利用OM和SEM分析了激光熔化沉积快速成形300M钢薄板的显微组织, 测试了硬度随沉积高度的变化规律. 结果表明:薄板状试样具有细小、均匀的胞状树枝晶组织, 其显微组织随沉积高度增加变化显著, 底部 为贝氏体及马氏体回火组织, 中、下部为无碳化物贝氏体+岛状马氏体/奥氏体(M--A)组织, 中、上部为 马氏体和贝氏体的混合组织; 试样宏观硬度沿沉积增高方向呈台阶状变化, 3个硬度平台区分别对应于上 述3种不同的显微组织. 试样显微组织及硬度随沉积高度的变化是由于激光熔化沉积过程中不同沉积高度 处的材料经历的快速非稳态热循环历史不同, 从而发生不同的固态相变过程所致.
Thin plate of ultra-high strength steel 300M was fabricated by the laser melting deposition manufacturing process. Microstructure of the steel was analyzed by OM and SEM. The Rockwell hardness (HRC) profile was measured along depositing direction. Results showed that the as-deposited 300M steel plate had a rapidly solidified cellular dendrite structure. Solid-state phase transformation microstructure of the 300M steel varied notably with the increasing deposition height, with a tempered martensite and bainite mixed structure in the bottom part, a mixture of carbide-free bainite and island-like matensite-austenite duplex structure in the middle-lower part and a mixed martensite-bainite structure in the middle-upper part. The hardness profile varied as stepwise with the increasing deposition height. The step-like hardness profile and the variable post-deposition transformation microstructures along the depositing direction were caused by the particular cyclic thermal behavior of the laser melting deposition manufacturing process.
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