Characterization of inclusions and second-phase particles in high-Mn TWIP steels microalloyed

What is it about?

In recent years there has been an increase in the field of research of advanced steels that have excellent mechanical properties combining high strength with excellent ductility. Within this range of advanced steels are the stable austenitic phase steels at room temperature of twinning induced plasticity known as TWIP. An important aspect to highlight about TWIP steels is their addition with different microalloying elements, generally less than 0.20 wt. %, which are forming precipitated phases such as carbides, nitrides and carbonitrides, and directly or indirectly control and/or modify microstructure and mechanical properties in these steels. Microalloying elements can cause a higher degree of hardening due to the formation of precipitates and grain refinement. The present research work studies the inclusions and second-phase particles formed in Fe–21Mn–1.3Si–1.6Al TWIP steels microalloyed with Ti, Nb, V, Mo and Ti/B in as-solution condition. TWIP steels melted in induction furnace were homogenized and hot-rolled at 1200 °C with reduction of 60 %. Subsequently, rolled plates were solubilized at 1100 °C followed by water quench. Thermodynamics-based predictions of inclusions and second-phases of different TWIP steels were carried out using JMatPro®V.9.1.2. Metallographic characterization was carried out by light optical and scanning electron microscopies (LOM, SEM), while second-phase particles characterization was performed using energy dispersion spectroscopy (SEM-EDS). Also, Vickers microhardness tests were carried out in accordance to ASTM E92 standard. In general, results showed the formation of inclusions of AlN and MnS at higher temperatures, which act as nuclei points for the precipitation particles of each type of microalloying element (TiN, TiC, Nb (C, N), VC and MoC) at lower temperatures. The studied TWIP steels exhibit similar microhardness values, since the microalloying elements are mostly dissolved in solid solution. The TWIP steels microalloyed with V and Ti exhibited the highest microhardness values.

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