Effect of nitrogen on microstructure and corrosion resistance of Cr15 super martensitic stainless steel

Abstract

To investigate the influence of nitrogen on structure and corrosion resistance of Cr15 super martensitic stainless steels (SMSS), two types (N-free and N-0.12%) of specimens were quenched at 1050°C and tempered at different temperatures, and then, optical microscope, transmission electron microscopy, X-ray diffraction, potentiodynamic polarisation, immersion experiments and Kelvin Probe Force Microscope were used to characterize its microstructures and corrosion properties. The experimental results show that the microstructure in the N-free Cr15 super martensitic stainless steel is a biphasic tissue with alternating martensite and austenite distribution while quenched at 1050°C and tempered between 600 and 700°C. The nitrogen addition increases the content of austenite, and changes the austenite morphology significantly into the coarse block and strip distribution. What's more, micro-galvanic corrosion is formed between austenite and martensite, which deteriorates the corrosion resistance of the SMSS.

Effect of nitrogen and tempering temperature on microstructure evolution and mechanical properties of 0Cr15Ni6Mo2 martensitic stainless steel

“…However, the evolution of SEM microstructure with tempering temperature has not been studied in detail. Chang [3] found that the corrosion resistance of 0Cr15Ni6Mo2 martensitic stainless steel was significantly reduced after 0.12%N was added, but the influence of N on precipitates and mechanical properties was not mentioned in this paper. Jiang [5] studied the similarities and differences of the content of reversed austenite, microstructure morphology and growth rule of super martensitic stainless steels with different chromium content under the same heat-treatment process.…”

“…It can obtain better strength, plasticity and toughness through simple heat treatment, and has good resistance to the marine atmosphere, short-time sea water immersion, weak acid and other corrosive media [1,2]. It is widely used in aviation, aerospace, ship, water conservancy and other fields [3,4]. The chemical composition of the steel determines that there are 5–15% δ ferrite in the microstructure, and it will be stable at high temperature [5].…”