Molybdenum Tungsten Niobium On The Organization And Performance Of Fire-resistant Construction Steel

Based on low C-Si-Mn micro-alloy steel, the effects of Mo,W,Nb on microstruture and mechanical properties of fire-resistant for building were studied by varying the contents of Mo,W,Nb, and fire-resistant steels containing Mo and W were successfully developed. This paper studied the relations in detail among compositions,properties and microstruture of experimental steels by series of experiments, including test of mechanical properties,metallographic microstructure,spectroscopy analysis under scan electron microscope(SEM) and fine microstructure analysis of under transmission electron microscope(TEM), and discussed the effects of compositions,microstruture and precipitation on mechanical properties of fire-resisant steel, especially on high temperature strength.Addition of Mo,W can enhance strength and high temperature strength and debase toughness and ReL/Rm of steel. Advantageous effect of Mo on high temperature strength was more prominent, compared to equivalent W. The mechanical properties of steel is best when the contents of Mo or W are about 0.30% in the steel. It also found that Nb could substitute partial Mo to improve high temperature strength of steel, which can reduce the production cost and enhance economy. Microstructures of experimental steels are mainly F+P+B+a small amount of M/A, and B is one reason for the improvement of strength and debasement of toughness.According to the observation of TEM, it is discovered that there exist a lot of dispersive scrappy NbC,Nb(C,N)in both rolling and normalizing samples. The precipitations which are globularity or ellipse and very scrappy in size consist mainly in F and crystal boundary, This scrappy precipitations are high stability under high temperature,and are unlikely to assemble and grow, which are very advantageous to enhance high temperature strength of steel.