退火温度对441铁素体不锈钢组织性能的影响

Effect of annealing temperature on microstructure and properties of ferritic stainless steel 441

为探索超纯铁素体不锈钢热轧板材在退火过程中组织和力学性能的演变,对441进行了900~1 050℃的退火试验,利用OM、SEM和TEM表征了441在退火过程中显微组织的变化规律,并通过拉伸试验和冲击试验研究了退火温度对力学性能的影响。结果表明,随着退火温度升高,轧制组织发生再结晶,且晶粒逐渐长大。退火后441热轧板材中存在3种析出相,初生(Ti,Nb)(C,N)、二次Nb(C,N)和Laves相。Laves相仅在900~950℃退火样品中大量析出,尺寸约为几百纳米。441的屈服强度随着退火温度的升高先减小再增大,抗拉强度逐渐降低,而伸长率逐渐升高。形变强化对材料的屈服强度具有最大贡献,固溶强化次之,析出强化最小。冲击试验结果显示,1 000℃退火后441具有最低的韧脆转变温度,第二相与晶粒长大对材料韧性均有显著的不良影响。

To explore the microstructure evolution and mechanical properties of 441 ultra-purified ferritic stainless steel during annealing,441 hot-rolled plates were annealled at 900-1 050 ℃,and the microstructure were characterized by OM,SEM and TEM.The effects of annealing temperature on mechanical properties were studied by tensile test and impact test.The results show that the rolling structure recrystallizes and the grains grow gradually with increasing annealing temperature.There are three precipitates in 441 hot-rolled-annealed plate,primary(Ti,Nb)(C,N),secondary Nb(C,N)and Laves phase.A large number of Laves phase,with the size of hundreds nanometers,precipitates in samples annealed at 900-950 ℃.As the annealing temperature increases,the yield strength of 441 firstly decreases and then increases,the tensile strength decreases gradually,while the elongation increases continually.Deformation strengthening has the greatest contribution to the yield strength,followed by solution strengthening and precipitation strengthening.The impact test indicates that 441 plate has the lowest ductile to brittle transition temperature after annealing at 1 000℃,and Laves phase and grain growth are detrimental to the impact toughness of this material.