The effects of auto-tempering martensite on mechanical strength of a microalloyed steel containing boron and titanium.

Oil Country Tubular Goods (OCTG) steels are used in the form of tubes in the casing column of the oil well walls and exhibit tempered martensitic structure after quenching and tempering. In these steels, due to the high cost of chromium, nickel and molybdenum, an alternative is the replacement of these elements by boron, which increases the hardenability. In order to maintain the efficiency of boron in solution during the quenching, it is necessary to add titanium to form titanium nitrides (TiN), which inhibit austenitic grain growth and avoid the formation of boron nitride. Another factor is to evaluate the effect of heat treatment on the mechanical properties of this steel. In the present study were evaluated the microstructure, hardness and tensile properties of a microalloyed hot rolled steel containing boron and titanium after heat treatments. Samples of a coil were quenched at 850 and 1050°C and then tempered at 200 and 600°C. The results show that the hardness, yield stress and tensile strength after austenitization temperature at 1050°C are smaller, due to the formation of auto-tempering martensite in the quenching. [ABSTRACT FROM AUTHOR]