Abstract. Microstructures and properties of weldable quality low-alloy fire resistant structural steels (YS:
287–415 MPa) and TMT rebar (YS: 624 MPa) have been investigated. The study showed that it is possible to obtain
two-thirds of room temperature yield stress at 600°C with 0×20–0×25% Mo and 0×30–0×55% Cr in low carbon
hot rolled structural steel. Microalloying the Cr–Mo steel by niobium or vanadium singly or in combination
resulted in higher guaranteed elevated temperature yield stress (250–280 MPa). The final rolling temperature
should be maintained above austenite recrystallization stop temperature (~ 900°C) to minimize dislocation
hardening. In a quenched and self-tempered 600 MPa class TMT reinforcement bar steel (YS: 624 MPa), low
chromium (0×55%) addition produced the requisite yield stress at 600°C. The low-alloy fire resistant steel will
have superior thermal conductivity up to 600°C (> 30 W/m×k) compared to more concentrated alloys.