激光修復300M鋼的組織及力學性能研究

激光修復300M鋼的組織及力學性能研究Microstructure and Mechanical Properties of LaserForming Repaired 300M Steel

采用激光立體成形技術進行了300M鋼修復實驗,利用XRD、SEM及動態(tài)散斑等手段研究了激光成形修復300M鋼沉積態(tài)和熱處理態(tài)的組織及力學性能特征。結果表明,300M鋼基材區(qū)由馬氏體、貝氏體及少量殘余奧氏體組成;修復區(qū)由頂部的貝氏體組織,中部的馬氏體和貝氏體的混合組織,到底部的回火馬氏體組織呈現(xiàn)連續(xù)轉變;熱影響區(qū)則呈現(xiàn)為不均勻的馬氏體組織。經過淬火+回火處理后,各區(qū)域的組織變得均勻,均為回火馬氏體和貝氏體的混合組織。修復后沉積態(tài)試樣的拉伸性能遠低于鍛件標準。但經過熱處理后,修復試樣的各項力學性能指標均有顯著提高。應力-應變測試結果表明,沉積態(tài)和熱處理態(tài)試樣在彈性變形階段的應變都是均勻增加的,而超過最大拉伸強度后,局部應變在修復區(qū)急劇增加。這與試樣的組織協(xié)調變形能力及應變硬化指數(shù)有關。

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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