Seccond Phase Precipitation Behavior Of Ultra-high Nitrogen Austenitic Steel Containing Niobium And Vanadium

High nitrogen austenitic steel has excellent performance,high strength,corrosion resistance,abrasion resistance,good toughness and creep property.However,during the hot processing,welding and use of this kind of steel material,the second phase precipitated from the steel reduces the stability of austenite,which seriously affects the mechanical properties of the material.However,the second phase precipitation behavior is different from that of general austenitic steel,so it is of great significance and practical value to study the second phase precipitation behavior of this steel.Ultra-high nitrogen austenitic steel containing vanadium and niobium was selected as the research object,and the thermodynamic phase diagram,the law of the second phase precipitation and the effect of the second phase precipitation on the mechanical properties of the steel were studied.The main conclusions are as follows:A binary equilibrium phase diagram of ultra-high nitrogen austenitic steel containing vanadium and niobium was obtained.The liquidus temperature was 1455℃ and the solid phase temperature was 1335℃.The MX phase was precipitated from the liquid phase at 1251℃,and then dissolved in the austenitic phase at 1131℃.The equilibrium structure at room temperature is(γ+Cr2N+M23C6+Z+σ+α).The aging temperature was 700℃～1100℃,and the precipitation phases were Cr2 N,σ and M23C6.Cr2 N phase is a dense hexagonal structure,which precipitates at the grain boundary in a granular form,then grows into the grain in a cellular form with time.At 900℃,it also precipitates together with phase in a block form.Phase is a body-centered cubic structure,which precipitates in the crystal in the form of block,and exists in with Cr2 N phase.M23C6 is precipitated in grain boundaries and grains in granular form.With the increase of precipitation phase,the plasticity of steel was reduced,and the fracture mode of aging sample at 900℃ gradually changed from ductile fracture to brittle fracture,but the steel strength remained basically unchanged and the hardness increased.Figure 72;Table 13;Reference 60...