Directional Corrosion Behavior of Cold-Rolled and Annealed 304L Stainless Steel: Role of Residual Stress and Phase Transformation

Abstract

This study examines the microstructural evolution, phase transformation, and corrosion behavior of 304L stainless steel after 50% cold rolling and annealing within a temperature range of 400–850 °C. X-ray diffraction, scanning electron microscopy, and cyclic potentiodynamic polarization in 0.6 M NaCl are employed for analysis. Cold rolling induces significant martensitic transformation (≈62% volume fraction) and increases dislocation density by an order of magnitude. Corrosion resistance shows directional dependence, as rolling direction samples exhibit higher corrosion potential (≈−454 mV) and lower corrosion current density (≈17 μA cm⁻²), leading to a reduced corrosion rate (≈0.17 mmpy), whereas normal to rolling direction samples have a lower potential (≈−720 mV) and higher corrosion current density (≈34 μA cm⁻²), resulting in an increased corrosion rate (≈0.34 mmpy). Annealing shows a nonlinear effect on corrosion resistance, peaking at 575 °C with the lowest corrosion current density. At higher temperatures, recovery and recrystallization reduce dislocation density and shift residual stress from compressive to tensile, weakening passive film stability. Fine austenitic grains enhance repassivation but decrease corrosion resistance. Findings indicate that corrosion behavior is mainly governed by residual stress, dislocation density, and crystallographic defects rather than strain-induced martensitic transformation alone.