Structure and Phase Composition of Heat-Affected Zone of Austenite Steel After Deformation

Abstract

The paper presents the transmission electron microscopy (TEM) investigations of the thin film structure and phase composition of the heat-affected zone (HAZ) of a weld joint produced by manual metal arc welding (MMAW) of 0.12C–18Cr–10Ni–1Ti–Fe austenite steel exposed then to plastic deformation. The test machine INSTRON-1185 is used to perform quasi-static tensile tests at room temperature and a 1.7∙10–4 s–1 strain rate up to 5 and 37% deformations. TEM investigations are carried out within the HAZ, at a 1 mm distance to the weld line, in the direction of the parent metal and at 0.5 mm distance to the weld deposit. It is shown that MMAW results in the formation of e-martensite both in the parent metal and weld deposit regions. In the latter, γ → e phase transformation occurs faster. Plastic strain ranging between 0–5% throughout the HAZ leads to further γ → e phase transformation. In the weld deposit of the HAZ region, this phase transformation is also more intensive. Further increase in the degree of plastic strain from 5 to 37% results in γ → e → α phase transformation and an elastoplastic lattice distortion of the α-phase. The plastic flexure remains in the crystal lattice of the γ-phase. The bulk material in the HAZ region satisfies the following conditions: scalar dislocation density is higher than the excess, and internal shear stresses are higher than long-ranging.