JPH048155B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to submerged arc welding, which is capable of obtaining a weld metal with excellent strength and low-temperature toughness, for example, for high-tensile steel having a tensile strength of 80 Kgf/mm ^class 2 or higher. This relates to wires for [Prior Art] High-strength steel as described above is widely used in pressure vessels, steel bridges, various construction equipment, penstock pipes for pumped storage power plants, etc., but recently these welded structures have become larger and their range of application has increased. As the market continues to expand, the required properties for steel materials are becoming more stringent. For example, in order to cope with the soaring crude oil prices after the oil crisis, offshore structures are being constructed even in icy regions such as the Arctic Circle, and there is a demand for steel materials that have the strength and low-temperature toughness to withstand such harsh natural environments. It is rapidly increasing. Accordingly, it has recently become an important issue in the welding field to ensure the performance of welding materials comparable to that of the base metal. Specifically, the conventional
The low-temperature toughness value required for welds of HT80 series steel materials was previously set based on a value around -20℃, but recently safety evaluation in the low temperature range of -80℃ has become necessary. It's here. Moreover, in view of the recent severe international competition, cost reduction is an essential requirement, and in this sense, the submerged arc welding method with high welding efficiency is the most promising, and it meets the safety standards under the harsh conditions mentioned above. Various companies are actively developing wires for submerged arc welding that are compatible with the above. As a prior art relatively similar to the present invention which will be described later, there is an invention described in Japanese Patent Application Laid-open No. 157594/1983. However, this disclosed invention is completely different in purpose and structure from the present invention in the following points. In this disclosed invention, the components of the base material are also specified, and the objective is to be achieved by a combination of the base material and the welding material, but the present invention does not consider the interaction with the base material components as an issue. In the disclosed invention, the tempering embrittlement properties are particularly improved by post-weld heat treatment, whereas the present invention aims to ensure high performance in the as-welded state. The disclosed invention specifies Ti as an essential component for improving toughness, but in the present invention, Ti is replaced with Al,
It is optionally included as a deoxidizing component similar to Zr, V, and Nb, and the amount of Ti can be changed to Al, Zr,
It is specified by the relative content of Mo amount in combination with V, Nb, etc., and the purpose of adding Ti and the purpose of setting the content are completely different in the two inventions. [Problems to be solved by the invention] However, in submerged arc welding, welding conditions with relatively high heat input are adopted in order to effectively exhibit the characteristic of "high welding efficiency", and the weld metal per pass is reduced. Since the amount is large, the thermal effect on the base metal and the preceding weld metal is large, and it is extremely difficult to obtain a welded joint that simultaneously satisfies the above-mentioned high level of strength and low-temperature toughness. Under these circumstances, the present invention has developed a wire for submerged arc welding for high-strength steel, which can obtain weld metal that satisfies the above-mentioned strict requirements while maintaining the welding efficiency inherent in submerged arc welding. This is what we are trying to provide. [Means for solving the problems] The composition of the wire for submerged arc welding according to the present invention is C: 0.03 to 0.20% Mn: 1.60 to 3.00% Ni: 2.10 to 3.50% Mo: 0.30 to 1.50% Si: 0.25% Contains the following Cr: 0.20% or less, and one or more selected from the group consisting of Ti, Al, Zr, and Nb: 0.1% or less in total as an essential component, and Cu≦0.25% P≦0.015% S≦ The balance is limited to 0.015%, respectively, and the remainder consists of iron and unavoidable impurities. Among the above components, Ni, C, Si, Mo, Cr,
The gist is that the components are adjusted so that the respective contents of Ti, Al, Zr, V and Nb satisfy the relationship of the following formula. [Ni (%) + 30 × C (%)] ≦ 8 (%) 3Si (%) ≦ Mo (%) 3Cr (%) ≦ Mo (%) 10 × [Ti (%) + Al (%) + Zr (%) +V (%) + Nb (%)]≦Mo (%) [Operation] The reason for strictly determining the types and content ranges of the constituent elements will be explained below. C: 0.03-0.20% This is an essential element for obtaining a high-strength weld metal of, for example, 80 Kgf/mm ² , and if it is less than 0.03%, it will not be possible to ensure the desired strength. However, if it is too large, the weld metal will become excessively hard and its toughness will deteriorate, so it must be kept below 0.20%. Mn: 0.60-3.00% In order to ensure the desired weld metal strength with a relatively low C content, Mn must be contained at 1.60% or more. However, if it is too large, the metal structure becomes coarse and toughness becomes poor, so it must be kept at 3.00% or less. Ni: 2.10-3.50% In order to ensure high toughness at low temperatures such as -80°C, Ni must be contained at 2.10% or more.
However, even if the content exceeds 3.50%, no further effect of improving low-temperature toughness will be exhibited, which is not only economically disadvantageous, but also makes hot cracking more likely to occur due to interaction with C. It should be suppressed. Mo: 0.30% to 1.50% In addition to contributing to increased strength, Mo has the effect of improving hardenability and toughness, and if it is less than 0.3%, these effects will not be effectively exhibited. However, if it exceeds 1.50%, precipitation of carbides becomes significant, causing tempering embrittlement, which actually reduces toughness. Si: 0.25% or less Although it is an extremely important component as a deoxidizing agent, it precipitates as a low melting point oxide at grain boundaries and significantly impairs toughness. In order to avoid these problems, even the maximum amount
Must be kept below 0.25%, and more reliably
It is desirable to keep it below 0.18%. Cu: 0.25% or less Cu is a component mixed in as a copper plating material for wire rust prevention. If it is too much, it will have an adverse effect on low temperature toughness, so it must be kept at 0.25% or less. P and S: Both 0.015% or less These are harmful elements that are mixed in as impurities in iron, which is a basic element, and have a negative effect on all welding performance such as toughness, bending performance, and crack resistance.
Each must be kept below 0.015%. [Ni (%) + 30C (%)] ≦ 8% As mentioned above, submerged arc welding is performed with a relatively large heat input, but if the amount of Ni is too large, high temperatures will occur along the dendrites that have grown in the weld metal as mentioned above. It was found that cracks are more likely to occur, and that these high-temperature cracks vary significantly depending on the amount of coexisting C. Therefore, we conducted an experiment to clarify the interaction between the amount of Ni and the amount of C that affects hot cracking, and as shown in Figure 1, we found that it is possible to suppress [Ni (%) + 30 × C (%)] to 8% or less. It has become clear that hot cracking can be reliably prevented. Incidentally, Figure 1 shows the results of an experiment in which the interaction between Ni and C on hot cracking was investigated using the method described below. That is, as shown in Fig. 2A and B, a high tensile strength steel plate (HT80...650mm ^l ) with a beveling (Y beveling) in the center of a restraining plate (SS41...900mm ^w x 1,300mm ^l x75mm ^t ) 1 is used. x 38 mm ^t ) 2 was subjected to restraint welding W and submerged arc welding using wire and flux having the chemical compositions shown below, the restraining plate was removed and the occurrence of hot cracking was investigated using an X-ray transmission test method. <Wire components> C: 0.04-0.19% Mn: 1.80-1.95% Si: 0.12-0.16% Mo: 0.75-0.78% Cr: tr Ni: 2.2-3.3% Cu: 0.14-0.16% (including plating Cu) P :0.004~0.006 S:0.002~0.006% <Flux> Same as those used in the examples below <Welding conditions> Wire diameter: 4.0mmφ Current: 700A (AC) Voltage: 34V Speed: 50cm/min Preheating temperature :150℃ As is clear from Figure 1, even if the Ni and C contents are within the specified ranges,
If [Ni (%) + 30C (%)] exceeds 8%, hot cracking occurs, and in order to eliminate hot cracking, the above value must be kept below 8%. 3Si (%) ≦ Mo (%) Si is an effective element as a deoxidizing component and also effective in improving welding workability, but as mentioned above, it becomes a low melting point oxide and precipitates at grain boundaries, reducing toughness. significantly decreases However, the present inventors have confirmed that the toughness-inhibiting effect of Si is significantly suppressed by Mo, and it is recommended that the Si content be suppressed to 1/3 or less of the Mo content. For example, it has become clear that the toughness-inhibiting effect of Si is completely abolished by Mo. By the way, Figure 3 shows how toughness is affected by the following method.
This shows the results of an experiment investigating the interaction between Si and Mo. That is, a high tensile strength steel plate (HT80...400mm ^w) with a beveled upper part is used as the two restraining members (SS41...50mm ^t x 150mm ^w , 2 pieces) 1, 1 shown in Fig. 4A and B.
× 500 mm ^l × 50 mm ^t ) 2 were restraint welded and latent arc welded using wire and flux having the following chemical composition, and then an impact test was conducted on the welded portion. <Wire components> C: 0.08-0.10% Mn: 1.82-1.94% Si≦0.23% Mo: 0.34-1.41% Cr: tr Ni: 2.82-2.88% Cu: 0.14-0.16% (including plated Cu) P: 0.004 ~0.006 S: 0.002~0.005% <Flux> Same as the example below <Welding conditions> Wire diameter: 4.0mmφ Current: 700A (AC) Voltage: 34V Speed: 35cm/min Preheating/interpass temperature: 150± 25℃ <Impact test> JIS Z from a position 7 mm below the plate thickness surface of the welded part
3112 Collect a No. 4 test piece and conduct an impact test at -80°C. ◎: _v E _-80 >6Kgf・m ○: _v E _-80 =3.5~6Kgf・m ×: _v E _-80 <3.5Kgf・m As is clear from Figure 3, the Si content is within the specified range. Even if 3×Si (%) is within
If it exceeds Mo (%), the low temperature toughness value is poor, and in order to obtain the desired low temperature toughness value, 3×
The content rates of both must be adjusted so as to simultaneously satisfy the requirement of Si (%)≦Mo (%). In the present invention, in addition to the above structure, the strength is further increased by containing an appropriate amount of Cr in the wire, and a deoxidizing element selected from the group consisting of Ti, Al, Zr, V and Nb is added. By containing one or more types, the soundness of the weld metal is improved (prevention of weld defects such as blowholes) and strength is improved. However, if the Cr content is too large, low temperature toughness will deteriorate, so 0.2
% or less, and [Ti, Al,
If the total amount of [Zr, V, Nb] is too large, the low temperature toughness will deteriorate, so it must be kept at 0.1% or less. In addition, the toughness-inhibiting effects of Cr and [Ti, Al, Zr, V, Nb] tend to be suppressed by Mo, similar to the case of Si. According to the investigation of the interaction with
It was confirmed that a high level of low-temperature toughness can be ensured by adjusting the content of each element so as to satisfy the requirement of (%)]≦Mo. The present invention is constructed as described above, and by strictly specifying the constituent elements and content of the wire, it is possible to obtain a weld metal with excellent strength, low-temperature toughness, and crack resistance. The flux used in combination with the wire of the present invention may be either a fused type or a fired type, but in order to prevent the segregation of alloy elements in the weld metal and obtain a better welded joint, alloy elements may be added. A highly basic, low-hydrogen-based calcined flux that does not contain carbon dioxide is most suitable. [Example] Wires for submerged arc welding (4.0 mmφ, including Cu plated) having chemical components shown in Tables 1 (1) and (2) were produced. On the other hand, after blending the flux raw materials having the blend structure shown in Table 2, silicate sodium water glass was added, granulated, baked at 500 DEG C., and the particle size was adjusted to 10 to 100 mesh to obtain a dispersed flux. Submerged arc welding was performed under the following conditions using this scattered flux and each of the above wires, and after welding, tensile test pieces (JIS Z 3111 Al No.) were taken from the center of the plate thickness of each welded part.
And an impact test piece (JIS Z
3112 No. 4) was sampled and subjected to a tensile test at room temperature and an impact test at -80°C. Prior to collecting the test pieces, the presence or absence of weld cracks was confirmed by UT inspection. In addition, the diffusible hydrogen of the weld metal (according to JIS Z 3116) determined by separately conducted test fluxes was 0.5 to 0.5, regardless of the wire composition.
It was confirmed that the amount was 1.5ml/100gr. The results are shown in Table 4 (1) and (2). <Welding conditions> Base material: High tensile steel (HT80) Chemical composition is 50mm as shown in Table 3 ^Current : 700A Voltage: 30V Speed: 40cpm Preheating temperature: 150℃

【table】

【table】

【table】

【table】

[Table] From these experiments, the following can be considered. Wires Nos. 23 to 29 are examples that satisfy all of the specified requirements of the present invention, and good results were obtained in terms of tensile strength, low-temperature toughness, and cracking resistance. On the other hand, wires Nos. 1 to 22 are comparative examples that lack any of the requirements stipulated by the present invention, and have some performance problems as described below. No. 1: Tensile strength is low due to insufficient C content. No. 2: Low-temperature toughness is poor because the amount of C is too large, and weld cracking occurs because (Ni + 30C) exceeds 8%. No. 3: The amount of Si is too large and 3×Si (%) is Mo.
(%), so low-temperature toughness is poor. No. 4: Strength is insufficient due to insufficient amount of Mn. No. 5: Low temperature toughness due to too large amount of Mn. No. 6: Low-temperature toughness is lacking due to insufficient Ni content. No. 7: Because the amount of Ni is too large, the low-temperature toughness is rather low, and hot cracking occurs. No. 8: Low-temperature toughness is low because 3×Si (%) exceeds Mo (%), and strength is also low because the amount of Mo is insufficient. No. 9: Low-temperature toughness is rather low because the amount of Mo is too large. No.10: Low-temperature toughness is poor due to excessive Cu content. No. 11: Hot cracking occurs because Ni (%) + 30 (%) exceeds 8. No. 12: 3×Si (%) exceeds Mo (%), so low temperature toughness is low. No.13: Low-temperature toughness is poor due to excessive Cr content. No. 14: Low-temperature toughness is poor because 3×Cr (%) exceeds Mo (%). No.15: Low-temperature toughness is poor due to excessive Ti content. No. 16: Low-temperature toughness is still insufficient because the amount of Al is too large. No. 17: Low-temperature toughness is poor because the sum of (Ti+Al+V) exceeds 0.10%. No.18-20: 10×(Ti+Al+V+Zr) is Mo
It has poor low temperature toughness. No. 21, 22: Since none of Cr, Ti, Al, V, Zr, and Nb are included, the yield strength and tensile strength tend to be insufficient. [Effects of the Invention] Although the present invention is configured as described above, the key point is to strictly define the chemical composition of the wire, especially [Ni (%) + 30
×C (%)], the mutual relationship between 3 × Si (%) and Mo (%), and furthermore, 3 × Cr (%) and 10 × [Ti (%) + Al
(%) + Zr (%) + Nb (%)] and Mo (%), it has the strength and low-temperature toughness to withstand the harsh operating conditions mentioned above. Moreover, it has become possible to provide a wire for submerged arc welding for high-strength steel that exhibits excellent hot cracking.

[Brief explanation of drawings]

Figure 1 shows the effects of Ni (%) and 30×C on hot cracking resistance.
Graph of experimental results showing interactions in (%), second
The figure is an explanatory diagram of the welding method adopted in the experiment shown in Figure 1, and Figure 3 shows the effects of Mo (%) and 3×Si (%) on low-temperature toughness.
FIG. 4 is a graph of the experimental results showing the interaction of . 1...Restriction plate, 2...High tensile strength steel plate, W...Restriction welded part.

Claims (1)

[Claims] 1 C: 0.03 to 0.20% (weight %: the same below) Mn: 1.60 to 3.00% Ni: 2.10 to 3.50% Mo: 0.30 to 1.50% Si: 0.25% or less Cr: 0.20% or less , and one or more selected from the group consisting of Ti, Al, Zr, V, and Nb: contains 0.1% or less in total as an essential component, and is limited to Cu≦0.25%, P≦0.015%, S≦0.015%, respectively. , the remainder consists of iron and unavoidable impurities, and among the above components, Ni, C, Si, Mo, Cr,
A wire for latent arc welding for high-strength steel, characterized in that the contents of Ti, Al, Zr, V, and Nb satisfy the relationship of the following formula. [Ni (%) + 30 × C (%)] ≦ 8 (%) 3Si (%) ≦ Mo (%) 3Cr (%) ≦ Mo (%) 10 × [Ti (%) + Al (%) + Zr (%) +V (%) +Nb (%)]≦Mo (%)