Influence of stress concentrator shape and testing temperature on impact bending fracture of 17Mn1Si pipe steel

A common tendency in transportation pipeline development, particularly, for main gas and oil pipelines, is a gradual increase in their service life and performance [1]. The problem is particularly acute since the pipelines often operate in unfavorable weather conditions, e.g., at low temperatures. A challenging task in this respect is to extend the service life of pipe steels by improving their mechanical properties [2]. Specifically, the fracture toughness – the major characteristics of crack resistance has to be increased. Main detrimental factors affecting the strength and crack resistance of pipe steels are attributed to tensile stresses and corrosion of the outer surface of pipes arising in underground conditions due to delamination or rupture of protective coating and localized corrosion of the inner surface [3]. Currently available approaches to characterizing the base metal ductility allow estimating the dynamic crack initiation conditions that are crucial for the prevention of gas and oil pipeline failure [4]. It requires development of robust methods for the fracture energy determination in pipe steels with account of the shape of stress concentrators. These data can be used to account for the influence of embrittlement factors on the impact deformation resistance of pipe steels. Furthermore, modern low-carbon steels produced by thermomechanical processing of the initial sheet have different sensitivity to the concentrator shape and temperature/force loading parameters. It is therefore important to understand the fracture mechanisms operating at different stress stiffness values. The present paper is aimed at obtain a deeper insight into the influence of the notch shape on the impact fracture of 17Mn1Si steel at different temperatures with a focus on the low temperature fracture behavior.