JPS6254020A - Manufacture of stainless clad steel sheet superior in ductility and corrosion resistance - Google Patents

Abstract

PURPOSE:To inexpensively obtain the titled clad steel sheet, by composing inner layer part of ultralow C steel contg. limited quantities of Al, N, Mn and prescribed quantities of Ti, Nb in clad steel sheet having surface layer of austenitic stainless steel. CONSTITUTION:Inner layer part is made of ultralow C steel sheet contg. by weight <=0.0045% C, <=1.0% Mn, <=0.080% Al, <=0.0050% N and Ti and/or Nb under <=0.15% (Ti+Nb) further satisfying an inequality. Steel having surface layer part made of austenitic stainless steel at least at one side and the thickness of 2.5-30% cladding ratio at one side is hot rolled. Thereafter this is annealed at >=950 deg.C, or cold worked by >=10% draft after annealing at >=900 deg.C and annealed at >=950 deg.C.

Description

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

(Conventional technology) Steel plates, as typified by copper 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 Al-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, 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.

Clad steel plates made of ordinary steel and stainless steel have a high affinity for Cr and C (there was a problem that diffusion of C from the ordinary steel layer to the stainless steel layer occurred, resulting in a decrease in mechanical strength.To prevent this , by adding a carbide forming element system to the ordinary steel side, C
A technology has been disclosed to prevent the spread of
15310, Japanese Patent Publication No. 58-19381, and US Pat. No. 3,693,242).

However, in these disclosed technologies, C and Ni are large, and
Since a large amount of Tfi is used, sufficient workability cannot be obtained and the cost is high. Furthermore, as another method for preventing diffusion of C, methods of plating the interface layer with Ni or inserting a Ni foil have been proposed, but these methods have the problem of significantly increasing costs. Furthermore, the manufacturing method relied solely on welding and assembling the product in a sandwich shape and then hot-pressing it.
Yield was low (and cost was high).

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 provides an inexpensive method for producing a clad steel plate that has the highest degree of ductility and corrosion resistance, and also has excellent thermal conductivity.

(Means for Solving the Problems) An object of the present invention is to provide a three-layer stainless steel clad plate in which the inner layer is made of ultra-low carbon steel and both surface layers are made of austenitic stainless steel. C≦0.
0045%, Al≦o, oso%, Mn≦i,
o%, N≦O, OO50% and an ultra-low carbon steel plate containing one or two of Ti and Nb, (Ti+Nb)
The surface layer is made of austenitic stainless steel and the inner layer is 0.15% or less and satisfies the following formula 1 on at least one side, and the thickness of the surface layer is on one side and the cladding ratio is 2.
Hot rolling 5%-30% steel and then annealing at 950°C or higher, and after hot rolling and annealing at 900°C or higher 1
This is a method for producing a stainless clad steel sheet with excellent ductility and corrosion resistance, which is characterized by cold working at 0% or higher and annealing at 950°C or higher.

The present invention will be explained in detail below.

First, C, Al, N, 11 in the inner layer of the steel sheet of the present invention
The reason for limiting vIn will be described.

When C exceeds 0.0045%, not only does the ductility decrease, but also it is necessary to increase the amount of (Ti + Nb) to ensure excellent deep drawability.Also, when C exceeds 0.0045%, Chromium carbide tends to precipitate at the interface between the inner layer and the surface layer, deteriorating corrosion resistance.

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 steel manufacturing, 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 (the preferable range is 0.0010 ~0.0040-.

Al has a content of 0.00 for deoxidation and to maximize the effect of improving aging and processability by adding Nb%Ti.
It is necessary to use 5% or more, 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, in view of 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 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 poor 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 and Nb are added to the inner layer, and the amount of Ti and Nb in the inner layer is determined 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 C and Nt, it is necessary to set one formula, that is, the chemical equivalence ratio with C and N to 0.8 or more.

(Here, the corner, Ti, C, and N are weight percent of the valley elements.) By setting this chemical equivalence ratio to 1.0 or more, the effects of the present invention are maximized. Moreover, since the ductility decreases as the amount of (Ti+Nb) increases, 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 G 4303. For example, in 5US304, the C amount is 0.0
It is 8% or less.

Next, we will discuss the reasons for limiting the cladding ratio (ratio of the thickness of the cladding material (austenitic stainless steel) to the thickness of the cladding steel). If the cladding ratio is less than 2.5%, the surface SUS layer is likely to tear and the inner layer will be exposed, impairing corrosion resistance, so the lower limit of the surface SUS layer should be set to 2.
5% or more, 5% or more on both sides. Furthermore, if the cladding ratio exceeds 30% on one side and 60% on both sides, the cost advantage of cladding decreases, so the upper limit of the cladding ratio is set to 30% or less on one side (60% or less on both sides).

When only annealing is performed after hot rolling, the annealing is performed at 950°C or higher. If the annealing temperature is less than 950°C, the surface stainless steel member will not undergo sufficient recrystallization and grain growth, and will not have sufficient height and ductility. Therefore, the annealing temperature after hot rolling should be 950°C or higher.

When cold rolling is performed after hot rolling annealing, recrystallization and solution treatment can be performed at 900° C. or higher. Thereafter, cold working is performed at a reduction rate of 10% or more, and annealing is performed at 950° C. or more. If the cold rolling rate is less than 10%, there is no effect of cold rolling. There is no particular upper limit to the rolling reduction ratio, but from the viewpoint of workability, it is usually desirable to set it to about 90 rolls 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, SUS overlaying on common steel is desirably carried out by a casting method from the viewpoint of cost. 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 Ni foil to be placed between the surface layer and the inner layer (
It has the excellent effect of being able to reduce costs.

Figure 1 shows C0.04%, Si0.02%, Mn0.3%
, NO,0025%, Al0.050% inner layer, and 5U
A three-layer stainless clad steel shell consisting of the surface of S304 and the components of the present invention (C0,0035%, Si0.02%, M
n0.3%, NO,0030%, Al0.036%, T
The steel of the present invention (B) consisting of an inner layer of i0907%) and a surface layer of SUS was hot-rolled into 4 pieces at a finishing temperature of 910°C.
Annealed at ℃.

Subsequently, after cold rolling to a plate thickness of 0.5 to 0.8 fi, 1100℃
This figure shows the strength-ductility balance of a three-layer stainless clad steel sheet annealed with a cladding ratio of O to 60%.

The present invention-a4(A) has higher ductility than the comparison m(B) at the same tensile strength.

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

The process is to manufacture the 250-thick clad slab of the present invention using the casting method described above; 4. It was hot rolled to onm and annealed at 1100°C, then cold rolled to o, sm and annealed at 1100°C.

Only Bm indicates the properties of the hot-rolled and annealed sheet by BH.

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.

(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 the drawing]

Figure 1 shows the tensile strength and ductility (total elongation) of the inventive steel and comparative steel.
This is a chart showing the relationship between Agent: Patent Attorney Tatsuo ChanokiRS (0%)

Claims (1)

[Claims] 1 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. In the above, 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+3.43N)≧0.8...Steel that has a surface layer made of type 1 austenitic stainless steel on at least one side, and the thickness of the surface layer is 2.5% to 30% on one side. hot rolled, then 9
A method for producing a stainless clad steel sheet with excellent ductility and corrosion resistance, characterized by annealing at 50°C or higher. In an ultra-low carbon steel sheet containing 2C≦0.0045%, Mn≦1.0%, Al≦0.080%, N≦0.0050% and one or two of Ti and Nb, the amount of (Ti+Nb) An inner layer portion that is 0.15% or less and satisfies the following formula 1 and (Nb/7.74C) +
[Ti/(4C+3.43N)≧0.8...Steel that has a surface layer made of type 1 austenitic stainless steel on at least one side, and the thickness of the surface layer is 2.5% to 30% on one side. hot rolled, then 9
A method for producing a stainless clad steel sheet with excellent ductility and corrosion resistance, characterized by cold working by 10% or more after annealing at 00°C or higher, and annealing at 950°C or higher.