Microalloying Effects in Hot Rolled Low Carbon Steels Finished at High Temperature
As part of a program to improve the toughness of steels for structural shapes and thick plates, the effects of columbium (niobium) (0 to 0.24 pct) or vanadium (0 to 0.23 pct) in conjunction with aluminum (0 to 0.06 pct) on the properties of hot-rolled 0.1 pct carbon steels were determined. Experiments were conducted on a laboratory mill to obtain 25 mm (1 in.) plate. Although the primary interest was to improve toughness in materials finished above 980 °C (1800°F), finishing temperatures in the range 845 to 1150 °C (1550 to 2100 °F) were investigated. Impact properties of columbium steels finished above 980 °C (1800°F) were very poor. This effect was attributed to the presence of acicular Widmanstatten structures and relatively coarse grain-boundary precipitates. Toughness improved dramatically at finish-rolling temperatures of 955 °C (1750 °F) and below as a result of the combined effects of grain refinement and reduced precipitation hardening. For the vanadium steels, variations in finish rolling temperature did not have such a marked effect on properties. Aluminum additions considerably lowered the impact transition temperature of the vanadium steels. Although aluminum also improved the impact properties of the columbium steels, the effect was not sufficient to produce good toughness in steels finish-rolled above 980°C (1800°F). Thus, although superior properties may be obtained in the columbium steels finished below 925°C (1700°F), vanadium steels generally had better impact properties at higher finishing temperatures
vanadium and niobium microalloyed steel, structural shapes and thick plate, aluminium, finishing rolling temperature, toughness.
J. M. Chilton & M. J. Roberts
Product Metallurgy Section, Homer Research Laboratories, Bethlehem Steel Corp., Bethlehem, PA, 18016
Metallurgical Transactions A, Vol. 11A, Oct., 1980， pp.711-1721 (Vanitec Publication - V0184)