On-line solution treatment process for welding production of 304 stainless steel thin-walled tube

The steel strip is made into steel tube by rolling and welding step by step. The hardness of the steel tube increases due to the early work hardening, which will significantly affect the secondary forming processing of the tube. In this paper, the effects of solution temperatures, solution cooling conditions and types of solution shielding gas on the microstructure and properties of 304 stainless steel thin-walled tube were studied by building an on-line solution treatment test platform in the 304 stainless steel tube production line. The results show that increasing the solution treatment temperature in the experimental temperature range will increase the grain size of the heat-affected zone and the base metal and promote the solid solution of carbides in and along the austenite grains, so as to significantly reduce the hardness of the heat-affected zone and the base metal. The ferrite distributed along the austenite grain boundary in the weld zone is partially dissolved, and the grain size increases to a small extent, so the hardness of the weld zone decreases slightly. However, adjusting the cooling conditions has little effect on the hardness of the weld and base metal. When argon is used as the solution treatment protective gas, the average hardness of the base metal of the tube can be reduced to 188.7 HV, which is 11.0% lower than that without solution treatment. When hydrogen is used as solution treatment protective gas, the average hardness can be reduced to 182.7 HV, which is 13.8% lower than that without solution treatment. Through microstructure observation, hardness test, flaring and flattening mechanical properties test, the solution-treated tubes under the two protective gas conditions all meet the national standards.