JP5510118B2 - Method for producing high-tensile steel plate excellent in chemical conversion treatment and production apparatus therefor - Google Patents

Description

  The present invention provides a method for producing a high-strength steel sheet excellent in chemical conversion treatment by efficiently removing the Si-containing oxide layer after annealing in the production of a high-Si high-strength steel sheet excellent in chemical conversion treatment, and It relates to the device.

  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. . Even if a coating such as electrodeposition coating is applied on the surface of such a steel sheet with poor chemical conversion treatment, a coating film with good adhesion cannot be obtained, and the corrosion resistance after coating is deteriorated.

  Various techniques have been proposed so far to solve such problems. For example, in Patent Document 1, a liquid in which a gas is dissolved under pressure is sprayed from a liquid injection device arranged on the exit side of an 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, the surface is ground to a specific thickness, and then pickled and oxidized. A method of removing is disclosed.

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

  However, when annealing a high-tensile steel sheet containing 0.5 mass% or more of Si, not only a very strong and thick Si-containing oxide layer is formed on the steel sheet surface, It is unevenly distributed corresponding to the roughness form.

  Therefore, when surface grinding is performed on the continuous annealing side, heavy grinding is necessary to remove a strong and thick Si-containing oxide layer. Since the steel plate surface after grinding becomes a new surface with very high activity, the steel plate surface after heavy grinding becomes very susceptible to rusting together with the coolant supplied during grinding.

Even when the steel plate surface is rusted, the pickling efficiency of the surface layer is hindered by the iron oxide of the surface layer, and it is difficult to uniformly remove the surface layer oxide.
Moreover, since the deformation resistance increases due to the solid solution strengthening accompanying the addition of Si and the rolling load in cold rolling increases, the shape of the steel sheet tends to be disturbed. Typical methods for controlling the shape of a steel sheet during rolling include roll bending and roll shift. However, the shape control ability of these shape control actuators is limited, so the surface sharpness is relatively high. Steel sheets in a high state are conveyed to a continuous annealing line.

  When a steel sheet in which such shape defects remain is subjected to continuous annealing, similar shape defects remain even after continuous annealing. For this reason, it was difficult for the conventional methods described in Patent Documents 1 to 5 to uniformly remove the surface layer oxide.

  Therefore, in the present invention, the Si-containing oxide layer formed on the surface of the steel sheet during annealing is efficiently removed, and the method for producing a high-tensile steel sheet excellent in chemical conversion treatment and the method for producing the same are used. An object is to provide a manufacturing apparatus.

  The inventor repeatedly studied a method for producing a high-tensile steel sheet having excellent chemical conversion properties by efficiently removing the Si-containing oxide layer formed on the steel sheet surface during annealing, and obtained the following knowledge.

  Rust generation occurs when coolant adheres to the new steel surface exposed after heavy grinding, but as a result of various studies on the relationship between elapsed time after grinding and removal efficiency by pickling, It has been found that if the time to equipment is within a predetermined time, the removal efficiency in pickling is not affected. That is, in order to prevent rust generated on the surface after grinding, a drying step for removing the grinding coolant is provided, and the time until the steel plate after surface grinding reaches the pickling treatment is set within 60 seconds.

  Also, a method for efficiently removing the Si-containing oxide layer formed during continuous annealing on steel sheets with large shape defects (high surface steepness) after cold rolling, such as high-Si steels. As a result, in the pre-process of continuous annealing (for example, the final rolling stand exit side of cold tandem rolling), a steel plate shape meter is installed to measure the shape (steepness) of the surface of the steel plate before annealing. It was found that the Si-containing oxide layer can be efficiently removed by adjusting the conditions for grinding the steel plate surface after annealing according to the measured steepness of the steel plate surface. As specific grinding conditions, for example, the grinding amount is adjusted by adjusting the number of rotations of the grinding body (rotary grinding body), the amount of rolling reduction, and the supplied coolant flow rate.

  Since the shape measurement of the steel sheet surface with the shape meter covers the entire length in the longitudinal direction of the steel sheet, appropriate surface grinding conditions can be applied even in the unsteady part during acceleration / deceleration in cold rolling, The surface oxide can be uniformly removed.

  In the present invention, mechanical grinding is combined with chemical grinding. In other words, by performing pickling as chemical grinding after mechanical grinding, the remaining oxide layer whose peel strength has decreased due to grinding can be efficiently removed, and uniform grinding over the entire surface where no oxide layer remains partially A surface is obtained.

  The present invention has been made based on the above findings and has the following characteristics.

  In the first invention, in performing surface grinding treatment and pickling treatment after continuous annealing of a high-tensile steel sheet containing 0.5% or more of Si by mass%, during the surface grinding treatment, high tension before continuous annealing is used. According to the steepness of the steel sheet, one or more of the number of revolutions of the grinding body, the reduction amount and the coolant flow rate supplied to the grinding body are adjusted, and the steel sheet after the surface grinding treatment is pickled. It is the manufacturing method of the high-tensile steel plate excellent in chemical conversion property characterized by making time to reach | attain within 60 second.

  The second invention is the method for producing a high-tensile steel sheet excellent in chemical conversion treatment property according to the first invention, wherein the surface grinding treatment is performed by at least a pair of upper and lower rotary grinding bodies.

The third invention is excellent in chemical conversion treatment as described in the first or second invention, characterized in that the reduction amount of the steel sheet mass by grinding and pickling is 4.0 g / m ² or more in terms of Fe. It is a manufacturing method of a high-tensile steel plate.

  A fourth invention is a steel sheet manufacturing apparatus used in the manufacturing method according to any one of the first to third inventions, has a continuous annealing facility, and the steepness of the steel sheet surface upstream of the continuous annealing facility. A shape measuring means for measuring the rotational speed of the grinding body, the amount of reduction and the supply when the steel sheet surface is ground on the downstream side of the continuous annealing equipment based on the steepness measured by the shape measuring means. A surface grinding means capable of adjusting any one or two or more of the coolant flow rate, and further a pickling facility provided downstream thereof.

  According to the present invention, even in a high-Si steel sheet, the surface layer oxide generated by annealing can be completely removed, and a good chemical conversion film can be formed over the entire surface of the steel sheet. In addition to workability, it can improve corrosion resistance after painting.

It is a schematic block diagram which shows an example of the manufacturing apparatus of the steel plate to which the manufacturing method of the high-tensile steel plate which concerns on this invention is applied. It is a figure for demonstrating an example of embodiment in this invention. It is a figure for demonstrating an example of embodiment in this invention. It is a figure for demonstrating an example of embodiment in this invention.

  Hereinafter, an example of the best mode for carrying out the present invention will be described.

  In the method for producing a high-tensile steel plate of the present invention, a steel plate containing 0.5% by mass or more of Si is used. For the steel sheet composition, if the Si amount 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 without special pretreatment. The amount of Si is 0.5% by mass or more. The upper limit of the amount of Si is not particularly specified, but if the amount of Si in the steel exceeds 3% by mass, the workability of the steel sheet tends to deteriorate, so the amount of Si is preferably 3% by mass or less. For other components, C, Mn, P, S, Sol. Even in a steel sheet to which an appropriate amount of Al, Cr, Mo, Ti, Nb or the like is added, the gist of the present invention is not impaired.

  FIG. 1 is a schematic configuration diagram illustrating an example of a steel plate manufacturing apparatus to which a high-strength steel plate manufacturing method according to the present invention is applied. The steel plate manufacturing apparatus shown in FIG. 1 continuously anneals a steel plate 1 that has been cold-rolled by a tandem rolling mill 2, and a rotating grinding body 5, a draining device 7, and pickling are provided on the exit side of the continuous annealing equipment 4. Facility 8 is arranged. And it is the structure wound up with the coiler 10 through the temper rolling mill 9. FIG.

  In FIG. 1, the tandem rolling mill 2 is represented as a four-stage stand, but the present invention is not limited to the four-stage type, and may be a six-stage or cluster type rolling stand. Moreover, although the number of rolling stands of the tandem rolling mill 2 is shown as five stands in FIG. 1, it is not limited to this.

  The surface grinding equipment to which the method for producing a high-strength steel sheet according to the present invention is applied does not need to be a continuous equipment with a continuous annealing equipment. For example, a continuously annealed steel strip can be applied to an independent surface grinding line.

  As a first step of removing the surface oxide film, mechanical grinding by the rotary grinding body 5 is performed on the surface oxide film generated during the continuous annealing. The grinding means is not particularly limited, and any of a polishing cloth, a wire brush, a nylon brush with abrasive grains, an elastic grindstone roll or the like may be used. The abrasive grain number of JIS-R6001 standard is # 60 to # 400. # 80 to # 240 is preferable. Further, the rotational speed of the grinding body is preferably 600 to 1500 rpm.

  In the mechanical grinding, grinding means (for example, rotation) according to a command 11 from a controller (not shown) according to the steepness of the steel plate measured by the shape meter 3 provided on the exit side of the tandem rolling mill 2 as the previous process. Any one or more of the number of rotations, the reduction amount and the supply coolant flow rate of the grinding body 5) are adjusted. The rolling amount of the grinding means (for example, a rotating grinding body such as a brush) is preferably 1 to 4 mm. Here, the amount of reduction is the distance in the steel plate thickness direction between the reference position and the actual installation position, with the position where the rotary grinding body contacts the steel plate surface as the reference position.

The coolant flow rate is preferably 1000 to 5000 L / min / m ² in terms of flow density (a coolant flow rate per unit area / unit time).

  Here, the grinding conditions corresponding to the steepness are obtained in advance as follows. That is, from the experimental data and operation data arranged for each material (material, plate thickness, plate width dimensions), grinding conditions that can secure a predetermined grinding amount for the steel plate steepness measured by the shape meter 3 I ask for it.

FIGS. 2 to 4 show that the steel content is 0.5 mass% or more and the operation data obtained by surface grinding and pickling on the annealing side are 4.0 g / m ² or more in terms of steepness and Fe. This is the result of arranging the relationship with the grinding conditions necessary to obtain 15.0 g / m ² or less.

In the controller, for example, based on the graphs shown in FIG. 2 to FIG. 4, the grinding condition of the grinding means corresponding to the steel plate steepness is calculated to adjust the grinding condition. Here, in the above-described embodiment, the grinding condition is changed by an amount that is linearly proportional to the steel sheet steepness, but the present invention is not limited to this. For example, the steepness of the steel sheet and the grinding conditions may be associated with each other in a stepped shape or a quadratic or higher curve.
Here, the steel sheet steepness (%) is represented by δ / L × 100, where δ is the steel plate wave height in a certain section (constant length) L in the longitudinal direction of the steel sheet. The steel plate wave height is the warp height of the steel plate when the steel plate cut out in a certain section L is placed on a horizontal surface plate.

  The method for measuring the steepness of the steel plate is not particularly limited, but a non-contact type shape meter such as a contact type shape meter or electromagnetic suction type that calculates the load distribution in the plate width direction measured by a load cell or piezoelectric element as the plate shape should be used. Can be measured.

  By adjusting the coolant flow rate supplied from the coolant header 6 to the rotating grinding body 5, the contact area between the rotating grinding body 5 and the steel plate 1 is adjusted, and dropped abrasive grains and grinding powder that are thought to promote grinding The dwell time changes, and the grinding amount can be adjusted. Adjustment of the rotational speed and reduction amount of the grinding body is the same in that the contact area between the grinding body and the steel plate changes.

  In the above mechanical grinding, it has been described that the grinding means is adjusted according to the steel sheet steepness measured by the shape meter 3, but when the shape meter 3 is installed in the continuous annealing equipment 4, The steepness of the steel plate in the continuous annealing equipment 4 may be applied to the command value to the controller.

  In this way, it is only necessary to measure the steepness of the steel sheet by the shape meter 3 and set the grinding conditions in the previous stage of the grinding process. Therefore, before the grinding process (for example, the output of the continuous annealing equipment 4). The shape meter 3 may be installed on the side in front of the rotating grinding body 5).

  After mechanical grinding, the grinding coolant adhering to the steel plate surface is removed by the draining device 7. The draining means is not particularly limited, and any of a ringer roll, a drying dryer, etc. may be used.

  In the present invention, by passing through the pickling equipment 8 after mechanical grinding, the acid penetrates into the boundary between the base material exposed by removing the Si-containing oxide by mechanical grinding and the remaining Si-containing oxide layer. The remaining Si-containing oxide layer is peeled off. The pickling solution used for the pickling equipment 8 is preferably hydrochloric acid or sulfuric acid having a concentration of 5% by volume or more, and the pickling is preferably performed for 5 seconds or more, more preferably 8 seconds or more.

The time until the steel plate 1 after surface grinding reaches the pickling equipment 8 is within 60 seconds.
This is because, if it exceeds 60 seconds, rust generated on the surface of the steel sheet grows and the removal efficiency in the subsequent pickling decreases.

When the total reduction in the mass of the steel sheet by mechanical grinding by the rotating grinding body 5 and chemical grinding by the pickling equipment 8 is less than 4.0 g / m ^{2 in} terms of Fe, the Si-containing oxide layer is uniformly distributed over the entire surface. Since there is a possibility that a surface state in which the chemical conversion crystal is lost without being removed, the total reduction in the mass of the steel sheet is preferably 4.0 g / m ² or more in terms of Fe. The upper limit of the total amount of reduction in the steel sheet mass is not particularly specified, but if the reduction in the steel sheet mass exceeds 15.0 g / m ² , the material yield tends to deteriorate and the work efficiency tends to deteriorate. The total reduction amount is preferably 15.0 g / m ² or less.

  Here, the reduction | decrease amount of the steel plate mass was calculated | required as follows. In other words, two coils of the same steel type and the same production conditions are prepared, and the former coil is ground, pickled, and temper rolled, and the latter coil is tempered and rolled without grinding and without pickling. Manufactured. Among both coils, from steel part longitudinal T part (TOP), M part (MIDDLE), B part (BOTTOM), steel plate without grinding without pickling (latter coil), steel plate with grinding and pickling (former coil) ) Was cut out by a certain area, and the mass of the steel sheet was measured, and the difference between the two was calculated by dividing it by the area of the cut out, whereby the amount of reduction in the mass of the steel sheet by grinding and pickling was determined.

  In the present embodiment of FIG. 1, two pairs of rotary grinding bodies 5 are shown. However, the present invention is not limited to this, and the required appearance quality and performance of the product can be obtained. For example, only one pair of the rotating grinding bodies 5 may be arranged, or three or more pairs of the rotating grinding bodies 5 may be installed as long as an installation space for equipment can be secured.

  By using the steel plate manufacturing method shown above, it is possible to completely remove the surface layer oxide generated by annealing even in the case of a high Si content steel plate, and to form a good conversion coating over the entire surface of the steel plate surface. Become. Moreover, as a manufacturing apparatus used for a method of manufacturing a high-strength steel sheet excellent in chemical conversion processability, it has a continuous annealing facility, and has a shape measuring means for measuring the steepness of the steel sheet surface on the upstream side of the continuous annealing facility, On the downstream side of the continuous annealing equipment, surface grinding means capable of adjusting conditions for grinding the steel sheet surface based on the steepness measured by the shape measuring means, and further provided with pickling equipment on the downstream side thereof. Therefore, the present invention is not limited to the configuration shown in FIG.

  Hereinafter, the present invention will be described based on examples.

In a steel plate manufacturing apparatus shown in FIG. 1, after continuous annealing of a high-tensile steel plate having a plate thickness of 1.2 mm and a plate width of 950 mm and having a Si concentration of 0.4 to 1.5 mass%, mechanical grinding and chemical The surface oxide layer was removed by combining grinding and temper rolling was performed. Table 1 shows the composition of the steel plate used, the grinding conditions, and the chemical conversion treatment evaluation results of the obtained steel plate.
The line speed at the time of continuous annealing was 90 mpm, and the steel sheet steepness before continuous annealing was 0.8 to 1.6% as a result of measurement by a contact type shape meter installed on the tandem rolling mill outlet side. It was.

  Here, in the mechanical grinding, an abrasive brush with abrasive grain number # 80 of JIS-R6001 standard was used, and the rotation direction was up-cut (rotation opposite to the steel plate conveyance direction). The drying process was performed with a ringer roll after brush grinding. The pickling conditions for chemical grinding were 60 ° C. and 10% by volume sulfuric acid as the acid, and the pickling time was 10 seconds in terms of line speed.

  Moreover, about the chemical conversion property of a steel plate, the sample was extract | collected from the coil longitudinal direction (T: front-end | tip part, M: intermediate part, B: tail end part) about the steel plate after temper rolling, and the following method evaluated.

  In the chemical conversion treatment, the chemical conversion treatment was performed using a commercially available chemical conversion treatment agent (Palbond PB-L3020 manufactured by Nihon Parkerizing Co., Ltd.) under the conditions shown in Table 2 after degreasing, washing with water, and a surface adjustment step.

  After the chemical conversion treatment of the high-tensile steel plate, 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. It was evaluated as ◯, and when 1 field of view with an area ratio exceeding 5% was observed, Δ was evaluated when 2 fields or more were recognized.

  In the present invention example, the rotational speed, brush reduction amount and coolant flow rate of the rotating grinding body are adjusted by a command from the controller according to the steel sheet steepness measured at the rolling mill outlet side in the cold tandem which is the previous process. 2 to 4 were controlled.

For example, no. 2, the brush reduction amount is set to 2.9 mm when the steepness corresponding to the position of the longitudinal steel plate passing through the rotating grinding body is 0.8% based on FIG. 3, and when the steepness is 1.2% It was adjusted to change to 3.1 mm.
The amount of reduction in the steel plate mass was determined as follows. In other words, two coils of the same steel type and the same production conditions are prepared, and the former coil is ground, pickled, and temper rolled, and the latter coil is tempered and rolled without grinding and without pickling. Manufactured. Among both coils, from steel part longitudinal T part (TOP), M part (MIDDLE), B part (BOTTOM), steel plate without grinding without pickling (latter coil), steel plate with grinding and pickling (former coil) ) Was cut out by a certain area, and the mass of the steel sheet was measured, and the difference between the two was calculated by dividing it by the area of the cut out, whereby the amount of reduction in the mass of the steel sheet by grinding and pickling was determined. The amount of decrease in Table 1 indicates the average value of the measured values in the T part, M part, and B part.

  As shown in Table 1, no. 2 to 4 are examples of the present invention. No. 1 is a reference example and no. 5-7 are comparative examples.

  No. Since No. 1 has a low amount of Si in steel, good chemical conversion processability is obtained regardless of grinding conditions. No. Although the amount of reduction in the steel plate mass of 5 is within the scope of the invention, satisfactory grinding is not performed at the rolling unsteady portion of the coil leading end where the steel plate steepness is unstable, and some Si-containing oxides are observed. It was done. For this reason, even in the chemical conversion treatment, crystals were partially lost, resulting in a chemical conversion treatment failure. No. In No. 6, since the mechanical grinding conditions were not adjusted according to the steepness of the steel plate, the formation failure occurred over the entire length of the coil. No. No. 7 did not satisfy the present invention from the mechanical grinding to the pickling, and the chemical conversion was poor due to the decrease in pickling efficiency.

  On the other hand, No. which is an example of the present invention. It can be seen that in any of 2 to 4, a good chemical conversion film can be obtained over the entire surface, and a high-tensile steel plate excellent in coating adhesion and excellent in strength and workability can be obtained.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Tandem rolling mill 3 Shape meter 4 Continuous annealing equipment (continuous annealing furnace)
5 Rotating grinding body 6 Coolant header 7 Draining device 8 Pickling equipment (pickling device)
9 Temper rolling mill 10 Coiler 11 Steel plate shape information

Claims (4)

  When performing surface grinding treatment and pickling treatment after continuous annealing of high strength steel plate containing 0.5% or more of Si by mass%, depending on the steepness of the high strength steel plate before continuous annealing during the surface grinding treatment. Adjusting one or more of the rotational speed of the grinding body, the amount of reduction and the coolant flow rate supplied to the grinding body, and the time until the steel plate after the surface grinding process reaches the pickling equipment The manufacturing method of the high-tensile steel plate excellent in chemical conversion processability characterized by making it within 60 second.   The method for producing a high-tensile steel sheet excellent in chemical conversion property according to claim 1, wherein the surface grinding treatment is performed by at least a pair of upper and lower rotary grinding bodies. The method for producing a high-tensile steel sheet having excellent chemical conversion properties according to claim 1 or 2, wherein a reduction amount of the steel sheet mass by grinding and pickling is 4.0 g / m ² or more in terms of Fe.   An apparatus for manufacturing a steel sheet used in the manufacturing method according to any one of claims 1 to 3, comprising a continuous annealing facility, and having a shape measuring means for measuring the steepness of the steel sheet surface upstream of the continuous annealing facility. Then, on the downstream side of the continuous annealing equipment, when grinding the steel sheet surface based on the steepness measured by the shape measuring means, any one of the rotational speed of the grinding body, the amount of reduction, and the supplied coolant flow rate is selected. An apparatus for producing a steel sheet, comprising surface grinding means capable of adjusting one or two or more, and further pickling equipment downstream thereof.

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