JP4818880B2 - Method for producing bake hardenable cold rolled steel sheet with excellent ductility and room temperature aging resistance - Google Patents

Description

  The present invention relates to a method for producing a bake-hardening cold-rolled steel sheet that is hardened by strain aging in a paint baking process, and is particularly suitable for materials for automobiles and household electrical appliances, building materials, etc., and has high ductility and room temperature aging resistance. The present invention relates to a method for producing an excellent bake-hardening cold rolled steel sheet. In addition, the present invention includes a manufacturing method in which the surface of the cold-rolled steel sheet is further subjected to a surface treatment such as Zn plating or alloyed Zn plating for rust prevention.

  A cold-rolled steel sheet that develops yield elongation in a stress-strain curve generates a wrinkle pattern called a stretcher strain during pressing. Moreover, when the solid solution C remains in the cold-rolled steel sheet, strain aging proceeds at room temperature and yield elongation occurs. In particular, in order to achieve both moldability and dent resistance, that is, characteristics that do not easily dent when hit with stepping stones, Bake Hardenabiliy (BH) The steel sheet to which) is applied has a problem that aging proceeds at room temperature.

  Therefore, conventionally, the solid composition C and N in the steel are ensured by optimizing the component composition and the manufacturing conditions up to the annealing step, and further, a movable transition is introduced by temper rolling to suppress normal temperature aging. Further, in order to promote the introduction of movable dislocations in the cold-rolled steel sheet, it is necessary to increase the elongation by temper rolling, thereby improving the normal temperature aging resistance. However, when the elongation rate of temper rolling is increased, the ductility of the cold-rolled steel sheet deteriorates and the formability of the product may be impaired.

  For such problems, a method has been proposed in which temper rolling is performed using a small-diameter roll, movable dislocations are introduced into the surface layer of the steel sheet, the influence of processing on the inner layer is suppressed, and formability is maintained. (For example, see Patent Document 1).

  However, when temper rolling is performed at a low elongation using a conventional rolling mill, the shape such as flatness may be impaired. In addition, variation in elongation rate occurs in the plate width direction, and sufficient room temperature aging resistance cannot be obtained at a site where the elongation rate is insufficient. On the other hand, in the sheet width direction of the cold-rolled steel sheet, the formability deteriorates when the elongation rate is increased so that a sufficient elongation rate can be secured even at a portion where the local elongation rate is the lowest.

Until now, as a method of performing rolling with a uniform reduction ratio in the sheet width direction, a method using a light reduction rolling mill provided with divided backup rolls has been proposed (see, for example, Patent Document 2). However, the rolling mill described in Patent Document 2 relates to a method of manufacturing a thick steel plate having a thickness of 5 mm or more, and there is no description regarding materials such as normal temperature aging resistance and ductility.
JP 11-314103 A JP 2002-66603 A

  The present invention has been proposed in view of such conventional circumstances, and is excellent in ductility and room temperature aging resistance capable of ensuring the homogeneity of the material in the plate width direction without impairing the shape. It aims at providing the manufacturing method of a bake hardenable cold-rolled steel plate.

  Conventionally, in order to have sufficient room temperature aging resistance in the full width of the steel sheet, the elongation rate of temper rolling is required to be 0.8% or more, assuming a decrease in the local elongation rate, Therefore, it has been difficult to avoid deterioration of moldability. Accordingly, the present invention provides a temper rolling in which the bake-hardening cold-rolled steel sheet in which the amount of solid solution C and solid solution N is secured is reduced by the rolling mill that supports a small-diameter work roll with a divided backup roll. Is a method that makes it possible to produce a bake-hardenable cold-rolled steel sheet having excellent ductility and room temperature aging resistance without impairing the homogeneity of the shape and the material in the sheet width direction. It is as follows.

(1) In mass%,
C: more than 0.0005% and 0.0500% or less,
Si: 1.00% or less,
Mn: 3.00% or less,
P: 0.100% or less,
S: 0.100% or less,
Al: 1.000% or less,
N: 0.1000% or less, the balance being Fe and inevitable impurities, the total amount of solute C and solute N is more than 0.0005% and 0.0050% or less, and the plate thickness is 0 .3~2.0mm, for the cold-rolled steel sheet plate width is 600~2000mm,
One or both of the upper and lower roll assemblies has a support mechanism for supporting a work roll having a diameter of 30 to 300 mm by a divided backup roll divided into three or more in the axial direction, and is loaded on each of the divided backup rolls. In order to obtain a predetermined elongation rate so that the elongation rate in the sheet width direction is uniform by a rolling mill provided with a load detection device for detecting the load to be detected and a reduction device for independently raising and lowering the divided backup roll After calculating the required rolling load, the rolling load for each part in the sheet width direction is detected, and the temper rolling with an elongation of 0.1 to less than 0.8% is performed while controlling the rolling load for each part. A method for producing a bake hardenable cold rolled steel sheet having excellent ductility and room temperature aging resistance.
(2) Further, the cold-rolled steel sheet is in mass%,
It is excellent in ductility and normal temperature aging resistance as described in (1) above, containing 0.0001 to 0.1% by mass of any one or more of Nb, Ti and B A method for producing a bake hardenable cold rolled steel sheet.
(3) Further, the cold-rolled steel sheet is in mass%,
The ductility and resistance as described in (1) or (2) above, wherein 0.001 to 1.0% by mass of any one or more of Mo, Cr, V and W are contained in total. A method for producing a bake hardenable cold rolled steel sheet with excellent aging at room temperature.
(4) Bake hardening with excellent ductility and room temperature aging resistance according to any one of (1) to (3), wherein the work roll has a surface roughness Ra of 0.2 μm or more. Of manufacturing cold rolled steel sheet.
(5) Bake hardening with excellent ductility and room temperature aging resistance according to any one of (1) to (4), wherein the surface of the cold rolled steel sheet before temper rolling is plated. Of manufacturing cold rolled steel sheet.

  As described above, according to the present invention, a bake-hardening cold-rolled steel sheet excellent in ductility and non-aging resistance at room temperature is produced without damaging the shape such as flatness and suppressing local surface quality degradation. can do. Further, depending on the steel type, the industrial contribution is remarkable, such as the restriction on the components and production conditions that have been the cause of the decrease in productivity can be relaxed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The rolling mill of the present invention has a support mechanism in which at least one of the upper and lower roll assemblies supports a work roll by a divided backup roll divided into three or more in the axial direction, and is loaded on each divided backup roll. An independent load detection device that detects the load to be detected and an independent reduction device that raises and lowers each divided backup roll individually are arranged.

  By adopting this split backup roll, the elongation in the sheet width direction becomes uniform even at low elongation, and by adopting a small diameter work roll, movable dislocations are introduced into the surface layer of the steel sheet, and the bake-hardening cold-rolled steel sheet at room temperature. Improves aging resistance. In the temper rolling of the present invention, since the change in sheet thickness is small, the rate of change in the length in the rolling direction, that is, the elongation rate is specified.

  When temper rolling is performed on a cold-rolled steel sheet that has secured a solid solution C amount and a solid solution N amount after annealing by a rolling mill having a small-diameter work roll of the present invention, the ductility and resistance at room temperature are maintained without damaging the shape. A bake-hardening cold-rolled steel sheet having excellent aging can be produced.

  As shown in FIG. 1, the rolling mill of the present invention is supported by split backup rolls 3 and 4 in upper and lower inner housings that move up and down by a pass line adjuster 1 using an electric motor and a main reduction device 2 using hydraulic reduction. The upper and lower work rolls 5 are provided. The pass line adjuster 1 is a device that adjusts the pass line in response to a change in roll diameter when the roll is replaced. Further, the main reduction device 2 has a mechanism for detecting the position of the hydraulic cylinder, whereby the reduction position is measured.

  Furthermore, the upper and lower work rolls 5 having a diameter of 30 to 300 mm are supported by divided backup rolls 3a to 3d and 4a to 4e that are divided in the axial direction, as shown in FIG. In addition, a load detection device that detects a load that is independently applied to each of the divided backup rolls 3a to 3d and 4a to 4e, and a reduction mechanism that moves the divided backup rolls 3a to 3d and 4a to 4e independently And a position detection mechanism for detecting the position of each divided backup roll. Although not shown, the upper and lower work rolls 5 are rotated by a drive motor to transmit torque necessary for rolling. Furthermore, a work roll chock used for replacing the work roll 5 is provided in the inner housing.

The present inventors performed temper rolling of a bake-hardening cold-rolled steel sheet using the rolling mill shown in FIGS. 1 and 2, and investigated the relationship between the elongation rate of temper rolling, ductility and age-hardening resistance.
First, in mass%, C: more than 0.0005% and 0.0500% or less, Si: 1.00% or less, Mn: 3.00% or less, P: 0.100% or less, S: 0.100% or less , Al: 1.000% or less, N: 0.1000% or less, and if necessary, one or more of Nb, Ti, B in total, 0.0001 to 0.1%, One or two or more of Mo, Cr, V, and W in total contained 0.001 to 1.0%, and the remainder was made by melting and casting steel composed of Fe and inevitable impurities.

  The obtained steel slab was hot-rolled and cold-rolled to obtain a cold-rolled steel plate having a thickness of 0.8 mm. Annealing of the cold-rolled steel sheet is performed with the annealing temperature in the range of 750 to 850 ° C., the annealing time in the range of 40 to 100 seconds, and the cooling rate in the range of 60 to 120 ° C./second. It adjusted so that the sum with the amount of solute N might be more than 0.0005% and 0.0050% or less.

  Next, these steel sheets were subjected to temper rolling with an elongation of 0.3% by the rolling mill shown in FIGS. Further, as a comparative example, temper rolling with an elongation of 0.3% and 1.4% was performed using a normal light rolling mill composed of a work roll having a diameter of 300 mm and an undivided backup roll. From these cold-rolled steel plates, No. 5 test pieces of JIS Z 2201 were produced with the rolling direction as the longitudinal direction for every 100 mm of plate width. In addition, the tensile test piece was produced within one week after the temper rolling, and the tensile test piece was stored at −40 ° C. until the tensile test was performed.

  Using these tensile test pieces, a tensile test was performed in accordance with JIS Z 2241, and the yield elongation and total elongation were measured. Furthermore, the measurement of the yield elongation is performed after holding in a constant temperature room at 25 ° C. for 30, 60, 90 days, and the minimum number of days in which a remarkable yield elongation of 0.2% or more is observed is determined at room temperature aging resistance. It was used as an index. In addition, it is assumed that sufficient room temperature aging resistance is obtained when yield elongation does not appear in the test after 90 days.

FIG. 3 shows the total elongation measured by conducting a tensile test without holding at 25 ° C. after temper rolling. Moreover, the result of having evaluated normal temperature aging resistance is shown in FIG.
3 and 4, it can be seen that the steel sheet produced according to the present invention exhibits excellent normal temperature aging resistance while maintaining higher ductility than conventional temper rolling.

Hereinafter, the manufacturing method of the bake hardenable cold rolled steel sheet excellent in ductility and room temperature aging resistance of the present invention will be described in detail.
First, the reason for limitation related to temper rolling, which is the most important process in the present invention, will be described.

(Rolling mill)
In an ordinary temper rolling mill, when temper rolling is performed with the elongation rate lowered, the elongation rate becomes non-uniform in the sheet width direction. In particular, the elongation of temper rolling becomes insufficient at the end of the steel sheet, and room temperature aging resistance cannot be ensured. Therefore, in the present invention, the temper rolling is performed by the above-described rolling mill having a mechanism capable of appropriately adjusting the elongation of the steel sheet depending on the portion in the sheet width direction.
The rolling mill of the present invention divides a backup roll in the plate width direction and controls each divided backup roll independently. That is, after calculating the rolling load necessary to obtain a predetermined elongation, the rolling load for each part in the sheet width direction is detected, and the rolling load is controlled by a separately provided reduction device. Thereby, even when the elongation rate in temper rolling is low, the elongation rate in the sheet width direction can be made uniform.

(Elongation: 0.1% or more and less than 0.8%)
Even if the rolling mill of the present invention is used, if the elongation is less than 0.1%, the purpose of shape correction cannot be achieved. For this reason, the minimum of elongation is made into 0.1% or more. Further, when the elongation is 0.8% or more, the ductility of the cold-rolled steel sheet is lowered, and the workability is lowered because the proof stress is larger than that of the original sheet, so the upper limit of the elongation is 0.8%. Less than. Preferably it is less than 0.6%, more preferably less than 0.5%.

(Work roll diameter: 30-300mm)
When the diameter of the work roll for temper rolling is less than 30 mm, it becomes difficult to control the rolling and it becomes difficult to ensure a uniform rolling reduction in the longitudinal direction, so the lower limit is set to 30 mm. In addition, when the diameter of the work roll for temper rolling exceeds 300 mm, deformation progresses uniformly in the thickness direction, and formability deteriorates when temper rolling is performed at a reduction rate that can ensure normal temperature aging resistance. End up. Therefore, the upper limit of the roll diameter is 300 mm.

(Work roll surface roughness Ra: 0.2 to 3.0 μm)
By increasing the surface roughness Ra of the temper rolled work roll, the coefficient of friction between the work roll and the surface of the cold-rolled steel sheet increases, and even in a region where the applied load is locally lowered, it slides. Disappears and the shape becomes good. Moreover, since introduction of movable dislocations into the surface layer of the cold-rolled steel sheet is promoted, it is preferable to perform temper rolling using a work roll having a large surface roughness Ra. In order to obtain this effect, the surface roughness Ra is preferably set to 0.2 μm or more. The upper limit of the surface roughness Ra is not particularly provided, but is preferably 3.0 μm or less from the viewpoint of practicality such as the surface quality of the cold-rolled steel sheet.

Next, the reason for limiting the chemical components will be described.
(C: more than 0.0005% and 0.0500% or less)
C is an important element that contributes to the expression of BH properties. If the C content is 0.0005 or less, the effect of the present invention is not sufficiently exhibited, so the lower limit is made more than 0.0005%. On the other hand, if the amount of C exceeds 0.0500%, the amount of solid solution C increases and the normal temperature aging resistance deteriorates, so the upper limit is made 0.0500% or less.

(N: 0.1000% or less)
N is an element inevitably contained in the steel. If the N content exceeds 0.1000%, the amount of solid solution N increases and the normal temperature aging resistance deteriorates, so the upper limit is 0.1000% or less. And Moreover, since N is also an element contributing to the expression of BH property, it is preferable to contain more than 0.0005%.

(Solution C and Solution N: Total 0.0005% over 0.0050% or less)
Controlling the total amount of one or both of the solid solution C and the solid solution N is important for achieving both BH property and room temperature aging resistance. If the total of one or both of the solid solution C amount and the solid solution N amount is 0.0005% or less, a sufficient bake hardening amount (BH amount) cannot be obtained. On the other hand, when the total of one or both of the solid solution C and the solid solution N exceeds 0.0050%, the room temperature aging resistance can be ensured while ensuring high ductility even when the temper rolling in the present invention is performed. However, since age hardening occurs, the upper limit is made 0.0050% or less. Moreover, since the higher BH property is obtained as the total of one or both of the solid solution C amount and the solid solution N amount increases, the lower limit is preferably 0.0080% or more, and is preferably 0.0010% or more. Is more preferable.

  The amount of solute N can be determined by analyzing the filtrate according to the steel-nitride type nitrogen determination method described in the appendix of JIS A 5523. For the amount of dissolved C, the filtrate after collecting the precipitate is directly analyzed by electrolytic extraction, or the amount of C in the precipitate collected by electrolytic extraction is quantified and evaluated by the difference. It doesn't matter. Ag is preferably used as a filter for filtering insoluble residue.

(Si: 1.00% or less)
(Mn: 3.00% or less)
(P: 0.100% or less)
Si, Mn, and P are elements inevitably contained in the steel and have the effect of improving the strength. However, if the content is excessive, the workability is impaired, so the upper limit is Si: 1. 00% or less, Mn: 3.00% or less, and P: 0.100% or less are preferable. In order to decrease the strength and improve the ductility, it is preferable that the upper limits of Si, Mn, and P are 0.500% or less, 1.000% or less, and 0.050% or less, respectively.

(Al: 1.000% or less)
Al is a deoxidizer and contributes to the improvement of strength. However, if it exceeds 1.000%, the workability deteriorates, so it is preferable that the upper limit is 1.000% or less. In particular, in order to improve ductility, the upper limit of Al is preferably 0.100% or less.

(S: 0.100% or less)
Since S is an impurity and deteriorates workability, it is preferably reduced. If added over 0.100%, the ductility is greatly deteriorated, so the upper limit is preferably made 0.100% or less.

  Furthermore, you may add the 1 type (s) or 2 or more types of Nb, Ti, B, Mo, Cr, V, and W as needed. In addition, when content of these elements is less than a preferable minimum, since a remarkable effect is not expressed and it does not have a bad influence, it is regarded as an impurity.

(Nb, Ti, B: Total 0.0001% or more and 0.1000% or less)
Nb and Ti form carbides and nitrides, and B is an element that forms nitrides. Therefore, in order to control the amount of solid solution C and the amount of solid solution N to an optimum range, Nb, Ti, Any one or two or more of B may be added. However, if the total addition amount of Nb, Ti, and B is less than 0.0001%, the effect of addition is not noticeable, so 0.0001% or more is preferably set as the lower limit. Further, if Nb, Ti, and B are added in excess of 0.1000% in total, the recrystallization temperature rises and the material may be deteriorated, so the upper limit is preferably made 0.1000% or less in total.

(Mo, Cr, V, W: Total 0.001% or more and 1.000% or less)
Since Mo, Cr, V, and W are elements that generate carbides and contribute to improvement of normal temperature aging resistance, any one or more of these may be added. However, if the total of these addition amounts is less than 0.001%, the effect of addition is not noticeable, so 0.001% or more is made the lower limit. Further, if adding over 1.000% in total, the ductility deteriorates greatly, so 1.000% or less is made the upper limit.

  The raw materials for obtaining the above components are not particularly limited, but in addition to the method of adjusting the components by iron ore as a raw material and using a blast furnace and a converter, scrap may be used as a raw material, or this may be melted in an electric furnace. . When scrap is used as all or part of the raw material, elements such as Cu, Ni, Sn, Sb, Zn, Pb may be included.

  The manufacturing method of the cold-rolled steel sheet before the temper rolling may be a conventional method, and the steel may be melted and cast, and hot-rolled, pickled, cold-rolled, and annealed to obtain a cold-rolled steel sheet. Furthermore, surface treatment such as plating may be performed. The steel slab used for hot rolling is not particularly limited, and it may be manufactured by a continuously cast slab or a thin slab caster. It is also suitable for processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.

In order to reduce the anisotropy of the steel sheet, the hot rolling finishing temperature is preferably higher than the Ar3 transformation point. Moreover, about hot rolling, you may employ | adopt the continuous hot rolling process which joins the steel piece after rough rolling, and performs finish rolling. Further, in the continuous hot rolling process, finish rolling may be performed in the ferrite region.
Winding in hot rolling is preferably performed at 600 ° C. or higher in order to reduce the amount of solid solution C and solid solution N by the formation of carbides and nitrides. When Nb, Ti, and B are added, carbides and nitrides containing these elements are generated excessively, and the amount of solid solution C and solid solution N cannot be sufficiently obtained, and the bake hardenability may be lowered. Therefore, when these elements are added, it is preferable to set the coiling temperature in hot rolling to 650 ° C. or lower in order to avoid excessive precipitation.
The cold rolling rate is preferably 50 to 90% from the viewpoint of productivity.
The annealing temperature is preferably higher than the recrystallization temperature in order to ensure ductility, and is preferably 950 ° C. or lower from the viewpoints of restrictions due to manufacturing equipment and productivity.
It is also possible to obtain a sufficient amount of solid solution C and solid solution N by generating precipitates at a coiling temperature of 650 ° C. or higher, annealing at a high temperature after cold rolling, and dissolving the precipitates. In this case, the annealing temperature is preferably 760 ° C. or higher, and the more preferable annealing temperature is 850 ° C. or higher.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and is implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

Example 1
In Example 1, steel having chemical components shown in Table 1 was melted and cast, and a steel piece was hot-rolled and cold-rolled to obtain a cold-rolled steel plate having a thickness of 0.8 mm. Nb, Ti, B and other blanks in Table 1 mean that the analytical value was less than 0.001%. Steel No. Annealing of the cold-rolled steel sheets A to J is performed with the annealing temperature in the range of 750 to 850 ° C., the annealing time in the range of 40 to 100 seconds, and the cooling rate in the range of 60 to 120 ° C./second. The amount of dissolved C and the amount of dissolved N were adjusted. The amount of dissolved C was evaluated by directly analyzing the filtrate after collecting the precipitate by electrolytic extraction. The amount of solute N was determined by analyzing the filtrate according to the steel-nitride type nitrogen determination method described in the appendix of JIS A 5523.

  Steel No. The cold-rolled steel sheet of J is an example in which the total amount of solute C and solute N is reduced because the amount of Ti added is excessive with respect to the C and N contents. Steel No. The cold rolled steel sheet of K has a composition of steel No. Although it is the same as the cold-rolled steel sheet of H, the annealing temperature was set to 900 ° C., the annealing time was set to 40 seconds, and the cooling rate was set to 60 ° C./second. This is an example of more than the range.

  These steel sheets were subjected to temper rolling with various elongation rates using the rolling mill shown in FIGS. A work roll having a diameter of 300 mm and a barrel length of 2070 mm is supported by a divided backup roll having a diameter of 550 mm and a barrel length of 230 mm divided into nine in the axial direction.

  Table 2 shows the conditions and mechanical properties of temper rolling. The No. 5 test piece of JIS Z 2201 had the rolling direction as the longitudinal direction, and the sampling position in the plate width direction was the end part, the central part, and a quarter part that was in between. In addition, the tensile test piece produced the tensile test piece within one week after temper rolling, and was stored at -40 degreeC until the tensile test was implemented. The yield stress, tensile stress, and total elongation in Table 2 represent the average of the test results at the end, center, and 1/4 part. For the total elongation, the end, center, and 1/4 part. The difference between the maximum value and the minimum value at the three locations was determined and indicated as ΔEL.

Moreover, the normal temperature aging resistance is the minimum in which a tensile test piece was held in a thermostatic chamber at 25 ° C. for 0, 30, 60, 90 days and a tensile test was performed, and a remarkable yield elongation of 0.2% or more was observed. The number of days was evaluated.
Furthermore, when there is a difference in elongation in the sheet width direction of the steel sheet, the shape of the steel sheet deteriorates, so the quality of the shape was evaluated visually. For example, when the elongation at the end in the plate width direction of the steel plate is large, the edge is repeatedly undulated, and when the center is large, the middle is repeatedly undulated. Moreover, the local expansion | swelling which the specific site | part of a board width direction undulates, and these may be seen combining. “◯” indicates that such deterioration of the shape cannot be visually determined, and “×” indicates that it can be determined.
In addition, a tensile test was performed in accordance with JIS G 3135 appendices using a similarly collected tensile test piece, and a bake hardening amount (BH amount) was measured.

As shown in Table 2, the cold-rolled steel sheet obtained by the production method of the present invention has sufficient bake hardenability, has excellent room temperature aging resistance in the entire region in the sheet width direction, and exhibits high ductility. I understand that.
On the other hand, the production No. 1 was carried out at 0.3% elongation using a conventional light rolling mill. In No. 2, since the elongation rate became insufficient toward the end of the plate width, the room temperature aging resistance was good at the central portion in the plate width direction, but decreased at the end and ¼ portion. In addition, production No. No. 3 is an example in which temper rolling with a high elongation rate is performed with a conventional rolling mill, and the variation in elongation in the sheet width direction is large. Production No. Since No. 7 has a large elongation at temper rolling, the ductility is reduced.
Production No. 10 is an example in which temper rolling was not performed, the room temperature aging resistance is insufficient, and the shape is also deteriorated. Production No. No. 16 is a steel No. having a small total amount of solute C and N. Since J is an example of temper rolling, the BH property is insufficient. Production No. No. 17 is a steel No. with a large total amount of solute C and N. This is an example of temper-rolling K, and the room temperature aging resistance is insufficient.

(Example 2)
In Example 2, the steel NO. The cold-rolled steel sheets A and F were annealed in the same manner as in Example 1, and then subjected to temper rolling with the rolling mill of the present invention having work rolls having a diameter of 300 mm with different surface roughness Ra. Thereafter, the mechanical properties at each point of the plate width were measured in the same manner as in Example 1, and the measurement results are shown in Table 3. Table 3 shows the production No. in Table 2 in which the surface roughness Ra of the work roll was 0.13. The results of 1 and 11 are also shown for comparison.

  As is apparent from Table 3, in steels having the chemical components of the present invention, temper rolling using a work roll having a large surface roughness Ra ensures room temperature aging resistance even when the elongation is reduced. It is possible to obtain a bake-hardenable cold-rolled steel sheet having more excellent ductility.

(Example 3)
In Example 3, the steel No. shown in Table 1 was used. The cold-rolled steel sheets of B and D were subjected to continuous hot dip galvanization in which the maximum temperature reached 800 ° C. and immersion in a galvanizing bath followed by alloying treatment at 500 ° C. for 20 seconds. Thereafter, in the same manner as in Example 1, temper rolling was performed using the rolling mill of the present invention, and the mechanical properties at each point of the sheet width were measured. The measurement results are shown in Table 4.

  As is apparent from Table 4, in the steel having the chemical components of the present invention, after plating before temper rolling, temper rolling under the conditions of the present invention is performed, and the seizure excellent in room temperature aging resistance and ductility. A curable cold-rolled steel sheet is obtained.

It is a schematic diagram of the rolling mill of this invention. It is a schematic diagram of the division | segmentation backup roll of this invention. It is a figure which shows the uniformity of the total elongation of the board width direction by this invention. It is a figure which shows the uniformity of the normal temperature aging resistance of the board width direction by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Passline adjustment machine 2 Main reduction device 3, 4 Backup roll 3a-3g Division backup roll 4a-4h Division backup roll 5 Work roll

Claims (5)

% By mass
C: more than 0.0005% and 0.0500% or less,
Si: 1.00% or less,
Mn: 3.00% or less,
P: 0.100% or less,
S: 0.100% or less,
Al: 1.000% or less,
N: 0.1000% or less, the balance being Fe and inevitable impurities, the total amount of solute C and solute N is more than 0.0005% and 0.0050% or less, and the plate thickness is 0 .3~2.0mm, for the cold-rolled steel sheet plate width is 600~2000mm,
One or both of the upper and lower roll assemblies has a support mechanism for supporting a work roll having a diameter of 30 to 300 mm by a divided backup roll divided into three or more in the axial direction, and is loaded on each of the divided backup rolls. In order to obtain a predetermined elongation rate so that the elongation rate in the sheet width direction is uniform by a rolling mill provided with a load detection device for detecting the load to be detected and a reduction device for independently raising and lowering the divided backup roll After calculating the required rolling load, the rolling load for each part in the sheet width direction is detected, and the temper rolling with an elongation of 0.1 to less than 0.8% is performed while controlling the rolling load for each part. A method for producing a bake hardenable cold rolled steel sheet having excellent ductility and room temperature aging resistance. Furthermore, the cold-rolled steel sheet is in mass%,
Baking excellent in ductility and room temperature aging resistance according to claim 1, characterized in that any one or more of Nb, Ti and B is contained in a total amount of 0.0001 to 0.1% by mass. Manufacturing method of hardenable cold rolled steel sheet. Furthermore, the cold-rolled steel sheet is in mass%,
The ductility and room temperature aging resistance according to claim 1 or 2, characterized by containing one or more of Mo, Cr, V, and W in a total amount of 0.001 to 1.0 mass%. Method of bake-hardening cold-rolled steel sheet with excellent resistance.   The surface roughness Ra of the work roll is 0.2 µm or more, and the bake-hardenable cold-rolled steel sheet having excellent ductility and room temperature aging resistance according to any one of claims 1 to 3. Production method.   The surface of the cold-rolled steel sheet before the temper rolling is plated, and the bake-hardenable cold-rolled steel sheet excellent in ductility and room temperature aging resistance according to any one of claims 1 to 4. Production method.

Images