JP3207538B2 - High corrosion resistant clad steel sheet with remarkably excellent interfacial fracture resistance during processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high corrosion-resistant clad steel sheet having excellent interfacial fracture resistance during processing, which is used as a structural material for general processing including construction materials and automobiles.

[0002]

2. Description of the Related Art Conventionally, steel plates used in construction, kitchen appliances, automobiles, etc. have been used by painting or plating their surfaces in order to increase their corrosion resistance. Is increasing. For example, demands are increasing in various fields such as building skins and kitchen utensils that require long-term aesthetics, automobile mufflers that are exposed to high-temperature environments and are highly corroded, tanks and piping in various plants.

[0003] On the other hand, stainless steel is excellent in terms of corrosion resistance, but has poor workability and costs significantly higher than ordinary steel because Cr and Ni are added. For this reason, as a steel sheet excellent in corrosion resistance and low in production cost, a clad steel sheet in which the surface layer is made of stainless steel having good corrosion resistance, or the inner layer is made of inexpensive ordinary steel with Cr and Ni-added high corrosion resistance steel being developed.

However, the following problems are pointed out in these high corrosion-resistant clad steel sheets. That is, if the amounts of C and N in the surface layer and the inner layer are not sufficiently reduced, a very hard and brittle martensitic phase is formed at the interface of the inner layer during the heat treatment, which causes breakage at the interface during processing. .
In addition, in the clad steel sheet manufactured by hot rolling compression bonding or explosion, which is currently the mainstream, since the component change from the surface layer to the inner layer occurs rapidly at the interface, the workability of the surface layer and the inner layer is It is greatly different, and when subjected to severe processing, the interface becomes a starting point of destruction, so that the workability as a steel sheet is inferior to that of a single sheet.

To solve this problem, Japanese Patent Publication No. 58-1531
No. 0, Japanese Patent Publication No. 1-7138, JP-A-62-5
Means of reducing the C content of ordinary steel as disclosed in Japanese Patent No. 4020 and further adding C-fixing elements such as Ti and Nb and various elements can be considered. Corresponding interfacial failure cannot be avoided. As another method, a method of plating the interface layer with Ni or inserting a Ni foil has been proposed, but the use of Ni causes an increase in cost.

[0006]

DISCLOSURE OF THE INVENTION The present invention is problematic in a clad steel sheet that achieves both high corrosion resistance and low cost.
It is possible to suppress the destruction at the interface due to the formation of the martensite phase at the interface due to the remaining solid solution C and N, and the destruction at the interface due to the sudden change in the properties in the plate thickness direction. An object of the present invention is to provide a clad steel sheet having workability.

[0007]

Means for Solving the Problems The present invention has been obtained as a result of a study on the components of the surface steel and the inner steel to solve the above-mentioned problems. At the same time that the inner layer steel has low C and N components, an appropriate amount of Ti, Nb or the like is added to form a carbonitride, thereby suppressing the generation of hard martensite at the interface. (2) In order to avoid abrupt component change at the interface, a clad steel sheet is formed into a clad steel sheet having a structure in which the layers are formed by a casting method and the inner layers are mixed in an appropriate range without being completely separated. On the point.

That is, according to the present invention, (1) the surface layer comprises C:
0.0007 to 0.0800%, Cr: 10.0 to 2
5.0%, Ni: 3.0 to 15.0%, N: 0.001
0 to 0.0800%, and the inner layer is C: 0.0
005 to 0.0150%, N: 0.0010 to 0.02
00%, containing any one or two of Ti and Nb and satisfying the following formula,

(Equation 6) Furthermore, the ratio of the inner layer Cr to the surface layer Cr is given by

(Equation 7) A steel sheet having a multi-layer structure cast in such a manner that the ratio of the surface layer to the total thickness is 2 to 30% on one side (4 to 60% in the case of both surface layers). The high corrosion-resistant clad steel sheet having remarkably excellent destructibility, and (2) the surface layer has a C content of 0.0007 to 0.080 by weight%.
0%, Cr: 10.0 to 25.0%, Ni: 3.0 to 1
5.0%, N: 0.0010 to 0.0800%, Ti,
Containing one or two of Nb and satisfying the following formula:

(Equation 8) Inner layer: C: 0.0005 to 0.0150%, N: 0.0
010 to 0.0200%, containing any one or two of Ti and Nb, and satisfying the following expression;

(Equation 9) Furthermore, the ratio of inner layer Cr to surface layer Cr is

(Equation 10) A steel sheet having a multi-layer structure cast in such a manner that the ratio of the surface layer to the total thickness is 2 to 30% on one side (4 to 60% in the case of both surface layers). It is a highly corrosion-resistant clad steel sheet with remarkably excellent destructibility.

[0009]

Hereinafter, the present invention will be described in detail. First, the components of the surface layer will be described. The reduction of C improves the workability of the surface layer itself, and suppresses the generation of a martensite phase at the interface, thereby suppressing the destruction at the interface and improving the workability of the clad steel sheet. In addition, the lower the better, the more the corrosion resistance is improved by suppressing the precipitation of Cr carbide.
However, excessive reduction leads to an increase in cost, so the upper limit is set to 0.
0800%, and the lower limit is 0.0007%.

[0010] N is an element which acts in the same manner as C with respect to workability, and the lower the N, the better the characteristics. However, excessive reduction leads to an increase in cost, so the upper limit is set to 0.0800% and the lower limit is set to 0.0010%.

[0011] Cr is an essential element of the present invention, that is, an element essential for improving the corrosion resistance of the surface layer. The addition amount is not particularly limited, but the optimum addition amount is determined according to the development of corrosion resistance, use, required characteristics and cost. It was limited to 10.0 to 25.0% from a general viewpoint. Ni is an element having the same action as Cr, and is limited to 3.0 to 15.0% from the same viewpoint as Cr.

Ti is added as necessary to form Ti carbides and Ti nitrides, to reduce solid solution C and solid solution N in the steel sheet and to improve the properties of the steel sheet. That is, the addition improves the workability of the surface layer itself, suppresses the diffusion of C and N into the inner layer and avoids the deterioration of the workability of the inner layer, thereby improving the workability of the clad steel sheet and also improving the martensite at the interface. By suppressing the generation, destruction at the interface is suppressed, and the workability of the clad steel sheet is improved. And C to T
Since it is fixed as i carbide, Cr carbide hardly precipitates and corrosion resistance is improved. However, excessive addition raises the recrystallization temperature, so that the final annealing temperature must be increased, which increases energy costs. Nb is an element having the same action as Ti. Consider the addition cost and consider the appropriate range

[Equation 11] And

Next, the components of the inner layer will be described. The reduction of C improves the workability of the inner layer itself, and also suppresses the generation of a martensite phase at the interface, thereby suppressing fracture at the interface and improving the workability of the clad steel sheet. However, excessive reduction leads to an increase in cost.
50%, and the lower limit is 0.0005%. In particular, for applications where workability is important, the upper limit is made 0.0030%.

N is an element acting similarly to C, and the lower the N, the better the characteristics. However, excessive reduction leads to an increase in cost, so the upper limit is set to 0.0200% and the lower limit is set to 0.0010%. In particular, for applications where workability is important, the upper limit is set to 0.0040%. Ti and Nb suppress C diffusion,
It is added to ensure high workability. The required quantity is C, N
If it depends on the amount and is small, the above effects cannot be obtained. Excessive addition results in an increase in cost and coarsening of precipitates, not only losing the effect of suppressing grain growth, but also deteriorating workability.

(Equation 12) And

Next, a measure for obtaining the desired interfacial fracture resistance will be described. Up to now, methods for producing a multilayer steel sheet include a cast-in method, a casting method (two-nozzle casting method), a hot-rolling compression bonding method, and an explosion method. The present inventors have studied the state of the property change at the interface with these manufacturing methods and the fracture phenomenon from the interface during heavy working.As a result, the multilayer steel sheet manufactured by a method other than the casting method has a property change at the interface. It has been found that, because of the rapid separation of components, destruction from the interface is likely to occur during strong working. In addition, even when the casting method was used, when the components of the inner layer were completely separated, destruction from the interface was also observed. In particular, when the Ni content in the surface layer was high and the surface layer was in an austenitic phase, the destruction from the interface became remarkable. As a result, in order to achieve the desired interfacial fracture resistance in the present invention, the production method was limited to the casting method, and a slight mixing of the surface steel and the inner steel was essential. If this mixture is too large, the surface Cr,
The desired corrosion resistance cannot be achieved due to a decrease in the Ni concentration, and the workability of the inner layer and, consequently, the workability of the clad steel sheet deteriorate due to the inclusion of Cr and Ni in the inner layer. Therefore, the ratio of the surface layer Cr to the inner layer Cr is

(Equation 13) Limited to.

Next, the thicknesses of the surface layer and the inner layer will be described. The thickness of the surface layer of the steel sheet is 2% or more of the total thickness, considering that the high corrosion-resistant steel of the surface layer is broken and the iron surface is exposed and the corrosion resistance is impaired during the cold rolling process during manufacturing or the forming process of the product. 4% or more for both surface layers). The upper limit is preferably 30% or less of the total thickness (in the case of both surface layers, the total is 60% or less in both surface layers). This is because one of the objects of the present invention is to reduce the cost by reducing the amount of expensive Cr and Ni used, and the purpose of the steel of the present invention is to use Cr and Ni on the surface layer by using high workability steel for the inner layer steel. This is because the workability deterioration due to the addition is compensated for and the high workability is achieved in the clad steel sheet as a whole.

The steel sheet of the present invention is used after being hot-rolled after casting and, if necessary, passed through a hot-rolled sheet annealing, cold rolling and annealing line. Ma
Also, corrosion resistance, heat resistance, cutting like normal stainless steel
Mo, Cu, Ta, W, Zr, S
The effect of the present invention is not impaired even if e is added.
No. Further, the steel sheet produced by the method according to the present invention is zinc,
It can also be used as a material for surface-treated steel sheets plated with tin, chromium, aluminum, etc.

[0018]

EXAMPLE The molten steel for the surface layer and the inner layer was adjusted to the components shown in Table 1, and a multilayer slab was obtained by a two nozzle casting method. The thickness of the surface layer was the same for both surface layers, and the ratio of both surface layers to the total thickness was 20%. These slabs were annealed after hot rolling and cold rolling, and their properties were evaluated. The results are shown in Table 2.

The steel sheet of the present invention (sample numbers 1, 2, 3, 7, 1)
0,12,13,15) achieve high workability, whereas the comparative steel has crackability from the interface of the inner surface layer, or excessive workability of Cr and Ni from the surface layer to the inner layer. Not good.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

As described above, according to the present invention, it is possible to produce a high corrosion resistant clad steel sheet which is hardly broken from the interface and has excellent workability.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor, Rikuhiko Ito 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Yawata Works (56) References JP-A-1-301184 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00 B21B 1/38 B32B 15/01 C22C 38/50

Claims (2)

(57) [Claims] C .: 0.0007 to 0.0800%, Cr: 10.0 to 25.0%, Ni: 3.0 to 15.0 %, N: 0.0010 to 0.0800%, and the inner layer is C: 0.0005 to 0.0150%, N: 0.0010 to 0.0200%, any one of Ti and Nb or Including two types and satisfying the following formula, Further, the ratio of Cr in the inner layer to Cr in the surface layer is given by the following equation: A steel sheet having a multi-layer structure cast in such a manner that the ratio of the surface layer to the total thickness is 2 to 30% on one side (4 to 60% in the case of both surface layers). Highly corrosion-resistant clad steel sheet with remarkably excellent destructibility. 2. The surface layer has a content of C: 0.0007 to 0.0800%, Cr: 10.0 to 25.0%, Ni: 3.0 to 15.0%, and N: 0.0010% by weight. 0.0800%, containing one or two of Ti and Nb, and satisfying the following expression. The inner layer contains C: 0.0005 to 0.0150%, N: 0.0010 to 0.0200%, and any one or two of Ti and Nb, and satisfies the following expression. Further, the ratio of Cr in the inner layer to Cr in the surface layer is given by A steel sheet having a multi-layer structure cast in such a manner that the ratio of the surface layer to the total thickness is 2 to 30% on one side (4 to 60% in the case of both surface layers). Highly corrosion-resistant clad steel sheet with remarkably excellent destructibility.