Microstructural stability of Q460FRW fire-resistant steel

Abstract

The precipitates in Q460FRW fire-resistant steel under equilibrium state were calculated using Thermo-Calc thermodynamic software. The evolutions of matrix and precipitates in this steel before and after high temperature exposure at 600℃ were experimentally observed and analyzed using optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy (TEM). The results show that the precipitates under equilibrium state at 600℃ are carbides including M23C6, M7C3 (M=Fe, Cr, Mo, Mn) and MX (M=Nb,Ti;X=C,N). The matrix of this steel at TMCP (thermo-mechanical control process) state consists of granular ferrite and acicular ferrite. After soaking at 600℃, M/A constitutes decompose gradually, while the acicular ferrite is transformed into bulk ferrite. Besides, longer exposure time brings about larger size of M7C3 particles, while the size of MX particles increases after short time heating and keeps constant with longer exposing time. During the heating process, no M23C6 particles are found, while most of Mo addition contributes to solid-solution strengthening effect.

Keywords

• q460frw
• m/a constitute
• precipitate
• microstructural evolution