JPS5825435A - Manufacture of deep drawing cold rolling steel plate which is excellent in surface quality and state by continuous annealing - Google Patents

Abstract

PURPOSE:To obtain a deep drawing cold rolling steel plate which is excellent in its surface shape and suitable for an automobile outside plate, by adding Al, etc. to dead low C steel of a specific composition, executing hot rolling, cooling and cold rolling under the specific conditions, and after that, annealing it continuously. CONSTITUTION:Steel consisting of <=0.006wt% C, 0.04-0.30% Mn, <=0.01% N, 2 times of N content -0;15% Al, and the balance Fe and impurities is melt- manufactured. This steel is hot rolled at a finish temperature 830-900 deg.C, is cooled at a mean colling speed 60 deg.C/sec, and is wound up at <=600 deg.C. Subsequently, it is pickled, is cold-rolled, and is made to pass through a continuous annealing line. Also, with regard to steel contaning <=0.10% C, 2 times of N content -0.10%, A and more than one kind of Nb and V 3-15 times of C, the same process as above is executed. According to this composition and control for lowering a rolling temperature, it is possible to obtain a cold rolling steel plate which is free from needle-like defect, etc. caused by residual scale, satisfactory in its surface quality and excellent in its deep drawing property.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a cold-sharpened steel plate for deep drawing with excellent surface properties by continuous annealing.

Generally, cold-rolled steel sheets are used for a wide range of applications such as the exterior panels of automobiles, but they usually require excellent workability such as deep drawing properties as well as strict surface quality, and in this case, surface treatments such as painting are required. The surface quality of the underlying cold-rolled steel sheet is extremely important.

On the other hand, cold-rolled steel sheets with excellent S-drawing properties were conventionally manufactured using the box annealing method, but in recent years, with the development of recrystallization annealing methods for cold steel sheets, emphasis has been placed on manufacturing steel sheets with excellent production efficiency and material quality. It has come to be. However, the production of cold-rolled steel sheets by continuous annealing involves a thermal cycle of rapid heating, short-time soaking, and rapid cooling, which is different from conventional zero-box annealing. It was extremely difficult to obtain squeezability.

For this reason, in the production of steel sheets for deep drawing by continuous annealing, conventional methods have been used to coarsen carbon and nitrides in the steel in order to facilitate the growth of crystal grains during continuous annealing. After that, it was common to perform high-temperature winding at 600°C or higher. However, in the case of high-temperature writing treatment at 600°C or higher, the abundance of 1gnetai) (Fe, 04)0 increases in the oxide layer formed on the surface of the steel sheet, and as a result, in the next pickling process, Since the descaling property is significantly inhibited, there is a drawback that the surface quality of the steel sheet is deteriorated. In order to avoid this drawback, reducing the pickling rate to completely remove scales inevitably increases costs.

Therefore, in order to improve the surface quality, the winding temperature should be increased to 600°C.
It is obvious that it is desirable to lower the temperature to below .degree. C., but measures are needed to make this possible.

As a conventional technology for obtaining continuously annealed material by low-temperature coiling that is comparable to high-temperature coiled material, there is a manufacturing method in which B-added low carbon aluminum killed steel is coiled at 625°C. J 1980 VoJ.

66, s, 366) L However, this method has a winding temperature of 600
℃ or higher, and the r value deteriorates as B is added, so this cannot be said to be an essential solution.

Also, JP-A-1@55-58333KC: α001~α0
035- ultra-low carbon al-electrokilled steel slab at 1200℃
Heat at a low temperature below and heat gIII! A method for setting the temperature t to 530° C. or higher is disclosed. 7. However, this method has the disadvantage that the slab heating temperature is low, making it impossible to make the crystal grain structure and component elements uniform in the slab, resulting in poor homogeneity of the final product.

In addition, in hour @ 51-33056, Zr, Nb, V, Cr,
A.I.

A manufacturing method is disclosed in which one or two selected from among the above are added, the nine slabs are heated at a winding temperature of 500°C or more and 700°C or less, and mechanical bending and elongation is caused in the heating process of continuous annealing. . However, this method has the drawback that the precipitation of fine carbonitrides progresses due to mechanical bending and stretching during heating, so even if a high r value is obtained, the strength is poor.

An object of the present invention is to eliminate the drawbacks of the prior art in the manufacturing method of a cold strength steel sheet for deep drawing by continuous annealing, and to provide a method for manufacturing a cold strength steel sheet having excellent straightness properties and deep drawing properties. .

This object of the present invention is effectively achieved by the four inventions summarized below.

The gist of the first invention is as follows. That is, at a weight ratio of 1: C: α006 or less, Ml: α0
4 to 11301 N: Q, 01- or less t- In a method for producing a cold-rolled steel sheet for deep drawing by controlled rolling and continuous annealing of a gold-containing steel billet, the amount of Ajt-N content of the basic component is twice as much as the Ajt-N content. The finishing temperature wrinkles of the steel billet range from 830 to α15, with the remainder consisting of Fe and unavoidable impurities.
a step of hot rolling at 900° C.; a step of cooling the steel at an average cooling rate of 60° C./@ec or less until 700° C. after the end of the hot rolling; and a step of cooling in a temperature range of 600° C. or less; A method for producing a cold-rolled steel sheet for deep drawing with excellent surface properties by continuous annealing, comprising the steps of pickling a strip in a conventional manner, cold rolling it, and then continuously annealing it. .

The gist of the second invention is as follows. That is, in terms of weight ratio, C: 0.010- or less, Mn: a,
04 to α3G-, N: In the method for manufacturing a cold-rolled steel sheet for deep drawing by controlled positive arc and continuous annealing of a steel slab containing α01- or less, in addition to the basic components, Aj is added to 2 of the N content.
The finish of a steel billet containing 3 to 15 times the C content, and one or two of Nb and V in a range of 3 to 15 times the C content, with the remainder being F and inevitable impurities. A step of hot rolling at a temperature of 830 to 900°C, and an average cooling rate of 60°C/700°C after the hot rolling is completed.
sec or less and coiling at a temperature range of 600° C. or less; and a step of pickling the hot rolled steel strip in a conventional manner, cold rolling it, and then continuously annealing it. This is a method for producing cold-rolled steel sheets for deep drawing with excellent surface properties through continuous annealing.

The gist of the II3 invention is that the finishing temperature of a steel slab having the same composition as the first invention is 830°C or higher, and the temperature range from 830 to 980°C is set at a total reduction rate of 40qII or higher or a forward arc speed of 200 m/ step 1 of hot rolling at a temperature of at least min. min, cooling to 700° C. after the end of the hot rolling at an average cooling rate of 60° C./sec or less, and rolling the steel in a temperature range of 600° C. or less; A method for producing a cold-rolled steel sheet for Kumon drawing which has excellent surface properties by continuous annealing, the method comprising the steps of pickling a strip in a conventional manner, cold-rolling it, and then continuously annealing it. be.

The gist of the fourth invention is that the finishing temperature of a steel piece having the same composition as the second invention is 830°C or higher, and
A step of hot rolling in a temperature range of 30-980°C at a full rolling reduction of 40° or higher or a rolling speed of 200 m/min or higher, and an average cooling rate of 60°C/see or lower until 700°C after the end of the hot rolling. A continuous process characterized by comprising the steps of cooling and coiling at a temperature range of 600° C. or lower, and a step of pickling the hot-rolled steel strip in a conventional manner, cold rolling it, and then continuously annealing it. This is a method for producing cold-rolled steel sheets for deep drawing that have excellent surface properties due to annealing.

First, the experimental results that formed the basis for obtaining the present invention will be explained. Steel added with Nb and AI as shown in Table 1 is
It was melted in a D converter, subjected to RH degassing treatment, and made into a slab by continuous casting.

[ After soaking the above slab at 1300℃, rough rolling
A hot rolled sheet with a thickness of 2.8 m was prepared by finish rolling. During finish rolling, the entrance temperature should be set to approximately 1
The rolling temperature was changed to two types, 100℃ and about 1040℃, and the finishing temperature was changed to 11℃. ? Mllll in fi
, winding it into a coil while changing the temperature in the range of 730 to 470℃? Ta. After pickling this hot-rolled steel plate, the reduction rate was 75.
'Ji cold rolling is carried out, and then the continuous annealing line is used to maintain the temperature at 830°C for 40S@c at a heating rate of 20'C/sec as shown in Figure 1, and then at 20°C/sec.
Annealing is performed using a heat cycle that cools at a cooling rate of 9.

For this annealed material, yield stress (ys), tensile strength T8), elongation (Ej), r value 1 aging index (AI) tv
The effects of finishing temperature and winding temperature were investigated and shown in Figure 2, @, Q, (n, ■), respectively.

As is clear from Figure 2, for the specimen material with a high finishing temperature of 930°C, the elongation and r value deteriorate rapidly when the IIk temperature is lowered to below yooj, whereas when the finishing temperature is 870°C,
It has been found that the hot rolling temperature is as low as 600°C and the nine test materials can be coiled at a low temperature of 600°C or less to obtain cord properties comparable to high-temperature finished straight arc and high-temperature rotary material. From this basic experiment, we obtained the following important findings.

(b) C: When hot rolling steel made of ultra-low carbon of 01- or less with addition of Nb and An, the precipitation of carbonitrides during hot rolling is strongly promoted by lowering the rolling temperature. be able to.

(b) After hot rolling the hot rolled steel strip rolled by the above method,
Slow cooling to 0°C promotes the precipitation and coarsening of the carbonitrides, so it is then rapidly cooled to 600°C or less.
A cold steel sheet for deep drawing that has the same elongation and r value as conventional high-temperature rolled material even when it is cut at a temperature of 0° C. or lower can be produced by a continuous annealing method.

(U) When the coiling temperature is 600℃ or less, the presence of magnetite (Fe, 04) in the oxidized layer on the surface of the steel sheet is drastically reduced.O improves pickling properties and produces cold-rolled steel sheets with excellent surface properties. Obtainable.

As a result of microscopic observation of the precipitates in the hot-rolled sheets in this experiment, the present inventors found that even if the finishing temperature was lowered for the same winding S change, the precipitates were thought to have precipitated after the γ→α transformation below xooX. It was found that fine precipitates were reduced.

Next, using the slab with the composition shown in Table 1 above, the rolling reduction ratio and rolling speed were varied as the hot rolling conditions, and the coiling temperature after hot rolling was changed in the range of 730-470°C as in the previous experiment. Nine hot-rolled steel strips were pickled under the same conditions, cold-rolled, and then continuously annealed to investigate the effects of hot-rolling conditions on elongation, r-value, and other properties.

As a result, the material quality after continuous annealing improved as the rolling reduction rate and rolling speed during hot normal arcing increased, and the quality of the material after continuous annealing improved even when low-temperature winding at 600°C or less was performed, similar to when the rolling finish temperature was lowered. The reason for this is not necessarily clear, but when the rolling reduction rate and rolling speed are increased, carbon and nitride precipitation occurs during hot rolling, as is the case when the finishing temperature is lowered. This is considered to be the result of the effect of reducing fine precipitates that inhibit grain growth during continuous annealing.

This experiment described the case where the Nb and Aj-added steel shown in Table 1 was used as the test material, but the test material was V-added, which is an element that forms nitrides in the austenite region like Nbk and Aj. We also confirmed the same effect as above.

Next, the reasons for limiting the steel composition in the present invention will be explained.

C: If C exists in a large amount in a solid solution state before cold rolling and continuous annealing, it will have a negative effect on the material properties targeted by the present invention, especially the aging resistance and deep drawing properties, so it needs to be at least 40.0111+. There is. However, when A1 is added alone, A
1 does not affect the fixation of ω precipitation, so considering this, O,
It was limited to OO6- or less.

Mn: Mn is a useful element because it combines with 8 and prevents hot embrittlement, and therefore requires at least 0.04-.
If it exceeds α3091, the strength and deep drawability deteriorate, so it was limited to a range of 0.04 to O, aO*.

N: Similar to NFiC, if a large amount of N is present in the form of solid droplets, it will deteriorate the aging resistance and deep drawability of 411, which is the object of the present invention, so the smaller the better, preferably 0.008-
The upper limit was αG1m1.

Aj, Nb, VA AI, Nb, and V are all important elements in the present invention, and these elements are effective in precipitating and fixing harmful N or C in a solid solution state. Furthermore, steel containing these elements can have excellent deep drawability and surface texture in low-temperature coiling and continuous annealing by controlling hot rolling conditions. For both Nb and V, both C and -N can be precipitated and identified.

However, rather than adding Nb or V alone to fix both C and N, 4Nb-AJ4 L < d V -A
It is possible to take advantage of the mutual precipitation promoting effect of carbon and nitrides such as AjN%NbC and VC, and increase the ductility due to the addition of excessive Nb and V. deterioration can be suppressed.

If the amount of AJ added is less than twice the N content, N fixation will not be sufficient and if it exceeds α15s, it will not only deteriorate ductility but also increase surface defects due to An-based inclusions.
It can be limited within the range of N1 to α15%, but when LNb and ■ are coexisting, if the AJ amount exceeds α1G-, the ductility will deteriorate significantly, so in this case, Q should be 10- or less. be.

In addition, when Nb and V are added at the same time, the C content effective for fixing C precipitation is required to be three times or more, but Nb.

If the amount of V becomes too large and exceeds 15 times the amount of C, the properties targeted by the present invention, especially ductility, will be deteriorated, as in the case of AJ, so it is limited to a range of 3x(, 1 to 15xC).

Next, the reasons for limiting the manufacturing process will be explained. First, as for the steel melting method, a top-blown converter method may be used, but a combination with a degassing method or a bottom-blown converter method is advantageous. The production of steel slabs may be carried out by conventional ingot-forming methods and blooming rolling methods.
Alternatively, a continuous casting method may be used.

Next, hot rolling will be explained. Hot rolling is one of the most important steps in the present invention.

First, the purpose of soaking is to homogenize the material of the steel billet and to dissolve as much as possible the nitrides and nitrides present in the previous history. Required rolling reduction rate and temperature in rolling.

The rolling mill and the straight arc method are not an essential problem as long as conditions such as rolling speed are satisfied. The first point of the positive arc conditions is proper control of the rolling temperature, and in the present invention, the lower the rolling temperature, the more advantageous it is.

The finishing temperature was limited to 830-900°C.

At low temperatures below 830°C, it is difficult to control the plate thickness, and at finishing temperatures above 900°C, elongation and r-value deteriorate, as is clear from the inventors' basic experiments shown in Figure 1. It shouldn't be taken.

If the finishing temperature is set at 830 to 900°C and the cooling conditions for one roll are secured, sufficient material quality and surface texture can be obtained for the purpose of the present invention, but it is also effective to control the rolling reduction and rolling speed during hot rolling. . That is, the object of the present invention can be achieved by increasing the rolling reduction ratio and rolling speed. Especially when the rolling temperature is 850 to 980℃, the total rolling reduction is 40-40℃.
If the rolling speed is above 200 m/mh or the rolling speed is 200 m/mh or above, excellent materials can be obtained with low-temperature winding material.

If this limitation is exceeded, the desired material quality of the present invention cannot be secured.

The rolling reduction ratio does not need to be 401 or more in one pass within the above temperature range, and the total rolling reduction may be 401 or more during multi-pass rolling.The restrictions on the rolling reduction ratio and rolling speed during hot rolling are independent of each other. This is the minimum requirement when using it as a factor.

If any of the conditions is definitely satisfied, it may be determined by appropriately combining those conditions.Furthermore, the finishing temperature should be 830℃ or higher, and if the above conditions are satisfied, it is necessary to set an upper limit. There is no.

In the present invention, the cooling conditions at the winder St after hot rolling are also important.

It is necessary to slowly cool down to 700 degrees Celsius after heating at an average cooling rate of 60 degrees Celsius or less, and by rapid cooling exceeding 6 G/sec, it is necessary to secure the elongation and r value targeted by the present invention. The unique cooling pattern up to 700℃ is II! Although it is not necessary to limit the temperature to #, O slow cooling is particularly effective in improving material quality in the temperature range of 800 to 750°C.

Next, the winding temperature is limited to 600℃ or less.

This is because if the temperature exceeds 600°C, the abundance of magnetite in the scale layer increases, impairing the pickling properties and making it impossible to obtain excellent surface properties. Therefore, it is desirable to slowly cool the material at 700° C. in the previous step and then rapidly cool it to 60° C. or less. Generally speaking, the lower the coiling temperature after hot rolling, the better the pickling properties, but in the case of the present invention, it is 550 to 400 from the viewpoint of cooling capacity, shape of the steel sheet, etc.
It is best to pile in a temperature range of 30°F.

In addition, steps to further improve the descaling properties in the next pickling process, such as water cooling after winding the hot rolled steel strip into a coil, or adding a light reduction pass/pass before pickling, are used. The addition does not pose any hindrance to the present invention.

Next, there is no need to particularly regulate the cold rolling method, and a normal method may be used, but it is desirable to ensure a rolling reduction of 60 or more.

Next, regarding the continuous annealing process, if the soaking temperature ranges from the recrystallization temperature to the Acs transformation point, there is no need to particularly regulate the heating and cooling conditions. For this purpose, the soaking temperature is preferably as high as possible, below the A c H transformation point, and the cooling rate of the annealed bale is preferably 700°C. It is not necessary as it has little effect on

By satisfying the above-mentioned limiting conditions, it is possible to produce a cold-rolled steel sheet for deep drawing with excellent surface properties.

Example LD converter and RH having the chemical composition shown in Table 2
It was melted using a degassing furnace.

This molten steel was made into steel slabs with a thickness of 220 mm using a continuous casting method.
After soaking at 300°C, hot rolling was performed. In the hot-pressure process, a 4-row rough rolling mill is used to form a sheet bar with a thickness of 35EIIIl, and then a 7-stand tandem finishing straight-edge mill is used to form a hot-air steel strip with a thickness of 28mm, in this case. The rolling temperature, normal arc speed, rolling reduction, finishing temperature and winding temperature are as shown in Table 3.

Table 3: In all cases of 1-4 test steel floors 1 to 4, the average cooling rate from the finishing temperature to 700'C1 was approximately 24°C/sec.
It was set as constant. It is clear from the meeting table that the test steel TLK
11 is a case where the finishing temperature is 860°C, *low finishing temperature is 480°C, and low-temperature winding is performed.

NE12 is the case where the finishing temperature is 5I900°C and the total rolling reduction from the 411th roll F4 to the seventh final roll F7 from the finishing mill entry side is set to 67-.

Na3 is rolled at a rolling speed of 415 in the temperature range of 980 to 930°C.
In the case of a large angle of m/min, it becomes too much, Nn4Fi
870-960t, D temperature range 3! lom/mJno
This is a case of high-speed rolling and low-temperature winding of 450° C. with a high rolling reduction of 62°C, both of which satisfy the hot rolling conditions of the present invention.

Each of the nine test steels wound into the above coil was pickled in the usual manner,
It was passed through a normal cold rolling process S with a rolling reduction of 7191 to form a cold rolled sheet with a thickness of α8.

Each of the test steel sheets thus obtained was continuously annealed under the conditions shown in Table 1, and then cooled to room temperature at an average cooling rate of 25'C/sec.

The mechanical properties of each cold-rolled steel sheet after undergoing the above process are also shown in Table 4.

The aging index (AI) in the Da@* table is the deformation stress after tensile prestrain of 7.51, and the deformation stress after the tensile prestrain of 7.51, and the deformation stress after unloading of 10σ×30m1n.
It is expressed as the amount of increase in descending stress after heat treatment.It is clear from Table 8 that the elongation of the steel samples 1 to 40 according to any of the methods according to the present invention is 46g4 or more. Showing characteristics equal to or higher than s i*'br,
A cold-rolled steel sheet with excellent deep drawing properties was obtained. The aging index (AI) of each of the specimens was &29/- or less, indicating that they had slow aging properties.

Furthermore, the surface texture inspection results showed that although some defects were observed due to non-metallic inclusions and due to contact with rolls during annealing, they There were no needle defects caused by scale sb.

As is clear from the above examples, the steel composition of the present invention is C: 0.010 or less, Mn: α04 to α30, and N:
In addition to regulating α019G or less, include the amount necessary to fix %Ajf:N, or Nb.

Add either or both of (2) at the same time to precipitate and fix N and C, and further during hot arcing.

The rolling temperature is lowered in order to promote the precipitation of nitrides and nitrides during hot rolling. Alternatively, increase the rolling reduction rate or increase the rolling speed. After hot rolling, slowly cool to 700°C to prevent the precipitation and coarsening of carbon and nitrides, and then roll it up. By using a conventional method of pickling, cold rolling, and continuous annealing of the steel sheet, we were able to achieve the following effects.

0) Cold rolled steel sheet after continuous annealing has an elongation of 46 or higher and an r value of L
It shows a rating of 7 or higher and has excellent deep drawing properties.

(b) The finished cold abrasive plate has very good surface quality with almost no needle defects caused by residual scale.

f9 The cooling plate according to the present invention has an aging index of 12#/- or less and is slow aging.

In the description and examples of the present invention, only cold-rolled steel sheets by continuous annealing have been described, but the present invention can be applied to the production of most surface-treated steel sheets that require excellent workability and surface texture. can. For example, Rai/
It can be applied to a hot-dip metal plating method using an internal annealing method or an electrolytic metal plating method in which annealing is performed in a separate process. This is a book for the following reasons.

(1) Continuous annealing, which is one of the requirements of the present invention, suffices as long as the soaking temperature is within the range H from the recrystallization temperature to the AC ■ transformation point.

佽) The material is ultra-low carbon steel, and the amount of added special elements is extremely small, so the adhesion between the base steel and the surface coating layer is good.

[Brief explanation of drawings]

Figure 1 shows the heat cycle in continuous annealing of a cold-rolled steel plate in the basic experiment of the present invention. Time/temperature-wire circuit two factors; Indicates the influence of finishing temperature and coiling temperature on the mechanical properties of rolled steel sheets, where CA is yield stress, (b) is tensile strength, 0 is elongation, 0 is j value, and ■ is change in aging index (AI). FIG. Agent Takeo Nakamichi 111 Figure 11 □

Claims (1)

[Claims] ω weight ratio C:αOOS* or less, Mn: 0.
04~αs01. In a method for manufacturing a cold steel plate for deep drawing by controlled positive arc and continuous annealing of a steel billet containing N: 0.01- or less, the basic component Aj is reduced to an N content of 0.
The finishing temperature of a steel piece in the range of 2 times to α15-grooves, with the remainder consisting of Fe and unavoidable impurities, is 830 to 900.
℃ hot rolling process and 70℃ after the hot normal arc is completed.
G'C1 is cooled at an average cooling rate of 60'C/sec or less and rolled in a temperature range of 600°C or less, and the hot-hardened steel strip is pickled in a conventional manner and cold rolled, followed by continuous rolling. 1. A method for producing a cold abrasive steel plate for deep drawing which has excellent surface properties through continuous annealing, the method comprising the steps of annealing. (2) C: (LO=10- or less, M n
: 0.04 to α80 Ls, N : Q, containing 011 or less In a method for producing a cold rolled steel sheet for deep drawing by O-controlled rolling and continuous annealing, AJ is added to the N content in the basic components. Includes a range from twice that of to al〇-. and 1 type 4 or 2 of Nb and V with a C content of 3
~ 15 times as much as Fe and unavoidable impurities.The finish temperature of the steel piece is set at 830 to 900°C, and the hot rolling process is carried out, and the average cooling rate is up to 700°C after the end of the hot normal arc. The method includes a step of cooling at 6 G'C/sec or less and winding at a temperature range of 600° C. or less, and a step of pickling the hot rolled steel strip in a conventional manner, cold rolling it, and then continuously annealing it. 1. A method for producing a cold steel sheet for deep drawing which has excellent surface properties by continuous annealing. (3) Weight ratio: C: α00691 or less, Mn: α04
~α30g, N: In a method for producing a cold arc steel plate for deep drawing by controlled forward arc and continuous annealing of a steel slab containing α019g or less, in addition to the basic components, KAj is in the range from twice the N content to 11591Gt. The finishing temperature of the steel billet is 830°C or higher, and the remaining part is F1a and unavoidable impurities.
% or more or at a rolling speed of 200 ml min or more, and cooling to 700°C after the end of the hot rolling at an average cooling rate of 60°C/sec or less.
a step of winding in a temperature range of 0° C. or lower, and a step of continuously annealing the hot rolled steel strip after pickling and cold rolling by a conventional method. 1. A method for producing a cold-rolled steel sheet for deep drawing with excellent surface properties through continuous annealing, characterized by comprising: In addition to the above-mentioned basic components, the method for producing cold-rolled steel sheets for deep drawing by straight arc and continuous annealing includes Nb, The finishing temperature of the steel slab is 830°C or higher, and the temperature range is 830°C to 980°C under the total pressure. Get off at 40- or more or rolling speed 200
ml min or more, and an average cooling rate of 60°C/s until 700°C after the hot rolling is completed.
EC or lower and coiling at a temperature range of 600°C or lower; and a step of pickling the hot rolled copper strip in a conventional manner, cold rolling it, and then continuously annealing it. A method for producing cold-rolled steel sheets for deep drawing with excellent surface properties through continuous annealing.