JPH06136485A - Cast clad cold rolled steel sheet for deep drawing - Google Patents

Abstract

PURPOSE:To obtain a corrosion resisting clad cold rolled steel sheet excellent in deep drawability by controlling the amount of inclusions in a joining boundary layer in the cast and joined structure of a Cr-containing steel and an ordinary low carbon steel. CONSTITUTION:The clad cold rolled steel sheet is constituted of a layer A, composed of a steel having a composition consisting of <=0.03% C, 3-30% Cr, <=0.02% N, further one or more elements among Ti, Zr, and Nb by the amounts satisfying the relations in C/12+N/14<1.2 (Ti/48+Zr/91+Nb/93), and the balance Fe with inevitable impurities, and a layer B, composed of a steel having a composition consisting of <=0.03% C, <=0.02% N, further one or more elements among Ti, Zr, and Nb by the amounts satisfying the relations in C/12+N/14<1.2 (Ti/48+Zr/91+Nb/93), and the balance Fe with inevitable impurities. This steel sheet has a cast structure which consists of the layer A and the layer B or where an intermediate layer is composed of the layer B and both sides are composed of the layer A, and the amount of inclusions in the joining boundary layer is regulated to a value two or less times the average amount in both these steels A and B. By this method, the corrosion resisting clad cold rolled steel sheet having extra deep drawability can be produced in a practically non-aging state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cast clad cold rolled steel sheet of Cr-containing steel and ordinary steel having excellent corrosion resistance and deep drawability.

[0002]

2. Description of the Related Art A clad material is a metal having unique properties.
For example, titanium and stainless steel, steel and stainless steel are laminated with an inexpensive material to a required thickness by a rolling method, a bombardment method, a casting method, a build-up method, etc., and have great economic value. Among them, since the stainless clad steel plate has excellent corrosion resistance, it is manufactured by many kinds and various manufacturing methods. And a clad steel sheet obtained by rolling a clad steel material of high corrosion resistance steel such as titanium alloy and low carbon steel or low carbon low alloy steel to a predetermined thickness at a temperature of 900 to 1150 ° C.
A method for producing a clad steel sheet having excellent corrosion resistance and toughness, in which a solution treatment is carried out by holding it for 0 seconds or more and cooling it at a rate of 0.5 ° C./second or more ”, and in JP-A-2-254121,“ Cr: 18-27%, Ni: 15-30%, Mo: 4
.About.7%, B: 0.0010 to 0.0055%, N: 0.
A stainless steel containing 10 to 0.25% and the balance being Fe and unavoidable impurities is superposed on at least one surface of a steel plate such as carbon steel, and the temperature is 1100 to 1250 ° C.
Many methods are introduced in patent gazettes and the like, as disclosed in "A method for producing a clad steel sheet for seawater-resistant, which comprises heating to 1, hot rolling and cooling at 1 ° C / sec or more." Such a clad steel plate has high strength, high corrosion resistance as well as high corrosion resistance required when it is used in various chemical reaction vessels that handle fluids containing hydrogen at high temperature and high pressure, marine structures or equipment that uses seawater. It is intended to provide a structural material having toughness, weldability and the like. However, in order to construct a stainless clad steel sheet having excellent properties required for structural materials in this way, a material to which a large amount of alloying elements has been added is used, and hot rolling or subsequent solution treatment as described above is used. Since the product is processed, the workability is extremely low, and there is a problem that it is used only for products with a light workability.

As a stainless clad steel sheet with improved workability, for example, as disclosed in Japanese Patent Laid-Open No. 62-54020, "C: <0.0045%, Mn: ≤1.
Austenitic stainless steel is superposed on at least one surface of an ultra low carbon steel containing a small amount of Al, Ti, Nb in 0%, hot rolled and annealed, and if necessary, cold worked to 10% or more and annealed again. , A method for producing a stainless clad steel sheet with excellent ductility and corrosion resistance. "
As described in the example of Japanese Patent No. 5310, "A clad material of austenitic stainless steel and an ultra-low carbon steel containing a carbon fixing element Ti is hot-rolled and pickled, and then 0.7 mm. Cold rolled to 900
There is also a method of manufacturing a clad plate that has no carburizing defects at the joint boundary that is heat treated at ℃. The austenitic stainless clad cold-rolled steel sheet obtained by cold-rolling and annealing the hot-rolled clad material as described above has improved workability compared to the hot-rolled clad steel sheet, but has a strong workability such as automobile parts. There was a problem that many fractures occurred in the parts that received.

Therefore, austenitic stainless clad cold-rolled steel having improved workability, in particular deep drawability, by adding carbonized elements such as Ti and Nb to stainless steel to fix C and N which form a solid solution in the steel. Although steel sheets have been developed and used, parts subject to ultra-deep drawing, such as automobile gasoline fuel tanks, have had the problem of fracture. Therefore, at present, gasoline fuel tanks for automobiles, which are subjected to ultra-deep drawing, contain carbonitride elements such as Ti, Nb and the like in the C in steel.
A plated steel sheet is used in which lead and tin are plated on the surface of an ultra-low carbon cold-rolled steel sheet in which N and N are fixed and the deep drawability is improved. Recently, due to global environmental problems, there is a movement to use alcohol fuel for automobile fuel instead of conventional gasoline fuel, and it contains 3 to 20% of Cr element and may contain Ti, Nb, etc. An ultra-low carbon steel sheet, which is selected and added in a small amount, is coated with tin plating, and a chromate film or an epoxy resin film is further coated on the steel sheet for alcohol or alcohol-containing fuel containers.

However, in such a steel plate, when the shape of an automobile fuel tank has become complicated in recent years and subjected to severe forming processing, a hard and brittle alloy layer formed in the plating layer reaches the plating surface as a starting point. There is a problem that cracks are generated, corrosion is caused, and corrosion resistance is deteriorated.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the Cr-containing clad steel sheet conventionally used, and specifies the components of each layer to be joined by the casting method. It is intended to provide a Cr-containing clad cold-rolled steel sheet having excellent corrosion resistance in deep drawing.

[0007]

In order to achieve the above object, the present invention provides C: 0.03% or less, Cr: 3 to 30%,
N: 0.02% or less, one or two of Ti, Zr and Nb
Or more and, if necessary, Mo: 2% or less, and the relationship between the content of C and N and the total addition amount of one or more of Ti, Zr, and Nb is C / 12 + N / 14.
<1.2 (Ti / 48 + Zr / 91 + Nb / 93), A layer composed of steel with the balance being Fe and inevitable impurities, C: 0.03% or less, N: 0.02% or less, Ti , Zr, Nb, or one or more of
In addition, the relationship between the C and N contents and the total addition amount of one or more of Ti, Zr, and Nb is C / 12 + N / 1.
4 <1.2 (Ti / 48 + Zr / 91 + Nb / 93), with the balance being the B layer made of steel consisting of Fe and unavoidable impurities, the A layer and the B layer or the B layer as an intermediate layer In the cast-bonded structure having the A layer, the inclusions in each of the bonded boundary layers are deep-drawing cast clad cold-rolled steel sheets having a content not more than twice the average amount of the A and B layer steels.

The present invention will be described in detail below. One side of the clad steel sheets to be superposed is an A layer, and the steel components thereof are C: 0.03% or less, Cr: 3 to 30%, N: 0.
02% or less, and one or more of Ti, Zr, Nb, and C, N content and Ti, Zr, Nb
The relationship with the total addition amount of 1 or 2 or more of C / 12
+ N / 14 <1.2 (Ti / 48 + Zr / 91 + Nb /
93) with the balance being Fe and inevitable impurities.

The steel of the A layer is composed mainly for corrosion resistance. Of these, C is an effective component for imparting appropriate strength to the steel, but an excessive content forms a Cr carbide to further improve corrosion resistance. Has an effect of deteriorating workability, so its upper limit is limited to 0.03% or less.

N is T which will be described later in the hot rolling process.
Although it has an effective effect of forming fine nitrides with added components such as i and Zr and making the crystal grains fine, on the other hand, there is a problem that workability is deteriorated. Therefore, in the present invention, the N component is limited to 0.02% or less so as not to impair the object of the present invention. C and N deteriorate the non-aging property of steel,
It is preferable to minimize the amount as a harmful component that deteriorates the workability of the bonding boundary layer and causes embrittlement.

Cr is contained in an amount of 3% or more as an effective component for imparting corrosion resistance to steel. On the other hand, if the content exceeds 30%, the hot workability and the required workability of the clad steel sheet are significantly deteriorated. In the present invention, Ti,
One or more of Zr and Nb are contained. These elements are C / 12 + from the relationship with the contents of C and N.
N / 14 <1.2 (Ti / 48 + Zr / 91 + Nb / 9
3) and C and N contained in the steel.
Is fixed to carbonitride and most of it is invalidated Mo is
2% or less is added as an effective component for imparting corrosion resistance to alcohol fuel, and an excessive content exceeding 2% causes a problem that steel strength is improved and workability is impaired.
In addition, Cu and Ni are advantageous in improving the corrosion resistance, but they are also austenite-forming elements, and when the steel structure becomes austenite, there are problems that cracking occurs and deep drawability deteriorates. Therefore, these may be appropriately contained depending on the required properties, as long as they do not become austenite at room temperature.

On the other B layer, C: 0.03% or less,
N: contains 0.02% or less and one or more of Ti, Zr and Nb, and contains C and N and T
The relationship with the total addition amount of one or more of i, Zr, and Nb is C / 12 + N / 14 <1.2 (Ti / 48 + Zr
/ 91 + Nb / 93) with the balance being Fe and unavoidable impurities.

The steel of the B layer is composed of the composition of ordinary steel which secures the workability, especially the deep drawability, and has a composition of 0.03 of the C component.
% Or less and 0.02% or less of the N component are preferably as small as possible as harmful components that deteriorate workability, as in the case of the A steel. Further, the contents of C and N components and Ti, Z
The relationship with the total addition amount of one or more of r and Nb is the same as that of the A steel. Above all, a steel sheet to which a small amount of Ti has been added has a characteristic in which deep drawability is remarkably improved. In addition, although not particularly limited, B (boron) is added to the steel of the B layer in an amount of 0.00 to give secondary work cracking resistance.
You may contain 5% or less.

Further, the steels of the A layer and the B layer having the above-mentioned composition are joined to two layers of the A layer and the B layer, or a combination in which the B layer is the central layer and the both sides thereof are the A layers, In order to produce a clad steel sheet having a high joining strength at a joining boundary with few inclusions, it is necessary to produce it by a casting method. In addition, the inclusions such as P and S in the joint boundary layer and oxides of various components are formed in an amount not more than twice the average amount of both steels in the A and B layers. This is a necessary condition for producing a rolled steel sheet. Also, in this case A
Considering the corrosion resistance and workability, the plate thickness ratio of the B layer and the B layer is
The layer thickness of the B layer may be adjusted to 70 to 95% of the total thickness.

The clad cold-rolled steel sheet of the present invention obtained by controlling the steel composition and the amount of inclusions in the joining layer as described above is melted to a predetermined composition in a melting furnace such as a converter or an electric furnace. After making two types of molten steel into clad steel pieces by the casting joining method,
It is manufactured through a normal clad steel plate manufacturing process. Next, examples of the present invention will be described.

[0016]

EXAMPLE A molten steel melted in a converter is cast by a casting method to produce a clad steel piece consisting of an A layer and a B layer, and the clad steel piece is heated to 1200 ° C. for 4 hours, and then a continuous hot rolling mill. At a finishing temperature of about 930 ° C, a plate thickness of 4 mm was obtained, and it was wound at about 730 ° C. The hot rolled clad steel sheet was pickled, cold rolled at 80%, and then continuously annealed at 830 ° C. for 60 seconds. The evaluation of the characteristics was performed by using the material which was skin-passed by 1%. Table 1 shows the steel component compositions of the clad cold-rolled steel sheets A and B thus manufactured. The characteristics are shown in Table 2.

Sample sections Nos. 1 to 11 and 13 used in the experiment are sandwich structures of A layer, B layer and A layer, and the ratio of the B layer to the total thickness is about 80%. The material of sample division number 12 has a two-layer structure of A layer and B layer, and the ratio of the B layer to the total thickness is about 90%.

The r value shown in Table 2 was obtained as an average value of 0 °, 45 °, 90 ° and 135 ° in the rolling direction using JIS No. 5 tensile test pieces. Regarding the interface defect, the fracture form during tensile deformation was observed and judged by the presence or absence of cracks from the interface. The existence probability of inclusions was determined by the existence ratio of inclusions existing at the interface with the mother layer. Regarding corrosion resistance, after forming a cold-rolled clad steel plate into a fuel tank, seal a test solution of toluene 42.5cc + isooctane 42.5cc + corrosive methanol 15cc + distilled water 1cc at room temperature for 1 hour.
As a result of being left for a month, a steel plate in which no abnormality was observed was marked with ◯, and a steel plate in which rust was observed was marked with x. Regarding the aging resistance, after 10% tensile, aging treatment was performed at 100 ° C for 60 minutes, and then stress change (AI: aging inde
x). Generally, an AI of 3 kg / mm ² or less can be judged to be substantially non-aging. The existence ratio of inclusions in the bonding boundary layer to the base materials (A and B layers) is the ratio of the number of inclusions observed per unit area, where the numerator is the value of the bonding boundary layer and the denominator is the base material. The value indicates the average value.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

Experiment numbers 1, 2, 3, 4, 9, 12 in Table 2
Is a steel of the present invention and exhibits excellent properties such as deep drawability, corrosion resistance and aging resistance. In particular, the Mo-added material of Experiment No. 2 has excellent corrosion resistance. A high r-value was obtained with the material of Experiment No. 9 in which C and N were reduced as much as possible (By the way, the r-value of the A layer material alone of Sample No. 12 in Table 1 was 1.62, which is equivalent to that of the steel of the present invention. Significantly lower). As described above, the steel according to the present invention achieves deep drawability which has hitherto been impossible to achieve with stainless steel.

On the other hand, the material of Experiment No. 5 in which the amount of Cr in the A layer is below the range of the present invention has poor corrosion resistance. In addition, C of A layer
Sample classification number 1 in Table 1 in which the amount of r was above the range of the present invention
No. 0 material has poor hot workability and cracks occur during continuous hot rolling.
Subsequent experiments became impossible and the material properties could not be confirmed (hence omitted in Table 2). In the material of Experiment No. 6 in which the A layer is austenite, the r value of the A layer is about 1, so that a high r value cannot be obtained even as a multi-layer steel sheet. C
/12+N/14<1.2 (Ti / 48 + Nb / 93 +
In Experiment Nos. 7 and 8 which did not satisfy the condition of Zr / 91) in the A layer or the B layer, the r value was low, cracking occurred at the interface, and the aging resistance was poor. Material of experiment number 10 is B
The slab of the layered material is machined, then immersed in molten A steel, and manufactured by a cast-in method in which the A steel is multilayered on the surface. In this method, the inclusions in the interface are nearly five times as large as those in the parent phase, and fracture occurs at the interface.

[0024]

INDUSTRIAL APPLICABILITY The present invention provides a corrosion-resistant steel sheet having ultra-deep drawability which has never existed until now in a substantially non-aged state, and is considered to be used in a wide range in an alcohol fuel tank for automobiles, etc. Above all, an extremely large effect is expected.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B32B 15/18 C21D 8/04 A 7412-4K C22C 38/28 (72) Inventor Toshinori Mizuguchi Fukuoka Prefecture 1-1 Hibata-cho, Tobata-ku, Kitakyushu City Inside the Yawata Works, Nippon Steel Corporation

Claims (2)

[Claims] 1. C: 0.03% or less, Cr: 3-30
%, N: 0.02% or less, and 1 of Ti, Zr and Nb
One or two or more kinds are contained, and the relationship between the content of C and N and the total addition amount of Ti, Zr and Nb is C / 12 +
N / 14 <1.2 (Ti / 48 + Zr / 91 + Nb / 9
3), the balance being A layer made of steel consisting of Fe and inevitable impurities, C: 0.03% or less, N: 0.
02% or less, further containing one or more of Ti, Zr, Nb, and the content of C and N and Ti, Z
The relationship with the total amount of r and Nb added is C / 12 + N / 14 <
1.2 (Ti / 48 + Zr / 91 + Nb / 93), with the balance being B layer composed of steel consisting of Fe and unavoidable impurities, A layer and B layer, or B layer as an intermediate layer In the cast joint structure with the A layer, the inclusions in each of these joint boundary layers are 2% of the average amount of both the A and B steels.
A cast clad cold-rolled steel sheet for deep drawing, which is characterized by being no more than double. 2. C: 0.03% or less, Cr: 3 to 30
%, N: 0.02% or less, Mo: 2% or less, and T
containing one or more of i, Zr, and Nb, and
The relationship between the contents of C and N and the total addition amount of Ti, Zr, and Nb is C / 12 + N / 14 <1.2 (Ti / 48 + Z
r / 91 + Nb / 93), with the balance being an A layer composed of steel consisting of Fe and inevitable impurities, and C: 0.0
3% or less, N: 0.02% or less, and Ti, Zr, N
It contains one or more of b, and the relationship between the content of C and N and the total addition of Ti, Zr, and Nb is C /
12 + N / 14 <1.2 (Ti / 48 + Zr / 91 + N
b / 93), with the balance being a B layer composed of steel consisting of Fe and unavoidable impurities, a cast joint structure in which the A layer and the B layer, or the B layer is an intermediate layer and both outer layers are A layers. In addition, the cast clad cold-rolled steel sheet for deep drawing, characterized in that the inclusions in each of these joint boundary layers are not more than twice the average amount of both the A and B layer steels.