Corrosion Behavior Of Chromium-manganese Stainless Steel In Simulated Acidic Food Environments

In recent years, stainless steel kitchen utensils are favored by consumers because of their beautiful appearance and easy to clean. Due to the lack of nickel resource in China, stainlee steels with manganese partly replacing for nickel have rapidly developed. However, to some extent, shortage of nickel element reduces the corrosion resistance of stainless steel, which will result in excessive release of metal elements in food environments. Taking in too much these elements will endanger people’s health. So studying the corrosion and dissolution behavior of chromium-manganese stainless steels in food environments has important theoretical and practical significance. Chromium-manganese stainless steels and 304 SS were used as research materials in this thesis. The corrosion behavior of stainless steels in simulated acid food environment was studied by electrochemical test, ICP-AES, SEM and XPS methods. The influence of chloride ions(Cl-), temperature, surface roughness and alloying elements on the corrosion behavior was also discussed.The influence of chloride ions on corrosion and dissolution behavior of BN4 stainless steel was studied. The results show that BN4 stainless steel can passivate in the boiling acetic acid solution with or wihout Cl- ions, but Cl- ions may accelerate the corrosion and dissolution process. Stable dissolution rate of metal elements in these two kinds of solutions follow the sequence: Fe > Mn > Cr > Ni. The preferential dissolution of Fe and Mn elements promots the enrichment of Cr in passive films which are mainly composed of chromium oxides and hydroxides. Cl- ions slightly promote the dissolution of Fe and Mn elements, but make little difference on the dissolution of Cr and Ni.The influence of temperature and roughness on corrosion behavior of BN4 SS in simulated acid food environment was studied. The results show that corrosion potential drops, passive current density increases, pitting potential of stainless steel decereases linearly with the solution temperature increase. With the increase of the surface roughness of stainless steel, the polarization resistance reduces slightly because of the increase of defect concentration in the passive films. At the same time, the pitting potential drops, passive current density increases and the corrosion resistance of stainless steel decreases noticeably.The influence of alloying elements on the corrosion and release behavior of stainless steels in simulated acidic food environment was studied. The results show that BN1, BN4 and 304 stainless steels can passivate and maintain low corrosion rate in the boiling acid food environment. Polarization resistance values of three kinds of stainless steels increase with immersion time, which follow the sequence: 304 SS > BN4 > BN1. Dissolution amount of elements in 1 h and 13 h follow the order: Fe > Mn > Cr > Ni. Sequence of dissolution amount of Fe, Mn and Cr from these three stainless steels is: BN1 > BN4 > 304 SS. Sequence of dissolution amount of Ni is: 304 SS > BN4 > BN1. The higher Mn content, lower Cr and Ni contents result in the formation of weaker protective passive film on BN1 stainless steel, which leads to the relatively high dissolution of Fe, Mn and Cr elements. Dissolution rate of Ni was very low for these three stainless steels, the dissolution amount of Ni is relatively higher for the stainless steel with larger Ni content.