| Popis: |
The influence of boron on the mechanical properties of niobium microalloyed steels was investigated by comparing the variations of rolled strips with and without boron and titanium addition. Chemical analysis, metallography, mechanical properties, hardness and hot-torsion tests were performed to characterize rolled samples with different chemical composition. In order to meet this goal, two different chemical composition for microalloyed steel were designed: Chemical composition A, relative to an ASTM A1018 HSLA (High Strength Low Alloy) grade 50, niobium microalloyed steel, standard, low residuals and target carbon and manganese content of 0.08% and 1.25% respectively. And a chemical composition B, identical to chemical composition A, but with the addition of boron and titanium. One heat of each steel was produced in the BOF (Blast Oxygen Furnace) process, followed by Vacuum Degassing and Slab Continuous Casting. One slab of each heat was rolled into coil, on a Steckel Mill, from which diverse samples were collected at different locations along the length. The characterization tests results presented are for those samples that were rolled under processing conditions closer to the initial planning for both steels. The steel B presents highest values of the yield strength, tensile strength and hardness, lower elongation and larger grain size. This experiment suggests that the boron addition to the HSLA steel, niobium and titanium bearing, allows the achievement of higher yield strength, tensile strength, hardness and lower elongation. |
