JPH0521676B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial applications 9%Cr-1~2%Mo steel has sufficient oxidation resistance and high high temperature strength at 560~600℃, so it has recently been used in place of austenitic stainless steel for boiler equipment for thermal power generation and in the nuclear power industry. It is used in high-temperature, high-pressure containers, etc. Recently, there has been a trend for these structures to be used at even higher temperatures. The present invention relates to a low-hydrogen coated arc welding rod that produces a 9% Cr-1 to 2% Mo weld metal with excellent creep properties and crack resistance when welding these structures. Conventional technology Until now, various studies have been conducted on coated arc welding rods used for welding 9%Cr-1~2%Mo steel, but when used at 600~650℃, the conventional 9%
Since the weld metal using a %Cr-1 to 2%Mo welding rod has low creep strength, the design stress must be kept low, which shortens the durability of the welded structure. Moreover, when welding steel plates with a thickness of 10 mm or more,
There were also problems with on-site construction, such as the cracking not stopping unless preheated to 175°C or higher. In order to solve these problems,
58995, C in the coating and/or core wire,
By limiting the amounts of Mn, Si, Cr, Mo, Al, N, and Ni added, and adding Al and N selectively,
We are working to improve the low temperature toughness and temper embrittlement of %Cr-1/2 to 1%Mo steel weld metal. Also, Tokukai Akira
Publication No. 58-86997 further attempts to improve high-temperature strength and welding workability by limiting the amount of metal carbonate, metal fluoride, and metal oxide in the coating material. No improvement in cracking resistance has been achieved. In addition, 9Cr−2Mo
For steel welded structures, C, Si, Mn, Cr, Mo,
Weld metals containing Ni, Al, N, Ti, O, Nb, and V are listed, but Ni, Al, N, Ti, O, Nb,
It does not attempt to significantly improve creep strength by actively adding V, and it merely indicates the metal composition to be included in the weld metal, and does not indicate the method and range of addition of each alloy element to the welding material. Not specified, but has excellent creep strength and cracking resistance 9
A coated arc welding rod for %Cr-1 to 2%Mo steel has not yet been provided. Furthermore, Japanese Patent Application Laid-Open No. 16792/1983 describes Nb and V.
It has been stated that ferrite layer and carburized layer are prevented from forming and thus are effective in improving creep strength. However, it has not yet been possible to provide a coated arc welding rod for 9% Cr-1 to 2% Mo steel with excellent properties. Problems to be Solved by the Invention The present invention provides a low-hydrogen coated arc welding rod that has high creep rupture strength and excellent cracking resistance of the weld metal when welding 9% Cr-1 to 2% Mo steel. It provides: (Means for Solving the Problems) The gist of the present invention is that V, Nb, Cr,
Mo or further Ni in weight% 0.02≦(V) in the core + (V) in the coating material x 0.28≦0.22 0.02≦(Nb in the core) + (Nb in the coating material) x 0.20≦
0.11 8.5 ≦ Core wire (Cr) + Coating material (Cr) × 0.35 ≦ 11 0.8 ≦ Core wire (Mo) + Coating material (Mo) × 0.35 ≦
2.5 0.05≦ Core wire (Ni) + Coating agent (Ni) + 0.35≦
Added in the range of 1.9, Mg0.8-4.5%, carbonate 10-70
%, a fluorine compound of 5 to 30%, and a coating material containing a deoxidizing agent, an arc stabilizer, and a binder other than those mentioned above, coated around the core wire. It is a welding rod. Note that the core wire used in the present invention includes Nb, V, Cr,
Chemical components other than Mo and Ni are C0.10% or less, Si0.3%
Below, Mn is 1.0% or less, P is 0.02% or less, S is 0.02% or less, Cu is 0.10% or less, and the balance is Fe and unavoidable impurities. The cause of the decrease in the creep strength of the weld metal during welding of 9%Cr-1~2%Mo steel is that the weld metal is heated to a high temperature, which causes the C and carbon in the weld metal to decrease.
Fe combines to precipitate Fe ₃ C, and by further heating for a long time, this carbide becomes M ₂₃ C ₆ , M ₆ C (M
refers to a metallic element), and the carbide becomes coarser. Therefore, as a result of many years of research, the present inventors have found that by co-adding appropriate amounts of V and Nb to the welding rod, fine V ₄ C ₃ and NbC are precipitated in the weld metal, and M ₂₃ C ₆ ,
We have discovered that creep rupture strength can be significantly increased by controlling the precipitation state of M ₆ C so that it does not become coarse over a long period of time. Furthermore, we have found that it is effective to add an appropriate amount of Mg to the coating material in order to improve the cracking resistance of the weld metal, which deteriorates as the strength increases. Since Mg is a strong deoxidizing element, when added to the coating material, it significantly reduces the amount of O in the weld metal, suppresses the formation of inclusions, improves the ductility of the weld metal, and prevents the oxidation of V and Nb. To prevent, V ₄ O ₃ ,
This is because it promotes the precipitation of NbC fine carbides and fixes C, thereby reducing the susceptibility to cracking caused by C. (Function) The present invention has been made based on this knowledge, and the function will be explained in detail below. One of the features of the present invention is that V and Nb are used in the welding rod.
V ₄ C 3 , V 4 C ₃ ,
The purpose is to precipitate fine carbides of NbC to significantly increase creep rupture strength at temperatures of 600 to 650°C. Table 1 shows 2.4% rutile, 42% lime carbonate, 14% fluorite, 5% barium carbonate, and Fe-Si (45% Si).
11%, metal Mn0.5%, Fe-Ti (45%Ti) 1.5%,
Metal Cr7.1%, Fe-Mo (61%Mo) 4.7%, Fe-V
(53%V) 0~1.6%, Fe-Nb (67%Nb) 0~1.0
%, binder 8.2%, and the remainder is iron powder.
C0.02~0.05%, Si0.01~0.03%, Mn0.43~0.52
%, Cr6.7~7.1%, Mo0.47~0.52%, V0.002~
0.232%, Nb0.003~0.126% diameter 4.0mm, length 400
20 types of welding rods were created by coating coated core wire with an outer diameter of 6.3 mm, drying and firing, and created 20 types of welding rods.
This shows the results of welding and creep testing in accordance with A5.4. In this case, the weld metal was prepared under the following conditions: preheating pass temperature 175℃, current 160A, and welding heat input 21kJ/cm, and after post-heat treatment at 750℃ for 50 minutes, a creep test piece was taken.
A creep test was conducted at ℃ to determine the breaking strength after 1000 hours.

[Table] As a result, as a coated arc welding rod, V and
It has been found that good creep rupture strength can be obtained by adding Nb at a certain ratio. In addition, the amount of V and Nb in the core wire coating material of the welding rod is
It was found that the relationship with creep rupture strength can be better understood by expressing it with equations (1) and (2). V amount (weight%) = core wire (V) + coating material (V) x 0.28
...(1) Amount of Nb (weight%) = Core wire (Nb) + Coating material (Nb) x 0.20 ...(2) In equations (1) and (2), V and Nb in the coating material are respectively The reason for multiplying by coefficients of 0.28 and 0.20 is that it was found that the respective contents in the core wire were equivalent. As is clear from Table 1, welding rods No. 1 and 3 in which the amount of V defined by formula (1) added to either the welding rod core wire or the coating material or both is less than 0.02%;
The creep rupture strength of Nos. 10, 11, and 23 is less than 10 Kgf/mm ² regardless of the amount of Nb added. Furthermore, the creep rupture strength of welding rods Nos. 1, 2, and 14 with an Nb content of less than 0.02% as determined by equation (2) is still less than 10 Kgf/mm ² regardless of the amount of V added. On the other hand, the amount of V in equation (1) is 0.02 to 0.22%, and the amount of Nb in equation (2) is
0.02~0.11% welding rod No. 4, 5, 6, 12, 13,
The creep rupture strength of 15, 16, 18, 19, 21 and 24 is 10 Kgf/mm ² or more due to the precipitation of fine carbides due to the synergistic effect of V and Nb, especially when the V amount is 0.12
%, welding rods No. 6, 13, 16, with Nb content around 0.07%,
18 had significantly higher creep rupture strength. However, welding rod No. 7 with V content exceeding 0.22%,
The creep rupture strength of welding rods No. 9, 17, 20, 22, 26 and welding rods No. 8, 9, 17, 25, and 26 with Nb content exceeding 0.11% is expected to be due to the precipitation of fine carbides due to the synergistic effect of V and Nb. It was not possible, and it was low at less than 10Kgf/mm ² . From the above results, the amount of V and Nb added to either or both of the core wire and coating material of the welding rod in weight% is 0.02≦(V) in the core wire + (V) in the coating material×0.28≦0.22 0.02≦ Core wire (Nb) + coating material (Nb) x 0.20≦
The range was set to 0.11. In other words, when adding only to the core wire, V is 0.02~
0.22%, Nb is 0.02-0.11%, and when added only to the coating material, V is 0.07-0.79% and Nb is 0.1-0.55%.
It is. When adding V and Nb to either or both of the core wire and the coating material, any ratio of V and Nb can be selected as long as it is within the above range. Next, the present invention adds Mg to the coating material, improves ductility by reducing the amount of O in the weld metal, and improves ductility by adding Mg to the coating material.
By fixing C by promoting the precipitation of fine Nb carbides, the cracking resistance of weld metal is greatly improved. Figure 1 shows V in the welding rod at 0.103% and Nb at 0.052%.
%, Cr 9.04%, Mo 1.12%, in the coating material.
9% Cr-1% with a rod diameter of 4 mm by changing the amount of Mg added
Prototype of 11 types of welding rods for Mo steel, 9% of plate thickness 20mm
Using Cr-1%Mo steel, the welding current was
This figure shows the results of a U-type welding agent cracking test conducted under the conditions of 160A and welding heat input of 17kJ/cm, and the preheating temperature at which cracking stops. As is clear from Figure 1, the cracking stop preheating temperature gradually decreases by adding Mg, and while the cracking stopping temperature of the welding rod without Mg is 200℃, the preheating temperature when Mg is added is 3%.
In the case of welding rods with a certain amount of additive, the temperature drops to 50℃.
If Mg is less than 0.8%, the effect of improving cracking resistance is not sufficient, and if it exceeds 4.5%, cracking resistance will not improve, and on the contrary, the arc during welding becomes unstable and spatter increases. However, welding workability becomes worse.
The Mg addition range was set to 0.8 to 4.5%. In addition, the Mg added to the coating material includes Mg alone,
It can also be added as an alloy such as Al-Mg or Ni-Mg. In this case, it has been confirmed that similar effects can be obtained if the amount of Mg in the alloy is within the above range. Next, in order to obtain a weld metal with sufficient creep rupture strength and oxidation resistance as a welding rod for 9%Cr-1~2%Mo steel, the amount of Cr in the welding rod can be calculated using equation (3). I found out. Cr amount (weight%) = Core wire (Cr) + Coating material (Cr)
×0.35 ……(3) Figure 2 shows that V in the welding rod is 0.136% and Nb is 0.086%.
%, Mo is 1.52%, and Mg in the coating is 2.8%.
This shows the results of investigating the relationship between creep rupture strength and crack arrest preheating temperature by varying the amount of Cr. As is clear from FIG. 2, if the Cr content in the welding rod according to equation (3) is less than 8.5%, the creep rupture strength of the weld metal is insufficient. On the other hand, when the Cr content is 8.5% or more, the creep rupture strength increases and reaches a maximum at about 10%, and when it exceeds that, the creep rupture strength decreases again. Furthermore, the cracking arrest temperature of the weld metal was 125°C or lower when the Cr content was up to 10.9%, but when it exceeded 11%, it rapidly rose to 175°C or higher. Therefore, the amount of Cr added to either or both of the core wire and coating material of the welding rod of the present invention was set to the following range in weight percent. 8.5≦(Cr in the core wire) + (Cr in the coating material)×0.35≦11 In other words, if Cr is added only to the core wire, it is 8.5
~11%, 24.3 to 31.4 when added to coating only
%, and when adding from both the core wire and the coating material, any ratio can be selected as long as it is within the above range. In addition, the amount of Mo in the welding rod to obtain a weld metal with sufficient creep strength and cracking resistance as a welding rod for 9%Cr-1~2%Mo steel can be summarized by equation (4). I found it. Amount of Mo (weight%) = Core wire (Mo) + Coating material (Mo) × 0.35...(4) Figure 3 shows V in the welding rod at 0.118% and Nb at 0.072.
%, Cr is 8.92%, and Mg in the coating is 3.2%, and the relationship between creep rupture strength and crack stop preheating temperature is investigated by varying the amount of Mo. As is clear from FIG. 3, when the amount of Mo in the welding rod according to equation (4) is less than 0.8%, the creep rupture strength of the weld metal is low. On the other hand, when Mo is added in an amount of 0.8% or more, the creep rupture strength gradually increases, but even if it is added in excess of 2.5%, the effect of improving the creep rupture strength relative to the amount added is small, and the cracking resistance of the weld metal is rather reduced. When the weld metal deteriorated to 2.68% or higher, the preheating temperature at which cracking of the weld metal stopped was 175℃ or higher. Therefore, the amount of Mo added to either or both of the core wire and the coating material of the welding rod of the present invention was set to the following range in weight percent. 0.8≦ Core wire (Mo) + Coating material (Mo) x 0.35≦
2.5 In other words, if Mo is added only to the core wire, 0.8
~2.5%, 2.3 to 7.1 when added to coating only
%, and when adding from both the core wire and the coating material, any ratio can be selected as long as it is within the above range. Next, the welding rod of the present invention contains CaCO ₃ and
Carbonates such as BaCO ₃ , MgCO ₃ , MnCO ₃ at 10-70%
%contains. These carbonates decompose in the arc, producing CO ₂ gas, exfoliating the molten metal from the atmosphere, lowering the gas partial pressure of hydrogen and nitrogen in the arc atmosphere, and producing basic slag. have an effect. If the amount added is less than 10%, the melting point of the slag decreases, the encapsulation properties of the slag deteriorate, and good beads cannot be obtained. In addition, the amount of gas generated to insulate the atmosphere is insufficient, causing pits and blowholes, and an increase in the amount of hydrogen in the weld metal.
Cracking resistance deteriorates. On the other hand, if it is added in excess of 70%, the amount of gas generated will be excessive, resulting in frequent pitting, the melting point of the slag will rise, the fluidity of the slag will deteriorate, and the compatibility with the welding base material will become uneven. Bead shape deteriorates. Therefore, the range of carbonate added to the coating material of the welding rod of the present invention is 10 to 70%.
shall be. In addition, CaF ₂ , BaF ₂ ,
Fluorine compounds such as MgF ₂ , MnF ₂ , and LiF all lower the melting point of slag and create slag with good fluidity. In addition, fluorine decomposed in the arc reacts with hydrogen in the molten metal and molten slag, lowering the hydrogen pressure in the weld metal and creating a weld metal with good crack resistance. If the amount of these additives is less than 5%, appropriate slag fluidity cannot be obtained, the bead shape is poor, pits are formed, and the amount of hydrogen in the weld metal increases, causing cracks. On the other hand, if it is added in excess of 30%, the slag will lack viscosity, resulting in poor bead shape, weakening of the sheath, and poor welding workability. Therefore, the range of the fluorine compound added to the coating material of the welding rod of the present invention is 5 to 30%. In the present invention, by further adding Ni to either the core wire or the coating material, or both,
We have discovered that by controlling the amount of martensite produced in the weld metal obtained by welding, it is possible to further increase creep strength while maintaining cracking resistance. It was also found that the relationship between the Ni content and creep rupture strength and cracking resistance can be better explained by expressing the Ni content in the welding rod using equation (5). Ni amount (weight%) = Core wire (Ni) + Coating material (Ni) x 0.35...(5) Figure 4 shows V in the welding rod at 0.066% and Nb at 0.048%.
%, Cr 9.18%, Mo 1.52%, and Mg in the coating material 2.2%, and the amount of Ni varied to investigate the relationship between creep rupture strength and crack stop preheating temperature. As is clear from this experimental result, according to equation (5),
When the Ni content is 0.05% or more, creep rupture strength gradually increases while cracking resistance is maintained. However, even if Ni was added in excess of 1.9%, the effect of increasing the creep rupture strength relative to the amount added was small, and the cracking resistance gradually deteriorated, and at 2.3%, the cracking stop temperature suddenly increased. This is thought to be due to the effect of a rapid increase in the amount of martensite in the weld metal, increasing cracking susceptibility. Further, when the Ni amount is less than 0.05%, almost no improvement in creep rupture strength due to Ni is observed. Therefore, the amount of Ni added to either or both of the core wire and coating material of the welding rod of the present invention was set to the following range in weight percent. 0.05≦ Core wire (Ni) + Coating material (Ni) × 0.35≦
1.9 In other words, when adding Ni only to the core wire,
0.05~1.9%, 0.15~ when added to coating only
5.4%; when adding from both the core wire and the coating material, any ratio can be selected as long as it is within the above range. Next, what is the deoxidizing agent to be included in the coating material?
Single metals such as Mn, Ti, Si, Zr, Al, Fe−
Si, Fe-Mn, Fe-Ti, Fe-Al, Fe-Si-Mn,
Iron alloys such as Fe−REM−Ca−Si and Fe−Ca−Si,
These refer to respective alloys such as Zr-Si.
The range of the deoxidizing agent added is not particularly limited, but a range of 7 to 25% is desirable in terms of deoxidation and welding workability. Furthermore, the arc stabilizer refers to iron powder, alkali components, rutile, etc., and the addition range is preferably 45% or less. Binder refers to binder components such as water glass _represented by sodium _{silicate and} potassium silicate. It is desirable to use water glasses with indicated molar ratios ranging from 1.5 to 3.5. The welding rod of the present invention is manufactured by applying the above-mentioned coating material around the core wire using a conventional welding rod coating method, and then firing the coated material at 300 to 550° C. to remove moisture. The weight of the coating material is 25-35% of the weight of the welding rod.
It is desirable to do so. EXAMPLES Next, the effects of the present invention will be explained in more detail using examples. Table 2 shows the core wire (4.0 mm diameter each) composition, coating material composition, and various test results of the welding rods of the present invention and welding rods used for comparison.

【table】

【table】

【table】

【table】

[Table] In Table 2, A1 to A14 are welding rods of the present invention, and B1 to B8 are comparative welding rods. Welding metal by these welding rods at 600℃, 1000hr
The creep rupture strength at 650℃ and 1000 hours for some welding rods was determined. In addition, we conducted a U-shaped weld cracking test (JIS Z3157) to investigate the cracking resistance of weld metal, and welding workability testing. The weld metal from which the creep rupture test pieces were taken was prepared based on AWS A5.4 with a welding current of 160 A and a welding heat input of 21 kJ/cm. In addition, the U-shaped weld cracking test (JIS Z 3157) was performed on 9% Cr-
Using 2% Mo steel, welding current 160A, welding heat input
The test was conducted under conditions of 17kJ/cm, temperature of 20℃, and relative humidity of 60%, and the preheating temperature required to stop cracking was determined. The creep rupture strength of the welding rod of the present invention at 600°C for 1000 hours is as follows: Welding rod B2 with V and Nb less than 0.02%, or V0.22% or more and Nb 0.11% or more;
Compared to B3, B5, B6, B7, and B8, welding rods A3, A5, A7, A8, A9, A10, which are significantly improved due to the precipitation effect of V ₄ C ₃ and NbC, and especially contain 0.07% or more of Ni,
A11, A14, 10Kg even at 650℃ and 1000hr
It exhibited high strength of f/mm ² or more. In addition, the crack stop preheating temperature in the U-shaped weld cracking test was determined by the welding rod without Mg added to the coating material.
B1, B2, B3, B5, and B7 all have a temperature of 175°C or higher, whereas all of the welding rods of the present invention containing Mg have a temperature of 125°C or lower, especially welding rods containing about 3% Mg. A2, A10, and A12 have dropped to 50℃. Furthermore, comparison bar B1 has a creep rupture strength of 10 kg.
f/mm ² or more, but since the carbonate content was small, the fluidity of the slag was poor, welding workability was poor, and the cracking stop temperature was high due to the insufficient amount of gas generated. In addition, B2 had a small amount of fluoride, and B3 had too much fluoride, so both had poor slag fluidity and a highly uneven bead shape, resulting in poor welding workability. Since B4 contained less carbonates and fluorides, the amount of gas generated was small, and pitting occurred, so the creep rupture test and U-shaped weld cracking test were discontinued. B5 had a high carbonate content and low fluoride content, so the fluidity of the slag was extremely poor, the slag did not cover the bead, and the bead shape was poor. B8 is
Because the amount of Mg added was too large, the arc became unstable, there were many spatters, and welding workability was poor. (Effects of the invention) As described above, the welding rod of the present invention has a 9% Cr-
Compared to a welding rod made of 1-2% Mo steel, the creep rupture strength at 600-650°C is significantly increased, and the cracking resistance of the weld metal is further improved. This is something that cannot be achieved with conventional 9%Cr-1~2%Mo steel welding rods, and it will greatly contribute to the development of various industries.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of Mg in the coating material and the preheating temperature to stop cracking. Figure 2 shows the inside of the welding rod.
FIG. 3 shows the relationship between the amount of Cr, the amount of Mo in the welding rod (FIG. 3), and the amount of Ni in the welding rod (FIG. 4), and the respective rupture strengths and crack stop temperatures.

Claims (1)

[Claims] 1 V, Nb, Cr and Mo are added to either or both of the core wire or the coating material in the ranges shown below (wt%), Mg is 0.8 to 4.5%, and carbonate is 10 to 10%.
70% fluorine compound, 5 to 30% fluorine compound, and a coating material containing a deoxidizing agent, an arc stabilizer, and a binder other than those mentioned above, is coated around the core wire. Arc melting stick. V: 0.02 ≦ core wire (V) + coating material (V) × 0.28 ≦ 0.22 Nb: 0.02 ≦ core wire (Nb) + coating material (Nb) ×
0.20≦0.11 Cr: 8.5≦core wire (Cr) + coating material (Cr)×0.35
≦11 Mo: 0.8≦ Core wire (Mo) + Coating material (Mo) ×
0.35≦2.5 2 V, Nb, Cr, Mo, and Ni are added to either or both of the core wire or coating material in the ranges shown below (wt%), Mg0.8 to 4.5%, and carbonate.
10-70% fluorine compound, 5-30% fluorine compound, and a coating material containing a deoxidizing agent, an arc stabilizer, and a binder other than those mentioned above, is coated around the core wire. coated arc welding rod. V: 0.02 ≦ core wire (V) + coating material (V) × 0.28 ≦ 0.22 Nb: 0.02 ≦ core wire (Nb) + coating material (Nb) ×
0.20≦0.11 Cr: 8.5≦core wire (Cr) + coating material (Cr)×0.35
≦11 Mo: 0.8≦ Core wire (Mo) + Coating material (Mo) ×
0.35≦2.5 Ni: 0.05≦core (Ni) + coating material (Ni)×
0.35≦1.9