Dependence of the anisotropy of the mechanical properties of steel on the degree of contamination with nonmetallic inclusions

Abstract

Investigations have shown that for vacuum steel the coefficients of anisotropy (ratio of the specific values of the mechanical properties for transverse and longitudinal samples) are close to 0.9 for plastic characteristics and for the fatigue limit, while for ordinary steel these values are,as a rule,considerabl y lower. Only brittle inclusions of the type of oxides and silicates affect the anisotropy of the fatigue limit, while the deformable inclusions (sulfides) affect the ductility. The anisotropy of the fatigue limit increases with increasing strength and plastic deformation of the material. The anisotropy of the plastic characteristics is still more dependent on these factors. The purity of the steel affects the anisotropy of the impact toughness (Table 1). After electroslag remelting no nonmetallic inclusions bigger than grade 1 are found in the steel. The anisotropy of such bars decreases in connection with the increasing impact toughness of longitudinal samples. Detailed investigations of the anisotropy of the fatigue and mechanical characteristics have been made on 40KhNMA and 45KhNMFA steels with various degrees of plastic deformation [5]. The tests of 40KhNMA steel were made on smooth and notched samples subjected to longitudinal and transverse stresses (see Table 2). The results of metallographic examination and also measurements of the reduction in section of transverse samples are presented in Table 2. From the table it is evident that the difference in the amounts of large inclusions influences the value of the reduction in section of transverse samples. The high value of Ctrans for B 2 (by comparison with A2) can be explained by the lower concentration of hydrogen. It should also be noted that the degree of plastic deformation was lower for sample B 2 than for B 1. In samples A 1 and A2, and also C1 and C 2 (with the same degree of plastic deformation) the more contaminated material is characterized not only by lower values of plastic characteristics but also lower values of true strength determined by rupture of transverse samples (Table 3). In Table 3 are presented also the values of the coefficients of anisotropy of the properties of the materials tested. These coefficients are lower for contaminated materials, the effect of the degree of contamination on the anisotropy of the specific reduction in section being especially notable. In addition to smooth samples, the tensile strength of notched samples was tested. From Table 4 it is evident that the relative decrease of the momentary strength induced by nonmetallic inclusions is approximately the same for longitudinal and transverse samples. The effect of contamination of the metal on the momentary tensile strength of longitudinal samples is the result of the action of multiaxial stresses at the notch. The small effect of the direction of the cut in notched samples onthe tensile strength is explained in the same manner. The dependence of the tensile strength of notched samples on the degree