Vacuum carburization is a chemical-termical process, that consists of
carburization in vacuum, followed by heat treatment. With a process of vacuum
carburization surface hardness that improves wear resistance, and dynamic
strength are increased. In comparison to conventional carburiziation methods,
where temperatures ranging from 900 to 950 °C are used, the absence of
oxygen allows for higher carburizing temperatures of up to 1050 °C. The aim of
the thesis was to analyze the microstructure and mechanical properties of
16MnCrS5 steel after vacuum carburization. The carburizing was performed at
1020 °C, followed by quenching in N2 gas. After vacuum carburization, in order
to reduce the size of the crystal grains, the steel was quenched again in oil at a
temperature of 850 °C. In diploma work, the effect of elevated carburizing
temperatures in vacuum furnace on mechanical properties of steel,
microstructure, and environmental impact was studied. After vacuum
cementation and oil quenching of the vacuum carburized steel, the mechanical
properties were compared with a reference sample made of hardened steel. We
found that oil quenching after vacuum carburizing process improved yield
strength and tensile strength. Yield strength after vacuum carburizing was 433
MPa and tensile strength 748 MPa, while after oil quenching yield strength (589
MPa) and tensile strength (943 MPa) were both increased. Compared to
quenched reference sample, which had a yield stress of 499 MPa and a tensile
strength of 939 MPa, the mechanical properties after vacuum carburization
decreased slightly, but were improved by additonal quenching. With oil
quenching carburized case depth also increased, from 1,812 mm to 2,788 mm.
Due to increasing prices in the energy source market and our wish to lower the
impact on the environment, the effects of processes on the environment and
cost were also studied. Three processes, which were vacuum carburization, oil
quenching of vacuum carburized specimens in a quenching furnace, and
already established gas carburization in a quenching furnace, were compared.
Vacuum carburization and repeated quenching after vacuum carburization have
shown a lower rate of harmful environmental effects compared to gas
carburizing, where the released CO2 amount was higher by 79 %.
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