JPS6150716B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for submerged arc welding of low-temperature steel, and in particular, by specifying the welding wire and flux used, the mechanical properties of the weld metal and the
The present invention relates to a method for submerged arc welding of low-temperature steel that satisfies all requirements such as radiation penetration ability and welding workability. Ferrite-based low-temperature materials such as 5.5% Ni steel and 9% Ni steel are mainly used as materials for containers for transporting or storing low-temperature liquids such as liquefied propane gas and liquefied natural gas.
Ni alloy steel is used. Of these, 9% Ni steel is A-353 (NNT material) and A-553 according to ASTM standards.
(QT material), the tensile strength is 70.3 to 84.4Kg/ ^mm2 , and the 0.2% proof stress is 52.7Kg/mm2 for NNT material.
mm ² or more, QT material has an extremely high performance of 59.8 Kg/mm ² or more, and the impact value at -196°C is 3.5 Kg/mm ² or more. Naturally, when performing welded construction using these materials, the required properties of the welded part must be comparable to those of the base metal. As a specific means to meet these requirements, it is common to use a welding wire with an appropriate composition and to perform appropriate heat treatment after welding. However, for large structures such as liquefied natural gas tanks, heat treatment after welding is not possible, so it is common to use Ni-based alloy welding materials to obtain excellent low-temperature toughness even when welded. . For example, manual welding using a covered arc welding rod or TIG welding is used to weld 9% Ni steel, and the manual welding material used is AWS-A5.11-
ENiCrFe1~4 is also used as TIG welding material by AWS
-A5.14-ERNiCr-3, ERNiCrFe-6 or Mo
A material equivalent to ERNiCrMo-4, etc., whose content has been increased to 15-20%, is used. On the other hand, although submerged arc welding has excellent welding efficiency, the welding heat input is large and the weld metal is significantly diluted by the base metal, making it difficult to obtain sufficient crack resistance and mechanical properties. Until now, it has hardly been put into practical use for welding large structures. However, it has been confirmed that cracking resistance can be improved by using a welding material with a high Mo content, such as the ERNiCrMo-4 mentioned above, and by using a flux with an appropriate composition. Submerged arc welding methods using welding materials are also beginning to be put into practical use in some areas. However, when a welding material containing a large amount of Mo is used, the X-ray transmission performance of the weld metal becomes extremely poor, making it difficult to inspect weld defects, and the weld bead tends to sag, resulting in poor workability and bead shape. It has been pointed out that problems such as low mechanical strength of weld metal occur, low productivity of welding wire, and high wire prices due to the use of large amounts of expensive Mo, making it unsuitable for practical use. It is hard to say that this is the best method. However, submerged arc welding is superior to other welding methods in terms of welding efficiency.
It would be extremely meaningful to overcome the above drawbacks and improve the practicality of submerged arc welding. The present inventors focused on the above-mentioned circumstances and believed that in order to overcome the difficulties of the submerged arc welding method described above, it is necessary to eliminate the obstacles associated with the combined use of Mo. With the aim of developing a method that can ensure high cracking resistance, we have been conducting intensive research focusing on the composition of welding wire and flux. The present invention was made as a result of such research, and its composition is as follows: Ni≧60%, 10%≦Cr≦30%, C≦1%, Si≦
2%, Fe≦15%, N: 0.001-0.05%, Nb≦
4%, Mn≦10%, Al≦1%, Ti≦1%, Mo≦5
% and one or more elements selected from the group consisting of W≦5%, MgO: 5 to 40%, metal carbonate: 5 to 40%, metal fluoride: 5 to 50%, In addition to containing SiO ₂ ≦20%, Nb≦30%, Mn≦50%, Al≦8%, Ti≦8
%, Si≦5%, C≦3%, Ni≦30%, Cr≦10
%, Mo≦10%, W≦10%, the grain size is 100 mesh or less, and the ratio of the total amount of alloy components to the entire flux is 60% or less. A sintered flux is used, and the flux contained in the wire and/or flux is
The gist of the first invention lies in adjusting the amounts of Nb and Mn so as to satisfy the following formula, and in place of the above flux, a flux obtained by essentially adding TiO ₂ ≦15% to the above flux. The gist of the second invention resides in that the second invention has the same configuration as the first invention except for using. 2W _Nb +F _Nb = 8.2 to 30% 5W _Mo +F _Mo = 22.5 to 50% [W _Nb : Nb content in welding wire F _Nb : Nb content in flux W _Mo : Mn content in welding wire F _Mo : Mn content in flux] That is, in the present invention, the composition of the welding wire and flux to be used, in particular the content of Nb and Mn, is specified, and the amount of N, which is a gas component, is limited to improve the resistance of the weld metal. By improving crackability and other properties, it was possible to reduce or omit Mo. The structure and effects of the present invention will be explained below based on the basis for specifying the composition of the welding wire and flux, but the following does not limit the present invention and may be adapted to the spirit of the above and below. All suitable modifications and implementations within the scope are within the scope of the present invention. First, Nb and Mn, which are most important in the present invention, will be explained. These have the effect of increasing the tensile strength, cracking resistance, etc. of the weld metal through a mutual effect, and also enhance welding workability such as slag removability.
That is, when Nb is used alone, as the content increases, the 0.2% yield strength of the weld metal improves, but the tensile strength and low-temperature toughness significantly decrease, and the slag releasability also deteriorates. On the other hand, Mn alone has no effect on increasing tensile strength or low-temperature toughness. However, when Nb and Mn are simultaneously present in the weld metal, the tendency of Nb to lower the tensile strength and low-temperature toughness, as well as the tendency to lower slag removability, is alleviated or eliminated by the coexisting Mn. These additive effects are effectively exhibited by making the weld metal contain 4.1 to 15% Nb and 4.5 to 10% Mn, and no additive effects are observed below the lower limits. Furthermore, if the amount of Nb is too large, the tensile strength and low temperature toughness will be significantly reduced, and if the amount of Mn is too large, elongation, drawing and welding workability will deteriorate. By the way, Nb and Mn are supplied as alloy components in the welding wire and flux, and there is no essential difference in supplying them from either source. However, Nb
When Nb and Mn are supplied from flux, the yield in the weld metal is 1/2 for Nb and 1/5 for Mn, whereas when supplied from welding wire, the yield is almost 100%. Therefore, when supplying these from welding wire and/or flux, the amount of Nb (W _Nb ), the amount of Mn (W _Mo ) in the welding wire, and the amount of Nb ( F _Nb ) and the amount of Mn (F _Mo ) may be determined. 2W _Nb +F _Nb = 8.2 to 30 (%) 5W _Mo + F _Mo = 22.5 to 50 (%) Among these alloying elements, when Nb is supplied from a welding wire, the amount of Nb in the wire exceeds 4%. If this happens, the yield during wire manufacturing will be extremely low, so the amount of Nb in the wire should be kept at 4% or less, and the shortage should be supplied from flux. Next, other components contained in the welding wire will be explained. Ni is an essential component for obtaining excellent low-temperature toughness as welded, and if it is less than 60%, a weld metal with sufficient performance cannot be obtained. There is no particular upper limit, but considering the balance with other essential alloy components, the upper limit is thought to be around 80%. Cr forms a solid solution in Ni and has the effect of strengthening the matrix and increasing tensile strength and low-temperature toughness, and in order to effectively exhibit these effects, it is necessary to contain 10% or more in the wire. Moreover, if the content exceeds 30% in the wire, the tensile strength of the weld metal becomes too high, resulting in insufficient ductility. A small amount of C has the effect of increasing tensile strength, and a portion of Nb may be replaced with C.
However, if it is too large, low temperature toughness and cracking resistance will be impaired, so it must be kept at 1% or less. Si acts as a deoxidizing agent and increases tensile strength, but if it exceeds 2%, low temperature toughness and cracking resistance decrease. Although Fe slightly increases tensile strength, it tends to decrease low temperature toughness. But 15
There is no actual harm if the amount is less than %. In addition, N is generally considered to be a harmful element, and 0.05%
If it exceeds this range, the low temperature toughness and cracking resistance will deteriorate, especially in the component composition of the present invention, so it must be kept below this range. However, in the present invention, even a small amount has a significant effect of increasing the tensile strength of the weld metal, so it is essential to contain it in an amount of 0.001% or more. Furthermore, in addition to the above-mentioned alloy components, the welding wire may contain one or more of Al, Ti, W, Mo, etc., if necessary. That is, when added in small amounts, Al and Ti have the effect of improving blowhole resistance, as well as increasing tensile strength and welding workability. However, care should be taken because if both Al and Ti exceed 1%, low-temperature toughness, cracking resistance, and welding workability will be adversely affected. Mo has the effect of increasing tensile strength and improving low-temperature toughness and cracking resistance, but if it exceeds 10%, welding workability will decrease significantly, and
As the wire penetration ability becomes poor, the wire productivity also decreases. Furthermore, although W has the effect of increasing tensile strength, it should be kept at less than 10%, as its high melting point causes it to segregate in the weld metal, reducing mechanical properties and reducing wire productivity. be. Next, we will discuss other components in the flux.
First, MgO is an essential component for increasing the basicity of the slag and improving its fluidity and peelability, and must be contained in an amount of at least 5%.
However, if it exceeds 40%, the slag releasability will deteriorate, so it should be kept below this. Metal carbonates have the effect of increasing the basicity of slag, lowering the hydrogen partial pressure in the atmosphere near the welding area by decomposing and producing CO ₂ gas, and improving the mechanical properties of the weld metal. is required. But 40%
If it exceeds this, the fluidity of the slag deteriorates, resulting in deterioration in the bead shape and the removability of the slag. The metal carbonates include carbonates of alkali metals or alkaline earth metals such as BaCO ₃ , CaCO ₃ , Li ₂ CO ₃ , MgCO ₃ , etc.
Examples include MnCO ₃ and the like, and these can be used alone or in combination of two or more. The metal fluoride has the effect of improving the fluidity of the slag and improving the bead shape, and needs to be added in an amount of 5% or more. However, if it exceeds 50%, arc stability and slag releasability deteriorate, which is not preferable. Specific examples of metal fluorides include
Examples include AlF ₃ , BaF ₂ , CaF ₂ , MgF ₂ , Na ₃ AlF ₆ and the like, and these can be used alone or in combination of two or more. SiO ₂ has the effect of imparting appropriate viscosity to the slag and improving welding workability, but if it is added in an amount exceeding 20%, the basicity of the slag decreases and the cracking resistance of the weld metal deteriorates. Furthermore, if too much TiO ₂ is added, the basicity of the slag will decrease and the cracking resistance will deteriorate, similar to the case with SiO ₂ .
Furthermore, slag seizure becomes significant, but as long as it is less than 15%, these actual damages are hardly noticeable. In addition, the flux used in the present invention includes:
Similar to Nb and Mn mentioned above, various other alloy components such as Al,
Ti, Si, C, Ni, Cr, Mo, W, etc. can also be blended. The effects of adding these alloy components are essentially the same as those explained in the section on welding wires, with Al, Ti, and Si acting as deoxidizing agents;
Improves the blowhole resistance and tensile strength of weld metal. Further, Ni, Cr, Mo, W, and C contribute to improving tensile strength, low-temperature toughness, cracking resistance, etc. The blending ratios of these alloy components are Al≦8%, Ti≦8%, Si≦5, considering the yield of weld metal.
%, C≦3%, Ni≦30%, Cr≦10%, Mo≦10
% and W≦10%. In addition, when these alloy components are mixed into the flux, the total blending ratio thereof, including the above-mentioned Nb and Mn, must be 60% or less. However, if it exceeds 60%, the alloy components will oxidize and burn during the firing process, reducing welding workability and deteriorating the mechanical properties of the weld metal. Furthermore, the flux used in the present invention is limited to the sintered type, because in the molten type, the alloy components are oxidized or altered during the melting stage, and the above-mentioned effects that should be expected from the alloy components are effectively exerted. This is because it is not done. The specific manufacturing method for sintered flux is not particularly limited, but the most common method is to knead a predetermined amount of raw material powder with water and a binder (sodium silicate, potassium silicate, etc.), and then This method involves adjusting the particle size after drying and firing at a temperature (usually around 300 to 600°C). In this case, the particle size of the alloying components mixed in the flux must be 100 mesh or less. The reason for this is that if the grain size of the alloy components in the blended raw materials is coarse, they will not be distributed uniformly during flux production, and the alloy elements will segregate in the weld metal, resulting in deterioration of mechanical properties.
These problems do not occur if the alloy components are fine particles of 100 mesh or less. By the way, as a technique similar to the present invention, Japanese Patent Laid-Open No. 51-83032 and Japanese Patent Publication No. 51-14975, which were proposed by the applicant of the present invention, are known. However, the former technology is aimed at increasing the strength of 75Ni-15Cr coated arc welding rods, which have been in practical use for some time, and it is not possible to perform submerged arc welding of 75Ni-15Cr, which was previously considered impossible. This should be strictly distinguished from the present invention, which made this possible. On the other hand, the latter technology concerns Inconel-based welding wire, and does not mention the correlation with flux components, and although this welding wire is effective for manual welding, it is not suitable for automatic welding. When applied, the cracking resistance and strength are insufficient and a satisfactory effect cannot be obtained. In contrast, in the submerged arc welding method of the present invention, based on the knowledge and experience described above, the compositions of the welding wire and flux are specified, and the correlation between the alloy components, especially Nb and Mn, is determined. By setting each content in consideration of various factors, and in combination with limiting the amount of N in the welding wire and limiting the particle size of alloying elements in the flux, welding can be carried out as welded regardless of whether it is manual welding or automatic welding. However, it has become possible to provide a welded part having excellent mechanical properties such as low-temperature toughness and cracking resistance, but these structures and effects cannot be imagined from the invention of the above-mentioned publication. The present invention is configured as outlined above, and has a 9%
Contains Ni steel, 8.5% Ni steel, 5% Ni steel, etc.
It can be widely used in welded construction using Ni low-temperature steel as the base material. Next, examples of the present invention will be shown. Example 1 A welding wire having the composition shown in Table 1 and a flux shown in Table 2 were combined, and submerged arc welding was performed under the following conditions, and welding workability and mechanical properties of the obtained weld metal were investigated. The results are summarized in Table 3. [Submerged arc welding conditions] Test method: NV20-2 Wire diameter: 1.6mmφ Current polarity: DC Welding current: 300A Welding voltage: 30 to 32V Welding speed: 30cm/Preheating of denominator material: None Interpass temperature: 150℃ or less Flux : Used after drying at 250℃ for 1 hour. However, in Table 1, codes A to E are welding wires that satisfy the requirements of the present invention, and code F is a welding wire that lacks the requirements of the present invention (the amount of Si, N, and Fe is too high. (and insufficient Cr content) shows welding wire. Also, in Table 2, the symbols A, B, D, E, F, G, H, J, L and M
The fluxes that meet the requirements of the present invention are fluxes that do not meet the requirements (symbol C: excessive amount of _SiO2 ).
Insufficient amount of MgO, code I: Excessive amount of TiO ₂ indicates insufficient metal carbonate, code K: insufficient amount of metal fluoride).

【table】

【table】

【table】

[Table] From Tables 1 to 3, the following considerations can be made. (1) Even if the welding wire is appropriate, if the composition of the flux other than the alloy components deviates from the requirements of the present invention, welding workability deteriorates and is not practical (Experiment Nos. 3, 6, and 12). (2) Even if the welding wire and flux individually meet the requirements other than the alloy components of the present invention, the amount of Nb (2W _Nb + F _Nb ) and Mn (5W _Mo + F _Mo ) contained in both If the requirements of the present invention are not met, the mechanical properties of the weld metal, especially the low-temperature toughness (impact test value), will be poor (Experiment Nos. 5 and 9).
and 13). (3) Even if the (2W _Nb + F _Nb ) and (5W _Mo + F _Mo ) amounts happen to meet the requirements of the present invention, if the component compositions of the wire and flux each lack the requirements of the present invention, welding workability may be affected. Both the mechanical properties of the weld metal and the weld metal became insufficient, and the object of the present invention could not be achieved at all (Experiment No. 16). (4) In contrast to these, examples (experiment numbers 1, 2, 4, 7, 8, 10,
11, 14 and 15) are extremely excellent in both workability and mechanical properties. Example 2 Using welding wire C shown in Table 1 and flux H shown in Table 2, butt welding of 9% Ni steel was carried out under the following welding conditions. [Welding conditions] Welding wire diameter: 1.6mmφ Current characteristics: DC Welding current: 200~300A Welding voltage: 26~32V Welding speed: 25~60cm/Preheating of denominator material: None Interpass temperature: 150℃ or less Flux: 250℃ After drying for 1 hour, welding position: horizontal groove shape and lamination method: as shown in Figure 1. Table 4 shows the mechanical properties of the joints obtained. However, the tensile test is based on JIS Z 3121, and the impact test is based on JIS Z.
3112 No. 4 (average value of 3 tests), vertical bending test was conducted according to ASME Sec FigQ-7.3.

[Table] As is clear from Table 4, the welded joints obtained by the submerged arc welding method of the present invention are extremely excellent in all aspects of tensile strength, low-temperature toughness, and bending performance.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the groove shape and layered method of welding experiments employed in Examples.

Claims (1)

[Claims] 1 Ni≧60%, 10%≦Cr≦30%, C≦1%, Si
≦2%, Fe≦15%, N: 0.001-0.05%, Nb
≦4%, Mn≦10%, Al≦1%, Ti≦1%, Mo≦
5% and one or more elements selected from the group consisting of W≦5%, MgO: 5-40%, metal carbonate: 5-40%, metal fluoride: 5-50% , SiO ₂ ≦20%, Nb≦30%, Mn≦50%, Al≦8%, Ti≦8
%, Si≦5%, C≦3%, Ni≦30%, Cr≦10
%, Mo≦10%, W≦10%, the grain size is 100 mesh or less, and the ratio of the total amount of alloy components to the entire flux is 60% or less. A sintered flux is used, and the flux contained in the wire and/or flux is
A method for latent arc welding of low-temperature steel, characterized by adjusting the amounts of Nb and Mn so as to satisfy the following formula. 2W _Nb +F _Nb =8.2~30% 5W _Mo +F _Mo =22.5~50% However, W _Nb : Nb content in welding wire F _Nb : Nb content in flux W _Mo : Mn content in welding wire F _Mo : Mn content in flux 2 Ni≧60%, 10%≦Cr≦30%, C≦1%, Si
≦2%, Fe≦15%, N: 0.001-0.05%, Nb
≦4%, Mn≦10%, Al≦1%, Ti≦1%, Mo≦
5% and one or more elements selected from the group consisting of W≦5%, MgO: 5-40%, metal carbonate: 5-40%, metal fluoride: 5-50% , _SiO2 ≦20%, _TiO2 ≦15%
In addition, Nb≦30%, Mn≦50%, Al≦8
%, Ti≦8%, Si≦5%, C≦3%, Ni≦30%,
Contains at least one alloy component selected from the group consisting of Cr≦10%, Mo≦10%, and W≦10%, has a grain size of 100 mesh or less, and has a ratio of the total amount of alloy components to the entire flux. Use a sintered flux with a content of 60% or less, and
A method for latent arc welding of low-temperature steel, characterized by adjusting the amounts of Nb and Mn so as to satisfy the following formula. 2W _Nb +F _Nb =8.2~30% 5W _Mo +F _Mo =22.5~50% However, W _Nb : Nb content in welding wire F _Nb : Nb content in flux W _Mo : Mn content in welding wire F _Mo :Mn content in flux