Influence of the process speed in laser melt injection for reinforcing skin-pass rolls

Laser melt injection is a technology for producing metal matrix composite (MMC) layers on tools such as skin-pass rolls by injecting hard particles into a laser-induced weld pool. However, low process speeds prevent the application of laser melt injection on a large scale. To overcome this drawback, a new approach is presented: High-speed laser melt injection (HSLMI) is a promising method for generating highly wear-resistant MMC layers on tools with high productivity. For the first time, high process speeds of up to 100 m/min were reached with HSLMI of spherical fused tungsten carbide (SFTC) particles into the steel 1.2362 that is used for skin-pass rolls. In this paper, the influence of the process speed on the microstructure and on the wear resistance of the MMC layer is investigated. The microstructure of the steel matrix changes from a dendritic to a needle-shaped structure when process speeds of 60 m/min or higher are applied. Furthermore, the steel matrix often features cracks. The SFTC particles show a dissolution seam. It was found that both the crack susceptibility and the SFTC dissolution can be reduced significantly by increasing the process speed. The wear behavior of the MMC layers was studied in a pin-on-plate test. It was found that the SFTC reinforcement leads to a significant improvement in wear resistance over the nonreinforced steel substrate. The wear volume was reduced from 3.6 to 0.1 to 0.3 mm3 by an SFTC particle-reinforcement. Abrasion was the substantial wear mechanism.