Effect of heat treatment on microstructural evolution,mechanical properties and tribological properties of H13 steel prepared using selective laser melting

H13 tool steel was successfully prepared by selective laser melting(SLM)technology.The effects of heat treatment on the microstructure,mechanical properties,and tribological properties of SLMed H13 steel were investigated.The heat treatment process involved a solution treatment and a double aging treatment of the deposited H13 tool steel prepared by SLM.The aim is to optimize the microstructure and mechanical properties of SLMed H13 steel.Due to the rapid heating and cooling effects of SLM,carbide precipitation in the deposited H13 steel was not uniform and residual stresses were present.The purpose of the solution treatment is to dissolve the solution at a high temperature to eliminate the residual stresses and defects introduced by the SLM-forming structure.The solution treatment and first aging treatment produced the precipitation of small carbides at the grain boundaries and inside the crystals,which increased the hardness of SLMed H13 steel.The hardness increased from 538±4.0 HV of the as-deposited sample to 548±5.8 HV of samples after the first aging treatment.Accordingly,the ultimate tensile strength and the elongation at break decreased from 1882 MPa and 11.5%in the as-deposited sample to 1697 MPa and 7.9%in those after the first aging treatment,respectively.Furthermore,the friction coefficient and wear rate in the as-deposited sample decreased from 0.5160 and 2.36×10^(–6)mm^(−3)N^(−1)m^(−1)to 0.4244 and 1.04×10^(–6)mm^(−3)N^(−1)m^(−1),respectively.However,the distribution of carbides inside the crystals was not uniform.The second aging treatment adjusted the morphology of carbide precipitation and made it more uniform,but the precipitation of carbides grew and settled at the bottom of the grain boundaries.The hardness decreased to 533±6.7 HV compared with that with the first aging treatment,but the ultimate tensile strength and plasticity reached a balance(1807 MPa,14.05%).Accordingly,the friction coefficient and wear rate also showed a stable and decreasing trend(0.4407,0.98×10^(–6)mm^(−3)N^(−1)m^(−1)).

Influence of powder oxidation on powder properties and formability in H13 hot-work steels processed by electron beam melting

The oxygen content of metal powder is decisive for the recyclability of powder.The research on the effect of oxygen content on powder properties and material formability has practical significance for economical production with additive manufacturing while preventing the waste of resources.Here,we deliberately oxidized the powder by baking at high temperature to increase the oxygen content in the powder and gave the calculation method of the oxygen content in the powder oxidation film.The majority of oxygen element was found in the oxide particles in the powder and the oxide flm on the powder surface,which did affect the flowability of the powder.It is worth noting that the increase in the oxygen content does not change the phase of H13 steel,but it can promote the molten pool flow and obtain a smoother surface.The increase in the oxygen content in the powder is not the decisive factor for the formability and defects of the printed samples.It is the combined effect of the powder deformation,the increase in the oxygen content,and the impurity pollution after repeated use,which leads to the limitation of repeated utilization of the powder.