Study On Thermoplasticity Of Lean Duplex Stainless Steel 2101

Lean duplex stainless steel is a new type of duplex stainless steel in which the element Ni is replaced by the low-cost austenitizing elements N and Mn,while the Mo condent is also reduced.Besides reducing the cost greatly,the yield strength of lean duplex stainless steel can reach twice as much as the normal austenitic stainless steel,while ensured good corrosion resistance and mechanical properties.However,compared with traditional duplex stainless steel,lean duplex stainless steel has worse thermoplasticity,suffers more cracks during rolling process.These shortages greatly restrict its application.In this paper,the lean duplex stainless steel 2101(LDX2101)was chose as the object of study,by comparing with the traditional duplex stainless steel 2205(DSS2205),thorough research was conducted focused on hot deformation behavior of lean duplex stainless steel,The research includes four aspect,the microstructure characteristic of duplex stainless steel,N migration between ferrite and austenite phase and its effect on the thermoplasticity,effect of hot deformation process on thermoplasticity and annealing process on the mechanism property of hot rolling plate.By the study on the efifect of cooling speed and clement segregation on the microstructure of the different position in LDX2101 continuous casting slzab,the a/y microhardness difference was found resulting the poor thermoplasticity of the specimens at the edge.The effect of element Mn and Ni on grain size,phase ratio,precipitates and ?/? microhardness difference was analysed.And based on the thermoynamic calculation and the interaction of the alloy elcements,the solubility product formula of Cr2N in LDX2101 and DSS-2205 was obtained.The study of nitrogen redistribution between a/y phases during warming and cooling shown that the nitrogen migration behavior differs between the ferrite and austenite phases during temperature changes.By comparing the difference nitrogen migration rule between in LDX201 and DSS2205,It was shown that the nitrogen migration quantity and migration rate was related with the interaction of Mn,Ni and N.The effect of nitrogen migration on ?/? microhardness difference and Cr2N precipitation was also studied.At the same time,the migration was found during isothermal hot deformation.It was clear that the different distortion degree between the ferrite and austenite phase resulted in the change of nitrogen solubility of the two phases,and then caused nitrogen migration.The stress-strain curve,microstructure evolution and strain partitioning in a/y phases of LDX2101 during different hot deformation process were studied,it was clear that the effect rule of a/y microhardness difference on the deformation coordination.The influence mechanism of the deformation temperature,strain rate and rolling pass on the thennoplasticity was investigated.The results showed that the improvvement of deformation temperature increase on thermoplasticity is not obvious,because the strain concentrated in ferrite and the recrystallization degree of austenite was small,the overall softening of the matrix is not obvious;However,when the deformation rate decrease,the strain partitioning ratio of austenite increase,promoting its the recrystallization degree,this made the matrix softens significantly.On the other hand,increasing the rolling pass could decrease the strain partitioning difference between ferrite and austenite and then promote the deformation coordination.The best annealing process of LDX2101 was confirmed by room temperature tensile carried out for hot rolled plate after annealing.The effect of annealing temperature on elongation was related to the Cr2N precipitation along a/a and a/y boundary.The effect of holding time on the elongation is the results of interaction of the degree of recovery and recrystallization of the a/y phases and the secondary austenite precipitated on the ferrite matrix.On this basis,we found that the best annealing process of LDX2101 hot rolled plate is 1000? for 1h.