JP4838627B2 - High Si content steel sheet with excellent surface properties, production method thereof, and high Si content steel material for production thereof - Google Patents

Description

  The present invention belongs to a technical field relating to a high Si content steel sheet having excellent surface properties, a method for producing the steel sheet, and a high Si content steel material for production thereof.

  When manufacturing a steel plate by hot rolling, a steel material (slab) is heated in a heating furnace, and then hot rolling (rough rolling, finish rolling) is performed. In high-tensile steel sheets used for automobiles and the like, Si is generally added from the viewpoint of securing strength and formability.

  However, in Si-added steel sheets with high Si content, it is difficult to completely remove the Si-based scale (firelite) generated on the steel surface during heating by descaling, and the scale remains unrolled and rolled. Then, Si scale (firelight) is pushed into the steel surface, which deteriorates the surface properties of the steel sheet. If the Si-based scale (firelight) remains and is removed on the surface of the steel sheet (which becomes a striped scale), the Si-based scale (firelight) is uniformly removed even after pickling. Unevenness occurs on the surface of the steel sheet, which becomes the starting point of fatigue failure.

  Therefore, there is a need for steel sheets with good surface properties after hot rolling.To that end, scale properties with sufficiently good peelability are obtained before rough rolling and finish rolling, and efficient descaling is achieved. There is a need to do.

In a high Si content steel of 0.5 mass% or more in Si amount: after heating at less than the eutectic temperature (1173 ° C.) of FeO—Fe ₂ SiO ₄ generated at the interface between the steel and the scale layer, high pressure water of 40 MPa or more is added. It has been proposed to remove the scale using this method (Japanese Patent Laid-Open No. 2000-254724). However, even when heated below 1173 ° C., in the case of high-Si steel, a very dense and strong Fe ₂ SiO ₄ layer is formed at the interface, and it is difficult to remove even with high-pressure water. Causes scale.

On the other hand, in JP 2005-297008 A, a melt phase of FeO-Fe ₂ SiO ₄ is formed by first-stage heating at 1173 ° C. or higher, and then wedge-shaped in steel by second-stage heating at less than 1173 ° C. Forming a composite scale of FeO and Fe ₂ SiO ₄ at the interface between the solidified phase of FeO-Fe ₂ SiO ₄ and the steel that has penetrated, eliminating the wedge-shaped solid phase of FeO-Fe ₂ SiO ₄ , flattening, and peeling A technique for improving the above is disclosed. However, in this method, it is difficult to uniformly flatten the wedge portion, and there is a risk of lack of stability, for example, it becomes easy to induce variation in surface properties after descaling.

In addition, methods for defining heating conditions and rolling conditions are disclosed in Japanese Patent Laid-Open Nos. Hei 6-1992728, Hei 44-247829, and Japanese Patent Laid-Open No. 2000-273579, which define scale removal (descaling) conditions. Although methods are disclosed in Japanese Patent Application Laid-Open Nos. 6-279923 and 2000-15323, it is difficult to completely remove scales, and Si-based scales (firelights) are formed on the surface of a steel sheet after hot rolling. ) Remains mottled and a steel sheet having sufficient surface quality cannot be produced.
JP 2000-254724 A JP 2005-297008 A JP-A-6-192728 Japanese Patent Laid-Open No. 4-247829 JP 2000-273579 A JP-A-6-279923 JP 2000-15323 A

  The present invention has been made paying attention to such circumstances, and its purpose is to provide a high Si-containing steel sheet having a small striped scale and excellent surface properties, a method for producing the same, and a high Si material for the production thereof. It intends to provide the contained steel material.

  In order to achieve the above object, the present inventors have intensively studied, and as a result, completed the present invention. According to the present invention, the above object can be achieved.

The present invention, which has been completed in this way and has achieved the above object, relates to a high Si content steel sheet excellent in surface properties, a method for producing the same, and a high Si content steel material for the production thereof. The manufacturing method of the high Si content steel plate excellent in the surface property of Claims 1-2 (The manufacturing method of the high Si content steel plate excellent in the surface property which concerns on 1st- 2nd invention), The surface property of Claim 3 An excellent high Si content steel plate (high Si content steel plate excellent in surface properties according to the third invention), a high Si content steel material (No. 1) for producing a high Si content steel plate excellent in surface properties according to claims 4-5 . 4-5 , a high Si-containing steel material for producing a high Si-containing steel sheet having excellent surface properties according to the invention, and has the following configuration.

That is, the method for producing a high Si content steel sheet having excellent surface properties according to claim 1 is: C: 0.01 to 0.2% by mass, Si: 0.2 to 2.0% by mass, Mn: 0.2 to 3.0% by mass, P: 0.001 to 0.1. Including: mass%, S: 0.001 to 0.1 mass%, B: 0.0025 to 0.05 mass%, Cu: 0.001 to 0.05 mass% and / or Ni: 0.05 mass% or less, and the balance from Fe and inevitable impurities When the high Si content steel material is heated at 900-1170 ° C and then hot-rolled, it should be descaled at least once with high-pressure water of 10 MPa or more before the start of finish rolling in this hot rolling. A feature of the present invention is a method for producing a high Si-containing steel sheet having excellent surface properties [first invention].

The method for producing a high-Si content steel sheet having excellent surface properties according to claim 2 , wherein the high-Si content steel further contains at least one of Al: 0.01 to 0.05 mass% and Cr: 0.01 to 0.3 mass%. is an excellent method for producing a high Si-containing steel sheet surface properties of 1, wherein [second invention].

The high Si content steel plate excellent in surface properties according to claim 3 is a high Si content steel plate excellent in surface properties obtained by the method for producing a high Si content steel plate excellent in surface properties according to claim 1 or 2. Third invention].

The high Si content steel material, which is a material for producing a high Si content steel sheet having excellent surface properties according to claim 4 , is heated at 900 to 1170 ° C., then hot-rolled and descaled to achieve high Si content. It is a high Si content steel material used when producing a steel plate containing C: 0.01 to 0.2 mass%, Si: 0.2 to 2.0 mass%, Mn: 0.2 to 3.0 mass%, P: 0.001 to 0.1 mass%, S : 0.001 to 0.1% by mass, B: 0.0025 to 0.05% by mass, Cu: 0.001 to 0.05% by mass and / or Ni: 0.05% by mass or less , remaining Fe and inevitable impurities It is a high Si content steel material as a material for producing a high Si content steel plate having excellent surface properties [ fourth invention].

6. The high Si content steel material as a raw material for producing a high Si content steel sheet having excellent surface properties according to claim 5 further contains at least one of Al: 0.01 to 0.05 mass% and Cr: 0.01 to 0.3 mass%. 4. A high Si-containing steel material as a raw material for producing a high-Si content steel sheet having excellent surface properties according to item 4 [ fifth invention].

  According to the method for producing a high Si content steel sheet having excellent surface properties according to the present invention, a high Si content steel plate having few striped scales and excellent surface properties can be obtained.

  According to the high Si content steel material for producing a high Si content steel plate having excellent surface properties according to the present invention, a high Si content steel plate having few striped scales and excellent surface properties can be obtained.

  The high Si-containing steel sheet with excellent surface properties according to the present invention has excellent surface properties with few striped scales. Therefore, even after pickling, the surface becomes a starting point such as fatigue failure. Therefore, it can be suitably used as a high Si-containing steel sheet having excellent surface quality.

When high-Si steel is heated in a furnace at a temperature below 1173 ° C, a thick and strong Fe ₂ SiO ₄ (firelite) is uniformly formed at the interface between the scale (FeO; wustite) and the steel, as shown in Fig. 1. Occur and worsen descalability. When the heating temperature exceeds 1173 ° C., as shown in FIG. 2, the eutectic liquid phase of FeO and Fe ₂ SiO ₄ penetrates into the grain boundary of the steel surface layer and bites into a wedge shape and hardens. Sex worsens. 1 and 2 are schematic diagrams.

  In order to improve the scale peelability (descaling property) at the time of descaling while reducing the scale loss as much as possible, it is effective to obtain a scale property with good peelability when heated at less than 1173 ° C.

The inventors of the present invention have changed an alloy element (an element to be contained in a high Si-containing steel, that is, an additive element to a high Si-containing steel) that changes the Fe ₂ SiO ₄ layer formed at a temperature lower than 1173 ° C. into a structure having good peelability As a result, it has been found that the addition of B and P dramatically improves the scale peelability during descaling. That is, a high Si content steel containing B and P as alloy elements can obtain a scale property with good peelability when heated at less than 1173 ° C. Therefore, the scale peelability during descaling is high. I found out that it would improve dramatically.

The reason and mechanism for dramatically improving the scale peelability by adding B and P will be described below. B during scale formation, and concentrated in the vicinity of the interface between the P is scale and the steel, and further diffuse into the upper layer of the scale, the Fe ₂ SiO ₄ layer inhibits uniform generation of Fe ₂ SiO ₄ layer is distributed, Fe diffusion from the inside of the steel is promoted to form a mixed layer of FeO and Fe ₂ SiO ₄ . Furthermore, the mixed layer of FeO and Fe ₂ SiO ₄ contains many bubbles. For this reason, the strength of the mixed layer itself is lower than that of the Fe ₂ SiO ₄ layer alone, and the mixed layer becomes brittle and is easily removed by descaling. Therefore, the scale peelability at the time of descaling is dramatically improved. The formation state of such a mixed layer is shown in FIG. FIG. 3 is a schematic diagram.

The present invention has been completed based on such knowledge, and relates to a high Si-containing steel sheet having excellent surface properties, a method for producing the same, and a high Si-containing steel material used for the production thereof. Among the high Si content steel sheets excellent in surface properties according to the present invention and the production method thereof and the high Si content steel materials for the production thereof thus completed, first, the high surface properties according to the present invention are excellent. The manufacturing method of the Si-containing steel plate is C: 0.01 to 0.2% by mass, Si: 0.2 to 2.0% by mass, Mn: 0.2 to 3.0% by mass, P: 0.001 to 0.1% by mass, S: 0.001 to 0.1% by mass, B: A high Si content steel material containing 0.0025 to 0.05 mass% and containing Cu: 0.001 to 0.05 mass% and / or Ni: 0.05 mass% or less and comprising the remainder Fe and inevitable impurities is heated at 900 to 1170 ° C. Then, when hot rolling, before the start of finish rolling in this hot rolling, descaling is performed at least once with high-pressure water of 10 MPa or more. It is a manufacturing method.

  According to the method for producing a high Si-containing steel sheet having excellent surface properties according to the present invention, since the high Si-containing steel material contains B and P, heating is performed at a temperature below 1173 ° C. as can be seen from the above knowledge. In this case, it is possible to obtain a scale property with good releasability. For this reason, scale releasability (descaling property) at the time of descaling is drastically improved. Therefore, it is possible to obtain a high Si-containing steel sheet having a small striped scale and excellent surface properties.

That is, the method for producing a high Si content steel sheet having excellent surface properties according to the present invention uses B and P added as a high Si content steel material, and scales a mixed layer of FeO and Fe ₂ SiO ₄ during heating. By forming it at the interface between steel and steel, the scale peelability during descaling was greatly improved. By adding B and P as described above, the scale peelability at the time of descaling can be improved even in the case of low temperature heating below 1173 ° C., without requiring a special heating method such as two-stage heating, It is possible to obtain a high Si-containing steel sheet having excellent surface properties with few stripe scales while minimizing scale loss.

  The reasons for limiting the numerical values of the components of the high Si content steel material and the production conditions (heating conditions, descaling conditions, etc.) in the method for producing a high Si content steel sheet having excellent surface properties according to the present invention will be described below.

(About components of high Si content steel)
In the production method of the high Si-containing steel sheet having excellent surface properties according to the present invention, for improving the scale detachment properties during descaling, trace elements to diffuse to the interface and the scale between the scale from base iron to Fe ₂ It inhibits uniform generation of SiO ₄ layer is dispersed the Fe ₂ SiO ₄ layer, by forming the FeO by eliminating barriers Fe diffusion from base steel and (Fe ₂ SiO ₄ layer), and Fe ₂ SiO ₄ A mixed layer of FeO is formed near the interface between the scale and steel. When the Fe ₂ SiO ₄ layer is dispersed, Fe diffusion from the ground iron proceeds, FeO and voids (bubbles) are formed and become brittle. Therefore, the scale peelability at the time of descaling is dramatically improved.

  For this purpose, addition of a small amount of B is very effective. In order to obtain this effect, the amount of B needs to be 0.0025% by mass or more. B: When the amount is less than 0.0025% by mass, it does not concentrate sufficiently at the interface between the base iron and the scale, does not sufficiently diffuse into the scale, and the effect cannot be obtained. However, when the amount of B exceeds 0.05% by mass, the effect is saturated. Therefore, B: 0.0025 to 0.05 mass%.

P, like B, has the property of diffusing from the ground iron to the interface with the scale and into the scale, and is effective in dispersing the Fe ₂ SiO ₄ layer. The amount of P necessary for dispersing the Fe ₂ SiO ₄ layer is 0.001% by mass or more. When P is less than 0.001% by mass, it does not concentrate sufficiently at the interface between the base iron and the scale, does not sufficiently diffuse into the scale, and the effect cannot be obtained. However, if the amount of P is too large (exceeding 0.1% by mass), grain boundary embrittlement of the steel tends to occur, so P: 0.1% by mass or less is necessary. Therefore, P: 0.001 to 0.1% by mass.

  S is also concentrated at the interface between the scale and the steel, and is effective in improving the peelability of the scale. In order to exert this effect, it is necessary to add S: 0.001% by mass or more. However, if the amount of S exceeds 0.1% by mass, the irregularities at the interface between the scale and the steel increase remarkably and scale flaws are liable to occur, so S: 0.1% by mass or less is necessary. Therefore, S: 0.001 to 0.1% by mass.

  C is an element necessary for strengthening steel, and addition of 0.01% by mass or more is necessary. However, if the amount of C is too large (exceeding 0.2% by mass), the steel will be hardened too much and scale peeling will be non-uniform, so C: 0.2% by mass or less is necessary. Therefore, C: 0.01 to 0.2 mass%.

  Mn is also an element necessary for strengthening steel, and it is necessary to add 0.2% by mass or more. However, if it exceeds 3.0% by mass, the steel is hardened too much, so it is necessary to make Mn: 3.0% by mass or less. Therefore, Mn: 0.2 to 3.0 mass%.

Conventionally, in the case of Si: 0.2% by mass or more, an Fe ₂ SiO ₄ layer is formed, and the scale peelability is deteriorated, so that the surface property is deteriorated. That is, when Si is less than 0.2% by mass, the Fe ₂ SiO ₄ layer is not formed, and the scale peelability does not become a problem. Since the present invention is intended to obtain a high Si-containing steel sheet with improved surface peelability by improving the scale peelability, it is necessary and necessary for Si: 0.2% by mass or more. The present invention is effective when Si: 0.2% by mass or more. However, when Si is more than 2.0% by mass, even if B and P are added as in the present invention, the Fe ₂ SiO ₄ layer is generated at a stretch and is not dispersed, so the scale peelability is very poor. It becomes impossible to suppress the scale wrinkle. From the above, Si: 0.2 to 2.0 mass%.

(About manufacturing conditions)
When hot-rolling a high Si-containing steel material, it is heated before hot rolling. The heating temperature need not be higher than the eutectic temperature (1173 ° C.) of FeO—Fe ₂ SiO ₄ . Rather, when the heating temperature is raised, scale loss becomes a problem, and when Si exceeds 0.5 mass%, eutectic wedge-shaped biting of FeO-Fe ₂ SiO ₄ occurs, and heating is performed at 1170 ° C. or lower. However, if the heating temperature is too low, the hot rolling load increases, so the temperature is set to 900 ° C or higher. Accordingly, the heating temperature is set to 900 to 1170 ° C. That is, a high Si content steel material is heated at 900-1170 ° C. In view of hot rolling load, the heating temperature is preferably set to 1000 ° C. or higher. The heating time is preferably 100 minutes or more from the viewpoint of rolling load, but if it exceeds 300 minutes, the scale loss increases, so 300 minutes or less is desirable.

  When hot rolling is performed after heating the high Si-containing steel material, descaling is performed at least once with high-pressure water of 10 MPa or more before the start of finish rolling in this hot rolling. In this descaling, the pressure of the high pressure water is set to 10 MPa or more because if it is less than 10 MPa, descaling becomes insufficient.

  This descaling may be performed from the exit side of the heating furnace to the start of hot rolling, may be performed during the rough rolling, or may be performed after the rough rolling and before the start of finish rolling. In this, when descaling is performed after rough rolling and before the start of finish rolling, the scale is destroyed to some extent in rough rolling and then descaling is performed, so the scale can be removed more efficiently. .

  The descaling is not limited to being performed once, and may be performed once or more. For example, descaling may be performed from the heating furnace exit side to the start of hot rolling, and further after rough rolling, descaling may be performed before finishing rolling.

High Si-containing steel In the method of producing a high Si-containing steel sheet having excellent surface properties according to the present invention further comprises a Cu and / or Ni. Moreover, what contains Al, Cr, etc. can be used. When using what further contains Cu as this high Si content steel material, it is set as Cu: 0.001-0.05 mass% . The reason is as follows. Cu concentrates at the interface between scale and steel, improving the scale peelability. In order to exert this effect, Cu: less than 0.001% by mass is insufficient, and Cu: 0.001% by mass or more is necessary. If the amount of Cu exceeds 0.05% by mass, the hot brittleness of the steel decreases, so Cu: 0.05% by mass or less is preferable. Therefore, when further containing Cu, Cu: 0.001 to 0.05 mass% .

In the case where a steel further containing Ni is used as the high Si content steel material, the Ni content is set to 0.05% by mass or less . The reason is as follows. When Ni content exceeds 0.05% by mass, Ni greatly affects the peelability of the scale and increases the interface roughness between the steel and the scale, which causes generation of scale defects. Therefore, when Ni is further contained, it is necessary to suppress the Ni content to 0.05% by mass or less .

In the case where a steel containing one or more of Al and Cr is further used as the high Si content steel material, it is desirable that Al: 0.01 to 0.05% by mass and Cr: 0.01 to 0.3% by mass [ second invention]. The reason is as follows. Al has a deoxidizing and denitrifying effect. This effect is insufficient when Al is less than 0.01% by mass, and is effective when Al is 0.01% by mass or more. When Al: more than 0.05% by mass, this effect is saturated. Therefore, when further containing Al, it is desirable to set it as Al: 0.01-0.05 mass%. Cr is an element that strengthens steel. This effect is insufficient when Cr is less than 0.01% by mass, and is effective when Cr is 0.01% by mass or more. When Cr: more than 0.3% by mass, the ductility of the steel is lowered and becomes insufficient. Therefore, when further containing Cr, Cr: 0.01 to 0.3% by mass is desirable.

  N is inevitably contained. That is, it is contained as an inevitable impurity. Since it is industrially difficult to make the N content less than 0.0005% by mass, the N content is usually 0.0005% by mass or more. When the N content exceeds 0.01% by mass, the aging deterioration becomes remarkable. Therefore, the N content is desirably suppressed to 0.01% by mass or less.

The high Si-containing steel material, which is a material for producing a high-Si content steel sheet with excellent surface properties according to the present invention, is heated at 900 to 1170 ° C. and then hot-rolled and descaled to achieve high Si content. It is a high Si content steel material used when producing a steel plate containing C: 0.01 to 0.2 mass%, Si: 0.2 to 2.0 mass%, Mn: 0.2 to 3.0 mass%, P: 0.001 to 0.1 mass%, S : 0.001 to 0.1% by mass, B: 0.0025 to 0.05% by mass, Cu: 0.001 to 0.05% by mass and / or Ni: 0.05% by mass or less , remaining Fe and inevitable impurities It is a high Si content steel material as a material for producing a high Si content steel plate having excellent surface properties [ fourth invention].

  According to the high Si content steel material of the material for producing the high Si content steel sheet having excellent surface properties according to the present invention, since this steel material contains B and P, the above knowledge and the above described surface texture according to the present invention. As can be seen from the explanations such as the operational effects relating to the manufacturing method of the high Si content steel sheet excellent in the above, it is possible to obtain a scale property with good peelability when heated at less than 1173 ° C., and therefore, at the time of descaling Scale peelability (descaling property) is dramatically improved, and therefore, a high Si-containing steel plate having less striped scale and excellent surface properties can be obtained.

  The reason for limiting the numerical value of the component in the high Si content steel material of the material for producing the high Si content steel plate excellent in the surface property according to the present invention is the case of the method for producing the high Si content steel plate excellent in the surface property according to the present invention described above It is the same. The high Si content steel material, which is a material for producing a high Si content steel sheet having excellent surface properties according to the present invention, is premised on being heated at 900 to 1170 ° C. and then hot rolled and descaled. The reason why the heating temperature is set to 900 to 1170 ° C. is the same as in the case of the method for producing a high Si-containing steel sheet having excellent surface properties according to the present invention.

The high Si content steel material for producing a high Si content steel sheet having excellent surface properties according to the present invention further contains Cu and / or Ni . Moreover, what contains Al, Cr, etc. can be used. Furthermore, when using what contains Cu, it is set as Cu: 0.001-0.05 mass% . The reason for this is the same as in the case of the method for producing a high Si-containing steel sheet having excellent surface properties according to the present invention described above.

Furthermore, when using Ni containing thing, content of Ni shall be 0.05 mass% or less . The reason for this is the same as in the case of the method for producing a high Si-containing steel sheet having excellent surface properties according to the present invention described above.

Furthermore, when using what contains 1 or more types of Al and Cr, it is desirable that Al: 0.01-0.05 mass% and Cr: 0.01-0.3 mass% [ 5th invention]. The reason for this is the same as in the case of the method for producing a high Si-containing steel sheet having excellent surface properties according to the present invention described above.

The high Si-containing steel sheet having excellent surface properties according to the present invention is a high S material having excellent surface properties obtained by the method for producing a high Si-containing steel sheet having excellent surface properties according to the first to second inventions of the present invention. i-containing steel sheet [ third invention].

  The high-Si content steel sheet having excellent surface properties according to the present invention has less stripe scale, as can be understood from the description of the effects and the like relating to the method for producing the high-Si content steel sheet having excellent surface properties according to the present invention described above. Therefore, even after pickling, the surface can be suitably used as a high Si-containing steel sheet having excellent surface quality with few irregularities that can cause fatigue fracture and the like on the surface. For example, it can be suitably used for automobiles and building materials.

  Examples of the present invention and comparative examples will be described below. The present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. include.

  After melting a high Si content steel material having the composition shown in Table 1, it was heated and forged to obtain a slab-shaped material for hot rolling (thickness: 240 mm, width: 1000 mm, length: 8500 mm).

Here, the high Si content steel materials of steel types A to H in Table 1 satisfy the composition requirements of the high Si content steel materials in the method for producing a high Si content steel plate according to the present invention, and the high Si content according to the present invention. It also satisfies the composition requirements of the high Si content steel material for the production of the contained steel sheet .

  The high Si content steel materials of steel types I to N have the composition requirements of the high Si content steel material in the method for producing the high Si content steel plate according to the present invention, and the high Si content steel material as a material for producing the high Si content steel plate according to the present invention. It does not satisfy the composition requirements. That is, the high Si content steel material of steel type I is P: 0.15% by mass and does not satisfy P: 0.001 to 0.1% by mass, the high Si content steel material of steel type J is B: 0.0015% by mass, and B: The point which does not satisfy 0.0025-0.05 mass%, the high Si content steel material of steel type K is S: 0.16 mass%, the point which does not satisfy S: 0.001-0.1 mass%, and the high Si content steel material of steel type M is B: tr. B: The point that does not satisfy 0.0025 to 0.05 mass%, the high Si content steel material of steel grade L is Ni: 0.08 mass%, the Ni content exceeds 0.05 mass%, the high Si content of steel grade N The steel material is Cu: 0.09% by mass, and in terms of containing Cu in excess of 0.05% by mass, the composition requirements of the high Si content steel material in the method for producing a high Si content steel plate according to the present invention are also related to the present invention. It does not satisfy the composition requirements of the high Si content steel material for producing the high Si content steel sheet.

  After the above hot rolling material (slab) is heated in a heating furnace, it is descaled with high-pressure water of 10 MPa or more immediately after extraction from the heating furnace. Thickness: 1.8 mm) was manufactured. At this time, the heating temperature in the heating furnace, the heating time, and the descaling pressure (pressure of high-pressure water at the time of descaling) were changed as shown in Table 2. Note that descaling was performed by injecting high-pressure water from the heating furnace onto the slab immediately after extraction (at the descaling pressure shown in Table 2), and thereafter, rough rolling and finish rolling were performed to produce a high-Si content steel sheet.

About the high Si content steel plate (hot-rolled steel plate) manufactured in this way, the grade of the striped scale was investigated. This survey was conducted by collecting a 500mm square steel plate (sample) from a hot-rolled steel plate, pickling it, and examining the occurrence of irregularities on the surface of the steel plate, and evaluating the level of the striped scale based on the occurrence of irregularities. did. That is, when the hot-rolled steel sheet is pickled, the flange portion into which the scale of the striped scale is pressed appears as a dent. The appearance of the surface of the steel plate (sample) after the pickling is photographed. Then, a surface area (S ₁₎ of the flaw portion (recessed portion), and calculates the ratio (area ratio) to the total surface area of the steel sheet (sample) of the area (S ₁₎ (S _0), stripes the area ratio The rate of occurrence of a scale was taken. If this area ratio (that is, the striped scale occurrence rate) is R, then 100 × S ₁ / S ₀ = R (%). If this area ratio (that is, the striped scale occurrence rate) is 10% or less, it can be used as a product and is at an acceptable level, and those exceeding 10% are unusable as products. The 500 mm square steel plates (samples) were sampled one each from the coil front end, center, and rear end of the hot rolled steel plate.

The results of the investigation are shown in Table 2. In the case of No. 9 to 14, the high Si content steel material of the material for hot rolling, the composition requirement of the high Si content steel material in the method for producing the high Si content steel sheet according to the present invention is also the high Si content according to the present invention. Steel materials that do not satisfy the composition requirements of high Si content steel materials (steel grades I to N) are used. For this reason, striped scale generation rate [after pickling for the total surface area S ₀ of the steel plate (sample) The ratio (area ratio) R = 100 × S ₁ / S ₀ ] of the area S ₁ of the buttocks (dent part) of the product exceeds 10%, and the product is rejected.

In the case of No.15, the high Si content steel material of the material for hot rolling satisfies the composition requirement of the high Si content steel material in the method for producing the high Si content steel plate according to the present invention (the high Si content steel sheet according to the present invention). The material used for production also satisfies the composition requirements of high Si content steel, but the heating temperature in the heating furnace is over 1173 ° C, so the striped scale generation rate greatly exceeds 10%. The product is rejected. This is because the No. 15 high Si content steel material has an Si content exceeding 0.5 mass%, and when the Si content exceeds 0.5 mass%, if the heating temperature exceeds 1173 ° C, FeO-Fe ₂ SiO ₄ This is due to the occurrence of eutectic wedge-shaped biting.

  On the other hand, in the case of No. 1 to No. 8, it satisfies the requirements for the production method of the high-Si content steel sheet according to the present invention (composition requirements and production conditions for the high-Si content steel material), and the striped scale generation rate is 10% It is the following and is a pass level as a product.

  In the above examples and comparative examples, after heating the slab in a heating furnace, it is descaled with high-pressure water immediately after extraction from the heating furnace, and then hot rolled to produce a high Si content steel sheet. However, after the slab was heated in a heating furnace, it was hot-rolled, and after rough rolling in this hot rolling, descaling was performed with high-pressure water before the start of finish rolling, and then finish rolling. Even when a high Si content steel sheet is manufactured, the same tendency as in the above examples and comparative examples is obtained.

  According to the present invention, it is possible to obtain a high Si-containing steel sheet with less striped scale and excellent surface properties. Therefore, the present invention is suitable for producing a high Si-containing steel sheet with fewer striped scales and excellent surface properties. It can be used for and useful.

It is a schematic diagram which shows the condition of the scale formed when the conventional high Si content steel is heated at the temperature below 1173 degreeC. It is a schematic diagram which shows the condition of the scale formed when high Si content steel is heated at the temperature over 1173 degreeC. It is a schematic diagram which shows the condition of the scale formed when the high Si content steel material by the manufacturing method of the high Si content steel plate which concerns on this invention is heated at the temperature of 1170 degrees C or less.

Claims (5)

C: 0.01 to 0.2 wt%, Si: 0.2 to 2.0 mass%, Mn: 0.2 to 3.0 mass%, P: 0.001 to 0.1 wt%, S: 0.001 to 0.1 mass%, B: containing 0.0025 to 0.05 wt% In addition, when high-Si steel containing Cu: 0.001 to 0.05% by mass and / or Ni: 0.05% by mass or less and consisting of the remaining Fe and unavoidable impurities is heated at 900 to 1170 ° C. and then hot-rolled. A method for producing a high Si content steel sheet with excellent surface properties, characterized in that descaling is performed at least once with high-pressure water of 10 MPa or more before the start of finish rolling in this hot rolling. The high Si-containing steel is further Al: 0.01 to 0.05 wt%, Cr: 0.01 to 0.3 manufacturing method of the high Si-containing steel sheet having excellent surface properties according to claim 1, further comprising one or more mass%. A high Si content steel sheet having excellent surface properties obtained by the method for producing a high Si content steel plate having excellent surface properties according to claim 1 or 2 . A high-Si content steel material used when producing a high-Si content steel sheet having excellent surface properties by heating and descaling after heating at 900 to 1170 ° C., C: 0.01 to 0.2 mass, Si: 0.2-2.0 mass%, Mn: 0.2-3.0 mass%, P: 0.001-0.1 mass%, S: 0.001-0.1 mass%, B: 0.0025-0.05 mass% , and Cu: 0.001-0.05 mass % And / or Ni: 0.05% by mass or less, consisting of the balance Fe and inevitable impurities, a high Si content steel material as a material for producing a high Si content steel sheet having excellent surface properties. Furthermore, the high Si content steel material of the raw material for high Si content steel plate excellent in the surface property of Claim 4 containing 1 or more types of Al: 0.01-0.05 mass% and Cr: 0.01-0.3 mass%.

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