CN116057195A - Continuous casting method for steel and test solidification device for steel - Google Patents
Continuous casting method for steel and test solidification device for steel Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 249
- 239000010959 steel Substances 0.000 title claims abstract description 249
- 238000012360 testing method Methods 0.000 title claims abstract description 83
- 238000009749 continuous casting Methods 0.000 title claims abstract description 72
- 238000007711 solidification Methods 0.000 title claims abstract description 64
- 230000008023 solidification Effects 0.000 title claims abstract description 64
- 238000000034 method Methods 0.000 title claims description 45
- 230000004907 flux Effects 0.000 claims abstract description 54
- 238000001816 cooling Methods 0.000 claims abstract description 50
- 238000005266 casting Methods 0.000 claims abstract description 47
- 230000003746 surface roughness Effects 0.000 claims abstract description 42
- 238000010583 slow cooling Methods 0.000 claims abstract description 28
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 43
- 229910052799 carbon Inorganic materials 0.000 claims description 43
- 238000005336 cracking Methods 0.000 claims description 23
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 14
- 238000002425 crystallisation Methods 0.000 claims description 12
- 230000008025 crystallization Effects 0.000 claims description 12
- 238000002347 injection Methods 0.000 claims description 12
- 239000007924 injection Substances 0.000 claims description 12
- 239000013078 crystal Substances 0.000 claims description 10
- 229910002056 binary alloy Inorganic materials 0.000 claims description 6
- 238000010586 diagram Methods 0.000 claims description 6
- 239000002344 surface layer Substances 0.000 claims description 6
- 229910017112 Fe—C Inorganic materials 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 5
- INJRKJPEYSAMPD-UHFFFAOYSA-N aluminum;silicic acid;hydrate Chemical compound O.[Al].[Al].O[Si](O)(O)O INJRKJPEYSAMPD-UHFFFAOYSA-N 0.000 claims description 4
- 229910052850 kyanite Inorganic materials 0.000 claims description 4
- 239000010443 kyanite Substances 0.000 claims description 4
- 208000010392 Bone Fractures Diseases 0.000 abstract description 38
- 206010017076 Fracture Diseases 0.000 abstract description 38
- 239000002436 steel type Substances 0.000 abstract description 7
- 239000000203 mixture Substances 0.000 description 13
- 239000002893 slag Substances 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 6
- 238000005259 measurement Methods 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 230000006698 induction Effects 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 230000000007 visual effect Effects 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- 229910000954 Medium-carbon steel Inorganic materials 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 239000004575 stone Substances 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910004261 CaF 2 Inorganic materials 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
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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
- B22D11/108—Feeding additives, powders, or the like
-
- 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
- B22D11/16—Controlling or regulating processes or operations
-
- 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
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Continuous Casting (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Abstract
The invention can simply judge whether the molten steel to be continuously cast is a fracture risk steel grade, and optimize the operation condition of continuous casting based on the judgment, thereby preventing the fracture of cast pieces and the bad condition of continuous casting, and realizing the improvement of productivity. A test cast piece is produced by injecting molten steel to be continuously cast into a test solidification apparatus and cooling the molten steel, the surface roughness of the lower surface of the test cast piece is measured, when the surface roughness is equal to or higher than a predetermined threshold value, it is determined that the cast piece is a steel type which is likely to break when the molten steel is continuously cast, the continuous casting is performed using slow cooling mold flux suitable for preventing the break, and when the surface roughness is lower than the predetermined threshold value, it is determined that the cast piece is not likely to break when the molten steel is continuously cast, and the continuous casting is performed using strong cooling mold flux suitable for increasing the casting speed of the continuous casting.
Description
Technical Field
The present invention relates to a method for continuously casting steel for preventing breakage and steel leakage (break out) of a cast piece during continuous casting, and a test solidification apparatus for steel.
Background
When continuously casting a subcollector medium carbon steel having a C content of 0.09 to 0.17 mass%, cracking tends to occur on the surface of the cast piece. Specifically, the solidification shrinkage on the molten steel side of the solidified shell caused by the δ - γ phase transition during solidification causes a portion of the solidified shell having a high cooling rate to warp convexly with respect to the surface of the mold, thereby generating irregularities on the surface of the cast piece and causing uneven growth in the solidified shell. In the concave portion of the surface of the cast piece, the heat resistance increases due to the air gap, and the thickness of the solidified shell becomes small, so that strain is generated in the solidified shell, and solidification cracking occurs in the surface of the cast piece. The solidification cracking expands during the secondary cooling of the continuous casting, and grows into longitudinal cracking and transverse cracking. If the degree of solidification cracking of the cast slab is large, there is a risk of steel leakage due to the cracking.
Therefore, the following operations are generally performed in the continuous casting process: for a steel grade of a sub-peritectic carbon region (hereinafter referred to as "fracture risk steel grade") in which solidification fracture easily occurs during primary cooling in a mold, slow cooling in the mold is achieved by using slow cooling mold flux, thereby preventing fracture of a cast piece and occurrence of steel leakage.
If continuous casting is performed using slow cooling mold flux, the thickness of the solidified shell in the mold becomes small, and therefore, there is an increased risk of breakage of the solidified shell immediately below the mold and occurrence of steel leakage. Therefore, in the case of using slow cooling mold flux, it is necessary to reduce the casting speed of continuous casting so that the thickness of the solidified shell in the mold is not reduced.
In the case of continuous casting using slow cooling mold flux unnecessarily for steel grades other than the fracture risk steel grade, it is still necessary to reduce the casting speed of continuous casting, and productivity of continuous casting is lowered. Therefore, from the viewpoint of preventing the breakage of the cast slab and the occurrence of continuous casting failure and achieving an improvement in productivity, it is important to appropriately determine whether or not the molten steel is a breakage risk steel grade, and to continuously cast only the breakage risk steel grade with the slow cooling mold flux.
It is known that the range of carbon concentration corresponding to the peritectic region on the fe—c binary system equilibrium state diagram is actually changed by the influence of other alloy components. In view of these aspects, it is important to properly determine whether the molten steel is a fracture risk steel grade, and to optimize the operating conditions of continuous casting.
As described above, when the fracture risk steel grade is continuously cast, irregularities are generated on the surface of the cast piece. As an index for evaluating the irregularities, for example, the shape of the irregularities on the surface of the cast sheet such as the depth of the vibration marks can be used. Since the mold flux is pressed into the cast slab when the mold descends and the depth thereof increases due to solidification shrinkage occurring inside the solidified shell, the depth of the vibration mark of the fracture risk steel grade increases if the continuous casting conditions are the same.
Further, non-patent document 1 discloses a method including: the water-cooled plate was immersed in molten steel in an off-line manner to form a solidified shell on the plate, and the difference in thickness and the interval between the concave and convex portions of the solidified shell were directly measured to evaluate the non-uniformity of the solidified shell.
Further, non-patent document 2 discloses a baseA method for predicting whether a steel grade is at risk of cracking in an alloy composition. Specifically, a simulated Fe-C binary system equilibrium state diagram was calculated as a function of carbon concentration using a thermodynamic program for each steel grade. Then, based on the sub-peritectic regions in these simulated Fe-C binary system equilibrium state diagrams, the lower limit value (C a ) Upper limit value of carbon concentration (C) b ) Is formulated based on the variation of the other alloy compositions. According to whether the carbon concentration of the steel grade is C a ～C b To determine whether the molten steel is a fracture risk steel grade.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. 9-57413
Non-patent literature
Non-patent document 1: village, ocean et al, 3, "control of non-uniform solidification of sub-peritectic carbon steel in continuous casting mold", iron and steel (Cio-steel), 1992, vol.78, no.1, pp.105-112
Non-patent document 2: k. Blazeck and 3 others, "Calculation of the Peritectic Range for Steel Alloys", AISTech 2007Conference Proceedings,2007, pp.81-88
Non-patent document 3: the history of the tailing and 2 others, "influence of mold flux on initial solidification of sub-peritectic steel in continuous casting mold", iron and steel (iron-to-track), 2014, vol.100, no.4, pp.581-590
Disclosure of Invention
Problems to be solved by the invention
However, in the method disclosed in patent document 1, it is difficult to prevent the occurrence of the cast piece cracking by changing the kind of mold flux according to the depth of the vibration mark measured in the continuous casting, and there is a hidden danger that measures for preventing the occurrence of the cast piece cracking are not timely for the type of cracking-risk steel having serious unevenness.
In addition, in the method disclosed in non-patent document 1, the test of immersing the water-cooled plate in molten steel to form a solidified shell on the plate is complicated, and therefore, it is not suitable for evaluating the non-uniformity of the solidified shell for many types of steel.
In the method disclosed in non-patent document 2, it is sometimes not necessarily possible to appropriately determine the steel grade at risk of cracking, as to the steel grade in which it is empirically known that longitudinal cracking or transverse cracking occurs.
The present invention has been made to solve the above-described problems. That is, an object of the present invention is to provide a continuous casting method of steel and a test solidification apparatus of steel, which can easily determine whether or not molten steel to be continuously cast is a fracture risk steel type, considering that a peritectic region of molten steel to be continuously cast is changed due to an influence of an alloy composition, and can prevent fracture of a cast piece and occurrence of continuous casting failure, and can improve productivity by optimizing an operation condition of continuous casting based on the determination.
Means for solving the problems
In view of the above problems, the present inventors have conducted intensive studies and developments from a unique viewpoint, and as a result, have found that it is possible to easily and accurately predict whether or not molten steel is a fracture risk steel grade by producing a test cast piece from molten steel and evaluating the surface roughness thereof, and have completed the present invention.
The continuous casting method of steel and the test solidification apparatus of steel according to the present invention are as follows.
[1] A method of continuously casting steel, the method comprising: the method comprises the steps of manufacturing a test cast piece by injecting molten steel to be continuously cast into a test solidification device and cooling the molten steel, measuring the surface roughness of the lower surface of the test cast piece, performing the continuous casting by using slow cooling mold flux suitable for preventing the cast piece from cracking when the molten steel is continuously cast when the surface roughness is above a given threshold value, and performing the continuous casting by using strong cooling mold flux suitable for improving the casting speed of the continuous casting when the surface roughness is below the given threshold value.
[2] The continuous casting method of steel according to [1], wherein,
the threshold was 60 μm in terms of the arithmetic mean height of the surface roughness obtained by the method specified in ISO 25178.
[3]A method of continuously casting steel, the method comprising: a test cast piece is produced by injecting molten steel to be continuously cast into a test solidification apparatus and cooling the molten steel, the surface roughness of the lower surface of the test cast piece is measured, and the carbon concentration lower limit C of the component of the molten steel M with respect to the sub-peritectic region on the Fe-C binary system equilibrium state diagram is obtained for a plurality of molten steels M having the surface roughness of a predetermined threshold value or more a (mass%) and upper limit value C of carbon concentration b Influence coefficient alpha of (mass%) a,M 、α b,M Calculating the influence coefficients alpha of a plurality of molten steels M a,M 、α b,M The carbon concentration lower limit C of the sub-peritectic region of the molten steel M is determined by the following formulas (1) and (2) a (mass%) and upper limit value C of carbon concentration b (mass%) and the lower limit C of the carbon concentration in the peritectic region of the new molten steel is obtained from the components of the new molten steel different from the plurality of molten steels M by the following formulas (1) and (2) a The upper limit value C of the carbon concentration b Based on the obtained lower limit C of the carbon concentration a The upper limit value C of the carbon concentration b And the carbon concentration C (mass%) of the new molten steel are determined by the following formula (3) to obtain the carbon equivalent C of the new molten steel p (mass%) of the above carbon equivalent C p In the case of 0.09 to 0.17, the continuous casting of the new molten steel is performed using a slow cooling mold flux suitable for preventing the rupture of the cast piece during the continuous casting of the new molten steel, and the carbon equivalent C p When the casting speed is not in the range of 0.09 to 0.17, the continuous casting of the new molten steel is performed using strong cooling mold flux suitable for increasing the casting speed of the continuous casting,
[ mathematics 1]
[ math figure 2]
C p ＝0.09+{(C-C a )/(C b -C a )}×(0.17-0.09)···(3)。
[4] The method for continuously casting a steel according to any one of [1] to [3], wherein,
the slow cooling mold flux contains SiO 2 And CaO as a main component, caO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) 1.0 or more and less than 2.0, the crystallization temperature is 1100 ℃ or more, and the kyanite is crystallized as primary crystals.
[5] The method for continuously casting a steel according to any one of [1] to [4], wherein,
the strong cooling mold flux contains SiO 2 And CaO as a main component, caO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) Is 0.7 or more and less than 1.0, and the crystallization temperature is less than 1100 ℃.
[6] The method for continuously casting a steel according to any one of [1] to [5], wherein,
the test solidification equipment has a cooling rate of 10 at a depth of 1mm from the surface layer of the solidification shell of the molten steel 2 ～10 5 Cooling capacity in c/min.
[7] The method for continuously casting a steel according to any one of [1] to [6], wherein,
the injection rate (unit: kg/s) of the molten steel when the molten steel is injected into the test solidification device is 3 times or more the solidification rate (unit: kg/s) of the molten steel.
[8] The method for continuously casting a steel according to any one of [1] to [7], wherein,
the test solidification equipment has a bottom surface having a width and a depth of 10mm or more.
[9] A steel test solidification apparatus for manufacturing a test cast piece by injecting molten steel and cooling the molten steel,
the steel test solidification device comprises a surface layer 1mm from the solidified shell of the injected molten steelDeep cooling rate of 10 2 ～10 5 Casting mold at c/min.
[10] The steel solidification test device according to item [9], further comprising an injection device for injecting the molten steel into the mold, wherein an injection rate (unit: kg/s) of the molten steel by the injection device is 3 times or more as high as a solidification rate (unit: kg/s) of the molten steel in the mold.
[11] The steel test solidification device according to [9] or [10], wherein,
the mold has a bottom surface with a width and a depth of 10mm or more.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the steel continuous casting method and the steel test solidification apparatus of the present invention, it is possible to easily determine whether or not the molten steel is a steel grade in which the cast piece is liable to break during continuous casting, using the surface roughness or carbon equivalent of the lower surface of the test cast piece produced by injecting the molten steel to be subjected to continuous casting into the test solidification apparatus and cooling.
In addition, when it is determined that the cast piece is liable to be broken, the continuous casting is performed by using the slow cooling mold flux suitable for preventing the breakage, whereby the breakage and the steel leakage of the cast piece can be reliably prevented. In addition, when it is determined that a broken steel grade is unlikely to occur, the productivity of continuous casting can be improved without lowering the casting speed by performing continuous casting using strong cooling mold flux suitable for increasing the casting speed of continuous casting.
Drawings
Fig. 1 is a schematic view showing an example of a test solidification apparatus used in the continuous casting method of steel according to the present invention.
Fig. 2 (a) and 2 (b) are photographs showing examples of surface roughness of the lower surface of a test piece produced by the test solidification apparatus of steel of the present invention.
Symbol description
1. Test solidification device for steel
2. Casting mould
21. Bottom surface
3. Injection device
31. Crucible pot
32. High-frequency induction coil
33. Tilting table
W width
Depth D
H height
S steel sample (molten steel)
Detailed Description
Hereinafter, embodiments of a continuous casting method for steel and a test solidification apparatus for steel according to the present invention will be described with reference to the accompanying drawings.
Test solidification device of Steel
Fig. 1 shows an outline of a test solidification apparatus 1 used in the continuous casting method of steel according to the present embodiment.
As shown in fig. 1, the steel test solidification apparatus 1 according to the present embodiment includes: a casting mold 2 for producing a test piece by injecting molten steel S and cooling and solidifying the molten steel S, and an injection device 3 for injecting the molten steel S into the casting mold 2.
The mold 2 is a copper container having a substantially rectangular parallelepiped shape, and a water cooling device (not shown) is provided on a bottom surface 21 thereof. The thickness of the casting mold 2 and the capacity of the water cooling device are designed so that the following cooling capacity can be obtained: when the molten steel S was poured into the mold 2 and cooled to solidify, the cooling rate was set to 10 at a depth of 1mm from the surface layer of the solidified shell on the bottom surface 21 side of the mold 2 cooled by the water cooling device 2 ～10 5 DEG C/min.
In the present invention, the shape of the mold 2 of the test solidification apparatus 1 is not particularly limited, and the width W and the depth D of the bottom surface 21 of the mold 2 are preferably 10mm or more, and more preferably 40mm or more and 60mm or less, respectively. This is based on the following: it is known that the size of the lower surface of the test piece produced by the test solidification apparatus 1 is the same as the size of the bottom surface 21 of the mold 2, and when the surface roughness of the lower surface of the test piece is measured as described later, the interval between irregularities that can be confirmed by visual observation is in the range of 10mm to 40 mm. The surface roughness of the bottom surface of the mold 2 in contact with the lower surface of the test piece is preferably less than 30 μm in terms of the arithmetic average height of the surface roughness obtained by the method prescribed by ISO25178 "three-dimensional surface texture (surface roughness)". This is due to: as described later, when the surface roughness of the lower surface of the test piece is evaluated using the arithmetic average height of the surface roughness obtained by the method specified in ISO25178, the shape of the bottom surface 21 of the mold 2 affects the surface roughness of the lower surface of the test piece.
The injection device 3 includes: from Al 2 O 3 Or a crucible 31 having a bottomed cylindrical shape made of MgO, a high-frequency induction coil 32 for heating and melting the content in the crucible 31 so as to cover the outer periphery of the crucible 31, a tilting table 33 for tilting the crucible 31 while the crucible 31 is fixed and injecting the melt in the crucible 31 into the mold 2, a plurality of thermocouples (not shown) for measuring the temperature of molten steel in the crucible 31, and a temperature display device (not shown) for converting the output voltage of each thermocouple into temperature and displaying the temperature.
Hereinafter, a method of continuously casting steel using the above-described steel solidification test apparatus 1 will be described.
< manufacturing of test cast piece >
In the present embodiment, a steel sample (molten steel) S having the same composition as the target composition of molten steel to be continuously cast is poured into a crucible 31, and the crucible 31 is fixed to a tilting table 33. Further, a high-frequency induction coil 32 is provided so as to cover the outer periphery of the crucible 31, and the steel sample S in the crucible 31 is heated and melted. At this time, the heating of the steel sample S was continued until it was confirmed by visual observation of the operator that the steel sample S was molten, and it was confirmed that the temperature of the molten steel sample S displayed by the temperature display device was in the range of 1590 to 1610 ℃. Here, instead of visual observation by an operator, the output value from the thermocouple may be input to a computer to automatically determine whether or not the temperature of the molten steel sample S has reached a temperature in the range of 1590 to 1610 ℃.
Next, the high-frequency induction coil 32 is moved away from the crucible 31, the tilting table 33 is tilted, the crucible 31 is tilted, and the molten steel in the crucible 31 is testedThe sample S is injected into the casting mold 2. Then, the water cooling device of the mold 2 was operated, and the molten steel (steel sample) S injected into the mold 2 was cooled and solidified to prepare a test piece. At this time, the operation of the water cooling device was adjusted so that the cooling rate of a depth of 1mm from the surface layer of the solidified shell became 10 2 ～10 5 DEG C/min.
The cooling rate is based on the following report in non-patent document 3: when continuously casting a fracture risk steel grade by a practical continuous casting machine, the occurrence of uneven solidification becomes remarkable at a stage where the thickness of the solidified shell exceeds 1mm, and the cooling rate at this position is 10 3 ～10 5 DEG C/min. That is, in the cooling of the molten steel (steel sample) S in the test solidification apparatus 1, the cooling rate at the position where the occurrence of the uneven solidification becomes apparent in the practical continuous casting machine was reproduced.
In addition, if the tilting speed of the tilting table 33 is set to 3 times or more the injection speed (unit: kg/S) of the steel sample S injected into the mold 2 by the tilting table 33 in cooperation with the operation of the water cooling apparatus, the solidification speed (unit: kg/S) of the molten steel S in the mold 2 is set to be 3 times or more, irregularities are likely to be generated on the solidified shell surface when the molten steel S is in the peritectic region, and it is preferable to determine whether or not the steel type is a fracture risk steel type with higher accuracy.
An example of the lower surface of the test piece thus produced by the test solidification apparatus 1 is shown in a photograph in fig. 2. Fig. 2 (a) shows an example of the case where the steel sample S is a fracture risk steel grade, and fig. 2 (b) shows an example of the case where the steel sample S is not a fracture risk steel grade. When the steel sample S was a fracture risk steel grade, it was clearly confirmed that irregularities were generated on the lower surface of the test piece.
Production of test cast piece Using molten Steel in steelmaking Process
In an actual steelmaking process, the composition of molten steel during continuous casting may deviate from a target value. Therefore, in order to improve the accuracy of determining whether or not the molten steel is a fracture risk steel type, a test cast piece may be produced by collecting molten steel from a ladle containing molten steel to be continuously cast by a sampler, and directly injecting the molten steel into the mold 2 of the test solidification apparatus 1 and cooling the molten steel. In this case, if the sampler for collecting molten steel from the ladle has the function of the mold 2, it is not necessary to prepare the test solidification device 1 separately.
< measurement of surface roughness >)
Next, the height of the irregularities on the lower surface of the test cast piece produced as described above was measured by a measuring device such as a laser range finder, and the surface roughness of the surface roughness was calculated using the arithmetic average height specified in ISO 25178.
The calculation conditions of the surface roughness include measurement and evaluation area, interval between measurement points, and magnitude of cut-off wavelength. In the continuous casting method of steel and the test solidification apparatus of steel according to the present invention, the measurement and evaluation area, the interval between measurement points, and the size of the cut-off wavelength are not particularly limited, and are preferably as follows.
First, for measuring the evaluation area, the center is set to the center of the lower surface of the test piece, and the longitudinal and lateral lengths thereof are preferably set to 10mm or more, more preferably 40mm or more and 60mm or less, respectively. This is based on: it is known that the interval between irregularities which can be confirmed by visual inspection is in the range of 10mm to 40 mm. The distance between measurement points is preferably 10mm or less. The wavelength of the cutoff is preferably 800 μm.
Determination of whether to be a fracture risk Steel grade
Next, when the surface roughness (arithmetic mean height of surface roughness) of the lower surface of the test piece calculated as described above was 60 μm or more, it was determined that the molten steel having the same composition as the steel sample S was a fracture risk steel grade (a steel grade in which the piece easily breaks during continuous casting).
As described above, in the fracture risk steel type, the solidification shrinkage due to the δ—γ phase transition at solidification on the molten steel side of the solidification shell causes the portion of the solidification shell having a high cooling rate to be convexly warped with respect to the mold surface, and irregularities are generated on the surface of the cast piece. Thus, the surface roughness of the test piece was an index of whether or not the molten steel having the same composition as the steel sample S was a fracture risk steel grade.
Further, as for a plurality of types of molten steel, it is possible to use the result of determining whether each molten steel is a fracture risk steel type based on whether the surface roughness of the test piece is equal to or higher than a predetermined threshold value, and establish the carbon equivalent C as follows p Is a relation of (3).
That is, when the surface roughness of a test piece made of molten steel is equal to or higher than a predetermined threshold value and it is determined as a fracture risk steel grade, the carbon concentration lower limit value (C) of the peritectic region on the balance state diagram of the Fe-C binary system of each component element of the steel grade M is obtained a ) (mass%) and an upper limit value (C) of the carbon concentration b ) Influence coefficient alpha of (mass%) a,M 、α b,M . Then, regarding the various steel grades M, considering that the range of the carbon concentration of the peritectic region is changed by the influence of other alloy components, C is established as shown in the following formulas (1) and (2) a 、C b Is a relation of (3).
[ math 3]
[ mathematics 4]
Then, when determining whether or not the new molten steel (target steel) is a fracture risk steel grade, C is obtained from the composition of the target steel by the above formulas (1) and (2) a 、C b Based on the obtained C a 、C b And the carbon concentration C (mass%) of the target steel, the carbon equivalent C of the target steel was obtained by the following formula (3) p Instead of making this determination based on the surface roughness of the test piece (mass%).
C p ＝0.09+{(C-C a )/(C b -C a )}×(0.17-0.09)···(3)
At the carbon equivalent C p In the range of 0.09 to 0.17 mass%The target steel is located in the peritectic region, and can be determined as a fracture risk steel grade.
< selection of mold powder >)
Next, based on the above-described determination as to whether or not it is a fracture risk steel grade, it is selected which of the slow cooling mold flux and the strong cooling mold flux is used for continuous casting.
The slow cooling effect of the solidified shell by the mold flux can be obtained as follows: powder slag (powder slag) flowing into a gap between a casting mold and a solidified shell of a continuous casting machine is cooled and solidified on a surface of the casting mold, thereby forming a slag film, and a heat transfer resistance (heat transfer resistance) increases due to crystallization in the slag film. The composition of the covering slag is SiO as main component 2 And CaO, and Li added for adjusting the viscosity of the mold flux and the precipitation of crystals 2 O、Na 2 O、F、MgO、Al 2 O 3 Etc. A common seed crystal precipitated in the slag film is kyanite (Cuspidine: 3CaO.2SiOSiO) 2 ·CaF 2 )。
In order to suppress surface cracking of the cast slab, it is effective to achieve slow cooling of the solidified shell in the vicinity of the molten steel surface, and therefore, in order to impart an effect of suppressing longitudinal cracking to the mold flux, it is necessary to slowly cool the solidified shell by precipitating crystals instantaneously after the powder slag flows into the gap between the mold and the solidified shell.
Since it is considered that the mold flux having a high crystallization temperature and crystallizing out the gun stone as primary crystals has a function of slowly cooling the inside of the mold, such a slow cooling mold flux is used for a steel grade at risk of breakage and the casting speed is reduced, and occurrence of breakage and steel leakage can be reliably prevented, whereas productivity is maintained for a steel grade without risk of breakage by not using a slow cooling mold flux and not reducing the casting speed.
Specifically, when the surface roughness of the lower surface of the test piece calculated as described above is 60 μm or more, it is determined that the molten steel having the same composition as the steel sample S is a fracture risk steel grade, and continuous casting is performed using slow cooling mold flux suitable for preventing fracture. As slow cooling mold flux, in particularIn other words, a material comprising SiO may be used 2 CaO as a main component, caO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) A slow cooling mold flux of 1.0 or more and less than 2.0, a crystallization temperature of 1100 ℃ or more, and a crystallized kyanite as primary crystal.
The reason why the constituent components of the mold flux are set as described above is as follows. In CaO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) If the amount of the gun-shaped crystal is less than 1.0, the amount of the gun-shaped crystal precipitated in the slag film becomes insufficient, and the crystallization temperature becomes too low, so that a slow cooling function for preventing longitudinal cracking and transverse cracking cannot be imparted to the mold flux. In addition, caO is relative to SiO 2 Mass ratio (CaO/SiO) 2 ) When the amount is 2.0 or more, the crystallization temperature of the mold flux increases, the crystallization of the mold flux is excessively accelerated, friction between the mold and the cast piece increases, and steel leakage is likely to occur.
In addition, when the surface roughness of the lower surface of the test piece calculated as described above is less than 60 μm, it is determined that the molten steel having the same composition as the steel sample S is not a fracture risk steel grade (a steel grade in which the piece is less likely to fracture during continuous casting), continuous casting is performed using strong cooling mold flux suitable for increasing the casting speed of continuous casting. As the strong cooling mold flux, a mold flux containing SiO may be used 2 CaO as a main component, caO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) Strong cooling mold flux of 0.7 or more and less than 1.0 and crystallization temperature lower than 1100 ℃.
The reason why the constituent components of the mold flux are set as described above is as follows. In CaO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) If the amount is 1.0 or more, the amount of the gun crystal stone precipitated in the slag film increases, and the crystallization temperature becomes too high, so that the mold flux is given a slow cooling function, and the casting speed needs to be reduced. In addition, caO is relative to SiO 2 Mass ratio (CaO/SiO) 2 ) If the melting point of the mold flux is less than 0.7, the inflow amount into the mold is decreased, and there is a risk of occurrence of adhesive steel leakage (sticking breakout).
Examples
The steel grades a to d (medium carbon steel) shown in table 1 were fed and melted 1 to 2 times respectively by a converter and a vacuum degassing apparatus (secondary refining), and poured into a water-cooled mold of a vertical bending type continuous casting machine via a tundish (tunstand). Then, while strong cooling mold flux a or slow cooling mold flux B having the composition shown in table 2 was supplied to the surface of molten steel in the mold, continuous casting was performed at the casting speed shown in table 3, and cast pieces were produced.
By visually observing the surface of each cast piece obtained as a result of the above, it was confirmed whether or not surface breakage of the cast piece occurred. Specifically, the length of the crack was measured, and when a crack having a length of 10mm or more was confirmed, it was determined that the surface of the cast piece was broken.
Meanwhile, according to the continuous casting method of steel of the present invention, it was determined whether or not each of the steel grades a to d was a fracture risk steel grade based on whether or not the surface roughness of the lower surface of the test piece was 60 μm or more (inventive example). Further, by the method disclosed in the above-mentioned non-patent document 2, it was determined whether or not each of the steel grades a to d was a fracture risk steel grade (comparative example).
In the present example, molten steel was collected from a ladle containing molten steel to be continuously cast by a sampler, a test piece was produced from the molten steel, the height of irregularities on the lower surface of the test piece was measured, and the surface roughness of the surface roughness was calculated using an arithmetic average height Sa specified in ISO 25178.
In the comparative example, as disclosed in non-patent document 2, the lower limit value (C) of the carbon concentration in the peritectic region of each of the steel grades a to d was obtained by the following formulas (4) and (5) a ) (mass%) and an upper limit value (C) of the carbon concentration b ) (mass%).
C a ＝0.0896+0.0458×Al-0.0205×Mn-0.0077×Si+0.0223×Al 2 -0.0239×Ni+0.0106×Mo+0.0134×V-0.0032×Cr+0.00059×Cr 2 +0.0197×W···(4)
C b ＝0.1967+0.0036×Al-0.0316×Mn-0.0103×Si+0.14×11Al 2 +0.05×(Al×Si)-0.0401×Ni+0.03255×Mo+0.0603×V+0.0024×Cr+0.00142×Cr 2 -0.00059×(Cr×Ni)+0.0266W···(5)
Wherein Al, mn, si, ni, mo, V, cr and W in the formulas (4) and (5) are the contents (mass%) of the above elements.
Then, based on these lower limit value (Ca) (mass%) and upper limit value (C) b ) The carbon concentration C (mass%) of each of the steel grades a to d and the carbon equivalent C (mass%) were obtained by the following formula (6) p0 (mass%).
C p0 ＝0.17+{(C-C b )/(C b -C a )}×(0.17-0.09)···(6)
In the comparative example, at carbon equivalent C p0 When the content is within the range of 0.09 to 0.17 mass%, the steel grade is judged to be a fracture risk steel grade in the peritectic region.
TABLE 1
| Steel grade | C (mass%) | Si (mass%) | Mn (mass%) | P (mass%) | S (mass%) |
| a | 0.12 | 1.20 | 2.4 | 0.016 | 0.0013 |
| b | 0.08 | 0.01 | 0.3 | 0.010 | 0.0139 |
| C | 0.08 | 1.0 | 2.2 | 0.009 | 0.0009 |
| d | 0.07 | 0.01 | 2.2 | 0.011 | 0.0010 |
TABLE 2
TABLE 3
The surface roughness Sa of the test cast pieces of the steel grades a and b was 60 μm or more, and in the present example, it was determined as a fracture risk steel grade. Based on this determination, it was confirmed that if continuous casting was performed using slow cooling mold flux B with casting speed Vc set to 1.6m/min, cracking of the cast slab could be suppressed. On the other hand, the carbon equivalent C of the steel grades a and b obtained by the above formula (6) p Outside the range of 0.09 to 0.17 mass%,in the comparative examples, steel grades a and b were judged as steel grades without risk of cracking. Based on this determination, it was confirmed that cracking of the cast slab occurred when continuous casting was performed using the strong cooling mold flux a with the casting speed Vc set to 2.0 m/min.
The surface roughness Sa of the test piece of each of the steel grades c and d was smaller than 60. Mu.m, and in the present example, it was determined that the steel grade was not a fracture risk steel grade. Based on this determination, in the case where continuous casting is performed using the strong cooling mold flux a and the casting speed Vc is set to 2.0m/min, breakage of the cast piece does not occur, and productivity can be improved without lowering the casting speed Vc. On the other hand, the carbon equivalent C of the steel grades C and d obtained by the above formula (6) p In the range of 0.09 to 0.17 mass%, in the comparative examples, the steel grades c and d were judged as fracture risk steel grades. If based on this determination, it is necessary to perform continuous casting using slow cooling mold flux B and setting the casting speed Vc to 1.6 m/min. However, in practice, as described above, even if continuous casting was performed using strong cooling mold flux a and casting speed Vc was set to 2.0m/min, cracking did not occur in the cast pieces, and it was confirmed that productivity was unnecessarily impaired if slow cooling mold flux B was used and casting speed Vc was reduced based on the judgment of comparative example.
Claims (11)
1. A method of continuously casting steel, the method comprising:
a test cast piece is produced by injecting molten steel to be continuously cast into a test solidification apparatus and cooling the molten steel,
the surface roughness of the lower surface of the test piece was measured,
the continuous casting is performed using slow cooling mold flux suitable for preventing cracking of a cast piece when the molten steel is continuously cast, in the case where the surface roughness is equal to or greater than a given threshold value, and is performed using strong cooling mold flux suitable for increasing the casting speed of the continuous casting, in the case where the surface roughness is less than the given threshold value.
2. The continuous casting method of steel according to claim 1, wherein,
the threshold value is 60 μm in terms of the arithmetic mean height of the surface roughness obtained by the method specified in ISO 25178.
3. A method of continuously casting steel, the method comprising:
a test cast piece is produced by injecting molten steel to be continuously cast into a test solidification apparatus and cooling the molten steel,
the surface roughness of the lower surface of the test piece was measured,
for a plurality of kinds of molten steel M with the surface roughness above a given threshold, respectively obtaining a carbon concentration lower limit value C of the component of the molten steel M relative to a sub-peritectic region on an Fe-C binary system equilibrium state diagram a (mass%) and upper limit value C of carbon concentration b Influence coefficient alpha of (mass%) a,M 、α b,M ，
Calculating the influence coefficients alpha of a plurality of molten steels M a,M 、α b,M The carbon concentration lower limit C of the sub-peritectic region of the molten steel M is determined by the following formulas (1) and (2) a (mass%) and upper limit value C of carbon concentration b (mass%),
the lower limit C of the carbon concentration in the peritectic region of the new molten steel is obtained from the components of the new molten steel different from the plurality of molten steels M by the following formulas (1) and (2) a The upper limit value C of the carbon concentration b Based on the obtained lower limit C of the carbon concentration a The upper limit value C of the carbon concentration b And the carbon concentration C (mass%) of the new molten steel are obtained by the following formula (3) p (mass%),
at the carbon equivalent C p In the case of 0.09 to 0.17, the continuous casting of the new molten steel is performed using slow cooling mold flux suitable for preventing the rupture of the cast piece at the time of the continuous casting of the new molten steel, at the carbon equivalent C p In the case of being out of the range of 0.09 to 0.17, the connection of the new molten steel is performed using strong cooling mold flux suitable for increasing the casting speed of continuous castingThe casting is continued, and the casting is carried out,
C p ＝0.09+{(C-C a )/(C b -C a )}×(0.17-0.09)···(3)。
4. a continuous casting method of steel according to any one of claims 1 to 3, wherein,
the slow cooling mold flux contains SiO 2 And CaO as a main component, caO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) 1.0 or more and less than 2.0, the crystallization temperature is 1100 ℃ or more, and the kyanite is crystallized as primary crystals.
5. The continuous casting method of steel according to any one of claims 1 to 4, wherein,
the strong cooling mold flux contains SiO 2 And CaO as a main component, caO relative to SiO 2 Mass ratio (CaO/SiO) 2 ) Is 0.7 or more and less than 1.0, and the crystallization temperature is less than 1100 ℃.
6. The continuous casting method of steel according to any one of claims 1 to 5, wherein,
the test solidification device has a cooling rate of 10 at a depth of 1mm from the surface layer of the solidification shell of the molten steel 2 ～10 5 Cooling capacity in c/min.
7. The continuous casting method of steel according to any one of claims 1 to 6, wherein,
the injection rate (unit: kg/s) of the molten steel when the molten steel is injected into the test solidification device is 3 times or more the solidification rate (unit: kg/s) of the molten steel.
8. The continuous casting method of steel according to any one of claims 1 to 7, wherein,
the test solidification device has a bottom surface with a width and a depth of 10mm or more.
9. A steel test solidification apparatus for manufacturing a test cast piece by injecting molten steel and cooling the molten steel,
the steel test solidification device has a cooling rate of 10 at a depth of 1mm from the surface layer of the solidification shell of the molten steel to be injected 2 ～10 5 Casting mold at c/min.
10. The steel solidification test device according to claim 9, further comprising an injection device for injecting the molten steel into the mold, wherein an injection speed (unit: kg/s) of the molten steel by the injection device is 3 times or more as high as a solidification speed (unit: kg/s) of the molten steel in the mold.
11. The test solidification device of steel according to claim 9 or 10, wherein,
the mold has a bottom surface with a width and a depth of 10mm or more, respectively.
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| JPH10263769A (en) * | 1997-03-25 | 1998-10-06 | Kawasaki Steel Corp | Method for continuously casting steel |
| JP2012102359A (en) * | 2010-11-09 | 2012-05-31 | Sumitomo Metal Ind Ltd | Heat-treatable hot-dip galvanized steel sheet, and method of manufacturing the same |
| CN106687233A (en) * | 2014-09-11 | 2017-05-17 | 新日铁住金株式会社 | Mold flux for continuous casting of steel |
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| TW211531B (en) * | 1992-10-27 | 1993-08-21 | China Steel Co Ltd | A method for detecting casting skin breakout within casting mold in continuous casting operation |
| JPH0957413A (en) | 1995-08-30 | 1997-03-04 | Sumitomo Metal Ind Ltd | Method for preventing cracking and breakout of cast slab in continuous casting |
| JP2011025278A (en) * | 2009-07-24 | 2011-02-10 | Jfe Steel Corp | Adhesion evaluating method to solidified shell of mold powder, and solidification trial examination device in continuous casting mold |
| CN103990770A (en) * | 2014-05-15 | 2014-08-20 | 攀钢集团攀枝花钢铁研究院有限公司 | High-alkalinity high-lubricity continuous casting crystallizer casting powder and method for performing continuous casting on peritectic steel slab |
| CN106289037B (en) | 2016-07-19 | 2018-09-07 | 内蒙古科技大学 | A kind of continuous casting steel billet shell thickness eddy current detection method |
| JP6787238B2 (en) * | 2017-04-17 | 2020-11-18 | 日本製鉄株式会社 | Manufacturing method of steel for machine structure |
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| JP6871521B2 (en) * | 2019-03-13 | 2021-05-12 | 品川リフラクトリーズ株式会社 | Manufacturing method of mold powder and medium carbon rope |
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| JPH10263769A (en) * | 1997-03-25 | 1998-10-06 | Kawasaki Steel Corp | Method for continuously casting steel |
| JP2012102359A (en) * | 2010-11-09 | 2012-05-31 | Sumitomo Metal Ind Ltd | Heat-treatable hot-dip galvanized steel sheet, and method of manufacturing the same |
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