采用选区激光熔化(SLM)技术制备了4Cr5MoSiV1钢试样,研究了回火处理对显微组织和力学性能的影响。研究表明:SLM成形4Cr5MoSiV1钢试样在回火过程中发生了马氏体分解、残余奥氏体转变和碳化物析出,最终形成了稳定的铁素体和合金碳化物。试样经回火处理后,出现了晶粒形貌特征消失、晶粒尺寸增大等现象,导致其显微硬度和抗拉强度降低、断后伸长率增加。试样经450 ℃回火后析出了细小且均匀分布的碳化物,该碳化物通过沉淀强化作用使试样发生了二次强化。经600 ℃二次回火后试样的断后伸长率最大,为18.6%。未热处理和低温回火后试样的断口呈脆性解理断裂;中温回火后试样的断口呈准解理断裂;高温回火以及二次回火后试样的断口出现以韧性断裂为主的准解理断裂。

Herein, 4Cr5MoSiV1 steel samples are fabricated via selective laser melting (SLM), and the effect of tempering on microstructure and mechanical properties is investigated. Results show that tempering of SLM-fabricated 4Cr5MoSiV1 steel samples involves martensite decomposition, retained austenite transformation, and carbide precipitation, thus producing stable ferrite and alloy carbides. Post tempering, the sample's grain morphology disappears, and its grain size increases. In addition, the sample's microhardness and ultimate strength decrease, whereas its elongation increases. Post tempering at 450 ℃, fine and uniformly distributed carbides precipitate, contributing to precipitation strengthening and causing secondary strengthening of the sample. The sample's elongation after tempering twice at 600 ℃ increases to 18.6%. The fracture of unheated and low-temperature tempered samples is attributed to a brittle cleavage fracture. The fracture of the medium-temperature tempered sample is found to be a quasi-cleavage fracture. Finally, the fracture of the high-temperature tempered sample and twice-tempered sample exhibit a quasi-cleavage fracture dominated by ductile fracture.