Assembled slab manufacturing method, assembled slab, and clad steel plate manufacturing method

Abstract

In a method for manufacturing an assembled slab as a rolled raw material for manufacturing a clad steel sheet comprising a base material, and a cladding material joined to the base material, welding is performed using high-energy beam welding on a contact portion (6) between a base raw material (1) and a cladding raw material (2) on an end surface (12) of an assembled slab (10), and, in the high-energy beam welding, an aiming position (8) of a welding beam (7) is shifted from the contact portion (6) to a high thermal conductivity material side. Consequently, in the assembled slab (10), an imbalance between a weld portion (9) and a contact surface (11) can be eliminated, and therefore it is possible to provide: an assembled slab manufacturing method with which, when joining contact portions of different types of metals using high-energy beam welding, weld metal penetration is not formed in an unbalanced manner on one material side, and supplying a filler for welding is unnecessary; an assembled slab; and a clad steel sheet manufacturing method.

Description

[Technical Field]

[0001] The present invention relates to a clad steel plate comprising a base material and a clad material joined to the base material, and to an assembled slab as a rolling material for manufacturing the clad steel plate, a method for manufacturing the assembled slab, and a method for manufacturing the clad steel plate. [Background technology]

[0002] Stainless steel has excellent corrosion resistance, making it suitable for use in severely corrosive environments. Examples of such severely corrosive environments include oil well environments, high-chloride environments such as seawater or brackish water, and plant equipment and chemical tankers exposed to various acid solutions. Examples of equipment exposed to such severely corrosive environments include seawater desalination plants, flue gas desulfurization equipment, chemical storage tanks, structural components such as oil well tubular goods, pumps and valves, and heat exchangers. Stainless steel is used in applications where the equipment is exposed to such severely corrosive environments.

[0003] On the other hand, stainless steel is a high-alloy steel that contains a large amount of alloying elements such as Cr, Ni, and Mo to ensure corrosion resistance. Compared to carbon steel and low-alloy steel, the cost of materials, as well as the costs of processing and welding, are high. The steels used in the above-mentioned components are required to not only have excellent corrosion resistance, but also to have good mechanical properties such as strength and toughness as structural materials. To meet these requirements, the amount of alloy used increases. Furthermore, prices may fluctuate significantly due to rising prices of alloying elements. Therefore, the use of these alloying elements may be restricted, mainly due to cost considerations.

[0004] As mentioned above, when considering cost, it is effective to use clad steel plates as materials from the perspective of processing, welding, etc. Clad steel plates are materials made by bonding two or more different metals together, with one or all of the two or more metals being steel plates. In clad steel plates made by bonding two types of metals together, one metal is referred to as the "base metal" and the other metal (raw material) bonded to the base metal is referred to as the "clad material." Steel plates without bonding are hereinafter referred to as "solid steel plates." Solid steel plates made solely of high-alloy steel are made entirely of high-alloy steel and must possess both the required surface corrosion resistance and the mechanical properties of steel plates. In contrast, clad steel plates use high-alloy steel clad materials on the surface requiring excellent corrosion resistance. The thickness of the clad material is thinner than the overall thickness of the clad steel plate, allowing for a reduction in the amount of high-alloy steel used and material costs. In addition, by increasing the thickness ratio of the base material to the overall thickness of the steel plate and using carbon steel or low-alloy steel as the base material, which does not have corrosion resistance but has sufficient mechanical properties, the mechanical properties required of the steel plate can be satisfied. Furthermore, since the number of welding points where dissimilar materials are welded can be reduced, the cost of welding materials can also be reduced.

[0005] As described above, by using a clad steel plate made by bonding a base material and a clad material, a clad material with excellent corrosion resistance can be bonded to a base material with excellent mechanical properties, thereby obtaining a steel plate that has the excellent properties of both the clad material and the base material.

[0006] For example, a high-alloy steel or Ni-based alloy having the surface properties (e.g., corrosion resistance) required for the steel plate in the intended use environment may be used as the cladding material, and a carbon steel or low-alloy steel having the toughness and strength required for the intended use environment may be used as the base material. In such a case, not only can costs be reduced as described above, but the same properties (e.g., corrosion resistance) as those of a solid steel plate made of high-alloy steel and the same strength and toughness as those of carbon steel or low-alloy steel can be ensured. This allows for both economical and functional compatibility.

[0007] In the manufacture of clad steel plates using hot rolling, the rolled material before hot rolling is hereinafter referred to as the "assembled slab." In the assembled slab, the part that will become the base material of the clad steel plate is called the base material, and the part that will become the clad material of the clad steel plate is called the clad material.

[0008] For example, as described in Patent Document 1, clad rolled material is assembled by stacking clad material and base material so that the bonding surface is vacuum, and then sealing the four periphery of the bonding surface by welding. Examples of methods include electron beam welding in a vacuum, or a method in which holes for evacuation are pre-drilled, and the four periphery is welded in the atmosphere by arc welding or laser welding, followed by evacuation using a vacuum pump. The obtained clad rolled material may be subjected to hot rolling as is, or it may be assembled by applying a release agent between the clad materials so that the clad materials are layered in the following order: base material material-clad material-release agent-clad material-base material, and then the assembled slab is subjected to hot rolling.

[0009] Patent Document 2 discloses an assembled slab in which cladding materials are stacked with a release agent applied between them so that the structure is base material-cladding material-release agent-cladding material-base material, and then spacers made of the same material as the base material are placed on the four sides of the cladding material, and the butt surfaces between the spacers and the base material are laser beam welded.

[0010] Patent Document 3 discloses a composite slab for hot rolling, characterized in that when a base material and a cladding material are directly overlapped and welded around four sides, the penetration depth ω is adjusted when high-energy density welding is performed using an electron beam, laser, or the like.

[0011] Patent Document 4 discloses a method for manufacturing a clad steel plate in which a filler metal is supplied to the periphery of the joining surface of a composite metal plate while irradiating the joining surface with an electron beam parallel or at an oblique angle to perform a close-fitting weld. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2021-143387 [Patent Document 2] International Publication No. WO2020 / 175573 [Patent Document 3] Japanese Patent Application Publication No. 52-13456 [Patent Document 4] Japanese Patent Application Publication No. 62-45485 Summary of the Invention [Problem to be solved by the invention]

[0013] In the manufacture of clad steel plates using hot rolling, clad materials are stacked with a release agent applied between them in a base material-clad material-release agent-clad material-base material-base material configuration, and the resulting assembly is then subjected to hot rolling as an assembled slab. Patent Document 2 describes a method in which, as mentioned above, spacers made of the same material as the base material are placed on all four sides of the clad material and the butt surfaces between the spacers and the base material are laser-beam welded. This method requires the cost of procuring and processing the spacers. Furthermore, this method requires the removal of the spacer-positioned area after rolling, which can result in a decrease in rolling yield. It is also difficult to determine the boundary between the spacer and the product, and there is a risk of spacers remaining in the product.

[0014] As described in Patent Document 3, when high-energy beam welding is used to join dissimilar metals at their contact points, it has been found that penetration is formed unevenly on one side of the contact points. As a result, it has been found that the contact points between dissimilar metals cannot be welded to a sufficient depth. Furthermore, when joining is performed while supplying a filler metal to high-energy beam welding as described in Patent Document 4, costs are incurred for procuring the filler metal and for a device that supplies the filler metal to the high-energy beam welding machine.

[0015] The present invention relates to a clad steel plate comprising a base material and a clad material joined to the base material, and aims to provide an assembled slab as a rolling material for producing the clad steel plate, and a method for manufacturing the assembled slab, in which there is no need to place spacers made of the same material as the base material on the four sides of the clad material material, and when joining the contact points between dissimilar metals using high-energy beam welding, the penetration is not formed unevenly on one side of the contact points between the dissimilar metals, and there is no need to supply filler for welding, as well as a method for manufacturing an assembled slab and a method for manufacturing a clad steel plate. [Means for solving the problem]

[0016] That is, the gist of the present invention is as follows. [1] A manufacturing method of an assembled slab as a rolling material for manufacturing a clad steel plate having a base material and a clad material joined to the base material, wherein in the assembled slab, a portion that becomes the base material of the clad steel plate is called a base material material, and a portion that becomes the clad material of the clad steel plate is called a clad material material, The assembled slab is laminated in this order: a base material, a cladding material, a release agent, a cladding material, and a base material; A method for manufacturing an assembled slab, characterized in that welding is performed using high-energy beam welding at the contact portion between the base material and the cladding material at the end face of the assembled slab, and in the high-energy beam welding, the aiming position of the welding beam is shifted from the contact portion to the high thermal conductivity material side in accordance with the thermal conductivity of the base material and the cladding material, respectively. [2] A method for manufacturing an assembled slab according to [1], characterized in that the ratio γ of the thermal conductivity of the base material and the cladding material (the numerator is the one with the higher thermal conductivity) is 2.5 or more, and the deviation between the aiming position of the welding beam and the contact portion is 1 mm or more on the side of the high thermal conductivity material. [3] A method for manufacturing an assembled slab as described in [1], characterized in that, for the welded portion of the base material and the cladding material by the high-energy beam welding, in a cross section perpendicular to both the surface formed by the contact portion and the end face of the assembled slab, the ratio of the bead width W of the weld metal to the penetration depth D satisfies the following formula (1). 3.5 <D / W<5.0 (1) Here, the weld depth at the contact point between the cladding material and the base material is defined as "penetration depth D," and the width of the weld metal at the end face position is defined as "bead width W." [4] A method for manufacturing an assembled slab as described in [2], characterized in that, for the welded portion of the base material and the cladding material by the high-energy beam welding, in a cross section perpendicular to both the surface formed by the contact portion and the end face of the assembled slab, the ratio of the bead width W of the weld metal to the penetration depth D satisfies the following formula (1): 3.5 <D / W<5.0 (1) Here, the weld depth at the contact point between the cladding material and the base material is defined as "penetration depth D," and the width of the weld metal at the end face position is defined as "bead width W." [5] A method for manufacturing an assembled slab described in any one of [1] to [4], characterized in that the high-energy beam welding is electron beam welding, welding is performed in a vacuum of 0.1 kPa or less, the beam deflection is circular, the deflection diameter φ is 3 mm or more, and the deviation between the aiming position of the welding beam and the contact part is less than half the deflection diameter φ. [6] The method for manufacturing an assembled slab according to any one of [1] to [4], wherein the high-energy beam welding is laser welding.

[0017] [7] An assembled slab as a rolling material for manufacturing a clad steel plate comprising a base material and a clad material joined to the base material, wherein in the assembled slab, the part that becomes the base material of the clad steel plate is called the base material material, and the part that becomes the clad material of the clad steel plate is called the clad material material, The assembled slab is laminated in this order: base material, cladding material, release agent, cladding material, and base material; and the ratio γ of the thermal conductivity of the base material to the cladding material (the numerator is the one with the larger thermal conductivity) is 2.5 or more; a contact portion between the base material and the cladding material at an end surface of the assembled slab is high-energy beam welded; An assembled slab characterized in that, in a cross section perpendicular to both the surface formed by the contact portion and the end surface of the assembled slab, the penetration depth D of the weld metal of the weld portion is 22 mm or more, and the ratio of the bead width W to the penetration depth D satisfies the following formula (1). 3.5 <D / W<5.0 (1) Here, the weld depth at the contact point between the cladding material and the base material is defined as "penetration depth D," and the width of the weld metal at the end face position is defined as "bead width W."

[0018] [8] A method for producing a clad steel plate, characterized by rolling an assembled slab produced by the method for producing an assembled slab according to any one of [1] to [6], or the assembled slab according to [7], in a hot rolling process. [9] A method for manufacturing a clad steel plate according to [8], characterized in that after hot rolling, the four-circumference welded portion of the clad steel plate is cut and removed, and the clad steel plate is separated from the other clad steel plate at the starting point of a release agent applied to the boundary surface between the clad steel plates.

[0019] The present invention relates to a method for manufacturing an assembled slab as a rolling material for producing clad steel plate comprising a base material and a clad material joined to the base material, in which high-energy beam welding is used to weld the contact portion between the base material and the clad material at the end face of the assembled slab, and by shifting the aiming position of the welding beam from the contact portion toward the high thermal conductivity material in the high-energy beam welding, it is possible to eliminate any bias between the weld portion and the contact surface in the assembled slab. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a cross-sectional view of an assembled slab. [Figure 2A]FIG. 1 is a cross-sectional view showing the welding state (before welding) of a welded portion when the base material and cladding material are of the same quality. [Figure 2B] FIG. 1 is a cross-sectional view showing the welding state (after welding) of a welded portion when the base material and cladding material are of the same quality. [Figure 3A] FIG. 1 is a cross-sectional view showing the welding state of a weld when the base material and cladding material are different materials (when there is a deviation between the weld and the contact surface). [Figure 3B] 1 is a cross-sectional view showing the welding condition (a state in which the bias is eliminated) of a welded portion when the base material and cladding material are dissimilar. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention relates to a clad steel plate comprising a base material and a clad material joined to the base material, and is directed to an assembled slab as a rolling material for manufacturing the clad steel plate, a method for manufacturing the assembled slab, and a method for manufacturing the clad steel plate. FIG. 1 shows a cross-sectional view of an assembled slab 10. In the assembled slab 10, the portion that will become the base material of the clad steel plate is called base material 1, and the portion that will become the clad material of the clad steel plate is called clad material 2. As shown in FIG. 1, the assembled slab 10 is stacked in this order: base material 1, clad material 2, release agent 3, clad material 2, and base material 1. After the assembled slab 10 is hot-rolled, the contact portion 6 between the base material 1 and clad material 2 becomes the joining surface 14, and the contact surface between the clad material materials 2 with the release agent 3 sandwiched between them becomes the separation surface 15.

[0022] In the assembled slab of the present invention, as shown in FIG. 1, spacers made of the same material as the base material 1 are not placed on the four sides of the cladding material 2. Therefore, the cladding material 2 and the base material 1 are exposed and in contact with each other at the end face 12 of the assembled slab 10, and in the welding joint, the contact area 6 between the cladding material 2 and the base material 1 is welded to form a weld 9. High-energy beam welding is used to weld the contact area 6. Details of the weld 9 will be explained using FIG. 2B. In the assembled slab 10, when the ratio of the bead width W of the weld metal 4 of the weld area 9 to the weld depth Dmax satisfies the following formula (2), it can be assumed that the welding was performed by high-energy beam welding. 2.0≦Dmax / W (2) Here, we will explain how to determine the bead width W. As shown in FIG. 2B, the width of the weld metal gradually decreases as the depth from the end face 12 increases. Therefore, the width of the weld metal at the position of the end face 12 is defined as the bead width W. The distance to the deepest part of the weld metal is defined as the weld depth Dmax. The outer extent of the weld metal 4 of the weld can be determined by etching a cross section in the weld penetration direction with an appropriate etching solution and visually inspecting it, as shown in the example of the surface of FIG. 2B.

[0023] If the base material 1 and the cladding material 2 are made of the same material, and welding is performed by aligning the aiming position 8 of the welding beam 7 of the high-energy beam irradiation device 5 with the contact point 6 between the cladding material 2 and the base material 1 as shown in Figure 2A, then at the welded portion 9, the weld metal 4 formed by penetration will coincide with the position of the contact point 6, as shown in Figure 2B. However, it is obvious that the base material 1 and the cladding material 2 are dissimilar metals. When joining dissimilar metals at a contact point 6 using high-energy beam welding, it has been found that if the aiming position 8 of the welding beam 7 of the high-energy beam irradiation device 5 is aligned with the contact point 6 between the cladding material 2 and the base material 1 as shown in FIG. 3A , the weld metal 4 formed by penetration at the weld 9 does not coincide with the position of the contact point 6 and is formed biasedly on one of the metals. As a result, the contact point 6 between the cladding material 2 and the base material 1 cannot be welded to a sufficient depth. Here, the weld depth at the contact point 6 between the cladding material 2 and the base material 1 is referred to as the "penetration depth D." When the positions of the weld metal 4 and the contact point 6 coincide, the penetration depth D and the weld depth Dmax coincide (see FIGS. 2B and 3B ). When the positions of the weld metal 4 and the contact point 6 are misaligned, the penetration depth D becomes shallower than the weld depth Dmax (see FIG. 3A ).

[0024] Therefore, we investigated the cause of the phenomenon in which the welded portion 9 is formed biased toward one metal from the position of the contact portion 6. Regarding the position of the welded metal 4 of the welded portion 9, the penetration depth D was used as an index in a cross section perpendicular to both the surface (contact surface 11) that constitutes the contact portion 6 and the end face 12 of the assembled slab 10. A penetration depth D of 22 mm or more was considered to be good.

[0025] Next, various studies were conducted to determine the physical properties of the base material 1 and the cladding material 2, the degree of displacement of the weld zone 9 from the contact zone 6, and the degree of displacement when the target position 8 of the welding beam 7 of the high-energy beam irradiation device 5 was aligned with the contact zone 6 between the cladding material 2 and the base material 1. The penetration depth D was used as an indicator of the degree of displacement. Four types of materials (A (ordinary steel), B (ferritic-austenitic stainless steel), C (copper), and D (nickel)) shown in Table 1 were used as the welded materials to be combined. The chemical compositions and representative physical properties of each material are shown in Table 1. As a result, it was found that the displacement of the weld zone 9 from the contact zone 6 shifted toward B when combining A and B, toward A when combining A and C, and toward B when combining B and D. Comparing these results with the material properties revealed for the first time that the degree of displacement was determined not by differences in magnetic properties or melting points, but by differences in thermal conductivity. It was also found that when the thermal conductivity of the base material 1 and the cladding material 2 differs, the welding displacement distance increases in accordance with the degree of difference in thermal conductivity (hereinafter referred to as "ratio γ of the difference in thermal conductivity between the base material and the cladding material (γ = thermal conductivity of the high thermal conductivity material / thermal conductivity of the low thermal conductivity material)"). The weld metal 4 shifts toward the low thermal conductivity side.

[0026] [Table 1]

[0027] 3B, a test was conducted in which the aiming position 8 of the welding beam 7 of the high-energy beam irradiation device 5 was not aligned with the contact portion 6 between the cladding material 2 and the base material 1, but was shifted from the contact portion 6 by a distance z (hereinafter referred to as the "offset distance z"). As a result, it was found that by shifting the aiming position 8 toward the high thermal conductivity material, the deviation of the weld metal 4 from the contact portion 6 can be reduced, and as a result, the penetration depth D can be increased. The method for manufacturing an assembled slab of the present invention was made based on this finding, and is characterized in that the contact portion 6 between the base material 1 and the cladding material 2 at the end face 12 of the assembled slab 10 is welded using high-energy beam welding, and in the high-energy beam welding, the aiming position 8 of the welding beam 7 is shifted from the contact portion 6 toward the high thermal conductivity material.

[0028] Here, we investigated the relationship between the thermal conductivity ratio γ of the base material and the cladding material and the offset distance z to increase the penetration depth D. As a result, we found that the manufacturing method for assembled slabs of the present invention is clearly effective when the thermal conductivity ratio γ of the base material 1 and the cladding material 2 is 2.5 or greater, and that the effect can be effectively achieved by setting the deviation (offset distance z) between the aiming position 8 of the welding beam 7 and the contact portion 6 toward the high thermal conductivity material to 1 mm or greater. More specifically, when the offset distance z toward the high thermal conductivity material is within the range of the following formula (3) corresponding to the thermal conductivity ratio γ, the penetration depth D can be kept within a preferred range. 0.35×γ―0.86≦z≦0.35×γ+0.14 (3)

[0029] In the manufacturing method of the assembled slab of the present invention, for the welded portion 9 formed by high-energy beam welding of the base material 1 and the cladding material 2, it is preferable that the ratio of the bead width W of the weld metal to the penetration depth D in a cross section perpendicular to both the surface (contact surface 11) formed by the contact portion 6 and the end face 12 of the assembled slab satisfies the following formula (1). 3.5 <D / W<5.0 (1) Here, the welding depth at the contact point between the cladding material and the base material is the aforementioned "penetration depth D," and the width of the weld metal at the end face position is the "bead width W." By satisfying the inequality on the left side of formula (1), weld cracking during hot rolling can be suppressed, and by satisfying the inequality on the right side of formula (1), excessive welding allowance can be reduced, enabling efficient manufacturing. Furthermore, the present invention can be applied even if the welding beam for high-energy beam welding is angled or defocused, as necessary.

[0030] As the high-energy beam welding, electron beam welding and laser welding can be used. When electron beam welding is used as high-energy beam welding, it is preferable to perform the welding in a vacuum of 0.1 kPa or less. By performing welding in a vacuum of 0.1 kPa or less, the bonding surfaces of the base material 1 and the cladding material 2 can be properly bonded together and then welded and sealed. Furthermore, when electron beam welding is used, beam deflection can be used. It is preferable that the beam deflection be circular, with a deflection diameter φ of 3 mm or more. By deflecting the beam circularly, the effect of stirring the weld metal can be achieved, and by setting the deflection diameter φ to 3 mm or more, the effect of melting a wider area can be achieved. It is preferable that the upper limit of the offset distance z be set to half or less of the deflection diameter φ. This allows both materials to melt. When laser welding is used as the high-energy beam welding, a method can be used in which holes for evacuation are drilled in advance in the base material 1, and after welding all four sides by laser welding, evacuation is performed using a vacuum pump.

[0031] In the manufacturing method of the assembled slab of the present invention, high-energy beam welding can also be suitably used to join the cladding materials 2 at the end faces 12 of the assembled slab 10, and in this case, welding can be carried out with the offset distance z=0.

[0032] The assembled slab of the present invention manufactured by the manufacturing method of the assembled slab of the present invention is characterized in that the base material 1, cladding material 2, release agent 3, cladding material 2, and base material 1 are stacked in this order, the base material 1 and the cladding material 2 have a thermal conductivity ratio γ (the numerator is the one with the greater thermal conductivity) that differs by 2.5 or more, the contact portion 6 between the base material 1 and the cladding material 2 at the end face 12 of the assembled slab 10 is formed by high-energy beam welding, and in a cross section perpendicular to both the surface formed by the contact portion 6 and the end face 12 of the assembled slab 10, the penetration depth D of the weld metal 4 of the weld portion 9 is 22 mm or more, and the ratio of the bead width W to the penetration depth D satisfies the above formula (1). When the thermal conductivity ratio γ between the base metal material 1 and the cladding material 2 differs by 2.5 or more, if the aiming position 8 of the welding beam 7 of the high-energy beam irradiation device 5 is aligned with the contact portion 6 between the cladding material 2 and the base metal material 1 as in the conventional case, a misalignment occurs between the width center of the weld metal and the contact portion, resulting in a penetration depth D of less than 22 mm. In contrast, by applying the assembled slab manufacturing method of the present invention, the misalignment between the width center of the weld metal and the contact portion is reduced, and the penetration depth D is 22 mm or more, even when the thermal conductivity ratio γ between the base metal material 1 and the cladding material 2 differs by 2.5 or more.

[0033] The method for manufacturing a clad steel plate of the present invention is characterized by rolling an assembled slab manufactured by the method for manufacturing an assembled slab of the present invention or the assembled slab of the present invention in a hot rolling process. Since the assembled slab of the present invention does not use spacers as described in Patent Document 2, there is no need for the costs of procuring and processing spacers. Furthermore, since there is no need to remove the spacer placement portion after rolling, this does not cause a decrease in rolling yield, and there is no concern that spacers will remain in the product. Furthermore, since joining is not performed while supplying a filler metal as described in Patent Document 4, there is no need to spend money on procuring the filler metal or on a device for supplying the filler metal into a high-energy beam welding machine.

[0034] The method for manufacturing clad steel plate of the present invention further comprises, after hot rolling, cutting and removing the four-circumferential welded portion of the clad steel plate, and separating the clad steel plate from each other at the starting point of the release agent applied to the boundary surface between the clad steel plates to obtain each clad steel plate.

[0035] High alloy steels such as stainless steel and Ni-based alloys can be suitably used as clad steel plate cladding materials and clad steel slab cladding materials, while carbon steels, low alloy steels, and other steels can be suitably used as base materials for clad steel plates and base materials for assembled slabs. [Example]

[0036] The joining materials were materials A (common steel), B (austenitic stainless steel), C (copper), and D (nickel) shown in Table 1, and high-energy beam welding was performed using electron beam welding, with the combinations shown in Table 2. The high-energy beam welding conditions were electron beam welding in a vacuum of 0.1 kPa or less, with a circular beam deflection diameter φ of 3 mm for Nos. 1 to 11 in Table 2 and 2 mm for No. 12. The standard electron beam welding output was 16.8 kW. Nos. 1, 4 to 12 in Table 2 were at standard output, while Nos. 2 and 3 had a reduced output of 14.0 kW. As shown in Figure 3B, welding was performed with the aiming position 8 of the welding beam 7 of the high-energy beam irradiation device 5 offset from the contact point 6 by the offset distance z shown in Table 2.

[0037] In a cross section perpendicular to both the surface (contact surface 11) constituting the contact portion 6 and the end surface 12 of the assembled slab, the weld metal 4 was exposed by etching, and the bead width W and penetration depth D of the weld metal 4 were measured. The results are shown in Table 2.

[0038] [Table 2]

[0039] The quality of the obtained welded material was evaluated. The feasibility of rolling was evaluated using the penetration depth D and formula (1), with D ≥ 22 mm and formula (1) conforming being rated as S (pass), D ≥ 22 mm and formula (1) not conforming being rated as G (pass), and D < 22 mm being rated as X (fail). Yield loss was evaluated based on the weld depth Dmax, with Dmax≦40mm being rated S (pass), Dmax≦50mm being rated G (pass), and Dmax>50mm being rated X (fail). Regarding the overall evaluation, in the evaluation of whether rolling is possible and the yield loss, if both are S, it is S (pass); if either or both are G and do not contain X, it is G (pass); if either contains X, it is X (fail).

[0040] In invention examples 1, 4 to 7, the aiming position 8 of the welding beam 7 was shifted from the contact portion 6 toward the high thermal conductivity material, and the penetration depth D was 22 mm or more, achieving favorable results. In invention examples 2 and 3, the output of the electron beam welding was lower than the preferred range, and as a result, the output fell outside the preferred range of formula (1).

[0041] Comparative Example No. 8 was the result of welding the same materials together, and is outside the scope of the present invention. Comparative Examples Nos. 9 and 10 did not provide an offset when welding different materials, and Comparative Examples Nos. 11 and 12 shifted the aiming position of the welding beam from the contact area toward the low thermal conductivity material, and in all cases the penetration depth D was less than 22 mm. [Explanation of symbols]

[0042] 1. Base material 2. Cladding material 3. Stripping agent 4 Weld metal 5. High-energy beam irradiation device 6 Contact area 7 Welding Beam 8 Aiming position 9 Welded parts 10 Assembled slab 11 Contact surface 12 End face 14 Joint surface 15 Separation plane

Claims

1. A method for manufacturing an assembled slab as a rolling material for manufacturing a clad steel plate comprising a base material and a clad material bonded to the base material, wherein in the assembled slab, a portion that becomes the base material of the clad steel plate is called a base material material, and a portion that becomes the clad material of the clad steel plate is called a clad material material, The cladding material is a high alloy steel or a Ni-based alloy, and the base material is a carbon steel or a low alloy steel, The assembled slab is laminated in this order: a base material, a cladding material, a release agent, a cladding material, and a base material; welding the contact portion between the base material and the cladding material at the end face of the assembled slab using high-energy beam welding, and in the high-energy beam welding, shifting the aiming position of the welding beam from the contact portion to the high-thermal conductivity material side in accordance with the thermal conductivity of each of the base material and the cladding material; A method for manufacturing an assembled slab, characterized in that the ratio γ of the thermal conductivity of the base material and the cladding material (the numerator is the one with the higher thermal conductivity) is 2.5 or more, and the deviation between the aiming position of the welding beam and the contact portion is 1.1 mm or more on the side of the high thermal conductivity material.

4. 2. A method for manufacturing an assembled slab as described in claim 1, characterized in that, for the welded portion of the base material and the cladding material by the high-energy beam welding, in a cross section perpendicular to both the surface formed by the contact portion and the end face of the assembled slab, the ratio of the bead width W of the weld metal to the penetration depth D satisfies the following formula (1). 3.5<D / W<5.0 (1) Here, the weld depth at the contact point between the cladding material and the base material is defined as "penetration depth D," and the width of the weld metal at the end face position is defined as "bead width W."

5. The high-energy beam welding is electron beam welding, and welding is performed in a vacuum of 0.1 kPa or less, and the beam deflection is circular. The method for manufacturing an assembled slab according to claim 1 or claim 4, characterized in that the deflection diameter φ is 3 mm or more, and the deviation between the aiming position of the welding beam and the contact portion is less than half of the deflection diameter φ.

6. 5. The method for manufacturing an assembled slab according to claim 1, wherein the high-energy beam welding is laser welding.

7. An assembled slab as a rolling material for manufacturing a clad steel plate comprising a base material and a clad material joined to the base material, wherein in the assembled slab, a portion that becomes the base material of the clad steel plate is called a base material material, and a portion that becomes the clad material of the clad steel plate is called a clad material material, The cladding material is a high alloy steel or a Ni-based alloy, and the base material is a carbon steel or a low alloy steel, The assembled slab is laminated in this order: a base material, a cladding material, a release agent, a cladding material, and a base material; and the ratio γ of the thermal conductivity of the base material to the cladding material (the numerator is the one with the larger thermal conductivity) is 2.5 or more. a contact portion between the base material and the cladding material at an end surface of the assembled slab is high-energy beam welded; An assembled slab characterized in that in a cross section perpendicular to both the surface formed by the contact portion and the end surface of the assembled slab, the penetration depth D of the weld metal of the weld portion is 22 mm or more, and the ratio of the bead width W to the penetration depth D satisfies the following formula (1). 3.5<D / W<5.0 (1) Here, the weld depth at the contact point between the cladding material and the base material is defined as "penetration depth D," and the width of the weld metal at the end face position is defined as "bead width W."

8. A method for producing a clad steel plate, comprising rolling an assembled slab produced by the method for producing an assembled slab according to claim 1 or 4 in a hot rolling step.

9. A method for producing a clad steel plate, comprising rolling an assembled slab produced by the method for producing an assembled slab according to claim 5 in a hot rolling process.

10. A method for producing a clad steel plate, comprising rolling an assembled slab produced by the method for producing an assembled slab according to claim 6 in a hot rolling process.

11. A method for producing a clad steel plate, comprising rolling the assembled slab according to claim 7 in a hot rolling process.

12. A method for manufacturing a clad steel plate according to claim 8, characterized in that after hot rolling, the four-circumference welded portion of the clad steel plate is cut and removed, and the clad steel plate is separated from the other clad steel plate at the starting point of a release agent applied to the boundary surface between the clad steel plates.

13. A method for manufacturing a clad steel plate according to claim 11, characterized in that after hot rolling, the four-circumference welded portion of the clad steel plate is cut and removed, and the clad steel plate is separated from the other clad steel plate at the starting point of a release agent applied to the boundary surface between the clad steel plates.

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