循环热处理是提高18Ni(C250)马氏体时效钢力学性能的有效途径,循环热处理温度的选择是关键因素。在这项研究中,采用两步固溶处理的循环热处理工艺来研究循环热处理温度的影响,特别是第一固溶处理温度(920°C,950°C,和980°C),研究了18Ni(C250)马氏体时效钢的显微组织和力学性能。结果表明,随着循环热处理温度的升高,18Ni(C250)马氏体时效钢的平均晶粒尺寸先减小后增大。循环热处理温度达到950℃时,晶粒尺寸最小,表现出最佳的晶粒均匀性。此外,循环热处理温度的升高导致晶粒内部具有相同取向的马氏体板条的尺寸减小,随着低角度晶界的相对数量的增加。此外,随着循环热处理温度的升高,残余奥氏体的体积分数和尺寸呈单调增加,并且当温度从950°C升高到980°C时,升高速率变得明显更大。根据观察到的微观结构变化,分析了18Ni(C250)马氏体时效钢力学性能的变化规律。具体来说,随着循环热处理温度的升高,18Ni(C250)马氏体时效钢的抗拉强度最初增加,然后稳定,而伸长率和断裂韧性表现出单调增加。
Cyclic heat treatment is an effective approach for enhancing the mechanical properties of 18Ni(C250) maraging steel, and the selection of cyclic heat treatment temperature is a key factor. In this study, a cyclic heat treatment process with a two-step solution treatment is employed to investigate the influence of cyclic heat treatment temperature, specifically the first solution treatment temperature (920 °C, 950 °C, and 980 °C), on the microstructure and mechanical properties of 18Ni(C250) maraging steel. The results indicate that with an increase in the cyclic heat treatment temperature, the average grain size of the 18Ni(C250) maraging steel decreases initially and then increases. When the cyclic heat treatment temperature reaches 950 °C, the grain size is at its minimum, exhibiting optimal grain uniformity. Additionally, the increase in cyclic heat treatment temperature results in a reduction in the size of martensitic lath with the same orientation inside the grains, along with an increase in the relative quantity of low-angle grain boundaries. Furthermore, the volume fraction and size of retained austenite show a monotonous increase with the rise in the temperature of the cyclic heat treatment, and the rate of increase becomes notably larger when the temperature is raised from 950 °C to 980 °C. Based on the observed microstructural changes, the variation in the mechanical properties of the 18Ni(C250) maraging steel was analyzed. Specifically, as the cyclic heat treatment temperature increases, the tensile strength of the 18Ni(C250) maraging steel initially increases and then stabilizes, while the elongation and fracture toughness exhibit a monotonic increase.