Gradient 24CrNiMo steel was successfully fabricated via laser melting deposition (LMD). To explain the gradient properties of the sample, the microstructures of single-track and bulk samples were examined. Additionally, the texture characteristics and mechanical properties were investigated. The results indicated that as the molten pool cooled from a high temperature, the microstructure of the molten pool experienced a transformation of liquid → austenite → martensite because of the high cooling rate. The microstructure of the heat-affected zone (HAZ) transformed into austenite when heated, and the austenite transformed into martensite when cooled; thus, the microstructure in the HAZ was identical to that in the molten pool after cooling. Consequently, the surface of the bulk sample mainly consisted of martensite and a small quantity of lower bainite owing to the heat accumulation, while the microstructure in the interior of the bulk sample transformed from martensite into tempered martensite owing to the thermal cycling. Thus, the surface of the sample exhibited high strength and hardness, while the interior had better plasticity. The fracture mechanism exhibited dimple rupture features on both the surface and in the interior of the bulk sample; however, the interior had better toughness than the surface. A <100> texture was observed on the surface of the LMD sample, but the orientation of the grains was random in the interior of the sample owing to the multiple nucleation cycles of the grains.

通过激光熔化沉积（LMD）成功地制造了梯度24CrNiMo钢。为了解释样品的梯度特性，检查了单道和大块样品的微观结构。另外，还研究了织构特性和机械性能。结果表明，随着熔池从高温的冷却，由于冷却速率高，熔池的微观结构经历了液相→奥氏体→马氏体的转变。热影响区（HAZ）的组织在加热时转变为奥氏体，而在冷却时转变为马氏体。因此，热影响区中的微观结构与冷却后的熔池中的微观结构相同。所以，由于热量的积累，大块样品的表面主要由马氏体和少量的下部贝氏体组成，而大块样品内部的组织由于热循环而从马氏体转变为回火马氏体。因此，样品的表面表现出高强度和硬度，而内部具有更好的可塑性。断裂机理在散装样品的表面和内部均显示出凹窝断裂特征。但是，内部比表面具有更好的韧性。在LMD样品的表面上观察到<100>织构，但是由于晶粒的多个成核循环，晶粒在样品内部的取向是随机的。而大块样品内部的微观结构由于热循环而从马氏体转变为回火马氏体。因此，样品的表面表现出高强度和硬度，而内部具有更好的可塑性。断裂机理在大块样品的表面和内部都显示出酒窝破裂特征。但是，内部比表面具有更好的韧性。在LMD样品的表面上观察到<100>织构，但是由于晶粒的多个成核循环，晶粒在样品内部的取向是随机的。而大块样品内部的微观结构由于热循环而从马氏体转变为回火马氏体。因此，样品的表面表现出高强度和硬度，而内部具有更好的可塑性。断裂机理在大块样品的表面和内部都显示出酒窝破裂特征。但是，内部比表面具有更好的韧性。在LMD样品的表面上观察到<100>织构，但是由于晶粒的多个成核循环，晶粒在样品内部的取向是随机的。断裂机理在大块样品的表面和内部都显示出酒窝破裂特征。但是，内部比表面具有更好的韧性。在LMD样品的表面上观察到<100>织构，但是由于晶粒的多个成核循环，晶粒在样品内部的取向是随机的。断裂机理在大块样品的表面和内部都显示出酒窝破裂特征。但是，内部比表面具有更好的韧性。在LMD样品的表面上观察到<100>织构，但是由于晶粒的多个成核循环，晶粒在样品内部的取向是随机的。