The composition and properties of three constructional microalloyed steel with vanadium, niobium and nitrogen is investigated. High strength and ductility steel in rolling mill products and in forgings were revealed, manufactured according to various flow diagram. The resistance of microalloyed steels to grain growth during heating to 1300 °C has been established. The opportunity of realization of the forging heat forgings in their heat treatment is shown. Output testing was carried out of steels in the manufacturing crankshaft and engine connecting rods. For heavily loaded machine components, the use of 38G2AF, AC40H2NMAF and AC30X3NMAFB steels is recommended. High resistance to grain growth is shown when heating steels microalloyed with vanadium, niobium and nitrogen. High properties of the steel AC40H2NMAF, AC30X3NMAFB and 38G2AF make it possible to recommend them for the manufacture of heavily loaded parts - crankshafts and connecting rods. The possibility of realizing forging heat of forgings made microalloyed steels with vanadium, niobium and nitrogen during their heat treatment to ensure a high level properties and structural requirements.
Investigations are given of the influence of thermal, thermochemical treatment of die steels on the development of thermomechanical fatigue cracks depending on the temperature-force effects characteristic of hot deformation dies. As the evaluation criteria for the thermomechanical fatigue resistance of surface hardened die steels, the moment of nucleation, their quantity, and the depth of propagation were used. The study of the laws of the development of thermomechanical fatigue cracks in die steels in copper melts is carried out in an analogous manner, which provides a similarity to the operational loading of the material according to the local stress-strain state and the conditions of interaction with the molten melt. Dependences of the depth and number of cracks formed in 4X4VMFS DI22 die steel, hardened by various methods, on the number of loading cycles are established. It has been established that the performance of a stamping tool in a variant with diffusion hardening is determined by the specific laws of softening and destruction of contact zones. Moreover, the occurrence of cracks in the initial stages of operation is not decisive. The positive effect of boriding and nitriding on the performance of the dies is associated with increased structural stability of the diffusion saturation zones, which ensures the maintenance of a high level of mechanical characteristics of the tool working surfaces -hardness, strength, and as a result of high wear resistance. The analysis of the results of studies of the patterns of crack formation in steel 4X4VMFS DI22, subjected to various hardening methods, indicates the promising use of nitriding and boriding to increase the life of dies.
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