Enhancing the strength of steel grade 45 guide rails for ball rolling using the chemical-thermal carbonitriding method

The enhancement of guide rail strength for ball rolling applications is crucial to improving the durability and operational efficiency of the manufacturing process. One effective method for achieving this is carbonitriding, a chemical-thermal treatment that forms a hardened surface layer by saturating the material with both carbon and nitrogen at relatively low temperatures. This study was aimed at improving the mechanical properties of the guide bar used to hold balls on the rolling axis in ball rolling mills by chemical-thermal strengthening-carbonitration. Specimens of mild and medium carbon steel were used as tests. The process consisted in immersing the specimens in a bath with molten salts at a temperature of 570 °C and holding for 1.5 hours. The samples were then cooled in oil and then cleaned with high-pressure water. The study showed that the melt of salts based on urea and potassium carbonate saturates the steel surface with nitrogen and carbon, forming a hardened layer. The depth of the hardened layer depends on the exposure time, but after one hour, the penetration of diffusing substances slows down. This is due to the saturation of the steel crystal lattice with alloying elements (carbon and nitrogen) during carbonitration. The maximum hardening depth for high-alloy tool steels is 0.05-0.12 mm, for carbon steels 0.1-0.6 mm. Carbonitration can be used to increase the hardness, strength, wear resistance of balls without increasing the brittleness of the part.