Improving the Strength of Steels Produced Using a New Type of Laser Melting Technology
Keywords:
additive technologies, powder materials, fusion, hardening, chemical heterogeneityAbstract
The purpose of this work was to establish the causes of the inhomogeneity of the chemical compos ition of the metal obtained by the SLM technology. A powder raw material was produced from a monolithic alloy, followed by its fusion by the SLM method, the metal of laboratory melting of a low-carbon chromium-manganese-nickel composition based on iron served as the initial raw material. To determine the nature of the distribution of alloying chemical elements in the manufactured powder, electron microscopic images of thin sections were combined with X-ray spectral analysis data on cross sections of powder particles. As a result, it was found that the transition (Mn, Ni) and heavy (Mo) metals are uniformly distributed over the cross sections of the powders, and the mass fraction of silicon (Si) is uneven: in the center of the particles, in some cases, it is several times larger. The revealed feature in the distribution of silicon is presumably due to the formation of various forms of SiO4 during cooling of the resulting particles.
The internal structure of the manufactured powder is represented by a martensitic structure of packet morphology. After laser fusion, traces of segregation inhomogeneity in the form of a grid with cells of ~200 μm were revealed on etched sections. Segregation boundaries and fine-grained structure were the dominant mechanisms of steel hardening in the SLM process.
Under the conditions of compression of the samples obtained, the yield strength was 720 MPa, and the highest value deformation resistance reached 1050 MPa, which exceeds the performance of a monolithic material of a similar chemical composition. On the diagrams σ(ε) in the section of parabolic hardening, randomly located extrema of local hardening, followed by abrupt load drops. The shape of the diagrams indicates the inhomogeneous internal structure of the samples
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