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The surface quality of steel sheets for the production of components of automobile locking systems can affect their damage during long-term use. The paper discusses the results of partial experimental tests of selected steel sheets of the S420MC and S500MC grades recommended for this production. These are microalloyed high-strength thermomechanically rolled HSLA steel sheets with thicknesses of 2.3 µm and 2.0 µm. The chemical composition of both steels was experimentally determined, Vickers hardness measurement at HV10 load, EN ISO 4287 tensile test according to the ČSN EN ISO 6892-1 standard, surface roughness measurement by contact profilometry according to the ČSN EN ISO 4287 standard, metallographic analysis. The results showed higher hardness of steel of the lower strength class S420MC compared to steel S500MC. This apparent contradiction is explained by the different microalloying strategy of both materials, where S420MC steel is strengthened mainly by precipitation of vanadium carbides and carbonitrides / VC, V(CN)/, while in S500MC the grain refinement mechanism with precipitation of niobium carbides and carbonitrides / NbC, Nb(CN) prevails. The surface roughness of the steel sheets differs significantly. The above-mentioned conclusions of partial experimental tests predict the possibility of fatigue fractures of the locking systems, which will be experimentally verified subsequently.
Keywords: Steel sheets S420MC, S500MC, tensile test, hardness test, metallographic analysis, surface roughness, precipitation hardening, automotive industry, locking system© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.