2205双相不锈钢在增材制造和热处理过程中组织和力学性能的变化

Evolution of Microstructure and Mechanical Properties of 2205 Duplex Stainless Steel during Additive Manufacturing and Heat Treatment

为了研究激光粉末床熔合(LPBF)过程中双相不锈钢的固态相变和力学性能的变化规律,采用电子背散射衍射(EBSD)、电子探针(EPMA)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、原子探针层析技术(APT)和力学性能测试等方法对材料性能进行了表征。结果显示,采用LPBF技术制备的双相不锈钢(DSS)组织多为铁素体,柱状铁素体晶粒沿BD方向生长,具有很强的织构,相比于常规制造DSS屈服强度和极限抗拉强度得到了较大程度的提升,但延性下降。对采用LPBF技术加工的2205双相不锈钢进行1000℃退火处理后,组织可恢复到相平衡状态,塑性得到明显提高,-110℃时表现出优良的冲击韧性。此外,LPBF试样具有较高的强度和较低的塑性,这主要是因为铁素体组织中的N过饱和度更高,形成的Cr2N颗粒较多,因而位错密度较大,热处理后,细小的奥氏体晶粒弥散分布在铁素体基体中,在塑性变形时形成孪晶并导致位错塞积,从而抑制铁素体发生塑性变形,使材料具备较大的塑性变形容限。

In order to study the solid phase transformation and mechanical properties of duplex stainless steel during laser powder bed fusion(LPBF),the material properties were characterized by using methods such as electron backscatter diffraction(EBSD),electron probe microanalysis(EPMA),scanning electron microscopy(SEM),transmission electron microscopy(TEM),atomic probe tomography(APT),and mechanical properties testing.The results show that the microstructure of DSS prepared using LPBF technology is mostly ferrite,and columnar ferrite grains grow along the BD direction with strong texture.Compared with conventional manufacturing DSS,the yield strength and ultimate tensile strength have been greatly improved,but the ductility has decreased.After annealing at 1000℃,the microstructure of 2205 duplex stainless steel processed using LPBF technology can be restored to its phase equilibrium state,and the plasticity is significantly improved.It exhibits excellent impact toughness at-110℃.In addition,the LPBF sample has higher strength and lower plasticity,mainly due to the higher supersaturation of N in the ferrite structure,resulting in more Cr2N particles and higher dislocation density.After heat treatment,fine austenite grains are dispersed in the ferrite matrix,forming twinning during plastic deformation and leading to dislocation accumulation,thereby inhibiting plastic deformation of the ferrite and providing the material with a greater plastic deformation tolerance.