Air-cooling low-carbon bainitic steel

Abstract

Steel articles have a granular bainite microstructure on continuous air cooling, from hot working temperature, of a low cost, tough, high strength, low alloy (HSLA) steel having a composition which, in broadest scope, scope, consists essentially, by weight percent, of 0.08 to 0.25% carbon, 0.30 to 1.5% silicon, 2.0 to 3.2% manganese and 0.005 to 0.005% boron. The steel composition preferably contains, in one aspect of the invention: 0.08 to 0.18% carbon, 0.3 to 1.2% silicon, 2.1% to 2.5% manganese and 0.005 to 0.004% boron; and in another aspect: 0.08 to 0.18% carbon 0.7 to 1.2% silicon, 2.7 to 3.1% manganese, and 0.0005 to 0.004% boron. The steel optionally may contain, by weight percent: up to 0.10 calcium and up to.0.20%, preferably less than 0.01%, sulfur, or up to 0.10% lead; up to 0.10%, especially 0.04 to 0.10%, vanadium, and up to 1.5% chromium. The steel is substantially free of molybdenum, tungsten and other alloying elements, except for residual amounts.