Study On Mechanical Behavior And Microscopic Mechanism Of Lean Duplex Stainless Steel Under Tensile And Compression Deformation

Duplex stainless steel containing austenitic phase and ferritic phase has excellent mechanical properties and corrosion resistance at the same time,is widely used in construction,Marine,chemical transportation and other fields.In recent years,the lean duplex stainless steel which uses Mn-N alloying to replace the expensive Ni element has attracted wide attention.In particular,the phases of austenite components may behave as metastable,and martensitic transformation occurs during plastic deformation,forming a transformation induced plasticity(TRIP)effect,which significantly improves the work-hardening capacity and plasticity.In this paper,the mechanical behavior of a lean duplex stainless steel(nominal composition: 0Cr20Mn3Ni2Cu2Si2N)with TRIP effect was studied under the conditions of monotone tensile and compressive deformation.The difference of mechanical and energy response of the test steel under tensile and compressive deformation was compared,and the microscopic mechanism was explored combined by a series of microscopic characteristics.The main achievements are as follows:(1)Under tensile and compressive deformation conditions,the mechanical behavior of the test steel shows asymmetry,α ’martensitic transformation shows different evolution processes.Tensile deformation promotes the nucleation and development of α ’martensite,and the degree and speed of phase transformation are obviously higher than that of compression deformation.The TRIP effect under tensile deformation is more obvious,and the strength and work hardening properties are better.The hardening contribution induced by martensite per unit volume under tensile and compression conditions was quantified respectively.It was found that the stress increment caused by martensite per unit volume under compression condition was larger.(2)Under both tensile and compressive deformation conditions,the test steel showed anisotropy,and the strength and work hardening rate were higher along the RD direction than under the TD direction,which was mainly related to the interphase stress/strain distribution under the tensile and compressive conditions.The difference of partitioning methods also results in a higher martensitic transformation rate under RD loading than under TD loading.This aggravates the anisotropy of the samples together with the deformation texture difference between RD and TD samples.(3)Under compression conditions,compared with the specimens without prestrain,the test steel shows obvious secondary hardening after tensile predeformation,and the degree of hardening is positively correlated with the degree of prestrain.The microscopic defects introduced by the prestrain lead to more deformation sites of martensitic phase nuclei in the subsequent deformation of the sample and improve the degree of martensitic phase transformation.In addition,the decrease of work hardening rate caused by the offset of heterodislocation in high density dislocation highlights the martensitic hardening effect.