MICROSTRUCTURAL AND CORROSION BEHAVIOR OF MULTIAXIALLY FORGED MICROALLOYED STEEL

Abstract

Multi-axial Forging (MAF) is one of the techniques of severe plastic deformation, where samples are subjected to compressive forces to produce ultra-fine grained structure. An exceptional grain refinement (generally to nanometre level) can be obtained by this metal forming process with exceptionally high strength. In this present investigation, Micro-alloyed steel used for automotive and structural purposes were studied. Steel samples were processed via. MAF to produce ultrafine grained microstructure, which was later on confirmed by transmission electron microscopy (TEM), Electron backscattered diffraction (EBSD). The resulting properties and behaviours were correlated with structural properties by using optical microscopy, scanning electron microscopy (SEM) and TEM, and with mechanical properties by tensile and hardness tests. Furthermore corrosion properties of these steel samples were studied by using various corrosion testing methods like potentiodynamic polarization, cyclic polarisation and electrochemical impedance spectroscopy (ELS) tests in NaCl (3.5 wt %) solution. Furthermore these results were confirmed by immersion test done in same environment. In the end, surface morphology and severity of corrosion was characterized via SEM and optical profilometer.