JP2005152998A - Ultra-thick steel plate and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an ultra-thick steel plate having a uniform internal quality exceeding 200 mm in thickness at low cost.
SOLUTION: Two or more slabs are overlapped, and the composite slab is formed by welding four rounds of the overlapping surface, and the effective central stress sum Seff defined by the following formula (1) is 0.3 or more. A method for producing a super extra-thick steel plate having a thickness exceeding 200 mm, wherein the composite slab is hot-rolled under conditions.
Seff = Σ [(σtcmax / k ₀ ) -1] --- (1)
Here, Σ indicates the sum of the values of each pass through the rolling schedule.
However, (σtcmax / k ₀ ) −1 <0 is not added.
Further, σtcmax / k ₀ = 1.67 × (ld / hm) +0.5
Where ld: projected contact arc length
hm: Average plate thickness (average of input side plate thickness and output side plate thickness)
k ₀ : Deformation resistance [selection diagram] FIG.

Description

  The present invention relates to a super-thick steel plate and a method for manufacturing the same, and more particularly to a super-thick steel plate having a uniform internal quality exceeding 200 mm, and a method for manufacturing the same. Is.

  Ultra-thick steel plates having a thickness exceeding 100 mm have been conventionally used for pressure vessels, large structures, and the like. Such an extra-thick steel plate is required to have a uniform internal quality, in particular, because of its application. Such an extra-thick steel plate has been manufactured by split-rolling a steel ingot cast by the ingot method, but has a problem in economic efficiency.

  Therefore, Japanese Patent Publication No. 7-83946 (Patent Document 1), Japanese Patent Application Laid-Open No. 2-197383 (Patent Document 2), Japanese Patent Application Laid-Open No. 4-190902 (Patent Document 3), Japanese Patent Application Laid-Open No. 4-266402 (Patent Document). In Reference 4), a plurality of continuous cast slabs are overlapped, and the composite surface is formed by welding four rounds of the overlapped surface, and after the overlapped surface is vacuum-treated, it is hot-rolled to have a thickness of 100 mm or more. A method for producing an extra heavy steel sheet is described. In these prior arts, the reduction ratio is defined from the viewpoint of slab jointability, which is 2 or more in Patent Document 1, 3 or more in Patent Document 2, and 2.5 or more in Patent Documents 3 and 4, respectively.

  Japanese Patent Laid-Open No. 6-15466 (Patent Document 5) discloses that an amorphous metal is inserted between overlapping surfaces of a slab with a reduction ratio of 1.6 or more for the purpose of reducing the reduction ratio of the composite slab. A method of manufacturing a very thick steel plate having a thickness of 100 mm or more to be rolled is disclosed.

Japanese Patent Publication No. 7-83946 Japanese Patent Laid-Open No. 2-197383 Japanese Patent Laid-Open No. 4-190902 JP-A-4-266402 JP-A-6-15466

  However, the above prior art has the following problems. That is, in the prior arts disclosed in Patent Documents 1 to 4, since the reduction ratio is as large as 2 or more, the obtained product plate thickness is also 200 mm or less.

  In addition, the prior art disclosed in Patent Document 5 has a small reduction ratio, so that an extremely thick steel plate having a thickness of 200 mm or more can be obtained, but an expensive amorphous metal is required, which is not practical.

  Accordingly, an object of the present invention is to obtain a super-thick steel plate having a uniform internal quality exceeding 200 mm without using an expensive insert metal such as an amorphous metal.

  Therefore, as a result of examining the rolling conditions of the composite slab, the inventors of the present application only hot-rolled the composite slab without using an expensive insert metal if the effective central stress sum Seff is a predetermined value or more. The knowledge that the super-thick steel plate exceeding 200 mm in thickness excellent in bondability can be obtained was acquired.

  The present invention has been made on the basis of the above-described knowledge, and is characterized by the following.

  The invention described in claim 1 is characterized by a super-thick steel plate having a thickness exceeding 200 mm, in which two or more superposed steel plates are rolled and joined together.

  In the invention according to claim 2, two or more slabs are overlapped, and the four laps of the overlapping surfaces are welded to form a composite slab, and the effective center stress sum Seff defined by the following equation (1) is 0. The composite slab is hot-rolled under a condition of 3 or more to produce a super-thick steel plate having a thickness of more than 200 mm.

Seff = Σ [(σtcmax / k ₀ ) -1] --- (1)
Here, Σ indicates the sum of the values of each pass through the rolling schedule.
However, (σtcmax / k ₀ ) −1 <0 is not added.

Further, σtcmax / k ₀ = 1.67 × (ld / hm) +0.5
Where ld: projected contact arc length
hm: Average plate thickness (average of input side plate thickness and output side plate thickness)
k ₀ : Deformation resistance

  According to the present invention, it is possible to obtain a very thick steel plate having a uniform internal quality exceeding a thickness of 200 mm without using an expensive insert metal such as an amorphous metal.

  The present invention is a super-thick steel plate having a thickness exceeding 200 mm and does not use an expensive insert metal, and a method for manufacturing the same. The manufacturing method is to hot-roll a composite slab formed by superimposing two or more slabs and welding the four sides of the overlapped surface under rolling conditions where the effective center stress sum Seff shown below is 0.3 or more. It is.

Seff = Σ [(σtcmax / k ₀ ) -1] --- (1)
Here, Σ indicates the sum of the values of each pass through the rolling schedule.
However, (σtcmax / k ₀ ) −1 <0 is not added.

Further, σtcmax / k ₀ = 1.67 × (ld / hm) +0.5
Where ld: projected contact arc length,
hm: average plate thickness (average of input side plate thickness and output side plate thickness),
k ₀ : Deformation resistance.

In the above equation (1), σtcmax / k ₀ is the ratio between the compressive stress in the plate thickness direction during rolling and the deformation resistance, and is formulated by measuring the compressive stress in the plate thickness direction during rolling in a model rolling experiment. did.

  When two slabs are overlapped, the mating surface is at a position that is 1/2 the plate thickness. As a result of examining the bondability of the overlapped surface, it was found that if the effective center stress sum Seff is 0.3 or more, the overlapped surface is pressed well and no defect occurs in the bonded portion. Therefore, in this invention, the value of the effective center stress sum Seff is limited to 0.3 or more.

  In addition, in the case where three or more odd-numbered slabs are overlapped and rolled, the joint surface does not become half of the plate thickness but is closer to the surface layer. In such a case, the compressive stress and strain due to rolling are larger in the portion closer to the surface layer than in the central portion of the plate thickness. For this reason, it was found that under the condition that a mating surface having a thickness of ½ is pressure-bonded, even if the number of slabs is an odd number, the overlapping surface is pressure-bonded well and no defect occurs in the joint.

  In addition, since the center porosity of the slab to be used is smaller in size, the center porosity is preferably 1 mm or less. Further, the black skin is removed from the superposed surface of the slab by a method such as shot blasting or mechanical grinding. In particular, it is desirable to control the surface roughness below a certain level with a belt grinder or mechanical grinding. Further, it is preferable to perform hot rolling after welding the four circumferences of the overlapping surfaces and exhausting the air existing between the mating surfaces by a known appropriate means to make a vacuum state.

  As shown in FIG. 1, two continuous cast slabs 1 and 1 each having a thickness of 247 mm are overlapped, and a plurality of composite slabs 3 having a thickness of 494 mm are welded on the four sides of the overlapped surface (welded portion is indicated by 2). After forming and exhausting the air between the mating surfaces, the steel plate is heated to 1250 ° C. and hot-rolled under the condition that the effective center stress sum is 0.3 or more. A to D were produced. Next, the composite slab formed as described above was hot-rolled under the condition that the effective central stress sum outside the scope of the present invention was less than 0.3, and the comparative thick plate No. E and F were produced. And thick plate no. Each internal defect of A to F was investigated by an ultrasonic flaw detector. The results are shown in Table 1. In Table 1, those having few internal defects and having no problem as a product are indicated by “O”, and those having many internal defects and not resulting in a product are indicated by “X”.

  As is apparent from Table 1, the present invention thick plate No. AD had few internal defects of a product, and there was no problem as product evaluation. On the other hand, comparative thick plate No. It was found that E and F had many internal defects and had a problem with the product.

  From the above results, if the composite slab is hot-rolled under the condition that the effective central stress sum is 0.3 or more, a plate thickness of 200 mm with no defects at the joint portion of the overlapping surface can be obtained without using expensive insert metal. It was confirmed that an extra-thick steel plate exceeding that can be manufactured.

It is a schematic perspective view which shows a composite slab.

Explanation of symbols

1: Slab 2: Welded part 3: Composite slab

Claims (2)

  An ultra-thick steel plate having a thickness exceeding 200 mm, wherein two or more steel plates are superposed and pressure-bonded to each other. Two or more slabs are overlapped, and the combined surface is welded to form a composite slab, and the composite is obtained under the condition that the effective central stress sum Seff defined by the following equation (1) is 0.3 or more. A method for producing a super-thick steel plate having a thickness exceeding 200 mm, wherein the slab is hot-rolled.
Seff = Σ [(σtcmax / k ₀ ) -1] --- (1)
Here, Σ indicates the sum of the values of each pass through the rolling schedule.
However, (σtcmax / k ₀ ) −1 <0 is not added.
Also, σtcmax / k ₀ = 1.67 × (ld / hm) +0.5
Where ld: projected contact arc length
hm: Average plate thickness (average of input side plate thickness and output side plate thickness)
k ₀ : Deformation resistance

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