JPH1025540A - Cold rolled steel sheet for deep drawing, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve deep drawability even in the case of electric furnace steelmaking which unavoidably causes a contamination with tramp elements, by limiting the amounts of constituent elements to values in prescribed ranges, respectively. SOLUTION: The elements, which are specially noteworthy among the constituent elements, are as follows: C is important to obtain an excellent r-value of >=2.3 under proper amounts of Cu and Ni, and its content is regulated to <=0.0050wt.%; N, in the amount limited to 0.0040-0.0090wt.%, makes proper amounts of TiN present; Ti has a function of precipitating and fixing solid- solution C and N in steel in the form of carbonitride to prevent deterioration in deep drawability and further improving r-value, and its content is regulated to 0.014-0.10wt.%; and Cu and Ni are the elements (trap elements) difficult to remove at the time of reclamation of iron scrap and are undesirable in terms of deep drawability, but their existence in proper amounts are effective in refining the crystalline grains of hot rolled steel plate, so Cu and Ni are incorporated by <=0.96wt.% and <=0.88wt.%, respectively, in the range satisfying 0.0015<=Cu/64+Ni/59<=0.0150.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-rolled steel sheet for deep drawing and a method for producing the same, and more particularly to a method for producing a cold-rolled steel sheet which is excellent even in the case of using an electric furnace steelmaking method in which Trump elements such as Cu and Ni are inevitable. It is intended to stably obtain a cold-rolled steel sheet having deep drawability.

[0002]

2. Description of the Related Art In recent years, electric furnaces have been constructed worldwide.
It contributes to the production of steel bars. 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 the electric furnace material, the incorporation of an impurity element called a trump element is inevitable, and the mechanical properties are limited or the internal quality and surface quality are deteriorated due to the tramp element. It is not applied to so-called high-grade thin steel sheets typified by steel sheets, and its use is currently limited to general-purpose products even in the field of thin sheets. Therefore, the field of high-grade steel sheets is still the dominant blast furnace-converter process.

[0003] At present, not only in Japan, but also from worldwide market needs, there is an aspiration for the development of a technology capable of producing many types of steel materials including high-grade steel with less investment. However, as described above, if the production process of high-grade steel must be a blast furnace-converter process, a large investment is required for the construction of the equipment. In this regard, if the production of high-grade steel becomes possible with compact facilities such as electric furnaces,
The effect is immense.

[0004] Conventionally, various proposals have been made for the above-described high-grade thin steel sheet manufacturing technology (for example, Japanese Patent Publication No. 44-18066, Japanese Patent Publication No. 53-12889, and Japanese Patent Publication No. No. 56301), however, all of these technologies aim to reduce C and N as much as possible, and do not include any Trump elements such as Cu and Ni which are unavoidable when steel scrap is reused. No consideration has been given. Here, when an electric furnace or the like is used to reuse iron scrap, N in steel is 0.0040 wt%.
This is a higher level. Trump elements such as Cu and Ni contained in iron scrap are difficult to remove during refining and remain in steel. For this reason,
In order to produce hot-rolled steel sheets, cold-rolled steel sheets and surface-treated steel sheets with excellent workability and beautiful surface, hot metal is used as a raw material,
A method of reducing C and N as much as possible by taking a process of a converter, vacuum degassing, hot rolling and cold rolling, and further suppressing the mixing of a playing card element has been adopted.

However, on the other hand, there have been proposed some 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 including 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-ageing and excellent in cold press workability even with a high N content steel.
However, since the cold-rolled steel sheet contains a large amount of C of 0.0050 wt% or more, the cold-rolled steel sheet contains a relatively large amount of a tramp element as in the present invention (for example, the present invention steel # D-2). , # D-5) has an r of about 1.60 to 1.78.
Value, and cannot be said to have sufficient deep drawability. Japanese Patent Application Laid-Open No. 4-371528 proposes a technique for producing a cold-rolled steel sheet for deep drawing. However, the actual N content of the steel is 0.0025 wt% or less and the steel is contained in electric furnace steel. It only deals with steel with a lower level than the N content present, and the r-value of the resulting cold rolled steel sheet is less than 1.85,
It is hard to say that it has sufficient deep drawability. Furthermore, Japanese Patent Application Laid-Open No. 7-118795 proposes a technology for manufacturing a cold-rolled steel sheet having excellent workability, but has a substantial C content of 0.03.
Since it is as high as wt% or more, the obtained r value is also 1.83 or less,
After all, it is hard 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.
% Or more, it is difficult to expect sufficient workability. As described above, several techniques have been proposed to produce hot-rolled steel sheets, cold-rolled steel sheets, and surface-treated steel sheets with excellent workability from electric furnace steel including tramplement, but all of them have been proposed. It is hard to say that it has excellent workability, and its improvement has been strongly desired.

[0006]

DISCLOSURE OF THE INVENTION The present invention advantageously meets the above-mentioned demands. Even when an electric furnace steelmaking method in which mixing of trump elements is inevitable is used, the r value is reduced.
An object of the present invention is to propose a cold-rolled steel sheet having excellent deep drawability of 2.3 or more together with its advantageous production method.

[0007]

Means for Solving the Problems Now, the inventors of the present invention have conducted intensive studies in order to achieve the above object, and have found that Cu
It has been found that the effect of C and N on the r value is significantly different from the case of a conventional clean steel not containing such a trump element when a trump element such as Ni or Ni is contained. That is, C and N are considered to affect the r-value in the form of carbonitrides such as TiC and TiN. However, the behavior of carbonitrides on the formation of {111} recrystallized texture is conventionally known. Unlike the conventional case, it is better to have a small amount of TiC, but it has been newly found that, in the case of TiN, a good result can be obtained by leaving a certain amount of TiN, contrary to the conventional case.

[0008] In addition, the card elements Cu and Ni
It has also been found that by restricting the content of Nb to a predetermined range, the deep drawability can be further improved. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. C: 0.0050 wt% or less, Si: 0.2 wt% or less, Mn: 0.
5 wt% or less, P: 0.10 wt% or less, Al: 0.10 wt% or less,
S: 0.020 wt% or less, O: 0.010 wt% or less, N: 0.0040
0.0090 wt%, Ti: 0.014 to 0.10 wt%, Ti / 48− (N / 14 + S ^* / 32) ≧ C / 12 (where S ^* = 32
(S / 32 −0.3Mn / 55)) and Cu and Ni mixed as a trump element in a content of 0.96 wt% or less, Ni:
Cold-rolled steel sheet for deep drawing, characterized in that the content is suppressed to 0.88 wt% or less and 0.0015 ≦ Cu / 64 + Ni / 59 ≦ 0.0150.

[0010] 2. In the above item 1, the steel composition further comprises Nb:
A deep-drawn cold-rolled steel sheet having a composition containing one or two selected from 0.001 to 0.10 wt% and B: 0.0001 to 0.010 wt%.

3. When producing cold-rolled steel sheets for deep drawing by electric furnace-vacuum degassing process using iron scrap alone or iron scrap partially containing pig iron as a main raw material, in an electric furnace and a vacuum degassing furnace, the steel composition is C: 0.0050
wt% or less, Si: 0.2 wt% or less, Mn: 0.5 wt% or less, P:
0.10 wt% or less, Al: 0.10 wt% or less, S: 0.020 wt% or less, O: 0.010 wt% or less, N: 0.0040 to 0.0090 wt%, T
i: 0.014 to 0.10 wt%, Cu: 0.96 wt% or less, Ni: 0.88 wt
%, And Ti / 48− (N / 14 + S ^* / 32) ≧ C / 12 (where S ^* = 32
(S / 32 −0.3Mn / 55)) After adjusting the composition to satisfy 0.0015 ≦ Cu / 64 + Ni / 59 ≦ 0.0150, continuous casting was performed, and the obtained steel slab was heated to 900-1300 ° C. Reduction rate:
After hot rolling under the condition of 70% or more and rolling end temperature: 600 ° C or more, winding at a temperature of 800 ° C or less, then cold rolling at a draft of 50% or more, and then a temperature of 600 ° C or more A method for producing a cold-rolled steel sheet for deep drawing by an electric furnace-vacuum degassing process, wherein annealing is performed for 5 seconds or more at a time.

4. In the above item 3, the steel composition further contains Nb:
An electric furnace having a composition containing one or two selected from 0.001 to 0.10 wt% and B: 0.0001 to 0.010 wt%.
Manufacturing method of cold-rolled steel sheet for deep drawing by vacuum degassing process.

5. In 3 or 4, the method for producing a cold-rolled steel sheet for deep drawing by an electric furnace-vacuum degassing process, wherein the heating temperature of the steel slab is 900 to 1150 ° C.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, experimental results on which the present invention is based will be described. C: 0.0010-0.0130wt%, S
i: 0.02 wt%, Mn: 0.13 wt%, P: 0.01 wt%, S: 0.010
wt%, Al: 0.03 wt%, N: 0.0020 to 0.0130 wt%, Ti:
A sheet bar containing 0.03 to 0.10 wt%, Cu: 0.8 wt%, Ni: 1.0 wt% and O: 0.0020 to 0.0050 wt%, with the balance being substantially Fe, heated to 1050 ° C. After 890
After hot rolling at a finishing temperature of 90 ° C. and a total draft of 90%, it was wound at 600 ° C. on a coil and kept for 1 hour (air cooling). Then, after cold rolling at a draft of 80%, 8
Recrystallization annealing was performed at 30 ° C for 20 seconds. FIG. 1 shows the results of examining the effect of the C and N contents on the r value of the thus obtained cold rolled sheet. The r value was measured using a JIS No. 5 tensile test piece, and the average value in the rolling direction (L direction), a direction perpendicular to the rolling direction (C direction), and a direction at 45 ° to the rolling direction (D direction) was r = (R _L + 2r _D + r _C ) / 4.

As shown in the figure, the r-value of the cold-rolled sheet strongly depends on the amounts of C and N, C ≦ 0.0050 wt% and N: 0.00
By setting the content to 40 to 0.0090 wt%, a high r exceeding 1.85 is obtained.
The value was obtained. Here, it is considered that the influence of the C and N contents on the r value is caused by the formation of carbonitrides such as TiC and TiN. That is, in the steel containing Trump elements such as Cu and Ni, the behavior of the carbonitride on the {111} recrystallization texture formation of the cold-rolled sheet is different from that of the clean steel not containing the Trump elements, It was found that a smaller amount of TiC is better, but an appropriate amount of TiN, which is present in the steel, is more advantageous for {111} recrystallization texture formation. And this effect is obtained when the C content is 0.0050.
It is particularly advantageous when the content of N is not more than wt% and the N content is in the range of 0.0040 to 0.0090 wt%.

Next, C: 0.0025 wt%, Si: 0.02 wt%, M
n: 0.13 wt%, P: 0.01 wt%, S: 0.010 wt%, Al: 0.0
3wt%, N: 0.0050wt%, Ti: 0.05wt%, Cu: 0-3wt%
%, Ni: 0 to 3 wt%, O: 0.0020 to 0.0050 wt%, and the balance being 1250
Heat to ℃-after soaking, the total reduction rate is 90 at the finishing temperature of 890 ℃
% Hot rolled, wound up in a coil at 600 ° C., and kept for 1 hour (air cooling). Next, after cold rolling was performed at a rolling reduction of 80%, recrystallization annealing was performed at 830 ° C. for 20 seconds. FIG. 2 shows the results of examining the effect of the Cu and Ni contents on the r-value of the thus obtained cold rolled sheet.

As shown in the figure, the r value of the cold rolled sheet is Cu
And Ni content, these contents are 0.0015 ≦
By restricting Cu / 64 + Ni / 59 ≤ 0.015,
A high r value of 2.3 or more was obtained. Where Cu and N
The reason that the r value is improved by regulating the i content to a predetermined range is considered to be due to the effect of refining the crystal grains of the hot-rolled sheet. That is, in steel containing an appropriate amount of Trump elements such as Cu and Ni, the crystal grains of the hot-rolled sheet are refined, and as a result, {111} recrystallized texture develops after cold rolling and hot annealing, and the high r value Is considered to have been obtained. However, if the amounts of Cu and Ni are too large, it is thought that the r-value is degraded because the bad influence of Cu and Ni in the solid solution state becomes larger rather than the effect of crystal grain refinement of the hot-rolled sheet. In addition, the effect of such crystal refinement by Cu and Ni is particularly effective when the C content is 0.005 wt% or less.
And when the N content is in the range of 0.0040 to 0.0090 wt%, it is very advantageously exerted.

Hereinafter, the reason why the composition of steel is limited to the above range in the present invention will be described. C: 0.0050 wt% or less C is an important component in the present invention. In order to secure an excellent r value of 2.3 or more under an appropriate (Cu + Ni) amount described below, the content is 0.0050 wt% or less. It is necessary to

Si: 0.2 wt% or less Si has an effect of strengthening steel, and is added in a necessary amount according to a desired strength. However, if the content exceeds 0.2 wt%, the deep drawability deteriorates, so the content was limited to 0.2 wt% or less.

Mn: 0.5 wt% or less Mn has the effect of strengthening steel, like Si, and is added in a necessary amount depending on the desired strength. However, when the content exceeds 0.5 wt%, deep drawability deteriorates. Therefore, it was limited to 0.5 wt% or less. Conventionally, a relatively large amount of Mn must be added to prevent hot embrittlement due to S. However, in the present invention, S in steel is Ti
Since S is also precipitated and fixed, it is not necessary to particularly consider the addition of Mn at this point.

P: 0.10 wt% or less P also has an effect of strengthening steel, so that a necessary amount is added depending on the desired strength. However, if the content exceeds 0.10 wt%, workability and brittleness deteriorate. Therefore, it was limited to 0.10 wt% or less.

S: not more than 0.020 wt% 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, but in the present invention, most of S in steel is precipitated and fixed as TiS. 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 elements, but the effect is saturated even if added in excess of 0.10 wt%. , Which leads to deterioration of workability. Therefore, the content is limited to 0.10 wt% or less.

O: 0.010 wt% or less O is preferable because the smaller the amount of O, the better the workability. However, if the content of O is 0.010 wt% or less, there is no significant adverse effect, so the O content is limited to 0.010 wt% or less.

N: 0.0040 to 0.0090 wt% N is a particularly important component in the present invention, and it is important to limit its content to the range of 0.0040 to 0.0090 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, in order to form TiN, it is essential that a proper amount of TiN be present. Therefore, N is contained in the above range, which is considerably larger than that of conventional working steel.

Ti: 0.014% to 0.10% Ti is an important element in the present invention, and is reduced by precipitating and fixing solid solution C and N in steel as carbonitride.
This has the effect of preventing the deterioration of deep drawability due to N. Also,
By leaving an appropriate amount of nitride, it effectively contributes to improvement of the r value. However, if the content is less than 0.014 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 deep drawability is deteriorated. Limited to the wt% range. In order for Ti to form N, S and TiN, TiS in steel and to contribute to the formation of {111} recrystallization texture, which is advantageous for deep drawability, through the precipitates, the following formula is required. It is essential that the content be contained within a satisfactory range. Ti / 48− (N / 14 + S ^* / 32) ≧ C / 12 where S ^* = 32 (S / 32−0.3 Mn / 55) When S / 32−0.3 Mn / 55 <0, S ^* = 0.

Cu: 0.96 wt% or less Cu is an element that is difficult to remove when reusing iron scrap, and has conventionally been regarded as an undesirable element from the viewpoint of deep drawability. However, as described above, if the C and N contents in steel are adjusted according to the present invention, the content becomes 0.96 wt.
% Or less does not significantly affect the deep drawability, but rather effectively contributes to the refinement of the crystal grains of the hot-rolled sheet. Therefore, in the present invention, the content is limited to 0.96 wt% or less. When iron scrap is reused, at least about 0.02 wt% of Cu is inevitably mixed.

Ni: 0.88% by weight or less Ni, like Cu, is an element that is difficult to remove when recycling iron scrap. However, if the content is 0.88% by weight or less, it does not significantly affect deep drawability. However, since it is more effective in refining the crystal grains of the hot-rolled sheet, the content is limited to 0.88 wt% or less. The lower limit of the unavoidable amount of Ni is about 0.02 wt%.

0.0015 ≦ Cu / 64 + Ni / 59 ≦ 0.0150 Cu and Ni, when present in an appropriate amount, effectively contribute to the refinement of the crystal grains of the hot-rolled sheet.
It must be 0.0015 or more in terms of (Cu / 64 + Ni / 59). However, the content of (Cu / 64 + Ni / 59)> 0.0150 is
Conversely, since Cu and Ni in the solid solution state have an adverse effect, the content of Cu and Ni should be contained in a range satisfying 0.0015 ≦ Cu / 64 + Ni / 59 ≦ 0.0150. By controlling the Cu and Ni contents in this range, a high r value of r ≧ 2.3 can be obtained.

Although the essential components in the present invention have been described above, the present invention is only valid 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 elements other than those described above is permitted. For example, Nb or B can be considered as such an acceptable component, and its preferable content is as follows.

Nb: 0.001 to 0.10 wt% Nb contributes not only to the formation of carbides but also to the refinement of the crystal grains of the hot-rolled sheet. However, the content is 0.001wt%
If it is less than 0.10 wt%, no further effect can be obtained, and if it is added, the deep drawability deteriorates. Is preferred.

B: 0.0001 to 0.010 wt% B is an element that effectively contributes to improvement of the brittleness resistance in secondary working. However, if the content is less than 0.0001 wt%, there is no effect of addition, while if it exceeds 0.010 wt%, the deep drawability is deteriorated.
It is preferably set to wt%.

The same applies to the playing card element. The following playing card elements can be mixed in addition to Cu and Ni. Cr ≦ 1.0 wt%, Mo ≦ 0.5 wt% Each of Cr and Mo, like Cu and Ni, does not adversely affect the workability in the above range, 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.
It is about 02 wt% and that of Mo is about 0.005 wt%.

Sb ≦ 0.01 wt%, Sn ≦ 0.1 wt%, V ≦ 0.01 wt
%, Zn ≦ 0.01 wt%, Co ≦ 0.1 wt% Each of Sb, Sn, V, Zn and Co does not adversely affect the workability within the above range, but rather is a hot rolled sheet and a cold rolled sheet. Effectively contributes to the beauty of the surface. 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 order to exert the above effects, Sb: 0.0005 to 0.01 wt%, Sn: 0.00
1 to 0.1 wt%, V: 0.0001 to 0.01 wt%, Zn: 0.0005 to 0.
It is preferable to add 01 wt% and Co: 0.0005 to 0.1 wt%.

Next, a manufacturing method according to the present invention will be described. In the present invention, first, in an electric furnace, a mother melt is melted using iron scrap as a main raw material. At this time, pig iron can be used if necessary. Here, pig iron refers to hot metal obtained from the blast furnace method and its cold material (sea cucumber), as well as the COREX method,
It refers to hot metal, cold material, HBI (hot briquette iron), etc. obtained from the DIOS method. When such pig iron is used in combination, the ratio must be suppressed to 80 wt% or less. If the usage ratio exceeds 80 wt%, a large amount of oxygen is required to decarburize the carbon in pig iron, and it takes a long time to melt, which is not economical and bumping during operation This is because it easily occurs.

Next, in the vacuum degassing process, the alloying elements are added while degassing, and the components are adjusted so that the final composition is in a desired composition range. The molten steel whose composition has been adjusted to the desired composition is made into a thin steel sheet by the following steps. Casting Step The casting method is not particularly limited, but continuous casting is advantageous in terms of production efficiency.

Slab Heating Step The slab heating step is important in the present invention, and it is necessary to precipitate and fix the solute C and N as carbonitrides and coarsen the precipitates. Furthermore, by precipitating and fixing S in steel as TiS, it contributes not only to improvement in hot brittleness but also to improvement in workability. Here, in order to form and coarsen the carbonitride and TiS, it is advantageous that the slab heating temperature is low, and the effect of the present invention can be effectively exhibited at 1300 ° C. or less. In order to further improve workability, the temperature is preferably set to 1150 ° C. or lower. This is because if the slab heating temperature is higher than 1150 ° C, the precipitates are unlikely to become coarse, and the Trump elements such as Cu and Ni in the steel cause poor grain growth during cold rolling and annealing, so that This is because it is difficult to obtain a high El.

C: 0.0025 wt%, Si: 0.02 wt%, Mn: 0.13
wt%, P: 0.01wt%, S: 0.010wt%, Al: 0.03wt%,
N: 0.0050 wt%, Ti: 0.05 wt%, Cu: 0.3 wt%, Ni: 0.
2 wt%, Cu / 64 + Ni / 59 = 0.0081, O: 0.0020-0.0050
A sheet bar containing wt% and the balance substantially consisting of Fe was heated and soaked at 950 to 1250 ° C, and then subjected to hot rolling at a finishing temperature of 890 ° C and a total draft of 90%. Thereafter, the coil was wound at 600 ° C. and kept for 1 hour (air cooling). Then, after cold rolling was performed at a rolling reduction of 80%, recrystallization annealing was performed at 830 ° C. for 20 seconds. The result of examining the effect of the slab heating temperature on the El of the cold-rolled sheet thus obtained is shown in FIG.

As shown in the figure, the El of the cold-rolled sheet strongly depends on the slab heating temperature. By setting the slab heating temperature to 1150 ° C. or less, a high El of 54% or more was obtained. Here, it is considered that the influence of the slab heating temperature on El is caused by precipitates of the hot-rolled sheet. In other words, in steel containing an appropriate amount of Trump elements such as Cu and Ni, although the crystal grains of the hot-rolled sheet are refined, the precipitates are coarsened by low-temperature slab heating at 1150 ° C or less, which causes It is considered that a high El value was obtained because the grain growth was improved. This effect is achieved when the C content is 0.00
5 wt% or less, and the N content is 0.0040 to 0.0090 wt%,
Moreover, it is extremely advantageous when the range of 0.0015 ≦ Cu / 64 + Ni / 59 ≦ 0.0150 is satisfied.

However, even if the slab heating temperature is lower than 900 ° C., the workability is not further improved, and conversely, there is a disadvantage that a rolling trouble occurs due to an increase in the rolling load during hot rolling. The lower limit of the heating temperature was set at 900 ° C.

Hot Rolling Step In order to make the crystal grains of the hot-rolled sheet finer by hot rolling, the total draft during hot rolling must be 70% or more. The hot rolling finishing temperature (FDT) is A
The γ region above the r ₃ transformation point or the α region below the Ar ₃ transformation point may be used, but if the hot rolling finish temperature is too low, the rolling load during hot rolling will increase, so the FDT was limited to 600 ° C. or more. .

Winding Step The higher the coil winding temperature after hot rolling, the more advantageous the above-mentioned carbonitride and TiS coarsening is. However, if the coil winding temperature is too high, problems such as the scale becoming too thick occur. 800 ° C
Limited to the following.

Cold Rolling Step This step is necessary in order to obtain a high r value, and for that purpose, it is necessary to make the cold rolling reduction ratio: 50% or more. 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 must be subjected to recrystallization annealing. The annealing method may be any of a box annealing method and a continuous annealing method. Annealing temperature is 600 ° C or more and annealing time is 5 seconds or more. This is because if the annealing temperature is less than 600 ° C. or the annealing time is less than 5 seconds, recrystallization is not completed, so that 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 annealed steel strip may be subjected to a temper rolling of about 10% or less for shape correction and adjustment of surface roughness and the like. The cold-rolled steel sheet obtained by the present invention can be applied 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. The steel sheet of the present invention may be subjected to a special treatment after annealing or galvanization to improve the chemical conversion treatment property, weldability, press formability, corrosion resistance, and the like.

[0046]

【Example】

Example 1 Using scrap as a main raw material, molten steel having a component composition shown in Table 1 was produced by an electric furnace-vacuum degassing process.
After continuous casting of the obtained molten steel, it was hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled sheet having a thickness of 3.5 mm, and then cold-rolled under the same conditions shown in Table 2 to obtain a sheet having a thickness of 0.8 mm. After cold-rolled,
Some of them were subjected to recrystallization annealing in a continuous annealing line under the conditions shown in Table 2. A part of the cold-rolled sheet was led to a hot-dip galvanizing line and subjected to recrystallization annealing and plating under the conditions shown in Table 3. The results of examining the mechanical properties of the cold-rolled steel sheet and hot-dip galvanized steel sheet thus obtained are also shown in Tables 2 and 3. The tensile properties are JIS 5
It measured using the No. tensile test piece. The r value is measured by the 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 45 ° direction to the rolling direction (D direction) ) Was determined as r = (r _L + 2r _D + r _C ) / 4.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

As is clear from Tables 2 and 3, both the cold-rolled steel sheet and the hot-dip galvanized steel sheet produced according to the present invention had better deep drawability than the comparative examples.

Example 2 In the same manner, Table 4 was obtained by an electric furnace-vacuum degassing process.
Molten steel having the composition shown in Table 1 was produced. After continuous casting of the obtained molten steel, it was hot-rolled under the conditions shown in Table 5 to obtain a sheet thickness of 3.5.
mm hot-rolled sheet, and then cold-rolled under the same conditions as shown in Table 5 to obtain a 0.8 mm-thick cold-rolled sheet, and then partially recrystallized on a continuous annealing line under the conditions shown in Table 5. Annealing was performed, and the remainder was led to a hot-dip galvanizing line and subjected to recrystallization annealing and plating under the conditions shown in Table 6. The results of examining the mechanical properties of the cold-rolled steel sheet and the hot-dip galvanized sheet thus obtained are also shown in Tables 5 and 6.

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

[Table 6]

As is clear from Tables 5 and 6, both the cold-rolled steel sheet and the hot-dip galvanized steel sheet produced according to the present invention had better deep drawability than the comparative examples. In particular, when the slab heating temperature was 1150 ° C. or lower, an excellent El value could be obtained together.

[0056]

As described above, according to the present invention, the amount of C and N in the steel component is limited to a predetermined range, an appropriate amount of Ti is added, and the C is a tramp element.
By limiting the contents of u and Ni to a predetermined range, it is possible to obtain a cold-rolled steel sheet having the same excellent deep drawability as before even when using electric furnace steel containing a tramp element. it can. Further, in the method of the present invention, since the electric furnace steel method is used, not only the reuse of iron scrap can be expanded, but also the facility cost and the production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of C and N contents on r value.

FIG. 2 is a graph showing the influence of Cu and Ni contents on the r value.

FIG. 3 is a graph showing the effect of slab heating temperature on El.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Osamu Furukun 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Pref. Kawasaki Steel Research Institute Co., Ltd. No address) Inside the Kawasaki Steel Works, Mizushima Works

Claims (5)

[Claims] C: 0.0050 wt% or less, Si: 0.2 wt% or less, Mn: 0.5 wt% or less, P: 0.10 wt% or less, Al: 0.10 wt% or less, S: 0.020 wt% or less, O: 0.010 wt% or less, N: 0.0040 to 0.0090 wt%, Ti: 0.014 to 0.10 wt%, Ti / 48− (N / 14 + S ^* / 32) ≧ C / 12 (where S ^* = 32
(S / 32 -0.3Mn / 55)) and Cu and Ni mixed as a playing card element: Cu: 0.96 wt% or less, Ni: 0.88 wt% or less, 0.0015 ≦ Cu / 64 + Ni / A cold-rolled steel sheet for deep drawing, characterized in that it is controlled within the range of 59 ≦ 0.0150. 2. The cold-rolling for deep drawing according to claim 1, wherein the steel composition further comprises one or two selected from Nb: 0.001 to 0.10 wt% and B: 0.0001 to 0.010 wt%. steel sheet. When producing cold-rolled steel sheets for deep drawing by an electric furnace-vacuum degassing process using iron scrap alone or iron scrap partially containing pig iron as a main raw material, in an electric furnace and a vacuum degassing furnace, Steel composition: C: 0.0050 wt% or less, Si: 0.2 wt% or less, Mn: 0.5 wt% or less, P: 0.10 wt% or less, Al: 0.10 wt% or less, S: 0.020 wt% or less, O: 0.010 wt% In the following, N: 0.0040 to 0.0090 wt%, Ti: 0.014 to 0.10 wt%, Cu: 0.96 wt% or less, Ni: 0.88 wt% or less, and Ti / 48− (N / 14 + S ^* / 32) ≧ C / 12 (however, S ^* = 32
(S / 32 −0.3Mn / 55)) After adjusting the composition to satisfy 0.0015 ≦ Cu / 64 + Ni / 59 ≦ 0.0150, continuous casting was performed, and the obtained steel slab was heated to 900-1300 ° C. Reduction rate:
After hot rolling under the condition of 70% or more and rolling end temperature: 600 ° C or more, winding at a temperature of 800 ° C or less, then cold rolling at a draft of 50% or more, and then a temperature of 600 ° C or more A method for producing a cold-rolled steel sheet for deep drawing by an electric furnace-vacuum degassing process, wherein annealing is performed for 5 seconds or more at a time. 4. The electric furnace-vacuum according to claim 3, wherein the steel composition further comprises one or two selected from Nb: 0.001 to 0.10 wt% and B: 0.0001 to 0.010 wt%. Manufacturing method of cold-rolled steel sheet for deep drawing by degassing process. 5. The method for producing a cold-rolled steel sheet for deep drawing by an electric furnace-vacuum degassing process according to claim 3, wherein a heating temperature of the steel slab is 900 to 1150 ° C.