Non-Magnetic Steel Structure For A Steel Or Aluminium Making Process

Abstract

A non-magnetic steel structure for a steel or aluminium making process, which non-magnetic steel structure is arranged to enable penetration of a magnetic field from an electromagnetic stirrer or electromagnetic brake into a melt in a vessel for molten metal, wherein the non-magnetic steel structure includes manganese in the range 12-40 mass %.

Claims

1. A fully austenitic high manganese non-magnetic steel structure for a steel or aluminium making process, wherein the non-magnetic steel structure is one of a housing of an electromagnetic stirrer or electromagnetic brake, a window of a ladle, a window of an electromagnetic arc furnace or an aluminium furnace, a window of a casting mould, and a strand support roller for supporting semi-solidified strands, and wherein the non-magnetic steel structure consists of manganese in the range 12-40 mass %, carbon in the range 0.5-1.0 mass %, aluminium in the range 0.1-1.5 mass %, silicon in the range 0.05-1.5 mass %, the remaining content of the non-magnetic steel structure being composed of iron and impurities.

2. The non-magnetic steel structure as claimed in claim 1, wherein the manganese is in the range 12-30 mass %.

3. The non-magnetic steel structure as claimed in claim 1, wherein the manganese is in the range 16-30 mass %.

4. The non-magnetic steel structure as claimed in claim 1, wherein the manganese is in the range 18-30 mass %.

5. The non-magnetic steel structure as claimed in claim 1, wherein the manganese is in the range 20-30 mass %.

6. The non-magnetic steel structure as claimed in claim 1 wherein the manganese is in the range 20-25 mass %.

7. A vessel for molten metal for a continuous casting process, wherein the vessel for molten metal is one of an electric arc furnace and a ladle, which vessel comprises: a refractory material forming an internal lining of the casting vessel, and a non-magnetic steel structure wherein the non-magnetic steel structure is one of a housing of an electromagnetic stirrer or electromagnetic brake, a window of a ladle, a window of an electromagnetic arc furnace or an aluminium furnace, a window of a casting mould, and a strand support roller for supporting semi-solidified strands, and wherein the non-magnetic steel structure consists of manganese in the range 12-30 mass %, carbon in the range 0.5-1.0 mass %, aluminium in the range 0.1-1.5 mass %, silicon in the range 0.05-1.5 mass %, the remaining content of the non-magnetic steel structure being composed of iron and impurities, the non-magnetic steel structure forms part of an external shell of the refractory material and forms a non-magnetic window of the vessel for molten metal.

8. An electromagnetic stirrer or electromagnetic brake for a steel or aluminium making process, wherein the electromagnetic stirrer or electromagnetic brake comprises: an electromagnetic circuit arranged to generate a magnetic field, and a non-magnetic steel structure wherein the non-magnetic steel structure is one of a housing of an electromagnetic stirrer or electromagnetic brake, a window of a ladle, a window of an electromagnetic arc furnace or an aluminium furnace, a window of a casting mould, and a strand support roller for supporting semi-solidified strands, and wherein the non-magnetic steel structure consists of manganese in the range 12-30 mass %, carbon in the range 0.5-1.0 mass %, aluminium in the range 0.1-1.5 mass %, silicon in the range 0.05-1.5 mass %, the remaining content of the non-magnetic steel structure being composed of iron and impurities forming a non-magnetic housing of the electromagnetic circuit.

9. The non-magnetic steel structure as claimed in claim 2, wherein the manganese is in the range 16-30 mass %.

10. The non-magnetic steel structure as claimed in claim 2, wherein the manganese is in the range 18-30 mass %.

11. The non-magnetic steel structure as claimed in claim 3, wherein the manganese is in the range 18-30 mass %.

12. The non-magnetic steel structure as claimed in claim 2, wherein the manganese is in the range 20-30 mass %.

13. The non-magnetic steel structure as claimed in claim 3, wherein the manganese is in the range 20-30 mass %.

14. The non-magnetic steel structure as claimed in claim 2 wherein the manganese is in the range 20-25 mass %.

15. The non-magnetic steel structure as claimed in claim 3 wherein the manganese is in the range 20-25 mass %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0022] FIGS. 1A-B are schematic perspective views of examples of vessels for molten metal comprising non-magnetic steel structures; and

[0023] FIG. 2 schematically shows a perspective view of a steel or aluminium making process.

DETAILED DESCRIPTION

[0024] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0025] A non-magnetic steel structure and examples thereof will be described herein. The non-magnetic steel structure is adapted to be used in a steel or aluminium making process. This can be obtained by proper dimensioning of the non-magnetic steel structure, for example by adapting the thickness of the non-magnetic steel structure to be able to withstand the mechanical requirements in a steel or aluminium making environment, and by means of the chemical composition of the non-magnetic steel structure, which will be elaborated upon in the following.

[0026] The non-magnetic steel structure enables a magnetic field to penetrate through it. This is achieved by including manganese in the non-magnetic steel structure. By means of the manganese, the non-magnetic steel structure may obtain a fully austenitic steel structure. The non-magnetic property of the non-magnetic steel structure is thus obtained.

[0027] Preferably, the manganese is in the range 12-40 mass %, although a higher mass percentage manganese is also envisaged. The manganese replaces the chromium and nickel composition of austenitic stainless steel normally used in continuous casting for the non-magnetic window of vessels for metal making and for the housing of electromagnetic stirrers and electromagnetic brakes.

[0028] According to one variation, the non-magnetic steel structure comprises manganese in the range 12-30 mass %.

[0029] According to one variation, the non-magnetic steel structure comprises manganese in the range 16-30 mass %.

[0030] According to one variation, the non-magnetic steel structure comprises manganese in the range 18-30 mass %.

[0031] According to one variation, the non-magnetic steel structure comprises manganese in the range 20-30 mass %.

[0032] According to one variation, the non-magnetic steel structure comprises manganese in the range 12-25 mass %, for example 16-25 mass %, or 18-25 mass %, or 20-25 mass %.

[0033] The non-magnetic steel structure may further comprise carbon, aluminium and silicon. In general, the non-magnetic steel structure comprises substantially less carbon, aluminium and silicon, in mass %, compared to the manganese content.

[0034] According to one variation the non-magnetic steel structure comprises carbon in the range 0.5-1.0 mass %.

[0035] According to one variation the non-magnetic steel structure comprises aluminium in the range 0.1-1.5 mass %.

[0036] According to one example the non-magnetic steel structure comprises silicon in the range 0.05-1.5 mass %.

[0037] In addition to the above-mentioned chemical elements, the non-magnetic steel structure may comprise iron. According to one variation, the remaining content of the non-magnetic steel structure is composed of iron.

[0038] Table 1 below illustrates the required properties of non-magnetic steel material for electromagnetic applications (EM) in a steel or aluminium making environment. It furthermore provides the corresponding properties for high manganese steel as proposed in this disclosure and for austenitic stainless steel currently used in electromagnetic applications.

TABLE-US-00001 TABLE 1 General requirements of non-magnetic Properties of austenitic steel for EM stainless steel used in Properties applications Properties of HMS EM applications Magnetic Non-magnetic Fully non- Non-magnetic magnetic Magnetic stability Slightly unstable Stable Slightly unstable is okay Relative permeability Maximum 1.5 1.003 1.008 (AISI 304, 316) Resistivity m at 20 C. 0.6 0.62 0.72 (AISI 304), 0.74 (AISI 316) Yield strength (MPa), Min 215 400 215 (AISI 304), annealed 290 (AISI 316) Yield strength at 700 F. Min 130 Currently not 134 (AISI 304), known 159 (AISI 316) Elongation at 50% Uniform 70% (AISI 304), break in 50 mm elongation more 50% (AISI 316) than 50% Machining Good Special tools Good needed Cutting Gas cutting Plasma cutting Gas cutting Welding non-magnetic Acceptable Good Acceptable steel to each other Welding non-magnetic Difficult Good Difficult steel to carbon steel Hardness As austenitic Core 220 HB, skin 123 HB (AISI 304), stainless steel 550 HB after 149 HB (AISI 316), impact annealed Wear resistance Not required Extremely good Not required Materials cost As low as possible Less than half of stainless steel

[0039] The non-magnetic steel structure may for example be the housing of an electromagnetic stirrer such as a ladle stirrer or ladle furnace stirrer, an aluminium furnace stirrer, a strand stirrer, a final strand stirrer, a mould stirrer, an electromagnetic arc furnace stirrer, or an electromagnetic brake e.g. for a caster or mould. In these cases, the non-magnetic steel structure hence forms part of an electromagnetic stirrer or electromagnetic brake. Alternatively, the non-magnetic steel structure could define a non-magnetic window of a vessel for molten metal. In this case the non-magnetic steel structure, i.e. non-magnetic window, is adapted to be inserted into for example a ladle, an electric arc furnace, or a casting mould. Alternatively, the non-magnetic steel structure could form part of a non-magnetic strand support roller arranged to support strands exiting the casting mould. In the latter two cases, i.e. when the non-magnetic steel structure defines a non-magnetic window or a strand support roller, the non-magnetic steel structure enables the penetration of a magnetic field from electromagnetic stirrers.

[0040] In the following, examples of the non-magnetic structures described above, and examples of specific applications thereof will be provided with reference to FIGS. 1-2. FIGS. 1a and 1b show examples of vessels for molten metal which comprise a non-magnetic steel structure according to any variation described herein.

[0041] FIG. 1a depicts an example of a ladle 1 for a steel or aluminium making process. The ladle 1, which may be a treatment ladle and/or a ladle furnace and/or a transport ladle, forms a vessel into which melt may be tapped for example from an electric arc furnace. The ladle 1 comprises a refractory material 3 which forms an inner lining and defines the inner walls of the ladle 1. The ladle 1 further comprises a non-magnetic window 5, in the form of the non-magnetic steel structure. The non-magnetic steel structure hence forms an external wall of the ladle 1. In particular, the non-magnetic steel structure, i.e. the non-magnetic window 5, defines a wall which enables penetration of a magnetic field applied to the non-magnetic steel structure by means of an electromagnetic stirrer, not shown in FIG. 1a.

[0042] Typically, about one third of a ladle wall, facing the electromagnetic stirrer, may be made of non-magnetic material. To illustrate the economic benefits with the non-magnetic steel structure, a 130 tonnes ladle has a non-magnetic window which may weigh about 2.5 tonnes. The price of the HMS described herein is about half of that of austenitic stainless steel, which according to current prices would provide a cost reduction of about 4500 USD per ladle. The typical number of ladles in one mill is about 12, wherein the total savings for one installation is about 54 000 USD. Additional economical savings as well as material savings may be obtained due to the possibility to design non-magnetic windows with thinner walls than in currently existing non-magnetic windows.

[0043] FIG. 1b depicts an example of an electric arc furnace 7 for a steel making process. The electric arc furnace 7 forms a vessel into which solid metal material may be loaded. The electric arc furnace has electrodes 9 arranged to heat the solid metal material and the melt obtained by smelting the solid metal material. The electric arc furnace 7 has a refractory material 11 which defines the inner surface and inner walls of the electric arc furnace 7. The exemplified electric arc furnace 7 further comprises the non-magnetic steel structure in the form of a non-magnetic window 13, which forms an external wall or bottom shell of the refractory material 11 that defines the bottom of the electric arc furnace 7. An electromagnetic stirrer 15 placed below the electric arc furnace 7, and adjacent to the non-magnetic window 13 may thereby provide a magnetic field which is able to penetrate the non-magnetic window 13 into the melt, not shown in FIG. 1b.

[0044] As an example, for a 100 tonnes electric arc furnace, the weight of the non-magnetic window may be about 7 tonnes which can provide an economical saving of about 12500 USD per electric arc furnace by replacing an austenitic stainless steel non-magnetic window with the non-magnetic steel structure, even if the wall thickness is the same. Additional economical and material savings may be made if the thickness of the non-magnetic wall is reduced, which is a possibility because the yield strength is almost twice the yield strength of AISI 304 and about 40% higher than the yield strength of AISI 316.

[0045] The electromagnetic stirrer 15 has a housing 17 which may be a non-magnetic steel structure as described herein. The electromagnetic stirrer 15 further comprises an electromagnetic circuit, arranged within the housing 17, arranged to generate a magnetic field. The non-magnetic steel structure, i.e. the housing 17, enables a magnetic field to penetrate the housing without the induction of eddy currents in the housing.

[0046] As previously noted, in general any electromagnetic stirrer or electromagnetic brake for a steel or aluminium making process, e.g. a ladle stirrer or ladle furnace stirrer, an aluminium furnace stirrer, a strand stirrer, a final strand stirrer, a mould stirrer or an electromagnetic arc furnace stirrer, may comprise a housing which is a non-magnetic steel structure as described herein.

[0047] FIG. 2 shows an example of the production flow in a metal making environment 19, e.g. a steel making environment, with the purpose to illustrate for example where in the steel or aluminium making process the non-magnetic steel structure according to any variation described herein may be utilised. The general production flow is shown by means of the arrows. In the example of FIG. 2, a plurality of vessels for molten metal are provided with a non-magnetic steel structure according to any variation described herein. Furthermore, a plurality of electromagnetic stirrers are shown having a housing in the form of the non-magnetic steel structure according to any variation described herein.

[0048] In FIG. 2 the metal making process begins in the electric arc furnace 7 in which the melt is stirred by means of the electromagnetic stirrer 15. The melt is tapped into the ladle 1, in the example in FIG. 2 exemplified by a ladle furnace/transport ladle. An electromagnetic stirrer 21 is arranged to provide a magnetic field, penetrating the non-magnetic window 5, i.e. a non-magnetic steel structure according to any variation described herein, to stir the melt. The melt is then tapped to another ladle 23, wherein the melt is further tapped into a tundish 25. From the tundish 25, the melt is tapped into a casting mould 27 which has walls 29 made of the non-magnetic steel structure according to any variation described herein. An electromagnetic stirrer 31 is provided around the casting mould 27, arranged to stir the melt tapped into the casting mould 27. A semi-solidified strand 37 exits the casting mould 27 and is supported by strand support rollers 33, which together with the casting mould 27 defines the caster, as the semi-solidified strand 37 moves by means of the motor-driven support rollers 33 through the caster. An electromagnetic stirrer 35 is arranged behind the strand support rollers 33 to stir the semi-solidified strand 37.

[0049] For both the electromagnetic stirrer or electromagnetic brake housing and vessel for molten metal, the entire housing and/or the entire outer walls of the vessel for molten metal could be a non-magnetic steel structure according to any variation described herein. Alternatively, only the portion of the housing and/or the vessel for molten metal which should be penetrable to a magnetic field may be a non-magnetic steel structure according to any variation described herein.

[0050] An example of a suitable HMS material is manufactured by the company POSCO, called High Mn TWIP. In general any HMS which has a chemical composition according to the examples described herein may be utilised.

[0051] The non-magnetic steel structures, and electromagnetic stirrers, brakes and vessels for molten metal comprising such a non-magnetic steel structure, may beneficially be utilised in metal making, for example in steel production or aluminium production.

[0052] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.