JP2012132079A - Method and facility for producing steel sheet excellent in chemical conversion treatment property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method producible of a high tensile strength steel sheet excellent in chemical conversion treatment property by efficiently removing oxides in a surface layer of the steel sheet.SOLUTION: In a method for producing a steel sheet excellent in chemical conversion treatment property, a common steel sheet obtained by hot rolling and cold rolling and having an Si content of 0.5 mass% or more is continuously annealed, and then surface grinding treatment and pickling treatment are performed in this order. In the surface grinding treatment, one or more of a rotational frequency of a grinding body, rolling reduction and coolant flow rate supplied to a grinding part are adjusted according to a winding temperature of a steel sheet in a hot rolling process, and a time from the completion of the surface grinding treatment to the start of the pickling treatment is set to be within 60 seconds.

Description

The present invention relates to a manufacturing method and manufacturing equipment for a high Si-containing plain steel sheet excellent in chemical conversion processability. The steel plate to which the steel plate manufacturing method and manufacturing equipment according to the present invention are applied is, for example, Japan Iron and Steel Federation Standard (JFS).
A2001-2008) cold-rolled steel sheet and steel strip for automobiles, workable cold-rolled high-tensile steel sheet and steel strip for automobiles described in Japanese Industrial Standard (JIS G3135-2006), It is a normal steel high-tensile steel plate of 0.5% by mass or more, and does not include stainless steel plates or electromagnetic steel plates.

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.
Various techniques have been proposed so far to solve such problems. For example, Patent Document 1 sprays a liquid in which a gas is dissolved under pressure from a liquid ejecting apparatus arranged on the exit side of the annealing furnace. Thus, a method for removing the concentrate formed on the surface of the steel strip is disclosed. Further, in Patent Documents 2 to 5, after annealing with the oxygen partial pressure in the furnace atmosphere as a specific condition, cooling is performed at a specific speed, and then the surface of the steel sheet is ground to a specific thickness and then pickled. A method for removing the oxide film is disclosed.

JP 2002-275545 A JP 2003-226920 A JP-A-5-317949 JP-A-7-70724 JP-A-7-252624

  However, when a high-strength steel sheet containing 0.5% by mass or more of Si is annealed, a very strong and thick Si-containing oxide layer is formed on the surface of the steel sheet, and the Si-containing oxide layer is a steel sheet. The surface is unevenly distributed corresponding to the roughness form of the surface. For this reason, when performing surface grinding on the continuous annealing side, heavy grinding is necessary to remove the strong and thick Si-containing oxide layer, and the steel plate surface after grinding becomes a new surface with very high activity, Coupled with the adhesion of the coolant supplied during grinding, the steel plate surface after heavy grinding becomes very rusting. Even when the steel plate surface is rusted, the pickling efficiency of the surface layer is hindered by the surface pickling step, and it is difficult to remove the surface oxide uniformly.

  Moreover, since the deformation resistance is increased by the solid solution strengthening accompanying the addition of Si and the rolling load in the hot rolling is increased, the shape of the steel sheet is easily disturbed. When passing through the run-out table of the hot rolling line while the steel plate shape is disturbed, the cooling water tends to stay on the upper surface of the steel plate, resulting in variations in the hot rolling coiling temperature. On the other hand, when a large amount of Si is added to the steel, Si is selectively oxidized and the surface is concentrated. However, in the state where the oxide scale is present on the surface as after hot rolling, from the base material. The movement to the surface is suppressed, and conversely, the movement of oxygen into the interior is promoted. Internal oxygen combines with Si in the steel to form an internal oxide layer. However, since there is a correlation between the oxygen diffusion and the steel sheet temperature, the variation of the hot rolling coiling temperature is the same as the variation of the Si-containing internal oxide layer. Leads to.

Since the Si-containing internal oxide layer remains in the steel plate even after pickling, cold rolling, and annealing the hot-rolled plate, the steel plate after continuous annealing has a Si-containing oxide layer formed on the surface, directly below it. Has a Si-containing internal oxide layer that is unevenly distributed according to the hot rolling coiling temperature. For this reason, it is difficult for the conventional methods described in Patent Documents 1 to 5 to uniformly remove such Si-containing oxides.
Accordingly, an object of the present invention is to efficiently remove the Si-containing oxide layer formed on the steel sheet surface during annealing and the Si-containing internal oxide layer remaining inside the steel sheet, and to produce a high-tensile steel sheet excellent in chemical conversion treatment. It is in providing the manufacturing method which can be performed. Another object of the present invention is to provide a manufacturing facility suitable for carrying out such a manufacturing method.

  The present inventor has repeatedly studied a method capable of solving the above-described problems and efficiently producing a high-tensile steel sheet excellent in chemical conversion treatment. As a result, the following knowledge has been obtained. First, if the coolant adheres to the new steel surface exposed after heavy grinding, rusting will occur and the pickling efficiency will decrease, but the elapsed time after surface grinding and the removal of the oxide layer by pickling As a result of examining the relationship with the efficiency, it was found that by sufficiently shortening the time until the start of the pickling treatment after the surface grinding, the generation of rust can be suppressed and the pickling efficiency is not adversely affected.

In addition, as a result of investigating a method for efficiently removing the Si-containing oxide layer formed during continuous annealing and the Si-containing internal oxide layer that is unevenly distributed according to the hot rolling coiling temperature, a steel plate is used in the hot rolling process. The Si-containing oxide layer and the Si-containing internal oxide layer are efficiently removed by measuring the coiling temperature and adjusting the grinding conditions of the surface grinding treatment after the continuous annealing according to the hot rolling coiling temperature. I found that I can do it. Specific grinding conditions include the number of revolutions of the grinding body (rotary grinding body), the reduction amount, and the supplied coolant flow rate, and the grinding amount is adjusted by adjusting one or more of these.
The present invention has been made on the basis of the above-described findings and has the following gist.

[1] After continuously annealing a normal steel sheet having a Si content of 0.5 mass% or more obtained by hot rolling and cold rolling, surface grinding treatment and pickling treatment are performed in this order,
During the surface grinding process, one or more of the number of revolutions of the grinding body, the amount of reduction and the coolant flow rate supplied to the grinding part are adjusted according to the coiling temperature of the steel sheet in the hot rolling process, and surface grinding is performed. A method for producing a steel sheet excellent in chemical conversion treatment, characterized in that the time from the completion of the treatment to the start of the pickling treatment is within 60 seconds.
[2] In the manufacturing method of [1], the surface grinding treatment is performed using one 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. Manufacturing method.
[3] In the manufacturing method of [1] or [2], the amount of reduction in the mass of the steel sheet by surface grinding and pickling is 4.0 g / m ² or more. A method of manufacturing a steel sheet.

[4] Hot rolling equipment for producing hot rolled steel sheets, cold rolling equipment for cold rolling hot rolled steel sheets obtained by the hot rolling equipment, and annealing steel sheets obtained by the cold rolling equipment Of a normal steel sheet equipped with a continuous annealing furnace, a surface grinding apparatus for surface grinding the steel sheet annealed in the continuous annealing furnace, and a pickling facility for pickling the steel sheet surface-ground with the surface grinding apparatus. Manufacturing equipment,
The hot rolling equipment has a temperature measuring means for measuring the winding temperature of the steel sheet,
The surface grinding device can adjust one or more of the number of revolutions of the grinding body, the amount of rolling reduction, and the coolant flow rate supplied to the grinding part according to the coiling temperature measured by the temperature measuring means. There is a manufacturing facility for steel sheets.

  According to the present invention, the Si-containing oxide layer formed on the steel plate surface during annealing and the Si-containing internal oxide layer remaining inside the steel plate can be efficiently removed, and a good chemical conversion coating is formed over the entire surface. It is possible to produce a high-tensile steel plate that is excellent in chemical conversion treatment. For this reason, in a high-tensile steel sheet, not only strength and workability but also coating adhesion and post-coating corrosion resistance can be improved.

Explanatory drawing which shows typically one Embodiment of the manufacturing method and manufacturing equipment of the steel plate of this invention In this invention, the graph which shows an example of the coolant flow rate supplied to the rotation speed of the grinding body adjusted according to the hot rolling coiling temperature of a steel plate, the amount of reduction, and a grinding body

  As described above, the steel plate to be manufactured in the present invention is a high-tensile steel plate (ordinary steel plate) having a Si content of 0.5% by mass or more. When the Si content of the steel sheet is less than 0.5% by mass, the amount of Si concentrated on the steel sheet surface layer during annealing is small, and sufficient chemical conversion treatment properties are ensured even without special pretreatment. The upper limit of the Si content of the steel sheet is not particularly specified, but if the Si content 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. Here, the high-tensile steel sheet refers to a normal steel sheet having a tensile strength of 390 MPa or more obtained through hot rolling, cold rolling, annealing, temper rolling, and the like.

In the present invention, after continuously annealing a steel sheet having a Si content of 0.5% by mass or more obtained by hot rolling and cold rolling, surface grinding treatment and pickling treatment are performed in this order. During the grinding process, one or more of the number of revolutions of the grinding body, the amount of rolling reduction, and the coolant flow rate supplied to the grinding part are adjusted (controlled) according to the hot rolling coiling temperature of the steel sheet, and the surface grinding process is completed. The time from the start to the start of the pickling treatment is set to be within 60 seconds. Preferably, the amount of reduction in the mass of the steel sheet due to surface grinding and pickling is 4.0 g / m ² or more.

  FIG. 1 is an explanatory view schematically showing an embodiment of a production method and production equipment of the present invention, where (i) is a hot rolling line, (ii) is a cold rolling line, and (iii) is continuous annealing. Each shows a continuous processing line including a furnace. In the hot rolling line of (i), 2 is a finish rolling mill, 3 is a run-out table, 4 is a thermometer for measuring the coiling temperature of the steel sheet, and 5 is a coiler. As the thermometer 4, for example, a radiation thermometer or a contact thermometer can be used. In the cold rolling line (ii), 6 is a tandem rolling mill and 7 is a coiler. In the continuous processing line of (iii), 8 is a continuous annealing furnace, 9 is a surface grinding device, 10 is a draining device, 11 is a pickling facility, 12 is a temper rolling mill, and 13 is a coiler. In the surface grinding apparatus 9, 90 is a grinding body (rotary grinding body) for rotating and grinding the steel sheet surface, and 91 is a coolant supply nozzle.

  In the embodiment of FIG. 1, the finish rolling mill 2 and the tandem rolling mill 6 are four-stage stands. However, the present invention is not limited to this. For example, a six-stage rolling stand may be used. Good. Moreover, the number of rolling stands of the finish rolling mill 2 and the tandem rolling mill 6 is also arbitrary. In the embodiment of FIG. 1, the continuous annealing furnace 8, the surface grinding apparatus 9, and the pickling equipment 11 constitute a continuous line, but the surface grinding apparatus 9 and the pickling equipment 11 are independent from the continuous annealing furnace 8. It may be provided as a facility. However, in the present invention, in order to provide a certain time limit between the surface grinding treatment and the pickling treatment, the surface grinding device 9 and the pickling equipment 11 need to be provided in the same continuous line.

  In the embodiment shown in FIG. 1, a steel plate 1 rolled by a rough rolling mill (not shown) and a finish rolling mill 2 in a hot rolling line passes through a run-out table 3 and is then wound around a coiler 5. Next, the steel sheet 1 is cold-rolled by a tandem rolling mill 6 in a cold rolling line and then wound around a coiler 7. Next, the steel sheet 1 is continuously annealed in a continuous annealing furnace 8 of a continuous processing line, then surface-ground by a surface grinding device 9, pickled by a pickling equipment 11 via a draining device 10, and subsequently a temper rolling mill. After being temper-rolled at 12, it is wound around a coiler 13.

  In order to remove the Si-containing oxide layer generated during the continuous annealing and the Si-containing internal oxide layer remaining inside the steel sheet (hereinafter collectively referred to as “surface oxide”), in the present invention, the surface grinding apparatus 9 After mechanical grinding of the steel plate surface, pickling (chemical grinding) is performed with the pickling equipment 11, and this mechanical grinding and pickling are performed under predetermined conditions. By combining mechanical grinding and pickling (chemical grinding), even if surface oxide that cannot be removed by mechanical grinding remains, the surface oxide is removed by pickling because the peel strength is reduced by mechanical grinding. In particular, by applying the method of the present invention, the surface layer oxide can be efficiently removed, and a uniform post-treated steel plate surface can be obtained over the entire surface where no oxide remains partially.

In the embodiment of FIG. 1, mechanical grinding (surface grinding treatment) by the grinding body 90 is performed in the surface grinding apparatus 9 on the steel plate 1 continuously annealed by the continuous annealing furnace 8 as the first stage of surface oxide removal. Do. In this mechanical grinding, the coolant is supplied from the coolant supply nozzle 91 to the grinding portion by the grinding body 90.
The grinding body 90 is disposed to face each surface of the steel plate to be passed, and in this embodiment, the rotating shaft is constituted by a cylindrical rotating body (for example, a rotating brush) whose parallel to the steel plate width direction. For example, it may be configured by a cylindrical rotating body (for example, a rotating brush) whose rotating shaft is inclined with respect to the width direction of the steel sheet. Moreover, there is no special restriction | limiting in the grinding means of the grinding body 90, For example, abrasive cloth paper, a wire brush, a nylon brush with an abrasive grain, an elastic grindstone roll, etc. are applicable. When using a nylon brush with abrasive grains or the like, it is desirable that the abrasive grain number of JIS-R6001 standard is # 60 to # 400, preferably # 80 to # 240.
The surface grinding apparatus 9 of FIG. 1 includes two pairs of upper and lower pairs of grinding bodies 90 (rotary grinding bodies). However, the present invention is not limited to this, and required appearance quality and performance of the product. Can be provided, only one pair of grinding bodies 90 may be arranged, or three or more pairs of grinding bodies 90 may be provided if the installation space for equipment can be secured.

In the mechanical grinding by the surface grinding apparatus 9, a command from a controller (not shown) is given according to the hot rolling temperature of the steel sheet measured by the thermometer 4 provided on the outlet side of the run-out table 3 in the hot rolling line. As a result, one or more of the rotational speed of the grinding body 90, the amount of reduction, and the coolant flow rate supplied to the grinding body are adjusted (controlled). That is, the hot rolling coiling temperature of the steel sheet is sequentially measured by the thermometer 4 in the longitudinal direction of the coil, and grinding conditions (grinding body) according to the measured hot rolling coiling temperature of each part of the steel sheet while grinding one coil. 90 or more, one or more of the amount of reduction and the coolant flow rate supplied to the grinding section) are adjusted.
Here, since the frictional force between the grinding body and the steel plate 1 is changed by adjusting the rotational speed of the grinding body 90, the grinding amount can be adjusted. Further, the amount of grinding can be adjusted by changing the contact area between the grinding body and the steel sheet 1 by adjusting the reduction amount of the grinding body 90. In addition, by adjusting the coolant flow rate supplied from the coolant supply nozzle 91, the contact area between the grinding body 90 and the steel plate 1 is adjusted, and the fallen abrasive grains and grinding powder that are thought to promote grinding are retained. Time changes and the grinding amount can be adjusted by these.

The rotational speed of the grinding body 90 is preferably about 600 to 1500 rpm. Further, the rolling amount of the grinding body 90 is preferably about 1 to 4 mm. Here, the amount of reduction refers to the position of the grinding body in a state where the outer surface (working surface) of the grinding body 90 is in contact with the steel plate surface (contacted in a non-pressing state), and this reference position and the grinding body during grinding. It is the distance in the steel plate thickness direction between these positions. The coolant flow rate is preferably about 1000 to 5000 L / min / m ² in terms of flow rate density (a coolant flow rate per unit area / unit time). Therefore, it is preferable that adjustment of the rotation speed, reduction amount, and coolant flow rate of the grinding body 90 in accordance with the hot rolling coiling temperature of the steel plate is performed within the above preferable range.

Here, a grinding condition corresponding to the hot rolling coiling temperature of the steel sheet is obtained in advance, and one or more of the rotational speed of the grinding body 90, the amount of reduction and the coolant flow rate supplied to the grinding part according to this grinding condition. May be adjusted (controlled). In this case, an experiment in which grinding conditions that can secure a predetermined grinding amount with respect to the hot rolling coiling temperature of the steel plate measured by the thermometer 4 are arranged for each material (material, plate thickness, plate width dimensions). It is obtained in advance from data and operation data. 2 (a) to 2 (c) show the surface grinding treatment and the acidity based on the operation data obtained by performing surface grinding and pickling on the exit side of the continuous annealing furnace for a steel sheet having an Si content of 0.5 mass% or more. The grinding conditions necessary to reduce the amount of steel sheet mass reduction by washing to 4.0 to 30.0 g / m ² are arranged with respect to the hot rolling coiling temperature of the steel sheet. In the controller, for example, based on the relationship between the hot rolling coiling temperature and the grinding condition shown in FIGS. 2 (a) to (c), the grinding condition according to the hot rolling coiling temperature of the steel sheet is calculated, and the grinding body 90 Adjust (control) one or more of the rotational speed, the amount of reduction, and the coolant flow rate supplied to the grinding section. In FIGS. 2A to 2C, the grinding conditions are changed by an amount that is linearly proportional to the hot rolling temperature of the steel sheet. However, the present invention is not limited to this. Alternatively, the hot rolling coiling temperature and the grinding conditions may be associated with each other with a second-order or higher curve.

Since the measurement of the hot rolling coiling temperature by the thermometer 4 is performed over the entire length in the longitudinal direction of the steel sheet, the winding process of the hot rolling coil is performed by adjusting the grinding conditions according to such hot rolling coiling temperature. Appropriate surface grinding conditions can be imparted even in unsteady portions such as during acceleration / deceleration in this case, and thus surface oxide can be removed uniformly over the entire length of the coil.
The longitudinal position of the steel sheet 1 measured by the thermometer 4 and the longitudinal position of the steel sheet 1 mechanically ground by the grinding body 90 are matched by, for example, position information detection using a tracking roll or the like.

After the steel plate 1 is subjected to surface grinding (mechanical grinding) with the surface grinding device 9, the coolant adhering to the steel plate surface is removed by the draining device 10. There is no special restriction | limiting in the draining means of this drainer 10, 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 11. 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 11, 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.
In the manufacturing method of the present invention, the time from when the steel plate 1 completes the surface grinding process to the pickling equipment 11 and the pickling process is started is set to be within 60 seconds. If this time exceeds 60 seconds, rust generated on the surface of the steel plate grows, and the removal efficiency in the pickling treatment decreases.

Moreover, in the manufacturing method of this invention, the total of the reduction | decrease amount of the steel plate mass by the surface grinding process (mechanical grinding) by the grinding body 90 and the pickling process (chemical grinding) in the pickling equipment 11 is 4.0 g / m < ² >. The above is 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. In addition, the reduction amount of the steel plate mass can be obtained by a method as described in the examples, for example. In that case, it is good also considering the average of the calculated value in T part, M part, and B part of a coil as a reduction | decrease amount of steel plate mass.

  Further, the steel sheet production equipment of the present invention includes a hot rolling equipment for producing a hot rolled steel sheet, a cold rolling equipment for cold rolling the hot rolled steel sheet obtained by this hot rolling equipment, and this cold rolling. A continuous annealing furnace for annealing the steel sheet obtained by the equipment, a surface grinding apparatus for surface grinding the steel sheet annealed in this continuous annealing furnace, and an acid for pickling the steel sheet surface-ground by this surface grinding apparatus A hot-rolling equipment having temperature measuring means for measuring a coiling temperature of the steel sheet, and the surface grinding apparatus is measured by the temperature measuring means. One or more of the number of revolutions of the grinding body, the amount of reduction, and the coolant flow rate supplied to the grinding part can be adjusted according to the winding temperature of the steel plate, and one embodiment is shown in FIG. Although it is shown, it is not limited to the configuration of FIG.

  In the production facility shown in FIG. 1, a steel sheet having a Si content of 0.4 to 1.5% by mass is hot-rolled and cold-rolled, and the obtained ordinary steel plate (plate thickness 1.2 mm, plate width 950 mm) is obtained. After continuous annealing (line speed 90 mpm), surface grinding treatment (mechanical grinding) and pickling treatment for the purpose of removing surface oxides were sequentially performed, and then temper rolling was performed. The steel sheet immediately after the surface grinding was subjected to a draining process (drying process) with a draining device (Ringer roll). The coiling temperature of the steel sheet in the hot rolling process was measured with a radiation thermometer installed on the runout table exit side.

In the surface grinding process, a JIS-R6001 standard abrasive grain number # 80 abrasive-filled brush was used as the rotary grinding body, and the rotation direction was upcut (rotation opposite to the steel plate conveyance direction). The pickling treatment used a sulfuric acid bath having an acid concentration of 10% by volume at 60 ° C., and the pickling time was 10 seconds in terms of line speed.
Based on the line speed, the time from the completion of the surface grinding process to the start of the pickling process was calculated.
In the example of the present invention (coils No. 2 to No. 6), the rotational speed, rolling amount and coolant of the rotary grinding body according to the command from the controller according to the coiling temperature measured in the hot rolling process. Any one of the flow densities was adjusted (controlled) as follows based on the relationship between the coiling temperature and the grinding conditions shown in FIGS.

-Coil No. 2: Based on the relationship between the coiling temperature shown in FIG. 2 (a) and the amount of reduction of the grinding body, the hot rolling coiling temperature of the steel sheet portion passing through the rotary grinding body is set to 520 ° C to 550 ° C. Accordingly, the reduction amount of the rotary grinding body was controlled (for example, the reduction amount was 2.7 mm at a hot rolling coiling temperature of 520 ° C., and the rolling amount was 3.0 mm at a hot rolling coiling temperature of 550 ° C.).
-Coil No. 3: Based on the relationship between the winding temperature shown in Fig. 2 (c) and the rotational speed of the grinding body, the hot rolling coiling temperature of the steel sheet portion passing through the rotary grinding body is set to 500 ° C to 540 ° C. Accordingly, the rotational speed of the rotary grinding body was controlled (for example, the rotational speed of 1000 rpm at a hot rolling coiling temperature of 500 ° C. and the rotational speed of 1160 rpm at a hot rolling coiling temperature of 540 ° C.).
Coil No. 4: Based on the relationship between the coiling temperature shown in FIG. 2 (a) and the amount of reduction of the grinding body, the hot rolling coiling temperature of the steel sheet portion passing through the rotary grinding body is set to 500 ° C to 540 ° C. Accordingly, the amount of reduction of the rotary grinding body was controlled (for example, when the hot rolling coiling temperature was 500 ° C., the rolling amount was 2.5 mm, and when the hot rolling coiling temperature was 540 ° C., the rolling amount was 2.9 mm).
Coil No. 5: Based on the relationship between the coiling temperature and coolant flow density shown in FIG. 2 (b), depending on the hot rolling coiling temperature of the steel sheet portion passing through the rotary grinding body, 500 ° C. to 540 ° C. , controls the coolant flow density (e.g., Netsunobemakito at temperature 500 ° C. coolant flow density 2500L / min / ^{m 2,} the coolant flow density in Netsunobemakito temperature ^{540 ℃ 2100L / min / m 2} ) was.
Coil No. 6: Based on the relationship between the winding temperature shown in FIG. 2 (c) and the number of revolutions of the grinding body, the hot rolling coiling temperature of the steel sheet portion passing through the rotary grinding body is set to 500 ° C. to 540 ° C. Accordingly, the rotational speed of the rotary grinding body was controlled (for example, the rotational speed of 1000 rpm at a hot rolling coiling temperature of 500 ° C. and the rotational speed of 1160 rpm at a hot rolling coiling temperature of 540 ° C.).

  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. Processing and temper rolling were performed. For the other coil, only temper rolling was performed to produce a steel sheet that was not surface-polished and pickled. 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.

The manufactured steel sheet was subjected to degreasing, water washing, and surface adjustment in order under the conditions shown in Table 2, and then adjusted to a temperature of 43 ° C., a total acidity of 22 to 24, and a free acidity of 0.8 to 1.0. It was immersed in a commercially available chemical conversion treatment agent (“PB-L3080” manufactured by Nihon Parkerizing Co., Ltd.), then washed with water and dried.
Samples are collected from the T, M, and B parts in the coil longitudinal direction of the steel sheet subjected to the chemical conversion treatment, and the surface of each sample is observed with five fields of view at a magnification of 500 times with a scanning electron microscope to generate chemical crystals. Depending on the situation, chemical conversion treatment was evaluated as follows.
A: Uniform chemical crystals are formed with an area ratio of 95% or more in all five fields of view.
(Triangle | delta): The space | gap of the chemical conversion crystal | crystallization over 5% of area ratio is recognized in 1 visual field.
X: In two or more fields of view, a gap between conversion crystals having an area ratio of more than 5% is observed.

About each steel plate of each example, Si content, hot rolling temperature, grinding conditions, time from completion of surface grinding treatment to start of pickling treatment, reduction amount of steel plate by surface grinding treatment and pickling treatment, chemical conversion treatment Table 1 shows the evaluation results of the sex.
In Table 1, coil No. 1 as a reference example has a low Si content in the steel sheet, and therefore, good chemical conversion treatment properties are obtained regardless of grinding conditions.
Coil No. 7, which is a comparative example, is an example in which the grinding conditions are not adjusted in accordance with the hot rolling coil temperature, and the amount of reduction in the steel sheet mass is 4.0 g / m ² or more. Since the hot rolling coiling temperature is constantly high and stable compared to the T and B parts where the temperature tends to drop, the internal oxide layer formed corresponding to the hot rolling coiling temperature is subjected to surface grinding treatment. Thus, oxides which were not completely removed and remained partially were observed. For this reason, even in the chemical conversion treatment, crystals were partially lost, resulting in a chemical conversion treatment failure.

Coil No. 8, which is a comparative example, is also an example in which the grinding conditions are not adjusted according to the hot rolling coiling temperature, and the chemical conversion processability is poor throughout the coil longitudinal direction.
In the coil No. 9 as a comparative example, the coolant flow density was controlled according to the hot rolling coiling temperature in the same manner as the coil No. 5 as an example of the present invention, but from the completion of the surface grinding process to the start of the pickling process. Since the time did not satisfy the conditions of the present invention, the chemical conversion treatment performance became poor due to the decrease in pickling efficiency.
On the other hand, coils No. 2 to No. 6 as examples of the present invention all have a good chemical conversion treatment property over the entire length of the coil, and a high-tensile steel plate with excellent paint adhesion is obtained. It turns out that it is obtained.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Finishing mill 3 Runout table 4 Thermometer 5 Coiler 6 Tandem mill 7 Coiler 8 Continuous annealing furnace 9 Surface grinding device 10 Draining device 11 Pickling equipment 12 Temper rolling mill 13 Coiler 90 Grinding body 91 Coolant supply nozzle

Claims (4)

In performing the surface grinding treatment and the pickling treatment in this order after continuously annealing a normal steel sheet having a Si content of 0.5 mass% or more obtained by hot rolling and cold rolling,
During the surface grinding process, one or more of the number of revolutions of the grinding body, the amount of reduction and the coolant flow rate supplied to the grinding part are adjusted according to the coiling temperature of the steel sheet in the hot rolling process, and surface grinding is performed. The manufacturing method of the steel plate excellent in chemical conversion property characterized by making time from the completion of a process into the pickling process start within 60 second.   2. The method for producing a steel sheet excellent in chemical conversion treatment according to claim 1, wherein the surface grinding treatment is performed by using one pair or two or more pairs of upper and lower grinding bodies for grinding both surfaces of the steel sheet. The method for producing a steel sheet excellent in chemical conversion treatment according to claim 1 or 2, wherein a reduction amount of the steel sheet mass by surface grinding treatment and pickling treatment is 4.0 g / m ² or more. Hot rolling equipment for producing hot rolled steel sheets, cold rolling equipment for cold rolling hot rolled steel sheets obtained by the hot rolling equipment, and continuous annealing for annealing steel sheets obtained by the cold rolling equipment A normal steel plate manufacturing facility equipped with a furnace, a surface grinding device for surface grinding of the steel plate annealed in the continuous annealing furnace, and a pickling facility for pickling the steel plate surface-ground by the surface grinding device There,
The hot rolling equipment has a temperature measuring means for measuring the winding temperature of the steel sheet,
The surface grinding device can adjust one or more of the number of revolutions of the grinding body, the amount of rolling reduction, and the coolant flow rate supplied to the grinding part according to the coiling temperature measured by the temperature measuring means. There is a manufacturing facility for steel sheets.

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