EFFECT OF QUENCHING AND TEMPERING IN MICROALLOYED STEELS CONTAINING BORON AND TITANIUM
EFFECT OF QUENCHING AND TEMPERING IN MICROALLOYED STEELS CONTAINING BORON AND TITANIUM
The OCTG (Oil Country Tubular Goods) steels are used in the production
of casing and tubing for drilling system in petroleum industry. These
steels usually contain niobium, titanium and vanadium, which ensure
good toughness, high tensile strength and resistance to hydrogen
embrittlement. It has been known that titanium nitride can promote the
refinement of austenite grains with a uniformly dispersion of
precipitates in the steel matrix. Nowadays, several researches are
being done with boron addition in the microalloyed steels. Boron
increases hardenability and for the maximum effect, the concentration
should be in the range 0.001 to 0.003 wt%. In the present study the
hardness of one microalloyed steel was investigated after quenching
and tempering in different temperatures. At first, the steel
containing boron and titanium was manufactured by hot rolled until
a thickness of 7,2 mm. Afterward, samples in longitudinal orientation
with 15x150 mm were cut and heated at 850, 950 and 1050 °C for 30
minutes. Thereafter, all specimens were tempered in the range from 150
to 650 °C for 60 minutes. Both cooling were fulfilled with water at
23 °C. In all specimens, the averages of five measurements were
obtained with a load of 100 N using a Vickers hardness tester.
The results showed no significant deviations of the values of hardness,
after quenching in three temperatures and tempering in the established
range. It can be conclude that the titanium nitrides precipitate,
refine the austenitic grain during hot rolling and keep
characteristics of the martensitic transformation,
even in different quenching temperatures. In addition,
these nitrides favor the solubility of boron and carbon
in the matrix, with hardness increasing of the steel. Though, applying
small amounts of boron and titanium in the microalloyed steels,
there was no significant variation of hardness after quenching
in different temperatures.
Key words: Boron steels, TiN effect in quenching, Hardenability.