Fabrication of a high-strength steel article with inclusion control during melting
View Patent ↗A steel article is fabricated by providing an iron-base alloy having less than about 0.5 weight percent aluminum, melting the alloy to form a melt, adding calcium to the melt, thereafter adding aluminum to the melt to increase the aluminum content of the melt to more than about 0.5 weight percent aluminum, and casting the melt to form a casting. Other calcium additions may be made simultaneously with the adding of aluminum, and after the adding of aluminum but before casting the melt. The calcium additions deoxidize the melt to minimize the formation of clustered aluminum-oxygen-based inclusions.
1. A method for fabricating a steel article having more than about 0.5 weight percent aluminum, comprising the steps of
providing an iron-base alloy; thereafter
vacuum melting the alloy to form a melt, while reducing a free oxygen content of the melt to less than about 10 parts per million by weight; thereafter
adding calcium to the melt; and thereafter
casting the melt to form a casting having more than about 0.5 weight percent aluminum.
2. The method of claim 1 , wherein the step of providing includes the step of
providing the iron-base alloy having less than about 0.5 weight percent aluminum.
3. The method of claim 1 , wherein the step of providing includes the step of
providing the iron-base alloy having more than about 0.3 weight percent carbon.
4. The method of claim 1 , wherein the step of vacuum melting includes the step of
reducing the oxygen content of the melt by reacting the free oxygen with carbon.
5. The method of claim 1 , wherein the step of adding calcium includes the step of
adding calcium to the melt in an amount sufficient to react with all of the free oxygen in the melt.
6. The method of claim 1 , wherein the method includes a step of
adding aluminum to the melt to increase the aluminum content of the melt to more than about 0.5 weight percent aluminum, and wherein the step of adding calcium includes the step of
adding calcium prior to the step of adding aluminum.
7. The method of claim 1 , wherein the method includes a step of
adding aluminum to the melt to increase the aluminum content of the melt to more than about 0.5 weight percent aluminum, and wherein the step of adding calcium includes the step of
adding calcium concurrently with the step of adding aluminum.
8. The method of claim 1 , wherein the method includes a step of
adding aluminum to the melt to increase the aluminum content of the melt to more than about 0.5 weight percent aluminum, and wherein the step of adding calcium includes the step of
adding calcium after the step of adding aluminum.
9. The method of claim 1 , wherein the method includes a step of
adding aluminum to the melt to increase the aluminum content of the melt to more than about 0.5 weight percent aluminum, and wherein the step of adding calcium includes the steps of
adding a first calcium addition prior to the step of adding aluminum,
adding a second calcium concurrently with the step of adding aluminum, and
adding a third calcium addition after the step of adding aluminum.
10. The method of claim 1 , wherein the step of casting includes the step of
casting the melt to form the casting having from about 0.5 to about 1.3 weight percent aluminum.
11. The method of claim 1 , including an additional step, after the step of casting, of
mechanically working the casting.
12. The method of claim 1 , including an additional step, after the step of casting, of
mechanically working the casting to form a shaft.
13. A method for fabricating a steel article, comprising the steps of
providing an iron-base alloy having less than about 0.5 weight percent aluminum; thereafter
vacuum melting the alloy to form a melt; thereafter
adding aluminum to the melt to increase the aluminum content of the melt to from about 0.5 to about 1.3 weight percent aluminum;
adding calcium to the melt; and thereafter
casting the melt to form a casting.
14. The method of claim 13 , wherein the step of vacuum melting includes the step of
reducing a free oxygen content of the melt to less than about 10 parts per million by weight.