Thermal behavior and grain evolution of 24CrNiMoY alloy steel prepared by pre-laid laser cladding technology

Abstract

The unique thermal behavior during the multi-layer laser rapid manufacturing process brings about unique microstructure for the as-produced parts. In this paper, a comprehensive three-dimensional self-consistent transient temperature field model of 24CrNiMoY alloy steel by pre-laid laser cladding technology (PLLC) was established, and the reliability of model was verified by the experiment. The simulation results showed that as scanning speed increased (5, 7, 9 mm/s), the peak temperature, dimensions and liquid lifetime of the molten pool decreased, while the G × R increased and G/R decreased at the same position. With increasing layer, the peak temperature of molten pool and the temperature of the whole domain increased gradually until forming a dynamic balance. The contrast experimental results showed that with scanning speed increased, the average size of equiaxed grain increased (4.682, 5.012, 5.462 μm) and the average aspect ratio of columnar grain decreased (11.890, 11.411, 10.593). During the multi-layer process, grain growth modes were different along the deposition sections. The structure in parallel scanning direction mainly consisted of equiaxed grains, while in the overlapping direction were equiaxed and columnar grains. There was a clear columnar-to-equiaxed transition (CET) boundary that controls the change in grain types. The grain growth behavior of a multi-layered in vertical scanning direction section was different from that of a single track. All the above results illustrated that temperature field had a significant effect on the thermal behavior during PLLC process, which affected the grain evolution of 24CrNiMoY alloy steel.