摘要
新型耐热钢 12Cr是汽轮机高温转子部件的重要材料,对 20 mm厚 12Cr耐热钢进行了电子束焊接试验,系统研究了电子束焊接速度对 12Cr耐热钢接头微观组织与力学性能的影响.结果表明,焊缝组织主要由马氏体板条构成,其尺寸相比于母材更加细小均匀,随着焊接速度的增加,热输入减小,焊缝和热影响区的晶粒尺寸趋于细化.基于Kurdjumov-Sachs取向关系,将马氏体组织重构为原奥氏体晶粒(proto austenitic grain,PAG),证明焊接速度对原奥氏体晶粒尺寸影响较小,不同参数下焊接接头均具有较弱立方织构.力学性能结果表明,焊缝区的显微硬度显著高于母材,在厚度方向上焊缝平均硬度随着焊接速度的增加有所提高.接头焊缝的抗拉性能有所提升,所有拉伸试样均断裂于母材处,平均抗拉强度为 968 MPa,断口有韧窝,断裂机制为韧脆混合断裂.
Abstract
The 12Cr alloy represents a significant advancement in materials for high-temperature rotor components used in steam turbines.A systematic investigation was conducted through an electron beam welding experiment on 20 mm thick 12Cr heat-resistant steel,focusing on the influence of welding speed on the microstructural characteristics and mechanical properties of the welded joints.The findings reveal that the microstructure of the weld predominantly consists of martensitic lath,characterized by a finer and more uniform grain size compared to the base material.An increase in welding speed correlates with a reduction in heat input,resulting in a refinement of the grain size within both the weld and the heat-affected zone.Utilizing the Kurdjumov-Sachs orientation relationship,it was observed that the martensitic structure was reconstructed from the PAG,indicating that the welding speed has a negligible impact on the dimensions of the original austenite grains.Furthermore,the welded joints displayed a weak cubic texture across varying parameters.Mechanical property assessments demonstrated that the microhardness within the weld zone significantly exceeds that of the base material,with the average hardness value in the thickness direction of the weld increasing in conjunction with the welding speed.The tensile properties of the welded joints exhibited enhancement,as all tensile specimens failed within the base material,yielding an average tensile strength of 968 MPa.The fracture surfaces revealed a dimpled morphology,suggesting a mixed ductile-brittle fracture mechanism.
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