JPH11350037A - Production of stock for cold rolled steel sheet for working - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable energy saving and process reduction to impart excellent workability thereto and to obtain uniform characteristics therein by subjecting electric furnace molten steel contg. specified amounts of C, Si, Mn, P, S, Al, O, tramp elements, Ti and N to continuous casting into a thin slab having a specified sheet thickness, executing hot rolling under specified conditions and thereafter coiling it at a specified temp. SOLUTION: Molten steel having a compsn. contg., by weight, <=0.005% C, <=1.5% Si, <=1.5% Mn, <=0.10% P, <=0.020% S, <=0.10% Al and <=0.01% O, furthermore inevitably contg. 0.02 to 1.5% Cu and 0.02 to 2.0% Ni as tramp elements, contg. 0.01 to 0.10% Ti, in which the content of N is controlled to 0.004 to 0.009%, moreover contg. 0.001 to 0.10% Nb or 0.0001 to 0.01% B is subjected to continuous casting into a thin slab having 10 to 80 mm sheet thickness. This thin slab is subjected to hot rolling in such a manner that the starting temp. is controlled to <=1100 deg.C, the total draft to >=50%, the draft per pass to >=35% and the finishing temp. to >=600 deg.C and is coiled at <=800 deg.C.

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 steel sheet used as a material of a cold-rolled steel sheet for processing, and particularly to a method for producing Cu or
Stabilize cold-rolled steel sheets with excellent workability even when using the electric furnace steelmaking method in which Trump elements such as Ni are inevitable, and when using the thin slab process that contributes to energy saving and process saving. It is intended to propose a method of manufacturing a material that can be obtained by using the above method. The material for cold-rolled steel sheets for processing in the present invention is used not only as a material for cold-rolled steel sheets for processing, but also for various other processing steel sheets such as hot-rolled steel sheets for processing and surface-treated steel sheets for processing. Is what you can do.

[0002]

2. Description of the Related Art At present, not only in Japan, but also from worldwide market needs, there is an aspiration to develop a technology capable of producing many kinds of steel materials including high-grade steel with less investment.
The electric furnace steelmaking method can meet the above-mentioned demands because inexpensive scrap can be used as an iron source, and in recent years the construction cost is much lower than that of integrated blast furnace-converter equipment. It is built worldwide and contributes to the production of steel bars and the like. Recently, some electric furnace materials have entered the field of thin sheets such as hot-rolled steel sheets, cold-rolled steel sheets, and surface-treated steel sheets.

However, in electric furnace materials, the incorporation of impurity elements such as Cu and Ni, which are referred to as tramp elements, is unavoidable, and mechanical properties are limited due to such tramp elements, and internal quality and surface quality are reduced. Is degraded, so that it is not applied to so-called high-grade thin steel sheets typified by steel sheets for automobiles, and its use is currently limited to general-purpose products even in the field of thin sheets.

[0004] That is, in the case of producing steel using an electric furnace, iron scrap is often reused as an iron source, and therefore, N in steel reaches a high level of 0.004 wt% or more. In addition, Trump elements such as Cu and Ni contained in iron scrap are difficult to remove at the time of refining, so that they are unavoidable to remain in steel. These components deteriorate the mechanical properties and surface properties of the steel sheet for processing, and are not suitable for use in high-grade thin steel sheets.

[0005] Therefore, conventionally, in order to produce hot-rolled steel sheets, cold-rolled steel sheets, and surface-treated steel sheets having excellent workability and beautiful surface, hot metal from a blast furnace is used as a raw material, and a converter-vacuum degassing- By taking the process of hot rolling and cold rolling, C,
A method has been adopted in which N is reduced as much as possible, and furthermore, the mixing of playing card elements is suppressed. For example, Japanese Patent Publication No. 44-180
No. 66, Japanese Patent Publication No. 53-12889, Japanese Patent Publication No. 3-56301 and the like disclose techniques for reducing C and N as much as possible. In addition, these technologies use Cu and
No consideration is given to playing cards elements such as Ni, and therefore no electric furnace can be used.

On the other hand, there have been proposed several techniques for producing a hot-rolled steel sheet, a cold-rolled steel sheet, and a surface-treated steel sheet having excellent workability from an electric furnace steel containing a playing card element. For example, Japanese Patent Application Laid-Open No. 6-235047 proposes a technique for producing a cold-rolled steel sheet which is non-ageable and has excellent cold press workability even with a high N content steel. However,
The above cold-rolled steel sheet contains a large amount of C of 0.005 wt% or more. When a large amount of a trump element is contained, an r value of only about 1.60 to 1.78 can be obtained, and a sufficient depth is obtained. It cannot be said that it has drawability. In addition, Japanese Unexamined Patent Application Publication No.
JP-A-371528 proposes a technique for producing a cold-rolled steel sheet for deep drawing, but the actual N content of the steel is 0.3.
0025 wt% or less, and handles only steel with a level lower than the N content present in the electric furnace steel, and the r-value of the obtained cold rolled steel sheet is 1.85 or less, which is sufficient for deep drawing. It is hard to say that it has the nature. Also, Japanese Patent Application Laid-Open No.
No. 8795 proposes a method for producing a cold-rolled steel sheet having excellent workability. However, since the substantial C content is as large as 0.03 wt% or more, the obtained r value is also 1.83 or less. It is difficult to say that it has sufficient deep drawability. In addition, Japanese Patent Application Laid-Open No. 7-157840 proposes a method for producing a hot-rolled steel sheet having excellent weldability.
Since the content is 0.01 wt% or more, sufficient workability is hardly expected.

As described above, there have been proposed several techniques for producing a hot-rolled steel sheet, a cold-rolled steel sheet, and a surface-treated steel sheet having excellent workability from an electric furnace steel containing a playing card element. However, it is hard to say that it has sufficient workability, and its improvement has been strongly desired.

Therefore, recently, Japanese Patent Application Laid-Open Nos. Hei 9-235560, Hei 10-25540 and Hei 10
In Japanese Patent No. 25541, the N content is limited to 0.004 to 0.009% and the C content is set to 0.0028 wt% or less, so that a high r value exceeding 1.85 can be obtained even when the electric furnace steel including the trump element is used as a material. It is shown that it is possible. However, this technique is manufactured by a normal continuous casting-hot rolling process, and as to what properties are obtained when the hot rolling reduction is low, such as in a thin slab continuous casting process. Is not a suggestion. Further, in the normal continuous casting-hot rolling process, there is a problem of structural non-uniformity mainly due to a temperature difference in a coil longitudinal direction during rough rolling and finish rolling, but any improvement is provided in this regard. is not.

The thin slab continuous casting process is a method of directly manufacturing a thin slab having a thickness of 10 to 80 mm from molten steel by continuous casting. The rough rolling step in the hot rolling step can be omitted, and Significant simplification of the cold rolling equipment and remarkable energy saving can be achieved. However, the thin slab continuous casting process inevitably results in a lower total reduction ratio during hot rolling than the ordinary continuous casting-hot rolling process, which limits the mechanical properties of the final product. , As represented by steel plates for automobiles,
It has never been applied to so-called high-grade steel sheets,
Its use is currently limited to general purpose products.

[0010]

As described above, the field of high-grade thin steel sheets is still the dominant field in the blast furnace-converter process, and the next step is to use continuous cast normal thickness slabs. It is a unique hot rolling process. If the production of such high-grade steel can be made with a compact facility called an electric furnace-a thin slab continuous casting process,
The effects are immeasurable from the viewpoint of energy saving and reduction of capital investment.

The present invention advantageously satisfies the above-mentioned demands, and uses an electric furnace steelmaking method in which the incorporation of a trump element is inevitable, and further uses a thin slab continuous casting process that contributes to energy saving and process saving. Even so, an object of the present invention is to propose a method for producing a cold-rolled steel sheet material for processing, which has excellent workability with an r value exceeding 1.85 and has uniform characteristics in the coil longitudinal direction.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above object, and as a result, have found that a thin slab continuous casting process for producing a thin slab having a thickness of 10 to 80 mm by continuous casting. When manufacturing cold-rolled steel sheets for deep drawing at
Compared to the usual continuous casting-hot rolling process, r
In addition to the effect of the steel composition on the value, it was found that the conditions of hot rolling were significantly different. That is, in the case of manufacturing a cold rolled steel sheet material by an electric furnace-thin slab continuous casting process, the steel contains a suitable amount of Trump elements such as Cu and Ni, and an appropriate amount of N is precipitated as TiN while the steel is heated. It has been found that the r value can be improved by properly controlling the rolling start temperature and the hot rolling reduction.

Regarding the reason, C and N are TiC, Ti
It is thought that the r value is affected in the form of carbonitrides such as N. However, the behavior of such carbonitrides on the formation of {111} recrystallized texture is different from the conventional ones. It was newly found that, although a smaller amount is better as in the case of TiN, it is better to leave a certain amount of TiN to obtain better results, contrary to the conventional method.
In particular, in the thin slab continuous casting process in which the total draft during hot rolling is lower than that in the ordinary continuous casting-hot rolling process, the hot rolling start temperature is set to 11 during hot rolling.
It has been newly discovered that the effect of increasing the precipitation of TiN and making the crystal grains of the hot-rolled sheet finer can be obtained by carrying out the rolling at a high temperature under 00 ° C. and under high pressure. .

The present invention is based on the above findings. That is, the present invention provides a method for producing C: 0.005 wt% or less,
i: 1.5 wt% or less, Mn: 1.5 wt% or less, P: 0.10 wt% or less, S: 0.020 wt% or less, Al: 0.10 wt% or less, O: 0.01
wt% or less and Cu as a playing card element:
0.02 to 1.5 wt%, Ni: 0.02 to 2.0 wt% unavoidably, Ti: 0.01 to 0.10 wt%, and N:
Molten steel adjusted to the range of 0.004 to 0.009 wt% with a thickness of 10
Continuous casting into a thin slab of ~ 80 mm, and then rolling the obtained thin slab after or once without cooling,
1100 ° C or less, total reduction: 50% or more, at least 1
An electric furnace-thin slab continuous casting process, characterized in that hot rolling is performed under various conditions of a pass reduction ratio of 35% or more and a rolling end temperature of 600 ° C or more, followed by winding at a temperature of 800 ° C or less. The method for producing a cold rolled steel sheet material for processing according to

In the present invention, Nb: 0.001 to 0.10 wt.
%, B: one or two of 0.0001 to 0.01 wt% can be contained, and after continuous casting, the temperature difference of the thin slab in the coil longitudinal direction is reduced to 30 ° C. or less, and then hot rolling is performed. It is more preferable to apply.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, experimental results on which the present invention is based will be described. Electric furnace-C: 0.002 wt%, Si: 0.02 wt%, Mn: 0.03 wt% by vacuum degassing process
%, P: 0.01 wt%, S: 0.010 wt%, Al: 0.03 wt%,
N: 0.002 to 0.013 wt%, Ti: 0.03 to 0.10 wt%, Cu: 0.8
A steel containing wt% and Ni: 1.0 wt%, and the balance substantially consisting of Fe was smelted. The obtained molten steel was formed into a thin slab having a thickness of 40 mm by a continuous thin slab casting method, and then hot-rolled under the conditions of a hot finishing temperature of 900 ° C. and a coil winding temperature of 540 ° C. to obtain a thickness of 3.5 mm. A hot rolled sheet was used. At this time, the hot rolling start temperature is 1100 ° C or less, and the rolling reduction of at least one pass is 35%.
Hot rolling was performed under two conditions: the above conditions and a condition in which the hot rolling start temperature was higher than 1100 ° C. and the one-pass rolling reduction was less than 35%. Next, the obtained hot-rolled steel sheet was cold-rolled at a reduction of 80%, and then subjected to recrystallization annealing at 830 ° C. for 20 seconds.

FIG. 1 shows the results of examining the tensile properties of the obtained cold rolled sheet. The r value was measured by preparing a JIS No. 5 tensile test piece from the center in the longitudinal direction of the coil, and measuring the rolling direction (L direction), the direction perpendicular to the rolling direction (C direction), and 45 ° with respect to the rolling direction. The average value in the direction (D direction) is given by r = (r _L
+ R _C + 2r _D ) / 4. As shown in the figure, the r value of the cold rolled sheet obtained by hot rolling and cold rolling the material manufactured by the electric furnace-thin slab continuous casting process is N
Rolling start temperature is 1100 depending strongly on the content and hot rolling conditions.
1.85 ° C. or less, at least a reduction rate of at least one pass is 35% or more, and N: 0.004 to 0.009 wt% or more.
Is obtained.

Here, it is considered that the effects of the N content and the hot rolling conditions on the r value are caused by the formation of carbonitrides such as TiC and TiN and the crystal grain size. That is, when hot rolling a thin slab, the total rolling reduction at the time of hot rolling is low, so that the crystal grains of the hot-rolled sheet are less likely to be finer than in a normal continuous casting-hot rolling process. In this regard, by setting the electric rolling steel containing an appropriate amount of tramp elements such as Cu and Ni to a hot rolling start temperature of 1100 ° C. or less and a rolling reduction of at least one pass of 35% or more, It is considered that since the grains are refined and carbonitrides such as TiC and TiN are coarsened, {111} recrystallization texture is developed after cold rolling and annealing, and the r value is increased.

Further, in the thin slab continuous casting process adopted in the present invention, after the thin slab casting, the temperature difference of the thin slab in the longitudinal direction of the coil is reduced to 30 ° C. or less by passing the thin slab through a tunnel furnace also functioning as heat insulation. Therefore, hot rolling can be performed. Therefore, the hot rolling temperature in the coil longitudinal direction can be made uniform, and the difference in r value in the coil longitudinal direction can be further reduced. It is considered that this effect appears remarkably in electric furnace steel containing a large amount of N. That is, in electric furnace steel containing tramp elements such as Cu and Ni, an appropriate amount of TiN is used as described above.
The presence in steel is advantageous for the formation of {111} recrystallized texture in the cold rolled sheet. Since the form and precipitation state of such TiN in steel vary depending on the hot rolling temperature, if the hot rolling temperature fluctuates in the longitudinal direction of the coil, the r-value changes through the formation behavior of {111} recrystallization texture. It fluctuates in the direction. Therefore,
Reducing the temperature difference in the coil longitudinal direction before hot rolling can be achieved by reducing the difference in r value in the coil longitudinal direction in the present invention using a card containing a large amount of N with a playing card element such as Cu or Ni. It is particularly advantageous for

Next, the reason why the composition of steel in the present invention is limited to the above range will be described. (C: 0.0050 wt% or less) C is an important component in the present invention, and its content must be 0.0050 wt% or less to secure an r value exceeding 1.85. C content is 0.
If the content exceeds 005 wt%, it is difficult to obtain excellent workability. A particularly preferred range is 0.0028 wt% or less. (Si: 1.5 wt% or less) Si has the effect of strengthening steel,
The required amount is added depending on the desired strength. However,
If the Si content exceeds 1.5 wt%, workability will deteriorate, so 1.
It was limited to 5 wt% or less. In addition, the preferable content in the high workability cold rolled steel sheet is 0.5 wt% or less, and 0.2 wt% or less is preferable for further deep drawability.

(Mn: 1.5 wt% or less) Like Si, Mn has the effect of strengthening steel and is added in a necessary amount depending on the desired strength. However, when the Mn content exceeds 1.5 wt%, workability is increased. Is limited to 1.5 wt% or less. In addition, the preferable content in the high workability cold rolled steel sheet is 1.0 wt% or less, and 0.2 wt% or less is more preferable for further deep drawing. Conventionally, addition of Mn was required to prevent hot brittleness due to S. However, in the present invention, since S in steel is precipitated and fixed as TiS, Mn is used only for the purpose of increasing the strength. Is added. Therefore, when further workability is required rather than high strength, it is advantageous to reduce the Mn content to 0.05 wt% or less. (P: 0.10 wt% or less) Since P also has the effect of strengthening steel, it is added in a necessary amount depending on the desired strength, but when the P content exceeds 0.10 wt%, workability and brittleness deteriorate. Because
It was limited to 0.10 wt% or less. In addition, the preferable content in the high workability cold rolled steel sheet is 0.06 wt% or less, and 0.02 wt% or less is more preferable for further deep drawability.

(S: 0.020 wt% or less) S causes red hot embrittlement and increases cracking when the content in steel increases. For this reason, conventionally, such hot embrittlement has been prevented by forming MnS as described above. However, in the present invention, most of S in steel is precipitated and fixed as TiS. Few. However, too large a content of S is still unfavorable, so the content was limited to 0.020 wt% or less. (Al: 0.10 wt% or less) Al contributes not only to deoxidation but also to improve the yield of carbonitride forming components.
Even if it is added in excess of 10 wt%, the effect reaches saturation and rather causes deterioration of workability, so it was limited to 0.10 wt% or less. (O: 0.01 wt% or less) The smaller the amount of O, the better the processability is improved. However, if the content of O is 0.01 wt% or less, there is no significant adverse effect, so the content is limited to 0.01 wt% or less.

(N: 0.004 to 0.009 wt%) N is a particularly important component in the present invention, and its content is 0.004 to 0.009 wt%.
It is important to limit the range to ~ 0.009 wt%. This is because, as described above, when steel contains Trump elements such as Cu and Ni, the effect of N on the r value is different from the conventional one, and the {111} recrystallization texture can be more effectively reduced. This is because the formation of TiN requires an appropriate amount of TiN. Therefore, N is contained in the above range, which is considerably larger than that of conventional working steel.

(Ti: 0.001 to 0.10%) Ti is an important component in the present invention, and is reduced by precipitating and fixing solid solution C and N in steel as carbonitride and working with solid solution C and N. This has the effect of preventing deterioration of the properties. Also, by leaving an appropriate amount of nitride, it effectively contributes to improvement of the r value.
However, if the Ti content is less than 0.001 wt%, the effect of the addition is poor. On the other hand, if the content exceeds 0.10 wt%, no further effect is obtained, and conversely, the workability is deteriorated.
It was limited to the range of 0.001 to 0.10 wt%. In order for Ti to form N, S and TiN, TiS in steel and to contribute to the formation of {111} recrystallized texture, which is advantageous for deep drawability, through the precipitates, the following formula is required. It is preferable to contain it in a satisfying range. Ti / 48− (N / 14 + S ^* / 32) ≧ C / 12 where S ^* = 32 (S / 32 −0.3 Mn / 55)

(Cu: 0.02 to 1.5 wt% or less) Cu is an element that is difficult to remove when recycling iron scrap, and has conventionally been regarded as an undesirable element from the viewpoint of workability. However, as described above, if the C and N contents in the steel are adjusted according to the present invention, the Cu content of 1.5 wt% or less does not significantly affect the workability, but rather effectively reduces the crystal grain size of the hot-rolled sheet. Contribute. Therefore, in the present invention, 1.
It was limited to 5 wt% or less. When iron scrap is reused, at least about 0.02 wt% of Cu is inevitably mixed. (Ni: 0.02 to 2.0 wt% or less) Ni, like Cu, is an element that is difficult to remove when recycling iron scrap, but when the content is 2.0 wt% or less, it does not significantly affect workability. However, 2.0 wt
% Or less. The lower limit of the unavoidable amount of Ni is about 0.02 wt%.

Although the essential components in the present invention have been described above, the present invention can be realized as long as the above components are contained, and does not deny the addition of other elements. That is, as long as it is a component normally added as a working steel, the addition of components other than those described above is permitted. For example, Nb and B are considered as such allowable components, and the preferable contents thereof are as follows. (Nb: 0.10 wt% or less) Nb is a component that effectively contributes to the miniaturization of the hot-rolled sheet. However, if the Nb content is too large, the workability is degraded.
It is preferably at most wt%. (B: 0.01 wt% or less) B is a component that effectively contributes to improvement of the secondary workability. However, if the B content is too large, the workability is deteriorated.
It is preferable that the content be 0.01 wt% or less.

The same applies to the trump element, and the following tramp elements are allowed to be mixed in addition to Cu and Ni. (Cr ≦ 1.0 wt%, Mo ≦ 0.5 wt%) Cr and Mo are respectively
Like Cu and Ni, the above range does not adversely affect the workability, but rather effectively contributes to the refinement of the crystal grains of the hot-rolled sheet. The lower limit of the inevitable mixing amount of Cr is 0.02 wt%, and that of Mo is about 0.005 wt%. (Sb ≦ 0.01wt%, Sn ≦ 0.1wt%, V ≦ 0.01wt%, Zn ≦ 0.
01 wt%, Co ≦ 0.1 wt%) Sb, Sn, V, Zn and Co do not adversely affect the workability within the above range, but rather provide a beautiful surface of hot-rolled and cold-rolled sheets. Effectively contributes to Although the reason for this is not clear, it is considered that trace elements are concentrated on the surface during hot rolling and winding.
In addition, in order to exhibit the above-mentioned effect, Sb: 0.0005-
0.01 wt%, Sn: 0.001 to 0.1 wt%, V: 0.0001 to 0.01 wt
%, Zn: 0.0005 to 0.01 wt%, Co: 0.0005 to 0.1 wt% is preferred.

In the present invention, steel having the above-mentioned composition is melted by an electric furnace and cast into a thin slab of 10 to 80 mm by a thin slab continuous casting process. By adopting the thin slab continuous casting process, the hot rough rolling equipment which is indispensable in the conventional process is not required, and a compact hot rolling equipment can be realized. The method for producing the thin slab and the casting speed are not particularly limited, and may be in accordance with conventionally known methods and conditions.

(Thin Slab Heat Insulation Step) In the present invention, the temperature difference in the longitudinal direction of the thin slab is reduced to 30 ° C. or less by passing the thin slab through a tunnel-type heat insulation furnace before hot rolling as necessary. And hot-rolled.
In the present invention, it is important to precipitate and fix the solute C and N as carbonitrides. By precipitating and fixing S in steel as TiS, not only the improvement of hot brittleness but also the improvement of workability can be achieved. However, providing the thin slab to a heat retaining furnace before hot rolling is advantageous for the formation of such carbonitrides and TiS. In order to form carbonitrides and TiS, it is advantageous to keep the temperature of the thin slab low, and the effect of the present invention can be effectively exhibited at 1300 ° C. or less. In order to further improve the workability, it is preferable to keep the heat retaining temperature at 1200 ° C. or lower. However, even if the heat retention temperature is lower than 800 ° C., the further workability is not improved, and conversely, there is a disadvantage that a rolling trouble occurs due to an increase in rolling addition during hot rolling. The lower limit is preferably 800 ° C. In addition, the length, atmosphere, etc. of the tunnel-type insulated furnace may be arbitrary.

(Hot Rolling Step) In order to refine the crystal grains of the hot rolled sheet by hot rolling and to coarsen the carbonitrides such as TiC and TiN, the rolling start temperature: 1100 ° C. or less,
Total reduction rate: 50% or more, and at least one pass reduction rate: 35% or more. The hot rolling temperature is
(FDT) is, Ar ₃ may be transformation point or more γ region or Ar ₃ following α gamut transformation point but, since the hot rolling finishing temperature leads to too low an increase in rolling load during hot rolling, FDT 600
C. or higher. (Take-up temperature) The coil take-up temperature after hot rolling is higher for higher carbon dioxide and TiS, which is advantageous for coarsening.
If the temperature is too high, problems such as the scale becoming too thick may occur. The material for a cold-rolled steel sheet for processing thus obtained is then subjected to cold rolling to obtain a cold-rolled steel sheet. The hot rolled sheet can be used as it is as a hot rolled sheet for processing.

(Cold Rolling Step) This step is necessary to obtain a high r value, and for that purpose, the cold rolling reduction: 50%
It is necessary to do above. This is because if the rolling reduction is less than 50%, excellent deep drawability cannot be obtained. (Annealing Step) The cold-rolled steel sheet that has undergone the cold rolling step needs to be subjected to recrystallization annealing. The annealing method may be any of a box annealing method and a continuous annealing method. Annealing temperature is over 600 ℃,
Annealing time should be within 5 seconds. If the annealing temperature is less than 600 ° C. or the annealing time is less than 5 seconds, recrystallization is not completed, and therefore, excellent deep drawability cannot be obtained. In order to secure further deep drawability, annealing at 800 ° C. or more for 5 seconds or more is preferable.

The steel strip after annealing may be subjected to a temper rolling of 10% or less for shape correction, adjustment of surface roughness and the like.
The cold-rolled steel sheet obtained by the present invention can be used not only as a cold-rolled steel sheet for processing but also as an original sheet of a surface-treated steel sheet for processing. Examples of the surface treatment include zinc plating (including alloys), tin plating, and enamel. Further, the steel sheet of the present invention may be subjected to a special treatment after annealing or galvanization to improve the chemical conversion property, weldability, press formability, corrosion resistance and the like.

[0033]

[Example] Iron scrap is appropriately blended into raw materials, and the capacity is as follows:
100 t, Transformer: 100 MVA, Electrode: After melting the molten steel using an electric furnace of 28 inches, the molten steel was transferred to a ladle (tapping temperature: 1630 ° C), and then RH degassing furnace (0.1 tor
While performing the vacuum degassing treatment in r), the alloy components were added to adjust the component compositions shown in Table 1.

[0034]

[Table 1]

The molten steel thus obtained was formed into a thin slab having a thickness of 40 mm by continuous casting, and then passed through a tunnel-type insulated furnace (furnace temperature: 1000 ° C., furnace length: 100 m). Hot rolling (FET: Hot rolling start temperature, FDT: Hot rolling end temperature, R: Maximum rolling reduction, CT: Coil winding temperature, ΔFET
: Variation in hot-rolling start temperature, ΔFDT: variation in hot-rolling end temperature) to obtain a hot-rolled sheet having a thickness of 3.5 mm. In addition, about some thin slabs, the tunnel-type insulated furnace was turned off and hot rolling was performed substantially without using the tunnel-type insulated furnace. Next, hot rolling and recrystallization annealing or hot dip galvanizing were performed under the conditions shown in Table 2 to obtain a sheet thickness of 0.8
mm cold-rolled sheet and hot-dip galvanized sheet.

[0036]

[Table 2]

The results of examination of the mechanical properties of the thus obtained cold-rolled sheet and hot-dip galvanized sheet are also shown in Table 2. The tensile test uses a JIS No. 5 tensile test piece,
It was measured at the center of the coil. The r value is measured by a three-point method after 15% tensile prestrain is applied, and the rolling direction (L direction), the direction perpendicular to the rolling direction (C direction), and the rolling direction
The average value in the 45 ° direction (D direction) is represented by r = (r _L + 2r _D + r
_C ) / 4. In addition, the r values of the coil front and rear ends were also measured, and the difference (r _max -r _min ) was also determined.
From Table 2, Examples 1, 2, 3, 5, 7, and 8 are cold-rolled steel sheets and hot-dip galvanized steel sheets manufactured within the condition range of the present invention, and show high r values of 1.85 or more. Among them, Examples 1, 2, 3, 5, and 8 show uniform characteristics in the coil longitudinal direction. On the other hand, in Example 6, since the hot rolling start temperature was 1100 ° C. or higher, the r value was low. In Examples 9, 10, and 11, the r value was low because the steel composition was out of the condition range of the present invention.

As is clear from the above results, the cold rolled sheet and the hot-dip galvanized sheet manufactured within the scope of the present invention have excellent workability as compared with the comparative example, and furthermore, before hot rolling. When the temperature difference in the longitudinal direction of the thin slab is reduced in the heat retaining furnace, the characteristics are uniform in the coil longitudinal direction.

[0039]

As described above, according to the present invention, in the steel component,
In particular, while limiting the amount of N to a predetermined range, a predetermined amount of Ti
To obtain a cold-rolled steel sheet for processing having the same excellent workability as before, even when using electric furnace steel containing a playing card element and further manufacturing by a thin slab continuous casting process. Can be. Further, in the present invention, since the electric furnace steelmaking method and the thin slab continuous casting process are used, not only the reuse of iron scrap can be expanded, but also the equipment cost can be reduced and the manufacturing cost can be reduced.
Further, in the present invention, after continuous casting, the temperature difference of the thin slab in the coil longitudinal direction is reduced to 30 ° C. or less, and then hot rolling is performed. You can get a rolled steel sheet.

[Brief description of the drawings]

FIG. 1 is a diagram showing the influence of N content and hot rolling conditions on r value.

Continued on the front page (72) Inventor Takashi Sakata 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Corporation (72) Inventor Osamu Furukun 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Technology Laboratory Co., Ltd.

Claims (3)

[Claims] C: 0.005 wt% or less, Si: 1.5 wt% or less, Mn: 1.5 wt% or less, P: 0.10 wt% or less, S: 0.020 wt% or less, Al: 0.10 wt% or less, O: 0.01 wt% or less, and inevitably contain Cu: 0.02 to 1.5 wt%, Ni: 0.02 to 2.0 wt% as a playing card element, Ti: 0.01 to 0.10 wt%, and N: 0.004 to 0.009 The molten steel adjusted to the range of wt% is continuously cast into a thin slab with a sheet thickness of 10 to 80 mm, and then the obtained thin slab is cooled once or without cooling, and the rolling start temperature: 1100 ° C or less, total reduction Rate: 50% or more, reduction rate of at least one pass: 35%
Rolling end temperature: 600 ° C or higher, after hot rolling, then winding at a temperature of 800 ° C or lower, for cold rolled steel sheets for processing by electric furnace-thin slab continuous casting process. Material manufacturing method. 2. The electric furnace-thin slab continuous casting process according to claim 1, wherein one or two of Nb: 0.001 to 0.10 wt% and B: 0.0001 to 0.01 wt% are contained. Of cold rolled steel sheet material for processing. 3. The continuous casting of an electric furnace and a thin slab according to claim 1, wherein after the continuous casting, hot rolling is performed after the temperature difference of the thin slab in the coil longitudinal direction is reduced to 30 ° C. or less. Manufacturing method of cold rolled steel material for processing by process.