Fatigue damage of the surface layers of metal is a characteristic cause of failure of rolling bearings, gears and a number of other machine parts operating under cyclically repeated contact loads. Resistivity to the development of contact damage of steels obtained by hot forging porous blanks is determined by the presence of cohesive bonds between the particles of the base powder, as well as by the presence of non-metallic inclusions and grain size. The possibility of increasing the contact endurance of hot-deformed powder steels due to micro-doping with calcium has been studied. Iron powders with various content of impurities, as well as atomized powder of low-alloyed chromium-molybdenum steel were used as the basis for preparation of the blends. Calcium was doped as calcium carbonate. Mixing was performed in a planetary centrifugal mill. Samples for mechanical testing were obtained by hot forging porous blanks. After hot forging the samples were carburized to compensate for the loss of carbon in the surface layer. It has been established that doping calcium microadditives is favourable for increasing the energy content of damage under the conditions of exposure to contact-fatigue and bending loads. This is due to a decrease in the size of austenite grains at the expense of inhibition of their growth during the adsorption of calcium at the grain boundaries. Microalloying with calcium changes the localization of seats of contact fatigue damage. In samples-witnesses without microadditives of calcium cracks originate near non-metallic inclusions of sharp-angled shape in the near-surface zone. In microalloyed specimens the cracks are located in the subsurface layer in the area of Hertz maximum shear stresses.

The stability of the characteristics of the contact and low-cycle fatigue life of steels obtained from iron powders with different contents of alloying and microalloying elements, as well as impurities, has been studied. The carbon content in powder steels was varied. It has been established that doping Na or Ca microadditives contributes to an increase in the stability and absolute value of the parameters of the contact and low-cycle fatigue life of hot-deformed powder steels due to the activation of cohesive interaction on interparticle surfaces and carbon diffusion, which contributes to the formation of a homogeneous structure. Doping microadditives of Al contributes to an increase in the contact and low-cycle fatigue life of the powder steels in comparison with the samples-witnesses. However, the formation of zones of structural heterogeneity in steels containing more than 0.4 wt. % C, causes a decrease in the stability of these characteristics.

The feasibility of cohesion degree enhancement, mechanical properties, and contact durability of powder forged steels due to microalloying with aluminum was studied. Unalloyed iron powders with various impurity contents, as well as atomized powder of low-alloy chromium-molybdenum steel, were used as the basis for the producing mixtures. Aluminum was doped as ferroaluminum. Specimens for mechanical and fatigue tests were produced by powder forging. Post-heat treatment was carried out according to two flow routes. The first flow route included carburizing, hardening and low tempering. The second flow route corresponded to high-temperature thermomechanical processing, which was carried out immediately after the completion of hot repressing porous preform. It was found that doping aluminum microadditives in hot-deformed powder steels provides the feasibility of increasing bending strength, impact strength and fatigue life under contact or low-cycle loading. This is associated with an enhancement of the conditions for interparticle joining during hot forging due to the generation of interlayers of ferrite in the interparticle zones as well as to the activation of cohesive interactions as a result of accelerating the process of dynamic recrystallization