KR101767748B1 - Method for manufacturing a duplex stainless steel sheet containing high nitrogen with good surface quality - Google Patents
Method for manufacturing a duplex stainless steel sheet containing high nitrogen with good surface quality Download PDFInfo
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- KR101767748B1 KR101767748B1 KR1020150156701A KR20150156701A KR101767748B1 KR 101767748 B1 KR101767748 B1 KR 101767748B1 KR 1020150156701 A KR1020150156701 A KR 1020150156701A KR 20150156701 A KR20150156701 A KR 20150156701A KR 101767748 B1 KR101767748 B1 KR 101767748B1
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- molten steel
- nitrogen
- duplex stainless
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
- B22D11/002—Stainless steels
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Abstract
The present invention provides a method for manufacturing a high nitrogen duplex stainless steel capable of preventing the surface of a high nitrogen duplex stainless steel from swelling when producing a high nitrogen duplex stainless steel through a twin roll thin plate casting process.
Description
The present invention relates to high nitrogen duplex stainless steels, and more particularly, to a method for producing high nitrogen duplex stainless steels having excellent surface quality through a twin roll thin plate casting process.
In general, the twin roll thin plate casting process refers to a process comprising continuously supplying molten steel between a pair of rotating casting rolls to continuously produce thin plate products of several mm thickness from the molten steel. As shown in FIG. 1, a twin roll type thin
The molten steel is received in the
However, when the high nitrogen duplex stainless steel is produced through the twin roll type thin plate casting process as described above, the nitrogen gas is released during the solidification due to the difference in solubility of nitrogen and the surface is swollen as shown in the photograph of the surface of the duplex stainless steel of FIG. A phenomenon of rising may occur.
As shown in FIG. 2, when the cross section of the duplex stainless steel whose surface is swollen is observed, it can be seen that the central portion of the steel sheet is split and spreaded as shown in FIG. 3A on the swollen portion. In addition, as shown in FIG. 3B, it can be confirmed that pores are gathered in the central portion of the steel sheet. Therefore, it can be seen that the swelling phenomenon is caused by expansion of the nitrogen gas generated in the center portion of the steel sheet.
High nitrogen duplex stainless steels have a high nitrogen solubility of 2500 ~ 3500ppm in the liquid phase, but the solubility of nitrogen in the solid phase is reduced to 1200ppm. Therefore, if the high nitrogen duplex stainless steel of 2500 ppm is slowly solidified, nitrogen gas of 1300 ppm which is a difference in solubility is generated, and the nitrogen gas expands and a lot of bubbles are generated therein.
For the above reasons, it is difficult to cast high nitrogen duplex stainless steel by ordinary casting or ingot casting. On the other hand, in the twin roll thin plate casting process, the occurrence of bubbles due to rapid cooling and solidification can be reduced, and high nitrogen duplex stainless steel can be cast. However, when the nitrogen in the molten steel is increased through the twin roll thin plate casting process, the surface may be swollen due to the generation of nitrogen gas as shown in Figs. 2, 3a and 3b. in need.
The present invention provides a method for producing high nitrogen duplex stainless steel having excellent surface quality when manufacturing high nitrogen duplex stainless steel through a twin roll thin plate casting process.
One aspect of the present invention is a method for producing high nitrogen duplex stainless steel through a twin roll lamination casting process for producing a thin sheet by passing molten steel through two casting rolls rotating in opposite directions, Molybdenum containing molybdenum containing at least 0.06% Cr, 19.0 to 21.0% Mn, 2.8 to 3.2% Mn, 0.55 to 0.8% Si, 0.5 to 1.5% Ni, 2200 ppm or more N, The present invention provides a method for producing a high nitrogen duplex stainless steel having an excellent surface quality which maintains the amount of nitrogen in the molten steel to 2500 ppm or less before supplying the molten steel to a roll.
Another aspect of the present invention is a method for producing high nitrogen duplex stainless steel through a twin roll thin sheet casting process for producing a thin sheet by passing molten steel between two casting rolls rotating in opposite directions, : Fe, and other unavoidable impurities, including 0.02 to 0.06% of Cr, 19.0 to 21.0% of Cr, 2.8 to 3.2% of Mn, 0.55 to 0.8% of Si, 0.5 to 1.5% of Ni, The temperature of the molten steel is raised at a rate that the temperature of the molten steel is increased by 2 ° C or more based on 1520 ° C each time the amount of nitrogen in the molten steel is increased from 2500ppm to 10ppm, And the upper limit temperature is 1540 DEG C, which is excellent in surface quality.
According to the present invention, by manufacturing the high nitrogen duplex stainless steel through the twin roll type thin plate casting process, the surface of the finished high nitrogen duplex stainless steel can be prevented from being swollen.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a typical twin roll laminate casting apparatus.
FIG. 2 is a photograph of a phenomenon in which a surface of a high-nitrogen duplex stainless steel is swollen when a conventional method is manufactured.
FIG. 3A is a photograph of a section of the swollen portion in FIG. 2; FIG.
FIG. 3B is a photograph of a section of the slightly bulged portion in FIG.
4 is a graph showing a case where the surface of the high nitrogen duplex stainless steel is swollen according to the change of nitrogen of the molten steel.
5 is a graph showing a case where the surface of the high nitrogen duplex stainless steel is swollen according to the nitrogen amount of the molten steel and the molten steel temperature.
The present invention relates to a method for producing high nitrogen duplex stainless steels with good surface quality by preventing double plate defects caused by surface component developments occurring when high nitrogen duplex stainless steels are produced by a twin roll thin plate casting process .
The high nitrogen duplex stainless steel according to the present invention can be obtained by adding nitrogen to the general duplex stainless steel as high as 2,200 to 2,700ppm to adequately increase the stability of the austenite phase in the steel to adjust the rate at which martensite is generated during the transformation process, It is a steel improved to more than 40% level and improved formability. It is therefore very important to add high nitrogen to high nitrogen duplex stainless steels.
A method for producing a high nitrogen duplex stainless steel having excellent surface quality according to the present invention is characterized by comprising 0.02 to 0.06% of C, 19.0 to 21.0% of Cr, 2.8 to 3.2% of Mn, 0.55 to 0.8% of Si, 0.5 to 0.8% of Ni, 0.5 To 1.5%, N: 2200 ppm or more, the remainder Fe and other unavoidable impurities is supplied to the casting roll, the amount of nitrogen in the molten steel is kept at 2500 ppm or less.
When the high nitrogen duplex stainless steel of the present invention is produced through the twin roll thin plate casting process, that is, when the amount of nitrogen in the molten steel is maintained at 2500 ppm or less until the molten steel is supplied to the casting roll, It is possible to prevent the surface of the duplex stainless steel from swelling. Nitrogen in molten steel can contain a large amount of 3000 ppm or more. However, when the ferrite solid appears in the process of solidification, the nitrogen solubility in the solid decreases to 1200 ppm, and the remaining nitrogen segregates in the molten steel. Nitrogen concentration in the molten steel increases, and when it exceeds a certain level, nitrogen becomes a gas in the molten steel. When the gas pressure is higher than the static pressure of the molten steel, it expands to become a nitrogen pinhole. Therefore, the segregated nitrogen in the molten steel becomes a gas, and the pressure thereof is higher than the static pressure of the molten steel is about 2,400 to 2,500 ppm which is twice the nitrogen solubility of the ferrite phase.
Further, the method for producing high nitrogen duplex stainless steel having excellent surface quality of the present invention is characterized in that, every time when the amount of nitrogen in the molten steel is increased from 2500 ppm to 10 ppm until molten steel having the above-mentioned composition range is supplied to the casting roll, It is preferable to raise the temperature of the molten steel at a rate that raises the temperature by 2 DEG C or more based on 1520 DEG C, and more preferably, the temperature of the molten steel is increased at a rate of raising the temperature of the molten steel by 2 DEG C .
If the amount of nitrogen in the molten steel is maintained at 2500 ppm or less, the surface of the produced high-nitrogen duplex stainless steel can be prevented from swelling. However, in order to improve the material and corrosion resistance of the high nitrogen duplex stainless steel, It is advantageous. Therefore, in order to increase the allowable range of nitrogen, there is a method of raising the temperature of the molten metal to improve the solubility of nitrogen, and maintaining the temperature of the molten steel at a rate that raises the temperature by 2 ° C or more every time the temperature is increased from 2500ppm to 10ppm And more advantageously, it is more preferable to maintain the temperature of the molten steel at a rate of raising the temperature by 2 DEG C each time the temperature is increased by 10 ppm. The reason for raising the temperature in such a ratio is that if the temperature of the molten steel is increased, the production of equiaxed definition is delayed in the twin roll thin plate casting process. That is, when the temperature of the molten steel is low and equiaxed crystals are generated, nitrogen is concentrated around the equiaxed crystal, and nitrogen bubbles are generated and expanded. However, if the temperature of the molten steel is high and no equiaxed crystal is formed in the molten steel, the nitrogen is dissolved in the molten steel, so that no gaseous nitrogen is produced and the surface is not swollen unless the gaseous nitrogen is produced. When the amount of nitrogen in the molten steel is 2505 ppm, it is preferable that the temperature of the molten steel is increased by 1 ° C to 1521 ° C or more. When the amount of nitrogen in the molten steel is 2510ppm, the temperature of the molten steel is preferably increased by 2 ° C to 1522 ° C And when the amount of nitrogen in the molten steel is 2520 ppm, the temperature of the molten steel is preferably 1524 ° C which is increased by 4 ° C.
In the present invention, the upper limit temperature of the molten steel is preferably 1540 ° C.
That is, even if the temperature of the molten steel is maintained at a rate of raising the temperature by 2 ° C or more every time the amount of nitrogen in the molten steel is increased from 2500 ppm to 10 ppm, the upper limit can not exceed 1540 ° C.
If the temperature of the molten steel exceeds 1540 DEG C, there is a high possibility that a defect occurs at an edge portion of the cast strip, which is not preferable.
In the present invention, when the amount of nitrogen in the molten steel is 2500 ppm or more, it is preferable to increase the descending force of the casting roll by 25% or more as compared with when the amount of nitrogen in the molten steel is less than 2500 ppm. When the amount of nitrogen in the molten steel is 2500 ppm or more, it is possible to prevent the surface of the high-nitrogen duplex stainless steel from swelling only by raising the temperature of the molten steel at the above-mentioned ratio. However, It is possible to prevent the surface of the steel sheet from swelling more effectively. Here, it is preferable that the reduction force when the amount of nitrogen in the molten steel is less than 2500 ppm is preferably reduced by a ratio of 8 ton per width of the casting roll (8 ton / width of the strip). That is, when the amount of nitrogen in the molten steel is less than 2500 ppm and the width of the casting roll is 1312 mm, if a descending force is applied to the width of 1312 mm of the casting roll to reduce 8 tons, the amount of nitrogen in the molten steel is 2500 ppm or more , It is desirable to apply a descending force of 10 tons or more, which is 25% more than the reduction force for reducing 8 tons to the width of 1312 mm of the casting roll.
Here, as described above, solidification is uniformly received in the casting roll width direction at a casting roll reduction force of about 8 tons. If the reduction force is increased by 25% and the reduction force of the casting roll is increased to 10 tons, it can be achieved by reducing the rotation speed of the casting roll while keeping the casting roll gap constant. When the casting roll reduction force is increased, the thickness of the solidification shell produced by the two casting rolls is increased, and the rigidity of the solidification shell and the bonding strength of the two solidification shells are increased. Such an increase in the bonding force supports the force due to the expansion of the nitrogen gas, thereby preventing surface component development.
The phenomenon in which the surface of the high nitrogen duplex stainless steel swells is a phenomenon in which the pressure of the nitrogen gas gathered at the center of the steel plate overcomes the bonding force of the steel sheet and pushes the surface of the steel sheet. Therefore, If the force is increased, it is possible to prevent the surface of the high-nitrogen duplex stainless steel from swelling completely.
Hereinafter, the present invention will be described in detail with reference to examples of the present invention.
[ Example One]
The molten steel having the nitrogen content as shown in FIG. 4 was produced by 32 rolls of the twin roll type thin sheet casting apparatus shown in FIG. 1, and the high nitrogen duplex stainless steel was observed with the surface components, The arrow indicates the part of the nitrogen content where the part phenomenon occurred. In this case, the content is 0.03% of C, 20.0% of Cr, 3.1% of Mn, 0.7% of Si, 1.2% of Ni, the balance of Fe and other unavoidable impurities, and the temperature of the molten steel is 1525 ± 5 ° C And 8 tons of pressure drop was applied. As a result of the test, when the nitrogen content of molten steel is 2500 ppm or less, surface parts are not generated, whereas when the nitrogen content of molten steel exceeds 2500 ppm, surface parts are generated.
[ Example 2]
The steel according to any one of claims 1 to 3, wherein the steel contains 0.03% of C, 20.0% of Cr, 3.1% of Mn, 0.7% of Si, 1.2% of Ni and the balance Fe and other unavoidable impurities, Was controlled to a molten steel temperature shown in Table 1, and a high nitrogen duplex stainless steel was produced by the twin roll type thin sheet casting apparatus shown in FIG. 1, and the presence or absence of surface parts was observed. The results are shown in Table 1 below. The results of Table 1 are shown schematically in FIG.
(ppm)
(° C)
As shown in Table 1 and FIG. 5, when the nitrogen content of the molten steel is 2500 ppm or more, the surface component is not generated in the case where the molten steel temperature is controlled according to the present invention (Examples 1-5), whereas the nitrogen content (Comparative Example 1-6) in which the molten steel temperature is controlled under the condition deviating from the present invention when it exceeds 2500 ppm.
[ Example 3]
The steel sheet according to any one of claims 1 to 3, which contains 0.03% of C, 20.0% of Cr, 3.1% of Mn, 0.7% of Si, 1.2% of Ni, balance Fe and other unavoidable impurities, After the temperature was controlled to the molten steel temperature shown in Table 2, a high nitrogen duplex stainless steel was produced by the double-roll type thin sheet casting apparatus shown in Table 1 under the reduced load shown in Table 2, Table 2 shows the results.
(ppm)
(° C)
(25% increase)
(50% increase)
As shown in Table 2, as in Comparative Example 7, a phenomenon that the surface of the high nitrogen duplex stainless steel was swollen when a total of 8 tons was given to 1312 mm, which is the width of the casting roll, It can be confirmed that the phenomenon of swelling when the rolling force of the casting roll is increased to 10 tons and 12 tons as in Examples 6 and 7 can be more completely prevented.
While the illustrative embodiments of the present invention have been shown and described, various modifications and alternative embodiments may be made by those skilled in the art. Such variations and other embodiments will be considered and included in the appended claims, all without departing from the true spirit and scope of the invention.
100: twin roll thin sheet casting apparatus 110: casting roll
120: Ladle 130: Tundish
140: injection nozzle 150: meniscus shield
160: brush roll 170: edge dam
180: Lamination
Claims (5)
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.02 to 0.06% of C, 19.0 to 21.0% of Cr, 2.8 to 3.2% of Mn, 0.55 to 0.8% of Si, 0.5 to 1.5% of Ni, 2200 ppm or more of N, Wherein the amount of nitrogen in the molten steel is maintained at 2500 ppm or less before the molten steel is supplied to the casting roll.
Ni: 0.5 to 1.5%, N: 2200 to 2700 ppm, and the balance Fe and other unavoidable impurities are contained in an amount of 0.02 to 0.06% of C, 19.0 to 21.0% of Cr, 2.8 to 3.2% of Mn, 0.55 to 0.8% Each time the amount of nitrogen in the molten steel is increased from 2500 ppm to 10 ppm, the temperature of the molten steel is raised at a rate that the temperature of the molten steel is increased by 2 ° C or more based on 1520 ° C until molten steel containing impurities is supplied to the casting roll And an upper limit temperature of the molten steel is 1540 DEG C. The method of manufacturing a high nitrogen duplex stainless steel according to claim 1,
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US14/954,218 US9975170B2 (en) | 2014-12-11 | 2015-11-30 | Method for manufacturing duplex stainless steel sheet having high nitrogen content and good surface quality |
| CN201510921116.3A CN105695899A (en) | 2014-12-11 | 2015-12-11 | Method for manufacturing duplex stainless steel sheet having high nitrogen content and good surface quality |
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| KR20140178488 | 2014-12-11 | ||
| KR1020140178488 | 2014-12-11 |
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| KR101767748B1 true KR101767748B1 (en) | 2017-08-14 |
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