The influence of the structural condition of high-strength steel on the fractographic characteristics of the fracture structure when testing the specimens with a falling load (VPV, DWTT)

Abstract

Problem. The fracture structure of samples tested by a falling load (VPV, DWTT) of steel type 10G2FB, Х70 produced by the method of thermomechanical rolling with accelerated cooling was investigated. The DWTT fractures of high-viscosity ferrite-bainite sheet steel of thermomechanical rolling differ significantly from the fractures of ordinary hot-rolled or normalized steel. The results of a fractographic study of the topography of the DWTT samples fracture surface are presented in the paper. Metodology. The paper presents the results of a factographic study of the topography of the fracture surface of VPV sample. Steels with a ferrite-bainite structure after thermomechanical treatment were studied. Result. In the structure of fractures, elements of the "dimensional arrow" type were found. However, the current standards for the falling load test (DWTT) do not take into account the peculiarities of the structure of such fractures, which makes it difficult to identify them by the amount of viscous component. Fractures with splits and fractures of the "dimensional arrow" type can probably be recognized as a type of ductile fracture of high-viscosity thermomechanically rolled steel with a ferrite-bainite structure. Currently, the presence of splits in the fracture of VPV samples of high-viscosity steel is considered an unambiguous indicator of its generally viscous failure. Therefore, based on the similarity of the mechanisms of local destruction that form fractures with splits and fractures of the "dimensional arrow" type, the latter can probably be recognized as a specific type of viscous fracture of high-viscosity thermomechanically rolled steel with a ferrite-bainite structure. Enterprises need the creation of sample break scales for product quality control. Practical value. The conducted research made it possible to draw up scales that are used in the assessment of product quality at manufacturing plants.