JPH0462837B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a low-hydrogen coated arc welding rod that has good welding workability and low-temperature toughness. [Conventional technology] In recent years, with the development of energy resources in colder regions and deeper waters, welded structures have become larger and more sophisticated, and the requirements for welded joints have become even more severe, especially for storage tanks and offshore structures. Good low temperature toughness is required. Under these circumstances, conventional methods have been used to obtain welded joints with good low-temperature toughness.
Low hydrogen and low Ni welding rods ranging from 0.5% Ni to 3.5% Ni have been used. For example, as shown in JP-A No. 58-138591, by adding SiC to the MgCO ₃ -CaF ₂ coating material, it is possible to improve the pitting resistance, bead shape and bead appearance, and to improve welding workability. Hydrogen-based coated arc welding rods are known. However, this welding rod is designed with emphasis on workability, so in order to ensure toughness at low temperatures, it is necessary to weld with a relatively low welding heat input to make the weld metal microstructure finer and to create a high-dust structure. In addition, the low welding heat input causes the problem of hardening of the heat-affected zone of the base metal. Furthermore, Ni for obtaining toughness is expensive, and the welding rod is expensive, making it uneconomical. On the other hand, as shown in Japanese Patent Publication No. 60-5397, it is a low-hydrogen coated arc welding rod that can be welded with normal welding heat input to obtain joints with good low-temperature toughness.
By adding Ti and B ₂ O ₃ to the CaCO ₃ -CaF ₂ type coating material, appropriate amounts of Ti and B can be contained in the weld metal, and the structure of the weld metal can be made uniform and fine mainly due to the effects of Ti and B. There are some products that have good low-temperature toughness through granulation. However, this welding rod has disadvantages such as poor welding workability and a convex bead shape, especially in horizontal fillet welding. Furthermore, the present inventors have previously disclosed an invention in JP-A-59-4997 regarding measures to obtain good low-temperature toughness and to prevent the bead shape from becoming convex. This method mainly improves the bead appearance and bead shape by controlling the amounts of TiO ₂ , carbonates, and fluorides, and has shown considerable effects, but this method requires the coating material to be highly basic. Therefore, it is not always possible to obtain fully satisfactory results in terms of welding workability (undercut resistance, slag removability). [Problems to be Solved by the Invention] The present invention provides a low-hydrogen coated arc welding rod that provides a weld metal with good low-temperature toughness and has excellent bead shape, bead appearance, and welding workability. It is. [Means for Solving the Problems] The present invention is a low-hydrogen coated arc welding rod developed as a result of various studies in response to the above-mentioned circumstances, and its gist is that titanium oxide 13 to 23% by weight converted to _TiO2 , Ti, Si, SiC,
The total of one or more of Mg and Al is 0.1 _to 8% by weight, boron oxide or boron oxide compound is 0.05 to 2% by weight in terms of _B2O3 , _MgCO3 is 4 to 18% by weight,
Metal fluoride 0.1-17% by weight, _SiO2 1-15% by weight,
MgO9~22% by weight, Mn1~10% by weight, iron powder 10~50
% by weight, and the SiO ₂ content is Y (% by weight),
When the deoxidizing agent content calculated by Ti + Si + SiC + Mg + Al is X (weight%), the following condition is satisfied: 5≦Y+2X≦16, and further a binder is added to the coating material containing 0.5 to 6.5 weight% of Ni, It is a low-hydrogen coated arc welding rod made by coating a steel core wire. The feature of the present invention is that MgCO ₃ is mainly used as the CO ₂ source (combined use with other carbonates such as CaCO ₃ and MnCO ₃ is also considered), and appropriate amounts of TiO ₂ , MgO and SiO ₂ are added to improve welding workability. , by improving the bead shape and bead appearance, and adding appropriate amounts of one or more of Ti, Si, SiC, Mg, and Al to boron oxide and boron oxide compounds.
Ti and B are uniformly dissolved in solid solution to form a fine-grained, uniform structure, which significantly improves the low-temperature toughness of the weld metal. In other words, the MgCO ₃ −CaF ₂ based coating is
Compared to the CaCO ₃ -CaF ₂ based coating, a large amount of SiO ₂ is added and the coating is more acidic, so the welding workability is good as mentioned above. However, this coating is a strong deoxidizing agent.
Adding one or more of Ti, Si, SiC, Mg, and Al has the drawback that SiO ₂ is reduced, increasing the amount of Si in the weld metal and deteriorating toughness. In order to prevent this phenomenon, the present inventors, based on the above-mentioned knowledge, combined SiO ₂ with Ti, Si, SiC, Mg,
After a comprehensive comparative study of the relationship between Al,
By limiting the range to (B) shown in Figure 1, a weld metal with good low-temperature toughness that meets the purpose of the present invention can be obtained, and also has excellent bead shape, bead appearance, and welding workability. A low hydrogen-based coated arc welding rod with excellent performance can be obtained. The present invention will be described in detail below. [Function] Rutile, illuminite, iron sand, titanium slag, etc. are used as titanium oxides, but in addition to the function of adjusting slag formation and slag viscosity and improving slag encapsulation, Si is a strong deoxidizing agent. ,
It is added to reduce Ti in the weld metal by one or more of Mg, Al, Ti, and SiC,
If the _TiO2 equivalent value is less than 13% by weight, there is no effect;
If more than 23% by weight is added, the fluidity of the slag will increase, causing the slag to take the lead and deteriorating the bead shape.
A range of 13 to 23% by weight is suitable. Ti, Si, SiC, Mg, and Al have strong deoxidizing properties and reduce oxides. Si excluding Ti, SiC,
By adding Mg and Al to the coating, titanium oxide is reduced and an appropriate amount of Ti can be present in the weld metal without adding Ti itself to the coating. In addition to deoxidizing, Ti is added to improve low-temperature toughness in relation to B in the weld metal. No effect, 8
If added in excess of 0.1% to 8% by weight, the fluidity of the slag will deteriorate, resulting in deterioration of the bead shape, hardening of the weld metal, and deterioration of low-temperature toughness, so a range of 0.1 to 8% by weight is appropriate. Note that Ti, Si, Mg, and Al are Fe−
It is added with Ti, Fe-Si, Si-Mn, Al-Mg, etc. Boron oxides or boron oxide compounds are
B is supplied to the weld metal, and at the same time
It is added to improve low-temperature toughness in relation to Ti. The reason why B ₂ O ₃ is added from the coating in an oxidized form is that if it is added to the weld metal from a B alloy such as Fe-B, it may cause segregation and make it impossible to obtain stable low-temperature toughness. ,
By reducing B ₂ O ₃ and adding it to the weld metal, it is possible to distribute B uniformly, thereby making it possible to make the structure of the weld metal uniform. In this case, the same effect can be obtained by adding the boron oxide or boron oxide compound to water glass as a binder, stirring it, uniformly dispersing or dissolving it, and incorporating it into the coating material. I am sure that it will be done. Addition of boron oxide or boron oxide compound
If it is less than 0.05% by weight as B ₂ O ₃ , there will be little B in the weld metal and it will not be effective in improving low temperature toughness.
Adding more than 2% by weight increases the amount of B in the weld metal, making it more likely to cause hot cracking and lowering the low-temperature toughness. Note that the boron oxide or boron oxide compound herein refers to borax, anhydrous borax, natural borax, perovorite, kernite, and the like. MgCO ₃ acts as a gas generating agent and has the effect of protecting weld metal from the atmosphere.
If MgCO ₃ is less than 4% by weight, shielding failure occurs, pits and blowholes are likely to occur, and the low-temperature toughness of the weld metal decreases due to absorption of nitrogen gas. On the other hand, if it is added in excess of 18% by weight, the arc may become unstable and arc breakage may occur, and the viscosity of the slag increases, resulting in a convex bead shape. In addition, CaCO ₃ , SrCO ₃ , MnCO ₃ are
Since it has an effect similar to MgCO ₃ , a corresponding effect can be obtained even if a part of MgCO ₃ is replaced with these substances, that is, when MgCO ₃ and these substances are used together. Metal fluoride has the effect of reducing the amount of diffusible hydrogen in the weld metal and preventing the formation of pits and blowholes. If the metal fluoride content is less than 0.1% by weight, the above function will not be achieved significantly, and the diffusibility will decrease. As the amount of hydrogen increases, cracking resistance decreases, making pits and blowholes more likely to occur due to rust, oil, paint, etc. On the other hand, if it is added in excess of 17% by weight, the arc becomes unstable and the fluidity of the slag becomes excessive, deteriorating the bead shape. The metal fluoride mentioned here refers to CaF ₂ , Na ₃ AlF ₆ , MgF ₂ , AlF ₃ and the like. SiO ₂ acts as a slag forming agent and a viscosity modifier, and is a component that has a particularly large effect on viscosity. If it is less than 1% by weight, the fluidity of the slag becomes unstable, resulting in poor bead appearance and bead shape. Becomes convex. On the other hand, if it is added in excess of 15% by weight, the slag becomes hard and peeling becomes extremely difficult.
Since it is an acidic oxide, the basicity decreases significantly and the toughness of the weld metal deteriorates. MgO acts as a slag forming agent and a viscosity modifier, improving the encapsulation of the slag. 9
If it is less than % by weight, the above effect will not be exhibited significantly,
Undercuts occur due to lack of slag viscosity. On the other hand, if it is added in an amount exceeding 22% by weight, the viscosity of the slag increases, the encapsulation properties deteriorate, and the bead shape becomes convex. Mn is added as metallic manganese or ferromanganese, etc., and is added to function as a deoxidizing agent or alloying agent, as well as to ensure arc strength and arc spread during welding, and is added at 1% by weight.
If it is less than that, the mechanical properties of the weld metal cannot be sufficiently improved. On the other hand, adding more than 10% by weight is not preferable because hot cracking occurs. Iron powder improves arc stability and increases welding efficiency by increasing the amount of deposited metal, but if it is less than 10% by weight, the amount of welding becomes insufficient, resulting in poor bead elongation and poor welding efficiency. On the other hand, if it is added in an amount exceeding 50% by weight, the spread of the arc will be inhibited, and the encapsulating properties of the slag will be impaired, resulting in a convex bead shape. Next, SiO ₂ and strong deoxidizing agents Ti, Si, SiC, Mg,
It is essential to specify the amount of Al added, but it is also important to ensure an appropriate bead shape and appearance.
It was also confirmed that in order to obtain good low-temperature toughness of the weld metal, the amount of Si in the weld metal should be considered. That is, Figure 2 shows the results of investigating the influence of Si on vTrs of weld metal. According to this, it is clear that the low-temperature toughness can be significantly improved when the Si content of the weld metal is in the range of 0.13 to 0.38%. Therefore, based on the above findings, the _present inventors
As a result of an investigation to confirm the appropriate range of quantitative balance between Ti, Si, SiC, Mg, and Al, which are strong deoxidizing agents,
Let the SiO ₂ content be Y (wt%), and the strong deoxidizer content X (wt%) is X=Ti+Si+SiC+Mg+Al
When 5Y+2X16...(1) must be satisfied. Figure 1 is a graph that displays the conditions of equation (1) and the conditions of SiO ₂ and _the strong deoxidizing agent together. All of them satisfy the condition of being less than or equal to the upper limit value, but Y+2X>16, which is a region where equation (1) is not satisfied. Section B in the figure is an area that satisfies all the conditions. Section C in the figure indicates a region where both SiO ₂ and the strong deoxidizer satisfy the condition that they are at least the lower limit, but where Y+2X<5 and the formula (1) is not satisfied. That is, in part B in the figure, not only a weld metal with good low-temperature toughness is obtained, but also the bead shape, bead appearance, and welding workability are extremely good. However, part A in the same figure is a region where Y+2X>16, and the slag becomes more acidic and welding workability becomes better, but SiO ₂ is excessively reduced and the amount of Si in the weld metal exceeds 0.38%. The disadvantage is that low-temperature toughness deteriorates. On the other hand, part C in the same figure is Y
In the region of +2 will not be achieved. Ni is added to supplement the strength and toughness of the weld metal, and if it is less than 0.5% by weight, these effects will not be effectively exhibited. But these effects are 6.5
It reaches a saturation state at a weight percentage of 10% by weight, and even if it is contained beyond that level, the toughness hardly improves, and on the contrary, welding workability deteriorates. A coating material containing the above-mentioned components can be produced by coating a steel core wire with an adhesive such as water glass and drying the coated wire according to a normal welding rod manufacturing process. Furthermore, what is the steel core wire used in the welding rod of the present invention?
Refers to the core wire equivalent to JIS G 3523 Type 1 No. 1. Next, the effects of the present invention will be described in more detail based on Examples. [Example] As shown in Tables 1 and 2, an appropriate amount of water glass was mixed into coating materials with various compositions, and this was mixed into a 5mmφ×
A 700 mm mild steel core wire was coated and dried at a maximum temperature of 400°C to make welding rods A-1 to A-8 and B-1 to B-11. Root gap 1 ~ 1 with a V-bevel with a groove angle of 50° on a 20 mm thick aluminum killed steel plate using the above-mentioned test bar.
3 mm was taken, and downward welding was performed at a welding current of 220 A and a welding heat input of 18 KJ/cm. Thereafter, a 2 mm V-notched mechanical impact test piece was taken from 2 mm below the plate thickness surface on the final pass side and tested at -60°C. In the welding workability test, a steel plate (16 mm thick) coated with a 20 μm wash primer was placed in a horizontal fillet position.
The welding current was 230A and the rod operation ratio was 1.3. As for the judgment criteria, an impact value of 5 kgf-m or more at -60°C was considered good. In addition, ○ marks for welding workability are good, △
The mark means slightly defective, and the cross mark means defective.

【table】

【table】

〔Effect of the invention〕

As described above, the welding rod of the present invention is less expensive than conventional welding rods and has a high shear strength at low temperatures by specifying the types of compounded components that make up the coating material and setting the compounding ratio of each component within a specific range. It produces weld metal with good impact toughness, satisfies bead shape, bead appearance, and other welding performance, and can greatly contribute to the safety of marine structures and other structures, making it an industrial choice. The above effects are extremely remarkable.

[Brief explanation of drawings]

Figure 1 shows SiO ₂ content and Ti, Si, SiC, Mg, Al
A graph showing the relationship between content rates, Figure 2 is for weld metal.
2 is a graph showing the relationship between vTrs and the amount of Si in weld metal.

Claims (1)

[Claims] 1 Titanium oxide converted to TiO ₂ 13 to 23% by weight, the total of one or more of Ti, Si, SiC, Mg, and Al
0.1 _to 8% by weight, 0.05 to 2% by weight of boron oxide or boron oxide compound converted to _B2O3 ,
4-18 wt% _MgCO3 , 0.1-17 wt% metal fluoride, 1-15 wt% _SiO2 , 9-22 wt% MgO, Mn1
~10% by weight, containing 10-50% by weight of iron powder, and
SiO ₂ content is Y (weight%), Ti + Si + SiC + Mg +
When the deoxidizer content calculated by Al is X (wt%), the following condition is satisfied: 5≦Y+2X≦16, and a binder is added to the coating material containing 0.5 to 6.5 wt% Ni. , a low hydrogen-based coated arc welding rod characterized by being made by coating a steel core wire.