TW200404900A - Cu-containing steel excellent in surface quality and a method for producing the same - Google Patents

Abstract

The present invention provides a Cu-containing steel excellent in a surface quality which can avoid red-shortness caused by Cu during hot rolling, and provides a method for producing the same. This Cu-containing steel has oxide scale on the surface of the steel, and contains Cu-concentration (Ccu at 0.05 to 3 wt%), and also contains an amount of concentrated Cu (Ecu: μ g.cm<SP>-2</SP>), which is concentrated at the interface between oxide scale and the surface of the steel at per unit area, of less than 18.6 Ccu × d, where d is an effective steel thickness (mm) at a cross-sectional area of the steel divided by the total length of the cross-section. A production process of the steel comprises the steps of: heating the steel in a heating furnace under low oxygen content atmosphere condition for forming ustite scale layer only so that a melted Cu existing at an interface between oxide scale and the steel surface is vapourized or dispersed, or carrying out scale-removing treatment at least twice during a first hot rolling step after extracting the heated steel from a heating furnace.

Description

说明 Description of invention:

[^^ 明 户 斤 属 々 员 J The present invention relates to a steel-containing steel material having excellent surface characteristics manufactured by hot rolling and a method for manufacturing the same. More specifically, S relates to a copper-containing steel material having excellent surface characteristics that can suppress Cu from accumulating on the surface of the steel material and prevent red hot brittleness of the steel material during the heat treatment of the steel material before hot rolling, and a method for manufacturing the same. H Jii recycles and reuses many steel scraps as an iron source for steel materials. In the recovery of this steel scrap, when Cu is contained in the steel scrap, it is difficult to remove Cu by smelting, so Cu is kept mixed with the steel, resulting in problems during hot rolling and the like. That is, when the steel material is heated before hot rolling, Cu will be enriched at the interface between rust and ferrous iron, and when the Cu enrichment amount is too large, it will cause a red hot brittleness problem such as cracks on the surface of the steel material. To avoid this problem, the actual situation is to limit the amount of steel scrap containing CU. However, considering the increase in energy consumption during the production of steel from iron ore, or the increase in the amount of scrap iron stored in steel, it is better to use more steel scrap as an iron source in the future, so it is expected to develop even Cu containing It also does not produce red hot brittle steel. Generally speaking, hot rolled steel is manufactured by placing the steel into a heating furnace before hot rolling. It is heated by combustion gas for about 1 to 4 hours, and heated at a temperature of about 1100 to 1300 ° c. The furnace was drawn out, and then rust (descaling) was removed with high-pressure water, followed by hot rolling. Generally, the combustion gas supplied to the heating furnace contains oxygen, water vapor, and carbon dioxide exclusively oxidizing gases. Therefore, a rust layer is formed on the surface of the steel material heated to a high temperature in the heating furnace. The scale layer is mainly composed of iron oxides. Generally, from the 20042004900 layer, three layers of hematite (Fe203), magnetite (Fe304), and ferrite (FeO) are formed in this order. Then 'when iron is oxidized by an oxidizing gas in the combustion gas at a high temperature, when Cu, Ni and other metals are superior to iron, these metals will not oxidize, and 5 will be in the rust layer and the ferrous iron. Interface enrichment. In the case of Cu, there is only a few _% solubility in r iron. When the Cu enrichment exceeds this, Cu will appear as a metal phase. The melting point of Cu is 1080 ° C. Generally, the heating of steel before hot rolling is performed at a temperature higher than this temperature, so the liquid phase of Cu in the molten state is generated at the rust / fat iron interface. These will invade The grain boundary of the fertile grain iron cannot withstand the shear stress or hot tensile stress during hot rolling, and causes surface cracks, that is, red hot brittleness. It is currently known that the addition of Ni, which is almost equal to the Cu concentration, can effectively prevent such red hot brittleness caused by Cu. This is because by adding Ni, the solid solution limit of Cu in τ iron is increased, and because the melting point of the Cu-rich phase becomes higher, the occurrence of Cu at the rust scale / fertilizer iron interface can be suppressed (refer to, for example, special characteristics) Kaiping No. 7.242938). 15 In addition, in Japanese Patent Application Laid-Open No. 6-297026, the addition of Si also has the effect of preventing red hot brittleness. Once Si was added, iron olivine was formed near the rust / fat iron interface, at 1170. (: The above reacts with the iron ore in the rust to make the liquid phase oxidize. Because the liquid phase is mixed with the liquid phase of Cu, the liquid phase ^ invades &amp; the ferrous grain iron grain boundary. _ 2〇 * However, in the method of adding red to suppress the red hot brittleness caused by Cu, the cost is increased due to-making: the high-priced metal Ni. Also, the grain boundary oxidation during heating is promoted. It prevents the red hot brittleness caused by Cu, but hinders the peeling of the scale, leading to the occurrence of rust stains. H. Adding Si to prevent the red hot brittleness caused by ~ In the method of adding 6 200404900 added Si The peelability of the steel is very poor, so even if the high-pressure water is used to remove the rust before hot rolling, the rust will still remain, making the surface of the steel red, etc., and causing the surface characteristics to be damaged. In the washing step, since rust is difficult to dissolve during pickling, it not only increases the cost of the pickling step, but also reduces productivity. 5 [Akimoto] The object of the present invention is to provide an excellent Copper steel and its manufacturing method need not add chaos or Changing the composition of the steel in this way can suppress the red hotness and brittleness of the steel caused by CU when the copper-containing steel is hot-rolled, and more specifically, it contains 匸 ⑼3% by mass when heated. In order to solve the above-mentioned problem, the present invention is based on the following (丨) ~ (9). (1) An excellent surface The characteristic copper-containing steel is a steel-containing steel with rust on the surface, which is characterized by: 15 Cu Cu concentration (mass%) of the matrix is 0.05% or more and 3% or less, if the cross section of the steel perpendicular to the rolling direction When the cross-sectional area s is divided by its perimeter, and the effective thickness of the steel is d (mm), the Cu enrichment per unit of surface area Ecu (# g · cm · 2) that is concentrated near the interface between rust and ferrous iron is consistent with The relationship of formula (1):

Ecu &lt; 18.6CCuxd &_; (1) 〇2〇 A copper-containing steel with excellent surface characteristics, which is a copper-containing steel with rust on the surface, is characterized by: Cu concentration of the substrate CCu (mass ° / 〇) in Above 0.05%, if the cross-sectional area s of the cross section of the steel perpendicular to the rolling direction is divided by its perimeter, the effective thickness of the steel is d (mm), and in the temperature range of 100 (rc above 1300 t) 7 200404900 When the total matrix concentration of the red hot brittleness-inducing element, which is superior to iron and has a melting point below 1300t, is better than iron, the red hot brittleness-inducing element is enriched in rust and fertilizer particles. The total red hot brittleness-inducing element enrichment of the total enrichment amount per unit area of 2 near the interface of iron (v 5 cm · 2) conforms to the relationship of the following formula (2):

Ei &lt; 18.6Cixd ... (2) 〇 (3) The steel-containing steel with excellent surface characteristics as described in (2) above, wherein one of the aforementioned red hot brittleness-inducing elements is Cu, and the other is any of Sn, Sb, and As 1 or more. 10) A copper-containing steel material having excellent surface characteristics as described in any one of the above items ⑴ to ⑴, wherein the relationship between the matrix Ni concentration cNi (mass%) and the matrix Cu concentration ecu (mass%) conforms to the relationship of the following formula (3) : 0.061CCu2 + 0.32CCu + 0.0035 $ CNi $ 1.5 · (3). (5) 15 copper-containing steel materials having excellent surface characteristics as described in any one of (1) to (3) above, wherein the aforementioned copper-containing steel materials contain, by mass, 0.01% to 0.15%, Nb: 0.01 ~ 0.15%, V: 0.01 ~ 0 15% of any i or two or more types, P: 0 · 010 ~ 0 · 100〇 / 〇, s: 〇_〜〇〇50 ％, rem: One or two or more of 0.002 to 0.150%. (6) The copper-containing steel material having excellent surface characteristics as described in (5) above, in which 20 of the foregoing copper-containing steel materials contain at least one or more of carbides, nitrides, or carbons of Ti, Nb, and V Nitrides and precipitates having a particle size of 1011111 or more and 1 // m or less and a density of 105 or more per mm2. (7) A method for manufacturing a copper-containing steel material having excellent surface characteristics, which is a method for manufacturing a copper-containing steel material after heating the copper-containing steel material in a heating furnace. 8 200404900 method, characterized in that: When the Cu content of Cu (mass%) is 0.05% or more and 3% or less, while heating in the aforementioned heating furnace, the whole or part of the area in a heating furnace in which the surface temperature of the steel material is 1080 ° C or more is prepared as follows: The environment (low oxygen concentration environmental conditions) below the oxygen concentration p02 (volume%) shown in Table 5 of the formula (4), thereby forming rust scale formed by the ferrite and making it vertical after the hot rolling is completed. When the cross-sectional area s of the wearing surface of the steel in the rolling direction is divided by the effective thickness of the steel 1 of the circumference 1 and is d (mm), the surface area per unit surface area near the interface between the rust and the ferrous iron of the copper-containing steel is enriched. Cu enrichment ECu (// g · cm · 2) is less than 18.6CCuxd, φ 10 p02 = kp / (2wk〇… (4) Here, kp is the parabolic law speed constant (g2 · cm_4 ·), specifically Kp = kp〇xexp (-E / RT) ... (5) (kp〇 = 0.60g2 · cm-2 · s]), and E is activation Source (E = 140kJ 15 · mol · 1 · K · 1), R is the gas constant, T is the temperature (K), w is the oxidation increase (g · cnT2), and ki is the linear constant velocity constant (1 ^ = 9.640% · cm-2 ·%]. S-1). ❿ (8) —A manufacturing method of copper-containing steel with excellent surface characteristics, which is to heat the copper-containing steel in a heating furnace and start hot milk. Method 20 for manufacturing a copper-containing steel, characterized in that: _ The Cu content CCu (mass%) of the steel is set to 0.05% or more and 3% or less, after the steel is extracted from the heating furnace and before the hot rolling is started, The treatment of removing the scale deposit generated on the surface of the steel is performed more than 2 times, so that the cross-sectional area s of the cross section of the steel perpendicular to the rolling direction after the end of hot rolling is divided by the effective thickness of the steel of the circumference 1 and the degree is d ( mm), the Cu enrichment per unit surface area (&quot; g · cm · 2) enriched near the interface between rust scale and ferrous iron in copper-containing steel is less than 18.6 CCuxd. (9) Such as (7) A method for manufacturing a copper-containing steel material having excellent surface characteristics is a method for manufacturing a copper-containing steel material after heating the copper-containing steel material in a heating furnace. The feature is that after the steel material is extracted from the heating furnace and before the hot rolling is started, a removal treatment for removing rust and scale generated on the surface of the steel material is performed twice or more. The relationship between the occurrence of cracks on the surface of the steel caused by the red hot brittleness, the amount of Cu per unit surface area (Cu enrichment), and the effective thickness of the steel after the hot rolling of the steel is concentrated near the rust / fat iron interface. Figure 2 illustrates the Cu concentration distribution in the depth direction from the surface of a steel with rust on the surface. The GDS analysis results are used to determine the Cu content per unit surface area (Cu-rich) that is concentrated near the rust / fat iron interface of the steel. Quantitative) method. Fig. 3 is a graph showing the relationship between the number density of precipitates having a particle diameter of 10 nm and 1 // m and the depth of surface cracks. FIG. 4 is a diagram schematically showing an embodiment of a device from a heating furnace to a hot rolling mill which is suitable for implementing the first manufacturing method of the present invention, and schematically shows the formation status of the rust layer on the steel surface in this embodiment . Fig. 5 schematically shows an example of equipment from a heating furnace to a hot rolling mill suitable for implementing the second manufacturing method of the present invention, an example of a heating treatment condition borrowing this equipment example, and a rust layer on the surface of the steel material during the treatment. Generate a graph of the situation. Embodiment t] 1 In the past, only Cu that caused red hot brittleness was considered to be produced during the heating before hot rolling. However, the inventors have verified the results of public inspection and found that in addition to the Cu concentration at the 界面 y, rust / ferrous iron interface, Cu also has the following behavior. U) a, which appears as a liquid phase at the scale / fat grain iron interface, can easily move around the grain boundaries of scale. ⑴If it is rust scale that does not generate magnetite, that is, when the scale is formed by the iron ore, the liquid phase Cu will move from the scale / fat iron interface in the scale (grain boundary) to the scale surface Evaporate and scatter with the vapor of Cu or Cu0.

(c) When rust scale formed by three layers of hematite, magnetite, and ferrite is generated, C of 10 liquid phases moves from the scale recording / fertilizer iron interface within the rust scale (grain boundary), and Solid solution in the magnetite layer. Based on this new finding, the phenomenon of rust formation when copper-containing steel is heated is investigated. First, iron is oxidized at the rust / fertilizer iron interface. On the other hand, Cu, which is superior to iron, is not enriched without oxidation. Part of this enriched Cu stays at the rust / fat iron interface as known so far, and the remaining amount takes one of the above actions as newly discovered

One or more. At this time, the amount of Cu contained in the steel consumed by the oxidation is equal to the amount of CU enriched in the rust scale / fertilizer iron interface, the amount of Cu volatilized from the rust scale surface through the rust scale grain boundary, and the magnetite layer Total amount of solid solution cu. Therefore, in order to reduce the amount of Cu enriched at the rust scale / fertilizer iron interface to avoid red hot brittleness, the inventors conceived that it should be useful to increase the amount of volatile Cu and the amount of Cu solid-dissolved in the magnetite layer, and further Repeated review and completed the present invention. That is, in order to volatilize Cu from the surface of rust, it is necessary to generate rust from arsenite as described above, and the present invention obtains this condition by heating under a low oxygen concentration environment condition as described in detail later. In addition, in order to make Cu solidly dissolve in rust scale, the scale of the magnetite 11 is obtained by heating and forming three layers of hematite, magnetite, and ferrite. The cattle are drawn as follows: 5 brothers clearly said that by using high oxygen concentrations in environmental conditions and the object of the present invention, the steel is more than 0.05% and 3%. %, _ If 3% by mass is passed in a normal heating furnace, the chargeability will not occur. In addition, the effect of volute magnetite / U of CU silk maggots / U found on the surface of the super-layer with solid content, capacity, and volatility to be discovered from the surface will cause red hot brittleness during rolling. 10 Next, the steel composition which exerts the effect of this invention is demonstrated. As described so far, this series uses the action of Cu when raw scale is used to reduce the amount of Cu scale / fertilizer-iron interface enriched steel and its manufacturing method. The composition and structure of the scale generated on the steel are not changed. Valid within the scope of the article. Specifically, in terms of mass%, Si 3 / 〇 or less, Mn · 10% or less, p: 〇1% or less, s: 〇1% or less, Cr: 5% or less, A1 · 3% or less at 15%. Guilty ... effective within 1 catch. First, the invention in the scope of patent application is explained. The present inventors cast steel, apply heating, heat on various Cu content steels under various conditions such as various thicknesses of cast steel (50 mm to 250 mm), and effective thicknesses of various rolled steels (1 mm to 100 mm). Rolling. The heating at this time is performed by the combustion heating of 1 ^^ (}, the heating temperature is 1100 ° C ~ 1300 ° C, and the oxygen concentration in the heating environment is 0 ~ 5% by volume. By changing the oxygen concentration in the heating environment, for example, making low oxygen Concentration environmental conditions cause the formation of rust scale from the ferrite layer, and reduce the amount of Cu enriched at the rust scale / fertilizer iron interface (Cu enrichment amount), etc., to change various cu enrichment amounts. Under various conditions, investigate the occurrence of cracks on the surface of the steel caused by the red hot brittleness after hot rolling 12 200404900. Also, investigate the amount of Cu per unit surface area (Cu enriched near the rust / fat iron interface) of the hot rolled steel. Enriched ϊ). The results are shown in Figure 1. In this figure, those with red hot brittleness that damaged the appearance and causing problems on the product are indicated by +, those with slight red hot brittleness but without damaging the appearance are shown by △ The red hot brittleness is not visible from the naked eye, but it is indicated by ♦ if there is a slight red hot brittleness in the micro observation of the microscope, and the red hot brittleness is not seen by the micro observation by the microscope. From the figure, First of all, the Cu enrichment is related to the Cu of the matrix. The product of the concentration and the effective thickness of the steel has a good relationship. It is also known that the Cu-enriched amount in the range shown by the formula (1) does not cause red hot brittleness, which is an appearance problem.

Ecu &lt; 18.6Ccuxd ... (1) Here, ECu: Cu content per unit surface area (// g · cm-2) enriched near the interface between rust and ferrous iron. 15 CCu: Cu concentration of the matrix ( Mass%) d: Effective thickness of steel (mm) The effective thickness d of the steel used here is the steel wearing area s of the steel cross section perpendicular to the direction of the heat ^ divided by its circumference, as defined in the following formula (6) . 20 d = s / l If the pipe has most perimeters of the inner and outer perimeters, the total perimeter is used as the inner and outer perimeters. In addition, using the effective thickness of the steel defined in this way, even in the case of wires, rods, pipes, rails, and sections other than the plate, the hot brittleness expressed by the formula (1) can still be consistently evaluated. Avoidance conditions. The effective thickness of the steel 13 η 4 Η 200404900 is generally the thickness of the plate, the radius of the wire, and the thickness of the tube. Since the red hot brittleness is caused by Cu enriched at the rust scale / fertile grain iron interface, the less the amount of enriched Cu is, the better it is from the viewpoint of preventing red hot brittleness. The lower the constant value of the formula (0, the better From the results in Figure 1, it can be seen that, in order to control the occurrence of slight red hot brittleness that does not cause appearance problems, the coefficient of formula (1) is preferably below 9.3. It can only be connected with a micron field of view such as a microscope. The observed red hot brittleness is also completely controlled, so the coefficient of formula (1) is better than 4.5. The invention described in the first item of the patent application scope is based on the above formula (丨) as the main constituent of invention 10. Here, Describe a suitable method for determining the Cu enrichment at the rust / fertilizer iron interface. In order to determine the Cu enrichment, it is necessary to determine the average concentration of an area with a surface area of 0.01 mm2 or more. This is because it is enriched in rust / The Cu at the interface of the fertile grains appears as metallic Cu with a size of about 100nm to 1 / zm. If there is no sufficient area, the correct enrichment amount cannot be obtained. The simple method is to use glow discharge luminescence spectroscopy (Glow discharg optical emission spectro (metry; GDS) A method for obtaining the concentration distribution in the depth direction of steel materials. By this method, the average Cu concentration in an area of several mm2 can be measured from the surface of the steel material in the depth direction. A detailed explanation is available on page 471 of the edition metal. 20 Figure 2 shows an example of the Cu enrichment obtained from the GDS analysis results. In the same figure, the Cu (steel) is shown relative to the distance from the surface of the steel in the depth direction. ), 〇 (oxygen), Fe (iron) concentration distribution. Near the steel surface, the concentration of 〇 is high, and it can be seen that rust is present on the surface. From a distance of 3 to the surface of the steel, the concentration of 〇 gradually decreases, and the rust / Fat iron interface. Near the rust / fat iron interface

14 200404900 There is a peak of Cu. The Cu concentration in the matrix is 0.195% (basal Cu concentration). Cu concentration in areas higher than this is integrated in the depth direction (obtain the area of the oblique line in Figure 2) to determine the Cu enrichment per unit area. Here, in order to convert volume into mass, it is necessary to multiply the density by using the density of 7.86 g · cm-3 of iron. 5 The surface is not smooth like a wire with a small diameter, and when it is difficult to analyze by GDS, you can also use the X-ray microanalysis (Electron probe X-ray Microanalyser; ΕΡΜΑ) to analyze the vertical section of rust and fertilizer iron. . At this time, since Cu appears in a size of about 100 rnn to 1 // m, it is necessary to have an analysis field of at least 10 #m in the width direction in a direction balanced with the surface of the steel. From the results, the CU concentration is averaged in the width direction, and the average Cu concentration distribution in the depth direction perpendicular to the surface direction of the steel material is obtained. The enrichment amount of Cu can be obtained in the same manner as in the case of GDS analysis. This analysis method is also described in detail in, for example, the Japanese Metal Society's 6th edition of the metal handbook, pages 462 to 465. Next, the second item of the patent application scope is explained. 15 Red hot brittleness is mainly caused by Cu, but there are also promoting elements. That is, it has the same oxidation resistance as iron, and has a melting point of 13 ° C or lower in the temperature range from surface c to t, as well as ^. In the present invention, these elements including Cu are defined. It is a red hot brittleness-inducing element. These two, x, and x hot-brittleness-inducing elements appear at the scale / fertilizer-iron interface 20 / night phase when rust is generated. Then, the red-hot-brittleness-inducing element will be the same as that in the case of only Cu There are the following rotations: ⑷ moves through the grain boundaries in the scale recording, (b) the scale recording is formed by the iron ore surface, and (c) when the three layers are formed by hematite, magnetite, and iron ore. The scales are solid-soluble in magnetite. Therefore, more strictly, it is better to use in the temperature range above 100GC and below 13GG C. The oxidation resistance is better than iron and it is soluble at 15 942 200404900 at 1300. The total concentration of red hot brittleness-inducing elements per unit surface area that is enriched by the red hot brittleness-inducing element below ° C near the interface between rust and ferrous iron is replaced by the total expression of red hot brittleness-inducing element (E0). Cu enrichment (ECu), more preferably, it will be used above 1000 ° C and 1300. (: temperature below In the field of oxidation resistance, the total matrix concentration (ci) of the red hot brittleness-inducing element, which is the total matrix concentration of elements with iron and melting point below 1300 ° C, replaces the Cu concentration (CCu) of the aforementioned matrix. In addition to Cu, the invention of Sn, Sb, and As is specified, which is the third invention in the scope of the patent application. At this time, Cu, Sn, Sb,

As is the aforementioned red hot brittleness-inducing element, and the total enrichment (Ei) of the red hot brittleness-inducing element and the total matrix concentration (CO of the red hot-brittleness-inducing element) can be obtained. Next, the present invention in item 4 of the scope of patent application will be described. It is known that Ni can be suppressed by increasing the solubility of Cu in 7 _Fe

Red hot brittleness caused by Cu. In order to suppress this effect, in order to suppress the red hot brittleness caused in the past, the amount of Cu, which is almost equal to 15% of the Cu content of the matrix, is added in mass%, based on the mass. On the other hand, "the present invention is used to reduce the amount of Cu-enriched steel at the rust / fat iron interface" even if it is added less than the conventional Ni addition amount described above, or even without Ni addition, the red hot brittleness can be sufficiently suppressed. Then, in the present invention, the addition of Ni can further reduce the occurrence of 20,, and brittleness, which is a suitable implementation form. No. 4 of the scope of patent application, &amp; hair month is based on the relationship with the Cu concentration of the substrate to specify Ni when Ni is added. (Matrix Ni concentration). That is, even if the concentration of substrate radon is less than conventional, as long as it contains the formula (3) and Nl of 1 multiplier, the red hot brittleness can be suppressed more favorably. ^ If Nl / Chen is more than h5% to the right, the surface of the steel is prone to blemishes, which will damage the appearance. Therefore, it should be less than 5% red. 16 200404900 0.061CCu2 + 0.32CCu + 0.00035 $ CNi $ h5 ... (3). 'Here, CNi: Ni concentration of the matrix (mass%)

Ccu: Cii concentration (mass%) of the substrate * 5 Next, the invention in the fifth scope of the patent application will be described. -First, Ti, Nb, and V are added to prevent cracks caused by Cu. The heat treatment of an appropriate amount of steel containing these ridings can precipitate a large amount of Ti, Nb, V carbides, nitrides, or fine precipitates of carbonitrides in the steel. By this', the grain growth can be hindered, and the particle size of Vostian iron can be maintained in a fine # 10 state. Therefore, since most grain boundaries are formed per unit area of the scale / fertilized iron, the dispersible liquid phase Cu invades the Vostian iron grain boundaries, and the red hot brittleness caused by Cu is advantageously prevented. Regarding Nb and V, in addition to the above effects, since these oxides will form low melting point oxides with iron oxides (melting point of Nb &lt; oxides: 119,015 ° C, oxides containing V Melting point: 635 ° C), so it can promote the mixing of liquid cu into the rust scale, reduce the Cu enrichment existing at the rust scale / fertilizer iron interface, and prevent the hot brittleness caused by 〇11. 0 'is an element added to prevent red hot brittleness caused by Cu, and p and REM are more preferable. Each of these elements is an element segregated at the grain boundary, and the energy of the grain boundary is reduced by the segregation toward the grain boundary. Thereby, the infiltration of the Cu-enriched phase toward the grain boundary of Vostian iron can be suppressed ', and thus the red hot brittleness caused by Cu can be favorably prevented. Regarding P and REM, it also has the effect of making Vostian iron grains fine. This mechanism is due to the segregation of P in dendritic crystals, which can hinder the growth of grains. In addition, REM can precipitate a large amount of carbides, nitrides, or fine precipitates of carbonitrides in steel. 17 200404900 Therefore, it can hinder Vostian iron. As the grain grows, any of the above effects can advantageously prevent the red hot brittleness caused by Cu. Regarding P, in addition to the above-mentioned effects, since its oxides and iron oxides form low melting point oxides (melting point of oxides containing p: 960 ° C), it can promote 5 into liquid phase Cu to mix into rust, Reducing the cu enrichment at the rust / fat iron interface, thereby advantageously preventing the red hot brittleness caused by Cu. Regarding Ti, Nb and V, regardless of whether they are used alone or in combination with a plurality of species, the effect can be exhibited as long as it is 0.001% by mass or more. If it exceeds 0.15% by mass, the effect is saturated. Mass% is the upper limit. _ 10 Also, one or more of P, s, and REM must be used at the same time. Regarding p, the above-mentioned effect is exhibited at 0.010 mass% or more. However, once the P concentration exceeds 0.1100 mass%, the workability or ductility is deteriorated. Therefore, the upper limit value is 0.100 mass%. In addition, regarding REM, the above-mentioned effect is exhibited at 0.002 mass% or more, and the effect is saturated when it exceeds o ho mass%, so the upper limit value is 0.150 mass%. 15 On the other hand, because S is better than iron, it will be concentrated at the rust / fat iron interface when heated at high temperature. In addition, since S forms a low-melting sulfide with Cu (melting point of CuS 1067 ° C), it has the effect of promoting the incorporation of liquid-phase Cu into rust, and it can prevent the cracks caused by Cu. s concentration in mass ° /. The above can exert its effects, but as the concentration of s becomes higher, 20 is enriched at the interface with 8 to form sulfides, and its melting point is 94 (rc low melting point-so it will cause grain boundary brittleness. Once S concentration If it exceeds 0 050 mass%, the brittleness caused by FeS becomes very significant, so the S concentration is set to 0.001 mass% or more and 0.005 mass% or less. When S is contained in this manner, it is contained. The concentration of Mη satisfies the mass ratio Mn / S ^ 7, which is suitable for mitigating the brittleness caused by S. That is, when 18 200404900 steel contains Mη ', because S is fixed by MnS, it can be mitigated by S Brittleness. Here, the Mη concentration in the steel can be satisfied by the mass ratio ^^^: ^ 7. There is no particular upper limit of the Mη concentration. It can be appropriately set according to the purpose or application, but usually from the material Most of them are 2.5% by mass or less. In addition to the above-mentioned effects, S has the effect of inhibiting the growth of iron particles in Vostian and making the extreme diameter small by precipitating "into the steel. During the precipitation, MnS will be precipitated with the nitride that has precipitated out first. The diameter is more fine. As a result, the red hot and brittleness can be prevented. G Next, the invention in the patent application No. 6 will be explained. + The invention in the patent application No. 6 is about the invention in the patent application No. 5 Composition-adjusted steel material containing at least one mile of carbides, nitrides, or carbonitrides of any one of Ti, Nb, and V, and a precipitate having a particle size of 10 nm to 15 1 // m or less The number density is 105 precipitates / mm2 or more. The steel of the present invention investigates the number of fine precipitates above l0m and less than 1 // m. The survey method used here is to use a high transmission electron microscope. Observation at magnification (for example, 100,000 times observation of 100 fields of view, etc.) As a result, it is known that when the number density of fine precipitates above 10 nm φ and 1 / V m is increased to 105 per m 2 or more The Nichiji F can hinder the growth of the grains, keeping the particle size of Vostian iron in a fine state. Here, the particle size of the "spelled object" means the diameter of a circle.

19 200404900, it is not possible to suppress cracks, so it is important to make the number density above 5 pcs / mm2, so that the particle size of the precipitate at this time is above 10nm and below 1 to achieve the desired number density. As described above, for the steel of the present invention, the number density of fine precipitates having a particle size of 10 nm or less is 105 pieces / mm2 or more, which can suppress red hot brittleness favorably. The composition of these precipitates was investigated by analysis of energy dispersive spectroscopy (EDS) of the transmission electron microscope and analysis of the electron diffraction pattern, and it was confirmed that they were carbides, nitrides, or carbonitrides of Ti, Nb, and V. · 10 Next, the invention in item 7 of the scope of patent application for the first method of manufacturing a steel material having excellent surface characteristics without red hot brittleness will be described. As mentioned above, the present inventors have discovered the phenomenon that Cu is enriched in rust scale / fertile iron in the environment of low oxygen concentration under the condition of heating the copper-containing steel to generate rust scale formed by galena. Outside the interface, Cu will also volatilize from the scale recording surface. This first 15 manufacturing method is to use this phenomenon to suppress the red-hot kneeling caused by Cu. First, the low-oxygen concentration environmental conditions for the formation of rust scales formed from ferrite during iron oxidation and the high-oxygen concentration environmental conditions for the formation of rust scales formed from three layers of hematite, magnetite, and ferrite during the iron oxidation will be described. It is generally known that when iron is oxidized at high temperature, rust will be formed from the surface layer, which is formed by three layers of hematite 20 ore, magnetite, and ferrite. In this case, the amount of oxidation is performed by the parabolic law which is proportional to the square root of time. The oxidation rate at this time is expressed by the following formula. w = / &quot; (kpt) ... (7) dw / dt = kp / 2 / · (kpt) = kp / 2w ·· (8) 20 200404900 kp = kp〇xexp (-E / RT) ... (5 ) Here, w: oxidation increment (g · cm-2) t: time (s) 5 kp: parabolic law speed constant (kpO = 0.60g2 · cm · 2 · s_1) E: activated energy (E = 140kJ · Mol · 1 · K · 1) R: Gas constant T: Temperature (K) 10 15 Oxidation The growth of iron ions in rust scales with this parabolic law is a law of growth and rust scale growth, provided that the ambient gas There is oxygen sufficient for the reaction. This condition is called high oxygen concentration environmental conditions. However, when sufficient oxygen cannot be supplied from the gas phase to the surface of rust to maintain the above-mentioned parabolic law, the oxygen supply from the gas phase becomes a regular velocity. At this time, the oxidation rate is proportional to the oxygen concentration and becomes a linear rule expressed by the following formula. At this time, there is no hematite layer and magnetite layer, but rust scale formed by the ferrite layer. This condition is called a low oxygen concentration environmental condition. w = klp〇2t ... (9) dw / dt ^ kipo〗 (10) Here, h: speed constant of the rule of lines (9.6xl (T6g · cm · 2 · s · 1 · ο /. · 1) Po2: Oxygen concentration In fact, when the steel is heated by the combustion gas, the slower oxidation speed in the above parabolic law and linear law will speed up the oxidation rate. Therefore, the oxidation speed of iron is shown by formula (11). 20 200404900 dw / dt = min (kp / 2w, klp〇2) ··· (ιι) From the above, rust formed by 3 layers of hematite ^ magnetite and argonite 'will be generated and the oxidation will be performed by the parabolic law The high-oxygen concentration environmental conditions and the boundary conditions for the formation of low-oxygen-concentration red and low-oxygen concentrations generated by the ferrite shape are obtained from the equation (12) where the gasification rates of the two conditions are equal. Also, Since the relationship between the increase in oxidation and the thickness of the scale is obtained by the formula ⑼, the formula ⑷ and the formula are the oxygen that becomes the boundary between the high oxygen concentration environmental condition and the low oxygen concentration environmental condition. Equation (4) and formula + '(14) contains a parabola dependent on the temperature ίο 15 20 linear velocity constant kp scale thickness x or oxidation increase w, from which it can be clearly known that Cheng = the boundary of the secret piece The oxygen concentration does not depend only on the oxygen concentration, but depends on the thickness and temperature of the scale at this time to change the oxygen concentration that becomes the boundary. Kp / 2w = kipo2 ··· (12) w = x / 7519 ·· (13 ) Here, x: rust thickness (#m) 〇〇2 ^ ρ / (2wkj) ··· (4) P〇2 == 7519kp / 2xk "... (14) Then e Erming about the CU containing The behavior of steel when it is oxidized. The element containing a and oxidized% is better than iron. It will be enriched at the rust scale / fertilizer iron interface and liquid phase Cu will appear. If the temperature is above 10 oz. It appears in the liquid phase. Galena and liquid Cu have extremely high coatability. In addition, the grain boundaries of rust] have fine pores. The pores are connected in a mesh shape and are distributed. The coatability is related to the existence of pores inside the scale, and the liquid phase ~ can easily move in the scale by capillary phenomenon. That is, the liquid phase appearing in the lower part of the scale of the iron ore ^ 可 22 200404900 easily Move to the surface layer of scales. When rust formed by argilite is generated under the condition of low oxygen concentration, vapour pressure from the surface layer of recording scale is relatively high or volatilize. To volatilize Cu, it is necessary to It can generate low oxygen 5 concentration environmental conditions for rust scale formed by ferrite. This is due to the high oxygen concentration environmental condition towels that can form scales formed from hematite, magnetite, and ferrite. Cu will solid-solve in the magnetite layer. When rust is formed from the three layers of hematite, magnetite, and squaria under the condition of high oxygen exposure, the phenomenon of Cu solid-solution in the magnetite layer can be explained as follows. Considering scale inhibition After the action of trace metals in the steel at the time of formation, it is important to consider the solubility in the trace gold-like 10 scale. Cu hardly dissolves in ferrite, but it can be dissolved in large amounts in magnetite with spinel structure. This is because the composition of FeJeO4 to FeWuO4 can be changed while maintaining the spinel structure. Furthermore, if the equilibrium oxygen potential difference between Cu and Cu oxides is taken into consideration, it can be known that Cu can exist as an oxide in the upper part of the magnetite in the scale on iron. Therefore, 15 Cu is not only enriched in the scale / fertilizer iron interface, but also exists as a solid solution in the upper part of the ferrite layer near the surface of the scale. That is, under the high-oxygen concentration environment conditions that generate the scale formed by the three layers of hematite, magnetite, and ferrite, the liquid phase Cu appearing at the _ / fertilizer iron interface will borrow capillary phenomenon. The pores of scale boundaries are leached to move the simple scale upper layer, and when the magnetite 20 layer is present near the surface layer, Cu will be solid-dissolved in the magnetite layer. The first manufacturing method to prevent the red hot and brittleness of Cu is to heat the steel before heating it under low oxygen concentration environmental conditions to make Cu volatilize in the environment. As a result, Cu enriched at the scale / fat iron interface can be reduced, so red hot brittleness can be suppressed. In addition, since the oxidation rate is proportional to the gas concentration under low oxygen concentration environment conditions, reducing the 23 oxygen concentration can also reduce the amount of scale formation, and it also reduces the Cu that occurs at the scale recording / fertilizer iron interface. The role of quantity itself. In the case of oxidation under high oxygen concentration environment conditions, which are usually formed by three layers of hematite, magnetite, and ferrite, the part of Cu excluded from iron by oxidation will be dissolved in the 5 magnetite layer, but- The ratio of ㈣ will be enriched at the scale / fat iron interface. At this time, when the area s of the saki cross-section area perpendicular to the rolling direction of the hot rolled money is divided by the effective thickness of the steel of the perimeter 1, the unit is enriched in the unit near the interface between the scale and the ferrous iron of the copper-containing steel The Cu enrichment Ecu (&quot; g.cm-2) of the surface area is about 1 8.6 Ccuxd. Therefore, in the present invention of Taimingliangnn, as long as the amount of Cu enriched at the rust scale / 10 :: grain iron interface can be reduced, it can be enriched per unit surface area near the scale and fat iron interface. Although the Cu ^ Ecu (&quot; g · em-2) is less than 18 6 (^ uXd), the red hot brittleness can be avoided as described above. The phenomenon of Cu volatilization, as long as the scale is formed by the structure of galena It can maintain the performance. Therefore, the amount of Cu enriched at the scale recording / fertilizing iron interface can be reduced. At this time, since Cu must be moved in the liquidite scale recording in the ferrite phase, in the present invention, liquid Cu is generated. It is a premise that the Cu dazzling point is replaced. In addition, the environment during heating must be a low oxygen concentration environment condition below the oxygen concentration expressed by formula (4) or formula (14). Generated under low oxygen concentration environment conditions The rust scale formed from the ferrite ore is formed under the condition of high oxygen / chener ring, and the rust scale formed from the three layers of hematite, magnetite, and ferrite is used to reduce the concentration of oxygen under the condition of rust scale formation. When the environmental conditions change to high oxygen concentration conditions or vice versa, the rust structure also changes in accordance with the environmental conditions. For example, 'In the beginning, even if there was rust generated under high oxygen concentration environmental conditions, it was changed to 24 200404900 rust structure formed from ferrite during the change to low oxygen concentration environmental conditions on the way. At this time, at first, Cu dissolved in the magnetite layer under the high oxygen concentration environment conditions, once it migrates to the low oxygen concentration environment conditions, the rust scale is formed by the ferrite layer. It cannot be dissolved in the ferrite layer, and the surface layer of the rust cannot be dissolved. It volatilizes and releases into the ambient gas. Therefore, the surface of the steel becomes 10 ° C (5 ° C or higher, the entire range of the heating furnace does not need to be low oxygen concentration environmental conditions, as long as a part of the heating furnace area is under low oxygen Concentration environmental conditions, cu volatilization can occur in its field, so red hot brittleness can be suppressed. Under low oxygen concentration environmental conditions, Cu moves from the rust scale / fertilizer iron interface to the crystal grain boundary and volatilizes from the surface of the scale. As a result of the intensive review by the inventor, it was found that the time (I) when rust is generated and Cu moves within the rust when the 10 scale is generated is related to the temperature T w as shown in formula (⑴). Here, Should correspond to Represents the surface temperature of the material of formula ice time, above, is oxidized at a low oxygen concentration in the ambient conditions. Logio (t / 60) = -0.00301χΤ + 4.83 ··. (15) 15 20

In general, a combustion gas using coke oven gas or LNG as a fuel can be obtained by controlling the air ratio at the time of combustion in an environment with a high oxygen concentration environment and a low μ degree environment. When the air ratio is increased, the oxygen concentration in the combustion gas ring * is increased. If the air ratio is decreased, the oxygen ^ in the combustion gas environment is reduced. The oxygen concentration in the heating furnace can be measured by an oxygen concentration agent. 〃Environmental conditions of low oxygen concentration can be obtained by mixing inert gases such as nitrogen, chlorine and helium in the combustion gas, or by increasing the temperature of the steel. The present invention can also be implemented when a heating furnace such as an induction heating furnace or a high-frequency heating furnace that does not use a combustion gas is used. In this case, a non-oxidizing gas such as nitrogen, chlorine, or helium can be used as the ambient gas. 25 952 200404900 When some areas in the heating furnace are set to have low oxygen concentration environmental conditions, and other areas are set to have high oxygen concentration environmental conditions, it is advisable to set up partitions at locations that become the boundary between the areas. By setting up the next wall, the environmental conditions of low oxygen concentration and high oxygen can be clearly distinguished. 5 Also, a combustion method using a regenerator can be used as a heating method when the local area of the heating furnace is a low oxygen concentration environment condition and the other areas are a high oxygen concentration environment condition. In this combustion method, the combustion gas released from the burner will enter the heat storage chamber of the opposite burner, so the amount of combustion gas flowing out of other fields is small, and the environmental conditions in local areas can be easily changed. In Equation (4), the thickness of rust must be considered. However, it is impossible to measure the rust thickness at the time of actual steel sheet manufacturing. Therefore, the oxidization rate obtained by formula (11) is used as an integral, and the formula (13) is used to convert the thickness of scale to record. In this way, the thickness of rust in formation can be obtained by calculation. 15 At this time, the temperature of the required steel surface can be easily measured with a radiation thermometer. The temperature distribution of the steel can also be obtained from the temperature distribution of the environment by heat conduction calculation.

The low-oxygen concentration environmental conditions that Cu volatilizes from the surface of rust scale are expressed by the oxygen concentration below the formula (4) or (14). The thickness and temperature of rust scale can be changed by 20, which cannot be accurately described in a certain Below a specific oxygen concentration. However, the thickness of the rust scale generated in the heating furnace is 500 // m to 3000 // m. Based on this thickness condition, under the heating temperature condition from 1080 ° C to 1250 ° C, according to formula (4), as long as the oxygen If the concentration is 0.5% by volume or less, it becomes a low oxygen concentration environment condition, and Cu is evaporated in the environment, and red hot brittleness can be suppressed. 26 200404900 Fig. 4 is a schematic example of a suitable heating furnace for implementing the first manufacturing method of the present invention, and schematically shows the scale generation condition corresponding to the condition of milk temperature. In this state example, a steel material (flat steel blank) i 5 containing 0.05 to 3 mass% of Cu is inserted into the heating furnace 2 at normal temperature, heated at a temperature of 1100 to 1300 ° C, and heated at 1100 to 1300 °. After the temperature of C is extracted, the rust scale of the heating furnace is removed by a rust removing device (high-pressure water) 3, and then the hot rolling is performed by a hot rolling mill 4. The inventor is applicable, and the local area of the heating furnace is low. This is carried out under ambient conditions of oxygen concentration. In addition, in order to separate the field of low oxygen concentration environmental conditions from the field of high oxygen environmental conditions, a partition wall 5 is provided in the heating furnace. In the sample of “Haihai”, because the steel was heated under the conditions of low oxygen and high temperature, the generated rust was composed of ferrite. Once rust is formed and the steel is heated to a melting point of Cu above 1080 C and 1100 to 1300 C, as shown in Figure 4, Cu is concentrated at the rust / fertilizer iron interface and appears in the liquid phase. The liquid phase (: 11 penetrates the rust scale grain boundaries to reach the surface of rust scale 15 and is vaporized or oxidized with CuO vapor and scatters. Since the evaporation and scatter of Cu is performed during low oxygen concentration environmental conditions, the It can reduce the Cu enrichment at the rust / fat grain iron interface on the surface of the steel. In this way, the present invention can greatly suppress the Cu enrichment at the rust / fat grain iron interface, which can effectively prevent Cu caused by hot rolling. Red hot brittleness. As shown in the figure, the reduced Cu-enriched layer is indicated by a dashed line. 20 Next, the invention in item 8 of the patent application regarding the second manufacturing method for suppressing red hot brittleness will be described. The present invention is a new inventor The following three phenomena were found: 6 All users. (A) Cu appearing in the liquid phase at the rust / fat iron interface can easily move to the grain boundary of rust. ⑴ If it is a record that no magnetite is formed Scale, that is to say, the formation of a from iron ore, the liquid phase Cu will move from the rust scale / fertilizer iron interface within the rust scale (the 27 200404900 boundary) and reach the scale recording surface, with Cu or Cu. The vapor evaporates and scatters. ⑷ When it is formed, it is formed by three layers of hematite, magnetite and galena. In rust scale, the liquid phase c moves from the lin scale / fertilizer iron interface in the rust scale (grain boundary) and solid-solves in the magnetite layer. These properties have the characteristics of a liquid enriched in the rust scale / ferrite iron interface. The phase Cu is absorbed by the grain boundary of the scale 5 to move the Cu to the place where it leaves from the interface, that is, the rust scale has the property of absorbing Cu like a sponge. The steel is heated to remove the generated steel surface. Hot rolling after rust scale. Cu accumulation at the scale / fat grain interface at the rust scale generated during the heating stage is a problem of red hot brittle crumbs. Before hot rolling can be started, as long as it can be enriched due to hot heat When the amount is reduced by less than 10, the red hot brittleness can be suppressed. Usually, a rust removal treatment is performed before the hot rolling is started. The present invention performs the rust removal treatment two or more times. Generally, rolled steel Under the atmospheric environment, rust will be generated on the surface between the various rust removal treatments. The rust formation between the rust removal treatments and the effect of absorbing liquid phase Cu into the rust as described above. , More than 15 times more than the usual rust removal The amount of Cu enriched at the rust / fat iron interface is reduced, and the red hot brittleness can be suppressed. It is also clear from the above effects that the rust removal treatment of more than two times should be performed after the steel is heated and initially hot rolled. Before the implementation, the reoxidation of rust scale is necessary, and an oxidizing environment is required, and the atmospheric environment of ordinary rolling can be easily used. The rust scale at the time of reoxidation is regardless of the rust formed by ferrite. Scale, or rust scale formed by three layers of hematite, magnetite, and ferrite. Since rust scale can absorb liquid Cu in any case, it can reduce enrichment in rust scale / fertilizer particles. The role of Cu at the iron interface. Therefore, between the two or more rust removal treatments, the environment exposed to the steel is either a low oxygen concentration environmental condition or a high oxygen concentration environmental condition.

9SS 200404900 is fine. Because of the absorption by the liquid phase called scale, the temperature of the surface of the steel must be above the 108 point of Cu. In addition, the temperature of the steel surface can be easily set by a radiation thermometer. Under the high oxygen concentration of three scales that usually form hematite, magnetite, and ferrite _ ο ο Under the environmental conditions, the steel is heated, and the steel-like condition is read after the de-recording process. It has been known that After the hot rolling is completed, the cross-sectional area s of the cross section of the steel perpendicular to the light rolling direction divided by the effective thickness of the steel perimeter i is d (leg), then it is enriched in the ribs and fertilizers of the copper-containing steel per unit. The &amp; enrichment of the surface area (Ecubg.cm-2) is approximately 18 6 CcuXd. Therefore, in the present invention, as long as Kexin can reduce the accumulation of scale / fat iron interface, Cu enrichment per unit surface area that is concentrated near the interface between brain and fat iron can be enriched ^ (以. 咖啡 _2 ) Is less than 18.6CCuxd, which can avoid red hot brittleness as described above. 15 In order to reoxidize the steel between two or more rust removal processes, a heat treatment for reoxidation may be performed. The heating and / or heat preservation method in the reoxidation treatment can be used such as radiant heating or heat preservation by electric furnace, or induction heating or energization heating. This kind of heating can be used to report excellent energy efficiency, responsiveness, and control. Or heat preservation method, and as long as the temperature of the steel is high, the surface of the steel · 20 can be maintained at 108 (TC or higher) in the reoxidation treatment. It is also a good implementation form in terms of efficiency. In either method, as long as the surface of the steel is 1080t or more and it is an oxidizing environment, the purpose of the invention can be achieved, so only a method with good energy efficiency can be selected appropriately The oxidizing environment should use an atmosphere that can be easily used. There are known methods for removing rust and dirt by spraying high-pressure water on the surface of the steel, rolling the steel surface as the surface of the product, and even 29 200404900 as the surface of the product. The method of pressing the side of the steel material in the width direction can be appropriately selected or combined. Fig. 5 is a diagram for implementing the second manufacturing method of the present invention. It is recommended that the outline of the equipment and the rust formation condition in the equipment be displayed in a pattern. Here, the steel material 1 is heated in the combustion gas environment (south oxygen concentration environment conditions) in the heating 5 furnace 2. In this heating, the steel material Rust is formed on the surface, and liquid Cu appears at the rust / fat iron interface. A part of the molten (liquid) Cu moves through the rust scale grain boundary to reach the magnetite layer, and solid solution in the magnetite layer. The steel material heated at the time and the predetermined temperature is extracted from the heating furnace, and the scale of the heating furnace is removed by the derusting device (high-pressure water) 3. This removes the Cu that falls in the magnetite layer and the scale recording. Then, the steel is exposed to the atmosphere When moving in the environment, the surface of the steel is regenerated with rust by the oxygen in the atmosphere. This area is the reoxidation treatment zone 6. This is the liquid that appears in the heating furnace and remains on the surface of the ferrous iron after derusting. A part of the phase Cu is absorbed into the scale of the reoxidized rust scale, and moves to the magnetite layer to be dissolved or volatilized in the environment, so that the amount of Cu enriched at the rust scale / fertilizer iron 15 interface is reduced. The Cu-enriched layer is indicated by a dotted line in the figure. Then, before the hot rolling, the rust removal device (high-pressure water) 3 is used for rust removal, and then the hot rolling mill is used for 4 rolls. Since the amount of Cu enriched at the rust scale / fertilizer iron interface is reduced, the hot rolling can be advantageously prevented. Red hot brittleness at the time (surface cracks). Finally, the invention concerning the 9th scope of the patent application is explained. This is the first manufacturing method and the second manufacturing method that suppress red hot brittleness at the same time. The first manufacturing method is a method of heating steel. The second manufacturing method is a method for removing steel rust from heating to the initial | Kunming rolling. The two can be performed on the same day, and by simultaneously performing, the effect of suppressing red hot brittleness can be further improved.

30 200404900 (Example 1) Casting a steel material containing Cu and Sn, and conducting an experiment to manufacture a steel plate by hot rolling. The heating before hot rolling is based on the combustion heating, and the air ratio during combustion is variously changed. It is heated to a temperature of ~ 1250 ° C, and then hot rolled to produce steel plates of 5 kinds of steel thickness (effective steel thickness). The Cu concentration of the matrix, the Sn concentration of the matrix, and the Ni concentration of the matrix are shown in Table 1. In addition, the effective thickness of the obtained steel, the amount of Cu per unit surface area (Cu enrichment) enriched near the interface between rust and ferrous iron, and the surface area per unit concentrated near the interface between rust and ferrous iron The amount of Sn (Sn-enriched amount), the amount of Sb per unit of 10 surface area (Sb-enriched amount) enriched near the interface between rust and ferrous grains, and the unit per unit near the interface of rust and fertile grains Table 1 shows the amount of As on the surface area (the amount of As enrichment) and the occurrence of cracks due to the red hot brittleness of the surface. Cu enrichment and Sn enrichment were obtained by GDS analysis. The degree of occurrence of cracks due to red hot brittleness on the surface of the obtained steel sheet is determined by the following indicators :: no cracks occurred, 0: fine cracks occurred 15 but no quality or appearance problems, and X: quality or appearance problems became cracks . Cu, Sn, Sb, As in the red / hot brittleness-inducing element at the rust / fat grain iron interface has a small enrichment amount, and those satisfying the formulas (1) and (2) (Nο · 1 ~ 9) cannot be caused. Cracks caused by red hot brittleness of quality or appearance problems occur, and cracks caused by red hot brittleness of quality or appearance problems 20 occur if those who do not satisfy formulas (1) and (2) (No. 10 ~ 13). The Ni addition (Nο · 8,9) that satisfies the formula (3) does not cause red hot brittleness and can obtain excellent surface quality. From this, it is known that even in a steel sheet containing red and hot brittleness inducing elements of Cu and Sn, red hot brittleness does not occur during hot rolling. 31 200404900 Remarks The present invention Inventive invention Inventive invention | Inventive invention j Inventive invention | Inventive invention [Inventive invention | Comparative invention Comparative example Comparative example Comparative example Evaluation of red hot brittleness m 0 ❹ @ @ 0 o _ © XXXX Rust / Fertilizer interface enrichment (μ g cm 2) 5 〇o yr ^ d CO ooooo &lt; 0: τ ~ isif 〇o; 畤 CM d CO JSi m Q? N | m CM; od 5 Csl «? ο 5: rrs 〇ο id &lt; M oom &lt; 0 &lt; d | 407.7: Gan d &lt; D o L. :: .. one choice "m φ 丨 28,5 tOGJS 423Λ« D &lt; D .. T ^ .. 12.4 I 353 5 | Ο CSI mo &lt; 0 o | 35.0 I | 442 | L. service 3 J! $ 3 \ 2 |: .m: 1 30.4 j 55J f 1045,7 effective steel thickness (hidden) 2 § «M • vmm M o IgNMMfc? R— &lt; o: inverse. | 0.03 | om if 0,03 ί | 0Λ3! | 0Ό3 I | 0.03 j | 0.03 I r 0 & 5 | loo | 003 | 0.03 0 , 03 f 0J5 m &lt; | 0,003 0003 [0.080 0060 [0,003 0 fine 0.003 | 0Ό60 II 0.060 0.003 0,060 0Λ80 j ao〇3 | | 〇, 〇! 〇〇Λ10 f 0010 I 0.010 0,004 I | 0.004 | I 0,004 I 0.004 [涵 4: 0ΛΙ0 J 0 010 0,004 0.0 (34 C. ω 0Λ3 050 0,03 | 0.03, [exposed 050 j 1 0.50 1 0.50 1 0.50 1 0.03 j QM I 0.50 0,50 1 δ 0J0 | 1,20 f 0J0 I 0.10 I 0,10 1 120 I 1.20 j 1.20 o.to 0.10 f 120 j 1.20 f Cv | CO inch m:; m \ bu mm) o «ΜΜ» CM 'T * · ¢ 0

32 200404900 (Example 2), Casting steel materials containing Cu and Sn, and conducting experiments on hot-rolled steel plates. The heating of hot-rolled sintering was performed during combustion heating, and the air ratio during combustion was changed in various ways. 1100 ~ 1250X: After heating at a temperature, hot rolling is performed to manufacture wire rods each having 5 kinds of radius (steel thickness). The Cu concentration of the matrix, the% concentration of the matrix, and the Ni concentration of the matrix are shown in Table 2. In addition, the effective thickness of the obtained steel (the radius of the wire), the Cui (Cug concentration) per unit surface area concentrated in the vicinity of the interface between the scale and the ferrous iron, and the concentration in the vicinity of the interface between the scale and the ferrous iron Table 2 shows the amount of Sn per unit surface area (Sn-enriched amount), and the state of fragrant formation of cracks caused by the red hot brittleness of the surface. Cu enrichment and Sn enrichment were obtained from the analysis results of the cross section of the scale recording by epma. The degree of occurrence of cracks caused by the red hot brittleness on the surface of the obtained steel is determined by the following indicators: ◎: no cracks occur, micro cracks occur but there is no quality or appearance problem, x: quality or appearance becomes a problem crack. The red hot brittleness-inducing element at the rust / fat grain iron interface is 15 〇11,%, and the enrichment amount of Waiba 3 is very small and meets the formulas (1) and (2) (prices: 14 ~ 21). Cracks caused by red hot brittleness that cause quality or appearance problems occur. Those who do not satisfy formulas (1) and (2) (Nο · 22 ~ 24) occur due to red hot brittleness that causes quality parameters or appearance problems. crack. Addition of Ni that satisfies the formula (3) (No. 21) does not cause red hot brittleness and can obtain excellent surface quality. Based on this, it is known that, in the embodiment performed according to the present invention, even if the steel contains red and hot brittleness inducing elements of Cu and Sn, red hot and brittleness does not occur during hot rolling. 33 Table 2 No. Matrix concentration (% by mass) Effective thickness of steel (mm) Interface enrichment (β gem'2) Evaluation of red hot brittleness Cu Sn Ni Cu Sn 14 ^. 0.50 0.10 0.02 10 ^ 16.4 0.0 ◎ The present invention 15 0.50 0.10 0.02 5 21.2 0.2 _ © The present invention 16 1 3.00 1.30 0.02 5 268.1 121.8 L〇 丁 7X / 4 The present invention 17 0.05 0.03 0.02 5 3.8 2.3 ◎ The present invention 18 0.05 0.03 0.02 10 ^ 5.4 3.0 ◎ 0.50 0.10 0.02 5 45.7 8.6 〇 7 7, 4 The present invention 20 3.00 1.30 ^ 0.02 10 ^ 436.7 239.6 〇 Tai invention ^ 21 0.50 0.10 0.22 10 ^ 76.1 22.0 ◎ T, 4 The present invention 22 — 0.05 0.10 0.02 5 ^ 5.7 10.5 X Compare Example 23 0.50 0.10 0.22 47.4 10.8 X Comparative Example 24 3.00 0.10 0.02 10 ^ 692.6 17.0 X Comparative Example (Example 3) A steel containing Cu and Sn was cast, and an H-beam was produced by hot rolling. Heating before hot rolling In the case of combustion heating, the air ratio during combustion is variously changed, and heated at a temperature of 1150 ~ 130 (TC), and then hot rolling is performed to produce various types of steel (effective thickness of steel). Concentration,% of matrix The Ni concentration of the matrix is shown in Table 3. In addition, the effective degree of the obtained steel, the amount of Cu per unit surface area (Cu-enriched amount) collected in the vicinity of the interface between the scale and the ferrous iron, and the concentration in the rust The amount of Sn per unit surface area (Sn-enriched amount) near the interface between scale and fertilizer and iron, and the occurrence of cracks due to the red hot and brittleness of the surface are shown in Table 3. The Cu-enriched amount and Sn-enriched amount are GDS analysis was performed on one side of the joint, three sides of the inner side and outer side of the wing, and the average value of these was displayed. The degree of cracking caused by red hot brittleness on the surface of the steel plate was determined by the following indicators: No cracks occurred, 0: fine cracks occurred without quality or appearance problems, X: cracks with quality or appearance problems occurred. Cu, Sn2 enrichment of red hot brittleness inducing elements at the rust / fat iron interface Rarely 200404900 does not satisfy the formula (1) and formula (2) (Nο · 25 ~ 32) can not see the occurrence of cracks caused by red hot brittleness that causes quality or appearance problems, does not satisfy formula (1) and formula (2) ) (No. 33 ~ 35) will cause quality or appearance The cracks induced by red shortness Subjects guide. The Ni addition (No. 30, 31) that satisfies the formula (3) did not cause red heat and 5 brittleness, and could obtain excellent surface quality. From this, it is known that even in a steel sheet containing red and hot brittleness inducing elements of Cu and Sn in the examples according to the present invention, red hot and brittleness does not occur during hot rolling. Table 3 No. Matrix concentration (% by mass) Effective thickness of steel (mm) Interfacial enrichment (β gem &quot; 2) Evaluation of red-hot kneeling properties Cu Sn Ni Cu Sn 25 0.50 0.10 0.10 20 182.1 39.0 〇 This invention 26 1.20 0.50 0.30 28 507.1 306.7 〇 The present invention 27 0.50 0.10 0.10 12 49.6 15.8 ◎ The present invention 28 1.20 0.50 0.30 12 187.9 75.4 〇 The present invention 29 1.20 0.30 0.30 20 325.6 156.1 〇 The present invention 30 0.50 0.10 0.22 28 250.4 51.5 ◎ The present invention 31 1.20 0.50 0.82 28 598.4 278.7 ◎ The present invention 32 0.50 0.10 0.10 12 26.0 6.5 ◎ The present invention 33 0.50 0.10 0.10 20 240.8 41.4 X Comparative Example 34 1.20 0.50 0.30 20 487.9 156.9 X Comparative Example 35 1.20 0.50 0.55 20 542.6 193.6 X Comparative Example (Example 4)

10 Casting steels containing Cu and Sn and conducting hot rolling to produce seamless steel pipes. The heating before hot rolling is to change the air ratio during combustion during heating and heating at a temperature of 1100 to 1250 ° c. Then, hot rolling is performed to produce various thicknesses (effective thickness of steel). Seam steel pipes. The Cu concentration of the matrix, the Sn concentration of the matrix, and the Ni concentration of the matrix are shown in Table 4. In addition, the effective thickness of the obtained steel material 15 is enriched per unit surface area near the interface between rust and ferrous iron.

The amount of Cu (enriched Cu) and the occurrence of cracks due to the red hot brittleness of the surface are shown in Table 4 together. The 〇1 enrichment amount and the enrichment amount are obtained from the results of analyzing the cross-section surface of rust on the outer surface and the inner surface of the steel pipe with EpMA, and the average values are shown. The obtained steel sheet © a Red hot job caused the occurrence of cracks, with the following indicators as indicators: ◎ · No cracks occurred, 0: Micro cracks occurred but there were no problems with quality or appearance, X · Quality or appearance became problems Crack. At the rust scale / fertile grain iron interface, the red and hot brittleness-inducing element Cu and Sn have little enrichment and those satisfying formula (2) and formula (2) (No. 36 ~ 41) cannot be seen to cause quality or appearance problems. Cracks caused by red hot brittleness occur, and those that do not satisfy formula (丨) or formula (2) (No. 42 ~ 44) occur cracks caused by red hot brittleness that cause quality or appearance problems. The additive (Nο · 41) satisfying the formula (3) does not cause red hot brittleness and can obtain excellent surface quality. From this, it is known that even in a steel sheet containing red and hot brittleness inducing elements of Cu and Sn, the red hot kneeling property does not occur during hot rolling. Table 4

No. Matrix concentration (mass%) Steel has an interface enrichment amount Red hot and brittle Remarkable thickness (U gem'2) Evaluation of Cu Sn NT '(mm) Cu Sn Valence 36 0.40 0.11 0.05 1 10 64.8 23.9 〇 This invention 37 0.08 0.03 0.04 20 3.6 4.4 ◎ The invention 38 0.08 0.03 0.02 10 11.1 5.5 〇 The invention 39 0.40 0.11 0.05 20 65.9 24.6 ◎ The invention 40 0.08 0.03 0.07 20 21.3 11.5 〇 The invention 41 0.40 0.11 0.18 10 65.4 22.1 ◎ The invention 42 0.08 0.03 0.02 10 15.6 5.4 X Comparative Example 43 0.03 0.02 20 32.5 10.2 X Comparative Example 44 0.40 0.11 〇〇 ^^ 20 151 ^ 39.9 X Comparative Example 15 (Example 5) For components containing Cu, Sn, Sb, As In the steel material, one or two or more adjustment components of Ti, V, S, P, and REM were added, and the steel material was cast, and an experiment of manufacturing a steel plate by hot rolling was performed. The heating before hot rolling involves various changes in the air ratio during combustion during heating and heating at a temperature of 1100 to 1250 ° C, and then hot rolling is performed to produce a 3.2 mm thick steel plate. The composition of the matrix is shown in Table 5. In addition, the effective thickness of the obtained steel, the amount of Cu per unit surface area (Cu enrichment) concentrated near the interface between rust and scale and 5 grains of iron, and The amount of Sn per unit surface area (Sn enrichment), the amount of Sb per unit surface area (Sb enrichment) enriched near the interface between rust and ferrous iron, and The amount of As per unit surface area (As-enriched amount) and the occurrence of cracks due to the red hot brittleness of the surface are combined. 10 is shown in Table 5. Cu enrichment, Sn enrichment, Sb enrichment, and As enrichment were obtained from the GDS analysis results. The degree of occurrence of cracks caused by red hot brittleness on the surface of the obtained steel sheet is determined by the following indicators: ◎: no cracks occurred, 0: fine cracks occurred but no quality or appearance problems, X: cracks of quality or appearance problems occurred . The addition of Ti, V, Nb, and REM is within the scope of the present invention, and the red-hot brittleness-inducing element Cu at the rust scale / 15 fertilizer grain iron interface has a small enrichment of Sn, and satisfies the formula (1) and formula ( 2) (Nο · 45 ~ 53) can't see cracks caused by red hot brittleness which causes quality or appearance problems. Ti, V, Nb, REM φ are not added at all and do not satisfy formula (1) or formula (2) ) (Nο · 54 ~ 56), cracks caused by red hot brittleness causing quality or appearance problems. From this, it is known that, in the embodiment according to the present invention, even red steels containing red, hot brittleness induced elements such as Cu, Sn, Sb, As, etc., will not undergo red hot brittleness during hot rolling. 37 964 200404900 Table 5% f The present invention The present invention I The present invention | The present invention 1 The present invention j 1 The present invention 1 The present invention 1 1 The present invention j The present invention comparative example 1 The comparative example comparative example I Evaluation of red hot kneeling © @ © © © 0 XK 乂 Interface rich ¥ quantity (iJz cm ^ 2) g QO to 〇s 〇 &lt; um O o to HC \ | eg gas 5 &lt; d 0 〇 &lt; Si, 0 d Q cS O rt CO &lt; X3 p LiMJ 1 ts.e LIMJ 30.0 33 6 J d tp ¢ 4 m Kd L _ «&gt; 1 28.0 2S.〇 | 218 t1212 j &lt; Νί &lt; d 74.4 I 81.8 J steel Effective thickness (liob) CM O JSi &lt; Nf «Μ &lt; NT m &lt; rsr f4, want to REM? 1 1 1 1_0 Qjm 1 0.002 〇, ΟΒΟ] \ i ί -0 ί surface 1 ί 1 LB1} \ fi 1 t 1 &gt; 1 i [OJS1 1 0,1S} 5 1 ί i 1 i-om t ί 0 (3 1 I 1 Le 1 \ ί I MD ααο OiO 1 0,00 0 plus QM s oao surface 000 om | o Fine I 0.0D3 | mm | a_ 1 0,003 j | 0 J03] 1 0.060 j 1 0,060 1 Qmz 0.060 j 〇 Fine [0.003 I State 5SC 4 w2 & m I 0.010 0.010 | O.OtQ I 1 0.010Ί 1 0.004 j 0.004 1 0 1 0,004 I 0.010 j 0010 j om] 0.004 5 \ om om DJ0 ojo 1 OJO; i〇J8 &lt; X30 0,20 0J0 om OJO 0.50 U om 0,20 0.20 0.20 [0.50 0,50 CJ0: 2 ^ 0 10.10 1.20 m I 0.020 I ojoo QMQ I € .005 丨 0 side 1 0 application 0.006 j 0.030 j: 0 € 08 1 0.005 O.DOS j 00151 Cl [0M4 I 0 004 I 0,004 1 delete 0: 0,080 1 o delete ί aoos j 0.00s 1 Q.om 0,004 j 0 赖 i o.oio | 0,57 ass 丨 一 ._. .. one by one "§ 1 GJ7j 0J5 U42 0J? 0.85 M2 0,57 QB6 t.42 m L2 £ L 0.02: 0.20 LMlJ om 1 0,20 Nam Q2Q j 0.01 om _ 〇0.002 (0.05! 0J4 0.002 aos 0.002 1 om d 0,002 j DM [0 14 S. ΙΛ C〇m: ^ r 5 M Γ0 U7 SS;

38 200404900 (Consistent Example 6) The chemical composition is contained in mass%, and contains: C: 0.05%, Si: 0.01%, Mn: 0.25%. Ρ: 〇.〇12〇 / 〇 ^ s: 0.006% 'Cu: 1.64% &gt; Ni: 0.01% ^ Cr · 0.02% of steel, which is heated in a heating furnace using wLNG as the fuel. The oxygen concentration of the whole (heating zone and soaking zone) in the heating furnace is 0.5% by volume. 'The steel material with an initial rust thickness of 30 // m is heated for 90 minutes to 1230 ° C.' TC is maintained for 40 minutes. The oxygen concentration condition at this time is that the entire furnace is a low oxygen concentration environment. Then, the steel is drawn from the furnace and rust is removed by high-pressure water. The surface of the steel after hot rolling does not show red hot brittleness. On the other hand, when the entire heating furnace is heated under high oxygen concentration environment conditions with an oxygen concentration of 5% by volume, cracks due to red hot brittleness occur on the surface of the steel. (Example 7) The chemical composition is measured in mass%. Contains: C: 0.04%, Si: 0.01%, Mn: 0.333o / 〇, P: 0.010〇 / 〇, S: 〇〇〇〇〇 / 0, Cu: 0.74%, Ni: 0.04%, 15 Cr: 0.07% steel is heated in a heating furnace using combustion gas using coke oven gas as the fuel. The thickness of rust before being put into the heating furnace is 500. The heating furnace heating system is first under high oxygen environment conditions (oxygen concentration 5) Capacity ❶ / Q) Heat for 80 minutes to 1200 ° C, and keep 1200 ° Cx 20 minutes in this environment Then, separate the front and back by the next wall, and keep it at 200 ° C x 20 for 30 minutes under the low oxygen concentration environment condition (oxygen concentration 0.4% by volume), and then keep it under the surface oxygen concentration environment condition (oxygen concentration 5% by volume) again for 1200. ° Cx 30 minutes, and then withdrawn from the heating furnace. Then, the high-pressure water is used to remove the furnace rust on the surface of the steel for hot rolling. No cracks on the surface of the steel due to red hot brittleness can be seen on the surface of the steel after hot rolling On the other hand, if it is not placed in the heating zone, it is added as a low oxygen concentration environmental condition.

qc. K 39 200404900 Known in the hot zone Heating under high oxygen concentration environment conditions, that is, steel with a rust thickness of 500 # m before putting it into the heating furnace, under full high oxygen concentration environment conditions (oxygen concentration 5 capacity%) ) Under heating for 80 minutes to i200 ° C, and keep in the environment and temperature for 80 minutes, and then draw out 'high-pressure water derusting and hot rolling of steel under this heating condition, 5 red hot brittleness occurs on the surface of the steel after hot rolling The resulting cracks on the surface of the steel. (Example 8) In terms of mass%, the chemical composition contained: C: 0.05%, Si: 0.01%, Mn: 0.25% ^ P: 0.01l0 / 〇.s: 0.006% ^ Cu: 1.60 % &gt; Ni: 0.01% ^

Cr: 0.02% steel, which is heated in a heating furnace using LNG as the fuel. The thickness of rust before putting into the heating furnace is 500 / zm. This heating system makes the total oxygen content in the heating furnace 5% by volume. First heat the steel for 80 minutes to 12,000. 〇, maintaining 1200 Cx for 20 minutes in a 忒 environment. Heating during this period is equivalent to high oxygen concentration conditions. It was then heated to 1300 C and held for 30 minutes. After heating to i300 ° C for 10 minutes, it is equivalent to low oxygen concentration environmental conditions, and then, as the rust thickens, it migrates to 15 ^ oxygen concentration environmental conditions. Press the high pressure water to remove the rust on the steel surface for hot rolling. No cracks on the surface of the steel due to red hot brittleness were observed on the surface of the steel after hot rolling. #-方 'When the temperature of the steel is not increased during the heating process, that is, the thickness of the scale before being put into the heating furnace is 500_, all of which are heated under high oxygen concentration environmental conditions (oxygen. 20 degrees 5% by volume) 8 ○ minutes to 120 叱, and kept in this environment for 50 minutes. After the steel is drawn, high pressure water is used to record and hot-roll. The surface of the steel after hot rolling is cracked due to red hot brittleness. (Example 9) In terms of mass%, the chemical components contained: c: 2%, si: 0.02%, 40 200404900 Mn: 0.12%, p: 0.001%, s: 〇〇〇 7% · 1.02%, Ni: 0.02%, &amp; 0.03% of Saki, using coke money as heating, to change the oxygen concentration to a low oxygen concentration above the surface C. Environmental conditions The oxygen concentration was 2% by volume of the environmental conditions, and it was heated to 115 generations and maintained at this temperature for 1 hour. 5 Immediately after removing the steel from the heating furnace, remove the scale with high pressure water. The steel is then moved in the atmosphere and the scale is removed again with high pressure water just before the initial hot rolling. By this method ', a 25 mm-thick steel sheet is not cracked due to red hot brittleness. On the other hand, a steel plate with the same thickness of 2.5mm is heated under the same heating conditions for 10 hours, but the treatment of removing rust (derusting) by high-pressure water immediately after extraction from the heating furnace is not performed until the initial hot rolling is started. After the high-pressure water is used to record the breasts, the person is heated at an oxygen concentration of 0.5% by volume under low oxygen concentration environmental conditions (the present invention). The surface of the steel plate has no cracks caused by red hot brittleness, but When heating under an oxygen concentration environment of 2% by volume in high oxygen concentration environment conditions (compared to 15 cases), cracks due to red hot brittleness occurred on the surface of the steel plate. (Example 1) In terms of mass%, the chemical components contained: C: 0.05%, Si: 〇01%, Mn · 0.25%, p: 〇op%, s: 〇.〇〇6%, Cu: 161 〇 / 〇, Ni: 〇〇１〇 / 〇,

Cr ·· 0.02% steel is heated to 20 1230 C in a heating furnace using coke oven gas as a fuel and maintained at this temperature for 90 minutes. The ring of this sacrifice * brother's oxygen is the third capacity that is the high oxygen concentration environmental condition. /. . The steel material extracted from the heating furnace was pressed in the width direction with a pressure of 3% to remove rust on the surface of the steel material. Then, the steel is placed in a heat-shielding cover covered with a heat-insulating material, and the low temperature of the surface of the steel is 11 ° C. Hold C for 5 minutes. The environment during heat preservation is the atmosphere. After the heat preservation, the rust was removed again with 41 pressure water and hot rolled. X, it is prepared as a comparative example to perform hot rolling immediately after heating with high-pressure water to remove rust and scale. As a result, cracks did not occur on the surface of the steel material held in the heat shield of the example of the present invention, while cracks occurred on the surface of the steel material of the comparative example that was not heat-shielded. Industrial applicability As explained above, II. In the present invention, the steel composition needs to be changed, such as the meaning of addition, and the cause can also be produced when hot-rolling steel containing Cu0 05 ~ 3% by mass. The occurrence of red hot brittleness in steel materials of Cu, thereby providing a copper-containing steel material having excellent surface characteristics and a manufacturing method thereof. [Schematic diagram I is simple and clear] Figure 1 shows the occurrence of surface cracks on the steel due to red hot brittleness during hot rolling, and Cu per unit surface area that is concentrated near the rust / fat iron interface after hot rolling with the steel. The relationship between the amount of Cu (enriched Cu) and the effective thickness of the steel. Figure 2 illustrates the amount of Cu per unit surface area that is concentrated near the rust / fat iron interface of the steel by GDS analysis results from the surface of the steel with rust on the surface toward the depth. (Cu enrichment) method. Fig. 3 is a graph showing the relationship between the number density of precipitates having a particle size of 10 nm and 1 #m and the depth of surface cracks. Fig. 4 schematically shows an embodiment of a device from a heating furnace to a hot rolling mill suitable for implementing the first manufacturing method of the present invention, and at the same time schematically shows the formation status of the rust layer on the surface of the steel in this embodiment. . FIG. 5 is a diagram schematically showing an example of equipment from a heating furnace to a hot rolling mill suitable for implementing the second manufacturing method of the present invention, and an example of heat treatment conditions based on this equipment example, and a rust layer on the surface of the steel material during the treatment. Generate a graph of the situation. 200404900 [Representative symbols for main components of the drawing] 1 ··· steel (flat steel billet) 2… heating furnace 3 ·· derusting device (high pressure water) 5 4… hot rolling mill 5… partition 6… reoxidation treatment band

43

Claims (1)

200404900 Scope of patent application: 1. A copper-containing steel with excellent surface characteristics, which is a copper-containing steel with rust on the surface, which is characterized by: Cu Cu (mass%) of the matrix of 0.05% to 3% If 5 is the cross-sectional area s of the cross section of the steel perpendicular to the rolling direction divided by the effective thickness of the steel 1 of the perimeter 1 is d (mm), then it is concentrated in the unit surface area near the interface of rust and fertilizer iron. Cu enrichment ECu (// g · cm'2) conforms to the relationship of the following formula (1): Ecu &lt; 18.6CCuxd ··· (1) 〇10 2. —A copper-containing steel with excellent surface characteristics, which is the surface For those copper-containing steel materials with rust scale, the characteristics are: Cu concentration of the substrate CCu (mass%) is 0.05% or more and 3% or less. If the cross-sectional area s of the steel cross section perpendicular to the rolling direction is divided by its perimeter 1 The effective thickness of the steel is d (mm), and in the temperature range of 15 ° C from 1000 ° C to 1300 ° C, the concentration of red hot brittleness-inducing elements that is superior to iron and has a melting point below 1300 ° C is better When the total matrix concentration of red hot brittleness-inducing elements is Q, the red hot brittleness induces The red-hot brittleness-inducing element total enrichment Ei (· cm_2), which is enriched in elements per unit surface area near the interface between rust and ferrous iron, conforms to the relationship of the following formula (2): 20 Ei &lt; l8 .6Cixd ... (2). 3. For the copper-containing steel with excellent surface characteristics as described in item 2 of the scope of patent application, one of the aforementioned red hot brittleness-inducing elements is Cu, and the other is one or more of Sn, Sb, and As. 4. If any one of the scope of patent application No. 1 ~ 3 has excellent surface characteristics 44 200404900 For a copper-containing steel, the relationship between the matrix Ni concentration CNi (mass%) and the matrix Cu concentration CCu (mass%) conforms to the relationship of the following formula (3): 0.061CCu2 + 0.32CCu + 0.0035SCNiS 1.5 &quot; (3). 5. A copper-containing steel material with excellent surface characteristics as described in any of claims 1 to 3 in the scope of patent application, wherein the aforementioned copper-containing steel material is in mass% and contains: Ti: 0.01 to 0.15%, Nb: 0.01 to 0.15%, V: any one or more of 0.01 to 0.15%, and more: P: 0.010 to 0.100%, S: 0.010 to 0.050%, REM: one or two of 0.002 to 0.150% More than that. 6 · If the copper-containing steel with excellent surface characteristics is covered by item 5 of the scope of patent application, the above-mentioned copper-containing steel in 10 contains at least one or two or more kinds of carbides and nitrides of Ti, Nb, and V. Or a carbonitride and a precipitate having a particle diameter of 10 nm or more and 1 / zm or less and a density of 105 particles / mm2 or more. 7. · A method for manufacturing a copper-containing steel material having excellent surface characteristics, which is a method for manufacturing a copper-containing steel material after heating the copper-containing steel material in a heating furnace, and is characterized by: When the content CCu (mass%) is 0.05% or more and 3% or less, the surface temperature of the steel material is 1080 ° when heating in the heating furnace. In all or part of the areas in the heating furnace in the above state, an environment having an oxygen concentration p02 (capacity%) or less (low oxygen concentration 20 environmental conditions) represented by the following formula (4) is created, so that When rust is generated, and the cross-sectional area s of the wearing surface of the steel perpendicular to the rolling direction after the hot rolling is divided by the effective thickness of the steel 1 whose circumference is 1 is d (mm), it is enriched in the copper-containing steel. The Cu enrichment per unit surface area near the interface between rust and fertilized iron is Cu (/ zg • cm-2) less than 18.6 CCuxd, 45 200404900 P〇2 = kp / (2wki) ... (4) Here, kp is Parabolic law speed constant (g2 · cm-4 · s · 1), specifically: Bismuth kp-kp〇xexp (-E / RT)-(5) 5 (kp〇 = 0.60g2 · cm-2 · s · 1), and E is the activated energy (E = 140kJ · ηιοΓ1 · K · 1), R is the gas constant, T is the temperature (K), and w is the oxidation increase (g · cnT2), and ki is Rule of line speed constant (ki = 9.6x 10'6g · cm'2 ·% -1 · s'1) ° 8. —A method for manufacturing copper-containing steel with excellent surface characteristics. Add in heating furnace Then, a method for manufacturing a copper-containing steel material that starts hot rolling is characterized in that the Cu content CCu (mass%) of the steel material is 0.05% or more and 3% or less, and after the steel material is extracted from the heating furnace, the heat treatment is started. Before rolling, a treatment of removing rust and scale generated on the surface of the steel is performed twice or more, so that the cross-sectional area s of the cross section of the steel perpendicular to the rolling direction after the end of hot rolling 15 is divided by the effective thickness of the steel 1 At d (mm), the Cu enrichment Ecu (/ zg · · cm-2) per unit surface area that is concentrated near the interface between rust and ferrous iron in copper-containing steel is less than 18.6 CCuxd. 9. The manufacturing method of copper-containing steel with excellent surface characteristics, such as item 7 of the scope of patent application, is a method for manufacturing copper-containing steel after heating the copper-containing steel in a heating furnace, which is characterized by: After the steel material is extracted from the heating furnace and before the hot rolling is started, a removal treatment is performed on the surface of the steel material to remove the generated rust twice or more. 46