JPH11256237A - Production of cold rolled steel strip or hot dip plated steel strip excellent in workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high strength cold rolled steel sheet and a high strength hot dip plated steel sheet good in workability. SOLUTION: A steel slab having a compsn. contg. 0.0005 to 0.01% C, <=2.0% Si, 0.05 to 3.0% Mn, <=0.2% P, 0.0005 to 0.02% S, 0.5 to 3.0% Cu, 0.005 to 0.1% acid soluble Al <=0.007% N, 0.01 to 0.1% Ti and/or 0.01 to 0.1% Nb is reheated or directly fed and is subjected to hot rolling in such a manner that the finish rolling temp., is regulated to the Ar3 transformation point or above and the coiling temp. is made to 650 to 800 deg.C. Next, it is subjected to primary cold rolling at a cold rolling ratio of 10 to 60%, is pickled and is subjected to secondary cold rolling at a cold rolling ratio of >=20% and also to make the total cold rolling ratio together with the primary cold rolling ratio to 60 to 95%, and the obtd. cold rolled steel strip is annealed at the temp. of from the recrystallization temp. to 900 deg.C or is applied with hot dip plating after the annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cold-rolled steel strip or a hot-dip galvanized steel strip which is excellent in workability and suitable for use in automobile steel sheets, home electric appliances, electric machines, electronic materials and the like.

[0002]

2. Description of the Related Art In a cold-rolled steel strip to which Cu is added, the effect of strengthening the precipitation of Cu is exhibited only by performing a heat treatment at a relatively low temperature. Cu-added cold-rolled steel strip is a material that can take advantage of this property to obtain higher strength than conventional high-strength cold-rolled steel strip.
It is widely used in a wide range of fields such as automobiles, home appliances, electric machines, and electronic materials. In this type of application, excellent deep drawability is required because severe press working may be performed. In addition, considering the recent market where the beauty of products is a problem, having good surface properties is also an important requirement for increasing the product value.

[0003] In this type of cold-rolled steel strip, a steel whose composition is specified is made into a continuous cast slab or a solid slab having a thickness of about 250 mm, and the continuous cast slab or the solid slab is hot-rolled to a thickness of about 2 to 6 mm. It is manufactured by rolling, descaled by hot-rolled steel strip, pickling, cold rolling, and then recrystallization annealing. The hot-dip coated steel strip is manufactured by hot-dip plating after recrystallization annealing. The workability of the manufactured cold-rolled steel strip and hot-dip coated steel strip is evaluated based on the elongation obtained by a tensile test and the Rankford value which is an index of deep drawability. However, growth and Rankford values,
In addition to steel components, it is greatly affected by manufacturing conditions.
Therefore, various manufacturing conditions have been conventionally set in order to secure required workability.

[0004]

In particular, the coiling temperature during hot rolling greatly affects the elongation of the steel strip and the Rankford value. If the winding temperature is set higher, the elongation and the Rankford value increase, but if the hot-rolled steel strip is wound at an excessively high temperature, the oxidation of the steel strip surface proceeds during the cooling process after winding, resulting in thicker oxidation. Scale generated. As a result, in the subsequent pickling step, the descalability is reduced, and not only is productivity significantly impaired, but also the surface properties of the steel strip are adversely affected. In particular, in the Cu-added steel strip, the descaling property is significantly reduced. For this reason, setting the winding temperature to a higher value imposes restrictions from a practical point of view, and there is a limit in improving the elongation and the Rankford value by increasing the winding temperature.

The present invention has been devised in order to solve such a problem. The steel composition and the manufacturing conditions are comprehensively adjusted to set a relatively high winding temperature, and the pre-pickling process is performed. By performing cold rolling to increase the descaling property, it is intended to produce a cold rolled steel strip and a hot-dip steel strip having good surface properties and excellent workability without impairing productivity. I do.

[0006]

According to the production method of the present invention, to achieve the object, C: 0.0005 to 0.01% by weight, Si: 2.0% by weight or less, Mn: 0.05 to 0.05% by weight. 3.
0% by weight, P: 0.2% by weight or less, S: 0.0005-
0.02% by weight, Cu: 0.5-3.0% by weight, acid-soluble Al: 0.005-0.1% by weight, N: 0.007% by weight or less, Ti: 0.01-0. 1% by weight and / or N
b: A steel slab having a composition containing 0.01 to 0.1% by weight is reheated or directly fed, and is subjected to a finish rolling temperature _{Ar 3} transformation point or higher,
The hot-rolled steel strip is subjected to hot rolling at a winding temperature of 650 to 800 ° C., and the obtained hot-rolled steel strip is subjected to primary cold rolling at a cold rolling rate of 10 to 60%. The secondary cold rolling is performed so that the total cold rolling rate combined with the primary cold rolling is 60 to 95%, and the obtained cold rolled steel strip is heated to a recrystallization temperature of 90% or more.
Annealing at 0 ° C. or lower or hot-dip plating after annealing is characterized. The steel slab to be used is further Ni: 0.2
２．０2.0% by weight. B: 0.0
Steel slabs containing one or more of 002 to 0.002% by weight, Zr: 0.01 to 0.1% by weight, and V: 0.01 to 0.1% by weight can also be used.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, when a hot-rolled steel strip is manufactured from a steel slab alloy-designed according to the strength of a cold-rolled steel strip or hot-dip steel strip, the hot-rolled steel strip is coiled at a relatively high temperature. The high elongation and Rankford value of the cold-rolled steel strip or hot-dip coated steel strip are ensured. Oxidation scale tends to be easily generated due to a relatively high winding temperature, but the descaling property is improved by performing cold rolling at a cold rolling rate of 10 to 60% in a pre-pickling process. . Therefore, even if the oxide scale grows thickly, the oxide scale is easily removed from the surface of the steel strip under ordinary pickling conditions. Cold rolling before pickling is also effective in improving the surface properties of the obtained cold rolled steel strip or hot-dip steel strip.

Hereinafter, alloy components, contents, production conditions, and the like contained in steel to which the present invention is applied will be described. C: 0.0005 to 0.01% by weight C in the steel of the present invention is a component fixed as a carbide such as TiC and NbC. The lower the C content, the more the Rankford value and elongation are improved. The contents of Ti and Nb as the fixing elements can be reduced. Therefore, the upper limit of the C content is restricted to 0.01% by weight. However, 0.
If the C content is less than 0005% by weight, excessive decarburization refining is required in the steel making process, resulting in an increase in production costs.

Si: 2.0% by weight or less Si is an element that has an adverse effect on workability and plating property, and the elongation and the Rankford value tend to decrease as the Si content increases. However, since the reduction in workability is not so large compared to the improvement in strength, it can be used as an effective alloy component as a strengthening element for steel. In order to obtain the strength required as a high-strength steel sheet, it is preferable to contain 0.2% by weight or more of Si. However, when a large amount of Si exceeding 2.0% by weight is contained, even if cold rolling is performed as a pre-pickling step, the surface properties are not improved, and the workability is also reduced.

Mn: 0.05 to 3.0% by weight An effective component for preventing hot brittleness induced by S during hot rolling and increasing the strength of steel. To prevent hot brittleness, a Mn content of 0.05% by weight or more is required. When the Mn content is 0.50% by weight or more, the effect of improving the strength of the steel sheet becomes remarkable as in the case of Si. However, when a large amount of Mn exceeding 3.0% by weight is contained, workability is deteriorated. P: 0.2% by weight or less Like Si, it is a strengthening element that does not significantly deteriorate workability, and a necessary amount according to the strength required for a product is added. However, a large P content exceeding 0.2% by weight tends to reduce the secondary work brittleness resistance.

S: 0.0005 to 0.02% by weight Since the component induces cracking during hot working, the upper limit is restricted to 0.02% by weight. However, it forms sulfides with Mn, Ti, etc., affecting the formation of carbide-based precipitates,
Has the effect of improving the Rankford value. Also, 0.
Reducing the S content to less than 0005% by weight would require enormous costs for desulfurization refining in the steelmaking process. For this reason, in the present invention, the lower limit of the S content is set to 0.1.
0005% by weight.

Cu: 0.5-3.0% by weight Cu is an important alloy component for improving the strength of steel, and a necessary amount corresponding to the required strength is added. Cu is precipitated even by heat treatment at a relatively low temperature, and has an effect of strengthening the matrix. Such an effect becomes remarkable at a Cu content of 0.5% by weight or more. However, since it is also a component that induces hot embrittlement during hot working, the Cu content is restricted to 3.0% by weight or less. When a large amount of Cu exceeding 3.0% by weight is contained, even if Ni effective for preventing hot brittleness is added, the adverse effects caused by Cu cannot be prevented.

Al: 0.005 to 0.10 wt% Al is added as a deoxidizing agent and has an effect of fixing N. Such an effect is obtained when the Al content is 0.005% by weight or more.
It becomes remarkable in the content. However, when a large amount of Al exceeding 0.10% by weight is contained, oxide inclusions increase and workability and surface properties deteriorate. N: 0.007% by weight or less N is an unavoidable component and is fixed with Ti or the like.
However, when a large amount of N exceeding 0.007% by weight is contained, an increase in the amount of Ti, Nb, etc. necessary for fixing N is required,
Workability is degraded due to the increase in precipitates.

Ti: 0.01 to 0.1% by weight C and N, which form a solid solution in steel as an interstitial type, are fixed as carbonitrides and are combined with S to form sulfides. In order to improve the workability by forming sulfides and sufficiently reducing solid solution C and solid solution N, 0.03
A Ti content of 1% by weight or more is required. But,
Even if a large amount of Ti exceeding 0.1% by weight is contained, the effect of improving properties by adding Ti is saturated, and the production cost is rather increased. Nb: 0.01 to 0.1% by weight Carbonitride forming element similar to Ti, and C and N in steel
And has the effect of improving workability. Also, T
When added in combination with i, a composite precipitate is formed, and a relatively large precipitate is formed, thereby improving workability. Such effects become remarkable when the Nb content is 0.01% by weight or more, and is saturated at 0.1% by weight.

Ni: 0.2 to 2.0% by weight An alloy component added as necessary, exhibits an action of preventing hot brittleness caused by Cu, and is particularly effective in a system to which Cu is added. is there. In order to obtain such an effect, the Ni content is required to be at least about 1/3 or more of the Cu content, and when the content is 0.2% by weight or more, the effect of Ni addition becomes remarkable. However, a large amount of Ni exceeding 2.0% by weight
When the steel is added, the recrystallization-annealed steel strip has a hard microstructure, and the workability deteriorates.

B: 0.0002 to 0.002% by weight An alloy component added as necessary, which segregates preferentially at crystal grain boundaries and exhibits an effect of suppressing grain boundary embrittlement caused by P. . It also has the effect of preventing secondary processing cracks during press forming. Such an effect becomes remarkable at a B content of 0.0002% by weight or more. However, 0.002
A large B content exceeding% by weight impairs the growth of crystal grains and causes a reduction in workability. Zr, V: 0.01 to 0.1% by weight An alloy component added as necessary, and has an effect of forming carbonitride and fixing C and N. Also, Ti,
When combined with Nb, it also has the effect of further improving workability. These effects can be obtained by using 0.01% by weight or more of Zr.
And / or V content, but saturates at 0.1% by weight.

Hot rolling condition: finishing rolling temperature A _r3 transformation point or higher, winding temperature 650 to 800 ° C. In the present invention, both continuous casting slabs and bulk slabs can be used. Further, the hot slab after the continuous casting or the ingot may be directly conveyed to the hot rolling step, or may be reheated before the hot rolling step. The reheating temperature is to be set according to the steel composition, required characteristics, and the like, and is not particularly specified in the present invention.
Low temperature heating around 100 ° C. is preferred. Hot rolling is performed at a finish rolling temperature of _Ar3 transformation point or higher. When the finish rolling temperature is lower than the _{Ar 3} transformation point, not only a hot-rolled texture disadvantageous to the Rankford value is formed, but also
It becomes difficult to wind up in the temperature range specified in the present invention. Hot rolled steel strip is relatively high 650-800 ° C
It is wound up in the temperature range. By setting the winding temperature as high as 650 ° C. or higher, elongation and Rankford value are improved by actions such as coarsening of precipitates such as Ti-based carbides. Further, when performing mechanical descale in combination with cold rolling, the scale thickness increases within a certain range due to the progress of oxidation after winding, and the descalability is improved.
However, in high-temperature winding exceeding 800 ° C., the scale thickness becomes too large, and even if primary cold rolling is performed before pickling in a subsequent process, the descaleability is significantly deteriorated.

Primary cold rolling: Cold rolling rate 10 to 60% A hot rolled coil wound at a temperature of 650 to 800 ° C.
Oxidation proceeds after winding, so that descaling becomes difficult only by ordinary pickling or pickling combined with a tension leveler or the like. For this reason, the surface quality of the product steel sheet is greatly deteriorated by scale remaining after the pickling, or it is necessary to remarkably reduce the sheet passing speed at the time of pickling in order to obtain a sufficient descale, thereby lowering productivity. In the present invention,
In order to obtain a product having good surface quality without lowering the productivity, cold rolling is performed before pickling, and the scale is delaminated while mechanically pulverizing. As a result, descaling is sufficiently performed under ordinary pickling conditions. In order to improve the descalability by pickling, it is necessary to perform primary cold rolling of a hot-rolled steel strip at a cold rolling rate of 10% or more. 10%
The above cold rolling reduction is also effective in improving the product growth and Rankford value. However, in the primary cold rolling in which the cold rolling reduction exceeds 60%, although the elongation and the Rankford value are expected to be improved, the improvement of the descale property corresponding to the increase in the cold rolling reduction is not observed. In addition, the load on the cold rolling mill increases, which causes an increase in manufacturing cost.

Pickling By primary cold rolling, scale is partially removed from the surface of the steel strip. Particularly, in the case of cold rolling at a large cold rolling reduction, the scale removal rate is high. However, descale is not complete only by primary cold rolling, and scale remains on the steel strip surface. Since the surface quality of the product is deteriorated as it is, the primary cold-rolled coil is passed through a pickling tank, and the scale is sufficiently removed by pickling.

Secondary cold rolling after pickling: Cold rolling reduction of 20% or more Total cold rolling reduction of 60 to 95% combined with primary cold rolling The coil surface after pickling is descaled, but is usually used. It has pickling skin different from that of cold-rolled steel strip. Even in the aspect of the internal quality, even if the finish annealing is performed as it is, the properties required as ordinary cold rolled steel strip products are not satisfied. Therefore, after pickling, it is necessary to further perform secondary cold rolling. In order to obtain a surface skin having the same quality as that of a normal cold-rolled steel strip product, it is necessary to set the cold-rolling rate of the secondary cold rolling to 20% or more. Further, the mechanical properties required for workability, deep drawability, and the like as a product are affected by the total cold rolling ratio including the primary and secondary cold rolling. If the total cold rolling reduction is less than 60%, good characteristics cannot be obtained even when combined with a winding temperature of 650 to 800 ° C because of the low cold rolling reduction. But,
At a total cold rolling reduction of more than 95%, the effect of improving the workability by cold rolling tends to be saturated or rather reduced. On the other hand, an excessively high cold rolling rate causes an excessive load on the cold rolling, which causes an increase in manufacturing cost. Incidentally, the total cold rolling ratio in the present invention is calculated by subtracting the sheet thickness of the final product having undergone primary and secondary cold rolling from the sheet thickness of the hot-rolled steel strip, and dividing by the sheet thickness of the hot-rolled steel strip. .

Annealing after secondary cold rolling: not less than the recrystallization temperature and not more than 900 ° C. The cold-rolled steel strip is work-hardened and has extremely low workability. Therefore, in order to obtain the deep drawability required for a cold-rolled steel strip, annealing is performed at a recrystallization temperature or higher. The annealing method is set according to the steel composition, required characteristics, and the like, and any of continuous annealing and box annealing can be employed.
However, in any of the annealing methods, at an annealing temperature exceeding 900 ° C., α → γ transformation occurs and the crystal orientation is randomized, so that the deep drawability is significantly deteriorated. The cold-rolled steel strip manufactured in this manner is also used as a base plate for plating such as electroplating and vapor deposition plating. Also in this case, a plated steel sheet having excellent workability can be obtained. In the specification of the present application, a “cold rolled steel strip” is used in a sense that it includes the use as a plating base sheet of this kind.

Hot-dip coating after secondary cold rolling Hot-dip steel strip is manufactured by applying hot-dip plating made of Zn, Al or an alloy thereof. In the hot dip coating equipment, the steel strip before being immersed in the plating bath is heated to the recrystallization temperature or higher, and the same effect as the above-described annealing of the cold-rolled steel strip can be obtained. However, in any annealing method,
At an annealing temperature exceeding 900 ° C., α → γ transformation occurs and the crystal orientation is randomized, so that the workability is significantly deteriorated.
Also in this case, the annealing conditions, the plating conditions, and the like are not particularly limited, and conditions that are generally employed industrially are selected.

[0023]

EXAMPLES Example 1 A steel having the composition shown in Table 1 was melted in an electric furnace to obtain a 50 kg steel ingot.

[0024]

Each ingot was hot forged into a 35 mm thick steel slab, heated to 1130 ° C., and then hot rolled. Finishing temperature of hot rolling was set in the range of as eight hundred ninety to nine hundred and fifty ° C. the A _r3 transformation point or above for any of the steel. The finished sheet thickness takes into account the rolling rate in the subsequent cold rolling process,
It was set in the range of 2.2 to 7.0 mm. After hot rolling,
Into a salt bath furnace heated to 495-730 ° C,
By maintaining at a predetermined temperature for 2 hours, a treatment corresponding to the winding of the hot-rolled steel strip was performed. Next, the cold rolling rate is 5 to 45%.
For primary cold rolling and descaling by pickling. Furthermore,
Secondary cold rolling at a cold rolling reduction of 40 to 80%, and a sheet thickness of 0.6 to
A 1.4 mm cold rolled steel strip was manufactured. This cold-rolled steel strip was annealed to be heated to a temperature not lower than the recrystallization temperature and not higher than 900 ° C. The production conditions at this time are shown in Table 2 for each steel type.

[0026]

Table 3 shows the mechanical properties and surface texture of the annealed cold-rolled steel strip. The mechanical properties were measured using JIS No. 5 tensile test pieces. The Rankford value was measured by a three-point method after 15% tensile prestrain was applied, and the L direction (rolling direction), the T direction (direction inclined 45 degrees to the rolling direction), and the D
Direction (direction perpendicular to the rolling direction) (r _L + 2r)
It was determined as _T + r _D) / 4. The surface skin was judged by visual observation, and the case where the scale was completely removed was evaluated as good, and the case where one or more scale residues were recognized was evaluated as poor. In addition, as the embrittlement temperature for evaluating the secondary work cracking property, the temperature measured as follows was used. That is, a blank punched to a diameter of 90 mm is formed into a flat-bottomed cylindrical cup having a diameter of 33 mm by three-stage drawing with a drawing ratio of 2.7 at three stages, and immersed in refrigerants of various temperatures consisting of liquid nitrogen and an organic solvent, while having a tip angle of 60 mm. The punch was pushed in from the top of the cylinder, and the lowest temperature at which no brittle cracking occurred was measured.

[0028]

As can be seen from the investigation results in Table 3, in the cold-rolled steel strip satisfying the steel composition and the production conditions specified in the present invention, all show high elongation and Rankford values, and show good deep drawing. It is clear that it is a cold-rolled steel strip with good workability and workability. On the other hand, those using steel type number I having a steel composition outside the range specified in the present invention exhibited low elongation, Rankford value, and high secondary working crack temperature. Also,
Even if the composition satisfies the conditions of the present invention, if the manufacturing conditions are out of the range specified in the present invention, one or more of elongation, Rankford value, and secondary cracking temperature are bad values. showed that. From this, it was confirmed that a cold-rolled steel strip excellent in workability can be manufactured by using a combination in which the steel composition and the manufacturing conditions are specified.

Example 2 Steel having the composition shown in Table 4 was refined in a converter and a degassing furnace, and was continuously cast to a thickness of 250 m.
m, a slab having a unit weight of 13 tons was produced.

[0031]

After each slab was reheated to 1130 ° C. in a heating furnace, it was hot-rolled in a hot rolling mill, and finished to a sheet thickness of 1.2 to 7.7 mm at a finishing temperature in the range of 890 to 945 ° C.
Next, the hot-rolled steel strip was wound around a coil in a temperature range of 450 to 730 ° C. This hot-rolled steel strip was subjected to primary cold rolling at a cold-rolling rate of 5 to 55%, and then passed through a continuous pickling line having a hydrochloric acid-based pickling solution tank to be descaled. Next, the steel strip was again passed through a cold rolling mill and subjected to secondary cold rolling at a cold rolling reduction of 40 to 85% to produce a cold rolled steel strip having a thickness of 0.6 to 1.4 mm. This cold-rolled steel strip was passed through an annealing line and subjected to annealing by heating to a temperature higher than the recrystallization temperature to obtain a cold-rolled steel strip as a product. Table 5 shows the production conditions at this time, and Table 6 shows the properties of the obtained cold-rolled steel strip. As is clear from Table 6, even in the case of the cold rolled steel strip manufactured from the same steel material, in Test Nos. 16 and 24 in which the manufacturing conditions specified in the present invention are not satisfied, low elongation, Rankford value and high secondary working were obtained. The crack temperature was indicated. In addition, the surface skin was poor, and the productivity decreased due to the decrease in the pickling rate. On the other hand, the cold-rolled steel strips produced according to the present invention all exhibited high elongation and Rankford values, and had good deep drawability and workability.

[0033]

[0034]

Example 3: Various steel materials shown in Table 7 were used in Example 1.
Hot rolling, primary cold rolling, pickling, and secondary cold rolling were performed in the same manner as in the above. Table 8 shows the manufacturing conditions at this time.

[0036]

[0037]

Each of the cold-rolled steel strips was annealed at a temperature not lower than the recrystallization temperature and not higher than 900 ° C., followed by hot-dip plating. Table 9 shows the properties of the obtained hot-dip steel strip.

[0039]

As can be seen from the investigation results in Table 3, all the hot-dip galvanized steel strips satisfying the steel composition and the production conditions specified in the present invention show high elongation and Rankford values, and show good deep drawing. It can be seen that it is a hot-dip galvanized steel strip having good workability. On the other hand, those using steel type number T whose steel composition is out of the range specified in the present invention exhibited low elongation, Rankford value, and high secondary working crack temperature. Even if the composition satisfies the conditions of the present invention, if the manufacturing conditions are out of the range specified in the present invention, the elongation,
Either one or more of the Rankford value and the secondary cracking temperature showed a bad value. From this, it was confirmed that a hot-dip steel strip excellent in workability can be manufactured by using a combination in which the steel composition and the manufacturing conditions are specified.

Example 4 A steel having the composition shown in Table 10 was refined in a converter and a degassing furnace, and was continuously cast to a thickness of 250.
A slab with a unit weight of 13 tons was manufactured.

[0042]

Each slab was subjected to hot rolling, primary cold rolling, pickling, and secondary cold rolling in the same manner as in Example 3 to obtain a sheet thickness of 0.6-1.
A 4 mm cold rolled steel strip was manufactured. This cold-rolled steel strip was passed through a continuous hot-dip galvanizing line at a plating bath temperature of 450 ° C., and after giving an annealing effect by heating at a recrystallization temperature or higher, hot-dip coating was performed to produce a hot-dip coated steel strip as a product. . The production conditions at this time are shown in Table 11, and the characteristics of the obtained hot-dip galvanized steel strip are shown in Table 12. As is clear from Table 12, even in the hot-dip-coated steel strip manufactured from the same steel material, in Test Nos. 40 and 48 in which the manufacturing conditions specified in the present invention are not satisfied, low elongation, Rankford value, and high secondary working were obtained. The crack temperature was indicated. In addition, the surface skin was poor, and the productivity decreased due to the decrease in the pickling rate. On the other hand, the hot-dip galvanized steel strips produced according to the present invention all exhibited high elongation and Rankford values, and had good deep drawability and workability.

[0044]

[0045]

[0046]

As described above, in the present invention, the steel composition and the manufacturing conditions are combined under specified conditions, and the winding temperature after hot rolling is compared to improve the deep drawability and workability. The primary cold rolling is performed before pickling, with the temperature set to a relatively high temperature and the cold rolling reduction specified. Primary cold rolling before pickling improves scale releasability, even in hot rolling with a relatively high winding temperature, without causing deterioration in productivity in the descaling process due to pickling. A high-strength cold-rolled steel sheet and a high-strength hot-dip steel sheet having excellent workability by effectively utilizing the precipitation strengthening effect of Cu are manufactured.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/16 C22C 38/16

Claims (3)

[Claims] 1. C: 0.0005 to 0.01% by weight, S
i: 2.0% by weight or less, Mn: 0.05 to 3.0% by weight, P: 0.2% by weight or less, S: 0.0005 to 0.0
2% by weight, Cu: 0.5 to 3.0% by weight, acid-soluble Al:
0.005 to 0.1% by weight, N: 0.007% by weight or less, Ti: 0.01 to 0.1% by weight and / or Nb:
0.01 reheated or direct a steel slab having a composition comprising by weight%, the finish rolling temperature A _r3 transformation point or higher, subjected to a hot rolling coiling temperature 650 to 800 ° C., the resulting heat Primary cold rolling is performed on the rolled steel strip at a cold rolling rate of 10 to 60%, and after pickling, the cold rolling rate is 20% or more, and the total cold rolling rate combined with the primary cold rolling is 60 to 95%. Cold rolled steel strip or hot-dip galvanized steel strip with excellent workability to be subjected to secondary cold rolling in such a manner that the resulting cold-rolled steel strip is annealed at a recrystallization temperature of 900 ° C. or less and hot-dip after annealing. . 2. The steel slab according to claim 1, further comprising N
i: A method for producing a cold-rolled steel strip or hot-dip steel strip having excellent workability using a steel slab having a composition containing 0.2 to 2.0% by weight. 3. The steel slab according to claim 1 or 2,
Further, B: 0.0002 to 0.002% by weight, Zr: 0.
01 to 0.1% by weight, V: 0.01 to 0.1% by weight
A method for producing a cold-rolled steel strip or a hot-dip steel strip having excellent workability using a steel slab having a composition containing one or more kinds.