预热对激光熔化沉积成形12CrNi2合金钢组织与性能的影响

使用高功率光纤激光器的快速成形系统和电磁感应加热设备,分别在未预热和预热的情况下成形12CrNi2合金钢.通过扫描电镜观察成形件微观组织、维氏硬度计测试不同部位硬度、万能材料试验机测试不同方向的拉伸性能,研究预热对激光熔化沉积12CrNi2合金钢不同方向的组织、硬度、拉伸性能的影响.结果表明:未预热条件下,单道熔池组织为板条马氏体,块状成形件熔池为回火马氏体与贝氏体混合组织,XOZ截面与YOZ截面组织没有明显的组织差别,但YOZ截面整体硬度大于XOZ截面,同时两个截面均出现了大尺寸宏观裂纹缺陷,力学性能差.在预热条件下,熔池由于温度梯度降低发生贝氏体转变,单道熔池呈现性能优异的下贝氏体组织;块状成形件熔池没有发生回火马氏体转变,主要为粒状贝氏体.截面硬度分布较未预热下更为均匀.在拉伸方向及搭接方向均呈现高强度、低塑性特征,抗拉强度可达1189 MPa,屈服强度为951 MPa,伸长率仅为2.8%,性能没有明显的各向异性.预热能够降低熔池中温度梯度,减小热应力,有效控制裂纹缺陷,促进组织均匀化,降低组织、性能的各向异性,提高合金钢成型件力学性能.

Effect of preheating on the microstructure and properties of laser melting deposited 12CrNi2 alloy steel

In the case of preheating and non-preheating, the rapid prototyping system of high-power fiber laser and electromagnetic induction heating equipment was used to fabricate 12CrNi₂ alloy steel. The microstructure of the molded parts was observed under a scanning electron microscope, and the hardness test of different parts was conducted using the Victorinox hardness tester. The tensile properties in different directions were tested using the universal material testing machine. This study investigated the effect of preheating on the microstructure, hardness, and tensile properties of laser melting deposited 12CrNi2 alloy steel in different directions. The obtained results show that the microstructure of the single-channel molten pool without preheating is lath martensite, and the molten pool of block-shaped forming parts is tempered martensite and bainite mixed structure. No obvious structural difference between XOZ and YOZ sections is observed. However, the overall hardness of the YOZ cross section is larger than that of the XOZ cross section. Large-scale macroscopic crack defects appear in both sections, and the mechanical properties are poor. Under preheating conditions, bainite transformation occurs in the molten pool because of the decrease in the temperature gradient. The single-channel molten pool shows an excellent bainite structure. No tempered martensite transformation in the molten pool of block-shaped forming parts, mainly granular bainite, is observed. Cross-sectional hardness distribution is more uniform with preheating than without preheating. High tensile strength and low plasticity are detected in the tensile and overlap directions. The tensile strength is up to 1189 MPa, the yield strength is 951 MPa, and the elongation is only 2.8%. No obvious anisotropy in performance is observed. Preheating can reduce the temperature gradient in the molten pool, reduce the thermal stress, effectively control the crack defects, promote the homogenization of the microstructure, reduce the anisotropy of the microstructure and properties, and improve the mechanical properties of the alloy steel forming parts.