Post-weld Heat Treatment Improves the Mechanical Properties of Laser Welded Joints of Medium Manganese TRIP Steel

LIU Hongning; WANG Yanjun; YANG Shanglu; ZHU Zhengqiang

doi:10.7512/j.issn.1001-2303.2023.07.02

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Post-weld Heat Treatment Improves the Mechanical Properties of Laser Welded Joints of Medium Manganese TRIP Steel
Vol. 53, Issue 7, Pages: 9-15(2023)
DOI： 10.7512/j.issn.1001-2303.2023.07.02

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刘红宁，王艳俊，杨上陆，等.焊后热处理对中锰TRIP钢激光焊接接头组织及力学性能的影响［J］.电焊机，2023，53（7）：9-15.

LIU Hongning, WANG Yanjun, YANG Shanglu, et al.Post-weld Heat Treatment Improves the Mechanical Properties of Laser Welded Joints of Medium Manganese TRIP Steel[J].Electric Welding Machine, 2023, 53(7): 9-15.
刘红宁，王艳俊，杨上陆，等.焊后热处理对中锰TRIP钢激光焊接接头组织及力学性能的影响［J］.电焊机，2023，53（7）：9-15. DOI： 10.7512/j.issn.1001-2303.2023.07.02.

LIU Hongning, WANG Yanjun, YANG Shanglu, et al.Post-weld Heat Treatment Improves the Mechanical Properties of Laser Welded Joints of Medium Manganese TRIP Steel[J].Electric Welding Machine, 2023, 53(7): 9-15. DOI： 10.7512/j.issn.1001-2303.2023.07.02.

摘要

为解决中锰钢焊接接头的脆性断裂问题，研究了焊后热处理工艺对厚度为1.6 mm的中锰TRIP钢激光自熔焊接接头组织、静态力学性能以及锰元素分布的影响，热处理温度选择Ac1（奥氏体开始转变温度）和Ac3（奥氏体转变终止温度）之间，这和中锰钢轧制温度是相同的，可以保证更高的强度和韧性。研究结果表明：焊态试样焊缝区主要为马氏体组织，热处理后焊缝主要组织为回火马氏体，并伴有碳化物析出；在620 ℃热处理3 min后，焊接接头抗拉强度无明显提高，但延伸率相对于焊态接头提高了1 959.2%，主要原因是热处理缓解了锰元素在晶界上的偏析。焊态接头失效断口为典型的脆性断裂，并出现了较多的二次晶间裂纹，热处理后的接头失效断口出现了较多的凹坑和韧窝，呈现良好的韧性断裂特征。在热处理后试样的应力应变曲线中发现了二次屈服，通过VIC-3D数字图像关联（DIC）技术发现这是吕德斯带穿越焊缝遇到硬度较高的马氏体组织导致应力突增所致，最终在母材处发生颈缩并断裂。

Abstract

To solve the problem of brittle fracture in welded joint of medium manganese steel, this article studied the effect of post-weld heat treatment process on the microstructure, static mechanical properties, and distribution of manganese element of laser self-melting welded joint of 1.6 mm thick medium manganese TRIP steel. The heat treatment temperature was selected between Ac1 (austenite start transformation temperature) and Ac3 (austenite transformation termination temperature), which is the same as the rolling temperature of medium manganese steel, to ensure higher strength and toughness. The results showed that the weld zone of the as-welded sample was mainly composed of martensitic structure, while the weld zone after heat treatment was mainly composed of tempered martensite with carbide precipitation. After being heated at 620 ℃ for 3 minutes, the tensile strength of the welded joint did not increase significantly, but the elongation of the welded joint increased by 1959.2% relative to that of the as-welded joint. The main reason was that the heat treatment relieved the segregation of manganese element at grain boundaries. The failed fracture of the as-welded joint was a typical brittle fracture, with more secondary intergranular cracks. The failed fracture of the heat-treated joint showed more pits and toughness dimples and presented good toughness fracture characteristics. A secondary yield was found in the stress-strain curve of the heat-treated sample, and through the VIC-3D digital image correlation (DIC) technology, it was found that this was caused by the Lüders band encountering the martensitic structure with higher hardness across the weld zone, leading to a sudden increase in stress and ultimately causing necking and fracture at the base metal.

关键词

中锰TRIP钢激光焊接焊后热处理力学性能Mn元素偏析

Keywords

medium manganese TRIP steellaser weldingpost-weld heat treatmentmechanical propertyMn element segregation

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