Effect of Direct Microalloying of Boron-Containing Structural Steels on Their Structure and Mechanical Properties

Abstract

Under conditions of converter shop of JSC “ArcelorMittal Temirtau”, the authors have developed and implemented the direct microalloying technology of structural steels with boron. Microalloying was carried out due to boron recovery from the slags of the CaO–SiO2–B2O3–MgO–Al2O3 system formed in ladle furnaces. The use of the developed technology was provided in steels 08KP, 3SP, 3PS and 09G2S boron content of 0.0016–0.0050%, with a sufficiently high degree of metal desulfurization 36.8–51.7% and reduction in manganese ferroalloys consumption by 0.3–0.6 kg/t of steel, which improved the environmental situation by eliminating the use of fluorspar. For 09G2S steel, the yield σy and tensile σt strengths are higher for the experimental metal then for the steel without boron by an average 27 and 24 MPa, respectively. The elongation percentage of the metal with boron increased by an average 0.2%. The grain-size index of rolled metal of 08KP steel with a thickness of 2.0–2.5 mm, containing 0.001% of boron and a manganese concentration lowered to 0.18%, reaches 10.0 in contrast to 9.0 for the heats of the current production. The yield σy and tensile σt strengths are on average by 6.0 and 5.0 MPa higher for an experimental metal than for a comparative one. The percentage of elongation δ reaches 36.3% for the experimental metal unlike 33.3% for the heats of the current production. Experimental rolled metal of 3PС steel with lower concentration of manganese lowered by 0.02%, as well as with an average boron content of 0.001%, is characterized by an increased yield strength σy, tensile strength σt (on average by 2.0 and 9.0 MPa) and percentage of elongation δ reaching an average of 21.0% with fine-grained structure. The rolled metal of 3SP steel, microalloyed with boron and with a 4-mm thickness that contains manganese content reduced to 0.43%, is characterized by improved strength properties with preservation of plastic characteristics. The absolute value of the yield σy and tensile σt strengths of steel are by 4.0 and 2.0 MPa higher than the strength characteristics of steel without boron.