This paper focused on the effect of different laser scanning speed (4 mm/s, 5 mm/s, 6 mm/s and 7 mm/s) on the microstructural evolution of direct laser deposition (DLD) 12CrNi2 alloy steel, and analyzed the relationship between microstructure and performance of DLD-processed samples. The results showed that the microstructure in the middle of as-deposited samples consisted of a large amount of bainite, a small amount of martensite (M) and ferrite (F). With the increase of laser scanning speed, the fraction of ferrite decreased from 55.6% to 14.7%, while that of martensite increased from nearly 0% to 4.9%. Besides, as increasing the laser scanning speed, granular bainite (GB) transformed into lath bainite (LB) due to the increase of cooling rate, and the fraction of LB reached the maximum of 29.9% when the scanning speed was 7 mm/s. In addition, the functions about the relationship between laser scanning speed and phase fractions were fitted in order to provide a theoretical basis for the design of DLD process parameters. EBSD maps of as-deposited samples exhibited anisotropy due to the complex heat flux direction during the multi-layer laser deposition process. With the increase of laser scanning speed, the grain size showed a downward trend from 5.89 µm² to 3.44 µm². The sample fabricated at 7 mm/s contained more LB and M, leading to the highest mean microhardness of 355 ± 6 HV_0.2. The sample fabricated at 6 mm/s exhibited the best wear resistance due to its optimum combination of hardness and toughness. Because of a large amount of ferrite with optimal toughness, the sample fabricated at 4 mm/s had the best impact toughness of a_ku = 80 J/cm².

本文着眼于不同的激光扫描速度（4 mm / s，5 mm / s，6 mm / s和7 mm / s）对直接激光沉积（DLD）12CrNi2合金钢的组织演变的影响，并分析了DLD处理样品的微观结构与性能之间的关系。结果表明，样品中间的显微组织由大量贝氏体，少量马氏体（M）和铁素体（F）组成。随着激光扫描速度的提高，铁素体的份额从55.6％下降到14.7％，而马氏体的份额从接近0％上升到4.9％。此外，随着激光扫描速度的提高，由于冷却速率的提高，颗粒状贝氏体（GB）转变为板条贝氏体（LB），当扫描速度为7 mm / s时，LB分数达到最大值29.9％。此外，拟合了激光扫描速度与相分数之间关系的函数，为DLD工艺参数的设计提供了理论依据。由于多层激光沉积过程中复杂的热通量方向，沉积样品的EBSD图表现出各向异性。随着激光扫描速度的提高，晶粒尺寸从5.89 µm呈下降趋势。²至3.44 µm ²。以7 mm / s的速度制造的样品包含更多的LB和M，导致最高平均显微硬度为355±6 HV _0.2。以6 mm / s的速度制造的样品由于具有硬度和韧性的最佳组合，因此具有最佳的耐磨性。由于大量铁氧体具有最佳的韧性，因此以4 mm / s的速度制造的样品具有_ku  = 80 J / cm ²的最佳冲击韧性。