采用激光立体成形技术进行了300M钢修复实验,利用XRD、SEM及动态散斑等手段研究了激光成形修复300M钢沉积态和热处理态的组织及力学性能特征。结果表明,300M钢基材区由马氏体、贝氏体及少量残余奥氏体组成;修复区由顶部的贝氏体组织,中部的马氏体和贝氏体的混合组织,到底部的回火马氏体组织呈现连续转变;热影响区则呈现为不均匀的马氏体组织。经过淬火+回火处理后,各区域的组织变得均匀,均为回火马氏体和贝氏体的混合组织。修复后沉积态试样的拉伸性能远低于锻件标准。但经过热处理后,修复试样的各项力学性能指标均有显著提高。应力-应变测试结果表明,沉积态和热处理态试样在弹性变形阶段的应变都是均匀增加的,而超过最大拉伸强度后,局部应变在修复区急剧增加。这与试样的组织协调变形能力及应变硬化指数有关。
Laser forming repairing (LFR) technology is developed from the laser additive manufacturing, which has a high potential in high strength steel structures' repairing. 300M steel has been widely used in aviation and aerospace vehicles, to provide a high strength for aircraft landing gear and high strength bolts components, which in turn leads to a quick damage due to the severe service environment. If these damaged components can be repaired rapidly, the considerable savings in materials and costs can be achieved. In this work, the microstructure and mechanical properties of the LFRed 300M steel have been investigated. Results showed that the LFRed area can be clearly divided into three areas: the substrate zone (SZ), heat affected zone (HAZ) and repaired zone (RZ). The SZ was consisted of the mixture of martensite, bainite and a small amount of retained austenite. The HAZ presented an uneven martensite. The RZ presented an obvious heterogeneous microstructure, and the bainite, the mixture of martensite and bainite, and tempered martensite from the top to the bottom. After heat treatment, the microstructure became uniform with mixed tempered martensite and bainite. The tensile strength of the as-deposited LFRed 300M steel was far lower than those of the substrate. Its tensile strength and yield strength were 1459 MPa and 1163 MPa, respectively. After heat treatment, tensile strength (1965 MPa), yield strength (1653 MPa), elongation (11.7%) and reduction of area (38.4%) increased significantly and reached the same level of the substrate. Furthermore, compared to the as-deposited sample, the local strain of the RZ increased to 53% after heat treatment, and an obvious necking and breaking up happened as well. The strain hardening exponent of SZ and RZ were 0.1548 and 0.1138, which could be closely related to the compatible deformation capability.
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