Tailoring the process, microstructure and property is always regarded as an important study topic in selective laser melting (SLM) tool steel parts. Use high laser powder and high laser velocity to obtain martensite H13 parts and investigate the defects, microstructure and tensile properties under the different processing condition. The investigations show that when using a relative high laser volume energy density ω (130 J/mm3), a large surface tension diversity will occur between the front and rear of melt pool. In this situation, the liquid locates at the center of melt pool has a high tendency to flow toward the rear of melt pool, resulting in the projection phenomenon and accordingly causing a lower densification level. A low ω (52.0 J/mm3) leads to an overlarge dynamic viscocity μ and limites the flowability and wetability of melt, hence resulting in an inferior interlayer bonding. After SLM processing optimization, as ω is settled at 86.7 J/mm3, melt pool has appropriate dynamic viscocity ω and sound melt wetability, increasing the bonding between interlayers. In this situation, the densification level is improved to 98.2%, and the content of retained austenite is determined to be 3.4%, showing an excellent self-quenching effect of SLM. The mechanical property of SLM specimens shows anisotropy. The strength and elongation in building direction are lower than those in horizontal direction. Under the optimization parameter, the average tensile strength in building direction is 1 576 MPa and average elongation is 5.6%, showing that SLM processed H13 parts using high powder and velocity possess a high strength but toughness still require to be improved, which is derived from the microstructure heterogeneity, large thermal stress, and phase transformation stress. As such, how to improve the toughness of SLM processed H13 steel is an urgent problem to be solved, presently.
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