JP3291639B2 - Cold rolled steel sheet excellent in workability uniformity and method for producing the same - Google Patents

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, a hot-dip galvanized steel sheet and a method for producing the same, which have extremely small workability variations in a coil. is there. In addition, when the high-strength steel sheet of the present invention is applied to an automobile, the sheet thickness can be reduced, thereby improving fuel efficiency and contributing to a global environmental problem that has recently become a major problem. it can.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 58-185752, ultra-low carbon steel sheets have excellent workability and are therefore widely used for applications such as automobiles. In addition, devices for further improving the workability have been devised by defining the components and the production method of the ultra-low carbon steel. For example, Japanese Patent Application Laid-Open Nos.
JP-143228 and JP-A-4-116124 disclose that C, Mn, P in ultra-low carbon steel to which Ti is added.
It is disclosed that excellent workability can be obtained by minimizing the amount of such as. However, in these inventions, there is no description from the viewpoint of improving the yield at the ends of the coil in the width direction and the longitudinal direction, and neither is the technology of actively utilizing Ti sulfide as in the present invention. From the viewpoint of reducing the variation in the material, JP-A-3-170618 and JP-A-4-5222
There is a technique described in Japanese Patent Application Laid-Open No. 9-90. However, in these inventions, it is necessary to increase the rolling reduction in the finish hot rolling or to increase the winding temperature after the hot rolling, so that a large load is applied to the hot rolling process.

[0003] The effect of the present invention is similarly exhibited in a good workability high strength cold rolled steel sheet reinforced with P or Si. The technology relating to these steel sheets is disclosed in
-31827, JP-A-59-38337,
JP-B-57-57945, JP-A-61-2770
No. 31, No. 31, etc., none of them has been devised to improve the yield of the coil at the end in the width direction and the longitudinal direction, and also actively utilize Ti sulfide as in the present invention. It is not a technology to do.

[0004]

SUMMARY OF THE INVENTION Ti addition or Ti,
In the case of Nb-added ultra-low carbon steel, it is a common method to precipitate C as TiC or NbC by hot rolling after hot rolling, and to reduce solid solution C to secure the material after cold rolling annealing. I was This is the same also when strengthening with P or Si. However, at the width end and the end in the longitudinal direction of the hot-rolled coil, cooling at the time of winding and after winding proceeds extremely rapidly, so that precipitation of TiC and NbC is not sufficient, and the material at these parts is not sufficient. There was a problem that it deteriorated. Therefore, in practice, the ends of the hot-rolled sheet or the cold-rolled sheet are often cut off, and this has caused an increase in the production cost of the ultra-low carbon steel.

An object of the present invention is to provide a cold-rolled steel sheet, a hot-dip galvanized steel sheet, and a method for producing the same, in which the deterioration of the material in the width and longitudinal ends of the coil is extremely small.

[0006]

In order to solve the above-mentioned problems, the present inventors have actively utilized S in ultra-low carbon steel and optimized the ratio between the amount of Ti and the amount of S. The present inventors have made intensive studies to obtain a cold-rolled steel sheet having excellent workability uniformity by precipitating a specific precipitate by defining the amount of Mn and further reducing the fine precipitate.

As a result, S ≧ 0.004% and Ti *
= Ti-3.42N, it was found that it is effective to set Ti * / S ≧ 1.5 and Mn ≦ 0.11 %. Further, after winding after hot rolling, the ratio K of S precipitated as MnS in all S is K = (S% as M
It has been found that it is extremely important that (nS) / (total S%) satisfy K ≦ 0.2 in order to obtain uniformity of the material. This is because the amount of MnS precipitated out of the total S amount is reduced as much as possible, and Ti ₄ C ₂ S ₂ is positively precipitated, so that the solute C can be reduced by hot rolling to the finish. Even if the end of the coil is rapidly cooled during winding after hot rolling, the solid solution C is sufficiently fixed before winding, so that a large amount of solid solution C remains at the end of the coil, It is considered to be based on a mechanism in which deterioration of the material due to precipitation of carbides is reduced.

Further, in the case of the steel of the present invention, since a large amount of C is fixed as Ti ₄ C ₂ S _{2 in} the hot rolling step before winding,
It is better to actively lower the winding temperature in order to avoid the precipitation of fine carbides, rather than depositing the slightly dissolved C before hot rolling as fine precipitates by high temperature winding. It was also found that a better and more uniform material could be obtained.

The present invention has been made based on these findings, and the gist thereof is as follows. (1) By weight%, C: 0.0005 to 0.007%, M
n: 0.03-0.11%, Si: 0.005-0.8
%, Al: 0.005 to 0.1%, P: 0.2% or less,
S: 0.004 to 0.02%, N: 0.007% or less,
Ti: 0.01-0.1% and Ti * = Ti-3.42
In the case where N, Ti * / S is contained in a range satisfying 1.5, and the balance is composed of iron and unavoidable impurities. Further, the ratio K = (S%
as MnS) / (total S%) are K ≦ 0.2, below
The amount of C that precipitates as carbides expressed by the above equation (1) (= C% and
) Is 0.0003% or less. C% = (T−T 1 −T 2) / 4 + 12/93 × N 1 (%) (1) where T is obtained by electrolytic extraction in a non-aqueous solvent.
All deposited precipitates were analyzed chemically and analyzed as Ti compounds.
Ti amount (%) T1 = Ti amount precipitated as TiN, T1 = total N
% × 3.42 (%). T2 = Ti amount precipitated as Ti ₄ C ₂ S ₂ ,
By analyzing the amount of S (= S) in the residue check,
T2 = S × 3 (%) N1 = Nb amount when Nb is detected by chemical analysis
(%)

( 2 ) The cold-rolled steel sheet having excellent workability uniformity according to the above ( 1 ), further containing Nb: 0.002 to 0.05%. ( 3 ) The cold-rolled steel sheet according to the above (1) or (2 ), further comprising B: 0.0001 to 0.0030%.

( 4 ) A steel having the component according to any one of the above (1) to ( 3 ) is heated at a temperature of 1200 ° C. and a finishing temperature of (Ar ₃
-100) ° C hot rolling, winding in a temperature range from room temperature to 800 ° C, cold rolling with a draft of ≧ 60%, and annealing at a recrystallization temperature or higher. Manufacturing method of cold rolled steel sheet with excellent uniformity. ( 5 ) A steel having the component described in any one of (1) to ( 3 ) above is heated at a temperature of ≤1200 ° C. and a finishing temperature ≧ (Ar ₃
-100) ° C, rolled in a temperature range from room temperature to 800 ° C, cold rolled with a reduction of ≧ 60%, and re-rolled in a continuous hot-dip galvanizing line with an in-line annealing furnace. A method for producing a hot-dip galvanized steel sheet having excellent workability uniformity, characterized by annealing at a crystal temperature or higher and galvanizing during a cooling process.

( 6 ) After galvanizing, 400 to 6
( 8 ) The method for producing a hot-dip galvanized steel sheet having excellent workability uniformity according to ( 5 ), wherein the alloying treatment is performed in a temperature range of 00 ° C.

[0013]

The cold-rolled steel sheet and the method of manufacturing the same according to the present invention are based on ultra-low carbon steel to which Ti or Nb is added, or steel reinforced with P or Si.
The amount of Ti, the amount of specific sulfide and the amount of specific sulfide are limited, and C is sufficiently precipitated before winding after hot rolling, so that high-strength cooling with excellent workability uniformity in the longitudinal and width directions of the coil. This is to provide a rolled steel sheet. The reasons for the limitation are described below.

First, the reasons for limiting the chemical components will be described. As the amount of C increases, the amount of carbide forming elements such as Ti and Nb for fixing the C must be increased, so that the cost is increased, and solid solution C is formed at the end of the hot-rolled coil. Since a large amount of fine carbides such as TiC and NbC precipitate in the grains, they hinder the grain growth and deteriorate the workability. Therefore, the C content is 0.007%
Or less, but preferably 0.003% or less. On the other hand, from the viewpoint of the vacuum degassing cost, the lower limit of the C content is 0.0005%.

Since Si is effective as an inexpensive element for increasing the strength, it is utilized according to the desired strength level. However, if the amount exceeds 0.8%, YP sharply increases,
Since the elongation is reduced and the plating property is significantly impaired, the upper limit is made 0.8%. For hot-dip galvanizing, the amount of Si is preferably 0.3% or less from the viewpoint of plating properties. When high strength (350 MPa or more in TS) is not required, 0.1% or less is more preferable. The lower limit of the amount of Si is set to 0.005% for reasons of steelmaking costs.

Mn is one of the most important elements in the present invention.
One. That is, when the amount of Mn exceeds 0.11 %, M
Since the precipitation amount of nS increases, and as a result, the precipitation amount of Ti ₄ C ₂ S ₂ decreases, the cooling rate is high at the end of the hot-rolled coil even if high-temperature winding is performed, and the solid solution C Is left in a large amount or a large number of fine carbides are precipitated, thereby significantly deteriorating the material. Therefore, the Mn content is set to 0.11 % or less, and more preferably less than 0.10%. On the other hand, M
Even if the amount of n is less than 0.03%, no particular effect is obtained,
In addition, the lower limit is set to 0.03% because steelmaking costs are increased.

P is also actively used as an inexpensive and high-strength element like Si in accordance with the desired strength level. However, if the P content exceeds 0.2%, it causes cracks during hot or cold working, and the secondary workability is also significantly deteriorated. Further, since the alloying speed of hot-dip galvanizing is significantly slowed, the upper limit is 0.2%. From the above viewpoints, more preferably, the content is 0.08% or less. When high strength is not required, the content is more preferably 0.03% or less.

S is an extremely important element in the present invention, and the amount of S is set to 0.004 to 0.02%. When the amount of S is less than 0.004%, the amount of Ti ₄ C ₂ S ₂ deposited is not sufficient, and when wound at a low temperature, of course,
Even if the coil is wound at a high temperature, a large amount of solid solution C remains at the end of the coil, and fine growth of TiC or NbC impairs the grain growth during annealing and significantly deteriorates workability. On the other hand, if the S content exceeds 0.02%, hot cracking is likely to occur, and the same problem occurs because MnS and TiS precipitate more than Ti ₄ C ₂ S ₂ precipitates, resulting in uniform workability. Is not secured. In addition, S amount is 0.004-0.012%
Is a more preferable range.

The relationship between S and the amount of Ti is important. When Ti * = Ti−3.42N, Ti * / S ≧
1.5. If Ti * / S is less than 1.5, Ti ₄ C ₂
Since the precipitation of S ₂ is not sufficient and a large amount of TiS and MnS are precipitated, it is difficult to precipitate C before winding after hot rolling. Therefore, at the end of the hot-rolled coil, even if the winding temperature is increased, a large amount of solid solution C remains or fine carbides precipitate, resulting in extreme deterioration of the material. Ti * / S is preferably more than 2, and if more effect is desired, it is preferably 3 or more.

Al is at least 0.005 as a deoxidizing agent.
% Must be added. However, when the amount of Al exceeds 0.1%, not only the cost is increased but also the number of inclusions is increased, and the workability is deteriorated. Similar to C, N increases the amount of nitride-forming elements such as Ti and Al together with the increase in N, resulting in an increase in cost. In addition, an increase in precipitates causes deterioration of ductility, so a smaller N is desirable. Therefore, the N content is set to 0.007% or less, and preferably 0.003% or less.

Ti is added in an amount of 0.01 to 0.1%. Ti
If the amount is less than 0.01%, Ti ₄ C ₂ S ₂ cannot be precipitated before winding, and even if an amount exceeding 0.1% is added, not only the effect of fixing C is saturated but also. It becomes difficult to ensure the peel resistance of the plating layer during press molding. From the viewpoint of sufficiently precipitating Ti ₄ C ₂ S ₂ , it is preferable to add the Ti content in excess of 0.025%.

Further, in order to secure the material at the coil end, the ratio of the amount of S precipitated as MnS to the total amount of S
= (S% as MnS) / (total S%) must be K ≦ 0.2. Further, it is desirable that K <0.15. This (S% as MnS) is obtained as follows. That is, the precipitate is electrolytically extracted with a solvent that does not dissolve the sulfide (for example, a non-aqueous solvent). The obtained extraction residue is subjected to chemical analysis, and the amount of Mn is measured (= X (g)). At this time, assuming that the electrolysis amount of the entire sample is Y (g), (S% as MnS) = X
/ Y × 32/55 × 100 (%).

Nb has an effect of making the hot-rolled sheet finer and fixing C, and improves the deep drawability. Therefore, Nb is added in the range of 0.002 to 0.05% as necessary. If the addition amount is less than 0.002%, the effect of improving workability is slight. On the other hand, when Nb exceeds 0.05%, the effect of improving the deep drawability is saturated, and the ductility is significantly deteriorated. Since B strengthens the grain boundary and improves the secondary workability, B is added in an amount of 0.0001 to 0.0030% as necessary. B amount is 0.0
Below 001%, the effect is poor, and 0.003%
Even if added excessively, the effect is saturated and ductility is deteriorated.

The amount of carbon precipitated as carbides is 0.0003.
%, The amount of fine precipitates increases, the growth of crystal grains during annealing is suppressed, and the r value decreases. Therefore, the amount of C precipitated as carbide is set to 0.0003% or less. From such a viewpoint, C precipitated as a carbide having a diameter of 10 nm or less.
The amount is desirably 0.0001% or less.
The amount of C precipitated as carbide of 0 nm or less is 0.0002.
% Is preferable. C precipitated as carbide
The amount (= C%) is determined by performing a chemical analysis of all the precipitates obtained by electrolytic extraction in a non-aqueous solvent, and converting the amount of Ti (= T%) analyzed as a Ti compound into TiN. Ti amount to be deposited (= T1%) and Ti4 C2
It is calculated from the Ti amount obtained by subtracting the Ti amount (= T2%) precipitated as S2. If Nb is detected by the same chemical analysis, the amount (= N1%) is also added. Therefore, C = (T−T1−T2) / 4
+ 12/93 × N1. Here, T1 is T1 = all N
% × 3.42, and T2 is the amount of S in the extraction residue (=
S) is given by T2 = S × 3.

The raw material for obtaining the above components is not particularly limited, but scrap may be used as a raw material in addition to the method of preparing the components using a blast furnace and a converter using iron ore as a raw material. Is also good. When scrap is used as all or a part of the raw material, Cu, Cr, Ni, S
Elements such as n, Sb, Zn, Pb, and Mo may be contained.

Next, the reasons for limitation on the manufacturing process will be described. The slab to be subjected to hot rolling is not particularly limited. That is, it may be any as long as it is manufactured using a continuous cast slab or a thin slab caster. Continuous casting-direct rolling (CC-DR), in which hot rolling is performed immediately after casting.
Also suitable for processes such as

The heating temperature in the hot rolling is Ti ₄ C ₂
In order to increase the amount of S ₂ deposited as much as possible, it is essential that the temperature be 1200 ° C. or lower. In this respect, the temperature is preferably 1150 ° C. or lower. The finishing temperature in hot rolling is
In order to ensure press formability, the temperature must be (Ar ₃ -100) ° C. or higher. In the hot rolling, after the rough rolling, the bars may be joined and finish hot rolling may be continuously performed.

The present invention is characterized in that workability can be ensured even when the winding temperature after hot rolling is low. That is, according to the present invention, most of C is precipitated as Ti ₄ C ₂ S _{2 in} the process from the time of heating of hot rolling to the cooling after hot rolling, and the material is greatly improved even when wound at high temperature. I will not do it. Therefore, the winding may be performed at a temperature suitable for operation, and is performed in a range of room temperature to 800 ° C. Winding below room temperature only requires excessive equipment and has no particular effect. Also, 8
If the temperature exceeds 00 ° C., the crystal grains of the hot-rolled sheet become coarse, the oxide scale on the surface becomes thick, and the pickling cost increases. In the case of the steel of the present invention, if the winding temperature is high, the slightly dissolved solid solution C tends to precipitate as fine carbides, or the compound of P precipitates, and the material tends to be rather deteriorated. Therefore, the winding is preferably performed at a temperature of 650 ° C. or less. In order to completely avoid the precipitation of these harmful compounds, it is more preferable to wind at a temperature of 500 ° C. or lower. Furthermore, in order to reduce the time required for the temperature to drop to around room temperature after winding, 100
It is preferred that the film be wound at a temperature of not more than ° C. Needless to say, such low-temperature winding can reduce the manufacturing cost.

The rolling reduction of the cold rolling is set to 60% or more from the viewpoint of securing deep drawability. The annealing temperature in the continuous annealing is equal to or higher than the recrystallization temperature in order to secure workability. The recrystallization annealing temperature in the continuous hot-dip galvanizing line is equal to or higher than the recrystallization temperature for the same reason. Hot-dip galvanizing is performed from 420 to 50 from the viewpoint of plating properties and plating adhesion.
0 ° C is good. If the subsequent alloying treatment temperature is too low, not only the alloying reaction is too slow and impairs the productivity but also the corrosion resistance and the weldability deteriorate, and if it is too high, the plating peeling resistance deteriorates. It is preferred to do so. In order to obtain a plating layer having more excellent adhesion, it is necessary to use 480 to 550.
Alloying is preferably performed in the range of ° C.

The heating rate in the continuous annealing or continuous hot-dip galvanizing line is not particularly limited, and may be an ordinary rate or ultra-rapid heating at 1000 ° C./s or more. Various surface treatments such as electroplating may be performed in addition to hot-dip galvanizing.

[0031]

The present invention will be described in detail below with reference to examples. (Example 1) Table 1, Table 2 (continuation of Table 1-1), Table 3
(Continued in Table 1-2) and Table 4 (Continued in Table 1-3)
Ti-added ultra-low carbon steel having the chemical composition shown in
After tapping i, Nb-added ultra-low carbon steel in a converter and making it into a slab with a continuous casting machine, Tables 5 and 7 (continuation of Table 5-
2), Table 10 (continuation of Table 5-5) and Table 13 (Table 5
Hot rolling is performed under the conditions shown in -8).
Thereafter, it was wound around a coil at various winding temperatures. A sample was cut out from the center of the coil in the longitudinal direction, and the following processing was performed. That is, cold rolling was performed to 0.8 mm after pickling in a laboratory, and heat treatment equivalent to continuous annealing was performed. The annealing conditions are shown in Table 5, Table 8 (continuation of Table 5-3), Table 11 (continuation of Table 5-6), and Table 14 (continuation of Table 5-9). Thereafter, Table 6 (continuation of Table 5-1) and Table 9 (Table 5)
(Continued-4), Table 12 (Continued in Table 5-7) and Table 15 (Continued in Table 5-10), temper rolling was performed and subjected to a tensile test. Here, the tensile test and the measurement of the average Rankford value (hereinafter, r value) were performed using JIS No. 5 test pieces. The r value was evaluated at an elongation of 15%, and the values in the rolling direction (L direction), the direction perpendicular to the rolling direction (C direction), and the direction at 45 ° to the rolling direction (D direction) were measured. Was calculated by

R = (r _L + 2r _D + r _C ) / 4 The test results are summarized in Tables 6, 9, 12, and 15.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

[Table 6]

[0039]

[Table 7]

[0040]

[Table 8]

[0041]

[Table 9]

[0042]

[Table 10]

[0043]

[Table 11]

[0044]

[Table 12]

[0045]

[Table 13]

[0046]

[Table 14]

[0047]

[Table 15]

As is evident from Tables 5 to 15, it is understood that the steel having the components of the present invention can obtain excellent materials by winding at a temperature of 800 ° C. or less. In particular, the winding temperature is lowered, and the amount of carbon precipitated as carbide is reduced to 0.1.
When the content is 0003% or less, an extremely excellent material can be obtained. On the other hand, in the comparative steel, it became clear that the material was inferior in low-temperature winding.

(Example 2) Steel Nos. Of Tables 1 to 4 manufactured under the conditions shown in Tables 16 and 18 (continuation-2 of Table 16). 1, 3, 6,
11, 12, 13, 14, 24, 25, 28, 33, 3
5, 38, 39 cold rolled steel sheets (after hot rolling to 4 mm thickness,
The material properties in the longitudinal direction of the cold-rolled coil were examined using a cold-rolled coil having a thickness of 0.8 mm).

The test results are shown in Table 17 (continued in Table 16-1).
And Table 19 (continuation-3 in Table 16).

[0051]

[Table 16]

[0052]

[Table 17]

[0053]

[Table 18]

[0054]

[Table 19]

As is evident from Tables 16 to 19, the steels manufactured according to the scope of the present invention show excellent properties not only at the center of the coil but also at the end 10 m. On the other hand, in the case of the comparative steel, the material deteriorated remarkably toward the coil end, and in the case of low-temperature winding, the material became poor over the entire length of the coil. It is clear that this tendency becomes more pronounced at the ends.

Example 3 Samples 11, 22, and 34 of Tables 1 to 4 (actual machined slabs)
The effect of hot-rolling heating temperature on the material properties after cold-rolling annealing was investigated using JIS. In other words, the slab is
The sheet was heated to 000 to 1300 ° C., and hot-rolled at a finishing temperature of 940 ° C. to a thickness of 4.0 mm. The average cooling rate at the run-out table was 20 ° C./s, after which the coil was wound at 690 ° C. The total length of the coil was about 200 m. A sample was cut out from the same coil from the same position as in Example 1, cold-rolled to 0.8 mm after pickling, and then subjected to a heat treatment equivalent to continuous annealing in a laboratory. The annealing conditions were as follows: annealing temperature: 790 ° C., soaking: 50 s, cooling rate: 60 ° C./s up to room temperature. Thereafter, temper rolling was performed at a rolling reduction of 1.0%, and subjected to a tensile test.

The test results are summarized in Tables 20 and 21 (continuation of Table 20).

[0058]

[Table 20]

[0059]

[Table 21]

As is clear from Tables 20 and 21,
The steel produced according to the scope of the present invention is excellent not only in the center of the hot-rolled coil but also in the end thereof after cold rolling annealing. On the other hand, when the heating temperature is 120
When the temperature is higher than 0 ° C., the material after cold rolling annealing at the coil end portion is significantly deteriorated. (Example 4) The steel No. in Tables 1 to 4 was used. 5, 10, 11, 12, 22,
24 and 42, hot rolling was performed under the conditions shown in Table 22, followed by pickling with an actual machine, cold rolling at a rolling reduction of 80%, and passing through a continuous galvanizing line using an in-line annealing method. Planned. Table 22 shows the plating conditions at this time. Similarly, after temper rolling at a rolling rate shown in Table 22, mechanical properties and plating adhesion were evaluated. The results obtained are shown in Table 23 (continued from Table 22).

Here, the plating adhesion was determined by performing 180 ° contact bending and the peeling state of the zinc film from the amount of peel plating adhered to the tape after peeling off the adhesive tape after bonding the adhesive tape to the bent portion. The evaluation was based on the following five levels. 1: Large peeling, 2: During peeling, 3: Small peeling, 4: Trace amount of peeling,
5: No peeling

[0062]

[Table 22]

[0063]

[Table 23]

As is clear from Tables 22 and 23,
The alloyed hot-dip galvanized steel sheet manufactured according to the scope of the present invention has excellent properties regardless of the coil position. On the other hand, in the comparative steel, the variation in workability depending on the portion of the coil was large.

[0065]

As described above, according to the present invention, it is possible to lower the winding temperature after hot rolling, and to obtain a superior material uniformly in the longitudinal and width directions of the coil. The coil end that has been set can be used as a product.
Further, when the high-strength steel sheet of the present invention is applied to an automobile, the thickness can be reduced, thereby improving fuel efficiency and contributing to a global environmental problem that has recently become a major problem. , Its value is great.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C23C 2/28 C23C 2/28 (72) Inventor Kazuo Koyama 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Inside the headquarters (72) Inventor Manabu Takahashi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Headquarters (56) References JP-A-2-194126 (JP, A) JP-A-1-230748 (JP, A) JP-A-5-195148 (JP, A) JP-A-1-191748 (JP, A) JP-A-7-18336 (JP, A) JP-A-3-170618 (JP, A) JP-A-1-13058 (JP, A) JP-A-50-137816 (JP, A) JP-A-7-26330 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38 / 00-38/60 C21D 9/46-9/48

Claims (6)

(57) [Claims] C: 0.0005 to 0.00% by weight
7%, Mn: 0.03-0.11%, Si: 0.005
-0.8%, Al: 0.005-0.1%, P: 0.2
%, S: 0.004 to 0.02%, N: 0.007
% Or less, Ti: 0.01 to 0.1% and Ti * = Ti−
When it is set to 3.42 N, Ti is contained in a range satisfying Ti * / S ≧ 1.5, and the balance is composed of iron and unavoidable impurities. Further, the ratio of the amount of S precipitated as MnS to the total S amount K =
(S% as MnS) / (total S%) is K ≦ 0.2, and the amount of C precipitated as carbides represented by the following formula (1) (=
C%) is 0.0003% or less. C% = (T−T 1 −T 2) / 4 + 12/93 × N 1 (%) (1) where T is obtained by electrolytic extraction in a non-aqueous solvent.
All deposited precipitates were analyzed chemically and analyzed as Ti compounds.
Ti amount (%) T1 = Ti amount precipitated as TiN, T1 = total N
% × 3.42 (%). T2 = Ti amount precipitated as Ti ₄ C ₂ S ₂ ,
By analyzing the amount of S (= S) in the residue check,
T2 = S × 3 (%) N1 = Nb amount when Nb is detected by chemical analysis
(%) 2. Nb: 0.002 to 0.05%
The cold-rolled steel sheet according to claim 1 , wherein the cold-rolled steel sheet has excellent workability uniformity. 3. B: 0.0001 to 0.003
The cold-rolled steel sheet having excellent workability uniformity according to claim 1 or 2, which contains 0%. 4. The method of claim 1 heating temperature ≦ 1200 ° C. The steel having a component according to any one of 3, finishing temperature ≧ (Ar
₃ -100) subjected to hot rolling ° C., winding, a rolling reduction ≧ 60% cold rolling performed in a temperature range of 800 ° C. from room temperature,
A method for producing a cold-rolled steel sheet having excellent workability uniformity, further comprising annealing at a recrystallization temperature or higher. 5. A method according to claim 1 heating temperature ≦ 1200 ° C. The steel having a component according to any one of 3, finishing temperature ≧ (Ar
₃ -100) subjected to hot rolling ° C., coiling at a temperature range of 800 ° C. from room temperature, and then was subjected to rolling reduction ≧ 60% cold rolling, a continuous galvanizing line having a line within the annealing furnace A method for producing a hot-dip galvanized steel sheet having excellent workability uniformity, characterized by annealing at a recrystallization temperature or higher and galvanizing during a cooling process. 6. After galvanizing, 400-600.
The method for producing a hot-dip galvanized steel sheet having excellent workability uniformity according to claim 5 , wherein the alloying treatment is performed in a temperature range of ° C.