JPH0657377A - High corrosion resistant clad steel plate remarkably excellent in interface fracture resistance at working - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a highly corrosion-resistant clad steel plate that prevents damage due to interfacial peeling during processing. [Structure] Interfacial fracture resistance of a cast multi-layer structure consisting of a Ni-Cr type stainless steel containing a small amount of Ti and Nb in the surface layer if necessary, and a low carbon steel containing a small amount of Ti and Nb in the inner layer as needed. Excellent high corrosion resistance clad steel plate.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Steel plates used for construction, kitchen appliances, automobiles, etc. have been used by coating or plating on the surface to enhance their corrosion resistance. Is increasing. For example, demand is increasing in all fields such as building exterior panels and kitchen appliances that require long-term aesthetics, mufflers for automobiles that are highly corroded by being exposed to high temperature environments, tanks and piping in various plants.

On the other hand, stainless steel is excellent in corrosion resistance, but is poor in workability as compared with ordinary steel because of the addition of Cr, Ni and the like, and the cost is remarkably high. Therefore, as a steel plate having excellent corrosion resistance and low manufacturing cost, a stainless steel plate having excellent corrosion resistance in the surface layer, or a clad steel plate having Cr and Ni-added highly corrosion resistant steel and an inner layer made of inexpensive ordinary steel has been developed.

However, the following problems are pointed out in these highly corrosion resistant clad steel sheets. That is, if the C and N contents of the surface layer and the inner layer are not sufficiently reduced, a very hard and brittle martensite phase is formed at the interface between the surface and the inner layer during heat treatment, causing fracture at the interface during processing. .
In the current mainstream, clad steel sheets manufactured by hot-rolling compression bonding and explosion-bonding, the composition change from the surface layer to the inner layer occurs rapidly at the interface, so the workability of the surface layer and the inner layer is bordered by the interface. It is very different, and when subjected to severe working, the interface becomes the starting point of fracture, so that the workability as a steel plate is inferior to that of a single plate.

To solve this problem, Japanese Patent Publication No. 58-1531
No. 0, Japanese Patent Publication No. 1-7138, JP-A-62-5
Although it is conceivable to reduce the C content of ordinary steel as shown in Japanese Patent No. 4020 and further add C-fixing elements such as Ti and Nb, and various elements, a sudden change in the workability of the inner and outer layers can be considered. Corresponding interface destruction 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]

The present invention has a problem in a clad steel sheet that has both high corrosion resistance and low cost.
Suppresses the fracture at the interface due to the formation of martensite phase at the interface due to the residual solid solution C and N, and the fracture at the interface due to the abrupt change of the properties in the plate thickness direction, It is an object of the present invention to provide a clad steel plate that also has workability.

[0007]

Means for Solving the Problems The present invention was obtained as a result of studying the composition of surface layer steel and inner layer steel for solving the above problems, and the basic idea thereof is (1) surface layer steel, and The inner layer steel is made to have a low C and N composition, and at the same time, Ti, Nb and the like are added in appropriate amounts to form carbonitrides and suppress the generation of hard martensite at the interface. (2) In order to avoid a rapid change in the composition at the interface, a clad steel sheet having a structure in which multiple layers are formed by a casting method and the inner surface layers are not completely separated and mixed in an appropriate range. In point.

That is, according to the present invention, (1) the surface layer is C:
0.0007-0.0800%, Cr: 10.0-2
5.0%, Ni: 3.0 to 15.0%, N: 0.001
It is a component of 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, Nb and satisfy the following formula,

[Equation 6] Furthermore, the ratio of Cr in the inner layer and Cr in the surface layer is

[Equation 7] A steel sheet having a cast multi-layer structure such that the ratio of the surface layer to the total plate thickness is 2 to 30% on one side (4 to 60% in the case of both surface layers). Highly corrosion-resistant clad steel plate with remarkably excellent fracture resistance, and (2) surface layer, C: 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,
Satisfying the following formula while containing any one or two of Nb,

[Equation 8] Inner layer is 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 formula,

[Equation 9] Furthermore, the ratio of Cr in the inner layer and Cr in the surface layer is

[Equation 10] A steel sheet having a cast multi-layer structure such that the ratio of the surface layer to the total plate 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 plate with extremely excellent fracture resistance.

[0009]

The present invention will be described in detail below. 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 occurrence of the martensite phase at the interface to suppress the fracture at the interface and improve the workability of the clad steel sheet. Further, the lower the value is, the better the corrosion resistance by suppressing the precipitation of Cr carbide.
However, excessive reduction causes an increase in cost, so the upper limit is set to 0.
The lower limit is 0800% and the lower limit is 0.0007%.

N is an element that acts similarly to C in terms of workability, and the lower the value, the better the characteristics. However, excessive reduction causes an increase in cost, so the upper limit is made 0.0800% and the lower limit is made 0.0010%.

Cr is an essential element for improving the corrosion resistance of the surface layer, which is an important requirement of the present invention. The addition amount is not particularly limited, but the optimum addition amount is determined according to the expression of corrosion resistance, the application, required characteristics and cost. From a general viewpoint, it is limited to 10.0 to 25.0%. Ni is also 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 carbide and Ti nitride, reduce solid solution C and solid solution N in the steel sheet, and improve the characteristics of the steel sheet. That is, the workability of the surface layer itself is improved by the addition, and not only the workability of the clad steel sheet is improved by suppressing C and N diffusion into the inner layer and avoiding the workability deterioration of the inner layer, but also the martensite at the interface is improved. By suppressing the generation, the fracture at the interface is suppressed and the workability of the clad steel plate is improved. Further C to T
Since it is fixed as i-carbide, Cr carbide is less likely to precipitate and corrosion resistance is improved. However, since excessive addition raises the recrystallization temperature, the final annealing temperature must be raised and the energy cost rises. Nb is also an element having the same action as Ti. Considering the cost of adding these,

[Equation 11] And

Next, the components of the inner layer will be described. The reduction of C not only improves the workability of the inner layer itself, but also suppresses the occurrence of the martensite phase at the interface to suppress the fracture at the interface and improves the workability of the clad steel sheet. However, excessive reduction causes an increase in cost, so the upper limit is 0.01
50% and the lower limit is 0.0005%. Especially for applications where workability is important, the upper limit is made 0.0030%.

N is also an element that acts similarly to C, and the lower the value, the better the characteristics. However, excessive reduction causes an increase in cost, so the upper limit is made 0.0200% and the lower limit is made 0.0010%. For applications where workability is particularly important, the upper limit is made 0.0040%. Ti and Nb suppress C diffusion,
It is added to ensure high workability. The required amount is C, N
If the amount is small, the above effect cannot be obtained. In addition, excessive addition causes an increase in cost, coarsens precipitates, loses the effect of suppressing grain growth, and deteriorates workability, so the appropriate range is set.

[Equation 12] And

Next, a method for obtaining the target interfacial fracture resistance will be described. Heretofore, as a manufacturing method of a multilayered steel sheet, there are a cast-gurgling method, a casting method (two-nozzle casting method), a hot rolling compression bonding method, an explosive bonding method and the like. The present inventors have examined these manufacturing methods and the state of characteristic change at the interface, and the result of studying the fracture phenomenon from the interface during heavy working, and in the multi-layer steel sheet produced by a method other than the casting method, the characteristic change at the interface, that is, It has been found that, since the components are separated rapidly, breakage from the interface is likely to occur during heavy working. Further, even by the casting method, when the components in the inner and outer layers were completely separated, it was observed that the interface was broken. In particular, when the Ni content of the surface layer became high and the surface layer became an austenite phase, the fracture from the interface became remarkable. As a result, in order to realize the target interfacial fracture resistance in the present invention, the manufacturing method was limited to the casting method, and a slight mixing of the surface layer steel and the inner layer steel was essential. If this mixture is too large, surface Cr,
The Ni concentration decreases and the desired corrosion resistance cannot be achieved, and the workability of the inner layer, and eventually the workability of the clad steel plate, deteriorates due to the inclusion of Cr and Ni in the inner layer. Therefore, the ratio of surface layer Cr to inner layer Cr is

[Equation 13] Limited to

Next, the thickness of the surface layer and the inner layer will be described. The thickness of the steel sheet surface layer 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 corrosion resistance is impaired during cold rolling during manufacturing or during product forming 4% or more on both surface layers) is desirable. Further, the upper limit is preferably 30% or less of the total thickness (60% or less in both surface layers in the case of both surface layers). This is because one of the objects of the present invention is to reduce the cost by reducing the amounts of expensive Cr and Ni used, and the purpose of the steel of the present invention is to use highly workable steel for the inner layer steel, thereby making the surface layer Cr, Ni less. This is because the workability deterioration due to the addition is compensated to achieve high workability as a whole of the clad steel plate.

The steel sheet of the present invention is used after being hot-rolled after casting, and if necessary, hot-rolled sheet annealed, cold-rolled, and annealed at a line. It can also be used as a material for a surface-treated steel sheet produced by plating the steel sheet produced by the method of the present invention with zinc, tin, chromium, aluminum or the like.

[0018]

EXAMPLE A molten steel for the surface layer and the inner layer was adjusted to the composition shown in Table 1 to obtain a multi-layer cast product 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 layer totals to the total thickness was 20%. These slabs were hot-rolled, cold-rolled, and then annealed for characteristic evaluation. The results are shown in Table 2.

Steel sheet of the present invention (Sample Nos. 1, 2, 3, 7, 1
0,12,13,15) has achieved high workability, whereas the comparative steel has workability due to crack generation from the interface of the surface inner layer or excessive Cr and Ni mixing 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 manufacture a highly corrosion-resistant clad steel sheet which is less likely to be broken from the interface and has excellent workability.

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[Procedure amendment]

[Submission date] September 3, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

The steel sheet of the present invention is used after being hot-rolled after casting, and if necessary, hot-rolled sheet annealed, cold-rolled, and annealed at a line. Well
Corrosion resistance, heat resistance, and cutting like ordinary stainless steel
Mo, Cu, Ta, W, Zr, S to improve properties
The effect of the present invention will not be impaired even if e is added.
Yes. In addition, 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 plates plated with tin, chromium, aluminum, etc.

Front page continuation (72) Inventor Rokuhiko Ito 1-1 Tobahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Co., Ltd. Yawata Works

Claims (2)

[Claims] 1. A surface layer (element content is% by weight, the same applies hereinafter), 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 expressed by the following equation: A steel sheet having a cast multi-layer structure such that the ratio of the surface layer to the total plate thickness is 2 to 30% on one side (4 to 60% in the case of both surface layers). Highly corrosion-resistant clad steel plate with outstanding fracture resistance. 2. The surface layer, in% by weight, C: 0.0007-0.0800%, Cr: 10.0-25.0%, Ni: 3.0-15.0%, N: 0.0010-. 0.0800%, containing one or two of Ti and Nb and satisfying the following formula, The inner layer contains C: 0.0005 to 0.0150%, N: 0.0010 to 0.0200%, one or two of Ti and Nb, and satisfies the following formula, Furthermore, the ratio of Cr in the inner layer and Cr in the surface layer is A steel sheet having a cast multi-layer structure such that the ratio of the surface layer to the total plate thickness is 2 to 30% on one side (4 to 60% in the case of both surface layers). Highly corrosion-resistant clad steel plate with outstanding fracture resistance.