JPH0699758B2 - Manufacturing method of stainless clad steel plate with excellent workability and corrosion resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a stainless clad steel sheet having excellent workability, particularly deep drawability and corrosion resistance.

(Prior Art) As represented by steel sheets used for automobiles and household appliances, steel sheets are subjected to a phosphate treatment (chemical conversion treatment) after being pressed.
Then, paint is applied to provide corrosion resistance.

Conventionally, a low carbon Al-killed steel sheet has been used as a cold-rolled steel sheet having excellent deep drawability. Although corrosion resistance was imparted to these steel sheets by painting, the corrosion resistance was not sufficient.

On the other hand, in terms of corrosion resistance, the austenitic stainless steel sheet is the most excellent, but the cost is significantly higher than that of ordinary steel. Therefore, stainless steel plates have been developed as a steel plate that has low cost and excellent corrosion resistance.

In the ordinary steel and stainless clad steel plate, the affinity of Cr and C is high, and the diffusion of C from the ordinary steel layer to the stainless steel layer occurs, which causes the problem that the corrosion resistance decreases. In order to prevent this, a technique for preventing the diffusion of C by adding a carbide forming element to the ordinary steel side has been disclosed (Japanese Patent Publication No. 58-15310, Japanese Patent Publication No. 58-19381, US Pat. No. 3693242).

However, these disclosed techniques have a large amount of C and N, and Ti and
Since a large amount of Nb is used, sufficient workability cannot be obtained and the cost is high. Further, as another method for preventing the diffusion of C, a method of forming Ni plating on the interface layer or inserting a Ni foil has been proposed, but there is a problem that the cost becomes extremely high.

Moreover, since the manufacturing method also depends only on the method of hot-pressing after welding and assembling in the shape of Saint-Gerache, walking is low,
The cost was high.

(Problems to be Solved by the Invention) The present invention provides a method for producing a stainless steel clad steel sheet having excellent corrosion resistance, workability, and deep drawability.

(Means for Solving the Problems) The present invention is to provide a stainless clad steel plate having an inner layer or one side of an ultra-low carbon steel and a surface layer of an austenitic stainless steel, and the gist thereof is in terms of weight ratio. C
≦ 0.0045%, Mn ≦ 1.0%, Al ≦ 0.080%, N ≦ 0.0050%,
And an inner layer portion of ultra-low carbon steel containing one or two of Ti and Nb, a (Ti + Nb) content of 0.15% or less, and a content of the above elements satisfying the following formula 1, and Nb / 7.74C + Ti /(4C+3.43N)≧0.8…………1 formula (Nb, Ti, C and N are the weight% of each element) The inner layer has a surface layer made of austenitic stainless steel on at least one surface, and the surface layer has Is characterized by hot-rolling steel with a single-sided thickness of 2.5 to 30% and a clad rate of 2.5% to 30%, followed by hot-rolled sheet annealing, cold working by 10% or more, and annealing at temperatures below 950 ° C and 670 ° C. .

Hereinafter, the present invention will be described in detail.

First, the reasons for limiting C, Al, N and Mn in the ultra low carbon steel portion of the steel sheet of the present invention will be described.

When C exceeds 0.0045%, not only is the workability deteriorated, but it is necessary to increase the amount of (Ti + Nb) in order to secure excellent deep drawability. On the other hand, when C exceeds 0.0045%, chromium carbide tends to precipitate on the boundary surface between the ultra-low carbon steel layer and the SUS layer, and the corrosion resistance deteriorates.

The lower the amount of C, the better, but from the viewpoint of the melting cost in steelmaking, the lower limit is determined naturally, so there is no particular limitation. However, from the viewpoint of cost, it is not a good idea to make it less than 10 ppm, and the preferred range is 0.0010 to 0.0040% Is.

Al is required to be 0.005% or more for deoxidation and to maximize the effect of improving aging and workability by adding Nb and Ti, but if it exceeds 0.08%, the effect is saturated and the cost increases. A preferred range is 0.015 to 0.060%.

N reduces the workability improving effect of Nb and Ti, so it is set to 50 ppm or less, but it is preferable to set it to 40 ppm or less as much as possible from the viewpoint of workability. However, from the viewpoint of the current steelmaking technology, it is not a good idea to set it below 5 ppm from the viewpoint of cost.

If Mn exceeds 1.0%, the strength increases and the workability decreases, so the content is made 1.0% or less. If you do not intend high strength,
From the viewpoint of ensuring excellent workability, it is preferable to be 0.50% or less, and if it is 0.35% or less, the highest workability is exhibited. Further, the lower limit is preferably 0.05% or more in order to ensure excellent hot workability.

Next, in the present invention, Ti, Nb is added to the ultra-low carbon steel portion, but this Ti, Nb amount is excellent workability and to prevent workability deterioration due to aging, and the stainless steel portion from the inner layer to the surface layer. In order to suppress the diffusion of C to the
That is, the chemical equivalent ratio with C and N must be 0.8 or more.

(Here, Nb, Ti, C, and N are the weight% of each element.) By setting this chemical equivalent ratio to 1.0 or more, the effect of the present invention is maximized. Further, if the amount of (Ti + Nb) increases, the workability decreases, so it is limited to 0.15% or less. Austenitic stainless steel is used for the surface layer,
The ingredients may be in the ingredient range regulated by JIS G 4303. For example, in SUS304, the C content is 0.08% or less.

Next, the reason for limiting the cladding rate (thickness ratio of the cladding material (austenitic stainless steel) to the thickness of the cladding steel) will be described.

When the cladding rate is 2.5% or less, the surface SUS layer is ruptured and the inner layer is easily exposed, and the corrosion resistance is impaired.
The lower limit of the SUS layer is 2.5% or more on one side and 5% or more on both sides when both sides have SUS layers.

If the cladding rate exceeds 30% on one side and 60% on both sides, the cost merit due to cladding is reduced, so the upper limit of cladding is 30% or less (60% or less on both sides).
And

After hot rolling, it is annealed for recovery, recrystallization or solution treatment. This is to improve the workability of cold rolling. The annealing temperature is determined in relation to the hot rolling coiling temperature.
That is, when the coiling temperature is higher than 600 ° C., chromium carbide is precipitated in the stainless steel layer, and therefore high temperature annealing, for example, 1050 ° C. is necessary for solutionizing the chromium carbide. However, when the coiling temperature is 600 ° C. or lower, only low temperature annealing such as 850 ° C. is required for recovery recrystallization.

After this, cold working with a reduction rate of 10% or more,
Anneal at 70 ℃ or higher. If the cold rolling rate is 10% or less, the effect of cold rolling is not obtained. Although the upper limit of the rolling reduction is not particularly set, it is usually desired to be about 90% or less from the viewpoint of workability.

If the annealing temperature after cold rolling is 950 ° C. or higher, the texture of the ultra-low carbon steel is destroyed and a high r value cannot be obtained, resulting in poor deep drawability. On the other hand, if the temperature is lower than 670 ° C, recrystallization of the ultra low carbon steel is not completed, and a high r value and El cannot be obtained. A temperature of 775 ° C or higher is preferable for higher r-value and elongation.

It is desirable from the viewpoint of cost that the SUS overlaying on the ordinary steel in the present invention is performed by a casting method. This example will be described below.

A plain steel slab is used as the core material, and this is erected vertically. A mold is placed around this slab, and a fireproof frame is placed above the mold. A high-frequency heating coil is installed on the outer periphery of the refractory frame to heat the SUS molten metal that has flowed into the refractory frame and build up SUS on the outer periphery of the slab.

At this time, a flax is applied to the surface of the ordinary steel slab as the inner layer, and preheating is performed at 700 to 1000 ° C while preventing oxidation to complete the welding at the interface. In addition to this, in other methods, for example, rolling compression bonding, the method of the present invention does not require the Ni foil to be inserted into the boundary between the surface layer and the inner layer, and has an excellent effect that the cost can be reduced.

Fig. 1 shows the components of the present invention (C0.0035%, Si0.02%, Mn0.3%, N0.
A steel consisting of an inner layer of 0030%, Al0.036%, Ti0.07%) and a surface layer of SUS304 was hot rolled to 4 mm at a finishing temperature of 910 ° C and then annealed at 1050 ° C.

The relationship between the r-value and the post-cold annealing temperature of a three-layer stainless steel clad steel sheet annealed at 1100 ° C or lower after being cold-rolled to a sheet thickness of 0.5 to 0.8 mm is shown. According to the method of the present invention, a stainless steel plate having a high r value can be obtained.

(Examples) Table 1 shows the components of the inner layer and the surface layer of the stainless cladding steel of the present invention and the respective cladding rates.

The process is the casting method described above, to produce a 250 mm thick cladded slab of the present invention, hot rolled to 4.0 mm, annealed at 1050 ℃,
It was cold rolled to 0.8 mm and annealed at 1100 ° C or lower. Table 2 shows the cold-rolled sheet annealing temperature, tensile test value, and corrosion resistance of this steel sheet. The inventive steels show higher r-values than the comparative cladding steels.

(Effect of the Invention) As described in detail above, the present invention provides a stainless clad steel having excellent workability, corrosion resistance, and deep drawability, and its economic effect is great.

[Brief description of drawings]

FIG. 1 is a table showing the relationship between the cold rolling sheet annealing temperature and the r value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoji Otomo 46-59 Nakahara, Tobata-ku, Kitakyushu City, Fukuoka Prefecture 46-59, Tobata Plant Works, Nippon Steel Corporation (56) Reference JP 62-97783 (JP, A) )

Claims (1)

[Claims] 1. A weight ratio of C ≦ 0.0045%, Mn ≦ 1.0%, Al ≦ 0.080%, N ≦ 0.0050%, and one or two of Ti and Nb, and the amount of (Ti + Nb) is 0.15% or less. And the inner layer of ultra-low carbon steel in which the content of the above elements satisfies the following formula 1, and Nb / 7.74C + Ti / (4C + 3.43N) ≧ 0.8 ………… 1 formula (Nb, Ti, C and N are (% By weight of each element) A steel having a surface layer part made of austenitic stainless steel for at least one surface of the inner layer part, having a thickness of the surface layer part of one surface, and having a clad ratio of 2.5 to 30% is hot-rolled and then hot-rolled. A method for producing a stainless clad steel sheet having excellent workability and corrosion resistance, which comprises annealing a rolled sheet, cold working it by 10% or more, and annealing it at 950 ° C or less and 670 ° C or more.