JP5928396B2 - Method for producing high carbon hot-rolled steel sheet for cold rolling - Google Patents

Description

  The present invention relates to a method for producing a high carbon hot-rolled steel sheet, and particularly contains 0.1 to 1.3% by mass of C and 0.05 to 2.0% by mass of Si, and is used for cold rolling. It is related with the manufacturing method of what is called a high carbon hot rolled sheet steel for cold rolling.

  High-carbon hot-rolled steel sheet for cold rolling containing 0.1 to 1.3% of C and 0.05 to 2.0% of Si in mass% (hereinafter, the steel sheet may also be referred to as a steel strip) Is subjected to cold rolling at a rolling reduction of about 20% to 90% to obtain a high carbon cold rolled steel sheet. In this cold rolling, in order to facilitate rolling even with a small load, a relatively small diameter roll, for example, a small diameter roll having a roll diameter of about 70 mm to 150 mm is often used.

  Here, in particular, in a high carbon hot-rolled steel sheet for cold rolling with a large Si content containing 0.05% or more of Si, there is a surface defect called so-called glittering flaw after cold rolling with a small diameter roll as described above. There is a problem that it may be observed, resulting in an appearance defect.

Conventionally, the technique of patent document 1 and patent document 2 is known as a technique which suppresses a glitter wrinkle.
The technique described in Patent Document 1 relates to a method for manufacturing an austenitic stainless steel strip, and shot blasting with a rough surface roughness as a mechanical descaling treatment, and a grain boundary erosion groove depth as a chemical descaling treatment. After the nitric hydrofluoric acid (HF / HNO ₃ ) pickling is performed, the grain of the stainless steel strip surface is rolled in the next cold rolling using a small-diameter roll such as a Sendzimir mill. An object of the present invention is to solve the problem that a defective part such as a boundary erosion groove is crushed by a roll and a sparkle is generated. In Patent Document 1, an alkaline earth metal chloride solution is infiltrated into an oxide scale formed on the surface of an austenitic stainless steel strip subjected to hot rolling, followed by continuous annealing at a predetermined temperature, and then a predetermined mechanical strength. It is described that the above problem can be solved by applying a descaling process and a predetermined chemical descaling process.

  The technique described in Patent Document 2 relates to a method for producing a ferritic stainless steel, which is cooled after coiling a high-temperature ferritic stainless steel sheet that has been hot-rolled into a coil shape at 700 ° C. or higher. Or when the coil after hot rolling is subjected to box annealing at about 800 ° C., grain boundary segregation in the sulfuric acid in the subsequent descaling process causes the grain boundaries to be particularly dissolved, generating intergranular corrosion grooves. It is intended to solve the problem that the final product surface after cold rolling and annealing generates glittering dust (gold dust) and significantly impairs the surface quality. In Patent Document 2, the coil cooling condition after hot rolling of ferritic stainless steel or the annealing condition of the coil after cooling is controlled to promote recrystallization of the hot rolled steel strip, and during these heat treatments. A method for producing a ferritic stainless steel having a predetermined steel component composition is described in which the grain boundary segregation of phosphorus occurring in the above does not generate a grain boundary corrosion groove after the subsequent sulfuric acid pickling step.

JP-A-5-25666 JP 2001-32023 A

  However, the techniques of Patent Document 1 and Patent Document 2 are all intended to solve the problem of sparkle caused by intergranular corrosion grooves in stainless steel sheets, and the production of high-carbon hot-rolled steel sheets with different production conditions. Could not be applied.

  In particular, the present invention is a glitter that appears after cold-rolling a high-carbon hot-rolled steel sheet for cold rolling containing 0.1 to 1.3% of C and 0.05 to 2.0% of Si in mass%. It aims at providing the manufacturing method of the high carbon hot rolled sheet steel for cold rolling which can suppress generation | occurrence | production of a flaw.

  In the present invention, a high-carbon hot-rolled steel sheet for cold rolling before cold rolling is subjected to rolling under a light pressure with a roll having a relatively large diameter (also referred to as a large diameter roll). The inventors have found that the occurrence of glittering wrinkles can be suppressed even when cold rolling is performed with a small roll (also referred to as a small diameter roll), and the invention has been completed.

That is, the present invention is hot-rolled in the production of a high-carbon hot-rolled steel sheet for cold rolling containing C: 0.1 to 1.3% and Si: 0.05 to 2.0% by mass. Then, after the descaling treatment is performed, the surface roughness Ra is 0.6 μm or less, the roll diameter is 300 mm or more, and the rolling reduction is 1.0% or more and 20% or less. A method for producing a high carbon hot-rolled steel sheet for cold rolling is provided.
The high-carbon hot-rolled steel sheet for cold rolling manufactured by the above method should produce a high-carbon cold-rolled steel sheet that has excellent surface appearance without generating sparkle even when cold-rolled with a relatively small diameter roll. Can do.

  In the present invention, after the descaling treatment, spheroidizing annealing may be performed before the reduction is applied.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the high carbon hot-rolled steel sheet for cold rolling which can suppress generation | occurrence | production of the sparkle after cold rolling, and the high carbon cooling which is excellent in the surface appearance where generation | occurrence | production of the sparkle crack was suppressed. It becomes possible to provide a rolled steel sheet.

It is a schematic diagram which shows the surface state of the steel plate in the case of cold rolling using a small diameter roll. It is a schematic diagram which shows the surface state of the steel plate in the case of rolling using the large diameter roll in manufacture of the high carbon hot-rolled steel plate for cold rolling.

  As a result of detailed investigations on the occurrence of glittering flaws, the present inventors have found that the occurrence of glittering flaws in high-carbon hot-rolled steel sheets for cold rolling occurs frequently when Si is contained in an amount of 0.05% or more. I found out. In addition, as a result of observing the state of the steel sheet surface before and after cold rolling for the steel sheet with sparkle wrinkles, the crack wrinkles occurred in the part where the scale wrinkles peculiar to Si-containing steels, so-called red scale wrinkles occurred. As a result, it was found that the glitter wrinkles generated in the high carbon cold-rolled steel sheet are caused by red scale wrinkles formed in the hot-rolled steel sheet before cold rolling.

The mechanism for the occurrence of glittering wrinkles in the part where the red scale wrinkles occurred is assumed as follows.
FIG. 1 shows a schematic diagram of the surface state of a steel sheet in which glittering wrinkles occur during conventional cold rolling. In FIG. 1, the scale where the red scale is generated during hot rolling is removed by pickling, and a red scale ridge 2 having large irregularities is formed. When such a hot-rolled steel sheet is cold-rolled with a small-diameter cold-rolling roll 4, the ridges 2a of the unevenness of the red scale ridge 2 fall down in the red scale ridge 2, and the direction parallel to the plate surface in particular It is greatly stretched in the rolling direction and becomes a flake shape of about 10 to 100 μm on the surface of the steel sheet, and when it is exposed to light, it is diffusely reflected and glitters are observed and recognized as glittering wrinkles.

  The present inventors examined suppression of glittering wrinkles based on such findings. As a result, after descaling, hot-rolled steel sheets with red scale wrinkles and large irregularities formed are rolled with a large-diameter roll with a small stress in the rolling direction, and the red scale on the steel sheet surface before cold rolling. It has been found that the occurrence of glittering wrinkles due to subsequent cold rolling can be suppressed by reducing the collapse of the ridges 2a of the irregularities of the ridges 2 and crushing the height direction (sheet thickness direction) more.

  In a small-diameter roll, the flatness of the roll when a rolling load is applied is small, and a shearing force that is a stress in a direction parallel to the plate surface and a rolling direction stress acts on the steel sheet as a material to be rolled along with rolling. By the rolling direction stress (shearing force), as described above, the uneven peak 2a falls down and is greatly extended in the rolling direction. On the other hand, in the case of a large diameter roll, the flatness of the roll when a rolling load is applied is larger than in the case of rolling with a small diameter roll. The compressive stress in the plate thickness direction works greatly. For this reason, when rolling with a large-diameter roll, compared with rolling with a small-diameter roll, the collapse of the uneven portion 2a on the surface of the steel sheet can be reduced, and the height direction (sheet thickness direction) can be crushed more. . FIG. 2 shows a schematic diagram of rolling with a large-diameter roll of a hot-rolled steel sheet after descaling in the present invention. In the hot-rolled steel plate before cold rolling, the portion where the red scale ridge 2 is formed is largely crushed in the thickness direction by rolling using the large-diameter roll 5, and the unevenness is reduced. Thus, before cold rolling, rolling is applied using a large-diameter roll, and the ridges 2a of the unevenness of the red scale ridge 2 on the surface of the hot-rolled steel sheet are previously crushed in the height direction (plate thickness direction). By reducing the unevenness, even if cold rolling is performed thereafter, the collapse of the ridge 2a of the uneven portion is reduced, and it is prevented from being greatly stretched in the rolling direction, and the occurrence of glittering wrinkles is suppressed. It is thought that you can.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, in this invention,% which shows the component of steel means the mass% unless there is particular notice.

  The high-carbon hot-rolled steel sheet for cold rolling targeted by the present invention includes C: 0.1-1.3%, Si: 0.05-2.0%, and high-carbon hot-rolled steel sheet for cold rolling. For example, C: 0.1 to 1.3%, Si: 0.05 to 2.0%, Mn: 0.1 to 2.0%, P: 0.03% or less (preferably P: 0.020% or less), S: 0.035% or less (preferably S: 0.005% or less), N: 0.0100% or less, and Al: 0.050% or less. In addition, as other elements, Ni: 0.01-3.5%, Cr: 0.01-3.5%, Mo: about 0.01-3.0% may be contained, The balance is preferably inevitable impurities.

  In the present invention, the C content is set to 0.1 to 1.3% in order to obtain required properties such as strength after cold rolling. Si is an element effective for deoxidation, and the Si amount is set to 0.05% or more in order to obtain the effect. In order to obtain this effect, the Si content is preferably 0.1% or more, or more preferably 0.2% or more. If the Si content exceeds 2.0%, the hot-rolled steel sheet becomes hard and cold rolling becomes difficult, so the Si content is set to 2.0% or less.

  The high-carbon hot-rolled steel sheet for cold rolling is obtained by hot-rolling a steel having the above-mentioned composition with a hot rolling mill, then performing descaling treatment such as pickling, and performing spheroidizing annealing as necessary. Then, a roll having a surface roughness Ra of 0.6 μm or less and a roll diameter of 300 mm or more is applied with a reduction of 1.0% or more and 20% or less. The spheroidizing annealing is performed, for example, at a temperature of 600 ° C. or higher and an Ac1 transformation point or lower for about 8 to 40 hours. Further, spheroidizing annealing may be omitted.

  Here, the conditions of the hot rolling and descaling treatment may be in accordance with ordinary methods.

  The roll used for the rolling applied to suppress the occurrence of glittering wrinkles on the hot-rolled steel sheet after the descaling treatment needs to have a roll diameter of 300 mm or more. If the roll diameter is less than 300 mm, the effect of suppressing glitter wrinkles is small, and it is difficult to sufficiently suppress the glitter wrinkles. In addition, although a contact length will become long when a roll diameter becomes large, when a contact length becomes too long, since a surface pressure will fall and it will become difficult to obtain a reduction rate, it is preferable that a roll diameter shall be about 800 mm or less. If the surface roughness Ra of the roll is too rough, the effect of crushing the crests of the irregularities formed on the red scale ridges will be reduced and the effect of suppressing glittering creases will be reduced, or new irregularities will be added. Ra is required to be 0.6 μm or less in order to reduce the surface quality. Here, Ra is the arithmetic average height of JISB0601.

  Moreover, the rolling reduction applied by the roll having a roll diameter of 300 mm or more needs to be 1.0% or more and 20% or less. If the rolling reduction is less than 1.0%, the generation of glittering wrinkles cannot be sufficiently suppressed, and if the rolling reduction exceeds 20%, the deformation becomes too large and fine cracks may occur on the steel sheet surface. There is.

  The high-carbon hot-rolled steel sheet for cold rolling manufactured by the above manufacturing method suppresses the occurrence of glittering wrinkles even if it is cold-rolled by a cold rolling mill having a small diameter roll such as a reverse cold rolling mill. be able to. Specifically, the high carbon hot-rolled steel sheet for cold rolling manufactured by the above manufacturing method is subjected to cold rolling at a rolling reduction of 20% to 90% using a roll having a roll diameter of 70 mm to 150 mm, and glittering. It is possible to produce a high-carbon cold-rolled steel sheet having an excellent appearance while suppressing the generation of wrinkles. In the case of cold rolling, the above effects are not impaired even if intermediate annealing is performed during rolling.

  Steels having the composition shown in Table 1 are hot-rolled with a hot rolling mill to form a hot-rolled steel sheet with a thickness of 2.5 mm, then pickled as descaling, and then kept at 700 ° C. for 20 hours. After subjecting to spheroidizing annealing that gradually cools after annealing, the steel sheet was rolled under the rolling conditions shown in Table 2 to produce a hot-rolled steel sheet for cold rolling. Moreover, about the steel plate after descaling process, the presence or absence of red scale wrinkles was observed visually and the result is shown in Table 2.

  Next, the produced hot-rolled steel sheet for cold rolling was subjected to cold rolling at a roll diameter of 70 mm and a reduction rate of 30% to produce a cold-rolled steel sheet. About the obtained cold-rolled steel sheet, in order to make it easy to observe the occurrence of glittering wrinkles, an adhesive tape is attached to the surface of the obtained cold-rolled steel sheet in a range of 100 mm × 100 mm and peeled off, and then the surface of the cold-rolled steel sheet is visually observed. By observing, the presence or absence of occurrence of glitter wrinkles was evaluated. The results are shown in Table 2.

  Steel plate No. 1 made into a high carbon hot rolled steel plate for cold rolling by rolling under the rolling conditions of the present invention. In 1, 2, 4, 6, and 9, it can be seen that the occurrence of glittering wrinkles in the cold-rolled steel sheet after cold rolling can be suppressed even though red scale wrinkles were observed in the hot-rolled steel sheet.

  Steel plate No. 1 made of test steel A 10, steel plate No. 1 made of test steel B 11. Steel plate No. 1 made of test steel C No. 12 is a hot-rolled steel sheet for cold rolling which was not rolled after pickling and spheroidizing annealing, and glittering wrinkles were observed on the cold-rolled steel sheet after cold rolling.

  Test steel No. Steel plate No. A made of A No. 3, the roll diameter of the hot-rolled steel sheet for cold rolling was smaller than the range of the present invention, and glittering wrinkles were observed after cold rolling. The test steel No. Steel plate No. B made of B In No. 5, the roll diameter of the hot-rolled steel sheet for cold rolling was smaller than the range of the present invention, the rolling reduction was also low, and a sparkle was observed after cold rolling. Similarly, the steel plate No. In No. 14, the roll roughness was larger than the range of the present invention, and glittering wrinkles were observed after cold rolling. Further, a steel plate No. 1 made of the test steel B is used. No. 13 had a rolling reduction greater than the range of the present invention, and cracks occurred on the surface of the cold-rolled steel sheet.

  Steel No. Steel plate No. D made of D Nos. 7 and 8 are steel sheets No. 1 and No. 8 having a low Si content, no red scale wrinkles, and a roll diameter of 560 mm and cold rolling after 1.1% reduction. 8, Roll diameter: Steel plate No. 1 which was cold rolled after 0.5% reduction at 120 mm. No sparkle wrinkles were observed after cold rolling.

DESCRIPTION OF SYMBOLS 1 Steel plate 11 Steel plate surface 2 Red scale ridge 2a Red scale ridge 2b Red scale ridge valley 3 Flakes (glitter)
4 Cold rolling roll (small diameter roll)
5 Large diameter roll

Claims (2)

In mass%, C: 0.1 to 1.3%, Si: 0.05 to 2.0%, Mn: 0.1 to 2.0%, P: 0.03% or less, S: 0.035 % Or less, N: 0.0100% or less, Al: 0.050% or less, with the balance being hot in the production of a high carbon hot rolled steel sheet for cold rolling having a component composition consisting of Fe and inevitable impurities. After rolling and then descaling treatment, spheroidizing annealing is performed, and the surface roughness Ra is 0.6 μm or less, the roll diameter is 300 mm or more, and the rolling reduction is 1.0% or more and 20% or less. A method for producing a high-carbon hot-rolled steel sheet for cold rolling. As the component composition, at least one selected from Ni: 0.01 to 3.5%, Cr: 0.01 to 3.5%, and Mo: 0.01 to 3.0% by mass%. The manufacturing method of the high carbon hot rolled sheet steel for cold rolling of Claim 1 containing a seed | species.

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