Control of the concentrated-precipitation behaviour of Cr23C6 and its effect on the microstructure and properties of S600E sorbitic stainless steel

Abstract

The influences of heat treatment on the microstructure, element distribution, precipitation behaviour, mechanical properties, and corrosion resistance of S600E sorbitic stainless steel were studied. The influence of heat treatment on the precipitation kinetics of Cr23C6 was analysed through theoretical calculations. The results showed that the compositional nonuniformity of the hot-rolled experimental steel was eliminated with increasing solution temperature. The proportion of high-angle boundaries increased and the tempered sorbite structure coarsened with increasing tempering temperature. The main precipitated phases in the sorbitic stainless steel included large-sized Cr23C6 distributed along the grain boundaries and Nb and Ti carbides uniformly distributed within the grains. The temperatures with the fastest precipitation of M23C6 and MX phases were 870 °C and 950 °C, respectively, and the precipitation of MX could suppress the concentrated precipitation of Cr23C6 at the grain boundaries. By regulating the heat treatment process, the grain boundary area in the tempered sorbite structure was increased, the dissolution of Cr23C6 was promoted, and the precipitation kinetics of Cr23C6 were reduced, which suppressed the concentrated precipitation of Cr23C6 at the grain boundaries. Therefore, the mechanical properties and chloride pitting corrosion resistance of S600E sorbitic stainless steel were improved.

Keywords

• Tempered sorbite structure
• Cr23C6 concentrated-precipitation
• Solution temperature
• Precipitation kinetics
• Chloride pitting corrosion