Research on Microstructure Characteristics and Strengthening Mechanism of Low-Carbon Bainitic High Strength Steel Produced by CSP

This paper investigated the microstructure, precipitation behavior and strengthening mechanisms of low-carbon bainitic plates produced by CSP using the analysis methods of mechanical properties examination, SEM, TEM, EBSD and physicochemical phase analysis. Some micro-alloying elements were added auxiliary based on Si-Mn-Mo alloy system in the test steels and the rolling and laminar cooling processes were strictly controlled throughout the course of the industry experiment. The yield strength of test steels can reach 600 MPa and 700 MPa grades respectively through appropriate adjustments of chemical compositions and process parameters. The microstructures of the test steels with the yield strength of 600MPa and 700MPa mainly consist of granular bainite, as well as a small amount of quasi-polygonal ferrite and lath bainite respectively. The test steels both have the microstructure characteristics of fine grains, refined and dispersive precipitates and high dislocation density. Besides,they also have the characteristics of high yield strength, high elongation and excellent properties of low-temperature impact toughness and cold bending properties. It is found that the fine grain strengthening, precipitation strengthening and bainitic transformation strengthening are the main strengthening mechanisms through qualitative analysis and they are also the main reasons for the strength difference of the two test steels.