Determination of the relationship among the structure, properties and strain state of the 0.09C-2Mn-Si steel under tension

<jats:p>Introduction. Although structural transformations during plastic deformation are well studied, they remain a priority area of scientific research in the field of materials science. Different approaches converge on the fact that metal deformation develops from the microscale to the macroscale level and that the change in stages is an abrupt loss of structural stability, which inevitably ends with localization of shear and failure in the neck. The purpose of this study was to determine the relation of the plastic deformation stages to the structure, surface topography and micromechanical properties of a common structural material, namely grade 0.09C-2Mn-Si steel, subjected to uniaxial tension. Materials and methods. In this study, dumbbell-shaped flat specimens of 0.09C-2Mn-Si structural steel were studied before and after uniaxial tension. The tension process was simulated by the finite element method, and the distribution of the stress-strain state parameters was obtained. The structure was studied by optical and scanning electron microscopy. The surface roughness parameters were determined by optical profilometry. Kinetic microindentation was used to determine the micromechanical characteristics. Results and discussion. A direct correspondence is established among the roughness parameters, deformation stage, and strain level for the 0.09C–2Mn–Si steel. It is found that the strain values are the highest near the crack, that the structure contains no pronounced pearlite colonies, and that there are elongated ferrite grains with boundaries sometimes decorated by fragmented cementite plates. Strain induced discontinuities and elongated pores are clearly visible. The surface relief is caused by the sliding of meso and macrobands. The relationship between the mechanical properties of the steel and the structures obtained at various stages — from the onset of plastic deformation up to macrocrack formation — is analyzed. It is shown that the combined use of optical profilometry, structural characterization methods, and micromechanical tests during instrumented indentation enables reliable recording of structural changes in various regions of 0.09C–2Mn–Si steel specimens after static loading.</jats:p>