Study of Nanometer-Sized Precipitation and Properties of Fire Resistant Hot-Rolled Steel

Nanometer-sized precipitated carbides in a low carbon Ti-V-Mo bearing steel were obtained through hot rolling and air cooling and were investigated by transmission electron microscopy (TEM). The nanometer-sized interphase-precipitated carbides have been found to exhibit an average diameter of similar to 6.1 +/- 2.7 nm, with an average spacing of similar to 24-34 nm. Yield strength of 578 +/- 20 MPa and tensile strength of 813 +/- 25 MPa were achieved with high elongation of 25.0 +/- 0.5% at room temperature. The nanometer-sized precipitation exhibited high stability after annealing at high temperatures of 600 degrees C and 650 degrees C for 3 h. Average diameters of carbides were statistically measured to be similar to 6.9 +/- 2.3 nm and 8.4 +/- 2.6 nm after tempering at high temperatures of 600 degrees C and 650 degrees C, respectively. The micro-hardness was similar to 263-268 HV0.1 after high temperature tempering, which was similar to the hot-rolled sample (273 HV0.1), and yield strength of 325 +/- 13 MPa and 278 +/- 4 MPa was achieved at elevated temperatures of 600 degrees C and 650 degrees C, respectively. The significant decrease of yield strength at 650 degrees C was attributed to the large decrease in shear modulus.