JPS6297783A - Production of stainless clad steel plate excellent in ductility and corrosion resistance - Google Patents

Abstract

PURPOSE:To improve the ductility and corrosion resistance by forming the surface layer of austenitic stainless steel on the inner layer part composed of the very low carbon steel including the Ti and Nb of specified contents, then by performing a hot rolling at >= the sprescribed temp. CONSTITUTION:The inner layer clad part is formed by the vary low carbon steel containing Ti, Nb together with the component composition of <=0.0045% C, <=0.0080% Al, <=1.0% Mn and <= 0.0050% N. In this case, the total contents of Ti and Nb is limited <= 0.15% and the chemical equivalent of Ti, Nb to C, N is made to satisfy the equation (I). Then, after forming the thickness of the surface layer part of austenitic stainless steel at 2.5-30% cladding rate, it is hot-rolled at >=900. deg.C and wound further at <=600 deg.C. The Ti, Nb components in the inner layer part improves the workability and the diffusion of C to the surface layer part from inner layer part is controlled as well. Consequently the ductility and corrosion resistance are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a stainless clad steel sheet having excellent ductility and corrosion resistance.

(Conventional technology) Steel plates, as typified by steel plates used in automobiles and home appliances, are subjected to phosphate treatment (chemical conversion treatment) after press working.
Corrosion resistance is imparted by coating.

Conventionally, low carbon At-killed steel sheets have been used as cold-rolled steel sheets with excellent deep drawability. Although corrosion resistance is imparted to these steel plates by painting, the corrosion resistance durability was not sufficient. On the other hand, austenitic stainless steel plates are the best in terms of feeding properties, but they are significantly more expensive than ordinary steel. For this reason, stainless clad steel plates have been developed as steel plates that are low in cost and have excellent corrosion resistance.

Clad steel sheets made of ordinary steel and stainless steel have a high affinity for Cr and carbon (carbon diffuses from the ordinary steel layer to the stainless steel layer, resulting in a decrease in corrosion resistance.To prevent this, the ordinary steel side A technique for preventing the diffusion of C by adding carbide-forming elements to
53'IO, Japanese Patent Publication No. 58-19381, and US Pat. No. 3,693,242).

However, in these disclosed techniques, the amounts of C and N are large.

In addition, since a large amount of Ti, Nb is used, sufficient workability cannot be obtained and the cost is high. Another method for preventing C diffusion is to plate the interface layer with Ni or to
A method of inserting foil has also been proposed, but this method has the problem of significantly increasing cost. In addition, the manufacturing method relied only on a method of welding and assembling in a sandwich shape and then hot pressing, resulting in low yield (and high cost).

The inventors have already discovered that 2.5 to 1
A clad steel sheet with a 5% austenitic stainless steel layer was invented.

(Problems to be Solved by the Invention) The present invention relates to an inexpensive manufacturing method for a steel plate that has the highest degree of ductility, corrosion resistance, and excellent thermal conductivity. The present invention provides a method for manufacturing a stainless clad steel sheet with excellent ductility and corrosion resistance, which can omit the annealing step and can be manufactured at a lower cost.

(Means for Solving the Problems) An object of the present invention is to provide a stainless clad steel plate in which the inner layer is made of ultra-low carbon steel and the surface layer on at least one side of the inner layer is made of austenitic stainless steel. , its gist is as follows.

(1) C≦0.0045%, At≦o, oso%,
In an ultra-low carbon steel sheet containing ≦1.0 Ti, N content of 0.0050%, and one or two of Ti and Nb, (Ti
+Nb) content of 0.15% or less and satisfying the following formula 1, an inner layer made of ultra-low carbon steel and a surface layer made of austenitic stainless steel. The thickness of steel with a cladding ratio of 2.5% to 30% on one side is hot rolled at 900°C or higher, and then rolled up at 600°C or lower, or 600°C or higher.
T? : Characterized by the following heat treatment: (2) c≦
0.0045%, At≦o, oso%, Seed≦1.0
%, an ultra-low carbon steel sheet containing 0.0050% of N and one or two of Ti and Nb, in which the (Ti+Nb) amount is 0.15% or less and satisfies the following formula 1. and a surface layer made of austenitic stainless steel on at least one side of the inner layer, and the thickness of the surface layer is reduced by hot rolling steel with a cladding ratio of 2.5% to 30% on one side. , 600
It is characterized in that it is wound at a temperature of 0.degree. C. or lower, then cold worked by 10% or more without annealing the hot coil, and then annealed at 950.degree. C. or higher.

The present invention will be explained in detail below.

First, the C of the inner layer made of ultra-low carbon steel in the steel sheet of the present invention
, At, N, and Mn will be explained below.

If C exceeds 0.0045%, not only will ductility decrease, but also (Ti+Nb) is required to ensure excellent deep drawability.
It is necessary to increase the amount.

Moreover, when C exceeds 0.0045%, chromium carbide tends to precipitate at the interface between the inner layer and the surface layer, and corrosion resistance deteriorates.

Although it is better to have a smaller amount of C, the lower limit is naturally determined from the point of view of melting cost in steelmaking, so it is not particularly limited, but from the point of view of cost it is not a good idea to keep it below 10 ppm (the preferred range is 0.0010 to 0.0010). It is 0.0040%.

At is used for deoxidation and to maximize the effects of improving aging and corrosion resistance due to the addition of Nb and Ti.

0.005% or more is required, but if it exceeds o or oso%, the effect will be saturated and the cost will increase. The preferred range is 0.01
It is 5 to 0.060%.

N is 50 ppm because it reduces the workability improvement effect of Ti.
Although the content is set below, it is preferable to reduce the content to 40 ppm or less as much as possible from the viewpoint of processability. However, considering the current steel manufacturing technology, it is not a good idea to reduce the content to less than 5 ppm from the viewpoint of cost.

If the content exceeds 1.0%, the strength will increase and the workability will decrease, so it should be kept at 1.0% or less. If high strength is not intended, the content is preferably 0.50% or less in order to ensure excellent workability, and the highest workability can be achieved by setting the content to 0.35% or less.

Further, the lower limit is preferably 0.05% or more in order to ensure excellent hot workability.

Next, in the present invention, Ti% teeth are added to the inner layer.
The amounts of Ti and Nb are set to provide excellent workability and prevent deterioration of workability due to aging η, and to suppress diffusion of C from the inner layer to the stainless steel surface layer.

In addition to limiting the amounts of C and N, it is necessary to set one formula, that is, the chemical equivalence ratio with C and N to 0.8 or more.

(Here, Nb, Ti, C, and N are % by weight of the total weight.) By setting this chemical equivalent ratio to 1.0 or more, the effects of the present invention can be maximized. In addition, the amount of (Ti+Nb) is limited to 0.15% or less since ductility decreases as the amount increases. Austenitic stainless steel is used for the surface layer,
The components may be within the range regulated by JISG 4303. For example, in 5US304, C children are 0.08%.
It is as follows.

Next, the reasons for limiting the cladding ratio (the ratio of the thickness of the cladding material (austenitic stainless steel) to the thickness of the cladding) will be described. If the cladding ratio is less than 2.5%, the surface SUS layer will be easily torn and the inner layer will be exposed, and corrosion resistance will be impaired. If yes, the total on both sides shall be 5% or more. Additionally, if the cladding rate exceeds 30 inches on one side and 60% on both sides, the cost advantage of cladding decreases, so the upper limit of the cladding rate is 30 inches on one side.
% or less (60% or less when on both sides).

Although cladding can be done only on one side, it is desirable to provide SUS layers on both sides from the viewpoint of rollability.

When using the product as it is after hot rolling, the finishing temperature should be 900°C or higher. If the hot rolling finishing temperature is less than 900°C, the surface stainless steel portion will not sufficiently recrystallize during rolling, making it impossible to obtain high ductility. After hot rolling, roll it up at 600℃ or less, or
Heat treatment at 00°C or lower. When the winding or heat treatment temperature is high, Cr carbide is first precipitated at the boundary, and then carbide is precipitated throughout the stainless steel layer, which is the surface layer, resulting in deterioration of corrosion resistance.

Furthermore, precipitation of Cr carbides during cooling to the winding or heat treatment temperature after hot rolling must also be avoided. For this reason, it is desirable to control the C content of the stainless steel layer depending on the cooling after hot rolling. For example, if the cooling speed is 10°C/S or more (for example, a hot strip mill), a C amount of about 0.08% is acceptable, but if the cooling speed is less than 10°C/S, the C amount should be 0.02 to 0. It is desirable to reduce it to about .03%.

When cold rolling is performed after hot rolling, annealing after hot rolling is omitted, cold rolling is performed with a rolling reduction of 10% or more, and annealing is performed at 950° C. or higher. If the cold rolling rate is less than 10%, there is no effect of cold rolling, and it is desirable to increase the cold rolling rate to 30% or more. There is no particular upper limit to the rolling reduction ratio, but from the viewpoint of workability, it is usually desirable that it be about 90% or less. If the annealing temperature after cold rolling is less than 950° C., grain growth after recrystallization of the stainless steel layer will not be sufficient and high ductility will not be obtained.

In the present invention, it is desirable from the point of view of cost to perform SUS overlay on ordinary steel by a casting method. An example of this will be explained next.

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

At this time, flux is applied to the surface of the ordinary steel slab that will become the inner layer, and preheated to 700 to 1000° C. while preventing oxidation to completely weld the interface. Other than this.

Even with other methods, such as rolling crimping, the method of the present invention
There is no need to use i-foil as a boundary, and it has the excellent effect of reducing costs.

Figure 1 shows C0.04%, SiO.02%, Mn 0.04%.
A three-layer stainless clad steel consisting of an inner layer of 3% NO, 0025%, AtO, 050%, and a surface layer of 5US304, and the present invention components (C0,0035%, Si0.02
%, IVIno, 3%, NO, 0030%, AtO, 0
The steel of the present invention, which consists of an inner layer of 36% TiO, 07% TiO, and a surface layer of 5US3040, is hot-rolled to 41 at a finishing temperature of 910°C, then coiled at 600°C or lower, and then the hot-rolled sheet annealing is omitted to form a sheet. This figure shows the strength-ductility balance of a three-layer stainless clad steel sheet with a cladding ratio of O to 60%, which was cold rolled to a thickness of 0.5 to 0.8 and then annealed at 1100°C.

The steel of the present invention has higher ductility than comparative steels at the same tensile strength.

(Example) Table 1 shows the components and clad ratios of the inner layer and surface layer of three-layer stainless clad steels of the present invention and comparison.

A 25011oII thick clad slab of the present invention was manufactured by the above-mentioned casting method, hot-rolled to a thickness of 4.0 mm, and coiled at 600°C. After this, comparison @ A-1 was annealed at 1100°C, and the composition steel of the present invention was not annealed after hot rolling (B-
1, C-1, D-19゜Then cold-rolled to 0.8 degrees, 11
Annealed at 00°C. In addition, only steel B is shown as -2 due to the properties of the as-hot-rolled material. The tensile test value and corrosion resistance of this steel plate were
Shown in the table. The inventive steel exhibits higher ductility relative to tensile strength than the comparative clad steel.

(Effects of the Invention) As detailed above, the present invention provides a stainless clad steel with excellent ductility and corrosion resistance, and its economic effects are significant.

[Brief explanation of drawings]

Figure 1 shows the tensile strength and ductility (total elongation) of the inventive steel and comparative steel.
This is a diagram of the relationship between Agent: Patent Attorney Tatsuo Chanoki 2θ 30 41)! ;0
6θ 70TS (Kyf/1nrnsu

Claims (1)

[Claims] 1 C≦0.0045%, Al≦0.080% Mn≦1
．． 0%, N≦0.0050% and an ultra-low carbon steel plate containing one or two of Ti and Nb, in which the amount of (Ti+Nb) is 0.15% or less and satisfies the following formula 1. Inner layer made of steel and Nb/7.74C+Ti/(4C+3.43N)≧0.
8...The surface layer made of type 1 austenitic stainless steel is held on at least one side of the inner layer, and the thickness of the surface layer is made of steel with a cladding ratio of 2.5% to 30% on one side. A method for producing a stainless clad steel sheet with excellent ductility and corrosion resistance, which comprises hot rolling at 900°C or higher, winding at 600°C or lower, or heat treating at 600°C or lower. 2 C≦0.0045%, Al≦0.080%Mn≦1
．． 0%, N≦0.0050% and an ultra-low carbon steel plate containing one or two of Ti and Nb, in which the amount of (Ti+Nb) is 0.15% or less and satisfies the following formula 1. Inner layer made of steel and Nb/7.74C+Ti/(4C+3.43N)≧0.
8......Having a surface layer made of Type 1 austenitic stainless steel on at least one side of the inner layer,
The thickness of the surface layer is set to a cladding ratio of 2.5% to 30% on one side.
hot rolled steel, coiled at 600°C or less, then cold worked by 10% or more without annealing the hot coil,
A method for producing a stainless clad steel sheet with excellent ductility and corrosion resistance, characterized by annealing at 950°C or higher.