JP2014128814A - Manufacturing method of steel plate excellent in chemical convertibility and corrosion resistance after coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a high strength steel plate excellent in a chemical convertibility and a corrosion resistance after coating by eliminating a Si-containing oxide layer on a surface of the steel plate after the continuous annealing of a Si-containing high strength steel plate.SOLUTION: A surface grinding process including a grinding using an elastic grind stone is carried out after the continuous annealing of a steel plate containing 0.5 mass% of Si or more, an acid cleaning is carried out, and then a temper rolling is carried out. The surface grinding process is carried out so that the maximum height roughness Rz in a plate width direction after the surface grinding process is 3.0 μm or less. The temper rolling is carried out so that a ratio (LRa/CRa) of arithmetic average roughness (LRa) of the steel plate in a rolling direction to arithmetic average roughness (CRa) in a plate width direction after the temper rolling is 0.5 or more and 1.3 or less.

Description

  The present invention relates to a method for producing a high Si-containing steel sheet having excellent chemical conversion properties and post-coating corrosion resistance.

  In recent years, improvement in fuel efficiency of automobiles has been demanded from the viewpoint of conservation of the global environment. There is also a demand for improving the safety of automobiles from the viewpoint of occupant protection in the event of a collision. For this reason, it is necessary to reduce the weight and strength of automobile bodies, and recently, automobile parts have been actively reduced in thickness and strength.

  On the other hand, since many automobile parts are manufactured by press-forming steel sheets, the steel sheets are strongly required to have high press formability, particularly high strength and high ductility, that is, excellent strength-ductility balance. A high strength cold-rolled steel sheet having high ductility often contains a large amount of Si as a strengthening element, and an Si oxide is formed on the steel sheet surface during annealing.

  Therefore, such a high-strength cold-rolled steel sheet with a high Si content cannot be formed uniformly and finely even if chemical conversion treatment is performed in the next step, resulting in a partially deficient surface state. . On such a steel sheet surface with poor chemical conversion treatment, even if electrodeposition coating or the like is applied, not only a coating film with good adhesion can be obtained, but also the corrosion resistance after coating deteriorates.

  Until now, various techniques have been proposed to solve such problems. For example, Patent Document 1 discloses that a high-tensile steel sheet containing 0.5 mass% or more of Si is subjected to surface grinding treatment and acid treatment after continuous annealing. A method for producing a steel sheet excellent in chemical conversion treatment by removing the Si-containing oxide layer formed on the steel strip surface by performing a washing treatment is disclosed.

JP 2012-6128 A

  However, when continuous annealing is performed on a high-strength steel sheet containing 0.5 mass% or more of Si, a very strong and thick Si-containing oxide layer is formed on the steel sheet surface. In order to remove such a very strong and thick Si-containing oxide layer, heavy grinding is required when performing surface grinding on the exit side of the continuous annealing furnace.

  In surface grinding, grinding marks remain in the grinding direction, and sharp irregularities remain in the steel plate width direction on the steel plate surface subjected to heavy grinding as described above. When electrodeposition coating is applied to a steel sheet with such sharp irregularities remaining on the surface, when the peeling of the coating occurs, the peeling is enlarged starting from the sharp irregularities on the surface of the steel sheet, and the corrosion resistance after painting is greatly reduced. There was concern.

  Therefore, the present invention removes the Si-containing oxide layer present on the surface of the steel sheet after the continuous annealing to improve the chemical conversion treatment for the high-tensile steel sheet containing 0.5% by mass or more of Si, and after electrodeposition coating. An object of the present invention is to produce a high-strength steel sheet that is excellent in post-coating corrosion resistance, in which coating peeling is unlikely to occur.

  The present inventor has solved the above-mentioned problems and repeatedly studied on a method for efficiently producing a high-tensile steel sheet excellent in chemical conversion property and post-coating corrosion resistance, and obtained the following knowledge.

  That is, as a result of examining the relationship between the surface texture after surface grinding and the corrosion resistance after painting, the surface roughness after heavy grinding greatly affects the corrosion resistance after painting, and the maximum height roughness Rz of the steel sheet surface after surface grinding is After reducing the surface roughness anisotropy in the steel plate longitudinal direction (rolling direction) and steel plate width direction (plate width direction) by temper rolling after pickling after reducing to some extent, the corrosion resistance after coating can be improved. I found it.

  The present invention has been made on the basis of the above-described findings, and has the following gist.

[1] After continuously annealing a steel sheet containing 0.5% by mass or more of Si, after performing surface grinding treatment including grinding using an elastic grindstone, and then performing pickling treatment, temper rolling is performed. Surface grinding treatment is performed so that the maximum height roughness Rz in the plate width direction of the steel plate after the surface grinding treatment is 3.0 μm or less, and the arithmetic average roughness and the plate width direction in the rolling direction of the steel plate after temper rolling A method for producing a steel sheet excellent in chemical conversion treatment and corrosion resistance after coating, characterized by temper rolling so that the arithmetic average roughness of the above satisfies the following formula (1):
0.5 ≦ LRa / CRa ≦ 1.3 (1)
However, LRa in Formula (1) is the arithmetic average roughness Ra (μm) in the rolling direction of the steel sheet after temper rolling, and CRa is the arithmetic average roughness Ra (μm) in the sheet width direction of the steel sheet after temper rolling. ).

  [2] The surface grinding treatment is performed by using two or more pairs of upper and lower grinding bodies that grind both sides of the steel plate, and the steel plate having excellent chemical conversion property and post-coating corrosion resistance according to the above [1] Manufacturing method.

  According to the present invention, it has become possible to produce a high-tensile steel sheet containing 0.5% by mass or more of Si that ensures good chemical conversion properties and post-coating corrosion resistance. The steel sheet produced according to the present invention is suitable for automobile parts and the like that are required to be thin and have high strength.

It is a figure which shows typically an example of the manufacturing equipment with which the manufacturing method of the steel plate of this invention is applied.

Hereinafter, an example of an embodiment for carrying out the present invention will be described.
In the method for producing a steel plate of the present invention, a steel plate containing 0.5 mass% or more of Si is used. When the Si content of the steel sheet is less than 0.5% by mass, the Si-containing oxide layer formed on the surface layer of the steel sheet during annealing is slight, and sufficient chemical conversion treatment performance is ensured without special pretreatment. For this reason, steel sheets having a Si content of 0.5 mass% or more are targeted. The upper limit of the Si content of the steel sheet is not particularly specified, but if the Si content in the steel sheet exceeds 3% by mass, the workability of the steel sheet tends to deteriorate, so the Si content is desirably 3% by mass or less.

  About another component, even if it is the steel plate to which C, Mn, P, S, sol.Al, Cr, Mo, Ti, Nb etc. were added in an appropriate quantity, the effect of this invention is not impaired.

  Steel sheets produced by the production method of the present invention are, for example, cold rolled steel sheets and steel strips for automobiles described in the Japan Iron and Steel Federation Standard (JFS A2001-2008), automobiles described in Japanese Industrial Standards (JIS G3135-2006). In the steel sheet described in the workability cold-rolled high-tensile steel sheet and steel strip, it is a plain steel high-tensile steel sheet having a Si content of 0.5% by mass or more, and the tensile strength of the steel sheet produced by the present invention is approximately It is 390 MPa or more.

  Moreover, the steel content used for the manufacturing method of this invention, ie, the steel plate which uses for continuous annealing, for example, the Si content obtained by hot-rolling the steel containing 0.5 mass% or more of Si, and then cold-rolling. It is a steel plate (cold rolled steel plate) of 0.5 mass% or more.

FIG. 1 is a schematic configuration diagram illustrating an example of a steel plate manufacturing facility to which a steel plate manufacturing method according to the present invention is applied, and shows a continuous processing line including a continuous annealing furnace. Here, 1 is a steel plate, 2 is a continuous annealing furnace, 3 is a surface grinding device, 4 is a draining device, 5 is a pickling facility, 6 is a temper rolling mill, and 7 is a coiler. Moreover, in the surface grinding apparatus 3, 31 is an elastic grindstone roll, 32 is a backup roll that supports a steel plate, and 33 is a brush roll containing abrasive grains. In this embodiment, the surface grinding treatment is performed by grinding with an elastic grindstone roll (with an elastic grindstone). Grinding) and grinding with a brush roll containing abrasive grains.
In the continuous processing line shown in FIG. 1, the steel plate 1 is passed in the direction of the arrow in the figure, and after being continuously annealed in the continuous annealing furnace 2, the surface is ground by the surface grinding device 3, and passes through the water draining device 4. After being pickled in the washing equipment 5 and subsequently temper-rolled by the temper rolling mill 6, it is wound into a coil shape by the coiler 7.

  In this embodiment, as described above, the steel plate surface is ground (mechanical grinding) by the surface grinding device 3 and then pickled (chemically ground) by the pickling equipment 5. By performing pickling treatment that is chemical grinding after mechanical grinding, even if surface oxide that cannot be removed by mechanical grinding remains, the peel strength of the surface oxide is reduced by mechanical grinding. Easy to remove by washing. Therefore, the surface layer oxide can be efficiently removed, and a uniform post-treated steel sheet surface can be obtained over the entire surface where no oxide remains partially.

  Here, it is necessary to use an elastic grindstone for the surface grinding process performed in the present invention. This is because the elastic grindstone has a higher elastic modulus than other grinding bodies and does not bend, so that heavy grinding is possible even for a high-strength material containing Si.

  As shown in FIG. 1, the grinding process performed by the elastic grindstone roll 31 is performed by supporting the steel sheet with the backup roll 32 facing the elastic grindstone roll 31 with the steel sheet sandwiched between them. A pair of upper and lower elastic grindstone rolls 31 is formed with one elastic grindstone roll for grinding the (upper surface side) and the back surface side (lower surface side) of the steel plate. In addition, although both an elastic grindstone roll and a backup roll are circular shape here, in order to distinguish with another roll in FIG. 1, it has illustrated in the substantially polygonal shape.

  Further, the surface grinding process includes a grinding process using an elastic grindstone as described above, and it is preferable to perform surface grinding (mechanical grinding) by a plurality of passes, that is, using two or more pairs of upper and lower grinding bodies. . In the embodiment shown in FIG. 1, the surface grinding process is performed by the surface grinding apparatus 3 having two pairs of upper and lower pairs of grinding bodies, that is, one pair of upper and lower elastic grindstone rolls 31 and one pair of upper and lower pairs of abrasive rolls 33. Do.

  In mechanical surface grinding, the convex part on the steel sheet surface is preferentially ground, so two or more pairs of upper and lower grinding bodies are used for surface grinding by multiple passes, that is, the steel sheet has a plurality of front and back surfaces. By round grinding, sharp irregularities associated with heavy grinding can be smoothed, and by smoothing the ground, the difference in surface roughness between the steel plate longitudinal direction and the steel plate width direction is reduced, and anisotropy is reduced. It is further improved. Specific grinding conditions when performing surface grinding with multiple passes include making the abrasive grains used in the grinding body of the subsequent pass finer than the preceding pass, that is, increasing the grain count used in the post-pass grinding body than the preceding pass. It is preferable to make the elastic modulus of the grinding body in the subsequent stage pass smaller than that in the previous stage in order to smooth the sharp unevenness caused by heavy grinding.

In the embodiment of FIG. 1, an abrasive wheel roll and a nylon brush roll containing abrasive grains having a smaller elastic modulus than that of the elastic wheel roll are used as a grinding body, and a grinding body having a different elastic modulus is used. For example, instead of the nylon brush roll containing abrasive grains, an abrasive cloth roll (a belt conveyor) using abrasive cloth, a wire brush roll using a wire brush, or the like can be applied. . In addition, the abrasive grain number of an elastic grinding wheel roll or nylon brush roll containing abrasive grains is preferably JIS-R6001 standard abrasive grain number # 80 to # 1200, more preferably # 220 to # 800. Moreover, it is preferable that the rotation speed of a grinding body shall be 600-1500 rpm.
The surface grinding apparatus 3 in FIG. 1 includes two pairs of upper and lower pairs of grinding bodies. However, the present invention is not limited to this, and the pair of upper and lower elastic grindstone rolls (grinding bodies) may be a pair. Of course, three or more pairs of upper and lower grinding bodies may be provided as long as the installation space for the equipment can be secured.

Here, after performing the above-described surface grinding treatment, it is necessary to set the maximum height roughness Rz in the sheet width direction to 3.0 μm or less for the surface roughness of the steel sheet to be pickled. Here, Rz is the maximum height roughness Rz of the roughness curve defined by JIS B 0601 (2001). When the maximum height roughness Rz in the sheet width direction exceeds 3.0 μm, the arithmetic average roughness Ra in the rolling direction of the steel sheet after temper rolling and the arithmetic average roughness Ra in the sheet width direction of the steel sheet are expressed by the above formula (1 However, since the sharp concavo-convex groove may remain, coating peeling starting from the sharp concavo-convex groove is likely to proceed, and the corrosion resistance after coating is likely to be lowered.
Further, in order to set the maximum height roughness Rz in the plate width direction of the steel plate after the surface grinding treatment to 3.0 μm or less, in the surface grinding treatment, in particular, a sharp grinding groove is not given to the steel plate. What is necessary is just to use a fine abrasive grain by enlarging the grain number in the initial grinding pass. Preferably, Rz can be 3.0 μm or less by setting the abrasive grain numbers # 220 to # 800.

  The steel plate 1 is subjected to a surface grinding process (mechanical grinding) with the surface grinding device 3, and then the water draining device 4 removes the coolant used in the surface grinding and adhered to the steel plate surface. There is no special restriction | limiting in the draining means of this drainer 4, For example, a ringer roll, a drying dryer, etc. can be used.

  Next, pickling treatment (chemical grinding) is performed by passing the steel plate 1 through the pickling equipment 5. In this pickling treatment, the surface layer oxide is removed by mechanical grinding, the acid penetrates the boundary between the exposed base material and the remaining surface oxide, and the remaining surface oxide is peeled and removed. As the pickling solution used in the pickling equipment 5, hydrochloric acid or sulfuric acid solution having a concentration of 5% by volume or more, or nitric acid hydrochloric acid solution (for example, 5% by volume or more nitric acid and 0.5% by volume or more hydrochloric acid were mixed). Solution) and the like, and the pickling treatment is desirably performed for 5 seconds or longer, more preferably for 8 seconds or longer.

Here, the sum total of the reduction | decrease amount of the steel plate mass by the surface grinding process (mechanical grinding) by the surface grinding apparatus 3 and the pickling process (chemical grinding) in the pickling equipment 5 shall be 4.0 g / m < ² > or more. preferable. When the total amount of reduction in the steel sheet mass is less than 4.0 g / m ² , the surface layer oxide is not uniformly removed over the entire surface of the steel sheet, and there is a possibility that the surface state in which the conversion crystals are lost when the conversion treatment is performed. The upper limit of the total amount of reduction in the steel sheet mass is not particularly specified, but if the amount of reduction in the steel sheet mass exceeds 30.0 g / m ² , the material yield tends to deteriorate and the work efficiency tends to deteriorate. The total amount of decrease is preferably 30.0 g / m ² or less.

A steel plate 1 subjected to pickling treatment (chemical grinding) is a steel plate containing 0.5% by mass or more of Si subjected to surface grinding treatment (mechanical grinding) and pickling treatment (chemical grinding) as described above. The temper rolling is performed in the temper rolling mill 6 so that the surface texture of the slab satisfies the following formula (1). In addition, LRa in Formula (1) is arithmetic average roughness Ra (micrometer) of the rolling direction (longitudinal direction) of the steel plate after temper rolling, CRa is arithmetic average roughness of the steel plate width direction after temper rolling. Ra (μm). In the present invention, the arithmetic average roughness Ra is an arithmetic average roughness Ra defined by JIS B 0601 (2001).
0.5 ≦ LRa / CRa ≦ 1.3 (1)

  As described above, the steel plate surface that has been subjected to heavy grinding by surface grinding (mechanical grinding) has uneven grooves in the steel plate rolling direction (longitudinal direction of the steel plate), and then pickling treatment (chemical grinding). Even if it is performed, such uneven grooves remain on the surface of the steel sheet, and when electrodeposition coating is performed, peeling of the coating starting from such uneven grooves tends to proceed, and the corrosion resistance after coating deteriorates. For this reason, the surface texture of the steel sheet after the surface grinding treatment and the pickling treatment is adjusted by temper rolling so that the above-described formula (1) is satisfied by temper rolling.

  In the present embodiment, by separating the continuous uneven grooves in the longitudinal direction of the steel sheet due to the grinding lines generated by surface grinding with the unevenness of the temper rolling roll, coating peeling starting from the continuous uneven grooves is prevented. .

  Here, when the ratio (LRa / CRa) of the arithmetic average roughness LRa (μm) in the longitudinal direction of the steel sheet after the temper rolling and the arithmetic average roughness CRa in the width direction of the steel sheet is out of the range of the formula (1), If the anisotropy of the surface roughness is increased, there will be continuous concave and convex grooves in the longitudinal direction of the steel sheet or the width direction of the steel sheet as described above, and when electrodeposition coating is performed, coating with such uneven grooves as the starting point Peeling tends to proceed and the corrosion resistance after coating deteriorates. For this reason, in the present invention, the ratio (LRa / CRa) of the arithmetic average roughness LRa (μm) in the longitudinal direction of the steel sheet and the arithmetic average roughness CRa in the width direction of the steel sheet after temper rolling satisfies the above formula (1). The range is 0.5 to 1.3.

  In addition, although the roll used for normal temper rolling is less than 0.5-3.0 micrometers Ra, in order to adjust the above steel plate surface texture, the surface roughness (arithmetic average) of the roll used for temper rolling The roughness is desirably in the range of 3.0 to 8.0 μmRa. If the surface roughness is outside the above range, it may be difficult to create a surface texture by temper rolling.

  Moreover, by such temper rolling, the ratio (LRa / CRa) of the arithmetic average roughness LRa (μm) in the longitudinal direction of the steel sheet and the arithmetic average roughness CRa in the width direction of the steel sheet is made the range of the above-described formula (1). For example, this can be achieved by changing the roughness of the roll or adjusting the elongation of the steel sheet by changing the unit width load during temper rolling.

  By using the method for producing a steel sheet according to the present invention as described above, even if it is a high Si content steel sheet, the surface layer oxide generated by annealing is completely removed, and a good chemical conversion film is formed over the entire surface of the steel sheet surface. Is possible. Further, it is possible to obtain a high-tensile steel plate that does not cause deterioration in post-coating corrosion resistance due to anisotropy of the surface roughness.

  The steel sheet (sheet thickness 1.2 mm, sheet width 950 mm) obtained by hot-rolling and cold-rolling steel having a Si content of 0.5 to 1.5% by mass shown in Table 1 is shown in FIG. After continuous annealing (line speed: 100 mpm) using a production facility, surface grinding treatment (mechanical grinding) is performed for the purpose of removing surface oxides, and a water draining device (Ringer) is applied to the steel plate immediately after the surface grinding treatment. A draining treatment (drying treatment) was performed with a roll, and then pickling treatment and temper rolling were performed.

In this case, the surface grinding treatment is carried out as an abrasive grindstone roll of abrasive grain number # 220 of JIS-R6001 standard (Young's modulus: 137.2 MPa (= 14 kgf / mm ² )) and a brush roll containing # 100 abrasive grains. (Young's modulus: 19.6 MPa (= 2 kgf / mm ² )) was used, and the rotation direction was upcut (rotation opposite to the steel plate conveyance direction). In addition, the steel roll was used for the backup roll which hold | maintains a steel plate when grinding with an elastic grindstone roll. The rotation speed of each roll was 1200 rpm for the brush roll and 800 rpm for the elastic grindstone roll.

In the pickling treatment, a sulfuric acid bath having an acid concentration of 10% by volume at 60 ° C. was used, and the pickling time was 10 seconds. The amount of reduction in the mass of the steel sheet due to the surface grinding and pickling treatment was 13 to 15 g / m ² .

  In addition, about the manufactured steel plate, the reduction | decrease amount of the mass by a surface grinding process and a pickling process was calculated | required as follows. Prepare two coils of the same steel type corresponding to each example and the same manufacturing conditions from hot rolling to continuous annealing. One coil is used in each example, and surface grinding treatment and pickling are performed as described above. Processed. For the other coil, a steel plate without surface grinding and pickling treatment was produced. Cut out steel sheets of a certain area (200mm x 200mm square) from the T part (tip part), M part (intermediate part), and B part (tail end part) in the longitudinal direction of both coils, measure the mass, and cut them out By calculating the difference between the two by dividing the area, the amount of reduction in the steel plate mass by surface grinding and pickling treatment is obtained, and the average of the calculated values in the T, M, and B parts is reduced in the steel plate mass. The amount.

  Table 1 shows grinding conditions (grinding load (A / mm)) and temper rolling conditions (work roll surface roughness (WR roughness), elongation rate). Here, the grinding load is a load of a motor that rotates the elastic grindstone roll.

A test piece was collected from the steel plate after the surface grinding treatment and before the pickling treatment, and the maximum height roughness Rz defined in JIS B 0601 (2001) was measured in the plate width direction (C direction) of the steel plate. . The results are shown in Table 1.
Moreover, a test piece is taken from the steel sheet after the temper rolling, and the arithmetic average roughness specified in JIS B 0601 (2001) for each of the rolling direction (L direction) of the steel sheet and the width direction (C direction) of the steel sheet. The thickness Ra was measured, and the ratio of the Ra (μm) in the L direction to the Ra (μm) in the C direction (L direction Ra / C direction Ra) was determined. The results are shown in Table 1. In measuring Rz and Ra, the measurement length was 4.0 mm and the cut-off value was 0.8 mm.

  In addition, about the obtained steel plate, the tensile strength (TS) was 980 Mpa and elongation (EL) was 14% about the material calculated | required based on JISZ2241 using the JIS5 tension test piece.

  Furthermore, a test piece was collected from the steel sheet after the temper rolling, and the chemical conversion treatment property and the corrosion resistance after coating were evaluated by the following methods. The results are shown in Table 1.

Chemical conversion treatment After the steel plate manufactured was subjected to degreasing, water washing, and surface adjustment in sequence, chemical conversion treatment (liquid temperature: 43 ° C., immersion time 120 sec) using a chemical conversion treatment agent (Surfdyne SD2800 manufactured by Nippon Paint Co., Ltd.) ), And the surface is observed with a scanning electron microscope at 5 magnifications at 500 magnifications, and a uniform chemical crystal having an area ratio of 95% or more is generated in all 5 visual fields is marked as ◯ (good). When a gap exceeding 5% was observed even in one field of view, it was evaluated as x (defect).

After coating, a chemical treatment (Surfdyne SD2800 manufactured by Nippon Paint Co., Ltd.) was used for chemical conversion treatment (adhesion amount of chemical conversion coating: 2.0 to 2.5 g / m ² ). Electrodeposition coating (target film thickness: 25 μm) was performed using the coating material PN-150G. About the test piece after electrodeposition coating, the salt warm water immersion test (SDT) was done as follows, and the corrosion resistance after coating was evaluated.
In the salt warm water immersion test (SDT), the above-mentioned electrodeposition-coated test piece was provided with a cross-cut wrinkle (cross angle 60 °) with a cutter, immersed in a 55% 5% NaCl solution for 240 hours, and then the test piece. Was taken out, washed with water and dried, and then the tape was peeled off with a cellophane tape on the crosscut collar. And after tape peeling, the peeling width which developed in the steel plate longitudinal direction and the width direction from the crosscut collar was measured, and the corrosion resistance after coating was evaluated using the maximum peeling width in each direction as an index. Here, when the maximum peel width from the crosscut collar is 2.6 mm or less for both the maximum paint peel width in the L direction and the maximum paint peel width in the C direction, it is judged as “good” and the maximum peel width exceeds 2.6 mm. In this case, it was judged as x (defect).

  As shown in Table 1, it is a comparative example and No. No. 4 shows that the anisotropy of the surface roughness accompanying the surface grinding is not improved, the maximum coating peeling width is larger than the standard in either the L or C direction, and the corrosion resistance after coating is reduced. Moreover, No. which is a comparative example. As shown in FIG. 5, when the Rz in the C direction after the surface grinding treatment exceeds 3.0 μm, the corrosion resistance after coating is improved even if the surface roughness anisotropy in the L and C directions is improved by temper rolling. It turns out that it has fallen. On the other hand, in the present invention examples (No. 1 to 3), the maximum coating peeling width is small in both the L and C directions, and the coating peeling is suppressed, and not only the chemical conversion processability but also the high corrosion resistance after coating is high. It can be seen that a tensile steel plate is obtained.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Continuous annealing furnace 3 Surface grinding apparatus 4 Draining apparatus 5 Pickling equipment 6 Temper rolling mill 7 Coiler 31 Elastic grindstone roll 32 Backup roll 33 Brush roll containing abrasive grains

Claims (2)

After continuous annealing of a steel sheet containing 0.5% by mass or more of Si, surface grinding treatment including grinding using an elastic grindstone is performed, and then after pickling treatment, the surface grinding is performed in the temper rolling. Surface grinding treatment is performed so that the maximum height roughness Rz in the sheet width direction of the steel sheet after treatment is 3.0 μm or less, and the arithmetic average roughness in the rolling direction of the steel sheet after temper rolling and the arithmetic average in the sheet width direction A method for producing a steel sheet excellent in chemical conversion treatment and corrosion resistance after coating, characterized by temper rolling so that the roughness satisfies the following formula (1);
0.5 ≦ LRa / CRa ≦ 1.3 (1)
However, LRa in Formula (1) is the arithmetic average roughness Ra (μm) in the rolling direction of the steel sheet after temper rolling, and CRa is the arithmetic average roughness Ra (μm) in the sheet width direction of the steel sheet after temper rolling. ).   The said surface grinding process is performed using 2 or more pairs of upper and lower grinding bodies which grind both surfaces of a steel plate, The manufacturing method of the steel plate excellent in chemical conversion treatment property and corrosion resistance after coating of Claim 1 characterized by the above-mentioned.

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