Development of HSLA steel with high temperature tensile properties

The fire safety of high rise buildings, airport structures, stadium and auditorium has become a prime importance to ensure the safety of human life and demands for the development of fire resistant steel. Steel is generally defined as fire-resistant if yield ratio for the steel is in excess of 0.5 at 600°C for a holding time of one hour. The Yield ratio of fire resistant steel is defined as the ratio between yield strength at a specified elevated temperature to that at room temperature and is usually specified to be greater than 0.5 for less critical applications and greater than 0.6 at 600°C for the critical applications. Recent developments of fire resistant steels indicate the use of higher amounts of alloying elements primarily Mo that leads to increase in the cost of steel. Therefore the present work was intended to design a low cost leaner chemistry based Fire resistant steel that can be easily processed through hot strip route. The steel was targeted to achieve minimum of 350 MPa room temperature YS in addition to the fire resistant properties. The present work entails to Mo-V-Cr micro alloyed steel. The designed steels were characterized at room temperature and high temperature over a range of 450-600°C The high temperature properties of steel were evaluated using hot tensile facility in Gleeble 1500. It was found that the steels exhibited yield ratio in excess of 0.5, which met the desired target. This ratio was found to be higher than the equivalent plain carbon steel that has the ratio below 0.3 at 600°C. Fire resistance property of steel was attributed to the solute drag effect and the development of long range internal strain due to presence of coherent/semi-coherent precipitates of the micro alloying elements.