Local Characteristics of Ductile Fracture Surface in Spheroidized Steels

Abstract

It is possible to successfully propose the physical-metallurgical and structural conditions for the equilibrium between steel strength and toughness by designing structural parameters which have a positive effect on the relation between local and macroscopic fracture processes. In carbon steels and microalloyed steels for a wide range of technical uses, whose structure after heat treatment consists of a basic matrix of tempered lower bainite with precipitated carbides and sometimes other types of inclusions, toughness is dependent primarily on the size distribution of second phase particles, their volume ratio, and also the strength of the matrix/particle phase boundary and the mechanical properties of structural phases. By modelling and simulating the process of main crack formation during high-energy ductile fracture, it is possible to propose optimum physical-metallurgical and geometric parameters of steel structure in order to achieve the required relation between strength characteristics and toughness. This paper presents an analysis of results achieved in several tasks carried out to predict mechanical properties in ductile fracture, and it outlines potential future developments. The aims are to determine the limit characteristics of mechanical behaviour of structural steels which can be achieved with a view to the current structural situation and technological possibilities, and furthermore to propose future methods for determining relations between microstructure and toughness.