JPH08127840A - Multiply-layered steel layer for deep drawing excellent in corrosion resistance and production thereof - Google Patents

Abstract

PURPOSE: To make the corrosion resistance and deep drawability of a steel sheet compatible by specifying the compsn. of a multiply-layered steel sheet and increasing the contents of P and Cu in a specified thickness from the sur face and rear faces. CONSTITUTION: In a multiply-layered steel sheet in which the components in surface layer and internal layer are different, the components in the internal layer are constituted of, by weight, 0.0002 to 0.0090% C, 0.002 to 1.0% Si, 0.02 to 3.0% Mn, 0.002 to 0.030% P, 0.002 to 0.050% S, 0.002 to 0.100% Al, 0.0002 to 0.0100% N, one or two kinds of 0.005 to 0.10% Ti and Nb from the group of carbon nitride forming elements, and the balance Fe with inevitable impurities. In this multiplylayered steel sheet, in the case of the sheet thickness is defined as (t), the surface layer components at the part of 0.015 to 0.15t per one side from the surface and rear faces are regulated to the same as those in the internal layer components as for C, Si, Mn, S, Al, N, Ti and Tb, which are incorporated with 0.030 to 0.15% P and 0.15 to 2.0% Cu. If required, the surface is furthermore incorporated with B and Ni.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin steel sheet used for automobile bodies, home electric appliances, building materials and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Many attempts have been made to improve the corrosion resistance of steel sheets. For example, as shown in Japanese Patent Publication No. 57-14748, there is known a steel obtained by adding Cu and P to a low carbon Al killed steel. ing. However, since such a steel contains a large amount of Cu and P, it has a drawback that the workability is deteriorated although the corrosion resistance is improved.

[0003]

DISCLOSURE OF THE INVENTION The present invention is a multi-layer steel sheet and a method for producing the same, which has been made to solve the drawback that the workability deteriorates although the above steel has improved corrosion resistance.

[0004]

Means for Solving the Problems The gist of the present invention is, in a multi-layer steel sheet having different components in the surface layer and the inner layer, the weight ratio of C: 0.0002 to 0.0090% and Si: 0.002 as the inner layer components.
~ 1.0%, Mn: 0.02-3.0%, P: 0.002-0.030
%, S: 0.002-0.050%, Al: 0.002-0.100%,
N: 0.0002 to 0.0100%, Ti, N of carbonitride forming element group
b to Ti: 0.005 to 0.10%, Nb: 0.005 to 0.15%, one or two, the balance: Fe and inevitable impurities (the above component system is referred to as (A)), or the component system (A )
In addition to B: 0.0003 to 0.0050% and the plate thickness is t, the surface layer component of 0.015 t to 0.15 t per surface from the front and back surfaces is C, Si, Mn, S, Al, N, T
i, Nb, B, Fe and unavoidable impurities are the same as the components of the inner layer, and P: 0.030 to 0.15%, Cu: 0.
15 to 2.0% (the above surface layer component system is (B)), or Ni: 0.02 to 4.0 in addition to the component system (B).
% Multi-layer steel sheet for deep drawing with excellent corrosion resistance.

Further, according to the present invention, the steel having the above-mentioned inner layer component is injected vertically downward or obliquely downward into a mold for continuous casting, and a static magnetic field is applied to the entire width direction in the mold above the molten steel injection position. Then, the ascending flow of the steel is decelerated, and Cu and P or Cu are added to the steel above the position where the magnetic field is applied.
And P and Ni are added so that the molten steel in the upper part becomes the above-mentioned surface layer composition by stirring the injected gas, and a slab having the above-mentioned composition is formed by drawing the mold, and then the conventional method for steel plate production is applied. Based on hot rolling, descaling,
Cold rolled, annealed, the inner layer has the above-mentioned inner layer components, and the plate thickness is t, 0.015 t to 0.15 t per side from the front and back surfaces.
Is a cold-rolled steel sheet containing the above-mentioned surface layer component.

As described above, the reason why Cu and P are contained only in the surface layer is that Cu and P are necessary elements for improving the corrosion resistance, but Cu and P are also elements that increase the strength. If it is contained excessively, the strength becomes high and the workability also deteriorates. For this reason, it is desirable to refrain from containing as much as possible in applications where workability is required.

Therefore, in the present invention, the content of Cu and P is limited to only the surface layer portion required for corrosion resistance, Cu and P in the inner layer occupying more than half of the plate thickness are not contained much, and
By making the carbon content extremely low and precipitating the solid solution C and the solid solution N as much as possible to render them harmless to the workability, it is possible to secure the workability required as a part. Since the corrosion resistance can be secured in the surface layer portion, it is possible to obtain a deep drawing steel sheet having excellent corrosion resistance.

The reasons for limiting the components of the inner layer will be described. C
If it is less than 0.0002%, the cost for decarburization becomes extremely high and it becomes uneconomical, so 0.0002% is made the lower limit. Further, if it exceeds 0.0090%, even if a carbide forming element is added, the amount of carbide increases and the workability deteriorates.
% Is the upper limit. If Si is reduced to less than 0.002%, the manufacturing cost is significantly increased and the economic efficiency is impaired.
The lower limit is 002%, and if it exceeds 1.0%, the workability deteriorates, so 1.0% is the upper limit.

If Mn is reduced to less than 0.02%, the manufacturing cost will be dramatically increased and the economic efficiency will be impaired.
Is the lower limit, and if it exceeds 3.0%, the workability deteriorates, so 3.
The upper limit is 0%. If P is reduced to less than 0.002%, the manufacturing cost will increase dramatically and the economic efficiency will be impaired.
The lower limit is 0.002%, and if it exceeds 0.030%, the workability deteriorates, so 0.030% is the upper limit.

If S is reduced to less than 0.002%, the manufacturing cost is greatly increased and the economical efficiency is impaired. Therefore, 0.02% is the lower limit, and if it exceeds 0.050%, the workability deteriorates.
The upper limit is 050%. If Al is less than 0.002%, deoxidation will be insufficient and blowholes will occur in the steel, impairing cleanliness as a steel plate, cracks during pressing, and surface defects, so 0.002% is the lower limit, Also, if it exceeds 0.100%, the workability deteriorates, so 0.100% is made the upper limit.

N is preferably as small as possible, but 0.0002
If it is less than 0.1%, the manufacturing cost will increase significantly, so 0.0002% is the lower limit, and if it exceeds 0.0100%, the age hardenability becomes high and the workability deteriorates even if there are carbonitride forming elements. Since it is easy, the upper limit is 0.0100%. Carbon and nitride forming element groups, Ti and Nb, are added in order to precipitate and fix C and N in the steel and reduce solid solution C and solid solution N that deteriorate workability.

If the content of Ti is less than 0.005%, the amount of carbonitrides formed is insufficient, and the amount of solid solution C and solid solution N in the steel is increased to deteriorate the workability. Therefore, 0.005% is the lower limit, and 0.10% If the content exceeds 0.10%, the amount of solid solution Ti present in the steel increases, and in this case as well, workability deteriorates.
Is the upper limit.

If the amount of Nb is less than 0.005%, the amount of carbonitrides formed is insufficient and the amount of solute C and solute N in the steel is increased to deteriorate the workability. Therefore, 0.005% is the lower limit and 0.15% If the content exceeds 0.15%, the amount of solute Nb present in the steel increases, and in this case too, the workability deteriorates.
Is the upper limit.

When B is used for deep drawing, B may cause secondary work cracking, so B is added to prevent this. The addition of B dramatically improves the resistance to secondary work cracking. If the addition amount is less than 0.0003%, the effect of preventing secondary work cracking is lost, so 0.0003% is the lower limit, and
If the content exceeds 50%, the recrystallization temperature rises and annealing becomes difficult, or hot cracking occurs during hot rolling, so 0.0050% is made the upper limit.

Next, the reason for limiting the components of the surface layer will be described. The components of the surface layer are the same as the components of the inner layer except Cu, P and Ni, and Cu, P and Ni are added to the components of the inner layer. Cu is an essential element for ensuring corrosion resistance. Cu, in the presence of P, forms an amorphous rust layer at the boundary between the rust layer having a normal composition and the base iron when rust is generated on the surface of the steel sheet, and has an action of hindering the progress of rust. Improves the corrosion resistance of steel sheets. If it is less than 0.15%, the effect of improving the corrosion resistance cannot be sufficiently exerted, so 0.15% is made the lower limit.
Further, if the content exceeds 2.0%, the ductility deteriorates and cracks particularly occur during the overhanging process, so 2.0% is made the upper limit.

P is an element which, together with Cu, helps improve the corrosion resistance. Since it is contained in general steel, it is also contained in the components of the inner layer, but in the present invention, the content of the inner layer is made as small as possible from the viewpoint of ensuring workability, and the surface layer contains the amount necessary for ensuring corrosion resistance. If the amount contained in the surface layer is less than 0.030%, the effect of improving corrosion resistance is insufficient, so 0.030% is the lower limit, and if it exceeds 0.15%, cracking tends to occur during processing, so 0.15% is the upper limit. .

Ni is added to prevent surface cracks that occur when Cu is added. When producing steel containing Cu, if the heating temperature is high in the heating stage before hot rolling, cracks called net cracks occur on the surface.

Although it is added in order to prevent this, the amount of addition must be about 0.1 to 2.0 times the Cu content. Therefore, it is desirable that Ni is contained in 0.08 to 2.0%. In a manufacturing facility where the heating temperature can be lowered (for example, when heating at 1050 ° C. or lower is possible), surface cracking does not occur, and therefore addition is not necessary.

In the present invention, the above-mentioned surface layer component is provided,
The surface layer component is adjusted during continuous casting. The method, the steel having the above-mentioned inner layer component is injected vertically downward or obliquely downward with gas into a mold for continuous casting, and a static magnetic field is applied to the entire width direction in the mold above the molten steel injection position, The ascending flow of steel is slowed down, Cu and P or Cu, P and Ni are added to the steel above the position where the magnetic field is applied, and the molten steel at the top becomes the above-mentioned surface layer component by stirring the injected gas. In this way, the slab having the above-described composition is formed by drawing the mold.

This method will be described with reference to the drawings. FIG.
In FIG. 2, in the continuous casting mold 3 including the long-side mold 1 and the short-side mold 2, the lower end open type immersion nozzle 4 is arranged so as to be connected to a tundish (not shown). 3, a static magnetic field (N pole) 5 and a static magnetic field (S) for imparting a static magnetic field in the mold 3 are provided above the injection port 6 at the lower end of the immersion nozzle 4, which is the molten steel injection position.
5a is arranged so as to extend over the entire width of the long side mold 1, that is, the width of the slab 7.

At the time of casting, the molten steel 11 having the above-mentioned inner layer components is injected into the mold 3 by the immersion nozzle 4, and at the same time, gas is blown from the gas blowing port 8 of the immersion nozzle 4.

On the other hand, above the injection port 6 at the lower end of the dipping nozzle 4 at the pouring position of the molten steel 11, the static magnetic fields 5 and 5a arranged so as to cover the entire width of the long side mold 1 into the mold 3. An element 9 (Cu and P or Cu and P and N to be added to the molten steel 11 to be a surface layer is provided by applying a static magnetic field to the injected molten steel and decelerating the upward flow of the molten steel by this static magnetic field.
i) is added to make the upper molten steel in the mold 3 an alloy containing the above-mentioned surface layer components.

Then, this is continuously cast and drawn out as a slab 7, and as shown in FIG. 3, the above-mentioned surface layer component is added only to the surface layer 10a, and the inner layer 11a forms a multi-layer slab 7 which is the inner layer component. To cast.

The molten steel 11 injected from the immersion nozzle 4 into the mold 3 is, as shown by an arrow in the mold 3, when injected together with the gas from the injection port 6 of the immersion nozzle 4 in the vertical (downward) direction. It becomes a reverse reversal upward flow 12 and moves upward,
Here, a static magnetic field is applied by the static magnetic fields 5 and 5 a located above the injection port 6.

When a static magnetic field is applied in this way, the molten steel 11
The reversed upflow of No. 1 is rapidly decelerated, but the decelerated deceleration moves the molten steel 11 to the upper part of the static magnetic field 5, 5a, where the element 9 to be added to the molten steel 11 is added and the alloy molten steel 10 is added. Becomes

On the other hand, the gas injected vertically from the injection port 6 of the dipping nozzle 4 together with the molten steel 11 becomes finely dispersed as bubbles 13 and rises in the entire region of the molten steel, and is added above the added injection port 6. The molten element 9 is stirred to form a homogenized molten alloy steel 10.

Then, as a cast piece 7 is pulled downward from the mold 3, the molten alloy steel 1 above the static magnetic field 5, 5a
When the surface of the molten steel 11 is cooled and solidified, and is drawn and moved below the static magnetic fields 5 and 5a, the solidified molten steel 11 to which no additional element is added serves as the inner layer 11a, and only the surface is drawn and moved. At the same time, the solidified layer of the molten alloy steel 10 becomes the multi-layer cast piece 7 in which the surface layer 10a of the alloy steel in which the solidified layer is gradually expanded is formed.

In this way, by injecting the molten steel 11 vertically downward from the injection port 6 of the immersion nozzle 4 together with the gas,
After the injection flow of the molten steel 11 reaches the lower side, it is reversed by the buoyancy of the gas and rises to the ascending flow 12, but as the flow velocity at this time rises, it becomes gentle in the vicinity of the static magnetic fields 5 and 5a and is immersed. Above the injection port 6 of the nozzle 4, the upward magnetic field is rapidly suppressed by applying the static magnetic field by the static magnetic fields 5 and 5a.

Therefore, the alloy steel 10 above the static magnetic fields 5 and 5a is not greatly disturbed, and the molten steel 11 in the lower part of the mold 3 is also blocked by the static magnetic field and the molten steel itself rises. The molten steel 10 is not mixed by the flow 12, and the alloy steel 10a is reliably and stably formed in the inner layer 11a of the steel.
It is possible to obtain the multilayer cast slab 7 formed on the surface of the. However, the injection port of the immersion nozzle may be a one-hole type as shown in FIG. 1 or an ordinary two-hole type. The layer thickness of the surface layer 10a can be accurately controlled by the casting speed, that is, the drawing speed and the installation position of the static magnetic field.

In the present invention, the total thickness of the surface layer is t.
Then, 0.015 to 0.15t per side. The reason for this is that if the surface layer thickness is less than 0.015 t, sufficient Cu and P to form an amorphous rust layer at the boundary between the normal rust layer and the base metal cannot be supplied, so 0.015 t is the lower limit, If it exceeds 0.15 t, the proportion of the layer containing a high alloy component becomes high and the workability as the object of the present invention is impaired, so 0.15 t is made the upper limit.

Specifically, when a static magnetic field is installed in the mold, for example, the drawing speed is 0.3 to 2.0 m / min and the surface layer thickness is 10 to 3
It can be controlled to 0 mm, and the lower the drawing speed, the thicker the surface layer, and the higher the speed, the thinner the surface layer.

That is, the lower the speed, the longer the contact time of the surface of the molten alloy steel 10 with the mold 3, and
As the cooling time becomes longer, the thickness of the surface layer 10a which becomes the solidified layer becomes thicker, and conversely, the higher the speed, the shorter the contact time of the surface of the molten alloy steel 10 in the mold 3 and the cooling time. Surface layer 10a which becomes a solidified layer by shortening
This is because the thickness of is reduced.

Since the properties of the steel sheet of the present invention are not changed by mixing the components at the boundary between the inner layer and the surface layer,
Mixing of surface and inner layer components is allowed. The slab obtained as described above is made into a steel plate according to a conventional method for manufacturing a steel plate. First, the slab is continuously cast, cooled directly or once to an appropriate temperature, and then heated in a heating furnace. It is desirable that the heating temperature is about 900 ° C. to 1300 ° C. at which hot rolling can be performed.

The hot rolling performed after heating may be hot rolled below the A3 transformation point, but it is preferably at least the A3 transformation point because sufficient workability cannot be obtained. After hot rolling, the hot rolled steel sheet is wound at an appropriate temperature. The product can be used as it is, but if a steel plate with a thinner plate thickness or higher workability is required, then after performing descaling treatment such as pickling, cold rolling of 50% or more is performed. Then, it is annealed at a temperature higher than the recrystallization temperature to obtain a cold rolled steel sheet.
After cold rolling, skin pass rolling is performed to obtain a product.

Also, a hot rolled steel sheet obtained by the method of the present invention,
It is possible to perform hot dipping and / or electroplating on one side or both sides of the cold rolled steel sheet for the purpose of improving paintability, weldability, etc., and this does not depart from the present invention. Also,
It is of course possible to apply various treatments to the multilayer steel sheet of the present invention, for example, chromate treatment, phosphate treatment, treatment for improving phosphate treatment, lubricity improving treatment,
Even if the weldability improving treatment and the resin coating treatment are performed, it does not depart from the scope of the present invention, and various treatments can be additionally performed depending on the required characteristics.

[0036]

【Example】

Example 1 Molten steel having the components listed in Table 1 was prepared as an inner layer component.
Then, it was cast by the following method to obtain a steel plate. 1) Mold size 245 mm (short side) x 1200 mm (long side) Mold height 900 mm 2) Static magnetic field position (electromagnetic coil center position) molten steel surface 430 mm below 3) Immersion nozzle injection port position 50 mm below static magnetic field position 4) Immersion Nozzle inlet diameter φ90mm

[Table 1]

Into such a continuous casting apparatus, molten steel having the components of the inner layer shown in Table 1 was injected from the dipping nozzle into the mold together with 3.0 l / min of Ar gas, while the pure Cu wire was introduced from the static magnetic field into the molten steel in the upper part. And a cored wire having FeP as a core material were added, and a casting was performed at a drawing speed of 1.3 m / min while applying a static magnetic field of 5000 gauss. By controlling the addition rates of the pure Cu wire and the FeP wire, the Cu content in the surface layer portion is 0.29 to 1.21.
%, P content was 0.055 to 0.112%, and a multilayer cast slab having a uniformly generated surface layer portion having a surface layer portion thickness of 12 to 13 mm was obtained.

Then, the cast slab was heated to 1050 ° C., then hot rolled at 890 ° C., and wound at 700 ° C. to obtain a hot rolled steel plate having a plate thickness of 4.8 mm. The steel sheet was pickled to remove the scale and then cold rolled to obtain a 1.0 mm steel sheet. Then, continuous annealing was performed at 800 ° C. for 60 seconds, and
8% skin pass rolling was performed to obtain a cold rolled steel sheet. Further, as a comparative example, a steel plate consisting of only the inner layer component was manufactured by the same method except for the continuous casting method.

The corrosion resistance of these steel sheets was evaluated by salt spray and wetting,
It was evaluated by a corrosion test in which drying was repeated. In particular,
Immersion type phosphate treatment on steel plate (BTL30 manufactured by Nippon Parker
80), followed by cation electrodeposition coating (Nippon Paint Co., Powertop D-30, 20μ coating), cross-cut reaching the substrate, 5% NaCl salt spray at 35 ° C for 6 hours, → forced drying. Erosion depth of the cross-cut part was evaluated in mm unit when 80 cycles of corrosion acceleration test with 70 ° C, RH 60%, 4 hours, → cooling -20 ° C, 4 hours as one cycle.

The workability was evaluated by using a circular steel plate punched out to a diameter of 80 mm, subjecting a flat-bottomed cylinder to deep drawing at various drawing ratios, and determining the limiting drawing ratio.

The secondary workability was as follows. A circular steel plate punched out to a diameter of 60 mm was subjected to flat-bottomed cylinder deep drawing at a drawing ratio of 1.7 to form a cup, and the cup was kept at a predetermined temperature to give a conical shape to the cup. The punch was pushed in to generate cracks, and the highest temperature at which brittle fracture did not occur was evaluated as an index of secondary workability.

The evaluation results are shown in Table 2. From this table, the steel of the present invention has a smaller erosion amount in the cross-cut portion, the limiting drawing ratio exceeds 2.0, and the steel containing B has an excellent resistance to -80 ° C or less as compared with the comparative example. It shows the following workability and shows that it has excellent corrosion resistance and workability.

[Table 2]

Example 2 Molten steel having the component A in Table 1 as an inner layer component was prepared. Then, it was cast by the following method to obtain a steel plate. 1) Mold size 245 mm (short side) × 1500 mm (long side) Mold height 900 mm 2) Static magnetic field position (electromagnetic coil center position) Molten steel surface 430 mm below 3) Immersion nozzle injection port position 50 mm below static magnetic field position 4) Immersion Nozzle inlet diameter φ90mm

Into such a continuous casting machine, the molten steel shown in Table 1 was injected from the dipping nozzle into the mold together with 3.0 l / min of Ar gas, while the pure Cu wire and FeP were introduced into the molten steel from the static magnetic field. A cored wire having a core material and pure Ni wire are added, and a drawing speed of 2.5 m / min while applying a static magnetic field of 5000 gauss.
Casting was performed under three conditions of 3 m / min and 0.3 m / min. By controlling the addition rate of the pure Cu wire, the FeP wire, and the pure Ni wire, a slab having the components shown in Table 3 as the surface layer component was obtained.

[0045]

[Table 3]

Then, the cast slab was heated to 1250 ° C., then hot rolled at 890 ° C. and wound at 700 ° C. to obtain a hot rolled steel plate having a plate thickness of 4.0 mm. The steel sheet was pickled to remove scale, and then cold rolled to give a 0.8 mm steel sheet. Then, continuous annealing was performed at 800 ° C. for 60 seconds, and
8% skin pass rolling was performed to obtain a cold rolled steel sheet.

The corrosion resistance of these steel sheets was evaluated by salt spray and wetting,
It was evaluated by a corrosion test in which drying was repeated. In particular,
Immersion type phosphate treatment on steel plate (BTL30 manufactured by Nippon Parker
80), followed by cation electrodeposition coating (Nippon Paint Co., Powertop D-30, 20μ coating), cross-cut reaching the substrate, 5% NaCl salt spray at 35 ° C for 6 hours, → forced drying. Erosion depth of the cross-cut part was evaluated in mm unit when 80 cycles of corrosion acceleration test with 70 ° C, RH 60%, 4 hours, → cooling -20 ° C, 4 hours as one cycle.

The workability was evaluated by using a circular steel plate punched to a diameter of 80 mm, performing deep-drawing on a flat-bottomed cylinder at various drawing ratios, and determining the limiting drawing ratio. Table 4 shows the evaluation results. From this table, it is understood that the steel of the present invention has a smaller amount of erosion in the cross-cut portion and a limiting drawing ratio of more than 2.0, and has excellent corrosion resistance and workability, as compared with the comparative examples.

[0049]

[Table 4]

[0050]

According to the present invention, the surface of a steel sheet contains a large amount of Cu and P, which are elements having excellent corrosion resistance, and the interior of the steel sheet contains a small amount of Cu and P, which deteriorate workability. It is possible to provide a steel sheet having a low carbon content and containing a carbonitride forming element, and to obtain a steel sheet having both corrosion resistance and workability. Further, in the method for producing a steel sheet, the control of the surface layer thickness can be accurately controlled by the drawing speed of the cast slab and the static magnetic field installation position, so that a multi-layered steel sheet with stable surface layer thickness and excellent workability is produced. can do.

[Brief description of drawings]

FIG. 1 is a side view illustrating a casting method of the present invention.

FIG. 2 is a plan view illustrating a casting method of the present invention.

FIG. 3 is a cross-sectional view of a multi-layer cast piece cast according to the present invention.

[Explanation of symbols]

 3 Mold 4 Immersion Nozzle 5 Static Magnetic Field (N Pole) 5a Static Magnetic Field (S Pole) 6 Immersion Nozzle Inlet 8 Gas Inlet 9 Wire Containing Additional Element 10a Surface Layer (Solidified Layer of Molten Steel Having Surface Layer Components) 11 Molten Steel 11a Inner layer (solidified layer of molten steel)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B32B 15/01 A C22C 38/14 38/16

Claims (4)

[Claims] 1. In a multi-layer steel sheet having different components in the surface layer and the inner layer, C: 0.0002 to 0.0090%, Si: 0.002 to 1.0%, Mn: 0.02 to 3.0%, and P: 0.002 to 0.030 in terms of inner layer components. %, S: 0.002 to 0.050%, Al: 0.002 to 0.100%, N: 0.0002 to 0.0100%, from Ti and Nb of carbonitride forming element group Ti: 0.005 to 0.10%, Nb: 0.005 to 0.15% Or 2 types, the balance: Fe and unavoidable impurities are contained, and the plate thickness is t.
The surface layer component of the portion of 015t to 0.15t is C, Si, Mn,
S, Al, N, Ti, and Nb are the same as the components of the inner layer, and P: 0.030 to 0.15%, Cu: 0.15 to 2.0%, and a multi-layer steel sheet for deep drawing excellent in corrosion resistance. 2. A multi-layer steel sheet having different components in the surface layer and the inner layer, which has the component structure according to claim 1, and as an inner layer component and a surface layer component, in addition to the component according to claim 1, B: 0.0003 to 0.0050. % Multi-layer steel sheet for deep drawing with excellent corrosion resistance. 3. A multi-layer steel sheet having different components in the surface layer and the inner layer, having the inner layer component according to claim 1 or 2 as the inner layer component and having a plate thickness t, 0.015 t to 0.15 per side from the front and back surfaces. The surface layer component in the portion t is claim 1 or 2.
A multi-layer steel sheet for deep drawing, which contains Ni: 0.02 to 4.0% in addition to the listed surface layer components and has excellent corrosion resistance. 4. The steel having the inner layer component according to claim 1 or 2 is injected vertically downward or obliquely downward together with a gas into a continuous casting mold, and statically filled over the entire width direction in the mold above the molten steel injection position. A magnetic field is applied to slow down the ascending flow of the steel, Cu and P or Cu and P and Ni are added to the steel above the position where the magnetic field is applied, and the molten steel at the top is stirred by stirring the injected gas. A slab having the component composition according to claim 1, 2 or 3 is obtained by making the surface layer component according to claim 1 or 3 and drawing the mold. Then, hot rolling, descaling, cold rolling, and annealing are performed based on the ordinary method for producing a steel sheet, and the inner layer contains the component according to claim 1 or 2, and the sheet thickness is t.
Then, from the front and back surfaces, the cold rolling steel sheet containing the surface layer component of 0.015 t to 0.15 t per surface is the cold rolled steel sheet containing the surface layer component according to claim 1, 2 or 3, and it is a multi-layer for deep drawing with excellent corrosion resistance. Steel plate manufacturing method.