Microstructure and mechanical properties of micro alloyed high strength low carbon structural steels

Mechanical properties of structural steel are inherently tied to their microstructural characteristics, which hugely depends on the alloy composition. This research examines the microstructural characteristics and tensile properties of three hot-rolled E450 structural steels. The primary distinction among the three steels lies in their carbon and manganese (Mn) contents. The microstructural evolution was correlated with mechanical properties. Microstructural analysis revealed the formation of a ferrite–pearlite microstructure. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analyses were conducted to find the dominant strengthening mechanisms in all three steels. The steel with lower carbon and higher manganese content exhibited superior yield strength (580 ± 16 MPa) and tensile strength (657 ± 21 MPa), attributed to grain refinement, a higher low-angle grain boundary (LAGB) fraction, increased kernel average misorientation (KAM), and globular pearlite along the grain boundary, although with reduced elongation (~20.15 %). Conversely, the steel with higher carbon and lower manganese content shows coarser pearlitic lamellae and a greater proportion of high angle grain boundaries (HAGBs), leading to lower strength but enhanced ductility and hardness. These findings reinforce that microalloying and compositional tuning play critical role in microstructural development and mechanical performance of E450 structural steels.