Methods of making bainitic steel materials
Methods of making bainitic steels may involve austenitizing a quantity of steel by exposing the quantity of steel to a first temperature. A composition of the quantity of steel may be configured to impede formation of non-bainite ferrite, pearlite, and Widmanstätten ferrite. The quantity of steel may be heat-treated to form bainite by exposing the quantity of steel to a second, lower temperature. The second, lower temperature may be stabilized by exposing the quantity of steel to the second, lower temperature in the presence of a thermal ballast.
1. A method of making a bainitic steel, comprising:
austenitizing a quantity of steel by exposing the quantity of steel to a first temperature in a furnace, a composition of the quantity of steel being configured to impede formation of non-bainite ferrite, pearlite, and Widmanstätten ferrite;
permitting the quantity of steel to cool in air within the furnace to a second, lower temperature;
after permitting the quantity of steel to cool, heat-treating the quantity of steel to form bainite by exposing the quantity of steel to a third, still lower temperature;
stabilizing the second, lower temperature by exposing the quantity of steel to the third, still lower temperature within an enclosed container distinct from the furnace while the quantity of steel is surrounded in a thermal ballast consisting of solid, stationary particles enclosed within the container; and
permitting the quantity of steel to cool.
2. The method of claim 1 , further comprising homogenizing the quantity of steel by exposing the quantity of steel to a temperature greater than about 1,000° C. before austenitizing the quantity of steel.
3. The method of claim 1 , wherein austenitizing the quantity of steel by exposing the quantity of steel to the first temperature comprises exposing the quantity of steel to a temperature of about 1,000° C.
4. The method of claim 1 , wherein austenitizing the quantity of steel, the composition of the quantity of steel being configured to impede formation of non-bainite ferrite, pearlite, and Widmanstatten ferrite, comprises austenitizing the quantity of steel, the composition of the quantity of steel being between 0.62% and 0.78% by weight carbon, between 1.5% and 2.5% by weight silicon, between 1.75% and 2.5% by weight manganese, between 0.22% and 0.5% by weight molybdenum, between 1.0% and 1.8% by weight chromium, between 0.0% and 0.3% by weight cobalt, between 0.25% and 1.0% by weight aluminum, and the balance consisting essentially of iron.
5. The method of claim 4 , wherein austenitizing the quantity of steel comprises austenitizing the quantity of steel, the quantity of steel being free of nickel.
6. The method of claim 1 , wherein heat-treating the quantity of steel comprises maintaining the quantity of steel exposed to the third, still lower temperature for 2 days or more.
7. The method of claim 6 , further comprising maintaining the quantity of steel exposed to the third, still lower temperature for at least 4 days.
8. The method of claim 1 , wherein exposing the quantity of steel to the third, still lower temperature comprises exposing the quantity of steel to a temperature of between 200° C. and 300° C.
9. The method of claim 1 , wherein exposing the quantity of steel to the third, still lower temperature within the enclosed container while the quantity of steel is surrounded in the thermal ballast consisting of the solid, stationary particles, enclosed within the container comprises burying the quantity of steel within pre-heated alumina when exposing the quantity of steel to the third, still lower temperature.
10. The method of claim 9 , wherein permitting the quantity of steel to cool after stabilizing third, still lower temperature comprises air-cooling the quantity of steel.