Cu-sn-containing steel production method
The method addresses the challenge of stable conveyance and cracking in Cu-Sn-containing steel production by applying specific fluxes to incorporate Cu-Sn melts, ensuring stable conveyance and preventing surface defects in low-capacity heating furnaces.
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2024-09-06
- Publication Date
- 2026-06-17
AI Technical Summary
Existing methods for producing Cu-Sn-containing steel face challenges in maintaining stable conveyance and preventing surface cracking during hot working, particularly when using scrap with high Cu and Sn content, due to the formation of Cu-Sn melts that cause red shortness and cracking, and require costly Ni additions or high initial investment for equipment.
A method involving the application of a first flux with a liquid fraction of 10% at 1000°C and a second flux with 0% liquid fraction at 1400°C to the surface of a Cu-Sn-containing slab, followed by heating and hot working, to incorporate Cu-Sn melts into the flux and prevent adherence to conveyance surfaces.
Stable conveyance and prevention of surface cracking are achieved without costly Ni additions, even with low-capacity heating furnaces, by using a combination of fluxes to manage Cu-Sn melts effectively.
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for producing a Cu-Sn-containing steel, which can prevent surface cracking of the steel and maintain stable conveyance of the steel.Background Art
[0002] With the increasing demand for reducing CO 2 emissions, the use of an electric arc furnace in a steel making process has been expanding in recent years. In order to reduce production costs in a steel making process, it is necessary to use scrap having a high content of tramp elements, particularly scrap having a high content of Cu and Sn, as a raw material.
[0003] Removal of tramp elements in a refining process is difficult; some tramp elements inevitably remain in the steel. In a slab in which tramp elements (e.g., Cu and Sn) remain after a refining process (hereinafter referred to as a "Cu-Sn-containing slab" or simply as a "slab"), a Cu-Sn melt will be formed in the surface during a hot heating process. The Cu-Sn melt causes red shortness during a hot working process such as rolling, causing cracking in the surface of the steel (hereinafter referred to as the "Cu-Sn-containing steel" or simply as the "steel slab") after the hot working process. This makes it difficult to finally produce a hot-rolled steel sheet with excellent surface properties.
[0004] It is known that precipitation of a Cu-Sn-enriched melt in the surface of a Cu-Sn-containing slab during high-temperature oxidation of the slab, which may cause surface defects of the Cu-Sn-containing steel, can be inhibited and therefore cracking in the surface of the steel slab can be prevented by adding a predetermined amount of Ni to the Cu-Sn-containing slab. However, the addition of Ni is costly and cannot take advantages of the use of scrap with a high content of tramp elements.
[0005] In view of the fact that a Cu-Sn melt, which causes surface defects of a Cu-Sn-containing steel, is formed only in the surface of a Cu-Sn-containing slab, a method has been proposed which involves modifying the surface of a Cu-Sn-containing slab to prevent its surface cracking.
[0006] Patent Literature 1 discloses a method which involves melting a slab surface by plasma heating using a DC arc plasma, which is being vibrated by an AC magnetic field, and adding Ni only to the molten surface of the slab. Patent Literature 2 discloses a method which involves attaching a flux containing SiO 2 to the surface of a continuously cast slab containing Cu and Sn at a slab temperature in the range of not less than 1150°C, thereby forming a scale of FeO-SiO 2 -based low-melting point oxide liquid. A Cu-Sn melt is incorporated into the scale to prevent surface red shortness.Citation ListPatent Literature
[0007] PTL 1: Japanese Patent No. 5454132 PTL 2: Japanese Unexamined Patent Application Publication No. 6-297025 Summary of InventionTechnical Problem
[0008] While the method disclosed in Patent Literature 1 can reduce the cost of Ni addition, it requires a huge initial investment cost for equipment for AC magnetic field and arc plasma. The method disclosed in Patent Literature 2 is not applicable to hot working in a temperature range below 1150°C. Further, during conveyance of a slab, the flux may peel off the slab and adhere to fixed beams and movable beams which convey the slab, making it impossible to maintain stable conveyance of the slab.
[0009] The present invention has been made in view of the above situation. It is therefore an object of the present invention to provide a method for producing a Cu-Sn-containing steel, which can maintain stable conveyance of a Cu-Sn-containing steel without causing surface cracking of the steel even in hot working using a heating furnace with a low heating capacity.Solution to Problem
[0010] The present invention has the following features to solve the above problems. [1] A method for producing a Cu-Sn-containing steel, comprising: a hot heating step of attaching a first flux, which comprises at least one of B 2 O 3 , P 2 O 5 , K 2 O, PbO, Na 2 O-FeO, Na 2 O-SiO 2 , Na 2 O-TiO 2 , and Li 2 O-SiO 2 as a component, and has a liquid fraction of 10 mass % or more at 1000°C, to a surface of a Cu-Sn-containing slab such that the mass of the first flux per unit area of the surface of the slab falls within the range of not less than 50 g / m 2< and not more than 5000 g / m 2< , and then attaching a second flux, which has a liquid fraction of 0 mass % at 1400°C or lower, to the surface of the Cu-Sn-containing slab such that the mass of the second flux per unit area of the surface of the slab falls within the range of not less than 50 g / m 2< and not more than 5000 g / m 2< , and heating the Cu-Sn-containing slab at a temperature of not less than 1000°C and not more than 1400°C; and a hot working step of hot-working the Cu-Sn-containing slab. [2] The method for producing a Cu-Sn-containing steel according to [1], wherein the second flux comprises at least one of SiO 2 , MgO, Al 2 O 3 , and SiC. Advantageous Effects of Invention
[0011] According to the present invention, stable conveyance of a Cu-Sn-containing steel can be maintained without causing surface cracking of the steel even in hot working using a heating furnace with a low heating capacity.Brief Description of Drawings
[0012] [FIG. 1] FIG. 1 shows diagrams illustrating the effect of a flux on a Cu-Sn melt. [FIG. 2] FIG. 2 is a schematic plan view illustrating a conveyance condition of a Cu-Sn-containing slab in a heating furnace. [FIG. 3] FIG. 3 is a diagram showing a Cu-Sn-containing slab with a first flux and a second flux attached to the surface. [FIG. 4] FIG. 4 is a schematic view showing an overview of a flux spraying apparatus. Description of Embodiments
[0013] A method for carrying out the present invention will now be described. As used herein, the term "flux" may include both "first flux" and "second flux." The wording "first flux" or "second flux" refers to the respective flux.
[0014] The formation behavior of a Cu-Sn melt in the surface of a Cu-Sn-containing slab, as observed when the slab is heated to a high temperature and the surface of the slab is in an oxidized state (hereinafter referred to as a "high-temperature oxidized state"), and a flux attached to the surface of the slab will be described first using FIG. 1.
[0015] FIG. 1(a) shows a Cu-Sn-containing slab with no flux attached to the surface. FIG. 1(b) shows a Cu-Sn-containing slab with a flux, having a liquid fraction of 80% in a high-temperature atmosphere, attached to the surface. FIG. 1(c) shows a Cu-Sn-containing slab with a flux, having a liquid fraction of 5% in a high-temperature atmosphere, attached to the surface.
[0016] FIG. 1(a) schematically shows the state of the interface between the Cu-Sn-containing slab in a high-temperature oxidized state and a scale. As shown in FIG. 1(a), since Fe is more oxidizable than Cu or Sn, a scale layer is formed on the surface of the slab, while Cu and Sn are concentrated in the surface of the slab. The melting point of Cu is 1085°C, and the concentration of Sn in the slab surface reduces the melting point of the surface region further. Therefore, in a high-temperature atmosphere of 1000°C or higher, the Cu-Sn-enriched phase is a liquid phase, and this melt (hereinafter referred to as "Cu-Sn melt") penetrates into grain boundaries in the Cu-Sn-containing slab. The Cu-Sn melt serves as the source of embrittlement during hot working such as rolling; the larger the amount of the melt, the more cracking propagates in the depth direction.
[0017] FIG. 1(b) schematically shows the state of the interface between the Cu-Sn-containing slab and a scale, as observed when a flux, having a liquid fraction of 80% in a high-temperature atmosphere, has been attached to the slab. The scale formed by oxidation reacts and mixes with the liquid phase of the flux, resulting in the formation of a mixed state (mixed phase) of the flux and the scale on the surface of the slab, as shown in FIG. 1(b). The Cu-Sn melt, which has been present in the surface of the slab, is incorporated into the liquid phase of the mixed phase. Thus, the Cu-Sn melt can be removed without allowing it to penetrate into grain boundaries in the Cu-Sn-containing slab.
[0018] FIG. 1(c) schematically shows the state of the interface between the Cu-Sn-containing slab and a scale, as observed when a flux, having a liquid fraction of 5% in a high-temperature atmosphere, has been attached to the slab. In the state shown in FIG. 1(c), the flux does not sufficiently form a liquid phase; therefore, the scale formed on the slab surface does not sufficiently react and mix with the flux while oxidation of the slab surface proceeds. Accordingly, the slab surface and the flux are separated by the scale and, as in the high-temperature oxidized state shown in FIG. 1(a), the Cu-Sn melt penetrates into grain boundaries in the Cu-Sn-containing slab.
[0019] As described above using FIGS. 1(a) through 1(c), in order to remove a Cu-Sn melt present in the surface of a slab in a high-temperature oxidized state, it is necessary to prevent the separation of the surface of the slab and a flux by a scale. Thus, it is necessary to sufficiently liquefy a flux in a high-temperature atmosphere as in a heating furnace or the like.
[0020] In view of the above, the present invention focuses on a flux (hereinafter referred to as "first flux"), comprising at least one of B 2 O 3 , P 2 O 5 , K 2 O, PbO, Na 2 O-FeO, Na 2 O-SiO 2 , Na 2 O-TiO 2 , and Li 2 O-SiO 2 as a component, as a flux that achieves a liquid fraction of 10 mass % or more in a high-temperature atmosphere at 1000°C. As used herein, the term "Na 2 O-FeO" refers to the inclusion of both components, Na 2 O and FeO. The term "Na 2 O-SiO 2 " refers to the inclusion of both components, Na 2 O and SiO 2 . The term "Na 2 O-TiO 2 " refers to the inclusion of both components, Na 2 O and TiO 2 . The term "Li 2 O-SiO 2 " refers to the inclusion of both components, Li 2 O and SiO 2 .
[0021] The liquid fraction of a flux may be determined using an equilibrium diagram obtained by an experiment or a thermodynamic calculation. Alternatively, the liquid fraction of a flux may be evaluated in terms of a liquid fraction in a cross-section of a sample which has been held at a predetermined temperature and reached thermodynamic equilibrium, and which has then been frozen by a method such as water cooling.
[0022] In addition to at least one of the above-listed components, namely B 2 O 3 , P 2 O 5 , K 2 O, PbO, Na 2 O-FeO, Na 2 O-SiO 2 , Na 2 O-TiO 2 , and Li 2 O-SiO 2 , the composition of the first flux may also contain components that are unavoidably present, such as an oxide, a fluoride, a carbonate, and a metal, as long as the composition achieves a liquid fraction of 10 mass % or more at 1000°C.
[0023] A flux known as a mold flux for continuous casting, comprising SiO 2 , CaO, Li 2 O, Na 2 O, F, MgO, Al 2 O 3 , etc. as main components, can be used as the first flux as long as it has a liquid fraction of 10 mass % or more at 1000°C.
[0024] The base material of the first flux, comprising at least one of the above-listed components, namely B 2 O 3 , P 2 O 5 , K 2 O, PbO, Na 2 O-FeO, Na 2 O-SiO 2 , Na 2 O-TiO 2 , and Li 2 O-SiO 2 , may be an oxide, a carbonate, a fluoride, etc. A mixture of these base materials may also be used. The first flux may be in a pre-molten state when it is attached to the surface of a Cu-Sn-containing slab.
[0025] A conveyance condition of a Cu-Sn-containing slab will now be described using FIG. 2. FIG. 2 is a schematic plan view illustrating a conveyance condition of a Cu-Sn-containing slab S in a heating furnace. As shown in FIG. 2, fixed beams 11 and movable beams 12 are provided in the heating furnace to convey the Cu-Sn-containing slab S in a conveying direction A.
[0026] When the Cu-Sn-containing slab S is placed on the upper surfaces (skids) of the fixed beams 11 and the movable beams 12 in the heating furnace, the movable beams 12 periodically make a rotational movement with respect to the fixed beams 11 which are fixed in position, within a movement range in the vertical direction and in the conveying direction A. The Cu-Sn-containing slab S is moved (conveyed) along the conveying direction A by the periodic rotational movement of the movable beams 12.
[0027] When the Cu-Sn-containing slab S with the first flux attached to the surface is placed on the upper surfaces (skids) of the fixed beams 11 and the movable beams 12 in the heating furnace where the temperature is in the range of not less than 1000°C and not more than 1400°C, the liquefied first flux may peel off the Cu-Sn-containing slab S and adhere to the surfaces of the fixed beams 11 and the movable beams 12. As the number of times the Cu-Sn-containing slab S is conveyed increases, the amount of the adhering first flux becomes uneven at various positions on the fixed beams 11 and the movable beams 12, causing tilting of the Cu-Sn containing slab S in the height direction.
[0028] This may cause a displacement of the Cu-Sn-containing slab S in a width direction B, which is perpendicular to the conveying direction A, during conveyance of the slab, making stable conveyance of the slab difficult. Further, an increase in such a displacement in the width direction B may cause a trouble such as fall of the Cu-Sn-containing slab S in the heating furnace.
[0029] In the method for producing a Cu-Sn-containing steel according to this embodiment, in order to prevent the first flux from adhering to the fixed beams 11 and the movable beams 12, another flux (hereinafter referred to as the "second flux") having a higher melting point than the first flux is attached onto the first flux.
[0030] In particular, the second flux, which has a liquid fraction of 0 mass % at 1400°C or lower, is attached onto the first flux. This makes it possible to prevent the first flux from adhering to the fixed beams 11 and the movable beams 12 in the heating furnace where the temperature is in the range of not less than 1000°C and not more than 1400°C. The second flux preferably comprises at least one of SiO 2 , MgO, Al 2 O 3 , and SiC as a component from the viewpoint of reducing the reactivity of the second flux with the first flux, thereby reducing a compositional change of the second flux.
[0031] The state of the first flux and the second flux during the hot heating step will be explained using FIG. 3. FIG. 3 is a diagram illustrating the behavior of the first flux and the second flux on the surface of a Cu-Sn-containing slab during the hot heating step.
[0032] In the hot heating step, a Cu-Sn-containing slab is heated at a temperature of not less than 1000°C and not more than 1400°C. Liquefaction of the first flux, which has a liquid fraction of 10 mass % or more at 1000°C, proceeds on the surface of the Cu-Sn-containing slab. The scale formed by oxidation reacts and mixes with the liquid phase of the first flux, resulting in the formation of a mixed state (mixed phase) of the first flux and the scale on the surface of the Cu-Sn-containing slab, as shown in FIG. 3. On the other hand, the second flux, which has a liquid fraction of 0 mass % at 1400°C or lower, remains in a flux state, without liquefaction, on the surface of the first flux which is being liquefied.
[0033] A Cu-Sn melt, which has been present in the surface of the Cu-Sn-containing slab, is incorporated into the liquid phase of the mixed phase (the first flux and the scale). Thus, the Cu-Sn melt can be removed without allowing it to penetrate into grain boundaries in the Cu-Sn-containing slab. This makes it possible to prevent surface cracking of the Cu-Sn-containing steel even in hot working using a heating furnace with a low heating capacity.
[0034] Since the second flux remains in a flux state, without liquefaction, on the surface of the first flux, the first flux can be prevented from adhering to the surfaces of the fixed beams 11 and the movable beams 12. Thus, while the Cu-Sn-containing slab is being conveyed in the heating furnace, the first flux and the second flux remain on the surface of the Cu-Sn-containing slab without peeling off from the slab. This can prevent a displacement of the Cu-Sn-containing slab in the width direction, which is a direction perpendicular to the conveying direction, during convenance of the slab, making it possible to maintain stable conveyance of the slab.
[0035] As described above, in this embodiment, the second flux is attached onto the first flux to prevent the first flux from adhering to the fixed beams 11 and the movable beams 12 in the heating furnace. The same effect can be achieved for the Cu-Sn-containing slab S after it is extracted from the heating furnace; that is, when the Cu-Sn-containing slab S, which has undergone the hot heating step, is conveyed, for example, by conveying rollers after it is extracted from the heating furnace, the first flux can be prevented from adhering to the conveying rollers.
[0036] As shown in FIG. 3, in the hot heating step, the liquefied first flux and the non-liquefied second flux adhere to the surface of the Cu-Sn-containing slab. After the hot heating step, the Cu-Sn-containing slab may be subjected to an oxide removal step for removing the scale (descaling) from the surface of the slab. The scale, the first flux incorporating the Cu-Sn melt, and the second flux are removed in the oxide removal step. Thereafter, the Cu-Sn-containing slab may be subjected to a hot working step for hot-working the Cu-Sn-containing slab.
[0037] A method for attaching (supplying) a flux to the Cu-Sn-containing slab needs not be limited to a particular method; any appropriate method such as coating or spraying may be used. The flux may be in the form of a powder or a slurry. The flux may be dissolved or suspended in a liquid such as water, and the liquid may be applied to the slab. Like a common coating material, the flux may be mixed with an inorganic or organic mixing polymer or solvent.
[0038] A flux supply apparatus 10 will now be described using FIG. 4. FIG. 4 is a schematic view showing an overview of the flux supply apparatus 10. As shown in FIG. 4, in order to supply a flux 4, a slab 1 is placed on rollers 3 for placement or conveyance. The flux supply apparatus 10 has spray guns 2, disposed above and below the slab 1 on the rollers 3, to uniformly supply the flux 4 to the surface of the slab 1. A flux powder 5 and spray air 6 are mixed in a supply pipe 7, and the mixture is supplied through the supply pipe 7 to each spray gun 2. The amount of the flux 4 attached to the surface of the slab 1 can be adjusted by controlling the feed rate of the flux 4 in the supply pipe 7 and the conveying speed of the slab 1.
[0039] The attachment of the flux 4 to the lower surface of the slab 1, which is in contact with the rollers 3, may be performed by reversing the upper and lower surfaces of the slab 1 using a slab reversing apparatus, and attaching the flux 4 to the surface which is now the upper surface, or by supplying the flux from the spray gun 2, provided below the lower surface of the slab 1, while moving the slab 1 on the rollers 3. The flux 4 may be in a powder form when it is applied as a coating material. The flux 4 may be in a flocculent form. Such a flocculent flux may be attached to the slab using an adhesive.
[0040] The attachment (supply) of the fluxes to the slab 1 may be performed by first attaching the first flux to the slab 1, and then attaching the second flux onto the first flux. The attachment of the first and second fluxes to the slab 1 may be performed prior to the hot heating step of hot-heating the slab.
[0041] The amount of the first flux attached to the surface of the Cu-Sn-containing slab is preferably such that the mass of the first flux per unit area of the surface of the slab falls within the range of not less than 50 g / m 2< and not more than 5000 g / m 2< . If the amount of the first flux attached is less than 50 g / m 2< , the first flux cannot sufficiently incorporate a Cu-Sn melt, resulting in the undesirable occurrence of cracking in the surface of the steel slab after hot working. If the amount of the first flux attached exceeds 5000 g / m 2< , the first flux, supplied in such an excessive amount, may adhere to the rollers 3, etc., undesirably leading to early deterioration of the flux supply apparatus 10 and causing economic problems, such as increased costs, due to the excessive supply of the first flux.
[0042] The amount of the second flux attached to the surface of the Cu-Sn-containing slab is preferably such that the mass of the second flux per unit area of the surface of the slab falls within the range of not less than 50 g / m 2< and not more than 5000 g / m 2< . If the amount of the second flux attached is less than 50 g / m 2< , it is undesirably not possible to securely prevent the liquefied first flux from adhering to the fixed beams 11 and the movable beams 12. If the amount of the second flux attached exceeds 5000 g / m 2< , the second flux, supplied in such an excessive amount, may adhere to the rollers 3, etc., undesirably leading to early deterioration of the flux supply apparatus 10 and causing economic problems, such as increased costs, due to the excessive supply of the second flux.
[0043] The slab (Cu-Sn-containing slab), to which the fluxes are supplied, is heat-treated at a temperature of not less than 1000°C and not more than 1400°C, and then subjected to hot rolling (hot working). A heating temperature of less than 1000°C is undesirable because it increases the deformation resistance of the slab during hot working, leading to a reduction in rolling efficiency. A heating temperature of more than 1400°C is undesirable because of the possibility of failing to achieve predetermined steel material properties. The heating temperature of the slab (Cu-Sn-containing slab) is more preferably not less than 1000°C and not more than 1300°C.EXAMPLES
[0044] The following illustrates examples of Cu-Sn-containing steels produced based on the Cu-Sn-containing steel production method according to this embodiment.
[0045] In inventive examples, the surface of a Cu-Sn-containing slab (carbon steel), containing 1.0 mass % of Cu and 0.1 mass % of Sn, was coated with a first flux and with a second flux each 50,000 times. The slab was then placed in a heating furnace and heated (hot-heated) for 1 to 5 hours at an ambient temperature of not less than 1000°C and not more than 1400°C. Subsequently, the heated Cu-Sn-containing slab was subjected to hot working, consisting of rough rolling and finish rolling, to produce a Cu-Sn-containing steel (hot-rolled steel sheet) having a thickness of 2.3 mm.
[0046] In a comparative example, the surface of the same Cu-Sn-containing slab (carbon steel) was coated only with a first flux, and the slab was subjected to hot heating and hot working. In another comparative example, the same Cu-Sn-containing slab (carbon steel) was subjected to hot heating and hot working without performing, in advance, coating of the surface of the slab with a flux.
[0047] The components and the liquid fraction of the first flux used in the examples are shown in Table 1. The component and the liquid fraction of the second flux are shown in Table 2. The liquid fractions of the fluxes were determined by the following method. First, 10 g of a sample, obtained by mixing the components of the first flux shown in Table 1, was added to a platinum crucible, and the sample was melted by holding it at 1600°C for 1 hour in an electric resistance furnace, and then held at 1000°C for 48 hours. The sample was then frozen by water-cooling the side of the platinum crucible holding the sample, and the sample was cut such that it was semicircular when viewed from above the platinum crucible. A cross-section of the frozen sample was observed in an optical microscope, and the cross-sectional liquid fraction was measured by image analysis. The liquid fraction of the second flux was measured in the same manner except for no mixing of components. [Table 1]Components of first flux [mass %]Liquid fraction at 1000°C [mass %]SiO 2 CaONa 2 OF36.635.319.19.0100.0 [Table 2] Component of second flux [mass %]Liquid fraction at 1400°C [mass %]Al 2 O 3 100.00.0
[0048] In the inventive examples and the comparative examples, an evaluation was performed on the conveyance condition of the Cu-Sn-containing slab after hot heating. The conveyance condition was evaluated when the heated Cu-Sn-containing slab which had been extracted from the heating furnace, on rollers. In particular, the Cu-Sn-containing slab from the heating furnace was placed on the rollers, and conveyed on the rollers at a conveying speed of 100 mm / s, and the time of arrival of the slab at a predetermined position on the conveying path was measured. Arrival or non-arrival of the Cu-Sn-containing slab at the predetermined position was determined by detecting the slab using a laser rangefinder installed at the predetermined position. The measurement of the arrival time of the Cu-Sn-containing slab was made by measuring a time duration between the start time of conveyance of the slab on the rollers and the time of arrival of the slab at the predetermined position. In each example, conveyance of the slab on the rollers was performed 10 times, and the average of the time durations measured was used as the time duration in that example.
[0049] The evaluation of conveyance condition was made by comparing a time duration measured in each example, in which the Cu-Sn-containing slab was coated with the flux(es), with a reference time duration, which was a time duration as measured for the Cu-Sn-containing slab coated with no flux. The conveyance condition was evaluated as "good" when the time difference was less than 1 second, and evaluated as "poor" when the time difference was 1 second or more. The time difference of 1 second or more corresponds to a case in which a displacement (100 mm) of the Cu-Sn-containing slab occurred in the width direction perpendicular to the conveying direction.
[0050] The Cu-Sn-containing steel produced in each example was also inspected (evaluated) for surface cracking in the following manner. First, 10 Cu-Sn-containing steel sheets, each 1 m wide and 1 m long, were sampled at random in the rolling direction, and the 1 m x 1 m area (surface) of each sheet was divided into 100 equal squares each having an area of 10000 mm 2< . Next, the number of squares in which cracking had occurred was counted to determine the number per m 2< , and the results for the 10 steel sheets were averaged. The steel was evaluated as "good" when the occurrence frequency of cracking was 0.3 / m 2< or less, and evaluated as "poor" when the occurrence frequency of cracking was more than 0.3 / m 2< . The results of the examples are shown in Table 3. [Table 3]ExamplesFirst fluxSecond fluxAmount of second flux attached [g / m 2< ]Conveyance conditionOccurrence of crackingInventive Ex. 1presentpresent4000goodgoodInventive Ex. 2presentpresent1500goodgoodInventive Ex. 3presentpresent100goodgoodComp. Ex. 1presentabsent-poorgoodComp. Ex. 2absentabsent-goodpoor
[0051] As shown in Table 3, Comparative Example 2 is an example in which the Cu-Sn-containing slab, coated with no flux, was conveyed and hot-worked. As evaluated "good" in terms of "conveyance condition", it was confirmed that the Cu-Sn-containing slab was conveyed smoothly, without attachment of a liquefied flux to the conveying rollers, such that the time duration between the conveyance start time and the time of arrival of the slab at the predetermined position was minimum. Thus, the conveyance conditions in the other examples were evaluated based on the time duration measured in this example (Comparative Example 2). Since the slab of Comparative Example 2 was not coated with the first flux, the "occurrence of cracking" was evaluated as "poor".
[0052] As shown in Table 3, in Inventive Examples 1 to 3 and Comparative Example 1, the first flux was attached to the surface of the Cu-Sn-containing slab. The amount of the first flux attached was 400 g / m 2< per unit area of the surface of the Cu-Sn-containing slab. While the slab was coated with the first flux in Comparative Example 1, the slab was not coated with the second flux. Therefore, the liquefied first flux adhered to the conveying rollers. As a result, the time duration between the conveyance start time and the time of arrival of the slab at the predetermined position was longer than that of Comparative Example 2; thus, the conveyance condition was evaluated as "poor". On the other hand, because of coating of the slab with the first flux, the "occurrence of cracking" was evaluated as "good" in Comparative Example 1.
[0053] Inventive Examples 1 to 3 are examples in which the Cu-Sn-containing slab was coated with the first flux, and the second flux was coated onto the first flux. In Inventive Examples 1 to 3, the amount of the second flux attached was 100 to 4000 g / m 2< per unit area of the surface of the Cu-Sn-containing slab. In such a slab, the first flux was liquefied and the liquid incorporated a Cu-Sn melt during the hot working stage, while the second flux was not liquefied. This prevented the first flux from adhering to the conveying rollers. Therefore, the conveyance condition was evaluated as "good", and the Cu-Sn-containing steel was able to be produced stably without any trouble during conveyance. Furthermore, because of coating of the slab with the first flux, the "occurrence of cracking" was evaluated as "good" in Inventive Examples 1 to 3. Reference Signs List
[0054] 1slab 2spray gun 3roller 4flux 5flux powder 6spray air 7supply pipe 10flux supply apparatus 11fixed beams 12movable beams Aconveying direction SCu-Sn-containing slab
Claims
1. A method for producing a Cu-Sn-containing steel, comprising: a hot heating step of attaching a first flux, which comprises at least one of B2O3, P2O5, K2O, PbO, Na2O-FeO, Na2O-SiO2, Na2O-TiO2, and Li2O-SiO2 as a component, and has a liquid fraction of 10 mass % or more at 1000°C, to a surface of a Cu-Sn-containing slab such that the mass of the first flux per unit area of the surface of the slab falls within the range of not less than 50 g / m2 and not more than 5000 g / m2, and then attaching a second flux, which has a liquid fraction of 0 mass % at 1400°C or lower, to the surface of the Cu-Sn-containing slab such that the mass of the second flux per unit area of the surface of the slab falls within the range of not less than 50 g / m2 and not more than 5000 g / m2, and heating the Cu-Sn-containing slab at a temperature of not less than 1000°C and not more than 1400°C; and a hot working step of hot-working the Cu-Sn-containing slab.
2. The method for producing a Cu-Sn-containing steel according to claim 1, wherein the second flux comprises at least one of SiO2, MgO, Al2O3, and SiC.