Microstructure and properties of 09g2s steel processed by equal-channel angular pressing

Abstract

The effect of equal-channel angular pressing (ECAP) on the microstructure, mechanical, andcorrosion properties of low-carbon 09G2S steel was investigated. It was established that ECAPprocessing leads to the formation of an ultrafine-grained (UFG) state, accompanied by ferrite grainrefinement, an increase in dislocation density, fragmentation, and partial dissolution of cementite,as well as an increase in the fraction of globular carbide phases. These changes were analyzed indetail using electron microscopy and X-ray diffraction techniques. After four ECAP passes, theaverage ferrite grain size decreased from 11 μm to ~560 nm. Phase analysis revealed a redistributionof carbide precipitates: the mass fraction of lamellar cementite (Fe3C) decreased, while the contentof globular particles Mn23C6, Mn7C3, and Cr3C2 increased. X-ray line profile analysis performed bythe modified Williamson-Hall and Warren-Averbach methods demonstrated grain refinement andincreased dislocation density. According to the modified Williamson-Hall approach, the dislocationdensity increased from 1×1013 m−2 in the initial state to 1.5×1013 m−2 after four ECAP passes, while thesize of coherent scattering domains decreased more than fourfold. The modified Warren-Averbachmethod showed comparable trends. Corrosion tests indicated that the formation of the UFG structurewas accompanied by an approximately 1.3 fold increase in corrosion rate. It is concluded that theimprovement in strength and the reduction in corrosion resistance of 09G2S steel are associated withgrain refinement, an increase in grain boundary area, high defect density, and the redistribution ofcarbide phases.