austenite to a certain extent and slows down the transformation speed of martensite.(3)The austenite phase refining process strategy based on supersaturated single phase treatment + heavy cold rolling annealing was proposed.After the process is implemented,the average size of austenite phase can be refined,and the banded directional distribution of the two phases can be effectively improved after the traditional cold rolling annealing,and then the anisotropy can be improved to a large extent.In addition,the austenite phase size refinement can significantly improve the metastable austenite stability and reduce the transformation rate of deformation-induced martensite compared with the grain refinement caused by traditional cold rolling annealing.The TRIP effect occurs in a larger strain range,and the plasticity of the tested steel is significantly improved and the fracture elongation is significantly increased.