JPS62124230A - Manufacture of stainless clad steel sheet superior in workability and corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain the titled sheet, by not rolling ultralow carbon steel having inner layer part having a prescribed (Ti + Nb) content, etc., and surface layer part having a specified cladding ratio, then annealing the hot rolled plate, cold working and annealing the sheet. CONSTITUTION:Ultralow carbon steel contg. <=0.045% C, <=1.0% Mn, <=0.080% Al, <=0.0050% N and Ti or/and Nb and having the following condition is treated. Namely the steel is composed of an inner layer part contg. <=0.15% (Ti + Nb quantity) and satisfying the formula and of austenitic stainless steel, with surface layer part having thickness of 2.5-30% cladding ratio at one side. And the steel is hot rolled, then the plate is annealed, cold worked by >=10% and annealed at 670-950 deg.C C. Stainless clad steel sheet obtd. in such a way, has superior workability, especially deep drawability and corrosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a stainless clad steel sheet having excellent workability, particularly deep drawability 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 M-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.

In terms of corrosion resistance, austenitic stainless steel sheets are the best, 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.

In a clad steel plate made of ordinary steel and stainless steel, the affinity between Cr and C is high, and diffusion of C from the ordinary steel layer to the stainless steel layer occurs, resulting in a problem in which corrosion resistance is reduced. 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. 5B-1
5310, Japanese Patent Publication No. 5B-19381, and U.S. Pat. No. 3,693,242).

However, in these disclosed techniques, the amount of C and N is large, and
Since large amounts of Ti and Nb are used, sufficient workability cannot be obtained and the cost is also high. Furthermore, as another method for preventing C diffusion, methods have been proposed in which the interface layer is plated with N1 or Ni'i is inserted, but these methods have the problem of significantly increasing costs.

In addition, the manufacturing method relied only on welding and assembling in a sandwich shape and then hot pressing, resulting in low yields.
The cost was high.

The present inventors have already found that at least one side of the surface layer has a
A method for manufacturing a clad steel sheet having a 15% austenitic stainless steel layer was invented.

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

(Means for Solving the Problems) The present invention provides a stainless steel clad steel plate in which the inner layer or one side is made of ultra-low carbon steel and the surface layer is made of austenitic stainless steel, and the gist thereof is that C≦0. 0
045chi, A1. ≦0.080%.

Mn≦1.0%, N amount 0.0050% and Ti, )J
In ultra-low carbon steel sheets containing one or two of b.
Ti-+-Nb) content is 0.15% or less and satisfies the following formula 1: an inner layer or one side portion, and a surface layer made of 7.740 4C + 3.43N austenitic stainless steel on at least one side; The thickness of the section is one side and the cladding ratio is 2.
5%-30% steel is hot rolled and then annealed to 10%
It is characterized in that it is cold worked and annealed at a temperature of less than 950''C and 670°C or more.

The present invention will be explained in detail below.

First, C and M of the ultra-low carbon steel portion of the steel sheet of the present invention.

The reasons for limiting N and Mn will be explained.

If C exceeds o or ooass, not only will the workability deteriorate, but in order to ensure excellent deep drawability (Tl + N
b) It is necessary to increase the amount. Also, C is 0.004
When it exceeds 5%, chromium carbide tends to precipitate at the interface between the ultra-low carbon steel layer and the 808 layer, and corrosion resistance deteriorates.

It is better to have less all, but from the point of view of melting cost in steel manufacturing, the lower limit is naturally determined, 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 lOppm, and the preferable range is 0.0010 ~ It is 0.0040chi.

AQ is 0.00 for deoxidation and to maximize the effect of improving aging property and workability by adding Nb and Ti.
5% or more is required, but if it exceeds 0.08%, the effect will be saturated and the cost will increase. The preferred range is 0.015-0.0
It is 60%.

N reduces the workability improvement effect of Nb and Ti, so 50pp is added.
From the viewpoint of processability, it is preferable to reduce the amount to 40 ppm or less. 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 Mn exceeds 1.0%, the strength increases and workability decreases, so it is set to 1.096 or less. When 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 making it 0.50% or less. In addition, the lower limit is preferably o, os% or more in order to ensure excellent hot workability.

Next, in the present invention, Ti and Nb are added to the ultra-low carbon steel part, and the amounts of Ti and Nb are determined in order to provide excellent workability and prevent deterioration of workability due to aging, and for the stainless steel part from the inner layer to the surface layer. In order to suppress the diffusion of C into C, it is necessary to limit the amounts of C and N, and also to make the chemical equivalence ratio to 1, that is, 0.8 or more with C9N.

'i', 74C) + 3.43N (where Nb, Ti, C, and N are Tanimoto's weight t%) By setting this chemical equivalence ratio to 1.0 or more, the effect of the present invention is maximized. Demonstrated. Still (Ti+Nb)
As the amount increases, processability deteriorates, so it is limited to 0.15% or less. Austenitic stainless steel is used for the surface layer, and its components may be within the range regulated by JIS G4303. For example, in 5US304, C
The amount is 0.08% or less.

Next, we will discuss the reason for limiting the clad ratio (the ratio of the thickness of the clad material (austenitic stainless steel) to the thickness of the clad steel).

If the cladding ratio is less than 2.5%, the surface SUS layer will be easily torn and the inner layer will be exposed, which will impair corrosion resistance.
The lower limit of the surface SUS layer is 2.5% or more on one side, and SU on both sides.
When having an S layer, it is 5% or more on both sides.

Furthermore, if the cladding rate exceeds 30% on one side and 60cm on both sides, the cost advantage of cladding will decrease, so the upper limit of the cladding rate should be 30cm or less on one side (60% or less on both sides).

After hot rolling, annealing is performed for recovery, recrystallization, or solution treatment. This is to improve the workability of cold rolling. Also,
The annealing temperature is determined in relation to the hot rolling winding temperature. That is, when the winding temperature exceeds 600°C, chromium carbide precipitates in the stainless steel layer, so high-temperature annealing, for example, 1050°C, is required to make it a solution. However, when the winding temperature is 600°C or lower, low-temperature annealing, for example, 850°C, is sufficient for recovery recrystallization.

After this, cold working is performed at a reduction rate of 10% or more, and annealing is performed at a temperature of less than 950°C and a temperature of 570' or more.If the cold rolling rate is less than 10%, there is no effect of cold rolling.There is no upper limit on the rolling reduction rate. However, from the viewpoint of workability, it is usually desirable to have a diameter of about 90 inches or less.

If the annealing temperature after cold rolling is 950° C. or higher, the texture of the ultra-low carbon steel will be destroyed, making it impossible to obtain a high r value, and the deep drawability will deteriorate. Further, if the temperature is lower than 670°C, the recrystallization of the ultra-low carbon steel will not be completed, and a high r value and IJ will not be obtained. In order to further increase the r value and elongation, the temperature is preferably 775°C or higher.

In the present invention, SUS overlaying on ordinary steel is desirably carried out by a casting method from the viewpoint of cost φ). This example 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.

In addition, even with other methods such as rolling crimping, the method of the present invention does not require the insertion of N1 foil between the surface layer and the inner layer, and exhibits the excellent effect of reducing costs.

Figure 1 shows the components of the present invention (C0,0035%, Si0.0
2%, Mn 0.3%, NO, 0030%, Q
o, 036%, Ti0.07ch) and 5US30
A steel consisting of a surface layer of No. 4 was hot-rolled into four pieces at a finishing temperature of 910°C, and then annealed at 1°C and 50°C.

Subsequently, after cold rolling to a thickness of 0.5 to 0.8, it was heated to 1100°C.
The relationship between the annealing temperature of a cold rolled sheet and the r value of a three-layer stainless clad steel sheet annealed with a cladding ratio of 0 to 30% is shown below. According to the method of the present invention, a stainless clad steel plate with a high r value can be obtained.

(Example) Table 1 shows the components of the inner layer and surface layer of the stainless clad steel of the present invention and the respective clad ratios.

The process is to manufacture the 250 mm thick clad slab of the present invention using the casting method described above; 4. Hot rolled to orra, 1050°C
The material was annealed at 1,100° C. or lower, and then cold-rolled to 0.8 batches and annealed at 1100° C. or lower. Table 2 shows the cold rolled plate annealing temperature, tensile test value, and corrosion resistance of this steel plate. The inventive steel exhibits a higher r value than the comparative clad steel.

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

[Brief explanation of drawings]

FIG. 3 is a chart showing the relationship between cold rolled sheet annealing temperature and r value. Agent Patent attorney Tatsuo Chanoki

Claims (1)

[Claims] An ultra-low carbon steel plate containing C≦0.0045%, Mn≦1.0%, Al≦0.080%, N≦0.0050%, and one or two of Ti and Nb. , the inner layer part has a (Ti+Nb) content of 0.15% or less and satisfies the following formula 1, and (Nb)/(7.74C)+(Ti)/(4C+3.4
3N)≧0.8...A steel having a surface layer made of Type 1 austenitic stainless steel 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, After that, hot-rolled plate is annealed and cold-worked by 10% or more.
A method for producing a stainless clad steel sheet with excellent workability and corrosion resistance, characterized by annealing at a temperature below 670°C and above 670°C.