Studium vodíkové křehkosti v závislosti na chemickém složení a strukturním uspořádání cementačních ocelí

Abstract

The aim of this diploma thesis was to assess the effect of hydrogen on the mechanical properties of case-hardening steel 20MnCr5. The theoretical part of this diploma thesis describes the diffusion of hydrogen in steel. Furthermore, the thesis explains hydrogen embrittlement, its types and mechanisms, the influence of physical metallurgical factors, including the influence of microstructural components. Subsequently, case-hardening steels, their properties, types, chemical composition and mechanical properties are characterized. The effect of hydrogen was studied in three melts of case-hardening steel 20MnCr5 with different chemical composition and microstructural characteristics on electrolytically hydrogenated tensile bars. The resulting tensile test values showed that there was a decrease in ductility and reduction in area compared to the initial non-hydrated states. Subsequently, a fractographic analysis was carried out in order to determine the morphology of failure in the initial conditions, as well as in the hydrogenated samples. Fracture initiation then occurred mainly in segregation zones and on manganese sulphides.