INVESTIGATION OF THERMAL EXPOSURE AND ITS INFLUENCE ON THE MECHANICAL BEHAVIOR OF HIGH-STRENGTH LOW-ALLOY (HSLA) STEELS"

Abstract

This study investigates the effect of thermal exposure on the mechanical properties of 0.17% carbon High Strength Low Alloy (HSLA) steel, with annealing using Carbon Equivalent (CE) value. Steel samples were thermally subjected at temperatures ranging from 840°C to 990°C in 30°C increments, with soaking times of 30, 60, 90, and 120 minutes. samples were machine and evaluated for fatigue performance alongside other mechanical tests. Microstructural analysis was conducted using quantitative metallography with the point count method, while fractured surfaces were examined via scanning electron microscopy (SEM). Statistical analysis was performed using ANOVA and optimization techniques. The results reveal that increasing annealing temperature significantly enhances fatigue life, with samples annealed at 990°C exhibiting the highest fatigue cycles: 3.9 × 10³ cycles at 321.31 MPa and 1.3 × 10³ cycles at 1606.57 MPa. Samples annealed at 960°C showed comparable performance, while the control samples demonstrated the lowest fatigue resistance. Fatigue behavior, modeled using Basquin’s equation, indicated that fatigue life is primarily influenced by the fatigue strength exponent (b), which decreases with increasing annealing temperature. In terms of hardness and impact properties, the sample annealed at 840°C recorded the highest hardness (129.4 BHN) but the lowest absorbed impact energy (58.75 J). Conversely, annealing at 990°C resulted in the lowest hardness (118.6 BHN) and the highest impact energy absorption (66.65 J). ANOVA confirmed the statistical significance of the variations in mechanical properties across the annealing conditions at a 95% confidence level. Consequently, this work demonstrates that controlled annealing significantly enhances the fatigue and impact performance of HSLA steel by optimizing its microstructure, thereby enhancing its suitability for demanding engineering and construction applications