JP3204101B2 - Deep drawing steel sheet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to "bake hardenability, which is soft and good in press formability at the time of press forming, and increases in yield strength and tensile strength during baking of paint to ensure high strength" and "excellent." Tensile strength of 340M, which has "aging resistance" or "excellent secondary processing brittleness"
The present invention relates to a high-strength steel sheet for deep drawing of Pa or higher (cold-rolled steel sheet, electroplated steel sheet, hot-dip galvanized steel sheet), and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, in the automobile industry, measures to improve fuel economy by reducing the weight of a vehicle body have been aimed at, and as a result, thinning of materials has been strongly promoted. Along with this, a steel sheet having higher strength has been demanded from the viewpoint of ensuring safety at the time of collision and dent resistance (static dent resistance).
However, since the workability of steel sheets deteriorates as the strength of the steel sheets increases, the applicable sites of the high-strength steel sheets have to be naturally limited.

[0003] Accordingly, a high-strength steel sheet (cold-rolled) having the property of being soft at the time of forming and exhibiting excellent workability and of increasing yield strength and tensile strength after subsequent baking of paint (so-called bake hardenability). Steel sheets, electroplated steel sheets, and hot-dip galvanized steel sheets) have attracted attention, and their development has become increasingly competitive. And, for example, Japanese Patent Publication No. 60-4732
Japanese Patent Publication No. 61-45689 and Japanese Patent Application Laid-Open No. 61-276 disclose a method of obtaining excellent moldability and bake hardenability by securing the amount of dissolved C by adjusting the components and adding B.
No. 928 discloses an ultra-low carbon steel base,
Methods of obtaining steel sheets having excellent formability and bake hardenability by controlling the amounts by the amounts of C, N, S and Ti, Nb have been proposed. Furthermore, Japanese Patent Publication No. 5-30900 proposes a method for producing a high-strength steel sheet for deep drawing in which baking hardenability is imparted by performing carburization during recrystallization annealing.

[0004] However, these methods are known as "C,
In order to control the bake hardenability by adjusting only "the amount of solute C determined as a result of the relationship between the amounts of N and S and Ti and Nb" or "the amount of solute C secured by carburizing". In addition, due to lack of attention to other elements that affect the amount of solid solution C, it exhibits excellent normal-temperature aging properties and has a stable bake hardening amount of 25 to 55 N / mm ^2. It was not satisfactory as a method for producing the obtained high-strength steel sheet for deep drawing.

However, some methods have been proposed in which attention is paid to the influence of elements other than solid solution C, and an attempt is made to more precisely control the bake hardening amount by adjusting these. For example, Japanese Unexamined Patent Publication No. 3-28326 discloses an extremely low-carbon
A method for producing a cold-rolled steel sheet for processing, which exhibits high bake hardenability and good formability and aging properties by adjusting the Mn and S contents of a Ti-added steel, is disclosed. However, in this method, the control of the amount of bake hardening is not sufficient, and there is no concern that the result of lack of stability in terms of strength and aging at room temperature cannot be avoided.

Japanese Patent Application Laid-Open No. Hei 7-70648 discloses that "particularly, a Ti-added steel having a C content of 0.010 to 0.015% (hereinafter,"% "representing a component ratio is referred to as"% by weight ") is used as a base. By controlling the solid solution C content (calculated by C content, Nb content, Mn content, and P content), it is possible to obtain a high-strength steel sheet with a tensile strength of 340 MPa or more and high bake hardenability. Manufacturing Method "is disclosed. However, the high-strength steel sheet obtained by this method has not been sufficiently satisfactory in terms of deep drawability.

[0007] Solid solution strengthening, precipitation strengthening, fine grain strengthening, and the like are known as techniques for increasing the strength of a steel sheet. When the C content is increased, the amount of solid solution C increases to increase the strength. It is well known that, on the other hand, when the C content increases, it becomes difficult to improve the deep drawability. For example, Japanese Patent Application Laid-Open No. Hei 7-70648
As disclosed in Japanese Patent Publication No.
The above steel sheet "tends to have a tensile strength of 360 N / mm ² or more, so-called 340BH steel (tensile strength: 34
0N / mm ² ) and the deep drawability deteriorates accordingly.

[0008] Therefore, in the production of a bake hardenable high-strength steel sheet exhibiting excellent ductility and deep drawability, reduction of the C content, for example, C
It is conceivable to apply ultra-low carbon steel having the lowest possible content. However, as an industrial means for realizing high tensile strength of 340 MPa or more using ultra-low carbon steel having excellent deep drawability as a base, generally, a method of adding a reinforcing element such as Si, Mn, or P is used. However, if these elements are added in a large amount, there is a possibility that, for example, deterioration in processability in galvannealing and poor appearance due to P segregation or the like may be caused. Therefore, in order to realize a high tensile strength of 340 MPa or more without causing the above-mentioned adverse effects in a steel which has been reduced in carbon for improving the deep drawability, it is necessary to add a large amount of reinforcing elements such as Si, Mn, and P to increase the high strength. Instead, it was necessary to combine cost and labor-intensive other high strength methods. Therefore, in terms of economy, the use of ultra-low carbon steel was not actually preferable.

[0009] From the above, the object of the present invention is to have sufficient bake hardenability and excellent aging properties, exhibit soft and good press moldability during press molding,
It is an object of the present invention to establish means for industrially stably providing a high-strength deep-drawing steel sheet having a tensile strength of 340 MPa or more, which has excellent secondary work brittleness resistance.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have obtained the following findings (a) to (d). (a) In a steel sheet containing as much as 0.01 to 0.015% of C as disclosed in Japanese Patent Application Laid-Open No. 7-70648, the C content is relatively high, and in addition to the deterioration in workability, this high C content and Based on the finding that the deep drawability is poor due to the precipitation of a large amount of NbC due to the addition of Nb, the addition of a large amount of Si, Mn, P, etc. to the ultra-low carbon steel to increase the strength The present inventors, who were fully aware of the disadvantages to plating properties and the like caused by the above, first studied from various viewpoints the manufacturability of high-strength steel sheets for processing without using these techniques, Large amounts of Si, Mn and P are added to
Even if it does not increase to more than 01%, the C content is adjusted to the level of semi-extremely low carbon steel (C content is 0.0030% or more and less than 0.0050 %), and low-temperature winding is used during hot rolling. Then, it has been found that a sufficient strength level can be secured even if the amount of addition of Si, Mn, P and the like described above is reduced.

[0011] By the time this knowledge is reached, much more unexpected difficulties are involved. Because, when the C content level of the steel sheet is different, the influence of Si, Mn, P, etc. on the action of solute C changes, so that Si, M at a specific C content level changes.
This is because even if the degree of contribution of Mn, P, etc. to the strength improvement is known, there is a problem that the knowledge cannot be utilized if the C content level is different. In addition, as the C content is increased, the diffusion distance with carbide-forming elements (Ti, Nb, etc.) is shortened and the carbon is easily diffused. Therefore, the degree of carbide formation varies with the C content. This is because it was extremely difficult to predict the amount of solute C in regions where the C content level was different.

(B) The C content is 0.003% or more and 0.005 % or more.
% Of semi-ultra low carbon steel has a bake hardenability of “calculated solid solution C that can be calculated simply and can be adjusted by Nb.
It was also found that control was possible by "amount" and "Mn amount".

This finding will be described with reference to FIGS. 1, 2 and 3. That is, FIG. 1 shows the baking hardenability of the steel sheet and the calculated solid solution C
Amount {= Cal.Sol.C amount = Total.C− (12/93) Nb}, FIG. 2 shows the relationship between bake hardenability and Mn amount, and FIG. 3 shows bake hardenability and Cal. FIG. 5 is a graph showing the relationship between the amounts of Sol. C and Mn. The test that obtained the results was performed by the following method.

To prepare a test sample, first, Si: 0.01
%, P: 0.020 to 0.023%, S: 0.008%, Ti: 0.011 to 0.0
12%, Al: 0.04 to 0.05%, N: 0.0030% at the same level, C, Mn and Nb are C: 0.003 to 0.0094%, Mn: 0.16 to 0.
Twelve steel grades with a range of 19% and Nb: 0.010-0.035% were smelted in a laboratory, forged into a 25 mm thick slab, and hot rolled to a thickness of 6 mm at a finishing temperature of 900-940 ° C. Thereafter, the film was wound at two temperatures of 500 ° C. and 650 ° C.
Next, these hot-rolled steel sheets were mechanically ground by 1 mm on both sides, and then cold-rolled to a thickness of 0.8 mm, followed by recrystallization annealing in an annealing furnace. Here, the annealing was a cycle of heating to a predetermined temperature at a heating rate of about 10 ° C./s, holding at 810 ° C. for 50 seconds, and then cooling to room temperature at a cooling rate of about 10 ° C./s.
After annealing, a test sample was obtained by further applying a skin pass of 1.6%.

Each test sample thus obtained was subjected to an evaluation test for bake hardenability. The bake hardenability was evaluated based on the BH amount (difference in yield strength before and after baking heat after 2% tensile prestrain).

As can be seen from FIGS. 1 to 3, C: 0.0
BH content in semi-ultra low carbon steels of not less than 03% and less than 0.005 % is correlated with Cal.Sol.C content (calculated solid solution C content), but the dispersion is very large (see Fig. 1). Is too large to ignore (see FIG. 2).
However, as clearly shown in FIG. 3, the amount of BH is calculated as Cal.Sol.C.
It is clear that the interaction between the amount and Mn amount,
Since a clear correlation was recognized between the values of Cal.Sol.C and Mn and the BH amount arranged under a specific relationship,
It was found that the BH amount can be accurately estimated from the Cal.Sol.C amount and the Mn amount.

Therefore, the test was transferred to an actual machine line, and semi-ultra low carbon steel sheets of the above-described various components were manufactured on the actual machine line to produce B
The effect of the components on the H content was studied. The result was as shown in FIG. From the results shown in FIG. 4, the BH amount can be accurately estimated from the Cal.Sol.C amount and the Mn amount (Equation 10000 × Cal.Sol.C−420 × Mn + 80) even in the case of the steel sheet manufactured on the actual machine line. It can be seen that the prediction can be made with high accuracy by the above equation. The product manufactured in the above-mentioned laboratory (see FIG. 3) and the product manufactured in the actual machine line (see FIG. 4) are referred to as “Cal.Sol. In the relational expression between the amounts of Cal.Sol.C and Mn. It is considered that the difference between the coefficients of C and Mn is due to the difference in the amount of strain during hot rolling (in the actual machine line, the amount of strain during hot rolling is large, This is probably due to the effect of strain-induced precipitation).

(C) Further, although the problem of secondary working embrittlement cannot be avoided even in the case of a semi-ultra low carbon steel which is more advantageous than the ultra low carbon steel in terms of grain boundary strength, this semi The regulation on the amount of P alleviates the disadvantage relating to the resistance to secondary working embrittlement. In addition, when an appropriate amount of B is added, a remarkable improvement in the resistance to secondary working embrittlement is recognized.

The (d) The Then, by further examination of each of these findings matters semi ultra low carbon steel (C content: 0.0030% or more 0.0050
% Compared to ultra-low carbon steel by applying
Cal.Sol.C amount and Mn can be adjusted by Nb with baking hardenability combined with high strength method by increasing amount and low temperature winding.
By controlling by the amount, and by combining the aging improvement method by adding Ti and the method of controlling the P amount and improving the brittleness resistance by secondary addition by adding B,
A high-strength deep drawn cold-rolled steel sheet that achieves high strength of 340 MPa or higher in tensile strength, exhibits stable bake hardenability, excellent aging resistance, and secondary work brittleness, and has excellent plating properties. It became clear.

The present invention has been completed based on the above-mentioned knowledge aging and the like, and is characterized by the following deep-drawing steel sheet and the method for producing the same. C: 0.0030% to less than 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01~ 0.1%, N: 0.005% or less, the balance consists of Fe and unavoidable impurities, and the Ti content satisfies the condition of the following formula (1). The Cal.Sol.C content (calculated solid solution C content) and the Mn content 2) A deep drawing steel sheet which satisfies the condition of formula (2) and has stable bake hardenability and excellent aging at a tensile strength of 340 MPa or more. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]]

[0021] C: less than 0.0030% or more 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01~ 0.1% , N: 0.005% or less, B: 0.0003 to 0.0030%, the balance is composed of Fe and unavoidable impurities, and the Ti content is the condition of the following formula (1), and the Cal.Sol.C content (calculated solid solution (C content) and Mn content satisfy the condition of the following formula (2), and have a stable bake hardenability at a tensile strength of 340 MPa or more, and excellent aging resistance and secondary work brittleness resistance. Steel sheet for deep drawing. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]]

[0022] C: less than 0.0030% or more 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01~ 0.1% , N: 0.005% or less, the balance being Fe and unavoidable impurities, the Ti content satisfies the condition of the following equation (1), and the Cal.Sol.C content
A steel slab having (calculated solid solution C content) and Mn content satisfying the condition of the following formula (2) is hot-rolled in a temperature range of at least _three points of Ar and then 6
Winding at a temperature of less than 50 ° C., followed by pickling and cold rolling, followed by annealing at a continuous annealing line at a recrystallization temperature or higher, with a stable bake hardenability at a tensile strength of 340 MPa or higher and Manufacturing method of steel sheet for deep drawing with excellent aging properties. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]]

[0023] C: less than 0.0030% or more 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01~ 0.1% , N: 0.005% or less, B: 0.0003 to 0.0030%, the balance consists of Fe and unavoidable impurities, the Ti content satisfies the condition of the following formula (1), and the Cal.Sol.C content
A steel slab having (calculated solid solution C content) and Mn content satisfying the condition of the following formula (2) is hot-rolled in a temperature range of at least _three points of Ar and then 6
Winding at a temperature of less than 50 ° C., followed by pickling and cold rolling, followed by annealing at a continuous annealing line at a recrystallization temperature or higher, with a stable bake hardenability at a tensile strength of 340 MPa or higher and A method for producing steel sheets for deep drawing with excellent aging and secondary work brittleness resistance. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]]

Next, the reason why the chemical composition of the steel and the manufacturing conditions of the steel sheet are limited as described above in the present invention will be described together with the operation thereof.

[Action]

 [A] Chemical composition of steel

C: The lower the C content, the more advantageous the formability such as elongation and r value.
The C content must be 0.0030% or more in order to secure the strength of Pa or more while suppressing the added amount of Si, Mn, and P. On the other hand, when the C content is 0.0050 % or more, the amount of Nb added to control the amount of solid solution C to an appropriate amount increases, which leads to an increase in manufacturing cost, and furthermore, r which is an index of deep drawability.
Results in lower values. Therefore, C content is 0.0030% or more
It was determined to be less than 0.0050 %. In addition, Japanese Patent Application Laid-Open No.
High strength and bake hardenability required more than 340MPa in the invention described in 70648 JP is the C content is obtained not less than 0.010%, but come Combine cold winding as in the present invention Can be solved.

Si: Si is an effective component added for the purpose of deoxidizing steel and increasing the strength by solid solution strengthening.
If the content exceeds 0.2%, the surface properties, chemical conversion properties, and coating adhesion deteriorate, so the upper limit of the Si content is set to 0.2%.

Mn: Mn is one of the very important components in the present invention. First, if the Mn content is less than 0.07%, steelmaking costs increase, so it is necessary to secure a Mn content of 0.07% or more.

Since Mn has the effect of fixing S as MnS, the amount of Ti required for fixing S can be reduced with an increase in the Mn content, and the baking hardenability and aging properties are reduced. The solute C in the dominant steel precipitates as TiC. Furthermore, precipitation of MnS increases precipitation nuclei of carbides such as NbC and promotes precipitation, so that the amount of solid solution C in steel decreases. Dominates greatly. Therefore, it is necessary to adjust the content of Mn so as to satisfy the condition of the following formula (2), which represents the BH content together with the C and Nb content. 25 ≦ 10000 × Cal.Sol.C [%] − 420 × Mn [%] + 80 ≦ 55… (2) [However, Cal.Sol.C [%] = Total.C [%] − (12 / 93) Nb
[%]] Note that “10000 × Cal.Sol.C [%] −
If the value of “420 × Mn [%] + 80” is less than 25, the required amount of bake hardening cannot be ensured due to the relationship between deep drawability and strength. The curability becomes remarkably high, and the inconvenience that deterioration of aging property is caused appears.

By the way, when Mn is contained at a rate of 0.25% or more, the value of r, which is an index of deep drawability, decreases, and as can be seen from FIG. 2, the contribution of Mn to the BH amount decreases. The BH amount cannot be controlled by equation (2). Therefore,
The Mn content is in the range of 0.07 to 0.25% and the above formula
It is necessary to adjust to satisfy (2).

P: Like Si and Mn, P is a component necessary for ensuring the desired strength of the steel sheet, but if its content exceeds 0.05%, alloying treatment at the time of galvannealing is performed. P and P
The content was determined to be 0.05% or less. Preferably, the P content is adjusted to 0.015 to 0.05%.

S: S is an unavoidable impurity that accompanies steel, and as the S content increases, the amount of Ti necessary to fix S as a precipitate increases, and surface flaws due to red-hot embrittlement increase. You will be invited. Therefore, the upper limit of S content is 0.015%
It was decided.

Ti: Ti is also one of the important elements in the present invention, and has an effect of fixing S and N as precipitates. However, if the Ti content (%) does not reach "(48/14) N [%]", N in the steel cannot be fixed as TiN, which may lead to deterioration of aging. Meanwhile, Ti
If the content (%) exceeds "(48/14) N [%] + (48/32) S [%]", the excess Ti that remains without combining with N or S forms carbides with C. As a result, the amount of solid solution C is reduced, and the amount of bake hardening is adversely affected. Therefore, it is necessary to control the Ti content in a range satisfying the following equation (1). (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1)

Nb: Since Nb is an important element that controls the BH content of the steel sheet together with C and Mn, it is necessary to control the content so as to satisfy the above equation (2). On the other hand, if the Nb content is lower than 0.01%, the amount of Nb for fixing C is small, so that the bake hardenability becomes remarkably high, and the aging property is deteriorated. The contribution to high strength by reinforcement is small. On the other hand, when Nb is added in such a large amount as to exceed 0.04%, it becomes difficult to provide the steel sheet with bake hardenability, and the recrystallization temperature is increased. Therefore, it is also important to adjust the Nb content to 0.01 to 0.04%.

Al: Al must be contained at least 0.01% to fix oxygen in the steel and to improve the yield of Ti. On the other hand, excessive addition of Al leads to an increase in cost, so the upper limit of the Al content was set to 0.08%.

N: N is an unavoidable impurity that accompanies steel and degrades the material. Therefore, the upper limit of the N content is the allowable limit of 0.005%
It was decided.

B: B is a component that can be added as necessary because it has the effect of strengthening the grain boundaries and improving the resistance to secondary working brittleness of the steel sheet. The content of B is 0.0003%.
If it is less than the desired effect of the above-mentioned action cannot be obtained,
Even if the content exceeds 0.0030%, the effect is saturated, and the ductility is also deteriorated. Therefore, the B content is 0.0003 to 0.0030.
%.

[B] Manufacturing Conditions of Steel Sheet In manufacturing the steel sheet for deep drawing according to the present invention, first, a steel sheet having the above-described chemical composition manufactured by a continuous casting method and melted in a converter or the like in a usual manner. Hot rolling the slab hot or
Alternatively, a step of hot-rolling by reheating the slab once cooled to room temperature is adopted. In this case, if rolling is completed at less than _three points of Ar, the crystal orientation of the hot-rolled steel sheet becomes a direction unfavorable for deep drawability, so that hot rolling is completed at _three or more points of Ar.

The lower the hot rolling temperature is, the lower the temperature is 650 ° C.
(Preferably 600 ° C. or less). That is, FIG. 5 shows a case where a high-temperature winding (650 ° C. winding) and a case where a low-temperature winding (500 ° C. winding) are performed on a test sample similar to those obtained the results of FIGS. As compared with the mechanical properties, FIG. 5 also confirms that low-temperature winding is effective for increasing the strength of the steel sheet. And, in order to produce 340BH steel exhibiting excellent ductility and deep drawability, it is necessary to lower C, but it is suggested that low-temperature winding works effectively to increase strength in a low C region. be able to. It is to be noted that setting the winding temperature to less than 650 ° C. is preferable also from the viewpoint of line threadability and production stability.

The hot-rolled steel sheet rolled at a low temperature is then pickled in a conventional manner and subjected to cold rolling. In this case, the cold rolling conditions do not need to be particularly limited. However, since the deep drawability tends to improve with an increase in the cold rolling reduction, 6
It is desirable to set the cold rolling reduction to 0% or more.

Subsequently, the steel sheet after the cold rolling is annealed in a continuous annealing line (including a continuous galvanizing line). The annealing temperature need not be particularly limited as long as the temperature is higher than the temperature at which recrystallization is performed.

Hereinafter, the present invention will be described more specifically with reference to examples.

EXAMPLES First, a steel slab having the chemical composition shown in Table 1 was obtained using a conventional converter and a continuous casting machine.

[0042]

[Table 1]

Next, these slabs were placed in a conventional manner for 120 minutes.
After heating to 0 ° C., hot rolling was performed, and finish rolling was completed at 900 ° C., followed by winding at 600 ° C. to form a hot-rolled steel strip having a thickness of 4.0 mm. Thereafter, the hot-rolled steel strip is pickled, cold-rolled to a thickness of 0.8 mm, and then continuously annealed (CAL)
For recrystallization at a temperature of 820 ° C., or recrystallization at a temperature of 820 ° C. in a continuous hot-dip galvanizing line (CGL), followed by plating and alloying at a sheet temperature of 600 ° C. Then, after this, both the CAL material and the CGL material were subjected to temper rolling at an elongation of 1.4 to 1.6%.

Next, test pieces were cut out from the steel sheets thus obtained, and the tensile properties, r value and BH amount were measured, and an accelerated aging test (heat treatment at 100 ° C. for 60 minutes) was performed. In the accelerated aging test, ΔY calculated from the yield point elongation (YPE) after the aging test and the initial yield point elongation was calculated.
The aging was evaluated by PE. In addition, secondary work brittleness resistance of each steel plate was also investigated. The secondary work brittleness resistance was evaluated at a temperature at which brittle cracks occur when test pieces were formed into a cylindrical shape at a draw ratio of 1.8, placed on a truncated cone, and pressed while applying an impact. Furthermore, for hot-dip plated materials,
The plating properties during the actual machine line passing were investigated. Table 2 shows the results.

[0045]

[Table 2]

As shown in Table 2, each of the steel sheets according to the present invention has a high strength with a tensile strength of 340 MPa or more and an r-value.
Excellent deep drawability exceeding 1.5 and “25 (N / mm ² )
≦ BH ≦ 55 (N / mm 2) stable bake hardening amount of "and ΔYPE indicates excellent aging resistance of 0.1 or less. Further, the plating property in the galvannealing is also good.

On the other hand, in Comparative Examples 4, 5 and 8 , the “value of formula A” of the applied steel was less than 25, so that good bake hardenability was not obtained. In Comparative Examples 6 and 7 , the applied steel "A
Since the “value of the formula” exceeds 55, the bake hardening amount is large, and the aging property is poor. In Comparative Example 3 , the P content of the applied steel
Is more than the specified range of the present invention, so that the hot-dip galvanizing property is poor.

[0048] Further, a comparative example9However, the amount of C in applied steel is
Index of deep drawability, because it is out of the specified range.
R valueIs inferioring.

[0049]

As described above, according to the present invention, the present invention has a high tensile strength of 340 MPa or more, and has good and stable bake hardenability, excellent aging resistance, secondary work brittleness resistance and plating. High-strength deep-drawing steel sheet (cold-rolled steel sheet, electroplated steel sheet, hot-dip coated steel sheet, hot-dip galvanized steel sheet) that can exhibit stable properties and sufficiently meet the strict demands of automotive steel sheets And other industrially useful effects.

[Brief description of the drawings]

Fig. 1 Bake hardenability of steel sheet and calculated solid solution C content ｛= Cal.Sol.
It is the graph which showed the relationship with C amount = Total. C- (12/93) Nb}.

FIG. 2 is a graph showing the relationship between the bake hardenability of a steel sheet and the amount of Mn.

FIG. 3 is a graph showing the relationship between the bake hardenability of a steel sheet and the amounts of Cal.Sol.C and Mn.

Fig. 4 Baking hardenability and Cal.
It is a graph which shows the relationship with Sol.C and Mn amount.

FIG. 5 is a graph comparing the mechanical properties of a steel sheet in the case of performing high-temperature winding and in the case of performing low-temperature winding.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-7-126756 (JP, A) JP-A-5-195148 (JP, A) JP-A-5-230598 (JP, A) JP-A-63- 241122 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 9/46-9/48

Claims (4)

(57) [Claims] At 1. A weight ratio C: 0.0030% to less than 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01 to 0.1%, N: 0.005% or less, the balance is composed of Fe and unavoidable impurities, and the amount of Ti satisfies the condition of the following formula (1). Amount) and Mn amount satisfy the condition of the following formula (2). A deep drawing steel sheet having stable baking hardenability at a tensile strength of 340 MPa or more and excellent aging properties. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]] At 2. A weight ratio C: 0.0030% to less than 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01 to 0.1%, N: 0.005% or less, B: 0.0003 to 0.0030%, the balance is made up of Fe and unavoidable impurities, and the amount of Ti satisfies the condition of the following formula (1). The C content (calculated solid solution C content) and the Mn content satisfy the condition of the following equation (2). The baking hardenability is stable at a tensile strength of 340 MPa or more, and the excellent aging and anti-aging properties. Deep-drawing steel sheet with secondary work brittleness. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]] At 3. A weight ratio C: 0.0030% to less than 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01-0.1%, N: 0.005% or less, the balance consists of Fe and unavoidable impurities, the Ti content satisfies the condition of the following formula (1), and the Cal.Sol.C content
A steel slab having (calculated solid solution C content) and Mn content satisfying the condition of the following formula (2) is hot-rolled in a temperature range of at least _three points of Ar and then 6
Winding at a temperature of less than 50 ° C., followed by pickling and cold rolling, followed by annealing at a continuous annealing line at a recrystallization temperature or higher, with a stable bake hardenability at a tensile strength of 340 MPa or higher and Manufacturing method of steel sheet for deep drawing with excellent aging properties. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]] At 4. The weight ratio C: 0.0030% to less than 0.0050%, Si: 0.2% or less, Mn: 0.07~0.25%, P: 0.05% or less, S: 0.015% or less, Nb: 0.01~0.04%, Al: 0.01-0.1%, N: 0.005% or less, B: 0.0003-0.0030%, the balance consists of Fe and unavoidable impurities, and the Ti content satisfies the condition of the following formula (1). Sol.C amount
A steel slab having (calculated solid solution C content) and Mn content satisfying the condition of the following formula (2) is hot-rolled in a temperature range of at least _three points of Ar and then 6
Winding at a temperature of less than 50 ° C., followed by pickling and cold rolling, followed by annealing at a continuous annealing line at a recrystallization temperature or higher, with a stable bake hardenability at a tensile strength of 340 MPa or higher and A method for producing steel sheets for deep drawing with excellent aging and secondary work brittleness resistance. (48/14) N [%] ≤ Ti [%] ≤ (48/14) N [%] + (48/32) S [%] ... (1) 25 ≤ 10000 x Cal.Sol. C [% −420 × Mn [%] + 80 ≦ 55 (2) [However, Cal.Sol.C [%] = Total.C [%] − (12/93) Nb [%]]