JP6950294B2 - Manufacturing method of joints by multi-layer welding - Google Patents

Description

The present invention is based on a method for manufacturing a joint by multi-layer welding, more specifically, multi-layer welding using a thick steel plate having a thickness of 25 mm or more for structures requiring high toughness such as marine structures, buildings, bridges, and penstocks. It relates to a method of manufacturing a joint.

When manufacturing joints by multi-layer welding, such as when the ends of a pair of thick steel plates are butted against each other for welding, the weld heat-affected zone (HAZ:) of the steel plate that has undergone "two-phase region heating" caused by multi-pass welding. It is known that a high carbon martensite-austenite mixture (MA) is formed in the Heat-Affected Zone. In particular, when the "coarse grain region" heated in the vicinity of the welding line (FL: Fusion Line) in the preceding welding pass is subjected to "two-phase region heating" in the next pass, a significant decrease in toughness may occur. It has been pointed out.

Several proposals have been made in Patent Documents 1 to 4 and the like as measures for improving the toughness of such a "coarse grain region" + "two-phase region heating" region. The invention described in Patent Document 1 mainly reduces the amount of C to 0.001 to 0.02% among the components of steel and suppresses the formation of MA, but is often used to supplement the strength. Requires alloying elements. Further, the invention described in Patent Document 2 is to make a special alloy component in which Mn is increased to 2% or more and then Ti oxide is used, and the toughness is improved by fine granulation. Further, the invention described in Patent Document 3 suppresses the production of MA by further lowering the C content. Further, in the invention described in Patent Document 4, a large amount of Al is added in order to suppress the formation of MA. In all the inventions described in the patent documents, the existence of "coarse grain region" + "two-phase region heating" is allowed, and by devising the steel composition, fine graining and MA formation are suppressed and the toughness deteriorates. Although it is intended to be reduced, the production load is high because it requires the addition of an expensive alloy or a special manufacturing method.

On the other hand, Patent Document 5 proposes to control the lamination of 3 layers and 6 passes or less in multi-pass welding with a heat input amount of 30 kJ / cm or less. However, the purpose of this is to improve the fatigue characteristics by controlling the shape and residual stress of the weld toe, which is different from the toughness improvement.

Japanese Unexamined Patent Publication No. 9-11137 JP-A-2010-248590 Japanese Unexamined Patent Publication No. 2011-106014 Japanese Unexamined Patent Publication No. 2012-188749 Japanese Unexamined Patent Publication No. 2012-200782

Therefore, an object of the present invention is to improve the toughness of the weld heat-affected zone (HAZ) by a new method for manufacturing a joint by multi-layer welding, which is different from the above-mentioned conventional technique.

In order to solve the above problems, the present inventors investigated the effect of welding conditions of multi-pass welding on the toughness of HAZ. As a result, it was found that by controlling the heat input amount of welding and the lamination interval to a certain relationship, the region of "coarse grain region" + "two-phase region heating" that deteriorates the toughness of the welded portion can be eliminated. This eliminates the "coarse grain region" + "two-phase region heating" region, which was the source of toughness deterioration, and eliminates the need for expensive alloy addition and high-load steps for controlling the metallographic structure. Specifically, the following method for manufacturing a joint by multi-layer welding is provided.
(1) A method for manufacturing a joint by multi-layer welding using a thick steel plate having a plate thickness of 25 mm or more, wherein the heat input amount of each welding pass and the lamination interval of the weld metal are as follows (1):
0 <0.077 ・ H ^-1.18・ d ^3.26 ≦ 1.1 (1)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
A method for manufacturing a joint by multi-layer welding, which comprises performing welding that satisfies the above conditions.
(2) A method for manufacturing a joint by multi-layer welding using a thick steel plate with a plate thickness of 25 mm or more, in which the amount of heat input in the welding path of the welded portion adjacent to the weld heat affected zone and the lamination interval of the weld metal in the welded portion are The following equation (1):
0 <0.077 ・ H ^-1.18・ d ^3.26 ≦ 1.1 (1)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
The following equation (2):
0.077 ・ H ^-1.18・ d ^3.26 ＞ 1.1 (2)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
A method for manufacturing a joint by multi-layer welding, which is characterized by satisfying the above conditions.

According to the present invention, when manufacturing a joint by multi-layer welding, such as when welding a thick marine structure, a welding method for a steel material for performing multi-pass welding is devised, and welding heat input and each pass during welding are devised. By controlling the stacking interval of the above, it is possible to completely eliminate the portion where the deterioration of the toughness is remarkable. As a result, the HAZ toughness of a steel material that is subjected to multi-pass welding at the time of welding a thick marine structure or the like can be significantly improved, and the safety of the structure can be enhanced without reducing the welding productivity. In addition, it is possible to manufacture harsh materials having high strength and high toughness and other required values. Furthermore, the method for manufacturing a joint by multi-layer welding of the present invention does not attempt to improve the composition or metal structure of the steel sheet itself to improve the HAZ toughness, and therefore, unlike the conventional technique described above, the steel sheet It is possible to significantly improve the HAZ toughness of a thick steel sheet without adding a large amount of expensive alloy to the steel sheet or requiring any high-load process for controlling the metallographic structure of the steel sheet.

It is a schematic diagram explaining one Embodiment of the manufacturing method of the joint of this invention. It is a schematic diagram explaining another embodiment of the manufacturing method of the joint of this invention.

In the method of the present invention, a thick steel plate having an arbitrary composition having a plate thickness of 25 mm or more, for example, 50 mm or more and 100 mm or less can be used for welding to a member to be welded such as another steel plate, and is not particularly limited. Preferably, a thick steel plate having a thickness of 25 mm or more is used for structures requiring high toughness such as marine structures, buildings, bridges, and penstocks. Such a thick steel plate contains, for example, C: 0.03 to 0.15%, Mn: 1.0 to 2.5%, and Si: 0.01 to 0.5% in mass%. P: 0 to 0.05%, S: 0 to 0.05%, the balance consists of Fe and unavoidable impurities, Cu: 0 to 2%, Ni: 0 to 3%, Cr: 0 to 0.75%, Mo: 0 to 0.75%, Nb: 0 to 0.05%, V: 0 to 0.1%, B: 0 to 0.002%, Ti: 0 to 0.02 %, Al: 0 to 0.05%, N: 0 to 0.007%, and O: 0 to 0.005%, which further contain one or more.

In addition, as the welding method, coating arc welding, semi-automatic arc welding, TIG welding, MIG welding, CO ₂ gas arc welding, MAG welding, FCAW welding, submerged arc welding (SAW), etc. can be used to change the amount of heat input and the stacking interval. Any welding method that can be used will do. Further, as the joint, those that are multi-layer welding such as butt joints, cross joints, T-shaped joints, groove welding of square joints, and fillet welding are targeted. This is because in each case, the region of "coarse grain region" + "two-phase region heating" at the time of multi-layer welding becomes a remarkably tough embrittlement portion.

Further, in the method of manufacturing a joint by multi-layer welding of the present invention, for the purpose of improving the toughness of the welding heat-affected zone, the heat input amount of all the welding passes and the welding interval of the welding metal, or at least the welding heat-affected zone. The heat input amount of the welding path of the adjacent welded portion and the lamination interval of the welded metal in the welded portion are calculated by the following equation (1):
0 <0.077 ・ H ^-1.18・ d ^3.26 ≦ 1.1 (1)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
Includes welding that meets the requirements. Preferably, the above formula (1) is
0 <0.077 · H ^-1.18 · d ^3.26 ≤ 0.6.

When welding is performed in which at least the amount of heat input from the welding path of the welded portion adjacent to the weld heat affected zone and the lamination interval of the weld metal in the welded portion satisfy the above equation (1), any appropriate input is applied to the other welded portions. Welding can be performed by selecting the amount of heat and the lamination interval. However, from the viewpoint of increasing the welding efficiency, the heat input amount of the welding path and the lamination interval of the weld metal in at least a part or all of the other welded parts are determined by the following equation (2):
0.077 ・ H ^-1.18・ d ^3.26 ＞ 1.1 (2)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
It is preferable to perform welding that satisfies the above conditions. For the welded portion adjacent to the welded heat-affected zone, the toughness of the welded heat-affected zone is improved by performing welding satisfying the formula (1), and at least a part or all of the other welded portions are, for example, for example. Welding efficiency can be remarkably improved by welding at a wider stacking interval according to the formula (2). Although the upper limit is not specified for equation (2), welding becomes difficult if the stacking interval d becomes too large. Therefore, in general, 0.077 · H ^-1.18 · d ^3.26 ≤ 200 is set and the upper limit is set. Is, for example, 100, 50, 30, 20, 15 or 10.

More specifically with reference to the drawings, in one embodiment of the method for manufacturing a joint by multi-layer welding of the present invention, as shown in FIG. 1, the ends of a pair of thick steel plates are butted against each other by multi-layer welding. When manufacturing a joint, with respect to the first groove surface 1Aa which is the end surface of the first thick steel plate 1A and the first groove surface 1Aa provided at the end of the second thick steel plate 1B. Multi-layer welding is performed on the re-shaped groove portion 2 formed by the second groove surface 1Ba that is inclined at a constant angle. At that time, in the multi-layer welding, the heat input amount and the lamination interval of the weld metal 5 are the same not only in the welded portion (the portion along the weld line 4) adjacent to the weld heat affected zone 3 but also in all other welding paths. It is carried out by satisfying the formula (1). According to such a joint manufacturing method, the welding metal 5 stacking intervals are relatively small and uniform, and the number of welding passes is relatively large. Therefore, not only can the toughness of the welding heat-affected zone 2 be improved, but also the toughness of the welding heat-affected zone 2 can be improved. It is possible to realize the production of joints by welding with extremely high safety.

FIG. 2 is a schematic view illustrating another embodiment of the method for manufacturing a joint by multi-layer welding of the present invention. Since each configuration of the pair of thick steel plates and the groove portion is basically the same as that in FIG. 1, the same reference numerals are given and the description thereof will be omitted.

With reference to FIG. 2, when a joint is manufactured by abutting the ends of a pair of thick steel plates 1Aa and 1Ba and performing multi-layer welding at the groove portion 2, the joint is adjacent to the welding heat-affected zone 3 (that is,). The welded portion 6 (which is in contact with the groove surface 1Aa of the first thick steel plate 1A and the groove surface 1Ba of the second thick steel plate 1B, respectively) is welded in the same manner as in FIG. Improve the toughness of 3. On the other hand, the other welded portions 7 (that is, the welded portions that do not contact the groove surface 1Aa of the first thick steel plate 1A and the groove surface 1Ba of the second thick steel plate 1B) are welded at a wider laminating interval. , It can be seen that the welding efficiency is improved by reducing the number of welding passes.

Here, when the present inventors investigated the state of occurrence of the most embrittled portion during multi-layer welding, the final two passes of the occurrence of the most embrittled portion were "coarse grain or sub-coarse grain (1150 in the temperature range)". It was found that the case was "° C to 1550 ° C.)" followed by "α + γ two-phase region (particularly the temperature range of 700 to 740 ° C.)". In addition, as a result of the HAZ temperature history calculation of the multi-layered pile, it was found that such a portion does not exist in the HAZ depending on the conditions of the welding heat input and the stacking interval of each pass. This is because when the stacking interval is reduced, the overlap between the heat-affected areas of the preceding pass and the next pass becomes large, and the "coarse grain part" and "sub-coarse grain part" of the preceding pass change to the "fine grain area" of the succeeding pass. Because it goes on. Similarly, the "two-phase region heating" portion of the preceding pass is replaced with the "temper region" in the next pass. The "temper region" is a temperature region of "two-phase region (about 700 ° C.)" or less and 500 ° C. or higher, and when heated in this temperature region, MA, which is an embrittlement phase, is decomposed and toughness is significantly improved. Will be done. Further, in addition to reducing the lamination interval of the weld metal, if the heat input amount of the welding pass is increased, the "coarse grain portion" and "subgrain" generated in the preceding pass are expanded as the heat influence range of one pass is expanded. It was found that the "coarse grain part" and the "two-phase region heating" part were reduced.

The conditions to be satisfied for the heat input amount and the stacking interval of each pass found in this way are as follows.
0 <0.077 ・ H ^-1.18・ d ^3.26 ≦ 1.1 (1)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
Preferably, the above formula (1) is 0 <0.077 · H ^−1.18 · d ^3.26 ≦ 0.6.
Here, "0.077 · H ^-1.18 · d ^3.26 " is markedly embrittled by "two-phase region heating" among the "coarse grain part" and the "sub-coarse grain part" generated per 1 mm of the weld line. It represents the area of various parts. When this value is 1.1 or less, the area of the embrittled portion is very small and the toughness is greatly improved. Further, below 0.6, the embrittled portion is almost 0, and it is expected that the level will have almost no effect on toughness. For the above reasons, the upper limit is set to 1.1 or less, preferably 0.6 or less. On the other hand, if it is less than these values, the effect of the present invention can be sufficiently obtained, so the lower limit is set to more than 0.

The amount of heat input to each pass may be appropriately selected within the range satisfying the above formula (1), and is not particularly limited, but is a welding method generally applied when manufacturing a joint by multi-layer welding. Since the maximum amount of heat input is 400 kJ / mm, this is the upper limit, preferably 5 to 400 kJ / mm, more preferably 10 to 400 kJ / mm, and most preferably 20 to 400 kJ / mm. Here, the quality of a general welded portion has a problem that the toughness decreases as the amount of heat input increases. Therefore, as in the present invention, the toughness of the weld heat-affected zone can be improved by satisfying the above formula (1) in relation to the stacking interval even with a relatively high heat input amount of 10 kJ / mm or more. Is extremely surprising and surprising. Similarly, the lamination interval may be appropriately selected within the range satisfying the above formula (1), and is not particularly limited, but is generally 1.0 to 10 mm, and from the viewpoint of welding productivity, it is generally 1.0 to 10 mm. It is preferably 3.0 to 10 mm, more preferably 5.0 to 10 mm. In the present invention, the "lamination interval" is the number of weld metals laminated along the welding line (FL) divided by the distance of the welding line (FL), that is, "the number of weld metals laminated along the FL / It refers to the "distance of FL", and therefore, in the case of FL along the plate thickness direction, it is "the number of laminated weld metals in the plate thickness direction / plate thickness".

Next, a method of controlling the amount of heat input and the stacking interval will be described. First, the amount of heat input H (kJ / mm) is expressed by the following formula.
H = (EI) / 1000V (3)
Here, E: voltage (V), I: current (A), V: welding speed (mm / s). Therefore, in order to control the amount of heat input, the voltage, current or welding speed used for welding may be appropriately set. Next, the lamination interval can be implemented by controlling the welding amount (g / min) by welding. Here, the welding amount is the mass of the welding material that melts and solidifies in a unit time, and if this is large, the bulk of the welding bead becomes large and the lamination interval becomes large. It is known that the amount of welding is mainly determined by the current, the diameter of the welding wire, and the amount of protrusion of the welding wire (Tetsuya Fujita, Kazunori Hattori, Tadao Nakagome, Miyasuo Kagami, Mitsuhiro Kobayashi, Mari Mimura: "Matching" Verification of Strength Evaluation of Welded Metal Parts in Joints (Part 7 Number of Planned Passes and Number of Construction Passes) ”, Abstracts of Academic Lectures of the Japan Society for Architecture (Tohoku), (August 2009), p.683). Here, the amount of wire protrusion is the length from the end of the torch to the end of the welded wire, and can be controlled by adjusting the so-called "torch height" from the steel plate to the end of the torch. Welding Engineering Society Homepage JWES Joining / Welding Technology Q & A1000, No.Q07-02-03 (2004)). If the amount of protrusion of the welding wire is large, the electric resistance increases and the Joule heat generation increases accordingly, so that the amount of melting, that is, the amount of welding of the welding wire increases. In addition, a method of controlling the welding current, voltage, wire diameter, etc. can be adopted.

Hereinafter, examples of the present invention will be described. Table 1 shows the chemical composition and production conditions of the yield strength (YS) 420 N / mm ² and 500 N / mm ^{class 2} thick steel sheets for offshore structures (plate thickness 50 mm or 75 mm) used in this example. Here, the symbols representing the manufacturing methods in Table 1 mean the following heat treatment methods.
ACC: Accelerated cooling (water cooling to a temperature range of 400 to 600 ° C after controlled rolling and then cooling)
ACC + T: Tempering is performed in a temperature range of 400 to 600 ° C. after accelerated cooling.
DQ + T: After rolling, quenching is performed directly at a temperature of room temperature to 400 ° C., and then tempering is performed in a temperature range of 400 to 600 ° C.
RQ + T: After heating to the austenite temperature range in a heat treatment furnace, quenching is performed at room temperature, and then tempering is performed in the temperature range of 400 to 600 ° C.

In addition, Table 2 shows the welding conditions and the characteristics of the welded portion when the joint is manufactured by multi-layer welding using the obtained thick steel plate. Submerged arc welding (SAW), which is generally used as test welding, is used for welding, and the amount of heat input to the weld is 3.9 to 30 at the groove so that the weld penetration line (FL) is vertical. Welding was carried out with changes in the range of 0 kJ / mm. In Table 2, only when the welding conditions are changed between the "welded portion adjacent to the HAZ" and the "other welded portion", the "welded heat input amount (kJ / mm ² )" in the "other welded portion", “Laminating interval (mm)” and “0.077 ・ H ^-1.18・ d ^3.26 ” are described. The toughness of the weld was evaluated by the Charpy test and the CTOD (Crack Tip Opening Displacement) test. The Charpy test is a 2 mm V notch test piece with absorbed energy (vE-60) at -60 ° C at two locations, the notch position FL (boundary between WM (welded metal) and HAZ) and IC (boundary between HAZ and BM (base material)). ° C. (J)) was measured. The case where both absorbed energy values were 100 J or more was regarded as acceptable.

In addition, the CTOD test was carried out with a size of t (plate thickness) x 2t and the notch was 50% fatigue crack, and the notch positions were set to FL (boundary between WM and HAZ) and IC (boundary between HAZ and BM). Five tests were performed at 60 ° C. each. Here, δ _ave indicates the average value of the five test results of the crack opening displacement (δ), and δ _min indicates the lowest value among the five tests. In addition, the case where all these values were 0.3 mm or more was regarded as a pass.

In Table 2, No. Nos. 1 to 18 are based on the present invention. 19 to 26 are comparative examples. Here, in the case of Examples 1 to 18, the absorbed energy at −60 ° C. of the welding heat affected zone is 238 J or more, the δ _min when the CTOD value is FL notch is 0.70 mm or more, and δ _{min when the IC notch is used.} Showed good fracture toughness of 0.84 mm or more. Further, in Examples 4 and 8 in which the welded portion adjacent to the HAZ satisfies the above formula (1) and the other welded portions satisfy the above formula (2), the weld heat-affected zone also has good toughness. The total number of welding passes is increased as compared with the corresponding examples 3 and 7 (all welds were welded under the same conditions as the welds adjacent to the HAZ of Examples 4 and 8). I was able to reduce it. Specifically, in Example 4, it can be reduced by about 27% from 63 to 46 in Example 3, and similarly, in Example 8, it can be reduced by about 38% from 95 to 59 in Example 7. Therefore, the welding efficiency could be remarkably improved.

On the other hand, in the comparative examples, the embrittlement due to MA caused by the two-phase region heating was remarkable because the ^{above formula (1): 0 <0.077 · H -1.18} · d ^{3.26 ≤ 1.1 was not satisfied.} rice field. In addition, the absorbed energy value at Charpy-60 ° C. in the case of the FL notch is less than 100 J, and the average value and the minimum value of the crack opening displacement of the CTOD are also very low, especially in the FL portion, both are less than 0.10 mm. It was a value, and remarkable embrittlement was observed. From these comparisons, it can be seen that the present invention has a remarkable effect on improving toughness.

1A, 1B thick steel plate 1Aa, 1Ba Groove surface 2 Groove part 3 Welding heat affected zone 4 Welding line 5 Welded metal 6, 7 Welding part

Claims (3)

It is a method of manufacturing a joint by multi-layer welding using a thick steel plate with a plate thickness of 25 mm or more, and the heat input amount of each welding pass and the lamination interval of the weld metal are as follows formula (1):
0 <0.077 ・ H ^-1.18・ d ^3.26 ≦ 1.1 (1)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
A method of manufacturing a joint by multi-layer welding, which comprises performing welding that satisfies the above conditions (excluding a method of performing bottom welding by gas shielded arc welding and then top welding by submerged arc welding) . It is a method of manufacturing a joint by multi-layer welding using a thick steel plate with a plate thickness of 25 mm or more, and the heat input amount of each welding pass and the lamination interval of the weld metal are as follows formula (1):
0.15 ≤ 0.077 · H ^-1.18 ・ D ^3.26 ≤1.1 (1)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
A method for manufacturing a joint by multi-layer welding, which comprises performing welding that satisfies the above conditions. It is a method of manufacturing a joint by multi-layer welding using a thick steel plate with a plate thickness of 25 mm or more. (1):
0 <0.077 ・ H ^-1.18・ d ^3.26 ≦ 1.1 (1)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
The following equation (2):
0.077 ・ H ^-1.18・ d ^3.26 ＞ 1.1 (2)
(In the formula, H is the amount of heat input (kJ / mm), and d is the stacking interval (mm).)
A method for manufacturing a joint by multi-layer welding, which is characterized by satisfying the above conditions.

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