Kursk State University (Kursk, Russia):

N. A. Kostin, Cand. Eng., Associate Prof., e-mail: nikolay-kostin@yandex.ru

The article shows special features of hardening of die steels 5KhGS and 5Kh3GS, used as the materials for the parts exposed to cementation to hypereutectoid concentrations of carbon with the formation of carbide-containing structures. The article reveals the questions of die steels 5KhGS and 5Kh3GS carbonization in nitro-carbonic paste for using them as a material for the parts of die tools. The article gives the results of testing case-hardened parts made of die steels 5KhGS and 5Kh3GS and examining the microstructure of case-hardened layers. The cemented samples were quenched in a wide temperature range, from 780 to 1150 °C, with heating in salt baths and cooling in oil and tempering after quenching at temperatures from 150 to 550 °C in an air-atmosphere furnace. The microstructure of cemented steels on cross-sections was studied using the Quanta 650 FEG microscope by scanning electron microscopy. Layer-by-layer x-ray diffraction analysis of cemented and hardened samples was performed using the DRON-3 diffractometer in chrome k-radiation. The article depicts the test results of cemented parts made of steel grades 5KhGS and 5Kh3GS from which it follows that the cementation of the above-mentioned die steels extends the range of quenching temperatures and tempering temperatures at which their high hardness is provided. The article also contains the analysis of carbon concentration changes depending on the depth of diffuse layers of the samples tested. The article shows that cemented steels, hardened at 850 °C, can be used for the tools, working in the conditions of intensive wastage without serious strikes, steels hardened at 1150 °C (for secondary hardness) can be used for striking tools and the tools, working at high temperatures.

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