PHYSICO-CHEMICAL METHODS OF INCREASING THE CRACKING RESISTANCE OF ALLOY AM4.5KD (VAL10). NOTICE 2: DEVELOPMENT OF THE CRACK RESISTANCE TEST

Procesi littâ, 2023, Vol 3 (153), 18-24

Abstract

As the attempt to use the well-known “ring” test for crack resistance in the conditions of experiments to increase the crack resistance of the AM4.5Kd alloy (VAL10) using hydrogen treatment of the melt (that is, its gas saturation with water vapor) showed, the evaluation of the effectiveness of this type of impact with the help of this test may be unreliable due to low sensitivity of the sample. To eliminate this shortcoming and to obtain additional advantages, a new sample was developed, the design of which allows simulating the formation of a hot crack in real castings, namely, to ensure the creation of stress concentration in the casting, which hardens under conditions of difficult feeding. The casting is a prism with shoulders, in which tensile stresses arise when the melt solidifies. Difficult feeding conditions are created due to insulation of the middle part of the mold. An additional advantage of this sample compared to the “ring” one is the possibility of making samples for measuring the strength and plasticity of the cast metal directly from the body of the casting, as well as obtaining control samples that harden under the same thermal conditions, but in the absence of tensile stresses. In the course of research, it was established the existence of a dependence of the effect of the area of the formed crack on the resistance to bending failure, and a crack with minimal (in the experimental conditions) dimensions, the area of which is close to zero, reduces the value of the destructive load by 2.5 times, which leads to the conclusion , that not the degree of crack development, but only its complete absence can be regarded as a fact of positive influence on the crack resistance of the alloy of this or that investigated method of physical and chemical influence.