Trials to develop a C-Mn-Mo-Nb type fire-resistant steel have been carried out by adopting recrystallization rolling (RCR) + air cooling (AC),two-stage rolling (TSR) + AC and RCR + water cooling (WC).Both RCR and TSR followed by AC resulted in polygonal ferrite (F) + pearlite (P) microstructure,while F + bainite (B) microstructure was formed by RCR + WC.The plates with F+P microstructure show tensile strengths ≥490MPa,while those with F+B exhibit tensile strengths ≥590MPa.All the plates show favorable low yield ratios ≤ 0.75,good charpy v-notch impact property >101J at 0℃ and satisfactory high temperature strength (≥2/3 of room temperature yield strength retained at 600℃).
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