Manufacturing method of vertical narrow groove welded joint and vertical narrow groove welded joint

Abstract

This invention provides a method for manufacturing a vertical narrow-groove welded joint using thick-walled, high-strength steel with excellent weld toughness. Two steel pieces are butt-jointed via a narrow groove with a groove angle of less than 20°, and joined using a vertical gas-shielded arc welding method with lateral oscillation. The method calculates the ratio of the vertical welding rise speed v (mm / min) in the vertical gas-shielded arc welding to the reciprocal f (s) of the time required for one cycle of the lateral oscillation. ‑1 Adjust it to satisfy the range of v / 60 / f≤9.0.

Description

[0001] This application is a divisional application of patent application 201980049632.8 (International filing date: September 10, 2019, invention title: manufacturing method of vertical narrow groove welded joint and vertical narrow groove welded joint). Technical Field

[0002] This invention relates to a method for manufacturing welded joints used in various steel structures in the fields of shipbuilding, construction, and civil engineering. In particular, it relates to a method for manufacturing vertical narrow groove welded joints that improve the toughness of the welded part in vertical narrow groove welded joints where high-strength steel plates with a thickness of 40 mm or more are joined together by vertical narrow groove gas shielded arc welding, as well as the vertical narrow groove welded joints themselves. Background Technology

[0003] In recent years, steel structures in shipbuilding, construction, and civil engineering have become increasingly larger, and the steel used has also been actively developing towards higher strength and thicker walls. These steel structures are typically welded together and then precision-machined into the desired shape. Therefore, from the perspective of ensuring the safety of such welded steel structures (hereinafter also referred to as welded steel structures), the steel used must not only have excellent strength and toughness of the base material, but also excellent strength and toughness of the welded parts.

[0004] Furthermore, with the increasing size of welded steel structures and the use of thicker-walled steel, the amount of welding during the fabrication process, especially butt welding, has increased, leading to longer welding times and higher construction costs. To address this issue, narrow-groove gas-shielded arc welding (GSAW) can be considered. This method uses an electric arc welding technique to weld grooves with a gap narrower than the plate thickness. Compared to conventional GSAW, narrow-groove GSAW requires less welding, achieving higher welding efficiency and energy savings, thus potentially reducing construction costs.

[0005] Furthermore, vertical welding is sometimes required when fabricating welded steel structures. Electroslag welding is typically used for vertical welding. However, electroslag welding is essentially a single-pass welding process with a large heat input. Therefore, when welding steel plates thicker than 40mm, excessive heat input can result in reduced weld toughness. Therefore, there is a need for a high-quality and efficient welding method that utilizes the aforementioned narrow-groove gas-shielded arc welding for vertical welding.

[0006] To address this urgent need, Patent Document 1, for example, proposes a two-sided welding method. This method involves TIG welding of two U-shaped groove joints. An initial penetration weld is performed at the bottom of the groove on the front side, near or at the center of the plate thickness of the two U-shaped groove joints. Front-side layer welding continues until the weld bead height reaches 1 / 5 to 2 / 5 of the plate thickness (including the initial weld bead), or 4 / 5 to 3 / 5 of the plate thickness (including the initial weld bead), or the upper limit of the groove shoulder width shrinkage is approximately 2 mm. Then, back-side layer welding is performed from the bottom of the groove on the back side of the U-shaped groove joint to the top of the groove, followed by front-side layer welding from the remaining groove portion on the front side to the top of the groove. This welding method uses an inert gas to suppress slag and spatter generation, preventing layer defects and resulting in a low-deformation, high-quality two-sided layer weld.

[0007] Patent Document 2 proposes a narrow bevel welding method. In the narrow bevel welding method proposed in Patent Document 2, an electric arc is formed at the tip of a line protruding from the insertion point to the tip of the bevel extending in the welding direction. The tip of the line is repeatedly oscillated in a manner that traces an arc-shaped trajectory on the side opposite to the welding direction. The stop time and speed of the oscillation reversal are controlled to perform gas-shielded arc welding on the narrow bevel. At this point, a welding cycle is formed by the following steps: a first forward step, starting from the center position of the narrow bevel in the width direction and moving towards the vicinity of one bevel end, oscillating in the welding travel direction; a first forward step, stopping the oscillation for a specified time near one bevel end; a first reverse step, starting from the vicinity of one bevel end and moving towards the center position of the narrow bevel in the width direction, oscillating in the opposite direction of the welding travel direction; a second forward step, starting from the center position of the narrow bevel in the width direction and moving towards the vicinity of another bevel end, oscillating in the welding travel direction; a second forward step, stopping the oscillation for a specified time near another bevel end; and a second reverse step, starting from the vicinity of another bevel end and moving towards the center position of the narrow bevel in the width direction, oscillating in the opposite direction of the welding travel direction. Furthermore, the downward oscillation speed is faster than the upward oscillation speed. This prevents or suppresses spatter and poor fusion.

[0008] Patent Document 3 proposes a vertical welding method. This method involves arc welding a base material with the bevel wall positioned vertically to the left and right, while the welding torch is oscillating laterally. The welding pattern, as seen from the welding direction of the arc welding, forms an "8" shape in the first pattern portion along the left and right bevel walls and the second pattern portion connecting the root and opening sides of these first pattern portions. This method prevents uneven weld thickness, poor penetration, undercut, and poor weld appearance.

[0009] Patent Document 4 discloses a vertical electric welding apparatus. The vertical electric welding apparatus disclosed in Patent Document 4 comprises: a first electrode whose tip penetrates into the bevel; a second electrode that penetrates into the bevel at a position closer to the bevel opening side in the thickness direction x of the steel plate compared to the tip of the first electrode; a trailer that rises along the bevel; and a vibration structure supported by the trailer that drives the first and second electrodes to swing in the thickness direction x; furthermore, it supplies flux-cored welding wire to the bevel extending in the vertical direction z of the substantially vertically upright steel plate, while simultaneously welding upwards. This improves welding efficiency and enables single-pass welding of extremely thick steel.

[0010] Patent document 5 proposes a vertical narrow groove gas shielded arc welding method. This method involves joining two thick steel plates with a groove angle of less than 20°, a groove gap of less than 20 mm, and a plate thickness of more than 40 mm using a single-layer or multi-layer welding technique with transverse oscillation. At this point, the welding wire contains 0.015 to 0.100% by mass of REM, and a welding wire containing a total of 0.005 to 0.100% by mass of one or two types selected from Se and Te is used. During the initial layer welding, the angle of the welding torch relative to the horizontal direction is 10° to 75°, the welding heat input is below 500 kJ / cm, and the lateral oscillation depth in the plate thickness direction is 15 mm to 50 mm. When the width of the initial layer weld bead is set to W, the maximum lateral oscillation width in the plate thickness direction and the direction perpendicular to the welding line is set to (W-6) mm to W mm, and the welding torch is oscillated laterally. This stabilizes the weld bead shape, prevents welding defects, and yields a high-quality and high-toughness weld joint. Compared with conventional gas-shielded arc welding, it produces less spatter and significantly fewer welding defects, achieving high welding efficiency and greatly reducing welding construction costs.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2009-61483

[0014] Patent Document 2: Japanese Patent Application Publication No. 2010-115700

[0015] Patent Document 3: Japanese Patent Application Publication No. 2001-205436

[0016] Patent Document 4: Japanese Patent Application Publication No. 10-118771

[0017] Patent Document 5: Japanese Patent No. 6119948 Summary of the Invention

[0018] The TIG welding method proposed in Patent Document 1 uses a non-consumable electrode method. Compared with MAG welding and CO2 welding, which use steel wire as a consumable electrode, the welding efficiency of this method is much lower. Therefore, the two-sided welding method proposed in Patent Document 1 using TIG welding cannot be expected to significantly improve welding efficiency.

[0019] In the welding method proposed in Patent Document 2, the lateral oscillation direction of the welding torch is not the direction of the bevel depth, but the direction of the steel plate surface. Therefore, the welding torch must be oscillated laterally before the molten metal drips, requiring a low welding current of about 150A to suppress the amount of welding per pass (≒ heat input). Therefore, when this welding method is used for welding thick-walled steel, it results in a problem of increased stacked defects such as poor penetration and a significant decrease in welding efficiency due to the presence of numerous small-pass, multi-pass welding.

[0020] In the vertical welding method proposed in Patent Document 3, the face angle (groove angle) is as wide as 26.3 to 52°. The lateral oscillation of the welding torch also occurs in the groove depth direction, thus allowing for a relatively large welding volume per pass. However, the lateral oscillation in the groove depth direction is small, and the composition of the welding metal and welding wire is not considered. Therefore, it is necessary to suppress the welding volume (≒ heat input) per pass, resulting in a shallow welding depth of approximately 10 mm per pass. Consequently, when this method is applied to welding thick-walled steel, it also results in a problem of increased multi-pass, multi-layered welding, leading to more defects such as poor penetration depth, and reduced welding efficiency.

[0021] The electric arc welding apparatus proposed in Patent Document 4 can be used to join thick steel plates up to approximately 70 mm thick; however, the heat input increases significantly to approximately 360 kJ / cm. Therefore, the heat effect on the welded material (thick steel plate) increases, and the strength, toughness, and other characteristics of the weld joint decrease noticeably. Furthermore, in this two-electrode electric arc welding apparatus, a pressing mechanism with a ceramic backing on the back side of the bevel and a water-cooled copper pad on the surface (welding machine side) is indispensable. While this eliminates concerns about molten metal dripping, it complicates the welding apparatus. Moreover, this two-electrode electric arc welding apparatus is essentially a single-pass welding process, making it difficult to achieve multi-pass layered welding with low heat input.

[0022] The vertical narrow groove gas shielded arc welding method proposed in Patent Document 5 is a welding method accompanied by lateral oscillation. Therefore, in the welded joints of thick-walled high-strength steel containing a large number of alloying elements, there is a situation where the toughness of the parts repeatedly subjected to heat is significantly reduced.

[0023] The present invention addresses the problems of the prior art and aims to provide a method for manufacturing a vertical narrow groove welded joint with excellent weld toughness and a vertical narrow groove welded joint with excellent weld toughness.

[0024] It should be noted that "thick wall" here refers to a plate thickness (wall thickness) of 40mm or more, and "high strength" refers to a yield strength of 440MPa or more. Furthermore, "steel" includes steel plates, shaped steel, strip steel, and bars. Additionally, "narrow bevel" refers to a bevel angle of 20° or less. Moreover, this narrow bevel is suitable when the minimum bevel width (hereinafter also called bevel gap) between the steel materials being welded is 50% or less of the steel plate thickness (wall thickness) and less than 20mm.

[0025] In order to achieve the above objectives, the inventors first investigated the composition of thick-walled high-strength steel with a plate thickness (wall thickness) of 40 mm or more and a yield strength of 440 MPa or more, to ensure the mechanical properties required for the aforementioned welded steel structures. As a result, it was found that in order to stably manufacture the aforementioned thick-walled high-strength steel using a common manufacturing method combining hot rolling and cooling, the addition of a certain amount of alloying elements is essential. As part of the steel composition, C needs to be at least 0.03% by mass, and the composition needs to be adjusted so that the hardenability index defined by C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 (where C, Mn, Cr, Mo, V, Cu, Ni: the content of each element (by mass%), and the content of elements not present is 0.) satisfies the range of the following formula (1).

[0026] 0.40 ≤ C + Mn / 6 + (Cr + Mo + V) / 5 + (Cu + Ni) / 15 ≤ 0.50 ... (1).

[0027] Furthermore, when using vertical narrow-groove gas-shielded arc welding to join thick-walled high-strength steel to create welded joints, vertical welding accompanied by lateral oscillation was applied. An in-depth investigation was conducted into the reduction in toughness of the welded portion due to the heat effect of this lateral oscillation welding. The results revealed that when thick-walled high-strength steel with a large amount of alloying elements, as mentioned above, is used to create welded joints using lateral oscillation welding, areas repeatedly subjected to welding heat effects, especially those previously exposed to temperatures above 1100°C and then reheated to the Ac1 to Ac3 transformation temperature range (two-phase region), exhibit significantly embrittled microstructures. This is presumably due to the formation of a hard layer at the coarsened grains and their grain boundaries.

[0028] Therefore, in the aforementioned welding process, a detailed study was conducted on a scheme to avoid reheating areas (regions) previously exposed to temperatures above 1100°C to the Ac1 to Ac3 transition temperature range (two-phase region). As a result, it was conceived to adjust the welding conditions accompanying the lateral oscillation to an appropriate range. Specifically, it was found that if the vertical welding speed v (mm / min) is proportional to the reciprocal of the time required for one cycle of lateral oscillation f (s), then... -1 If the welding conditions accompanied by lateral oscillation are adjusted in a manner that satisfies equation (2), the toughness of the welded part will not be significantly reduced.

[0029] 2v / 60 / f≤9.0……(2)

[0030] By using vertical welding with lateral oscillation to satisfy the above equation (2), the area previously exposed to high temperatures above 1100°C will not be reheated to the temperature range (two-phase region) from the Ac1 to Ac3 transition points after one cycle of lateral oscillation. Therefore, it is possible to prevent a significant reduction in the toughness of the weld joint. It should be noted that the above equation (2) holds true regardless of the welding heat input.

[0031] This invention was developed based on the above insights. Specifically, the essence of this invention is as follows.

[0032] (1) A method for manufacturing a vertical narrow groove welded joint, wherein two steel materials are butt-jointed through a narrow groove with a groove angle of less than 20°, and joined by using a vertical gas shielded arc welding with lateral oscillation.

[0033] The above-mentioned steel has the following composition, containing, by mass %: C: 0.03-0.15%, Si: 0.01-0.10%, Mn: 1.0-2.5%, P: less than 0.02%, and S: less than 0.01%, and satisfies the following formula (1), with the remainder being Fe and unavoidable impurities, and having a yield strength of 440 MPa or more.

[0034] The vertical welding rise speed v (mm / min) of the above vertical gas shielded arc welding is the reciprocal of the time (s) required for one cycle of the above horizontal oscillation, f (s). -1 ) is adjusted to satisfy the range of the following formula (2).

[0035] 0.40≤C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15≤0.50……(1)

[0036] Wherein, C, Mn, Cr, Mo, V, Cu, and Ni represent the content (mass%) of each element, and the content of elements that are not present is 0.

[0037] 2v / 60 / f ≤ 9.0……(2)

[0038] (2) According to the manufacturing method of the vertical narrow bevel welded joint described in (1) above, wherein the transverse oscillation pattern of the welding torch viewed from the welding line direction is " The shape of the character.

[0039] (3) The manufacturing method of the vertical narrow groove welded joint according to (1) or (2) above, wherein the above-mentioned composition further contains, by mass %, one or more of the following: Al: 0.005-0.100%, Cu: 0.01-1.00%, Ni: 0.01-1.00%, Nb: 0.003-0.030%, Ti: 0.003-0.030%, N: 0.0020-0.0100%, and Ca: 0.0003-0.0030%.

[0040] (4) The manufacturing method of the vertical narrow groove welded joint according to (1), (2) or (3) above, wherein the above-mentioned composition further contains, by mass %, one or more of the following: Cr: 0.01-0.50%, Mo: 0.01-0.50%, V: 0.001-0.100%, B: 0.0003-0.0030%, Mg: 0.005-0.0100%, Zr: 0.0010-0.0200%, and REM: 0.0005-0.0100%.

[0041] (5) A vertical narrow groove welded joint, manufactured by any one of the manufacturing methods of vertical narrow groove welded joints described in (1) to (4) above.

[0042] (6) A vertical narrow groove welded joint, which is a vertical narrow groove welded joint in which two steel materials are joined by a narrow groove with a groove angle of less than 20°, wherein the steel materials have the following composition, containing, by mass %: C: 0.03-0.15%, Si: 0.01-0.10%, Mn: 1.0-2.5%, P: less than 0.02%, and S: less than 0.01%, and satisfying the following formula (1), with the remainder being Fe and unavoidable impurities, and a yield strength of more than 440 MPa, wherein the vertical narrow groove welded joint has an absorbed energy E at a Charpy impact test temperature of -20°C. -20 (J) refers to welded joints with a weld pressure of 80J or higher.

[0043] 0.40≤C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15≤0.50……(1)

[0044] Here, C, Mn, Cr, Mo, V, Cu, and Ni are the contents (mass%) of each element, and the contents of elements that are not present are 0.

[0045] (7) The vertical narrow groove welded joint according to (6) above, wherein the above composition further contains, by mass %, one or more of the following: Al: 0.005-0.100%, Cu: 0.01-1.00%, Ni: 0.01-1.00%, Nb: 0.003-0.030%, Ti: 0.003-0.030%, N: 0.0020-0.0100%, and Ca: 0.0003-0.0030%.

[0046] (8) The vertical narrow groove welded joint according to (6) or (7) above, wherein the above composition further contains, by mass %, one or more of the following: Cr: 0.01-0.50%, Mo: 0.01-0.50%, V: 0.001-0.100%, B: 0.0003-0.0030%, Mg: 0.005-0.0100%, Zr: 0.0010-0.0200%, and REM: 0.0005-0.0100%.

[0047] According to the present invention, even for thick-walled high-strength steel with a plate thickness of 40 mm or more and a yield strength of 440 MPa or more, it is possible to efficiently produce high-quality vertical narrow groove gas shielded arc welding joints with excellent toughness in the weld heat-affected zone, which greatly reduces the welding construction cost of welded steel structures and has a particularly significant effect in industry. Attached Figure Description

[0048] Figure 1 This is an illustrative diagram showing an example of a bevel shape.

[0049] Figure 2 This is an illustrative diagram schematically representing the key points of a vertical narrow-groove gas-shielded arc welding joint.

[0050] Figure 3 This is an explanatory diagram representing a horizontal swinging pattern.

[0051] Symbol Explanation

[0052] 1. Steel (material to be welded)

[0053] 2 Bevel surface

[0054] 3. Backing material

[0055] 4 Welding torch

[0056] 5 Welding wire Detailed Implementation

[0057] In the manufacturing method of the vertical narrow-groove gas-shielded arc welding joint of the present invention, the welded material is, for example, thick-walled high-strength steel with a plate thickness of 40 mm or more and a yield strength of 440 MPa or more. It should be noted that the plate thickness of conventional rolled steel is typically limited to 100 mm. Therefore, the plate thickness of the steel is preferably 100 mm or less.

[0058] First, the composition of the thick-walled, high-strength steel used (steel composition) will be explained. Hereinafter, the mass percentage in the steel composition will be abbreviated as %.

[0059] C: 0.03~0.15%

[0060] Carbon (C) is an element that increases the strength of steel. To ensure the desired high strength, it is contained at 0.03% or more in this invention. On the other hand, if it exceeds 0.15%, island-like martensite is easily formed near the weld, leading to a decrease in the toughness of the weld. Therefore, the C content is limited to the range of 0.03% to 0.15%. It should be noted that 0.05% to 0.10% is preferred.

[0061] Si: 0.01~0.10%

[0062] Si acts as a deoxidizer in steelmaking, and to achieve this effect, it needs to contain at least 0.01%. On the other hand, if it contains more than 0.10%, island-like martensite forms near the weld, leading to a decrease in the weld's toughness. Therefore, the Si content is limited to the range of 0.01% to 0.10%. It should be noted that 0.02% to 0.08% is preferred.

[0063] Mn: 1.0–2.5%

[0064] Mn is an element that improves the strength of steel. In this invention, it is contained at 1.0% or more to ensure the desired strength of the base material. On the other hand, if it is contained at more than 2.5%, the toughness near the weld is significantly reduced. Therefore, the Mn content is limited to the range of 1.0% to 2.5%. It should be noted that 1.2% to 2.2% is preferred.

[0065] P: below 0.02%

[0066] Phosphorus (P) promotes the formation of island-like martensite near the weld, but excessive P content can significantly reduce the toughness of the weld. Therefore, it is preferable to minimize P content, but P content below 0.02% is permissible. Therefore, in this invention, P content is limited to 0.02% or less. It should be noted that P content below 0.016% is preferred.

[0067] S: below 0.01%

[0068] Sulfide (S) mainly exists in steel as sulfide inclusions, and excessive amounts reduce the toughness of the steel. Therefore, S is preferably minimized, and levels below 0.01% are acceptable. It should be noted that levels below 0.005% are preferred.

[0069] In this invention, the composition is adjusted so that the above-mentioned components are in the above-mentioned contents, and the hardenability index (=C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15) satisfies the range of the following formula (1).

[0070] 0.40≤C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15≤0.50……(1)

[0071] (Where C, Mn, Cr, Mo, V, Cu, and Ni represent the content (mass%) of each element.)

[0072] It should be noted that when the element recorded in the above formula (1) is not present, the content of that element is used as zero in formula (1).

[0073] In this invention, molten steel with a specified composition is melted, and steel billets (slabs) are produced by continuous casting. These slabs are then reheated, hot-rolled, and cooled to produce thick-walled, high-strength steel of specified dimensions. It should be noted that, from the viewpoint of reducing manufacturing costs, this invention manufactures thick-walled, high-strength steel with minimal heat treatment. Therefore, the composition of the steel is such that the hardenability index Ceq (=C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15) is adjusted to within a specified range.

[0074] In this invention, the content of each component in the thick-walled high-strength steel is adjusted to be within the range of 0.40 to 0.50 for the hardenability index Ceq. That is, when the hardenability index is less than 0.40, the hardenability is insufficient, and the desired steel strength cannot be ensured. On the other hand, if the hardenability index exceeds 0.50, the hardenability increases too much, the toughness of the weld decreases, and the desired weld toughness cannot be ensured. Therefore, in this invention, the composition is adjusted to satisfy the above formula (1). It should be noted that a hardenability index Ceq of 0.42 to 0.48 is preferred.

[0075] The above-mentioned composition is basic. In this invention, in addition to the basic composition, it may further contain one or more elements selected from Al: 0.005-0.100%, Cu: 0.01-1.00%, Ni: 0.01-1.00%, Nb: 0.003-0.030%, Ti: 0.003-0.030%, N: 0.0020-0.0100%, and Ca: 0.0003-0.0030%. The preferred amounts of each element and the reasons for their addition are as follows.

[0076] Al: 0.005~0.100%

[0077] Al is an element that acts as a deoxidizer in steel, and to achieve this effect, it is preferable to contain 0.005% or more. On the other hand, if it exceeds 0.100%, not only does the toughness of the base metal decrease, but the toughness of the weld metal also decreases. Therefore, it is preferable to add Al in the range of 0.005% to 0.100%. It should be noted that 0.010% to 0.080% is more preferred.

[0078] Cu: 0.01~1.00%

[0079] Cu is an element that improves hardenability and helps to effectively ensure the desired high strength (base material strength). To achieve this effect, it is preferable to contain 0.01% or more. On the other hand, if it contains more than 1.00%, the above-mentioned effect saturates. Therefore, Cu is preferably added in the range of 0.01% to 1.00%. It should be noted that 0.020% to 0.080% is more preferred.

[0080] Ni: 0.01~1.00%

[0081] Ni is an element that improves both the strength (base material strength) and toughness of steel. To achieve this effect, it is preferable to contain 0.01% or more. On the other hand, the effect saturates when the content exceeds 1.00%. Therefore, it is preferable to add Ni in the range of 0.01% to 1.00%. It should be noted that it is more preferable to add more than 0.01% but less than 1.00%. Even more preferable is 0.20% to 0.80%.

[0082] Nb: 0.003~0.030%

[0083] Nitrogen (Nb) is a useful element that contributes to improving the strength of steel. To ensure the desired steel strength (base metal strength), it is preferable to contain 0.003% or more. On the other hand, if it contains more than 0.030%, the toughness of the weld decreases. Therefore, Nb is preferably added in the range of 0.003% to 0.030%. It should be noted that 0.008% to 0.025% is more preferred.

[0084] Ti: 0.003~0.030%

[0085] Ti is an element that helps improve the effective strength of steel, and during solidification, it precipitates as a nitride (TiN), suppressing the coarsening of austenite grains and contributing to improved toughness. To achieve this effect, it is preferable to contain 0.003% or more. On the other hand, if it contains more than 0.030%, the precipitated TiN may coarsen, potentially negating the aforementioned effects. Therefore, Ti is preferably added in the range of 0.003% to 0.030%. It should be noted that 0.008% to 0.0025% is more preferred.

[0086] N: 0.0020~0.0100%

[0087] Nitrogen (N) inhibits austenite grain growth through the formation of TiN, thus contributing to improved toughness. To achieve this effect, a content of 0.0020% or more is preferred. On the other hand, when the content exceeds 0.0100%, the heat during welding causes TiN to dissolve, increasing the amount of dissolved N and potentially reducing toughness. Therefore, N is preferably added in the range of 0.0020 to 0.0100%. It should be noted that 0.0030 to 0.0090% is more preferred, and 0.0035 to 0.0085% is even more preferred.

[0088] Ca: 0.0003~0.0030%,

[0089] Ca is an element that helps control the morphology of sulfide inclusions, thus contributing to improved toughness in steel. To achieve this effect, a content of 0.0003% or more is preferred. On the other hand, a content exceeding 0.0030% may lead to decreased cleanliness and deterioration of toughness. Therefore, Ca is preferably added in the range of 0.0003% to 0.0030%. It should be noted that 0.0005% to 0.0025% is more preferred.

[0090] Furthermore, it may contain one or more of the following as needed: Cr: 0.01–0.50%, Mo: 0.01–0.50%, V: 0.001–0.100%, B: 0.0003–0.0030%, Mg: 0.005–0.0100%, Zr: 0.0010–0.0200%, and REM: 0.0005–0.0100%.

[0091] Cr: 0.01–0.50%, Mo: 0.01–0.50%, V: 0.001–0.100%, and B: 0.0003–0.0030%.

[0092] Cr, Mo, V and B are all elements that help increase the strength of steel, and one or more of them can be selected as needed.

[0093] To achieve this effect, the preferred content is 0.01% or more of Cr, 0.01% or more of Mo, 0.001% or more of V, and 0.0003% or more of B. On the other hand, if Cr exceeds 0.50%, Mo exceeds 0.50%, V exceeds 0.001%, and B exceeds 0.0030% and is present in large quantities, it may negatively affect toughness. Therefore, when present, the preferred content is within the range of 0.01 to 0.50% of Cr, 0.01 to 0.50% of Mo, 0.001 to 0.100% of V, and 0.0003 to 0.0030% of B.

[0094] Mg: 0.005–0.0100%, Zr: 0.0010–0.0200%, and REM: 0.0005–0.0100%.

[0095] Mg, Zr, and REM are elements that improve the toughness of the base material and weld by dispersing as oxides. Furthermore, Mg, Zr, and REM are useful elements that contribute to improved toughness by controlling the morphology of sulfide inclusions, and can be included as needed. To achieve this effect, it is preferable that Mg is at least 0.005%, Zr at least 0.0010%, and REM at least 0.0005%. On the other hand, even if Mg and REM exceed 0.0100% and Zr exceeds 0.0200%, their effect saturates. Therefore, when Mg and REM are present, the content is preferably 0.0100% or less, and when Zr is present, the content is preferably 0.0200% or less.

[0096] The remaining components besides those mentioned above consist of Fe and unavoidable impurities. It should be noted that, as an unavoidable impurity, O (oxygen): 0.0080% or less is permissible.

[0097] Next, a preferred manufacturing method for the thick-walled high-strength steel used in this invention will be described.

[0098] The steel used in this invention is smelted in a common smelting furnace such as a converter or electric furnace, and preferably further refined in a common secondary refining furnace such as an RH degassing furnace. The molten steel, adjusted to the appropriate composition range described above, is then processed into steel billets such as slabs through a continuous casting process or an ingot-billing process. Next, preferably, the steel billet is hot-rolled to the desired size and shape and then cooled; followed by an accelerated cooling process after hot rolling; a process of direct quenching followed by tempering; a process of reheating and quenching followed by tempering; or a process of reheating and quenching followed by tempering, etc., to produce thick-walled high-strength steel with a plate thickness of 40 mm or more and a yield strength of 440 MPa or more. Particularly more preferably, the conditions of the accelerated cooling process and the tempering process are modified to achieve a plate thickness of 40 mm or more and a yield strength of 440 MPa or more.

[0099] Next, using two of the aforementioned thick-walled high-strength steel materials as welding materials, the two thick-walled high-strength steel materials are butt-welded through a narrow groove with a groove angle θ of 20° or less and a groove gap G of 20 mm or less. Furthermore, these thick-walled high-strength steel materials are joined together using a lateral oscillating vertical gas shielded arc welding method to create a single-layer or multi-layer vertical narrow groove gas shielded arc welded joint.

[0100] Here, the bevel shape can be a V-shaped bevel (including an I-shaped bevel and a "V-shaped bevel"). The bevel can be either a "V" bevel or a Y-bevel. Furthermore, a Y-bevel can be a multi-stage Y-bevel. Representative bevel shapes are shown below. Figure 1 . Figure 1 In the diagram, symbol 1 represents steel, and symbol 2 represents the bevel surface. Figure 1 (a) is an example of a V-shaped bevel. Figure 1 (b) is an example of a Y-shaped bevel.

[0101] The invention will now be described using a V-shaped bevel as an example. It should be noted that the same applies when using a Y-shaped bevel.

[0102] Beveling angle θ: below 20°

[0103] A smaller bevel angle θ for steel makes it more prone to defects such as poor fusion, but it allows for high-efficiency welding. Therefore, in this invention, the bevel angle is limited to 20° or less for high-efficiency welding. While an I-shaped bevel with a 0° bevel angle in a V-shaped bevel allows for the most efficient welding, from the viewpoint of construction stability, a bevel angle of 2–10° is preferred.

[0104] Bevel gap G: less than 50% of the steel plate thickness and less than 20mm

[0105] When the bevel gap G exceeds 50% of the steel plate thickness or exceeds 20 mm, molten metal tends to drip, making welding difficult. Therefore, measures such as reducing the welding current are necessary. However, reducing the welding current too much can easily lead to welding defects such as slag entrapment. Therefore, a bevel gap of 50% or less and 20 mm or less of the steel plate thickness is preferred. It should be noted that from the viewpoint of construction efficiency, a gap of 0 mm to 15 mm is more preferable.

[0106] In this invention, steel materials 1 and 1, which are used as welding materials, are stacked in single or multiple layers by using a horizontally swinging vertical (upward) gas shielded arc welding method. Figure 2 The diagram illustrates key points for welded joints using a V-groove and gas-shielded arc welding method. Here, Figure 2 Symbol 3 represents the backing material, symbol 4 represents the welding torch, and symbol 5 represents the welding wire (consumable electrode wire). In the gas-shielded arc welding method used, a common gas-shielded arc welding method can be used where an arc is generated between the consumable electrode wire and the material being welded (steel) while being shielded by a shielding gas, causing the electrode wire and the material being welded (steel) to melt. It should be noted that the electrode wire used in the gas-shielded arc welding method is preferably a solid welding wire facing the steel, corresponding to the strength of the steel being welded, for example, a tensile strength of 60 kg (HT-60 grade) as specified in JIS standards.

[0107] In the vertical (upward) gas shielded arc welding used in this invention, there are no particular limitations on the welding conditions. However, if the average welding current is too low, poor fusion and slag entrapment are likely to occur. On the other hand, if the average welding current is too high, the generation of molten metal dripping, fumes, spatter, etc., becomes significant. Therefore, the average welding current is preferably 250A to 400A. It should be noted that the welding voltage increases together with the welding current, but the welding voltage is only 25V to 40V, and the welding speed (upward) is 1 to 15cm / min. In addition, the shielding gas used can be common shielding gases such as carbon dioxide or a mixture of carbon dioxide and argon, and there is no particular limitation.

[0108] Furthermore, the vertical (upward) gas shielded arc welding method used in this invention is a vertical welding method using lateral oscillation. The lateral oscillation pattern of the welding torch is not particularly limited; however, from the viewpoint of suppressing molten metal dripping and the generation of welding defects, for example, from... Figure 3 (a) The preferred lateral oscillation pattern of the welding torch as seen in the welding line direction is " The character shape. If it is " The horizontal oscillating pattern in the shape of the letter "" moves the welding torch 4 parallel to the bevel surface 2, which can suppress the dripping of molten metal and the generation of welding defects. It should be noted that, as a… "Horizontal swing patterns other than fonts, for example, can be" Figure 3 The V-shape, trapezoid, and triangle shown in (b) to (d) represent the deepest point of the bevel during lateral oscillation (e.g., Figure 3 (a) The distance between points B and C on the back of the steel (1a) is usually about 0 to 10 mm.

[0109] It should be noted that the vertical narrow bevel welding used in this invention, such as Figure 3 As shown, it is not necessary to limit the lateral swing depth L in the plate thickness direction, or the lateral swing width W in the plate thickness direction and the direction perpendicular to the weld line. However, it is preferable to adjust the lateral swing depth L and the lateral swing width W appropriately according to the desired joint depth, and perform lateral swinging corresponding to the desired joint depth for welding.

[0110] Here, the lateral oscillation depth L in the thickness direction is preferably 15 to 50 mm. This is because if the lateral oscillation depth in the thickness direction is less than 15 mm, it may be difficult to obtain the desired joint depth. On the other hand, if the lateral oscillation depth in the thickness direction exceeds 50 mm, not only is it difficult to obtain the desired joint depth, but the welding heat input becomes excessive, making it difficult to ensure the desired mechanical properties in the heat-affected zone of the weld metal or steel. It should be noted that the lateral oscillation depth L is more preferably 20 to 40 mm in the case of single-layer welding, and more preferably 25 to 40 mm in the case of multi-layer welding. In addition, the stopping time during lateral oscillation (the stopping time of each point A, B, etc. in the lateral oscillation pattern) is preferably about 0 to 0.5 seconds. Furthermore, the lateral oscillation width W is preferably adjusted appropriately in a way that can prevent the generation of poor melting according to the distance between the bevels at the thickness position of the plate being welded.

[0111] In this invention, the vertical gas shielded arc welding accompanied by lateral oscillation is adjusted to the reciprocal f(s) of the vertical welding rise speed v (mm / min) and the time (s) required for one cycle of lateral oscillation. -1 If the range of the following formula (2) is satisfied, a vertical gas shielded arc welding head is manufactured.

[0112] 2v / 60 / f≤ 9.0……(2)

[0113] Here, one cycle of the lateral oscillation is half the time required for the minimum unit of reciprocating motion of the welding torch within the cross-section of the bevel. Specifically, Figure 3 (a) The time required for "A→B→C→D→C→B→A" is half of that required. Figure 3(b) represents half the time required for "A→B→C→B→A". Figure 3 (c) represents half the time required for the transition "A→B→C→D→A". Figure 3 (d) represents 1 / 2 of the time required for “A→B→C→A”.

[0114] Typically, in welding with lateral oscillation, repeated reheating of the same location frequently occurs, especially when areas previously heated above 1100°C are reheated to a temperature range above the Ac1 transformation point and below the Ac3 transformation point (two-phase temperature region). This results in a significant decrease in the toughness of the weld heat-affected zone. This is likely because when areas heated above 1100°C with coarsened austenite grains are reheated in the two-phase temperature region, inverse austenite transformation occurs at grain boundaries. Here, carbon (C) concentrates, forming a hard phase that is a significant factor in the reduction of toughness.

[0115] In this invention, the upward speed v of the vertical welding advance accompanied by lateral oscillation and the reciprocal f of the time required for one cycle of lateral oscillation are adjusted to satisfy the above-described equation (2). This prevents the area previously heated to above 1100°C from being reheated to a temperature range above the Ac1 transition point and below the Ac3 transition point (two-phase temperature range), and prevents significant deterioration of the toughness of the heat-affected zone, particularly the weld joint, in vertical narrow-groove gas-shielded arc welded joint.

[0116] It should be noted that the lower limit of 2V / 60 / F does not need to be specifically limited, but from the point of view of welding construction efficiency, a larger value is preferred.

[0117] The vertical narrow groove welded joint obtained by the above manufacturing method has an absorbed energy E at a Charpy impact test temperature of -20℃. -20 (J) A weld joint with a weld strength of 80J or higher is considered a joint with excellent weld toughness. Here, "weld joint" refers to the location where the ratio of weld metal to heat-affected zone at the bottom of the notch in the Charpy impact test of the joint is 1:1. This weld joint becomes the part with the lowest weld toughness; therefore, if the absorbed energy E at -20°C of the weld joint is... -20 If (J) is above 80J, the toughness of the joint with the lowest toughness is ensured, thus also ensuring the toughness of other welded parts of the welded joint.

[0118] The present invention will be further described below based on embodiments.

[0119] The molten steel with the composition shown in Table 1 was melted using a high-frequency melting furnace, and then cast into steel ingots (150 kg each) using a mold. The resulting steel ingots were heated and hot-rolled into steel sheets (thickness: less than 200 mm). The resulting steel sheets were then placed in a heating furnace and held at 1150°C for 2 hours, followed by hot rolling at a final rolling temperature of 700–900°C to produce thick steel plates (thickness: 40–100 mm). Next, accelerated cooling was performed at a rate of 3°C / s or more at the half-thickness position until the temperature at the half-thickness position reached 350°C (cooling stop temperature). Afterward, the plates were de-cooled to produce finished plates (base material).

[0120]

[0121] From the obtained product sheet (base material), JIS No. 4 specimens are taken at the 1 / 4 position of the sheet thickness, with the long side of the specimen perpendicular to the rolling direction. Tensile tests are performed according to JIS Z 2241 to determine the tensile properties of the steel (yield strength YS, tensile strength TS). Additionally, V-notch test pieces are taken at the 1 / 4 position of the sheet thickness, with the long side of the specimen parallel to the rolling direction. Charpy impact tests are performed at a test temperature of -40℃ according to JIS Z 2242-2005 to determine the absorbed energy vE of the base material. -40 (J). The results are shown in Table 2.

[0122]

[0123] Furthermore, two pieces of the obtained product plate (base material) are taken and butt-welded in the manner shown in Table 3, forming a narrow bevel shape. Vertical (upward) gas shielded arc welding with lateral oscillation is performed according to the welding conditions shown in Table 3 to create a vertical narrow bevel welded joint. It should be noted that in the vertical gas shielded arc welding, a 1.2mmφ solid welding wire (KC-500) facing 60kg grade steel is used as the welding wire. Carbon dioxide is used as the shielding gas. Furthermore, the bevel machining of the welded materials is performed using gas cutting; grinding or other bevel surface machining is not performed.

[0124]

[0125] A V-notch specimen was taken 2 mm below the surface of the fabricated weld joint, with the notch location representing the weld joint. It should be noted that the "weld joint" here refers to the location where the ratio of weld metal to heat-affected zone at the bottom of the notch is 1:1. Furthermore, a Charpy impact test was conducted at a test temperature of -20°C to determine the absorbed energy vE. -20(J). It should be noted that for each of the three samples tested, the average of the absorbed energy values ​​obtained is taken as the absorbed energy value (J) of the weld joint, and the toughness of the weld joint is compared.

[0126] The results are shown in Table 4.

[0127]

[0128] In all the examples of this invention, the yield strength of the base material is above 440 MPa, and the absorbed energy vE of the weld joint at a test temperature of -20°C is shown. -20 (J) A high absorbed energy value exceeding 80J results in a vertical narrow-groove gas-shielded arc weld joint with excellent weld joint toughness. On the other hand, in a comparative example outside the scope of this invention, the absorbed energy vE of the weld joint at a test temperature of -20°C... -20 (J) If the yield strength of the weld is less than 80J, the toughness of the welded part will decrease, or the yield strength of the base material will be less than 440MPa, resulting in insufficient strength as a structure.

Claims

1. A method for manufacturing a vertical narrow groove welded joint, comprising butt-jointing two steel materials through a narrow groove with a groove angle of less than 20°, and joining them by using a horizontally oscillating vertical gas-shielded arc welding method. The steel has the following composition, by mass%, containing C: 0.03-0.15%, Si: 0.01-0.10%, Mn: 1.0-2.5%, P: less than 0.02%, and S: less than 0.01%, and satisfies the following formula (1), with the remainder being Fe and unavoidable impurities, and having a yield strength of 440 MPa or more. The ascending speed v of the vertical welding of the vertical gas shielded arc welding and the reciprocal f of the time required for one cycle of the lateral swinging are adjusted to satisfy the following equation (2), The unit of the rising speed v is mm / min, the unit of the time is s, and the unit of the reciprocal f is s -1 , Wherein, C, Mn, Cr, Mo, V, Cu, and Ni are the contents of each element in mass percent, and the contents of elements that are not present are 0. 。 2. The method for manufacturing a vertical narrow groove welded joint according to claim 1, wherein, During the lateral oscillation, the lateral oscillation pattern of the welding torch viewed from the welding line direction is as follows: The shape of the character.

3. The method for manufacturing the vertical narrow groove welded joint according to claim 1 or 2, wherein, The composition of the ingredients, expressed in % by mass, further contains ingredients selected from... Al: 0.005–0.100%, Cu: 0.01–1.00%, Ni: 0.01–1.00%, Nb: 0.003–0.030%, Ti: 0.003–0.030%, N: 0.0020–0.0100%, and Ca: 0.0003–0.0030%. One or more of them.

4. The method for manufacturing a vertical narrow groove welded joint according to any one of claims 1 to 3, wherein, The composition of the ingredients, expressed in % by mass, further contains ingredients selected from... Cr: 0.01–0.50%, Mo: 0.01–0.50%, V: 0.001–0.100%, B: 0.0003–0.0030%, Mg: 0.005–0.0100%, Zr: 0.0010–0.0200%, and REM: 0.0005–0.0100%. One or more of them.

5. A vertical narrow bevel welded joint, manufactured by the manufacturing method of any one of claims 1 to 4.

6. A vertical narrow bevel welded joint, which is a vertical narrow bevel welded joint formed by joining two steel materials through a narrow bevel with a bevel angle of less than 20°. The steel has the following composition, containing, by mass%, C: 0.03–0.15%, Si: 0.01–0.10%, Mn: 1.0–2.5%, P: less than 0.02%, and S: less than 0.01%, and satisfies the following formula (1), with the remainder being Fe and unavoidable impurities, and having a yield strength of 440 MPa or more. a welded joint having an absorbed energy E at a test temperature of -20°C in a Charpy impact test -20 of 80 J or more, the absorbed energy E -20 in J, in, C, Mn, Cr, Mo, V, Cu, and Ni are the contents of each element in terms of mass%, and the contents of elements that are not present are 0.

7. The vertical narrow bevel welded joint according to claim 6, wherein, The composition of the ingredients, expressed in % by mass, further contains ingredients selected from... Al: 0.005–0.100%, Cu: 0.01–1.00%, Ni: 0.01–1.00%, Nb: 0.003–0.030%, Ti: 0.003–0.030%, N: 0.0020–0.0100%, and Ca: 0.0003–0.0030%. One or more of them.

8. The vertical narrow bevel welded joint according to claim 6 or 7, wherein, The composition of the ingredients, expressed in % by mass, further contains ingredients selected from... Cr: 0.01–0.50%, Mo: 0.01–0.50%, V: 0.001–0.100%, B: 0.0003–0.0030%, Mg: 0.005–0.0100%, Zr: 0.0010–0.0200%, and REM: 0.0005–0.0100%. One or more of them.

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