JPH0615466A - Manufacture of extremely thick wall steel plate - Google Patents

Abstract

PURPOSE:To reduce the rolling reduction ratio in the manufacture of an extremely thick-wall steel plate by a hot rolling while superposing a continuously cast slab or a thick wall steel plate manufactured from the continuously cast slab. CONSTITUTION:At the time of making a composite slab by superposing a continuously cast slab 1 or a thick wall steel plate 2, an amorphous metal is inserted between superposed surfaces and a central part in the thickness direction of the continuously cast slab 1 is made not to coincide with a central part in the thickness direction of a product. Then the hot rolling is executed by heating the composite slab over the melting temperature of the amorphous metal. The fault in interior quality is excluded even under a condition that the rolling reduction ratio in the hot rolling is low such as >=1.6, and the extremely thick wall steel plate of the thickness >=100mm having excellent quality can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an extremely thick steel plate having a thickness of 100 mm or more from a continuously cast slab.

[0002]

2. Description of the Related Art Extremely thick steel plates having a thickness of 100 mm or more have been conventionally used for pressure vessels such as nuclear reactors and heavy oil desulfurization reactors, and are recently also used for structural materials of buildings which are becoming higher in height. Due to its application, such an extremely thick steel sheet is required to have performance in the sheet thickness direction in addition to the performance in the rolling direction and the direction orthogonal to the rolling, and further, the uniformity of the inner quality is also required.

Conventionally, a method of slab-rolling a steel ingot obtained by an ingot method has been used for the production of an extremely thick steel sheet having a thickness of 100 mm or more, but there is a problem in that it is not economical. Therefore, a method for producing a continuous cast slab or an extra-thick steel sheet in which thick steel sheets produced from the continuous cast slab are superposed and hot rolled is proposed in JP-A-2-197383 and the like.

[0004]

According to this manufacturing method, by superposing the raw materials, an extremely thick steel plate having an arbitrary thickness is manufactured from the continuous casting slab. However, the continuous cast slab as a raw material, when the reduction ratio during hot rolling is small, blowholes inherent in the slab, particularly center porosity and the like existing in the central portion in the thickness direction, are not sufficiently crimped, It remains in the product steel sheet as defects such as scratches. Therefore, when the uniformity of the inner quality is required, as shown in Japanese Patent Application Laid-Open No. 2-197383, a reduction ratio in hot rolling is required to be 3 or more. It was unavoidable to increase.

An object of the present invention is to provide a highly efficient method for producing an extremely thick steel sheet which produces a high quality extremely thick steel sheet under a smaller pressure than a continuous cast slab.

[0006]

Means for Solving the Problems In order to economically manufacture an extremely thick steel plate having a thickness of 100 mm or more, a continuous slab or a thick steel plate manufactured from the continuous slab is stacked to form a composite slab. The method of hot rolling is considered to be optimal. Therefore, the present inventors studied the reduction of the reduction ratio in the hot rolling of the composite slab. As a result, by joining multiple materials in the composite slab through the liquid phase, a sound joint can be obtained, the reduction ratio can be reduced, and by using alumofus metal as the liquid phase insert material, the joining layer can be applied to the product. However, the use of liquid phase insert material does not cause inhomogeneity in the product thickness direction.Furthermore, when a continuous cast slab is used as the material, the center part of the product in the thickness direction is the product thickness. It was found that by stacking the materials so that they do not become the central part in the direction, crimping of blowholes etc. becomes easy and the internal quality can be improved even with a small reduction ratio.

The present invention has been made on the basis of the above findings, and when a continuous slab and / or thick steel plates produced from the continuous slab are superposed on each other to produce a composite slab, the superposed surface is preliminarily subjected to black skin removal. After processing, sandwich the alumous face metal on the overlapping surface, and overlap the materials so that the central part in the thickness direction of the continuous casting slab does not become the central part in the thickness direction of the product, and further around the overlapping surface. To form a composite slab, and then the manufactured composite slab is heated to a temperature above the melting temperature of alumophus metal and hot-rolled at a reduction ratio of 1.6 or more to produce an extremely thick steel plate with a thickness of 100 mm or more. The gist is a method for manufacturing an extra-thick steel plate, which is characterized in that

[0008]

In the method of manufacturing an extra-thick steel plate according to the present invention, when the composite slab is manufactured, the superposed surfaces are preliminarily subjected to the black scale removal treatment. This is because if there is a black skin on the overlapping surface,
This is because oxide-based inclusion defects are likely to remain at the joint interface, which is necessary from the viewpoint of ensuring the soundness of the joint. Shot blasting, mechanical grinding (polishing), or the like is used as the black skin removing process.

The materials whose superposed surfaces have been subjected to the black skin removal treatment are superposed by sandwiching an armophus metal between the superposed surfaces. The material is a continuous cast slab and / or a thick steel plate manufactured from the continuous cast slab. When the continuous cast slab is used in whole or in part, the center in the thickness direction of the slab is the center in the thickness direction of the product. So as not to be a part
It is necessary to consider the stacking order of the materials.

The reason why the alumophus metal is sandwiched between the overlapping surfaces is to complete sound joining at a temperature below the melting temperature of the raw materials and at a small reduction ratio. That is, since the insert material used for liquid phase diffusion bonding generally contains Si or B as a melting point depressing element, it is difficult to make it into a thin plate by a conventional manufacturing method such as rolling, but ductility due to alumofusing It is a rich foil and enables a sound joint to be secured. As for the component of Alumofus metal, it is generally said that the Ni base is well compatible with the material, and the bondability is good.
Here, from the viewpoint of manufacturing an integrated steel sheet, the Fe group is more desirable. The thickness is preferably 150 μm or less and thin. A method of superposing materials when using a continuous casting slab will be described later.

The materials superposed with the armophus metal sandwiched therebetween are made into a composite slab by welding the periphery of the superposed surfaces. Welding the periphery of the overlapping surface is to prevent the material from slipping during rolling,
It is not always necessary to suck and remove the air remaining between the mating surfaces as is done in the slab assembly when manufacturing the clad steel plate. However, this absorption and removal of air is still an effective means for ensuring the soundness of the joint in the present invention.

If the composite slab thus manufactured is heated to a temperature not lower than the melting point of alumophus metal and hot-rolled, it has a sound internal quality even if the rolling ratio is 1.6. An extremely thick steel plate having a thickness of 100 mm or more is manufactured. However, when a continuous cast slab is used as the material, if a reduction in the reduction ratio of 1.6 to 3.0 is attempted to obtain a sound product quality, as described above, the thickness of the slab will be reduced. It is necessary to consider the stacking order of the materials so that the center in the direction does not become the center in the thickness direction of the product.

Table 1 shows the relationship between the ultrasonic flaw detection result and the reduction ratio of a product when two continuous cast slabs are stacked and hot rolled at a reduction ratio of 0.5 to 2.0. In the case of three-slab rolling, it is shown in comparison with the case where a thick steel plate manufactured from a continuously cast slab is sandwiched between two slabs. In rolling of two slabs, internal defects are eliminated when the reduction ratio is 1.6 or more. Also, when a thick steel plate is sandwiched between slabs, the internal defect is eliminated when the reduction ratio is 1.6 or more. However, in single-slab rolling, three-slab rolling, etc., where the central portion in the thickness direction of the continuously cast slab becomes the central portion in the thickness direction of the product, internal defects are eliminated even when the reduction ratio is 2. Not done.

The reason for this is unknown in detail, but the rolling force at the central portion in the thickness direction of the product is insufficient as compared with other portions,
It is considered that if there is a central portion in the thickness direction of the slab where many blowholes and the like exist in this portion, the blowhole and the like cannot be sufficiently eliminated. Therefore, when the continuous casting slab is directly used for the composite slab, the continuous casting slab is superposed so that the central portion in the thickness direction of the product does not become the central portion in the thickness direction of the product. As such superposition, for example, as shown in FIG.
There is a two-layered combination (A), a sandwich structure (B) in which a thick steel plate 2 is sandwiched between two continuously cast slabs 1 and 1, a four-layered combination of the continuous cast slab 1 (C), and the like. There is no problem in overlapping (D) only the plates 2. By the way, as an unsuitable superposition, as shown in FIG. 2, there are three continuous casting slabs 1 (A), a structure in which the continuous casting slab 1 is sandwiched between thick steel plates 2 and 2 (B), and the like. .

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Various composite slabs were manufactured using the continuously cast slabs and thick steel plates whose component compositions are shown in Table 2. At that time, the overlapping surface is Rm by the black skin removal processing by shot brass.
It was finished to ax 25 μm, and Fe-based Armophus metal (Fe-0.5C-2Si-3B, liquidus temperature 1080 ° C., thickness 50 μm) was sandwiched between the overlapping surfaces and welded around the overlapping surfaces. The plan shape of the composite slab is all 2000 width
mm and length 3000 mm. Then, the various composite slabs produced were heated and rolled so that the temperature of the superposed surfaces became 1170 ° C., and the internal quality of the rolled product was examined by ultrasonic flaw detection. Table 3 shows the structure of the composite slab, rolling conditions, and ultrasonic flaw detection results.

In the examples of the present invention (Nos. 1 to 4), the reduction ratio was 3
Despite the following, good internal quality was obtained, and shear strength of 30 kgf / mm ² or more was also shown in the shear test of the bonded interface. In addition, in the tensile test (JIS4) in the plate thickness direction centered on the No. 1 joint, YS
73 kgf / mm ² , TS86 kgf / mm ² , El2
A good result of 2% was obtained. Further, in the present invention,
A combination of the same materials (No. 1, 2, 4) is desirable from the viewpoint of homogenizing the internal quality, but a combination of different materials (No. 3) can also obtain a good joint. A photomicrograph of the No. 3 bonded interface is shown in FIG. 3, but there are no defects at the bonded interface.

On the other hand, in Comparative Example No. 5, the central portion in the thickness direction of the continuous casting slab became the central portion in the thickness direction of the product, so the ultrasonic flaw detection result of the product was poor. Even if the center of the slab in the thickness direction is not the center of the product in the thickness direction, when the reduction ratio is less than 1.6 (N
In o. 6), the ultrasonic flaw detection results were poor due to incomplete crimping of glow holes and the like at the center of each slab, that is, at the 1/4 thick part of the product. When the black skin of the overlapping surface was not removed (No. 7), when the product was cut, peeling occurred from the central portion of the wall thickness. Without liquid phase diffusion bonding (No.
In the case of 8), even if the reduction ratio is the condition specified in the present invention, the diffusion bonding is not performed and the flaw detection result is poor.

[0022]

As is apparent from the above description, according to the method for manufacturing an extra-thick steel sheet of the present invention, an extra-thick steel sheet having a thickness of 100 mm or more and good quality is produced with a small reduction ratio of 1.6 or more. To be done. Therefore, the thickness of the material and the number of overlapping are reduced,
Reduction of steel plate manufacturing cost is achieved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a combination of materials in the method of the present invention.

FIG. 2 is a schematic diagram showing an example of an inappropriate material combination.

FIG. 3 is a micrograph showing a metal structure in a joint portion of an extremely thick steel sheet manufactured by the method of the present invention.

[Explanation of symbols]

 1 Continuous cast slab 2 Steel plate manufactured from continuous cast slab

Claims (1)

[Claims] 1. When producing a composite slab by superposing continuous cast slabs and / or thick steel plates produced from the continuous cast slabs, the superposed faces are preliminarily subjected to a black skin removal treatment, and then the superposed faces are made of alumos face. The metal is sandwiched, and the materials are superposed so that the central portion in the thickness direction of the continuous casting slab does not become the central portion in the thickness direction of the product, and further, the periphery of the superposed surface is welded to form a composite slab, and then , An extremely thick steel plate having a thickness of 100 mm or more is produced by heating the produced composite slab to a melting temperature of alumophus metal or higher and hot rolling at a reduction ratio of 1.6 or more. Steel plate manufacturing method.