A development study of Microalloyed steel (HSLA) through experimental exploration

Abstract

HSLA steel is indispensable to the development of modern and future civilisations. The selection of optimum solutionizing temperature range for microalloyed steel grades is of utmost importance as it can significantly reduce energy consumption. Reheating studies were carried out on two different micro-alloyed steel grades (strip samples) containing Niobium. The reheating temperature range and the effect of Niobium content on the final properties of the steel were established by performing a series of quench and temper experiments, followed by hardness testing. A different set of samples (of the same grades) were subjected to heating in a controlled atmosphere (Nitrogen atmosphere) to mark the differences as compared to heating in open (air) atmosphere. Hardness variation across the strip width was also tested. Microstructural analysis was done using SEM and EDX for further investigation of the results obtained. For both grades (and for both cases of heating in open and nitrogen atmosphere), hardness increased with an increase in solutionizing temperature. Also, at a particular solutionizing temperature, the hardness value was higher for the grade containing greater niobium content. This effect can be attributed to the increasing fraction of Niobium that dissolves into the solution (matrix) with increasing solutionizing temperature. However, after a particular temperature range, increasing the solutionizing temperature does not significantly increase the hardness, indicating the saturation of Nb levels in the solution.