JP2005177817A - Method for manufacturing ultra extreme-thick steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture an ultra extreme-thick steel plate which is homogeneous in the internal quality and has thickness of more than 200 mm at a low cost. <P>SOLUTION: By the manufacturing method of the ultra extreme-thick steel plate having > 200 mm thickness, a composite slab is formed by superposed two or more continuously cast slabs which are preliminarily worked and welding the circumference of the superposing surface and the composite slab is hot-rolled under the condition that the effective center stress sum Seff defined by the following formula (1) is ≥ 0.3 and reduction ratio is < 2. Above formula (1) is Seff = Σ((σtcmax/k<SB>0</SB>)-1), where, Σ shows the total sum of the value 1 at each pass through a rolling schedule. However, (σtcmax/k<SB>0</SB>)-1 < 0 is not added. Further, σtcmax/k<SB>0</SB>= ( 1.67 × (ld/hm) + 0.5 ), where, ld is the projected length of the arc of contact, hm is the average thickness ( the average of the thickness on the inlet side and the thickness on the outlet side ) and k<SB>0</SB>is the deformation resistance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing an ultra-thick steel plate, more specifically, two or more continuous cast slabs that have been subjected to preliminary processing are overlapped, and the heat is applied under the condition that the effective center stress sum Seff is 0.3 or more and the reduction ratio is less than 2. The present invention relates to a method for inexpensively manufacturing ultra-thick steel plates having a uniform internal quality exceeding 200 mm, which are cold-rolled and joined to each other.

  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.

  On the other hand, as a countermeasure against the center porosity existing in the center portion of the continuous casting slab, in Patent Documents 3 and 4, after primary reduction with a reduction ratio of 1.15 or more, secondary reduction with a reduction ratio of 2.5 or more is performed. It is described that the slab is reduced at a reduction ratio of 2.875 or more. However, since there is no significant difference from the prior art described in Patent Document 2 (a reduction ratio of 3 or more), it is not possible to expect an increase in the thickness of the final product.

  Further, in the case of thick plate products, the width and length are various, but the above-mentioned patent documents do not describe these countermeasures. Furthermore, there is no detailed examination on the rolling method, and only the minimum reduction ratio is specified.

Accordingly, the present invention provides (1) manufacturing conditions as a countermeasure against bonding and center porosity,
(2) Preliminary processing as a countermeasure against center porosity, (3) Examination of overlay conditions as a countermeasure against joining, and making a composite slab using a pre-processed continuous cast slab, and hot rolling this, An object of the present invention is to provide a method for producing an ultra-thick steel plate having an excellent thickness of 200 mm or more at a low cost.

  The present invention has been made to achieve the above object, and is characterized by the following.

  In the invention described in claim 1, two or more continuous cast slabs which have been subjected to preliminary processing are overlapped, and a composite slab is formed by welding four rounds of the overlapped surface, and the effective defined by the following formula (1) The composite slab is hot-rolled under the condition that the central stress sum Seff is 0.3 or more and less than the reduction ratio of 2.

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

  The invention according to claim 2 is the invention according to claim 1, wherein the effective center stress sum Seff defined by the equation (1) is 0.2 or more in the composite slab in which the number of continuous cast slabs is an odd number. It is characterized by hot rolling under conditions with a reduction ratio of less than 2.

  The invention according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the preliminary processing is to apply a reduction of 10 mm or more to the continuous cast slab.

  The invention according to claim 4 is characterized in that, in the invention according to any one of claims 1 to 3, the slab material is formed into a predetermined size and shape at the preliminary processing stage.

  According to the present invention, an ultra-thick steel plate having a uniform internal quality exceeding 200 mm in thickness can be obtained at low cost without using an expensive insert metal such as an amorphous metal.

  The present invention is a method for producing an extra-thick steel plate capable of obtaining an extra-thick steel plate having a thickness exceeding 200 mm without using an expensive insert metal, and the center porosity is pre-crimped by pre-processing the continuous cast slab. A slab material is prepared, two or more slab materials are overlapped, a composite slab is formed by welding four rounds of the overlapping surface, and an effective central stress sum Seff defined by the following equation (1) is 0. The composite slab is hot-rolled under a condition of 3 or more and less than a reduction ratio of 2 to produce an ultra-thick steel plate having a plate thickness exceeding 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.
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

  In addition, EB (electron beam) welding, MIG welding, SMAW (manual welding), etc. can be used for the welding of the 4 times of the overlapping surface at the time of forming a composite slab. Moreover, this invention is applicable also to stainless steel other than carbon steel.

  As a result of studying the joint surface state, heating conditions, and rolling conditions, which are factors affecting the joining of the slab material, as parameters, under the condition that the effective center stress sum Seff is 0.3 or more, the slab material It was confirmed that the joining was achieved even when the joining surface reached the most severe position at t / 2 (t: composite slab thickness). Therefore, in this invention, the value of the effective center stress sum Seff is limited to 0.3 or more.

  As a result of the same examination regarding the center-porosity, if a reduction of 10 mm or more is applied in advance to the continuously cast slab by preliminary processing such as rolling or forging, then rolling with an effective center stress sum Seff of 0.2 or more is performed. As a result, it was confirmed that the center porosity existing in the central portion of the continuous cast slab can be crimped, and this can be eliminated. As a result, the product plate thickness can be increased.

  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 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.

  In addition, ultra-thick steel plates with various widths and lengths can be manufactured by forming into dimensions and shapes in consideration of final product dimensions during preliminary processing. That is, it is possible to manufacture a wide ultra-thick steel sheet while securing an effective central stress sum Seff of 0.3 or more by performing tentering rolling during preliminary processing and straight rolling the subsequent composite slab. it can.

  Furthermore, in the case of rolling with the number of overlapping slab materials as an odd number, the joining surface does not become t / 2 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 center portion of the plate thickness. For this reason, the rolling conditions for joining are relaxed compared with the case where the joining surface comes to ½ of the plate thickness, and it is found that good jointability can be obtained if the effective central stress sum Seff is 0.2 or more. did.

  Next, the present invention will be described in more detail with reference to examples.

  A continuous casting slab of 250 mm × 1500 mm × 3000 mm was subjected to a pre-processing with a reduction amount of 10 to 30 mm by straight rolling to prepare a plurality of slab materials of 220 to 240 mm × 1500 mm × 3,000 to 3400 mm. Each composite slab was prepared by a slab having the same charge, and the black skin was removed from the surface of the slab material by shot blasting (the same applies to Examples 2 and 3 below). Next, two slab materials having the same thickness prepared in this manner were overlapped, and the four overlapped surfaces were welded to prepare four composite slabs having a thickness of 440 to 480 mm. The overlapping surface was welded by MIG welding, and after assembling by welding, vacuum treatment was performed to exclude air at the joint interface (the same applies to Examples 2 and 3 below). Next, each composite slab prepared in this manner was heated to 1200 ° C., and then hot-rolled (main rolled) by straight rolling, and No. having a length of 290 mm × 1500 mm × length. A plate product A to D was manufactured.

  Table 1 shows the reduction ratio and the effective central stress sum (Seff) in the main rolling at this time. Then, the presence / absence and bonding of the center porosity were investigated. The investigation on the presence or absence of crimping of the center porosity is performed by ultrasonic flaw detection (UT) on 1/4 and 3/4 cross sections, and the bondability is determined by ultrasonic flaw detection (UT) at the center of the plate thickness (bonding surface). It was done by doing. These results are also shown in Table 1.

  In addition, the ◯ mark in the UT results of the ¼ and 3/4 cross sections in Table 1 indicates that the center porosity is sufficiently crimped, and the x mark indicates that the crimping is insufficient. Moreover, the ◯ mark of the UT result of the joint surfaces in Table 1 indicates that the slab materials are sufficiently bonded by the main rolling, and the X mark indicates that the bonding is insufficient.

  Thick plate product No. in Table 1 B and No. As is clear from FIG. C, only the condition of effective center stress sum (Seff) is outside the scope of the present invention. In C, the joining of the slab material was insufficient.

  In contrast, a thick plate product No. 10 having a pre-processing of 10 mm or more and an effective central stress sum (Seff) of 0.3 or more is used. For all of A, B and D, even when the reduction ratio was less than 2, the joining of the slab material and the pressing of the center porosity were sufficient, and it was possible to produce an ultra-thick steel plate having excellent quality.

  A 250 mm × 1500 mm × 3000 mm continuous cast slab was preliminarily processed by a rolling reduction of 30 mm and tenter rolling to prepare a slab material of 220 mm × 1600 mm × 3200 mm. Next, two slab materials prepared in this way were overlapped, and the four sides of the overlapped surface were welded to prepare a composite slab of 440 mm × 1600 mm × 3200 mm. Next, after heating the composite slab thus prepared to 1200 ° C., it is hot-rolled (main rolling) by straight rolling with an effective center stress sum (Seff) of 0.30, and is 300 mm × 1600 mm × long A thick plate product having a thickness was produced. Then, the presence / absence and bonding of the center porosity were investigated. These investigation methods are the same as those in the first embodiment.

  In this example of the present invention, the product width (1600 mm) is wider than the slab width (1500 mm), and tentering rolling is necessary. However, tentering rolling is performed in preliminary processing, and in this rolling, the effective central stress sum is obtained by straight rolling. By performing rolling so that (Seff) is 0.30, the center porosity has sufficient pressure bonding and joining properties, and an ultra-thick steel plate having excellent quality can be produced.

  For comparison, a slab material of 220 mm × 1500 mm × 3400 mm was prepared by subjecting a continuous cast slab having the same dimensions as the above-described example of the present invention to a preliminary processing with a reduction amount of 30 mm. Next, two slab materials thus prepared were overlapped, and the four sides of the overlapped surface were welded to prepare a composite slab of 440 mm × 1500 mm × 3400 mm. Next, after heating the composite slab thus prepared to 1200 ° C., tenter rolling was performed by main rolling to produce a thick plate product having a length of 300 mm × 1600 mm × length. Then, the presence / absence and bonding of the center porosity were investigated.

  According to this comparative example, since the tenter rolling was performed in the main rolling, the effective center stress sum (Seff) was only obtained up to 0.24. For this reason, the bondability was insufficient.

  A 200 mm × 1500 mm × 3000 mm continuous cast slab was preliminarily processed with a rolling reduction of 73 mm by straight rolling to prepare a plurality of 127 mm × 1500 mm × 4720 mm slab materials. Next, three slab materials prepared in this way were overlapped, and the four sides of the overlapped surface were welded to prepare a composite slab of 380 mm × 1500 mm × 4720 mm. Next, the composite slab thus prepared was heated to 1200 ° C. and then subjected to straight rolling (main rolling) under the conditions that the effective center stress sum (Seff) was 0.22 and the reduction ratio was 1.3. A thick plate product having a length of 300 mm × 1500 mm × length was manufactured. Then, the presence / absence and bonding of the center porosity were investigated. These investigation methods are the same as those in the first embodiment.

  In this example of the present invention, three pre-processed slabs are assembled, but the effective central stress sum (Seff) is 0.22 because the joint surface is closer to the plate thickness surface layer than in the case of two sheets. Even in this case, the crimping and joining properties of the center porosity were sufficient, and an ultra-thick steel plate with excellent quality could be produced.

  For comparison, a slab material having a size of 190 mm × 1500 mm × 3150 mm was prepared by subjecting a continuous cast slab having the same dimensions as the above-described example of the present invention to preliminary processing with a reduction amount of 10 mm. Next, two slab materials prepared in this way were overlapped, and the four sides of the overlapped surface were welded to prepare a composite slab of 380 mm × 1500 mm × 3150 mm. Next, the composite slab thus prepared was heated to 1200 ° C. and then subjected to straight rolling (main rolling) under the conditions that the effective center stress sum (Seff) was 0.24 and the reduction ratio was 1.3. A thick plate product having a length of 300 mm × 1500 mm × length was manufactured. Then, the presence / absence and bonding of the center porosity were investigated.

  According to this comparative example, since the joint surface is far from the plate thickness surface layer as compared with the case where three slabs are assembled, even if the effective center stress sum (Seff) is 0.24, the joint property is insufficient. Met.

Claims (4)

Two or more continuous cast slabs that have been subjected to pre-processing are overlapped, and the composite slab is formed by welding the four sides of the overlapping surface, and the effective center stress sum Seff defined by the following equation (1) is 0.3. As mentioned above, the said composite slab is hot-rolled on conditions with a reduction ratio of less than 2, The manufacturing method of the ultra-thick steel plate exceeding 200 mm of board thickness characterized by the above-mentioned.
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   The composite slab having an odd number of continuous cast slabs is hot-rolled under the condition that the effective center stress sum Seff defined by the equation (1) is 0.2 or more and less than the reduction ratio 2. The method for producing a super thick steel plate having a thickness of more than 200 mm according to claim 1.   The method of manufacturing a super extra-thick steel plate having a plate thickness exceeding 200 mm according to claim 1, wherein the preliminary processing is to apply a reduction of 10 mm or more to the continuous cast slab.   The method for producing a super extra-thick steel plate having a plate thickness exceeding 200 mm according to any one of claims 1 to 3, wherein the slab material is formed into a predetermined size and shape in the preliminary processing stage.