Corrosion behavior of cold rolled and continuously heated SUS 304L stainless steel

Effect of continuous heating after cold deformation on the microstructural evolutions and corrosion behavior of SUS 304L metastable austenitic stainless steel was investigated. After cold rolling with the reduction in thickness of 80%, a microstructure consisting of elongated grains was obtained, in which the X-ray diffraction (XRD) analysis revealed the formation of 96 vol.% strain-induced martensite. The subsequent continuous heating up to 750 °C led to full reversion/recrystallization and the development of an ultrafine grained (UFG) microstructure with an average grain size of 0.45 µm. Continuous heating up to higher temperatures resulted in a significant grain growth, where the average grain size of samples that heated up to 850, 900, 950, and 1100 °C were obtained as 2.5 µm, 5.5 µm, 14 µm, and 45 µm, respectively. The Hall-Patch relationship of H = 155 + 106/√D was developed for the dependence of hardness on the average grain size (D). By grain refinement, corrosion current density (iCorr) increased leading to the worsening of uniform corrosion resistance. However, breakdown potential (EBr) increased by grain refinement, indicating the improved pitting resistance. The Hall-patch-type equations of iCorr = 0.0147 + 0.4458/√D and EBr = 0.1964 + 0.0695/√D were proposed for correlating the corrosion parameters to D.