The effect of chemical composition of steels working under impact loads and high temperatures on their structural characteristics and mechanical propertie

With a wide variety of alloying components for heat-resistant steels, chromium-molybdenum steels receive special attention. At the same time, complex alloying of 3Сr3Mo3 type steel deserves detailed study regarding the possibility of forming structure with developed austenitic dendrites, which should contain complex chromium and molybdenum carbides. When cooled in air, such steels form a martensitic structure, which guarantees increased impact toughness and heat resistance characteristics. Chromium-molybdenum carbides with optimal parameters for forming an industrial ingot have dimensions of the order of 2-3 microns. The main part of chromium and molybdenum is dissolved in the steel matrix.

To obtain a structure with optimal parameters for this steel, it is necessary to study the methods of its production and the influence of such methods on mechanical characteristics. The main optimization criterion should be the degree of structural homogeneity, which consists of the maximum saturation of the steel matrix with strong carbide-forming elements and the maximum fineness of the carbide component, which is evenly distributed in the matrix.

The proposed tool steel of the 3Сr3Mo3 type requires the absence of light elements in its composition because they either increase the size of chromium-molybdenum carbides by entering them as well as their combination with oxygen to form oxides that are located along the boundaries of austenite grains and significantly embrittle the steel. To improve the mechanical characteristics, the authors propose micro-alloing and modification of the steel with refractory elements, which can effectively further branch the crystallization front of the steel and increase its heat resistance due to partial dissolution in the matrix.

The specified type of steel with high values of impact toughness of more than 1.5 MJ/m2 and heat resistance with a tensile strength of more than 360 MPa at 700С can be used in mechanisms with particularly difficult operating conditions under multi-cycle shock mechanical loads. Thus, tool steels of the 3Сr3Mo3 type, under conditions of optimization of chemical composition and smelting and processing technology, can perform the function of structural steels for installations with extreme operating conditions.