JPH0238075B2 - ENSEIOYOBITAISHOKUSEINOSUGURETASUTENRESUKURATSUDOKOHANNOSEIZOHO - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a stainless clad steel sheet having excellent ductility and corrosion resistance. (Prior Art) Steel plates, as typified by steel plates used in automobiles and home appliances, are subjected to phosphate treatment (chemical conversion treatment) after press working, and are then painted to impart corrosion resistance. Conventionally, low carbon steel has been used as a cold rolled steel sheet with excellent deep drawability.
Al-killed steel plates have been used. 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 sheets have the best corrosion resistance, but are significantly more expensive than ordinary steel. For this reason, stainless clad steel sheets have been developed as steel sheets that are low in cost and have excellent corrosion resistance. In a clad steel plate made of ordinary steel and stainless steel, the affinity between Cr and carbon is high, which causes carbon to diffuse from the ordinary steel layer to the stainless steel layer, resulting in a decrease in corrosion resistance. In order to prevent this, a technique has been disclosed in which a carbide-forming element is added to the ordinary steel to prevent the diffusion of C (Japanese Patent Publication No. 15310/1981, Japanese Patent Publication No. 19381/1981, U.S. Patent No. 3693242). Publication No.). However, these disclosed techniques use large amounts of C and N, as well as large amounts of Ti and Nb, so that sufficient workability cannot be obtained and the cost is high. Furthermore, as another method for preventing the diffusion of C, methods have been proposed in which the interface layer is plated with Ni or Ni foil is inserted, but these methods have the problem of significantly increasing costs. Moreover, the manufacturing method relied only on a method of welding and assembling in the shape of a sandwich trench and then hot pressing, resulting in low yields and high costs. The inventors have already discovered that at least one surface area
A clad steel sheet with a 2.5-15% 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 and corrosion resistance and also has excellent thermal conductivity. The present invention provides a method for manufacturing stainless steel clad steel sheets with excellent ductility and corrosion resistance, which can be manufactured at a lower cost and which can omit the annealing step. (Means for Solving the Problems) An object of the present invention is to provide a stainless clad steel sheet 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. There is, and its gist is as follows. 1 Weight ratio: C≦0.0045%, Al≦0.080%, Mn
≦1.0%, N≦0.0050%, and one or two of Ti and Nb, with the balance being Fe and inevitable impurities (containing Si≦0.03% as inevitable impurities), (Ti＋
Nb) content is 0.15% or less and has an inner layer made of ultra-low carbon steel that satisfies the following formula, and a surface layer made of austenitic stainless steel on at least one side, and the thickness of the surface layer is clad on one side. Rate: 2.5~30% of the material, 900
Hot rolled to the final thickness at temperatures above ℃,
It is characterized by being able to be wound in a temperature range of 600℃ or less. [Nb/7.74C+Ti/(4C+3.43N)]≧0.8 and 2 Weight ratio: C≦0.0045%, Al≦0.080%, Mn
≦1.0%, N≦0.0050%, and one or two of Ti and Nb, with the balance being Fe and inevitable impurities (containing Si≦0.03% as inevitable impurities), (Ti＋
Nb) content is 0.15% or less and has an inner layer made of ultra-low carbon steel that satisfies the following formula, and a surface layer made of austenitic stainless steel on at least one side, and the thickness of the surface layer is clad on one side. Rate: 2.5~30% of the material, 900
Hot rolled to the desired thickness at temperatures above ℃,
The hot strip is wound in a temperature range of 600°C or lower, then subjected to cold working of 10% or more without annealing to obtain the final thickness, and then annealed in a temperature range of 950°C or higher. . [Nb/7.74C+Ti/(4C+3.43N)]≧0.8 The present invention will be described in detail below. First, the reasons for limiting C, Al, N, and Mn in the inner layer made of ultra-low carbon steel in the steel sheet of the present invention will be described. When C exceeds 0.0045%, not only does ductility decrease, but also (Ti) is added to ensure excellent deep drawability.
+Nb) amount needs to be increased. In addition, when C exceeds 0.0045%, chromium carbide tends to precipitate at the interface between the inner layer and the surface layer,
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 make it less than 10 ppm, and the preferable range is 0.0010 to 0.0040%. be. Al is required to be 0.005% or more for deoxidation and to maximize the effects of improving aging properties and workability due to the addition of Nb and Ti, but if it exceeds 0.080%, the effect will be saturated and the cost will increase. The preferred range is
It is 0.015-0.060%. Since N reduces the workability improvement effect of Nb and Ti,
The content should be 50 ppm or less, but preferably 40 ppm or less as much as possible from the viewpoint of processability. However, considering the current steelmaking technology, it is not a good idea to reduce the content to less than 5 ppm from the viewpoint of cost. If Mn 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, from the viewpoint of ensuring excellent workability,
The content is preferably 0.50% or less, and the highest workability can be achieved by setting the content to 0.35% or less.
In addition, the lower limit is preferably 0.05% or more in order to ensure excellent hot workability. Next, in the present invention, Ti and Nb are added to the inner layer, but the amounts of Ti and Nb are adjusted to ensure excellent workability and prevent deterioration of workability due to aging, and from the inner layer to the surface stainless steel part. In order to suppress the diffusion of C, in addition to limiting the amount of C and N, one formula, namely C,
The chemical equivalence ratio with N needs to be 0.8 or more. Nb/7.74C+Ti/4C+3.43N≧0.8...1 formula (here, Nb, Ti, C, and N are the weight% of each element) By setting this chemical equivalent ratio to 1.0 or more,
The effects of the present invention are maximized. Also, (Ti
+Nb) amount is 0.15 because the ductility decreases as the amount increases.
% or less. Although austenitic stainless steel is used for the surface layer, its components may be within the range regulated by JIS G 4303. For example, SUS
In 304, the amount of C is 0.08% or less. Next, we will discuss 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 steel). When the cladding ratio is less than 2.5%, the surface SUS layer is likely to tear, exposing the inner layer, and corrosion resistance will be impaired.
The lower limit for the surface SUS layer is 2.5% or more on one side, and if both sides have stainless steel, the total on both sides is 5% or more. In addition, the clud rate is over 30% on one side and 60% on both sides.
%, the cost benefit of cladding decreases, so the upper limit of cladding rate is 30% on one side.
or less (60% or less for 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 as is after hot rolling, set the finishing temperature to 900.
℃ or higher. When the hot rolling finishing temperature is less than 900℃,
The surface stainless steel portion does not recrystallize sufficiently during rolling, making it impossible to obtain high ductility. After hot rolling, it is rolled up at below 600℃ or heat treated at below 600℃.
When the winding or heat treatment temperature increases, 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. In addition, up to the winding or heat treatment temperature after hot rolling,
Precipitation of Cr carbides during cooling must also be avoided. For this reason, it is desirable to control the C content of the stainless steel layer according to cooling after hot rolling. For example, if the cooling rate is 10℃/S or more (e.g., hot strip mill), a C amount of about 0.08% may be sufficient, but if the cooling rate is less than 10℃/S, the C amount should be 0.02~
It is desirable to reduce it to about 0.03%. When cold rolling after hot rolling, annealing after hot rolling is omitted.
Cold rolled with a rolling reduction of 10% or more and annealed at 950℃ or more. If the cold rolling rate is less than 10%, there is no effect of cold rolling, and 30
% or more is desirable. There is no particular upper limit to the rolling reduction rate, but from the viewpoint of workability, it is usually desirable to keep it at around 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 preferable from the viewpoint of cost that the SUS layer be overlaid 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 around the outer periphery of this refractory frame to heat the molten SUS metal that has flowed into the refractory frame.
Fill it with meat. At this time, flux is applied to the surface of the ordinary steel slab that will serve as the inner layer, and a flux of 700 to 1000 is applied to prevent oxidation.
Preheat to ℃ to ensure complete welding of the interface. In addition,
Even with other methods, such as rolling crimping, the method of the present invention does not require inserting Ni foil into the boundary, and exhibits an excellent effect of reducing costs. Figure 1 shows C0.04%, Si0.02%, Mn0.3%, N:
0.0025%, Al: 0.050%, balance: 3-layer stainless clad steel consisting of an inner layer consisting of Fe and unavoidable impurities, and a surface layer of SUS304, and the present invention components (C0.0035%, Si0.02%, Mn0 .3%, N0.0030%,
The steel of the present invention, which consists of an inner layer consisting of Al0.036%, Ti0.07%, balance: Fe and unavoidable impurities, and a surface layer of SUS304 steel, was hot-rolled to 4 mm at a finishing temperature of 910℃, and then heated at 600℃ or less. This figure shows the strength-ductility balance of a three-layer stainless steel clad steel sheet with a cladding ratio of 2.5 to 60%, which was cold rolled to a thickness of 0.5 to 0.8 mm and then annealed at 1100°C without winding and then hot-rolled plate annealing. The steel of the present invention has higher ductility than comparative steels at the same tensile strength. (Example) Table 1 shows the components of the inner layer and surface layer of the present invention and comparative three-layer stainless steel clad steels, and the respective clad ratios. A 250 mm thick clad slab of the present invention was manufactured using the above-mentioned casting method, hot rolled to 4.0 mm, and coiled at 600°C. Thereafter, the comparative steel A-1 was annealed at 1100°C, and the steels of the present invention were not annealed after hot rolling (B-1, C-1, D-1). It was then cold rolled to 0.8 mm and annealed at 1100°C. Moreover, only B steel shows the properties of the as-hot-rolled material as B-2. Table 2 shows the tensile test values and corrosion resistance of this steel plate. The inventive steel exhibits higher ductility relative to tensile strength than the comparative clad steel.

【table】

【table】

[Table] (Effects of the Invention) As detailed above, the present invention provides a stainless clad steel with excellent ductility and corrosion resistance.
The economic effect is significant.

[Brief explanation of drawings]

FIG. 1 is a chart showing the relationship between tensile strength and ductility (total elongation) of the steel of the present invention and comparative steel.

Claims (1)

[Claims] 1 In terms of weight ratio, C≦0.0045%, Al≦0.080%, Mn≦1.0%, N≦0.0050%, and one or two of Ti and Nb, with the balance consisting of Fe and inevitable impurities. An ultra-low carbon steel plate (containing Si≦0.03% as an unavoidable impurity) with an inner layer made of ultra-low carbon steel that has a (Ti+Nb) content of 0.15% or less and satisfies the following formula, and an austenitic stainless steel. A material having a surface layer on at least one side, the thickness of the surface layer having a cladding ratio of 2.5 to 30% on one side, is hot rolled to the final thickness in a temperature range of 900°C or higher. , a method for producing stainless steel clad steel sheets with excellent ductility and corrosion resistance, which is characterized by winding at a temperature of 600℃ or less. [Nb/7.74C+Ti/(4C+3.43N)]≧0.8 2 Weight ratio: C≦0.0045%, Al≦0.080%, Mn≦1.0%, N≦0.0050% and one or two of Ti and Nb. An ultra-low carbon steel plate consisting of the balance Fe and unavoidable impurities (including Si≦0.03% as unavoidable impurities), with an amount of (Ti+Nb) of 0.15% or less and an ultra-low carbon steel that satisfies the following formula: A material having an inner layer and a surface layer made of austenitic stainless steel on at least one side, and the thickness of the surface layer having a cladding ratio of 2.5 to 30% on one side, is heated in a temperature range of 900°C or higher. The hot strip is hot rolled to the desired thickness, coiled at a temperature below 600°C, and then the hot strip is reduced by 10% without annealing.
After adding the above cold working to the final plate thickness, 950
A method for producing stainless steel clad steel sheets with excellent ductility and corrosion resistance, which is characterized by annealing at a temperature range of ℃ or higher. [Nb/7.74C+Ti/(4C+3.43N)]≧0.8