Microstructure and Micro-hardness of 4Cr5MoSiV1 Die Steels Fabricated by Selective Laser Melting

The 1Cr5MoSiV1 die steel samples arc fabricated by the selective laser melting (SLM) technique. The influence of laser linear energy density ri on microstructures, carbon loss and micro-hardness of samples is investigated. The results show that the microstructures of SLM-formed 1Cr5MoSiV1 die steel samples arc mainly martensite and a little amount of residual austenite. The decarburization reaction, splashing behavior and elemental ablation together cause carbon loss, and the carbon loss rate is as high as 17. 7% at eta = 950 J . m(-1). With the increase of eta, the grain sizes of samples increase, the carbon loss rate increases and the martensite content decreases. Under the same eta, the grain size and the carbon loss rate in the transition zones of samples arc the smallest, while those in the heat affected zones arc the highest. With the decrease of rl, the pore defects become more. When eta is too large, the cold cracks appear. When ri is 905 J . m(-1), the samples possess uniform microstructures, high densities, and relatively high micro-hardness (that in central zone of molten pool is 710.3 H V and that in transition zone is 732.1 HV).