Process for producing raw steel and aggregate for production thereof

Abstract

The invention relates to a process for producing low-nitrogen crude steel. This process includes melting directly reduced iron and/or scrap in a melting furnace with arc resistance heating to give a metallic melt and a slag. The metallic melt is removed from the melting furnace and used to charge a converter. The metallic melt is refined in the converter to give liquid crude steel. The liquid crude steel is tapped having a nitrogen content [N] of not more than 50 ppm, especially of not more than 30 ppm.

Claims

1. A process for producing low-nitrogen crude steel, comprising the following process steps: melting directly reduced iron and/or scrap in a melting furnace with arc resistance heating with a reducing atmosphere to give a metallic melt and a slag, removing the metallic melt from the melting furnace and using it to charge a converter, refining the metallic melt, wherein the nitrogen content [N] is lowered when the nitrogen content [N] of the metallic melt is above 50 ppm, or kept low or lowered further when the nitrogen content [N] of the metallic melt is below 50 ppm, in the converter to give liquid crude steel and tapping the liquid crude steel having a nitrogen content [N] of 50 ppm or less, wherein the metallic melt, immediately prior to the refining, has a ratio of carbon content to nitrogen content [C]/[N] of at least 20.

2. The process as claimed in claim 1, wherein the carbon content [C] of the metallic melt is increased in the melting furnace and/or in the converter.

3. The process as claimed in claim 2, wherein the metallic melt, immediately prior to the refining, has a ratio of carbon content to nitrogen content [C]/[N] of at least 100.

4. The process as claimed in claim 3, wherein the iron content (Fe) of the slag in the melting furnace is less than 30 wt. % [30 wt.-%] by weight.

5. The process as claimed in any of claim 4, wherein the metallic melt immediately prior to the refining has the following contents of trace elements: carbon [C]: at least 1.0 wt. %, not more than 5.0 wt. %, nitrogen [N]: not more than 450 ppm, optionally oxygen [O]: 0-50 ppm, optionally phosphorus [P]: 100-1500 ppm, optionally sulfur [S]: 0-1500 ppm, optionally silicon [Si]: 0-1.5 wt. %, optionally manganese [Mn]: 0-0.5 wt. %.

6. The process as claimed in claim 5, wherein the tapped liquid crude steel has the following contents of trace elements: carbon [C]: not more than 600 ppm, nitrogen [N]: not more than 50 ppm, oxygen [O]: at least 300 ppm, not more than 2300 ppm, optionally phosphorus [P]: 0-400 ppm, optionally sulfur [S]: 0-1500 ppm, optionally silicon [Si]: 0-300 ppm, optionally manganese [Mn]: 0-0.4 wt. %.

7. The process as claimed in claim 6, wherein the refining involves using a retractable water-cooled probe to blow oxygen onto the metallic melt, wherein the blowing time is at least 10 minutes and wherein argon is blown in via nozzles in the converter base.

8. The process as claimed in claim 7, comprising the following preceding step: producing directly reduced iron from iron ore in a shaft furnace with consumption of electrolytically produced hydrogen or with consumption of natural gas or with consumption of coking furnace gas.

9. The process as claimed in claim 2, wherein the metallic melt, immediately prior to the refining, has a ratio of carbon content to nitrogen content [C]/[N] of at least 200.

10. The process as claimed in claim 2, wherein the metallic melt, immediately prior to the refining, has a ratio of carbon content to nitrogen content [C]/[N] of at least 500.

11. The process as claimed in claim 2, wherein the metallic melt, immediately prior to the refining, has a ratio of carbon content to nitrogen content [C]/[N] of at least 1000.

12. A process for producing an ultra-low carbon steel, comprising the following steps: producing low-nitrogen crude steel by the process as claimed in claim 8, secondary metallurgical treatment of the crude steel produced, casting the crude steel in a continuous casting plant.

13. The process as claimed in claim 12, comprising the addition of a direct reduction plant upstream of the melting furnace with arc resistance heating.

Description

(1) The invention is elucidated in more detail by the figures. The figures show:

(2) FIG. 1 a flow diagram of the process of the invention for production of crude steel

(3) FIG. 2 a schematic diagram of a melting furnace with arc resistance heating

(4) FIG. 3 a schematic diagram of a converter

(5) FIG. 4 a schematic diagram of a direct reduction plant

(6) FIG. 1 shows a flow diagram of the process of the invention for production of low-nitrogen crude steel. In a first optional step, directly reduced iron is produced from iron ore in a shaft furnace. Alternatively, the directly reduced iron may also be bought in. In a subsequent step, the directly reduced iron is introduced into a melting furnace with arc resistance heating. In addition, it is optionally possible to introduce scrap as well into the melting furnace. In the melting furnace, iron and/or scrap are melted to give a metallic melt and a slag. Subsequently, the metallic melt is removed from the melting furnace and used to charge a converter. In the converter, the metallic melt is refined to give liquid crude steel. The liquid crude steel is subsequently tapped in the converter.

(7) FIG. 2 shows a melting furnace with arc resistance heating 13 in the form of a submerged electric arc furnace (SAF). The melting furnace 13 comprises a furnace vessel 15 lined on the inside with refractory material 17. Three electrodes 21, which are operated with AC, project into the interior 19. The metallic melt 23 is already within the interior 19. A layer of slag 25 has settled out on the metallic melt 23. Three electrodes 21 project into the slag 25. A current is thus formed between the electrodes 21, which runs through the slag layer 25 and heats the slag layer 25 through resistance heating. This heating is transmitted from the slag layer 25 to the metallic melt 23. The interior 19 is concluded at the top by a lid 29, through which the three electrodes 21 project. The electrodes 21 are designed as Sderberg electrodes.

(8) FIG. 3 shows a converter 31. The converter 31 comprises a converter vessel 33 having a refractory lining 35. In the converter vessel 33 is a metallic melt 37. A probe 39 that projects from the top into the converter vessel 33 can be used to blow oxygen onto the surface of the metallic melt 37. The converter 41 is closed at the top by a lid 38, through which the probe 39 is conducted. The converter base 41 has nozzles 43 through which an inert gas can be blown into the converter 31. The converter 31 has a lateral tapping orifice 45 through which the liquid crude steel can be removed by tilting the converter vessel 33 after the refining.

(9) FIG. 4 shows a schematic diagram of a direct reduction plant 51. The direct reduction plant 51 comprises the shaft furnace 53. In the shaft furnace 53 there is a reduction zone 55 and a cooling zone 57. The reduction zone 55 is disposed above the cooling zone 57. The shaft furnace 53 is filled with iron ore from the top. At the lower end of the shaft furnace 53, the directly reduced iron produced can be removed. At the same time, reduction gas is admitted into the shaft furnace 53 through the inlet 59. The reduction gas then flows through the iron ore in the reduction zone 55. Unconsumed reduction gas then exits again together with any gaseous reaction products at the outlet 61. The reduction gas thus flows through the reduction zone 55 counter to a direction of movement of the iron ore. After leaving the reduction zone 55, the directly reduced iron enters the cooling zone 57. In the cooling zone 57, the cooling gas flows through the iron sponge counter to the direction of movement of the iron. For this purpose, the cooling gas enters the shaft furnace 53 through the inlet 63. Unconsumed cooling gas exits again at the outlet 65 together with any gaseous reaction products. It is of course also possible for a certain proportion of the cooling gas to enter the reduction zone 55. It is likewise possible for a certain proportion of the reduction gas to enter the cooling zone 57. The cooling gas is preferably carbon-containing in order to bring about carburization of the directly reduced iron produced.