热处理对电弧熔丝增材制造核电用铁素体/马氏体钢微观组织与力学性能的影响

Effect of heat treatment on the microstructure and mechanical properties of wire arc additively manufactured ferrite/martensitic steel for nuclear applications

采用电弧熔丝增材制造(wire and arc additive manufacturing,WAAM)技术制备了低活化铁素体/马氏体钢(reduced activation ferrite/martensite steel,RAFM钢),通过光学显微镜、扫描电子显微镜和透射电子显微镜等观察微观组织变化,通过拉伸试验进行力学性能测试,研究了热处理工艺对其微观组织和力学性能的影响.结果表明,打印态的RAFM钢微观组织为铁素体+回火马氏体的双相组织,平均晶粒尺寸约为1.51μm.经过热处理,RAFM钢的晶粒尺寸没有明显增长(1.84μm),并在微观组织中保留了高密度位错.此外,热处理后高数密度TiO2二次相纳米颗粒在基体中析出,并弥散分布在基体中,其尺寸在5~10 nm.热处理后的RAFM钢抗拉强度显著提高,断后伸长率略微下降,其室温抗拉强度为1080 MPa,在650℃下测试的抗拉强度仍可达285 MPa.创新点:(1)系统研究热处理对电弧熔丝增材制造低活化铁素体马氏体钢的相组成、晶粒尺寸、析出相的影响.(2)阐明热处理对电弧熔丝增材制造低活化铁素体马氏体钢力学性能的强化机制.

Reduced activation ferritic/martensitic(RAFM)steel was fabricated by wire and arc additive manufacturing(WAAM)technology.The microstructural evolution was observed by optical microscope,scanning electron microscope and transmission electron microscope and the mechanical properties were tested by a tensile tester to study the effect of heat treatment on the microstructure and mechanical properties of WAAM RAFM steel.The results showed that the microstructure of as-built RAFM steel consisted of dual phases of ferrite and tempered martensite and the average grain size was about 1.51μm.After heat treatment,the RAFM steel showed no significant increase in grain size(1.84μm),and high-density dislocations were retained in the microstructure.In addition,a large number of TiO2 secondary phase nanoparticles,with the grain size of 5−10 nm,have precipitated and dispersed in the matrix after the heat treatment.The tensile strength of WAAM RAFM steel was significantly improved after heat treatment while the elongation after fracture was slightly reduced.The tensile strength of RAFM steel after heat treatment was 1080 MPa at room temperature and even at a temperature of 650℃,it can still reach about 285 MPa.Highlights:(1)The effect of heat treatment on the microstructure of WAAM RAFM steel was systematically studied in terms of phase structure,grain size and secondary phase precipitations.(2)The strengthening mechanism of WAAM RAFM steel after heat treatment was elucidated.