Direct laser metal deposition of a medium carbon low alloy steel was performed on a round bar sample. Taguchi design was used to investigate the effect of three process parameters with three different levels on the microstructure and properties of single- and multitrack clad samples. Microstructural analysis showed that coalesced bainite and lath martensite exist in the clad area. Two different kinds of cracks occurred in multitrack clad samples. When laser power is not sufficient or scanning speed is high, cracks can occur in the laser clad area because of the accumulation of trapped defects inside the molten pool, e.g., inclusions, voids, and low melting point constituents alongside insufficient molten metal back-filling at interdendritic regions. These cracks can be considered as solidification cracks. Another type of cracks can occur in previous tracks of multitrack clads which actually are the heat affected zones (HAZ) of newly deposited clad tracks, because of high tensile stress on HAZ and the presence of oxide and sulfide constituents at interdendritic regions. These cracks can be considered as reheating cracks. According to the result of Taguchi design experiments, using optimum laser parameters like high laser power, medium scanning speed, and sufficient powder feed rate, crackfree clad layers can be obtained via the prevention of formation of unfavorable constituents at interdendritic regions.

中文翻译：

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熔覆参数对24CrNiMo钢激光直接熔敷显微组织及缺陷的影响

在圆棒样品上进行中碳低合金钢的直接激光金属沉积。田口设计用于研究三个不同级别的三个工艺参数对单轨和多轨复合样品的微观结构和性能的影响。显微组织分析表明，复合区存在聚结贝氏体和板条马氏体。多轨复合样品中出现了两种不同的裂纹。当激光功率不足或扫描速度过快时，熔池内部会堆积夹杂物、空隙、低熔点成分等缺陷，同时熔融金属回填不足，激光熔覆区域会出现裂纹。在树突间区域。这些裂纹可以认为是凝固裂纹。另一种类型的裂纹可能出现在多轨包层的先前轨迹中，实际上是新沉积的包层轨迹的热影响区 (HAZ)，因为 HAZ 上的拉伸应力很高，并且在枝晶间区域存在氧化物和硫化物成分。这些裂纹可视为再加热裂纹。根据田口设计实验的结果，使用高激光功率、中等扫描速度和足够的粉末进料速度等最佳激光参数，可以通过防止在枝晶间区域形成不利成分来获得无裂纹的熔覆层。这些裂纹可视为再加热裂纹。根据田口设计实验的结果，使用高激光功率、中等扫描速度和足够的粉末进料速度等最佳激光参数，可以通过防止在枝晶间区域形成不利成分来获得无裂纹的熔覆层。这些裂纹可视为再加热裂纹。根据田口设计实验的结果，使用高激光功率、中等扫描速度和足够的粉末进料速度等最佳激光参数，可以通过防止在枝晶间区域形成不利成分来获得无裂纹的熔覆层。