为了提高材料表面的耐磨性,实现材料的强韧结合,采用激光热流密度均匀分布的二维离散式5×5点阵光斑,对蠕墨铸铁材料的激光相变硬化过程进行数值模拟,通过改变激光功率和激光加载时间,分析了硬化过程中温度场和硬化层的变化。结果表明:基于光束离散的激光相变硬化温度场分布形态与点阵光斑的空间分布相对应,在激光加载结束时,每个小光斑中心点的温度同时达到峰值,整个光斑中心点的温度因各光斑温度场的叠加而达到最高,且沿着各光斑中心点的温度分布呈波浪形;在截面上随着深度增加,温度逐渐降低,材料的整体温度随着激光功率的增大和激光加载时间的延长而升高;各激光离散光斑的硬化层均呈月牙形,随着激光功率增大,截面硬化层的分布基本不变,处于离散分布状态;随着激光加载时间延长,硬化层从离散形向整体月牙形转变,且数值模拟所得硬化层的最大深度随着2种激光参数的增大而增大;在激光光束离散相变硬化处理过程中,增大激光功率既可以满足材料表面激光辐照的高硬度强化区域与激光未辐照的低硬度非强化区域的强韧结合,又能够增加硬化层深度,而延长激光加载时间虽然可以获得更大的硬化层深度,但热传导传递能量具有累积作用,导致材料表面激光辐照区和非辐照区整体被强化,不能实现材料表面的强韧结合。

Laser transformation hardening of the vermicular graphite cast iron material is numerically simulated using a two-dimensional discrete 5×5 lattice spot exhibiting a uniform distribution of the laser heat flux density to improve the resistance of the material surface to wear and combine strength and toughness. Further, the changes of temperature field and hardened layer during the hardening process are analyzed by changing the laser power and laser loading time. The results denote that the distribution pattern of temperature field during the laser transformation hardening based on beam discretization corresponds to the spatial distribution of the lattice spot. At the end of laser loading, the center point temperature of each sub-spot reaches the peak value. The center point temperature of the whole area of the lattice spot is the largest because of the superposition of the temperature field of each sub-spot, and the temperature distribution along the center point of each sub-spot is wavy. As the depth increases along the cross section, the temperature gradually decreases, and the overall temperature of the material increases with the increasing laser power and laser loading time. The hardened layer of each laser spot is crescent-shaped. With an increase in the laser power, the distribution of the section of the hardened layer remains basically unchanged and exhibits a discrete distribution. With an increase in the laser loading time, the hardened layer changes from discrete to integral crescent shape. Additionally, the maximum depth of the hardened layer obtained using a numerical simulation increases with the increasing laser power and laser loading time. During the process of laser transformation hardening, increasing laser power combines strength and toughness between the high hardness of the laser irradiated reinforced area and the low hardness of the laser non-irradiated non-reinforced area on the surface of the material while increasing the depth of the hardened layer. Although increasing laser loading time can increase the depth of the hardened layer, the combination of strength and toughness of the material surface cannot be achieved because of the cumulative effects of heat conduction on the laser irradiated and non-irradiated areas on the material surface.