Cr-rich phase segregation in a ferritic AISI 430 stainless steel

J. M. BRUQUE ALMEIDA; C. V. TAPIA BASTIDAS; C. H. NOREÑA; C. P. RAMOS

Conferencia; ICAME 2023 - International Conference on the applications of the Mössbauer Effect; 2023

The use of ferritic stainless steel is of great importance for various industrial applications, from accessories in automotive manufacturing to machinery. In this type of steel, chromium (Cr), which is the main alloying component (> 13.6 % at.), brings good resistance to corrosion and great ductility. However, one of the disadvantages this steel faces is while working at high temperatures, since in the range (300 °C–550 °C) the so-called brittleness at 475 °C modifies the mechanical properties, decreasing its ductility and increasing its hardness. This is primarily due to the ferritic phase decomposition into an iron-rich phase (α) and a chromium-rich phase (α') [1-2].In this sense, ferritic AISI 430 stainless steel sheets have been heat treated at 900 °C for 2 h and subsequently aged during different periods of time at 475 °C with the aim of studying the precipitation of the Cr-rich phase (α’).This is part of a work already started some years ago in our group about the effect of α’ phase precipitation on hydrogen diffusion and trapping in this same steel [3].Samples so obtained were first characterized by optical and scanning electron microscopies. Transmission electron microscopy (TEM) and Mössbauer spectroscopy were employed to identify the presence of α and α’phases and infer the possible decomposition mechanism of the solid solution.The Cr-rich phase was identified by TEM in samples with an enough long exposure time. A detailed analysis by Mössbauer spectroscopy was performed, following the evolution of α’ and suggesting that the decomposition mechanism is likely due to nucleation and growth.