Controlling the toughness of the interface zone of welded joints of dissimilar 32G2 and 10Kh11N23T3MR steels during rotary friction welding

Problem. Despite numerous studies on the problems of rotary friction welding of dissimilar materials, there is a lack of data on the influence of welding parameters on the formation of brittle phases in the mating zone of carbon and austenitic steels, which affect the structural strength of the joints. Aim. The objective of this study is to evaluate the influence of the friction force on the impact toughness of the mating zone of welded joints made of 32G2 and 10Kh11N23T3MR steels. Methods. Welded hollow cylindrical workpieces made of these steels with an outer diameter of 73 mm and a wall thickness of 12 mm were performed with friction force varying from 70 kN to 210 kN. The remaining parameters were held constant: forging force of 280 kN, friction speed of 600 rpm, upsetting during heating of 6 mm, and forging time of 3 s. Optical and scanning electron microscopy with EBSD and X-ray spectral analysis were used to study the microstructure of welded joints. Impact toughness tests were conducted on specimens with a V-shaped stress concentrator in the joint zone at room temperature. A detailed factual analysis of the fractured specimens was conducted, including an analysis of the chemical composition of individual characteristic areas with distinct fracture morphologies. Results. It was established that the presence of a titanium carbide phase, which forms in the joint zone during diffusion of elements during welding, leads to embrittlement of the joint and a decrease in impact toughness. Reducing the heating force to 70 kN increases the volume of metal extruded during forging, effectively removing the brittle phase and ensuring toughness in the joint zone comparable to that of austenitic steel. Conclusions. The obtained results demonstrated the fundamental possibility of producing joints from 32G2 and 10Kh11N23M3TR steels, which have high viscosity, are of practical interest and can be useful in developing technological modes for welding electric motor shafts and turbocharger rotors.