JPH0790386A - Production of high strength cold rolled steel plate excellent in deep drawability and chemical convertibility - Google Patents

Abstract

PURPOSE:To obtain a high strength cold rolled steel plate having deep drawability and chemical convertibility exceedingly excellent than those of the conventional one by specifying steel sheet components and producing conditions. CONSTITUTION:Steel stock constituted of fundamental components contg., by weight, <=0.01% C, 0.1 to 2.0% Si, 0.5 to 3.0% Mn, 0.01 to 0.200% Nb, 0.0001 to 0.0080% B, 0.03 to 0.20% Al, 0.02 to 0.20% P,<=0.05% S and <=0.01% N, in which C and Nb are contained under such conditions that each of contents [%C] and [%Nb] satisfies the formula I and, furthermore, Si, Mn and P are contained under such conditions that each of contents [%Si], [%Mn] and [%P] satisfies the formula II is used. This steel stock is subjected to rolling at 50 to 95% total draft while lubrication is executed in the temp. range from the Ar3 transformation point or below to <=500 deg.C, is thereafter subjected to hot rolled sheet recrystallization treatment, next to cold rolling at 50 to 95% draft, then to recrystallization annealing at 700 to 950 deg.C and is thereafter subjected to carburizing treatment. Thus, the objective cold rolled steel plate having 35 to 65kgf/mm<2> tensile strength can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength cold-rolled steel sheet which is useful for applications such as automobile steel sheets which are required to have excellent deep drawability and chemical conversion treatability.

[0002]

^2. Description of the Related Art Conventionally, a cold-rolled steel sheet having a tensile strength of 30 to 45 kgf / mm ² and excellent deep drawability has been used for the purpose of reducing the weight of a vehicle body corresponding to the improvement of fuel consumption of an automobile. In order for the steel sheet to exhibit excellent deep drawability, it is necessary that the steel sheet has a high r value (Rankford value) and a good ductility (El.) As mechanical properties.

Various methods have been proposed for improving the deep drawability. For example, JP-B-44-17268, JP-B-44
-17269 and Japanese Examined Patent Publication No. 44-17270 disclose that the r value is 2.18 by subjecting a low carbon rimmed steel to cold rolling and annealing twice.
A method for manufacturing a cold-rolled steel sheet which has been improved to the above is disclosed. However, these methods involve cold rolling and recrystallization annealing.
It has to be performed one by one, and the energy and cost required therefor are enormous.

In recent years, there has been a rapid increase in the motivation to use higher strength steel sheets having a tensile strength of 45 to 65 kgf / mm ² for the purpose of reducing the weight of automobile bodies and improving safety. It is essential to develop steel sheets with a wide range of strength levels, from mild steel to high-strength steel, corresponding to individual automobile parts. Needless to say, automobile steel sheets are required to exhibit excellent deep drawability during press forming. Therefore, research and development have been conducted on steel sheets having a high r-value that is equal to or higher than that of conventional steel.

Conventionally, in the production of a high strength cold rolled steel sheet having deep drawability, a low carbon Al killed steel containing Si, Mn, P and the like as a strengthening component is subjected to ordinary hot rolling and then cooled. It was common to carry out hot rolling followed by recrystallization annealing. However, in order to obtain high strength, a large amount of the above-mentioned strengthening components must be contained, so that a texture unfavorable for deep drawability is formed and only a steel sheet having a low r value is obtained.

[0006] Further, as a characteristic particularly required for a steel sheet for automobiles, there is a pretreatment for coating, that is, a chemical conversion treatment property. If the chemical conversion treatability is not good, the subsequent baking coating will not be successful. However, since a large amount of reinforcing components such as Si, Mn, and P must be contained for the purpose of increasing the strength of the steel sheet, the chemical conversion treatability is significantly deteriorated.

[0007]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems. By specifying the steel sheet composition and manufacturing conditions, it is possible to obtain deep drawability and chemical conversion treatability that are far superior to those in the past. An object of the present invention is to propose a method for economically producing a cold-rolled steel sheet having a tensile strength of 35 to 65 kgf / mm ² .

[0008]

[Means for Solving the Problems] As a result of intensive research conducted by the inventors to improve deep drawing property and chemical conversion treatment property,
It has been found that a cold rolled steel sheet having excellent deep drawability and chemical conversion treatability can be obtained by limiting the steel components and manufacturing conditions as described below.

The gist of the present invention is as follows. (1) C: 0.01 wt% or less, Si: 0.1 to 2.0 wt%, Mn: 0.5
~ 3.0 wt%, Nb: 0.001 to 0.200 wt%, B: 0.0001 to 0.0
080wt%, Al: 0.03-0.20wt%, P: 0.02-0.20wt%,
S: 0.05 wt% or less and N: 0.01 wt% or less, and the contents of C and Nb are represented by the following formula [% C], [% Nb]
Nb] / [% C]: Under the condition that the relationship of 5 to 25 is satisfied, the contents of Si, Mn, and P are as follows: [% Si], [% Mn], and [% P] [% Si] / 28 + 200 [% P] / 31) / ([% M
n] / 55): it becomes a basic component containing the condition satisfying the 15-40 relationship, balance the steel material consisting of Fe and unavoidable impurities, Ar ₃ or less transformation point, at a temperature range of not lower than 500 ° C. After rolling with total reduction of 50% or more and 95% or less while lubricating, hot-rolled sheet recrystallization treatment is performed, and then cold rolling with a reduction of 50-95% is performed, and then 700- A method for producing a high-strength cold-rolled steel sheet excellent in deep drawability and chemical conversion treatability, which comprises performing recrystallization annealing in a temperature range of 950 ° C. and then performing carburizing treatment (first invention).

(2) In addition to the steel composition of the first invention, Ti: 0.005
.About.0.06 wt%, and the Ti content [% Ti] is N,
The following formula 48 ([% Ti] / 48-[% N] / 14-[% S] / 32) is used in relation to the contents of S and P [% N], [% S] and [% P]. ×
A method for producing a high-strength cold-rolled steel sheet excellent in deep drawability and chemical conversion treatability satisfying [% P] ≦ 0.0015 (second invention).

(3) In addition to the steel components of the first or second invention, Ni: 0.01-1.50 wt%, Cu: 0.1-1.5 wt% and Mo:
A method for producing a high-strength cold-rolled steel sheet which contains 0.01 to 1.50 wt% of one or more types and is excellent in deep drawability and chemical conversion treatability (third invention).

The results of the research on which the present invention is based will be described below. Experiment 1 C: 0.002 wt%, Si: 0.1-2.0 wt%, Mn: 0.5-3.0
wt%, P: 0.02-0.2 wt%, S: 0.005 wt%, Al: 0.05w
t%, N: 0.002 wt%, B: 0.003 wt% and Nb: 0.025 w
Various steel slabs with t% composition are heated at 1150 ℃-
After soaking, hot rolling with a hot rolling finish temperature of 700 ° C was performed while lubricating. Continued heating rate for the hot-rolled sheet obtained
After performing recrystallization annealing at 10 ℃ / s and 850 ℃ for 20s soaking, followed by cold rolling with a rolling reduction of 75%, recrystallization annealing at 850 ℃ and 20s followed by decarburization treatment. gave.

FIG. 1 shows the results of an investigation of the effect of the steel components on the r value of the cold rolled steel sheet thus obtained. As is clear from Fig. 1, the steel composition is (3 [% Si] / 28 + 200 [%
P] / 31) / ([% Mn] / 55): In the case of satisfying 15 to 40, it was found that the characteristic that the r value was 2.0 or more was obtained.

Experiment 2 C: 0.002 wt%, Si: 1.5 wt%, Mn: 2.0 wt%, P: 0.
10 wt%, S: 0.005 wt%, Al: 0.05 wt%, N: 0.002 wt%
%, Ni: 0.5 wt%, B: 0.003 wt% and Nb 0.0025 wt% steel slab (Ar ₃ transformation point: 860 ° C) of 1150
After heating and soaking at ℃, hot rolling was performed with or without lubrication at a hot rolling finish temperature of 600 to 980 ° C. Subsequently, the obtained hot-rolled sheet was subjected to recrystallization annealing at a heating rate of 10 ° C / s and a soaking condition of 850 ° C for 20 s, followed by cold rolling at a rolling reduction of 75%, and then at 850 ° C for 20 s. After recrystallization annealing, carburizing treatment was performed at 650 ° C.

FIG. 2 shows the results of an examination of the hot rolling finish temperature and the presence or absence of lubrication during hot rolling that affect the r value of the cold rolled steel sheet thus obtained. As is apparent from FIG. 2, when the hot rolling finish temperature is set to the Ar ₃ transformation point or lower while lubrication is performed, the characteristic that the r value is 2.0 or higher is obtained.

Furthermore, the inventors have controlled the carbon concentration in the plate thickness direction in the steel satisfying the component limiting conditions obtained in the above Experiment 1 and Experiment 2, that is, the carbon concentration in the plate thickness direction on one side or both sides of the steel plate. Regarding the distribution, the average carbon concentration in the layer corresponding to 10% of the plate thickness from the surface or in the layer closer to the surface is 1.3 times or more the carbon concentration of the base metal,
Further, it has been found that by setting the amount of increase in carbon concentration to 0.01 wt% or less, it becomes possible to manufacture a high-strength cold-rolled steel sheet with significantly improved chemical conversion treatment, and the present invention has been completed.

[0017]

As described above, according to the present invention, the steel composition is important, and the excellent deep drawability cannot be secured unless the manufacturing conditions correspond to it. Hereinafter, the reasons for limiting the range of each component and manufacturing condition will be described.

1. Composition (1) C: 0.01 wt% or less Due to requirements for material characteristics (deep drawability). That is, the deep drawability is improved as the amount of C is smaller, but if it is 0.01 wt% or less, no adverse effect is exerted, so the content is limited to 0.01 wt% or less.

(2) 0.1 to 2.0 wt% Si is contained according to the strength requirement. In order to obtain the desired strength, it is necessary to contain 0.1 wt% or more, and if it exceeds 2.0 wt%, it adversely affects the material properties such as deep drawability, so it is limited to the range of 0.1 to 2.0 wt%. did. (3) Mn: 0.5-3.0 wt% Due to strength requirements. That is, it is necessary to contain 0.5 wt% or more to obtain the desired strength, while 3.0 wt%
If it is contained in excess of%, the material properties such as deep drawability are adversely affected, so the content is limited to 0.5 to 3.0 wt%.

(4) Nb: 0.001 to 0.200 wt% Nb is an important component in the present invention. Nb has the effect of precipitating and fixing the solid solution C in the steel as a carbide to reduce it and preferentially forming crystal grains in the {111} orientation, which is advantageous for deep drawability. In addition, the inclusion of Nb has the effect of making the pre-rolling structure finer and preferentially forming the {111} orientation advantageous for deep drawability after hot-rolled sheet annealing. If the content is less than 0.001 wt%, these effects do not occur. On the other hand, if the content exceeds 0.200 wt%, no further improvement in the effect is seen, so the content was limited to 0.001 to 0.200 wt%.

(5) B: 0.0001 to 0.0080 wt% B is contained in order to improve the secondary processing brittleness resistance. If the content is less than 0.0001 wt%, there is no effect,
On the other hand, if the content exceeds 0.0080 wt%, the deep drawability deteriorates, so the content was limited to 0.0001 to 0.0080 wt%.

(6) Al: 0.03 to 0.20 wt% Al is added according to the necessary amount in order to perform deoxidation and improve the yield of carbonitride forming components, and the content is 0.03 wt%. If less than%, the effect is not
Even if the content exceeds 0.20 wt%, no further effect can be obtained, so the content was limited to 0.03 to 0.20 wt%.

(7) P: 0.02 to 0.20 wt% According to strength requirements. That is, to obtain the desired strength, it is necessary to contain 0.002 wt% or more, and 0.20 wt% or more.
If it is contained in excess of wt%, it adversely affects the material properties such as deep drawability, so it was limited to 0.02 to 0.20 wt%.

(8) S: 0.05 wt% or less The smaller the S content, the better the deep drawability.
If the amount of S is 0.05 wt% or less, it does not have an adverse effect.
Limited to less than 05wt%.

(9) N: 0.01 wt% or less If the content of N is smaller, the deep drawability is improved, but if the N content is 0.01 wt% or less, no adverse effect is exerted.

(10) [% Nb] / [% C]: 5 to 25 In the present invention, the above C and Nb are contained in respective contents [% C],
It is important that the content of [% Nb] satisfies the following formula: [% Nb] / [% C]: 5 to 25.
When [% Nb] / [% C] is less than 5, solid solution C in steel
However, the above-mentioned contract cannot be obtained. Also,〔%
When Nb] / [% C] is more than 25, a large amount of solid solution Nb remains in the steel, so that the {111} recrystallization texture of the hot rolled sheet does not develop and therefore the r value of the cold rolled annealed sheet Is low. Therefore, it is limited to [% Nb] / [% C]: 5 to 25.

(11) In the present invention, the above Si, Mn and P are
Each content [% Si], [% Mn] and [% P] is calculated by the following formula (3 [% Si] / 28 + 200 [% P] / 31) / ([% Mn] /
55): It is necessary to contain it under the conditions that satisfy the relationship of 15-40.
Si, Mn, and P are solid solution strengthening components as described above, and are contained according to required strength. However, Si and P are ferrite stabilizing components, while Mn is an austenite stabilizing component. Therefore, it is necessary to control the transformation point by adding an appropriate amount of both stabilizing components.
Here, (3 [% Si] / 28 + 200 [% P] / 31) /
If ([% Mn] / 55) is less than 15, the transformation point will decrease,
On the other hand, if it exceeds 40, the transformation point rises too much, so that it becomes difficult to refine the crystal grains of the hot-rolled sheet in the austenite region during hot rolling and accumulate the working strain in the ferrite region. Therefore, 15 ≦ (3 [% Si] / 28 + 200 [%
P] / 31) / ([% Mn] / 55) ≦ 40.

(12) Ti: 0.005 to 0.06 wt% In the second invention, Ti is contained in the range of 0.005 to 0.06 wt% and the Ti content [% Ti] is N, S or P. In relation to the contents [% N], [% S] and [% P], the following formula 48 ([% Ti] / 48-[% N] / 14-[% S] / 32) x
It is desirable to satisfy [% P] ≦ 0.0015. Ti has the effect of precipitating and fixing the solid solutions C and N in the steel to reduce it, and preferentially forming the {111} orientation, which is advantageous for deep drawability. However, Ti is
It is a phosphide-forming component, and if a large amount of solid solution Ti is present in steel, Ti-P compound precipitates during hot-rolled sheet annealing {11
1} Texture is not formed, and even if cold rolling or annealing is performed thereafter, the r value is not improved. So, in this invention,
Determine the amount of Ti in consideration of the P content, 48 ([% Ti] / 48
When [-% N] / 14-[% S] / 32) x [% P] exceeds 0.0015, the amount of Ti-P compound precipitated is large and the r value deteriorates, so 48 ([% Ti] / 48). -[% N] / 14-[% S] / 32) x
It was limited to [% P] ≦ 0.0015.

In the third invention, Ni: 0.01-1.50 wt%, Cu:
One or more of 0.1 to 1.5 wt% and Mo: 0.01 to 1.50 wt% are contained. All of these components are reinforcing components of steel. (13) Ni: 0.01 to 1.50 wt% Due to strength requirements. That is, in the third invention, Ni is contained according to the desired strength, but the content is
If it is less than 0.01 wt%, it has no effect. On the other hand, if it exceeds 1.50 wt%, it adversely affects the material properties such as deep drawability.
Limited to ~ 1.50wt%.

(14) Cu: 0.1 to 1.5 wt% Cu has the effect of strengthening the steel, and is contained according to the desired strength in the third invention, but the content is 0.1.
If it is less than wt%, it has no effect. On the other hand, if it exceeds 1.5 wt%, it adversely affects the deep drawability.

(15) Mo: 0.01 to 1.5 wt% Mo has the effect of strengthening the steel and is contained according to the desired strength in the third invention, but the content is 0.01.
If it is less than wt%, it has no effect, while if it exceeds 1.5 wt%, it adversely affects the deep drawability, so it was limited to 0.01 to 1.5 wt%.

2. Manufacturing Conditions The reasons for limiting the manufacturing conditions in the present invention will be described below. (1) Hot rolling In the hot rolling step, a finish rolling step is performed in which the total reduction amount is 50% or more and 95% or less while performing lubrication in a temperature range of Ar ₃ transformation point or less and 500 ° C. or more. If hot rolling is performed here in a temperature range higher than the Ar ₃ transformation point, the texture becomes random due to γ-α transformation after rolling, so that {111} on the hot rolled sheet.
No texture is formed and therefore only low r-values are obtained after cold rolling-annealing. On the other hand, even if the finishing rolling temperature is lowered to less than 500 ° C, a higher r value cannot be expected and only the rolling load increases, so the finishing rolling temperature is below the Ar ₃ transformation point.
Limited to above 500 ° C.

If the reduction ratio of this finish rolling is less than 50%, the {111} texture is not formed in the hot-rolled sheet, while
%, The disadvantage is that an unfavorable texture is formed in the hot-rolled sheet in the r value, so the content is limited to 50% or more and 95% or less.

Further, when finish rolling, that is, rolling below the Ar ₃ transformation point is made non-lubricating rolling, due to shear deformation due to frictional force between the roll and the steel sheet, crystal grains of {110} orientation unfavorable for deep drawability. Is preferentially formed on the surface layer of the steel sheet, and the improvement of the r value cannot be expected. Therefore, in order to secure deep drawability, it is necessary to carry out lubrication rolling.

Here, the roll diameter, the roll structure, the type of lubricant and the type of rolling mill in the above rolling may be arbitrary. Further, the process before the rolling is not particularly limited, for example, for the rolling material, after reheating or continuous casting of the continuous casting slab, immediately without lowering the temperature below the Ar ₃ transformation point, or heat retention treatment. It is preferable to use a sheet bar obtained by rough rolling the obtained sheet.

(2) Hot-rolled sheet recrystallization treatment step In the steel of the present invention, the hot-rolled finish temperature is not higher than the Ar ₃ transformation point, so that the hot-rolled sheet has a worked structure. Therefore, it is necessary to subsequently subject this hot-rolled sheet to recrystallization treatment to form crystal grains of {111} orientation. If the recrystallization treatment is not performed, the {111} orientation is not formed in the hot rolled sheet, so that a high r value cannot be expected even by the subsequent cold rolling-annealing. This hot-rolled sheet recrystallization treatment is performed by a winding step or a recrystallization annealing step after hot rolling. When performing recrystallization treatment from the winding step, the winding temperature is preferably 650 ° C or higher. Winding temperature is 650 ℃
If it is less than, it is difficult to recrystallize the hot rolled sheet,
Since it is difficult to form the 1} orientation, improvement of the r value cannot be expected even by subsequent cold rolling-annealing. When the recrystallization treatment is performed in the recrystallization annealing step, either batch annealing or continuous annealing is suitable, but continuous annealing is preferable, and the annealing temperature is preferably 700 to 950 ° C. If the annealing temperature is lower than 700 ° C, the {111} texture does not develop, and if it is higher than 950 ° C, the texture becomes random due to α-γ transformation.

(3) Cold rolling step This step is indispensable for obtaining a high r value,
Cold rolling is performed on the hot rolled annealed sheet at a reduction rate of 50 to 95%. The r-value of the steel sheet after cold rolling-annealing increases as the rolling reduction increases, but the r-value rather deteriorates when the rolling reduction exceeds 95%.

(4) Cold Rolled Sheet Annealing Process By annealing a cold rolled sheet having a worked structure at 700 to 950 ° C., a {111} texture is developed and a high r value is obtained. When the annealing temperature is lower than 700 ° C, the recrystallization structure is undeveloped and the obtained r value is low. Further, if annealing is performed at a temperature higher than 950 ° C, austenite-to-ferrite transformation occurs in the cooling process.
1} The recrystallization texture is randomized and only a low r value can be obtained. The recrystallization annealing may be either a box annealing method or a continuous annealing method, but the continuous annealing method is preferable.

(5) Carburizing It is important to adjust the carbon content of the surface layer on both sides or one side of the steel sheet so as to match the desired characteristics, and the C concentration distribution in the sheet thickness direction should be one side or Depth equivalent to 10% of plate thickness from the surface on both sides or 10% of plate thickness
The average C concentration is 1.3 times or more of the carbon concentration of the base metal and the C concentration increase amount is 0.01 wt%
Do the following: Such a carburizing treatment is carried out after recrystallization annealing, and then in a carburizing atmosphere during heating and holding or cooling in the ferrite region of 500 ° C or higher, or after recrystallization annealing, after cooling once, it is dissolved in the ferrite region of 500 ° C or higher. It is treated by heating and carburizing. Thus, {11
1) C does not adversely affect the r value because C penetrates into the surface after the recrystallized texture is sufficiently developed. On the other hand, the invading C changes the properties of the steel sheet surface layer, thereby improving the chemical conversion treatability. If carburizing is performed at a temperature higher than the Ar ₃ transformation point, austenite-to-ferrite transformation occurs in the cooling process.
The {111} recrystallized texture is randomized and only a low r value is obtained. As the carburizing atmosphere, a gas containing N ₂ + H ₂ as a main component and containing an appropriate amount of CO is used. And the carburizing conditions should be selected appropriately. In addition, among the heating, soaking, and cooling zones in the CAL facility, a method of performing the soaking zone under conditions suitable for carburization is particularly effective.

[0040]

EXAMPLES Steel slabs having various compositional compositions shown in Table 1 were prepared. In Table 1, the numerical values outside the range of the present invention are underlined.

[0041]

[Table 1]

These slabs were hot-rolled and then hot-rolled sheet annealed. The obtained hot-rolled sheet was pickled, cold-rolled to form a cold-rolled steel strip having a sheet thickness of 0.7 mm, recrystallization annealed in a continuous annealing facility, and then carburized. Table 2 shows these hot rolling conditions, hot rolled sheet annealing conditions, cold rolling conditions, cold rolled sheet annealing conditions and carburizing treatment conditions.

[0043]

[Table 2]

Table 2 also shows the results of an examination of the material properties and chemical conversion treatability of the cold-rolled steel sheet thus obtained. Here, the r value is obtained by the three-point method by giving 15% of tensile prestrain, and L direction (rolling direction), D direction (45 from rolling direction).
Direction) and C direction (90 ° from rolling direction)
The value was measured, and the average r value was calculated from the formula r value = (r _L + 2r _D + r _C ) / 4. Furthermore, the chemical conversion treatability degreases the steel sheet,
After washing with water, phosphate treatment is applied, especially at the beginning of the treatment (15 seconds)
The number of nuclei of phosphate was investigated. As the number of nuclei generated increases, the chemical conversion treatment film that is finally formed becomes more detailed,
It has been found that the properties of the subsequent coating film are excellent. The evaluation of this coating film is good for ○ and uneven for △.
Table 2 shows the mark and the presence of transparency.

[0045]

According to the present invention, by limiting the steel composition and the manufacturing method, it becomes possible to manufacture a high strength cold-rolled steel sheet having chemical conversion treatability and deep drawability which are far superior to those in the past.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the Si content, P content, and Mn content in steel on the r value of a product.

FIG. 2 is a graph showing the influence of hot rolling finish temperature and the presence / absence of lubrication during hot rolling on the r value of the product.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location C22C 38/16 (72) Inventor Makoto Imanaka 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporate Research & Development Co., Ltd. (72) Inventor Takashi Sakata 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Inside Steel Engineering Co., Ltd.

Claims (3)

[Claims] 1. C: 0.01 wt% or less, Si: 0.1 to 2.0 wt%, Mn: 0.5 to 3.0 wt%, Nb: 0.001 to 0.200 wt%, B: 0.0001 to 0.0080 wt%, Al: 0.03 to 0.20 wt. %, P: 0.02 to 0.20 wt%, S: 0.05 wt% or less and N: 0.01 wt% or less, and the above C and Nb are the respective contents [% C], [% N].
b] is a condition satisfying the following formula [% Nb] / [% C]: 5 to 25, and Si, Mn, and P are each content [% Si], [% Mn] and [% P] is the following formula (3 [% Si] / 28 + 200 [% P] / 31) / ([% Mn] /
55): it becomes a basic component containing the condition satisfying the 15-40 relationship, balance the steel material consisting of Fe and unavoidable impurities, Ar ₃ or less transformation point, lubricating alms at a temperature range of not lower than 500 ° C. While rolling the total reduction amount to 50% or more and 95% or less, the hot rolled sheet is recrystallized, and then the reduction rate is 50 to 95%.
Cold rolled steel sheet, followed by recrystallization annealing in the temperature range of 700 to 950 ° C, followed by carburizing treatment. High strength cold rolled steel sheet with excellent deep drawability and chemical conversion treatability. Manufacturing method. 2. The steel material contains Ti: 0.005 to 0.06 wt% in addition to the basic components, and the Ti content [% Ti] is the content of each of N, S and P [% N], In relation to [% S] and [% P], the following formula 48 ([% Ti] / 48-[% N] / 14-[% S] / 32) x
The method for producing a high-strength cold-rolled steel sheet having excellent deep drawability and chemical conversion treatability according to claim 1, which satisfies [% P] ≦ 0.0015. 3. The steel material contains one or more of Ni: 0.01 to 1.50 wt%, Cu: 0.1 to 1.5 wt% and Mo: 0.01 to 1.50 wt% in addition to the basic components. Alternatively, the method for producing a high-strength cold-rolled steel sheet having excellent deep drawability and chemical conversion treatability according to 2.