The influence of modification on the fracture of austenitic stainless steels under dynamic loads

Abstract

The paper presents the results of studying the cold resistance of cast stainless steels of austenitic grade and developed mathematical models showing the effect of cerium, boron, vanadium and copper on cold resistance, which is associated with austenite grain size, carbide phase and ferrite content in austenite after quenching, particle volumes, size and distance between particles of oxides, sulfides, titanium carbonitrides and the total content of non-metallic inclusions in cast stainless steel. It was established that with complex microalloying and modification of Ce, B, V and Cu, the impact toughness of stainless steels increases by 2.7-3.1 times, as a result of the increase of nucleation and crack propagation work. It showed that the crack nucleation and their development is associated with non-metallic inclusions, while in the original steels around non-metallic inclusions significant zones of brittle failure are observed, and in the fracture of complex microalloyed and modified steels there are practically no areas of brittle failure around non-metallic inclusions. It was established that the impact toughness and crack initiation and propagation of the investigated stainless steels are determined by the patterns of changes in such structural factors as the size of the austenite grain, the content of the carbide phase and ferrite in the austenite after quenching, the volume fraction, the size and distance between oxide particles, titanium sulfides and carbonitrides, as well as the total content of non-metallic inclusions. Mathematical models of the influence of structural factors have been developed, which show the predominant influence of non-metallic inclusions on the process of destruction of stainless steels under dynamic loads, in comparison with other structure characteristics, in conditions of negative temperatures is shown. It is established that the mechanism of influence of Ce, B, V and Cu on this process is connected, mainly, with dispersion of oxides and their more homogeneous distribution. Keywords: steel, toughness, fracture work, crack formation, crack propagation, modification.