冷却速率对激光热处理球墨铸铁中硬化层的影响

Effect of Different Cooling Rates on Hardened Layer of Nodular Cast Iron after Laser Heat Treatment

以冷却速率为切入点,研究激光热处理球墨铸铁过程中,不同冷却速率、功率密度和交互时间对球墨铸铁硬化层的影响。通过理论计算,利用不同的功率密度和交互时间获得了不同的冷却速率分布,对QT600-3球墨铸铁进行激光表面热处理。结果表明,在激光加工过程中各组参数表面温度在1 500~2 500℃,并且实际冷却速率与理论计算相比误差在6%左右,各组硬化层中都能出现熔凝区,但深度、硬度和晶粒分布均有不同。各组深度变化由0.5~0.8 mm,显微硬度变化由800~1 100 HV0.1,晶粒由混乱粗大到均匀细小。熔凝区显微组织和硬度值受冷却速率影响最大,其他区域由于离表面的距离较大,各组冷却速率均大幅缩减,趋于一致,所以硬度变化并不明显。硬化层深度与冷却速率呈正比关系,随冷却速率不断增加而逐渐加大,在保证激光能量密度相同的前提下,功率密度较交互时间对硬度层深度影响更大。

Taking the cooling rate as the cut-in point, the effects of cooling rates, power densities and interaction time on the hardened layer of ductile cast iron were studied in the process of laser heat treatment. Through theoretical calculations, different cooling rate distributions were obtained by using different power densities and interaction times, and laser surface heat treatment was performed on QT600-3 ductile iron. After laser heat treatment, it is found that the surface temperature of each group of parameters is 1 500~2 500 ℃, and the actual cooling rate is about 6% compared with the theoretical calculation above. The melting zone can occur in each group of hardened layers, but the depth, hardness and grain distribution are different. The depth variation of each group is 0.5~0.8 mm, the micro hardness varies from 800 to 1100 HV0.1, and the grains are coarse to fine. The microstructure and hardness of the fused zone are most affected by the cooling rate. Due to the large distance from the surface in other regions, the cooling rates of each group are greatly tend to be consistent, so the hardness change is not obvious.The depth of the hardened layer is proportional to the cooling rate, and gradually increases with the increase of the cooling rate. Under the premise of ensuring the same laser energy density, the power density has a greater influence on the depth than the interaction time.