关键词: 亚共析钢, 魏氏组织, 热处理工艺, 性能

Abstract: SA-106C seamless steel pipe product produced by an enterprise was found to have severe Widmanstatten structure and coarse grains in the forging billets, which led to a series of quality problems of the pipe billets after heat treatment, such as low impact properties, large dispersion of mechanical property indicators, and cold bending cracks. The causes of the Widmanstatten structure were analyzed based on the original heat treatment process, and the process was improved. The results show that the soaking temperature in the post-forging heat treatment process of the SA-106C steel pipe products deviates from the equilibrium precipitation temperature of ferrite, leading to the presence of Widmanstätten structure after post-forging heat treatment, which in turn causes the properties to fail to meet the technical requirements. Based on the original process, by adjusting the soaking temperature after forging to 750 ℃, which is within the α-ferrite precipitation temperature range of 700-800 ℃ for the SA-106C steel, and then performing hydrogen diffusion annealing at 650 ℃, the Widmanstatten structure can be completely eliminated. Moreover, the properties indicators of the forgings meet the technical requirements, the dispersion degree is significantly more concentrated compared with that by the original process, and the crack occurrence rate in the cold bending test is stably controlled below 2%.

Key words: hypoeutectoid steel, Widmanstatten structure, heat treatment process, properties