Electric-Arc Steelmaking (Patent No: 780323)

Inventor: Roeder, Gordon A.

Location: Burlington, ON

Comments: N/A

Description: The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of steelmaking which comprises charging an iron-bearing material into an electric-arc furnace, melting said iron-bearing material to form an open bath of molten metal, continuously charging a discrete, carbon-containing, iron-bearing material having a composition within the range of from about 76 per cent to about 99.5 per cent by weight total iron with a residual oxygen content of from about 0.1 per cent to about 1.75 per cent by weight into said bath at a controlled rate relative to power input such that the molten metal has substantially reached the desired tap temperature and carbon content concurrent with completion of the feeding of said iron-bearing material to the furnace.

2. A method of steelmaking comprising initially charging an electric-arc furnace having electrodes with scrap metal, fluxing, carbon and alloying additives, positioning the electrodes in proximity to said charge, applying power to said electrodes to direct arcs from said electrodes to said charge to form consolidated bore cavities having a trefoil-shaped pool of molten metal therein, continuously feeding discrete particles of iron-bearing material having a composition within the range of from about 76 per cent to about 99.5 per cent total iron having a residual oxygen combined with iron content of from about 0.1 per cent to about 1.75 per cent into said pool in proximity to arc flare locations while simultaneously and continuously applying power to melt and to refine said charge until up to about 80 per cent of the total melt charged is from said discrete particles and said entire charge is melted and refined, and tapping the refined steel from the furnace while the total energy consumption is within the range of from about 250 to about 700 KWH/ton of iron-bearing material, said steel having a carbon content of from about 0.02 per cent to about 1.8 per cent.

3. A method of steelmaking comprising initially charging an electric-arc furnace having electrodes with scrap metal, fluxing, carbon, and alloying additives, and discrete particles of iron-bearing material having a composition within the range of from about 76 per cent to about 99.5 per cent by weight total iron having a residual oxygen content of from about 0.6 percent to about 1.2 per cent by weight, positioning the electrodes in proximity to said charge, applying power to said electrodes to direct arcs from said electrodes to said charge to form bore cavities having molten metal therein for consolidation to form a unitary pool of said metal, continuously feeding additional discrete particles of material having said composition into arc flare locations while simultaneously and continuously applying power to melt and to refine said charge, until up to about 80 per cent of the total metal charge is from said discrete particles and said entire charge is melted and refined, and tapping the refined steel from the furnace while the total energy consumption is within the range of from about 250 to about 700 KWH/ton of iron-bearing material.

4. In a method as claimed in claims 1, 2 or 3, said bath comprising molten scrap metal having an initial carbon content higher than the carbon content of the refined steel.

5. In a method as claimed in claims 1, 2 or 3, said iron-bearing material being sponge iron produced in a rotary kiln fed hot to the furnace.

6. In a method as claimed in claims 1, 2 or 3, said iron-bearing material being carburized sponge iron.

7. In a method as claimed in claims 1, 2 or 3, said iron-bearing material being Ti02-bearing sponge iron.

8. In a method as claimed in claims 1, 2 or 3, said iron-bearing material being sponge iron particles of which at least 30 per cent is minus 3/16 inch in size.

9. In a method as claimed in claims 1, 2 or 3, said iron-bearing material being sponge iron particles minus 1/16 inch in size.

10. In a method as claimed in claims 1, 2 or 3, said iron-bearing material being fragmentized scrap with free-flowing mill scale or fine iron ore for providing a source of oxygen.

11. In a method as claimed in claims 1, 2 or 3, adding a carbon-bearing material to said bath before tapping the molten steel for recarburizing the steel as grey cast iron.

12. The method of claims 1, 2 or 3 in which the continuous feeding of the discrete particles into the arc flare locations occurs after the initial charge melting is substantially complete.

13. A method of steelmaking in an electric-arc furnace which comprises forming a bath of carbon-containing molten metal in said furnace having a slag layer, and continuously feeding a discrete, free-flowing, iron-bearing material having a composition within the range of from about 76 per cent to about 99.5 per cent by weight total iron with a residual oxygen content of from about 0.1 per cent to about 1.75 per cent by weight into said slag layer at a rate relative to the power input to maintain the desired bath temperature, and continuously withdrawing said molten metal for subsequent processing.

14. A method of steelmaking in an electric-arc furnace which comprises forming a bath of carbon-containing molten metal in said furnace having a slag layer, and continuously feeding a discrete, free-flowing, iron--bearing material having a composition within the range of from about 76 per cent to about 99.5 per cent by weight total iron with a residual oxygen content of from about 0.1 per cent to about 1.75 per cent by weight into said slag layer at a rate relative to the power input such that the molten metal has substantially reached the desired tap temperature and carbon content concurrent with completion of the feeding of said iron-bearing material to the furnace.

15. In a method as claimed in claims 13 or 14, said bath comprising molten scrap metal having a carbon content higher than the carbon content of the refined steel.

16. In a method as claimed in claims 13 or 14, said iron-bearing material being sponge iron produced in a rotary kiln fed hot to the slag layer.

17. In a method as claimed in claims 13 or 14, said iron-bearing material being carburized sponge iron.

18. In a method as claimed in claims 13 or 14, said iron-bearing material being Ti02-bearing sponge iron.

19. In a method as claimed in claims 13 or 14, said iron-bearing material being sponge iron particles of which at least 30 per cent is minus 3/16 inch in size.

20. In a method as claimed in claims 13 or 14, said iron-bearing material being sponge iron particles minus 1/16 inch in size.

21. In a method as claimed in claims 13 or 14, said iron-bearing material being fragmentized scrap with free-flowing mill scale or fine iron ore for providing a source of oxygen.

22. In a method as claimed in claims 13 or 14, adding a carbon-bearing material to said bath before tapping the molten steel for recarburizing the steel as grey cast iron.

23. The method of claims 13 or 14 in which the continuous feeding of the discrete particles into the bore cavity locations occurs after the initial charge melting is substantially complete.
CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

24. A method of steelmaking which comprises charging an iron-bearing material and slag producing constituents into a refractory lined electric-arc furnace, melting said iron-bearing material and slag producing constituents to form a slag covered open bath of molten metal, continuously charging a discrete, iron-bearing material constituting at least about 15 per cent by weight of the total charge and having a composition within the range of from about 76 per cent to about 99.5 per cent by weight total iron into said bath at a controlled rate relative to power input such that the molten metal has substantially reached the desired carbon content with completion of the feeding to the furnace of said iron-bearing material and any other additives.

25. A method of steelmaking comprising initially charging a refractory lined electric-arc furnace having electrodes with scrap metal, fluxing, carbon and alloying additives, positioning the electrodes in proximity to said charge, applying power to said electrodes to direct arcs from said electrodes to said charge to form consolidated bore cavities having a slag covered bath of molten metal therein, continuously feeding discrete particles of iron-bearing material having a composition within the range of from about 76 per cent to about 99.5 per cent total iron into said bath in proximity to arc flare locations while simultaneously and continuously applying power to melt and to refine said charge until at least about 15 per cent of the total melt charged is from said discrete particles and said entire charge is melted and refined, and tapping the refined steel from the furnace while the total energy consumption is within the range of from about 250 to about 700 KWH/ton of iron-bearing material.

26. A method of steelmaking in a refractory lined electric-arc furnace which comprises forming a bath of carbon-containing molten metal in said furnace having a slag cover and continuously feeding a discrete, free-flowing, iron-bearing material having a composition within the range of from about 76 per cent to about 99.5 per cent by weight total iron into said slag layer at a rate relative to the power input to maintain the desired bath temperature.

27. In a method of steelmaking as claimed in claims 24, 25 or 26, controlling said slag cover such that the arcs from the electrodes are immersed within said slag cover with no substantial direct radiation therefrom to the furnace lining.

28. In a method of steelmaking as claimed in claims 24, 25 or 26, controlling said slag cover such that the arcs from the electrodes are immersed within said slag cover with no substantial direct radiation therefrom to the furnace lining by varying slag electrical resistivity, fluidity, volume and density.

29. In a method of steelmaking as claimed in claims 24, 25 or 26, controlling said slag cover such that the arcs from the electrodes are immersed within said slag cover with no substantial direct radiation therefrom to the furnace lining by varying slag electrical resistivity, fluidity, volume and density, said electrical resistivity being varied by maintaining the slag basicity within the average range of from about 1.0 to about 1.5.

30. In a method of steelmaking as claimed in claims 24, 25 or 26, controlling the rate of charge of iron-bearing material and slag fluidity to avoid the formation of clusters or unmelted material on the slag cover.

31. In a method of steelmaking as claimed in claims 24, 25 or 26, agitating said molten bath during continuous charging of the iron-bearing material by the introduction of oxygen into the molten bath for reaction with carbon to provide a boiling action.

32. In a method of steelmaking as claimed in claims 24, 25 or 26, agitating said molten bath during continuous charging of the iron-bearing material by the introduction of oxygen into the molten bath for reaction with carbon to provide a boiling action, said oxygen being introduced by the charging of discrete ironbearing material having a residual oxygen content within the range of from about 0.1 per cent to about 1.75 per cent.

33. In a method of steelmaking as claimed in claims 24, 25 or 26, agitating said molten bath during continuous charging of the iron-bearing material by the introduction of oxygen into the molten bath for reaction with carbon to provide a boiling action, said oxygen being introduced by the charging of discrete iron-bearing material having a residual oxygen content within the range of from about 0.6 per cent to about 1.2 per cent.

34. In a method of steelmaking as claimed in claims 24, 25 or 26, agitating said molten bath during continuous charging of the iron-bearing material by the introduction of oxygen into the molten bath for reaction with carbon to provide a boiling action, said oxygen being introduced by lancing oxygen or oxygen-enriched air into the molten bath.

35. In a method of steelmaking as claimed in claims 24, 25 or 26, agitating said molten bath during continuous charging of the iron-bearing material by magnetomotive forces.

36. In a method as claimed in claims 26, said bath of molten metal formed by retaining a portion of a preceding heat in the furnace.

37. In a process as claimed in claims 24, 25 or 26, said discrete iron-bearing material being carbon containing sponge iron.

38. In a method as claimed in claims 24, 25 or 26, foaming said slag during continuous charging of the iron-bearing material for envelopment of the arcs by charging iron-bearing material of which at least 30 per cent is minus 3/16 inch in size.

39. In a method as claimed in claims 24, 25 or 26, foaming said slag during continuous charging of the iron-bearing material for envelopment of the arcs by charging an iron-bearing material such as granular sponge iron particles to the slag cover.

40. A method of steelmaking comprising initially charging a refractory lined electric-arc furnace having electrodes with scrap metal, fluxing, carbon and alloying additives, positioning the electrodes in proximity to said charge, applying power to said electrodes to direct arcs from said electrodes to said charge to form bore cavities having slag covered molten metal therein for consolidation to form a unitary pool of said metal, continuously feeding discrete particles of iron-bearing material selected from the. group of sponge iron, iron ore and iron oxide scale having a composition within the range of from about 76 per cent to about 99.5 per. cent by weight total iron with necessary silica, carburizing and oxidizing constituents into arc flare locations to provide slag control for submerging the arcs and facilitating melting of the iron-bearing material, simultaneously and continuously applying power to melt and to refine said charge until at least about 15 per cent of the total metal charge is from said discrete particles and said entire charge is melted and refined, agitating said slag covered molten metal during continuous charging of the iron-bearing material, and tapping the refined steel from the furnace while the total energy consumption is within the range of from about 250 to about 700 KWH/ton of iron-bearing material, and said steel has a carbon content of from about 0.02 per cent to about 1.8 per cent.