An experimental investigation of the effect of microstructural features on mechanical properties of EN8 steel

Abstract

Materials in almost all components are subjected to some kind of loading that must be correctly predicted to produce reliable designs. The understanding of a material's properties significantly impacts appropriate selection for a structure. This kind of material characterization is also important in the development of improved or new materials for high strength and novel applications. There are numerous metallurgical variables (composition and process parameters) that influence the physical and mechanical properties of materials. The aim of this work has been to study the influence of microstructure on mechanical properties of steel, specifically the effect of grain sizes within solid phase mixtures. Parameters for simple models of the variation of material properties with grain size can be determined. These models can then be incorporated in the material data sets of Finite Element Analysis programs which will then allow for structural analysis with zones in a material having different grain sizes. The deformation and damage behaviour of EN 8 steel have been stUdied with emphasis on the effects of grain size on the elastic-plastic response of the material. For that purpose, EN 8 specimens with a range of microstructures (grain size and phase) were prepared by heat treatment The microstructural features were carefully characterized using two different experimental surface microscopy techniques; Light Optical Microscope and Scanning Electron Microscope. The deformation and hardness characteristics have been studied with the help of tensile and hardness tests. The mechanical properties were determined as a function of microstructure (grain size and phase). The yield stress followed the classical Hall-Petch relation. The results indicated that tensile strength and hardness increases with decrease in grain size while elongation decreases. The main philosophy behind this research has been the study of the microstructure and information from the iron-carbon phase diagram together with numerical analysis of stress-strain data, in order, to understand the influence of grain size on mechanical behaviour of EN8 steel. This combination was then used to make general conclusions on mechanical behaviour of EN 8 based on heat treatment history.