A Conceptual Model for the Interaction between Carbon Content and Manganese Sulphide Inclusions in the Short-Term Seawater Corrosion of Low Carbon Steel

Abstract

Abstract:The critical role of manganese sulphide (MnS) inclusions for the initiation of the short-term growth of pitting or localized corrosion of low carbon steels has long been recognized. Classical results show that pitting probability and pitting severity increases with increased sulphide concentration for low carbon steels as a result of magnesium sulphides acting as local cathodes for initiating pitting corrosion. However, the iron carbides (cementite) in steels can also act as local cathodes for initiation of pitting corrosion. Herein it is proposed that there is competition between pits for cathodic area and that this will determine the severity of pitting and general corrosion observed in extended exposures. Preliminary experimental data for immersion exposures of up to 56 days in natural seawater of three low carbon steels show, contrary to conventional wisdom, greater pit depths for the steels with lower S content. However, the pit depth results are consistent with lower C/S ratios. This is considered to support the concept of cathodic competition between C and S. It is proposed that this offers explanations for a number of other phenomena, including the thus far unexplained apparently higher reactivity of some MnS inclusions.

Synergistic Effect of Al2O3 Inclusion and Pearlite on the Localized Corrosion Evolution Process of Carbon Steel in Marine Environment

“…A similar phenomenon has also been observed in ultra-low-carbon bainitic steel [10]. A galvanic couple is generally considered to exist between the steel matrix and the MnS inclusions, which is a common inclusion type [10,11]. In carbon steel, MnS can accelerate the dissolution of the matrix as a cathodic phase [10].…”

Effect of Micro-Segregation on Impact Toughness of 2.25Cr-1Mo Steel after Post Weld Heat Treatment

“…Particles with 2 µm diameters near the point X2 were found to be MnS (Mn: 51.33% and S: 36.06%) when analyzed by SEM-EDX. It has been reported in many studies that MnS inclusions have a negative effect on mechanical properties (impact, strength, elongation) [19][20][21]. The low impact value of the 21 ft-lb specimen is caused by the MnS inclusion.…”

“…Because of its high temperature creep strength, good hydrogen resistance, high toughness at high temperatures, and the ability to withstand high pressure hydrogen atmospheres (12)(13)(14)(15)(16)(17)(18)(19)(20)(21) and high temperature (400-450 ° C) and pressure use environments, 2.25Cr -1Mo Steel is widely used as a power plant boiler pipe material. [1][2][3][4] Because of its excellent mechanical properties, 2.25Cr-1Mo steel is widely used not only in thermal power plants but also in nuclear power plants, where high stability is required.…”

Causes of cracks of chemical apparatus made of austenitic steel

“…7.8% compared to 8.0% specified in the standard and sulfur. Increased sulfur content causes formation of manganese sulphides constituting local cathode areas, thus initiating pitting on the steel surface [7].…”