WO2015029106A1 - 連続鋳造方法 - Google Patents
連続鋳造方法 Download PDFInfo
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- WO2015029106A1 WO2015029106A1 PCT/JP2013/072721 JP2013072721W WO2015029106A1 WO 2015029106 A1 WO2015029106 A1 WO 2015029106A1 JP 2013072721 W JP2013072721 W JP 2013072721W WO 2015029106 A1 WO2015029106 A1 WO 2015029106A1
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- WIPO (PCT)
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- stainless steel
- tundish
- molten
- continuous casting
- molten 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
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/041—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds for vertical casting
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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
- B22D11/106—Shielding the molten jet
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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
-
- 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
- B22D11/111—Treating the molten metal by using protecting powders
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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
- B22D11/116—Refining the metal
- B22D11/117—Refining the metal by treating with gases
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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
- B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
- B22D27/003—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting by using inert gases
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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
- B22D31/00—Cutting-off surplus material, e.g. gates; Cleaning and working on castings
- B22D31/002—Cleaning, working on castings
Definitions
- This invention relates to a continuous casting method.
- molten iron is produced by melting raw materials in an electric furnace, and the produced molten iron removes carbon that deteriorates the properties of stainless steel in a converter and a vacuum degassing device. Refining including decarburization is performed to form molten steel, and then the molten steel is continuously cast to solidify to form a plate-like slab or the like. In the refining process, the final components of the molten steel are adjusted.
- Patent Document 1 describes a method for producing a continuous casting (continuous casting) slab using argon gas as an inert gas.
- the present invention has been made to solve such problems, and provides a continuous casting method that suppresses an increase in nitrogen content when casting a slab (metal piece) and reduces surface defects. With the goal.
- the continuous casting method injects molten metal in a ladle into a lower tundish, continuously injects the molten metal in the tundish into a mold, and releases metal pieces.
- nitrogen gas is supplied as a sealing gas around the molten metal in the tundish, and a spout of the injection nozzle for injecting the molten metal in the ladle into the tundish is provided in the tundish.
- the molten metal is injected into the tundish through the injection nozzle while being immersed in the molten metal, and the molten metal in the tundish is injected into the mold.
- the continuous casting method of the present invention it is possible to suppress an increase in the nitrogen content when casting a metal piece and reduce surface defects.
- FIG. 1 It is a schematic diagram which shows the structure of the continuous casting apparatus used with the continuous casting method which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the continuous casting apparatus at the time of casting with the continuous casting method which concerns on Embodiment 2 of this invention. It is the figure which compared the number of air bubbles which arise in a stainless steel piece between Example 3 and Comparative Example 3. FIG. It is the figure which compared the bubble number which arises in a stainless steel piece between Example 4 and Comparative Example 4. FIG. It is the figure which compared the bubble number which arises in a stainless steel piece between the case where a long nozzle is used in the comparative example 3 and the comparative example 3. FIG.
- Embodiment 1 FIG.
- a continuous casting method according to Embodiment 1 of the present invention will be described with reference to the accompanying drawings.
- a method for continuously casting stainless steel will be described.
- stainless steel is manufactured by performing a melting process, a primary refining process, a secondary refining process, and a casting process in this order.
- scrap or alloy which is a raw material for stainless steel
- scrap or alloy which is a raw material for stainless steel
- the primary refining process a rough decarburization process is performed to remove carbon contained by blowing oxygen into the molten iron in the converter, thereby producing a stainless steel molten steel and slag containing carbon oxides and impurities.
- Produces In the primary refining process, the components of the molten stainless steel are analyzed, and the components are coarsely adjusted by introducing an alloy so as to approach the target components. Furthermore, the molten stainless steel produced in the primary refining process is delivered to the ladle and transferred to the secondary refining process.
- molten stainless steel is put into a vacuum degassing device together with a ladle, and finish decarburization processing is performed. And pure stainless molten steel produces
- the ladle 1 is taken out from the vacuum degassing apparatus and set in the continuous casting apparatus (CC) 100.
- the molten stainless steel 3 of the ladle 1 that is a molten metal is poured into the continuous casting apparatus 100 and further cast into a slab-like stainless steel piece 3c as a metal piece by the mold 105 provided in the continuous casting apparatus 100, for example.
- the cast stainless steel piece 3c is hot-rolled or cold-rolled into a hot-rolled steel strip or a cold-rolled steel strip in the following rolling process (not shown).
- the continuous casting apparatus 100 has a tundish 101 which is a container for temporarily receiving the molten stainless steel 3 sent from the ladle 1 and sending it to the mold 105.
- the tundish 101 has a main body 101b whose upper part is open, an upper lid 101c that closes the upper part of the main body 101b and blocks it from the outside, and an immersion nozzle 101d that extends from the bottom of the main body 101b.
- the interior space 101a closed by these inside with the main body 101b and the upper cover 101c is formed.
- the immersion nozzle 101d opens from the bottom of the main body 101b to the inside 101a at the inlet 101e.
- the ladle 1 is set above the tundish 101, and a long nozzle 2 that is an injection nozzle for tundish extending through the upper lid 101 c of the tundish 101 to the inside 101 a is connected to the bottom of the ladle 1. ing. And the spout 2a of the lower front-end
- a plurality of gas supply nozzles 102 are provided on the upper lid 101 c of the tundish 101.
- the gas supply nozzle 102 is connected to a gas supply source (not shown), and sends a predetermined gas from the upper side to the lower side to the inside 101 a of the tundish 101.
- the upper lid 101c of the tundish 101 is provided with a powder nozzle 103 for pouring tundish powder (hereinafter referred to as TD powder) 5 (see FIG. 2) into the inside 101a of the tundish 101.
- the powder nozzle 103 is connected to a TD powder supply source (not shown), and sends the TD powder 5 to the inside 101 a of the tundish 101 from the upper side to the lower side.
- n5 consists of synthetic slag agents etc., and covers the surface of the molten stainless steel 3, thereby preventing the surface of the molten stainless steel 3 from being oxidized, maintaining the temperature of the molten stainless steel 3, and dissolving and absorbing the inclusions in the molten stainless steel 3.
- the powder nozzle 103 and the TD powder 5 are not used.
- a bar-like stopper 104 that is movable in the vertical direction is provided above the immersion nozzle 101d, and the stopper 104 extends from the inside 101a of the tundish 101 to the outside through the upper lid 101c of the tundish 101.
- the stopper 104 is capable of closing the inlet 101e of the immersion nozzle 101d at its tip by moving downward, and pulling the stainless steel 3 in the tundish 101 upward by pulling upward from the closed state of the inlet 101e. While flowing into the immersion nozzle 101d, the flow rate of the molten stainless steel 3 can be controlled by adjusting the opening area of the inlet 101e according to the amount of pulling up.
- a space between the penetrating portion of the upper lid 101c in the stopper 104 and the upper lid 101c is sealed and airtightness is maintained.
- the tip 101f of the immersion nozzle 101d at the bottom of the tundish 101 extends into the through hole 105a of the lower mold 105 and opens laterally.
- the through hole 105a of the mold 105 has a rectangular cross section and penetrates the mold 105 vertically.
- the through-hole 105a is configured such that the inner wall surface thereof is water-cooled by a primary cooling mechanism (not shown), and the molten stainless steel 3 inside is cooled and solidified to form a slab 3b having a predetermined cross section.
- a plurality of rolls 106 are provided at intervals to draw and transfer the slab 3b formed by the mold 105 downward.
- a secondary cooling mechanism (not shown) is provided between the rolls 106 to sprinkle and cool the slab 3b.
- the ladle 1 including the stainless steel 3 after the secondary refining is installed above the tundish 101. Further, a long nozzle 2 is attached to the bottom of the ladle 1, and the tip of the long nozzle 2 having the spout 2 a extends to the inside 101 a of the tundish 101. At this time, the stopper 104 closes the inlet 101e of the immersion nozzle 101d.
- a valve (not shown) provided in the long nozzle 2 is opened, and the molten stainless steel 3 in the ladle 1 flows down in the long nozzle 2 by the action of gravity and flows into the interior 101 a of the tundish 101.
- nitrogen (N 2 ) gas 4 having solubility in the molten stainless steel 3 is injected from the gas supply nozzle 102 into the interior 101 a of the tundish 101.
- air containing impurities existing in the interior 101 a of the tundish 101 is pushed out of the tundish 101 by the nitrogen gas 4, and the nitrogen gas 4 filling the interior 101 a seals the periphery of the molten stainless steel 3. Do not contact with other gases such as air.
- the surface 3 a of the molten stainless steel 3 inside the tundish 101 rises due to the flowing molten stainless steel 3.
- the rising surface 3a immerses the spout 2a of the long nozzle 2 in the molten stainless steel 3
- the depth of the molten stainless steel 3 in the interior 101a of the tundish 101 reaches a predetermined depth D
- the stopper 104 is raised, and the interior 101a
- the molten stainless steel 3 flows into the through hole 105a of the mold 105 through the immersion nozzle 101d, and casting starts.
- the molten stainless steel 3 in the ladle 1 is poured into the inside 101 a of the tundish 101 through the long nozzle 2, and the molten stainless steel 3 is replenished.
- the long nozzle 2 When the depth of the molten stainless steel 3 in the interior 101a is a predetermined depth D, the long nozzle 2 is formed in the molten stainless steel 3 so that the spout 2a has a depth of about 100 to 150 mm from the surface 3a of the molten stainless steel 3. Penetration is preferred. If the long nozzle 2 penetrates deeper than the above depth, it becomes difficult to pour out the molten stainless steel 3 from the spout 2a of the long nozzle 2 due to the resistance caused by the internal pressure of the molten stainless steel 3 accumulated in the interior 101a.
- the spout 2a is exposed when the surface 3a of the molten stainless steel 3 controlled to be maintained near a predetermined position at the time of casting fluctuates as described later. Then, there is a possibility that the poured molten stainless steel 3 hits the surface 3a and involves the nitrogen gas 4.
- the molten stainless steel 3 flowing into the through hole 105a of the mold 105 is cooled by a primary cooling mechanism (not shown) in the process of flowing through the through hole 105a, and the inner wall surface side of the through hole 105a is solidified to form a solidified shell 3ba.
- the formed solidified shell 3ba is pushed out of the mold 105 downward by the solidified shell 3ba newly formed above in the through hole 105a.
- the mold powder is supplied to the inner wall surface of the through hole 105a from the tip 101f side of the immersion nozzle 101d.
- the mold powder melts in the slag on the surface of the molten stainless steel 3, prevents oxidation of the surface of the molten stainless steel 3 in the through hole 105a, lubricates between the mold 105 and the solidified shell 3ba, in the through hole 105a. It plays a role of keeping the surface of the molten stainless steel 3 warm.
- a cast slab 3b is formed by the extruded solidified shell 3ba and the unsolidified molten stainless steel 3 inside, and the slab 3b is sandwiched from both sides by the roll 106 and further drawn downward.
- the drawn slab 3b is sprinkled and cooled by a secondary cooling mechanism (not shown) in the process of passing through between the rolls 106 to completely solidify the molten stainless steel 3 inside.
- the slab 3b is drawn from the mold 105 by the roll 106, and a new slab 3b is formed in the mold 105, whereby the slab 3b continuous from the mold 105 in the extending direction of the roll 106 is formed. Is formed.
- the slab-like stainless steel piece 3c is formed by feeding the cast piece 3b from the end of the roll 106 to the outside of the roll 106 and cutting the fed cast piece 3b.
- the casting speed at which the slab 3b is cast is controlled by adjusting the open area of the inlet 101e of the immersion nozzle 101d by the stopper 104. Furthermore, the inflow amount of the molten stainless steel 3 from the ladle 1 through the long nozzle 2 is adjusted so as to be equal to the outflow amount of the molten stainless steel 3 from the inlet 101e. Accordingly, the surface 3a of the molten stainless steel 3 in the inside 101a of the tundish 101 is controlled so as to maintain a substantially constant position in the vertical direction in a state where the depth of the molten stainless steel 3 is maintained in the vicinity of the predetermined depth D. Is done.
- the spout 2 a at the tip is immersed in the molten stainless steel 3.
- the vertical position of the surface 3a of the stainless steel 3 in the inner 101a was maintained substantially constant while the spout 2a of the long nozzle 2 was immersed in the stainless steel 3 in the inner 101a of the tundish 101.
- the cast state is called a steady state. Therefore, since the surface 3a is not sunk by the molten stainless steel 3 flowing in from the long nozzle 2 while casting is performed in a steady state, the nitrogen gas 4 does not get caught in the molten stainless steel 3 and flows into the molten stainless steel 3. Maintain contact with the gentle surface 3a. Thereby, even if it is the nitrogen gas 4 which has the solubility to the stainless steel molten steel 3, the penetration to the stainless steel molten steel 3 is suppressed low in a steady state.
- the spout 2a of the long nozzle 2 is immersed in the molten stainless steel 3 in the interior 101a of the tundish 101, the spout 2a, the bottom of the body 101b of the tundish 101, and the surface 3a of the stainless molten steel 3 in the interior 101a. And the squeezing of the surface 3a by the molten stainless steel 3 is limited to the short time until the spout 2a is immersed, thereby reducing the contamination of the molten stainless steel 3 by the entrainment of air or nitrogen gas 4 is doing.
- the initial casting stainless steel is affected by slight air or nitrogen gas 4 mixed in the molten stainless steel 3 in a short time until the spout 2a of the long nozzle 2 is immersed in the molten stainless steel 3 in the interior 101a of the tundish 101. Except for the steel slab 3c, the stainless steel slab 3c cast at other times occupying most of the casting time from the start to the end of casting is not affected by the mixed air and nitrogen gas 4 and is newly Mixing of nitrogen gas 4 is kept low. For this reason, in the stainless steel piece 3c that occupies most of the casting time, an increase in the nitrogen content from the state after the secondary refining is suppressed, and a small amount of mixed nitrogen gas 4 enters the molten stainless steel 3.
- Embodiment 2 In the continuous casting method according to Embodiment 2 of the present invention, the TD powder 5 is sprayed and coated on the surface 3a of the molten stainless steel 3 in the tundish 101 during casting in the continuous casting method according to Embodiment 1. Is. In the continuous casting method according to the second embodiment, since the continuous casting apparatus 100 is used as in the first embodiment, the description of the configuration of the continuous casting apparatus 100 is omitted.
- the spout 2a of the long nozzle 2 is immersed in the molten stainless steel 3 in the inner 101a of the tundish 101, while the molten stainless steel 3 in the inner 101a has a depth in the vicinity of the predetermined depth D.
- the amount of outflow of the molten stainless steel 3 from the immersion nozzle 101d and the amount of inflow of the molten stainless steel 3 through the long nozzle 2 are adjusted so that the surface 3a is in a substantially constant position. Therefore, on the surface 3 a of the molten stainless steel 3 covered with the TD powder 5, the TD powder 5 deposited by the injected molten stainless steel 3 is prevented from being disturbed, whereby the surface 3 a is exposed to the nitrogen gas 4. Contact is prevented. Therefore, while casting is performed in a steady state, the TD powder 5 continues to cut off the surface 3 a of the molten stainless steel 3 and the nitrogen gas 4.
- the TD powder 5 on the surface 3a of the molten stainless steel 3 fills the portion through which the long nozzle 2 has penetrated and covers the entire surface 3a. Therefore, the TD powder 5 continues to block the contact between the surface 3a of the molten stainless steel 3 and the nitrogen gas 4 until the end of the casting in which the molten stainless steel 3 disappears from the tundish 101.
- the molten stainless steel 3 in the inner portion 101 a is covered with the TD powder 5 during the steady state of casting after the dispersion of the TD powder 5 and until the end of the subsequent casting, and further the molten stainless steel in the ladle 1.
- 3 is poured into the molten stainless steel 3 in the inner 101a through the long nozzle 2 in which the spout 2a is immersed in the molten stainless steel 3 in the inner 101a.
- the molten stainless steel 3 does not come into contact with the nitrogen gas 4, and the mixing of the nitrogen gas 4 into the molten stainless steel 3 hardly occurs.
- the following detection results were sampled from a slab cast in a steady state excluding the initial stage of casting, and in the comparative example, the samples were cast at the same time as the sampling period of the examples from the start of casting. It is sampled from the slab.
- Table 1 shows the steel type, seal gas type / supply flow rate, injection nozzle type, and whether or not TD powder is used for each of the examples and comparative examples.
- the short nozzle in Table 1 means that the lower end of the short nozzle in FIG. 1 is substantially the same as the lower surface of the upper lid 101c of the tundish 101 when it is attached to the ladle 1 instead of the long nozzle 2. The length is short.
- Example 1 is an example in which a SUS430 stainless steel slab was cast using the continuous casting method of the first embodiment.
- Example 2 is an example in which a stainless steel slab of SUS430 was cast using the continuous casting method of the second embodiment.
- Example 3 is an example in which a stainless steel slab of ferritic single phase stainless steel (chemical component: 19Cr-0.5Cu-Nb-LCN), which is a low nitrogen steel type, was cast using the continuous casting method of the second embodiment. is there.
- Example 4 is an example in which a stainless steel slab of SUS316L (austenite low nitrogen steel type), which is a low nitrogen steel type, was cast using the continuous casting method of the second embodiment.
- Comparative Example 1 uses a short nozzle instead of the long nozzle 2 in the continuous casting method of the first embodiment, and uses argon (Ar) gas instead of nitrogen gas as a sealing gas, and SUS430 stainless steel slab This is an example of casting.
- Comparative Example 2 is an example in which a SUS430 stainless steel slab was cast using a short nozzle instead of the long nozzle 2 in the continuous casting method of the first embodiment.
- N pickup is the amount of nitrogen (N) pickup in the slabs cast in Examples 1-4 and Comparative Examples 1-2.
- Table 2 summarizes N pickups measured with a plurality of slabs cast for each of Examples 1 to 4 and Comparative Examples 1 and 2.
- N pick-up is the increase amount of the nitrogen component contained in the slab after casting with respect to the nitrogen component of the molten stainless steel 3 in the ladle 1 after final component adjustment in the secondary refining process, This is the mass of nitrogen component newly contained in the molten stainless steel in the casting process.
- N pickup is indicated by mass concentration, and its unit is ppm.
- Comparative Example 1 since the argon gas is used instead of the nitrogen gas as the seal gas, the N pickup is between 0 and 20 ppm, and the average is as low as 8 ppm.
- Comparative Example 2 since the short nozzle is used, the molten stainless steel poured into the tundish 101 knocks on the surface of the molten stainless steel in the tundish 101 and entrains a lot of surrounding nitrogen gas, so that the N pickup is 50 ppm. The average is as high as 50 ppm.
- the casting nozzle 2a of the long nozzle 2 is immersed in stainless steel in a steady state of casting, the surface of the molten stainless steel in the tundish 101 due to the poured molten stainless steel is prevented.
- the N pickup in Example 1 is between 0 and 20 ppm, and the average is as low as 10 ppm.
- the N pickup in Example 2 is between -10 and 0 ppm, and the average is as low as -4 ppm.
- the nitrogen content in the slab is less than that in the stainless steel after secondary refining, which is considered that the TD powder absorbs the nitrogen component in the stainless steel.
- the N pickup in Example 3 is also between -10 and 0 ppm, and the average is very low at -9 ppm.
- the N pickup in Example 4 is also between -10 and 0 ppm, and the average is very low at -7 ppm.
- argon gas which is an inert gas
- argon gas is contained in molten stainless steel
- most of it does not dissolve in the molten stainless steel and remains in the slab after being cast as bubbles, but most of the nitrogen that is soluble in molten stainless steel is nitrogen.
- nitrogen gas was used as the seal gas to dissolve in the molten stainless steel, it was hardly detected as bubbles from the slab. That is, in Examples 1 to 4 and Comparative Example 2, almost no bubbles were confirmed in the slab, while in Comparative Example 1, many bubbles that were surface defects were confirmed in the slab.
- FIG. 3 shows Example 3 and further comparative example 3 (steel type: ferritic single-phase stainless steel (chemical component: 19Cr-0.5Cu-Nb-LCN), seal gas: Ar, seal gas supply flow rate: 60 Nm. 3 / h, injection nozzle: short nozzle), a diagram comparing the number of bubbles of ⁇ 0.4 mm or more generated in the slab is shown.
- the number of bubbles per 10000 mm 2 100 mm ⁇ 100 mm region
- FIG. 3 the number of bubbles was 0 over the entire region, and in Comparative Example 3, bubbles were confirmed over almost the entire region, and 0 to 14 bubbles were confirmed at each measurement point. .
- FIG. 4 shows a comparison between Example 4 and further comparative example 4 (steel type: SUS316L (austenite low nitrogen steel type), seal gas: Ar, seal gas supply flow rate: 60 Nm 3 / h, injection nozzle: short nozzle).
- the figure which compared the number of air bubbles more than (phi) 0.4mm produced in a slab between is shown.
- the number of bubbles was 0 over the entire region, and in Comparative Example 4, bubbles were confirmed over almost the entire region, and 5 to 35 bubbles were confirmed at each measurement point. .
- the number of bubbles of ⁇ 0.4 mm or more generated in the slab in the comparative example 3 is cast in a steady state excluding the initial stage when the long nozzle 2 is used instead of the short nozzle in the comparative example 3.
- the figure which compared the bubble number of (phi) 0.4 mm or more which arises in another slab is shown.
- the number of bubbles per 10000 mm 2 100 mm ⁇ 100 mm area
- the number of bubbles was reduced as compared with Comparative Example 3, but 3 to 7 bubbles were confirmed over the entire region. Such a bubble reduction effect cannot be confirmed.
- Example 1 using the continuous casting method of the first embodiment while suppressing bubble defects in the slab to be substantially zero, N pickup in the casting process is compared with Comparative Example 1 in which nitrogen gas is not used as a seal gas. It can be kept down to the same extent. Therefore, the continuous casting method of Embodiment 1 is applied to the production of stainless steel having a low nitrogen content with a nitrogen component content of 400 ppm or less, instead of the conventional casting method using argon gas as a sealing gas. Is sufficiently possible, and further has an effect of reducing bubble defects. Further, in Examples 2 to 4 using the continuous casting method of the second embodiment, the N pick-up in the casting process is performed using the nitrogen gas as the seal gas while suppressing the bubble defect in the slab to be almost zero. It can be kept below 1 and almost zero. Therefore, the continuous casting method of Embodiment 2 can be sufficiently applied to the production of stainless steel of a low nitrogen steel type, and has the effect of suppressing bubble defects.
- the N pickup can be reduced by pouring the molten stainless steel using the long nozzle 2 in which the spout 2a is immersed in the molten stainless steel in the tundish 101 during the steady state of casting. Furthermore, the N pickup can be reduced to nearly zero by covering the surface of the molten stainless steel in the tundish 101 with TD powder during the steady state of casting.
- the present invention was applied to SUS409L, SUS444, SUS445J1, SUS304L, etc., and it was confirmed that the N pickup reduction effect and the bubble reduction effect as shown in Examples 1 to 4 were obtained.
- the continuous casting method which concerns on Embodiment 1 and 2 was applied to manufacture of stainless steel, you may apply to manufacture of another metal.
- the control in the tundish 101 in the continuous casting method according to the first and second embodiments has been applied to continuous casting, but may be applied to other casting methods.
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Abstract
Description
例えば、特許文献1には、不活性ガスとしてアルゴンガスを使用する連鋳(連続鋳造)スラブの製造方法が記載されている。
以下、この発明の実施の形態1に係る連続鋳造方法について添付図面に基づいて説明する。なお、以下の実施の形態では、ステンレス鋼の連続鋳造方法について説明する。
溶解工程では、ステンレス製鋼用の原料となるスクラップや合金を電気炉で溶解して溶銑を生成し、生成した溶銑が転炉に注銑される。さらに、一次精錬工程では、転炉内の溶銑に酸素を吹精することによって含有されている炭素を除去する粗脱炭処理が行われ、それによりステンレス溶鋼と炭素酸化物及び不純物を含むスラグとが生成する。また、一次精錬工程では、ステンレス溶鋼の成分が分析され、目的とする成分に近づけるために合金を投入する、成分の粗調整も実施される。さらに、一次精錬工程で生成したステンレス溶鋼は、取鍋に出鋼されて二次精錬工程に移される。
連続鋳造装置100は、取鍋1から送られるステンレス溶鋼3を一時的に受け止めて鋳型105に送るための容器であるタンディッシュ101を有している。タンディッシュ101は、上部が開放した本体101bと、本体101bの開放した上部を閉鎖し外部と遮断する上蓋101cと、本体101bの底部から延びる浸漬ノズル101dとを有している。そして、タンディッシュ101では、本体101b及び上蓋101cによってこれらの内部に閉鎖された内部空間101aが形成される。浸漬ノズル101dは、入口101eで本体101bの底部から内部101aに開口している。
また、取鍋1は、タンディッシュ101の上方にセットされ、タンディッシュ101の上蓋101cを貫通して内部101aに延びるタンディッシュ用注入ノズルであるロングノズル2が、取鍋1の底部に接続されている。そして、ロングノズル2の下方先端の注出口2aが、内部101aで開口している。また、ロングノズル2における上蓋101cの貫通部と上蓋101cとの間は、シールされ気密性が保たれている。
さらに、タンディッシュ101の上蓋101cには、タンディッシュ101の内部101aに、タンディッシュパウダー(以下、TDパウダーを呼ぶ)5(図2参照)を投入するためのパウダノズル103が設けられている。パウダノズル103は、図示しないTDパウダー供給源に接続されており、タンディッシュ101の内部101aに上方から下方に向かってTDパウダー5を送出する。なお、n5は、合成スラグ剤等からなり、ステンレス溶鋼3の表面を覆うことによって、ステンレス溶鋼3の表面の酸化防止作用、ステンレス溶鋼3の保温作用、ステンレス溶鋼3の介在物を溶解吸収する作用等を、ステンレス溶鋼3に対して奏する。なお、本実施の形態1では、パウダノズル103及びTDパウダー5は、使用されない。
ストッパ104は、下方に移動することによってその先端で浸漬ノズル101dの入口101eを閉鎖することができる他、入口101eを閉鎖した状態から上方に引き上げられることによって、タンディッシュ101内のステンレス溶鋼3を浸漬ノズル101d内に流入させると共に、引き上げ量に応じて入口101eの開口面積を調節してステンレス溶鋼3の流量を制御することができるように構成されている。また、ストッパ104における上蓋101cの貫通部と上蓋101cとの間は、シールされ気密性が保たれている。
鋳型105の貫通穴105aは、矩形断面を有し上下に鋳型105を貫通している。貫通穴105aは、その内壁面は図示しない一次冷却機構によって水冷されるように構成され、内部のステンレス溶鋼3を冷却して凝固させ所定の断面の鋳片3bを形成する。
さらに、鋳型105の貫通穴105aの下方には、鋳型105によって形成された鋳片3bを下方に引き出して移送するためのロール106が間隔をあけて複数設けられている。また、ロール106の間には、鋳片3bに対して散水して冷却するための図示しない二次冷却機構が設けられている。
そのまま図1を参照すると、連続鋳造装置100では、タンディッシュ101の上方に、二次精錬後のステンレス溶鋼3を内部に含む取鍋1が設置される。さらに、取鍋1の底部にはロングノズル2が取り付けられ、注出口2aを有するロングノズル2の先端がタンディッシュ101の内部101aに延びている。
このとき、ストッパ104は、浸漬ノズル101dの入口101eを閉鎖している。
よって、定常状態で鋳造が行われている間、ロングノズル2から流入するステンレス溶鋼3による表面3aのたたき込みが生じないため、窒素ガス4は、ステンレス溶鋼3に巻き込まれることなくステンレス溶鋼3の穏やかな表面3aと接触した状態を維持する。これにより、ステンレス溶鋼3への溶解性を有する窒素ガス4であっても、定常状態でステンレス溶鋼3への溶け込みが低く抑えられる。
従って、鋳造の定常状態時において、窒素ガス4をシールガスとして用いることによって、鋳造後のステンレス鋼片3cにおける気泡の発生を抑制することができ、さらに、タンディッシュ101内のステンレス溶鋼3に注出口2aを浸漬させたロングノズル2を介したステンレス溶鋼3の注入によって、二次精錬後の状態からの窒素含有量の増加を抑えることができる。
この発明の実施の形態2に係る連続鋳造方法は、実施の形態1に係る連続鋳造方法において鋳造時にタンディッシュ101内のステンレス溶鋼3の表面3a上にTDパウダー5を散布し被覆するようにしたものである。
なお、実施の形態2に係る連続鋳造方法では、実施の形態1と同様に連続鋳造装置100を使用するため、連続鋳造装置100の構成の説明を省略する。
連続鋳造装置100において、取鍋1がセットされ且つ取鍋1にロングノズル2が取り付けられたタンディッシュ101では、実施の形態1と同様に、ストッパ104によって浸漬ノズル101dの入口101eを閉鎖した状態で、取鍋1からタンディッシュ101の内部101aにロングノズル2を通じてステンレス溶鋼3が注ぎ込まれる。また、タンディッシュ101の内部101aにガス供給ノズル102等から窒素ガス4が供給され、窒素ガス4で満たされる。
よって、TDパウダー5で覆われたステンレス溶鋼3の表面3aでは、注入されるステンレス溶鋼3によって堆積しているTDパウダー5が乱れることが抑えられ、それによって、表面3aが窒素ガス4に露出し接触することが防がれる。従って、定常状態で鋳造が行われている間、TDパウダー5は、ステンレス溶鋼3の表面3aと窒素ガス4との間を遮断し続ける。
また、この発明の実施の形態2に係る連続鋳造方法に関するその他の構成及び動作は、実施の形態1と同様であるため、説明を省略する。
以下、実施の形態1及び2に係る連続鋳造方法を用いてステンレス鋼片を鋳造した実施例を説明する。
SUS430、フェライト単相系ステンレス鋼(化学成分:19Cr-0.5Cu-Nb-LCN)及びSUS316Lのステンレス鋼について実施の形態1及び2の連続鋳造方法を用いてステンレス鋼片であるスラブを鋳造した実施例1~4と、SUS430のステンレス鋼について注入ノズルとしてショートノズルを使用し、シールガスとしてアルゴンガス又は窒素ガスを用いてスラブを鋳造した比較例1~2とについて特性を評価した。なお、以下の検出結果は、実施例では、鋳造の初期を除く定常状態で鋳造されたスラブからサンプリングしたものであり、比較例では、鋳造開始からの実施例のサンプリング時期と同時期に鋳造されたスラブからサンプリングしたものである。
実施例2は、実施の形態2の連続鋳造方法を用いてSUS430のステンレス鋼スラブを鋳造した例である。
実施例3は、実施の形態2の連続鋳造方法を用いて低窒素鋼種であるフェライト単相系ステンレス鋼(化学成分:19Cr-0.5Cu-Nb-LCN)のステンレス鋼スラブを鋳造した例である。
実施例4は、実施の形態2の連続鋳造方法を用いて低窒素鋼種であるSUS316L(オーステナイト系低窒素鋼種)のステンレス鋼スラブを鋳造した例である。
比較例1は、実施の形態1の連続鋳造方法においてロングノズル2の代わりにショートノズルを使用し、且つシールガスとして窒素ガスの代わりにアルゴン(Ar)ガスを使用して、SUS430のステンレス鋼スラブを鋳造した例である。
比較例2は、実施の形態1の連続鋳造方法においてロングノズル2の代わりにショートノズルを使用してSUS430のステンレス鋼スラブを鋳造した例である。
比較例2では、ショートノズルを使用するため、タンディッシュ101内に注ぎ込まれたステンレス溶鋼が、タンディッシュ101内のステンレス溶鋼の表面をたたき込んで周囲の多くの窒素ガスを巻き込むので、Nピックアップが50ppmとなり、その平均も50ppmと高くなっている。
実施例1では、鋳造の定常状態時において、ロングノズル2の注出口2aをステンレス鋼に浸漬させることによって、注ぎ込まれたステンレス溶鋼によるタンディッシュ101内のステンレス溶鋼の表面のたたき込みが防がれ、窒素ガスはステンレス溶鋼の穏やかな表面と接触しているのみであるため、Nピックアップが比較例1と同程度に低くなっている。具体的には、実施例1でのNピックアップは、0~20ppmの間となり、その平均が10ppmと低くなっている。
実施例2~4では、鋳造の定常状態時において、ロングノズル2の使用に加えてTDパウダーによってタンディッシュ101内のステンレス溶鋼と窒素ガスとを遮断するため、Nピックアップが比較例1及び実施例1よりもかなり小さくなっている。具体的には、実施例2でのNピックアップは、-10~0ppmの間となり、その平均が-4ppmと非常に低くなっている。つまり、スラブにおける窒素含有量が、二次精錬後のステンレス溶鋼よりも少なくなっており、これは、TDパウダーがステンレス溶鋼中の窒素成分を吸収していると考えられる。また、実施例3でのNピックアップも、-10~0ppmの間となり、その平均が-9ppmと非常に低くなっている。さらに、実施例4でのNピックアップも、-10~0ppmの間となり、その平均が-7ppmと非常に低くなっている。
図3に示すように、実施例3では、全域にわたり気泡個数が0個であり、比較例3では、ほぼ全域にわたり気泡が確認され、各測点で0~14個の気泡が確認されている。
図4に示すように、実施例4では、全域にわたり気泡個数が0個であり、比較例4では、ほぼ全域にわたり気泡が確認され、各測点で5~35個の気泡が確認されている。
図5に示すように、ロングノズル2を使用した場合でも、比較例3よりも気泡個数は減少しているが、全域にわたり3~7個の気泡が確認されており、実施例1~4のような気泡低減効果は確認できない。
また、実施の形態2の連続鋳造方法を用いた実施例2~4では、スラブにおける気泡欠陥をほぼ0に抑制しつつ、鋳造工程でのNピックアップを、シールガスに窒素ガスを使用しない比較例1よりも低く抑え、ほぼ0とすることができる。従って、実施の形態2の連続鋳造方法は、低窒素鋼種のステンレス鋼の製造に適用することが十分に可能であり、さらに気泡欠陥を低く抑える効果を有している。
また、実施の形態1及び2に係る連続鋳造方法は、ステンレス鋼の製造に適用されていたが、他の金属の製造に適用してもよい。
また、実施の形態1及び2に係る連続鋳造方法におけるタンディッシュ101での制御は、連続鋳造に適用されていたが、他の鋳造方法に適用してもよい。
Claims (4)
- 取鍋内の溶融金属を下方のタンディッシュ内に注入し、前記タンディッシュ内の前記溶融金属を鋳型に連続注入して金属片を鋳造する連続鋳造方法において、
シールガスとして窒素ガスを前記タンディッシュ内の前記溶融金属の周囲に供給し、
前記取鍋内の前記溶融金属を前記タンディッシュ内に注入するための注入ノズルの注出口を前記タンディッシュ内の前記溶融金属に浸漬させつつ、前記注入ノズルを通じて前記タンディッシュ内に前記溶融金属を注入すると共に、前記タンディッシュ内の前記溶融金属を前記鋳型に注入する連続鋳造方法。 - 前記タンディッシュ内の前記溶融金属の表面上にタンディッシュパウダーを散布し、前記タンディッシュパウダーを前記溶融金属と前記窒素ガスとの間に介在させる請求項1に記載の連続鋳造方法。
- 前記注入ノズルの前記注出口を、前記タンディッシュ内の前記溶融金属に100~150mmの深さで貫入させる請求項1または2に記載の連続鋳造方法。
- 鋳造される前記金属片は、含有窒素の濃度が400ppm以下のステンレス鋼である請求項1~3のいずれか一項に記載の連続鋳造方法。
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CN105682826A (zh) | 2016-06-15 |
US20160207101A1 (en) | 2016-07-21 |
KR20160067100A (ko) | 2016-06-13 |
EP3040138A4 (en) | 2017-04-19 |
CN105682826B (zh) | 2017-11-24 |
TWI593482B (zh) | 2017-08-01 |
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