INFLUENCE OF FORGING FORCE ON THE FORMATION OF THE STRUCTURE AND MECHANICAL PROPERTIES OF MEDIUM-CARBON STEELS WELDED JOINTS IN ROTARY FRICTION WELDING

The increasing interest in the process of friction welding is associated with the wide spreading of this technology at the enterprises of mechanical engineering due to the technological advantages of this method and the high quality of welded joints of the similar and dissimilar metals and alloys. Rotary friction welding (RFW) is one of the types of welding using friction heating and is used for parts having the shape of a cylinder or a pipe. The main technological parameters of the RFW process are the force during heating, forging force, the rotation frequency during heating, and the burning-off length. All parameters are interconnected and influence the process of formation and the properties of a welded joint. The paper studies the influence of forging pressure on microhardness, tensile properties, and microstructure of welded joints from 32-2-Mn and 40-Cr-Ni steels. The authors analyzed the phase transformations occurring in the materials to be welded as a result of high temperature and deformation effects. The study showed the change in the length of the thermomechanically affected zone (TMAZ) depending on forging pressure. The results of microhardness distribution along the weld seam illustrate the formation of hardened and weakened zones. The paper presents the results of the breakdown and impact-viscosity tests of welded joints. The study showed the morphological features of fracture in the welded joint after the impact-bending tests. The study identified that the forging force affects the microstructural characteristics, the length of thermomechanically affected zone of the materials being welded, the mechanical properties, and the fractographic features of a welded joint during the impact-bending test. The authors give recommendations for determining the optimal forging force values.