关键词: 高氮奥氏体不锈钢, 连续驱动摩擦焊, 焊后热处理, 微观组织, 力学性能

Abstract: To extend the service life of non-magnetic steel drill pipes made of high-nitrogen austenitic stainless steel in directional drilling and reduce the production and use cost, continuous drive friction welding technology was used to weld the joint with the pipe body, and the welded joints were heat-treated in order to investigate the effect of heat treatment on the microstructure and mechanical properties of welded joints of non-magnetic steel drill pipe. The results show that the microstructure of the weld zone of the friction-welded joint is relatively fine, but the microstructure on both sides of the weld zone is elongated, and a small amount of carbonitride of Cr precipitates along the grain boundaries in the weld zone. After post-weld heat treatment, the microstructure of the welded joint is restored to uniformity, the precipitated phase is re-dissolved in the matrix, and the austenite grain grows further. Compared with the friction-welded joint, although the post-weld heat treatment makes the grain grow in the weld zone, resulting in a reduction in the hardness, yield strength, and tensile strength of the weld, it reduces the hardness gradient between the weld zone and the heat-affected zone and significantly improves the elongation and impact property of the welded joint. Current post-weld heat treatment improves joint toughness and hardness distribution but simultaneously causes strength loss, resulting in yield strength failing to meet API 7-1-2023 standards. Further optimization of the heat treatment process is required to achieve the optimal balance between strength and toughness.

Key words: high nitrogen austenitic stainless steel, continuous drive friction welding, post-weld heat treatment, microstructure, mechanical properties