International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The characteristics of crack growth near non-metallic inclusions under various loading conditions and the influence of laser treatment of steel on these processes are discussed. It is shown that crack development is accompanied by branching within fractured inclusions and in their clusters, as well as upon encountering structural defects in the steel matrix and dispersed second-phase particles. Conditions for crack growth inhibition associated with crack inhibition by plastic sulfides, the development of local relaxation processes in the steel matrix, and changes in the stress state are established. The influence of local microcomposite structures of the steel matrix, obtained under laser irradiation, on the inhibition of crack growth near non-metallic inclusions is demonstrated. The nature of crack growth near non-metallic inclusions was studied under various types of loading without laser irradiation and after preliminary laser treatment. Specimens of hot-rolled steel grades 08Al, 08Ti, 08, 08Cr18Ni10Ti, R7, M76, and GCr15 were subjected to tension and compression in vacuum at temperatures of 20…1200 °C using Instron-1195 and IMASH-9 units (grip movement speed of 1680 mm/min). Some steel specimens with polished surfaces were subjected to laser irradiation before deformation using GOS-30M and CVANT-16 units at pulse energy Wimp of 10…30 J. The heating rate was 105 °C/s, the pulse action time was (1.0…6.0).10-3 s, the cooling rate was 106 °C/s, and the radiation power density was 4 .104 kW/cm2.

During operation, under the influence of mechanical stress, temperature, and external environment, the initial structure of a railway wheel undergoes changes that lead to its fatigue-corrosion wear.
The wheels with different tread profiles that were removed from operation due to the maximum wear of the rims were studied. The studies were carried out using the metallographic method (Neophot-21) and scanning electron microscope JSM-35.
The causes of cracks and wear particles formation near the tread surface of railway wheels associated with phase and structural changes occurring during operation were analyzed. The possibilities of changing the tread profile due to uneven wear were established. It was shown that structural and phase changes near the tread surface are associated with the development of plastic shifts due to the action of external loads, thermal stresses during braking, and the formation of “white layers” when the metal is heated by the heat of braking and abrupt cooling when the brakes are turned off. The role of non-metallic inclusions and corrosion products of wheel steel in the formation of cracks near tread of railway wheels has been established.

The influence of non-metallic inclusions on the formation of defects in deformed steels and their role in providing crack resistance are considered. It is shown that non-metallic inclusions as stress and strain concentrators are one of the most dangerous sources of defect initiation in steels during pressure treatment. It has been established that the nature of cracks and the features of their growth near nonmetallic inclusions are determined by the type of inclusions, as well as by the scheme of the local stress state, which depends on the loading conditions. An analysis was made of the features of the initiation and development of the cracks near non-metallic inclusions of various types during tensile strain, compressive and bending deformation. It is shown that the most severe way of deformation for the inclusion-matrix system is tensile strain, the softest is compression.

The paper focuses on the degradation of molds that are used for the technology of high-pressure casting of Al and its alloys. The method of high-pressure casting of aluminum products is one of the widely used production methods, which at the same time meets the requirements for precision and productivity in the production of cars and various mechanical parts. In the high-pressure casting process, the molds are exposed to various thermal and mechanical loads, where the molds and their shaped parts are degraded. The paper presents the results of research focused on the use of duplex PVD coatings to increase the life of shaped parts of molds for high-pressure casting of Al and its alloys.