JP7055765B2 - 9Cr-1Mo Shielded metal arc welding rod for steel welding - Google Patents

Description

The present invention is used for welding Cr-Mo steel, has good welding workability, and can obtain good strength and toughness even when the post-weld heat treatment (hereinafter referred to as PWHT) temperature is 750 ° C. or higher, and 500. The present invention relates to a coated arc welding rod for welding 9Cr-1Mo steel, which can obtain a welded metal having good high temperature strength at ℃ or higher.

Due to the long-term shutdown of nuclear power plants due to the Great East Japan Earthquake, power generation by thermal power generation boilers using fossil fuels such as coal, natural gas and oil has increased since 2011. Such a thermal power plant consists of a boiler that produces high-temperature steam from the heat generated by burning coal and a turbine that uses steam to turn a generator. The boiler part is a coal saver that preheats water, an evaporator called a water wall that produces steam, a superheater that overheats the evaporator, and a reheat that reheats the steam whose pressure has dropped in the furnace after turning the turbine. It consists of a vessel, a main steam pipe that collects high-temperature main steam and reheated steam and sends them to a turbine, and a high-temperature reheated steam pipe, and most of the structural members are steel pipes. As for the materials used for steel pipes, the main steam pipe and high-temperature reheated steam pipe, which are thick members with a large diameter at high temperature, have a problem of thermal fatigue due to track stop, so the coefficient of linear thermal expansion is relatively small and heat is generated. A high Cr ferrite heat-resistant steel containing 9 to 12 Cr mass%, which is advantageous against fatigue, is applied.

Further, since such thermal power generation emits a large amount of carbon dioxide, which is a greenhouse gas, along with the power generation, improvement in power generation efficiency is required. In particular, coal-fired power generation emits more carbon dioxide per unit power generation than other fossil fuels, and so far, power generation efficiency has been improved by increasing the temperature and pressure of steam conditions.

In order to increase the high temperature and pressure of steam conditions, it is necessary to increase the high temperature strength and corrosion resistance of the materials, and various materials have been developed. In recent years, it has been desired to operate under higher high temperature conditions for the purpose of improving the efficiency of these businesses, and the development of 9Cr-1Mo steel shielded metal arc welding material as a welding material that can obtain weld metal with better high temperature strength characteristics. Is underway.

9Cr-1Mo steel is a heat-resistant steel having excellent high-temperature strength characteristics among Cr-Mo steels. 9Cr-1Mo steel is widely used in a pressure vessel of a thermal power generation boiler, and a shielded metal arc welding rod used therein is disclosed in Patent Document 1. Patent Document 1 defines C, Si, Mn, Ni, Cr, Mo, Fe, Ti, V, Nb, Co, W and N in a low hydrogen-based shielded metal arc welding rod, and CO ₂ in the coating agent. A low hydrogen-based shielded metal arc welding rod capable of obtaining a weld metal having excellent bar burn resistance and paintability and excellent defect resistance by specifying a converted value, a metal fluoride, and SiO ₂ is disclosed. There is.

According to the low hydrogen-based shielded metal arc welding rod disclosed in Patent Document 1, a weld metal having excellent rod burn resistance and coating property and also excellent defect resistance can be obtained, but PWHT is performed at 750 ° C. The mechanical properties at the time are not clear, and in particular, in order to secure high-temperature strength and toughness, it is necessary to adjust the Cr equivalent as an austenite stabilizing element to suppress the formation of δ-ferrite.

Further, Patent Document 2 defines C, Si, Mn, V, Nb, Cr, Ni, Mo, W, Ta, Nb, V, N and Ta / Nb in the shielded metal arc welding rod, and Co. Disclosed is a shielded metal arc welding rod for high Cr ferrite heat resistant steel that can secure the high temperature characteristics of the weld metal part after PWHT at 740 ° C. × 4 hours by specifying 0.5Co + Mn + Ni ≦ 3.5. Has been done.

However, when welding 9Cr-1Mo steel, most of the structural members are steel pipes, and welding is required to have full-posture weldability. In the shielded metal arc welding rod for high Cr ferrite heat resistant steel described in Patent Document 2, since the Ca conversion value and the F conversion value are not appropriate, the bead shape tends to be convex during circumferential welding, and all attitude welding is performed. There is a problem with sex. Further, from the viewpoint of ensuring the toughness of the weld metal part, although the austenite stabilizing element that suppresses δ ferrite is specified, the addition of the deoxidizing element that promotes the deoxidizing reaction and improves the defect resistance is insufficient. There is a problem that welding defects such as blow holes are likely to occur in the weld metal.

On the other hand, Patent Document 3 defines C, Si, Mn, Ni, Cr, Mo, W, V, Nb, B, Al, Co and N in the shielded metal arc welding rod, and the Cr, C and Disclosed is a welding material for high Cr ferritic heat-resistant steel that suppresses δ ferritic steel by satisfying 14Cr-220C-7Co with Co of 100 or less, and can obtain a sound weld metal with excellent pressure resistance while maintaining high temperature strength. Has been done.

However, when a shielded metal arc welding rod is used as the welding material described in Patent Document 3, the amount of oxygen in the weld metal is higher than that in TIG welding, and there is a problem in toughness and the like. Further, there is a problem that the addition of deoxidizing elements such as Si and Mn is insufficient, and welding defects such as blow holes are likely to occur in the weld metal.

Japanese Unexamined Patent Publication No. 2016-120719 Japanese Unexamined Patent Publication No. 10-175091 Japanese Patent Laid-Open No. 2000-271785

The present invention has been devised to solve the above-mentioned problems, and has good welding workability in welding 9Cr-1Mo steel, and good strength and toughness even when the PWHT temperature is 750 ° C. or higher. It is an object of the present invention to provide a shielded metal arc welding rod for 9Cr-1Mo steel welding which can be obtained and can obtain a weld metal having good high temperature strength at 500 ° C. or higher.

The gist of the shielded metal arc welding rod for 9Cr-1Mo steel according to the present invention is that in the shielded metal arc welding rod for 9Cr-1Mo steel welding, 9% Cr steel is used as a core wire, and one or both of the core wire and the coating agent are totaled. Then, in the core wire mass ratio shown in the following formula, C: 0.05 to 0.15%, Si: 0.1 to 1.0%, Mn: 0.7 to 1.5%, Ni: 0.1. ~ 0.6%, Cr: 9.0 ~ 11.0%, Mo: 0.5 ~ 1.5%, Nb: 0.02 ~ 0.20%, Cu: 0.01 ~ 0.15%, The coating agent contains Al: 0.1 to 0.8%, V: 0.1 to 0.4%, Mg: 0.3 to 1.5%, N: 0.02 to 0.10%. Is the total weight of the Si oxide in terms of SiO ₂ : 3 to 10%, the total value of the Zr oxide in terms of ZrO ₂ : 3 to 8%, and the total of the Al oxide. Total of Al ₂ O ₃ conversion values: 0.01 to 0.50%, total of Ca CO ₃ , CaF ₂ , and Ca O conversion values: 15 to 40%, total of metal fluoride F conversion values: 6 to 17 %, MgO: 0.1 to 1.0%, total of Na conversion value and K conversion value of Na compound and K compound: 1 to 3%, and Ca conversion value of CaCO ₃ , CaF ₂ , and CaO. The D value calculated by the total of F conversion values of the metal fluoride is 2.0 to 3.0, and the balance is Fe of the core wire, the coating agent of the coating agent, Fe content from the iron alloy, and It is characterized by being composed of unavoidable impurities.
Core wire mass ratio = content% in core wire + content% in coating agent x coverage rate / 100 ... (Equation)
(However, the content in the core wire is mass% with respect to the total mass of the core wire, the content% in the coating agent is mass% with respect to the total mass of the coating agent, and the coverage is the entire coated arc welding rod for 9Cr-1Mo steel welding. (Mass% of the coating agent by mass)

According to the shielded metal arc welding rod for 9Cr-1Mo steel of the present invention, welding workability is good, good strength and toughness can be obtained even when PWHT is 750 ° C. or higher, and high temperature strength at 500 ° C. or higher is good. It is possible to obtain high-quality weld metal, such as obtaining a high-quality weld metal.

The present inventors have prototyped various shielded metal arc welding rods in order to solve the above-mentioned problems in the shielded metal arc welding rods used for welding 9Cr-1Mo steel, and manufactured welding test pieces. The welded specimen was subjected to PWHT at 760 ° C. for 2 hours, and then the strength, toughness and high temperature strength of the weld metal at 500 ° C. were investigated. As a result, by defining the contents of C, Si, Mn, Ni, Cr, Mo, Cu, Al, Mg and N in the shielded metal arc welding rod, the formation of δ ferrite is suppressed even when the PWHT is 750 ° C or higher. However, by using a single-phase structure of martensite, the weld metal performance after PWHT was good in both strength and toughness, but sufficient high-temperature strength at 500 ° C. could not be obtained.

Therefore, as a result of reexamining the chemical composition of the obtained weld metal, fine precipitation was performed as carbides and nitrides by adjusting Nb and V, which are ferrite stabilizing elements, and precipitation strengthening was sufficient even at 500 ° C. or higher. It was found that high temperature strength can be obtained. On the other hand, a new problem has been clarified that the amount of δ-ferrite produced increases and the toughness decreases depending on the amount of Nb added, which is a ferrite stabilizing element.

Therefore, by optimizing the ferrite stabilizing elements Cr and Mo, good weld metal strength and toughness can be obtained even when the PWHT is 750 ° C or higher, and the weld metal has good high-temperature strength at 500 ° C or higher. Was found to be obtained.

Regarding welding workability, arc stability and spatter generation amount are appropriate amounts of Si oxide, Zr oxide, metal fluoride, Na compound and K compound, and slag encapsulation is Al oxide and CaCO ₃ . , CaF ₂ , CaO, and CaO, it was found that the slag releasability can be improved by specifying the ratio of MgO and CaCO ₃ , CaF ₂ , CaO and the metal fluoride by adding an appropriate amount.

Hereinafter, the composition of each component of the shielded metal arc welding rod for 9Cr-1Mo steel of the present invention and the reason for limiting the numerical value of the component composition will be described. The content of each component composition is expressed in% by mass and is simply described as%.

First, the reason for limiting the numerical value of the core wire mass ratio shown in the following formula for the total of one or both of the 9% Cr steel core wire (hereinafter referred to as core wire) and the coating agent will be described.

Core wire mass ratio = content% in core wire + content% in coating agent x coverage rate / 100 ... (Equation)
(However, the content in the core wire is mass% with respect to the total mass of the core wire, the content% in the coating agent is mass% with respect to the total mass of the coating agent, and the coverage is the entire coated arc welding rod for 9Cr-1Mo steel welding. (Mass% of the coating agent by mass)

[C: 0.05 to 0.15% by mass ratio of core wire to coating material]
C is added from the core wire, the coating materials Fe-Si, Fe-Mn, Fe-Cr, etc., and affects the hardenability of the weld metal and the precipitation of carbides during PWHT, ensuring the high temperature strength of the weld metal. It is an essential element for this. If C is less than 0.05% in terms of core mass ratio, the precipitation of carbides becomes insufficient during PWHT, and the high-temperature strength of the weld metal after PWHT decreases. On the other hand, when C exceeds 0.15% by mass ratio of the core wire, the precipitation of carbide becomes excessive and the toughness of the weld metal is lowered. Therefore, C is set to 0.05 to 0.15% in terms of the mass ratio of the core wire to the core wire of the coating agent. It is desirable that C is 0.10% or less from the viewpoint of the balance between the strength and toughness of the weld metal.

[Si: 0.1-1.0% by mass ratio of core wire to coating material]
Si is added from core wire, metal Si, Fe—Si and the like, and has the effect of accelerating the deoxidation reaction and improving the defect resistance of the weld metal. If Si is less than 0.1% by mass ratio of the core wire, the effect cannot be sufficiently obtained, welding defects such as blow holes are likely to occur, and the defect resistance is lowered. On the other hand, when Si exceeds 1.0% in terms of core mass ratio, precipitation of the Laves phase is promoted and the toughness of the weld metal is lowered. Therefore, the mass ratio of the core wire to the core wire of the coating agent is 0.1 to 1.0% for Si.

[Mn: 0.7 to 1.5% by mass ratio of core wire to coating material]
Mn is added from a core wire, a metal Mn, Fe-Mn, etc., and is a deoxidizing element like Si, and has an effect of promoting a deoxidizing reaction and improving the defect resistance of the weld metal. If Mn is less than 0.7% in terms of core mass ratio, the effect cannot be sufficiently obtained, welding defects such as blow holes are likely to occur, and defect resistance is lowered. On the other hand, when Mn exceeds 1.5% in terms of core mass ratio, nitride is deposited and the toughness of the weld metal is lowered. Therefore, Mn is set to 0.7 to 1.5% in terms of the mass ratio of the core wire to the core wire of the coating agent.

[Ni: 0.1-0.6% by mass ratio of core wire to coating material]
Ni is added from core wire, metal Ni, Fe-Ni, etc., and has the effect of adjusting the Cr equivalent as an austenite stabilizing element, suppressing the formation of δ-ferrite, and improving the toughness of the weld metal. If Ni is less than 0.1% by mass ratio of the core wire, the effect cannot be sufficiently obtained and the toughness of the weld metal is lowered. On the other hand, when Ni exceeds 0.6% in the core mass ratio, the high temperature strength of the weld metal after PWHT decreases. Therefore, the mass ratio of the core wire to the core wire of the coating agent is 0.1 to 0.6% for Ni.

[Cr: 9.0 to 11.0% by mass ratio of core wire to coating material]
Cr is a ferrite stabilizing element added from core wire, metal Cr, Fe-Cr, etc., and has the effect of improving corrosion resistance and oxidation resistance at high temperatures as well as improving the high temperature strength of the weld metal after PWHT. .. If Cr is less than 9.0% by mass ratio of the core wire, the precipitation of carbonitride becomes insufficient, and the high temperature strength of the weld metal after PWHT decreases. On the other hand, when Cr exceeds 11.0% in terms of core mass ratio, precipitation of δ-ferrite and carbonitride is promoted, and the toughness of the weld metal is lowered. Therefore, Cr is set to 9.0 to 11.0% in terms of the mass ratio of the core wire to the core wire of the coating agent.

[Mo: 0.5-1.5% by mass ratio of core wire to coating material]
Mo is added from core wire, metal Mo, Fe-Mo, etc., is a ferrite stabilizing element, and has the effect of increasing the strength of the weld metal by strengthening the solid solution. If Mo is less than 0.5% in terms of core mass ratio, the effect cannot be sufficiently obtained and the strength of the weld metal is lowered. On the other hand, when Mo exceeds 1.5% in terms of core mass ratio, precipitation of δ ferrite is promoted and the toughness of the weld metal is lowered. Therefore, Mo is 0.5 to 1.5% in terms of the mass ratio of the core wire to the core wire of the coating agent.

[Nb: 0.02 to 0.20% by mass ratio of core wire to coating material]
Nb is added from a core wire, Fe-Nb, etc., is a ferrite stabilizing element, and has the effect of finely precipitating carbides or nitrides and improving the high temperature strength of the weld metal after PWHT by strengthening the precipitation. If Nb is less than 0.02% in terms of core mass ratio, precipitation of carbonitride is insufficient and the high temperature strength of the weld metal after PWHT decreases. On the other hand, when Nb exceeds 0.20% in terms of core mass ratio, the precipitation of carbonitride in the weld metal becomes excessive, and the toughness of the weld metal decreases. Therefore, Nb is set to 0.02 to 0.20% in terms of the mass ratio of the core wire to the core wire of the coating agent.

[Cu: 0.01-0.15% by mass ratio of core wire to coating material]
Cu is added from a core wire, a metal Cu, or the like, and is an austenite stabilizing element and has an effect of increasing the strength of the weld metal by strengthening the solid solution. If Cu is less than 0.01% by mass ratio of the core wire, the effect cannot be sufficiently obtained and the strength of the weld metal is lowered. On the other hand, when Cu exceeds 0.15% in terms of core mass ratio, precipitation of δ ferrite is promoted and the toughness of the weld metal is lowered. Therefore, Cu is set to 0.01 to 0.15%.

[Al: 0.1-0.8% by mass ratio of core wire to coating material]
Al is added from core wire, metal Al, Fe—Al and the like, and has an effect of accelerating the deoxidation reaction and improving the defect resistance of the weld metal. If Al is less than 0.1% by mass ratio of the core wire, the effect cannot be sufficiently obtained, welding defects such as blow holes are likely to occur, and the defect resistance is lowered. On the other hand, when Al exceeds 0.8% in terms of core mass ratio, the deoxidation reaction is promoted, the amount of slag increases, and the slag encapsulation property deteriorates. Therefore, Al is 0.1 to 0.8% in terms of the mass ratio of the core wire to the core wire of the coating agent.

[V: 0.1-0.4% by mass ratio of core wire to coating material]
V is added from a core wire, Fe-V, etc., and is a ferrite stabilizing element like Nb. It also has the effect of finely precipitating carbides or nitrides and improving the high temperature strength of the weld metal after PWHT by strengthening the precipitation. Has. If V is less than 0.1% by mass ratio of the core wire, the precipitation of carbonitride is insufficient, and the high temperature strength of the weld metal after PWHT decreases. On the other hand, when V exceeds 0.4% in terms of core mass ratio, the precipitation of carbonitride in the weld metal becomes excessive, and the toughness of the weld metal decreases. Therefore, V is set to 0.1 to 0.4% in terms of the mass ratio of the core wire to the core wire of the coating agent.

[Mg: 0.3-1.5% by mass ratio of core wire to coating material]
Mg is added from the core wire, metal Mg and the like, and has the effect of accelerating the deoxidation reaction and improving the defect resistance of the weld metal. If Mg is less than 0.3% by mass ratio of the core wire, the effect cannot be sufficiently obtained, welding defects such as blow holes are likely to occur, and the defect resistance is lowered. On the other hand, when Mg exceeds 1.5% in the core mass ratio, the protective cylinder melts non-uniformly, and the droplets grow large and migrate, so that the arc becomes unstable. Therefore, Mg is set to 0.3 to 1.5% in the core wire mass ratio of the core wire and the coating agent.

[N: 0.02 to 0.10% by mass ratio of core wire to coating material]
N is added from the core wire, Mn nitride, Cr nitride and the like, and has the effect of combining with Cr, Nb, V and the like to form a nitride in the weld metal and increasing the strength of the weld metal. If N is less than 0.02% in terms of core mass ratio, the formation of nitrides in the weld metal becomes insufficient, and the strength of the weld metal decreases. On the other hand, if N exceeds 0.10% in terms of core mass ratio, it does not dissolve in the weld metal and welding defects such as blow holes occur. Therefore, N is 0.02 to 0.10% in the mass ratio of the core wire to the core wire of the coating agent.

Next, the reason for limiting the numerical value of each component composition in the coating agent will be described and printed. The composition of each component in the following coating agents shall be expressed in% by mass with respect to the total mass of the coating agent, and when expressing the mass%, it shall be simply described as%.

[Total SiO ₂ conversion value of Si oxide in the coating agent: 3 to 10%]
Si oxide is added from potash feldspar, silica sand, synthetic mica, water glass, etc., and the purpose is to adjust the melting point of the coating agent to uniformly melt the protective cylinder, and to regulate the droplet transfer and stabilize the arc. Added. If the total SiO ₂ conversion value of the Si oxide is less than 3%, the protective cylinder melts unevenly and the arc becomes unstable. On the other hand, if the total SiO ₂ conversion value of the Si oxide exceeds 10%, the amount of slag becomes excessive and the slag encapsulation property deteriorates. Therefore, the total value of Si oxides in the coating material in terms of SiO ₂ is set to 3 to 10%.

[Total ZrO ₂ conversion value of Zr oxide in the coating agent: 3 to 8%]
Zr oxide is added from zircon sand, zircon flower, zirconium oxide, etc., and is added for the purpose of adjusting the melting point of the coating agent to uniformly melt the protective cylinder, regularizing the droplet transfer, and stabilizing the arc. .. If the total ZrO ₂ conversion value of the Zr oxide is less than 3%, the protective cylinder melts unevenly and the arc becomes unstable. On the other hand, when the total of the ZrO ₂ conversion values of the Zr oxide exceeds 8%, the fluidity of the slag deteriorates and the slag encapsulation property deteriorates. Therefore, the total ZrO ₂ conversion value of the Zr oxide in the coating material is 3 to 8%.

[Total Al ₂ O ₃ conversion value of Al oxide in the coating agent: 0.01 to 0.50%]
Al oxide is added from potassium feldspar, Al ₂ O ₃ and the like, and has the effect of adjusting the melting point and viscosity of the coating agent, improving the slag fluidity, and uniformly encapsulating the slag. If the total Al ₂ O ₃ conversion value of the Al oxide is less than 0.01%, the effect cannot be obtained and the slag encapsulation property deteriorates. On the other hand, when the total Al ₂ O ₃ conversion value of Al oxide exceeds 0.50%, the slag peeling property deteriorates. Therefore, the total Al ₂ O ₃ conversion value of Al oxide in the coating agent is 0.01 to 0.50%.

[Total Ca conversion values of CaCO ₃ , CaF ₂ , and CaO in the coating agent: 15-40%]
Like Al oxide, CaCO ₃ , CaF ₂ , and CaO have the effect of adjusting the melting point and viscosity of the coating agent, improving the slag fluidity, and uniformly encapsulating the slag. If the total Ca conversion value of CaCO ₃ , CaF ₂ , and CaO is less than 15%, the effect cannot be obtained and the slag encapsulation property deteriorates. On the other hand, when the total Ca conversion value of CaCO ₃ , CaF ₂ and CaO exceeds 40%, the amount of spatter generated increases. Therefore, the total Ca conversion value of CaCO ₃ , CaF ₂ , and CaO in the coating agent is 15 to 40%.

[Total F conversion value of metal fluoride in the coating agent: 6 to 17%]
Metal fluoride can be added from NaF, LiF, CaF ₂ , AlF ₃ , K ₂ ZrF ₆ , K ₂ SiF ₆ , BaF ₂ , etc., the melting point of the flux is adjusted, the protective cylinder is uniformly melted, and droplet transfer is performed. Has the effect of stabilizing and improving arc stability. If the total F conversion value of the metal fluoride is less than 6%, the effect cannot be obtained and the arc becomes unstable. On the other hand, when the total F conversion value of the metal fluoride exceeds 17%, the slag peelability deteriorates. Therefore, the F conversion value of the metal fluoride in the coating agent is set to 6 to 17%.

[MgO in coating agent: 0.1 to 1.0%]
MgO in the coating agent is added from magnesia clinker or the like and has an effect of improving slag peelability. If the MgO content is less than 0.1%, the effect cannot be obtained and the slag peelability is deteriorated. On the other hand, when MgO exceeds 1.0%, the droplet transfer becomes poor and the amount of spatter generated increases. Therefore, MgO in the coating agent is set to 0.1 to 1.0%.

[Total of Na conversion value and K conversion value of Na compound and K compound in the coating agent: 1 to 3%]
Na compound and K compound are added from potassium feldspar, NaF, K ₂ SiF ₆ , solid components of water glass, etc., and have the effect of finely growing droplets to adjust droplet migration and reduce the amount of spatter generated. Have. If the total of the Na-converted value and the K-converted value of the Na compound and the K compound is less than 1%, the effect cannot be obtained and the amount of spatter generated increases. On the other hand, when the total of the Na-converted value and the K-converted value of the Na compound and the K compound exceeds 3%, the melting point of the protective cylinder becomes low, the melting point becomes uneven, and the arc becomes unstable. Therefore, the total of the Na-converted value and the K-converted value of the Na compound and the K compound in the coating agent is 1 to 3%.

[D value = total of Ca CO ₃ , CaF ₂ , and Ca O converted values in the coating agent / total F converted values of metal fluoride: 2.0 to 3.0]
The D value is a value obtained by dividing the Ca conversion values of CaCO ₃ , CaF ₂ , and CaO in the coating material by the sum of the F conversion values of the metal fluoride, and the slag melting point and the amount of slag produced are adjusted to form the weld. It adjusts the melting point of metal and slag and is an index showing slag peelability. If the D value is less than 2.0, the effect cannot be obtained and the slag peelability deteriorates. On the other hand, if the D value exceeds 3.0, the arc becomes unstable. Therefore, the D value is set to 2.0 to 3.0.

The reason for limiting the numerical values of the constituent requirements of the shielded metal arc welding rod for 9Cr-1Mo steel of the present invention has been described above. Others are Fe of the core wire, Fe content of iron alloys such as Fe—Mn, Fe—Si, Fe—Al, Fe—Cr, and Fe—Ni of the coating agent, and unavoidable impurities. The unavoidable impurities P and S are preferably as low as possible from the viewpoint of toughness and crack resistance of the weld metal.

The method for manufacturing the shielded metal arc welding rod is not particularly limited, but a coating agent mixed and mixed with the core wire is prepared, and wet mixing is performed while adding water glass to the coating agent, and the coating agent is applied around the core wire. It is preferable to produce the product by drying and firing at 150 to 450 ° C. for 1 to 3 hours after coating.

Hereinafter, the effects of the present invention will be described in more detail by way of examples.

Various 9Cr-1Mo steels made by using a core wire made of 9% Cr steel having a diameter of 3.2 mm and a length of 350 mm shown in Table 1 and coated with a coating agent having various component compositions shown in Table 2 and dried. We made a prototype of a shielded metal arc welding rod for welding.

Welded metal performance, defect resistance, and welding workability were investigated using various prototype 9Cr-1Mo steel welding coated arc welding rods. In each survey, 9Cr-1Mo steel conforming to ASME SA387 Grade91 shown in Table 3 was applied as a base material.

To evaluate the performance of the weld metal, use the above steel plate with a thickness of 20 mm, perform a weld metal test at a welding current of 140 A according to AWS A5.5, perform PWHT at 760 ° C. for 2 hours, and then perform a tensile test piece from the weld metal part. , High temperature tensile test pieces and impact test pieces were collected and subjected to tensile test at room temperature, tensile test at high temperature and impact test.

In the evaluation of the tensile test at room temperature, the tensile strength at room temperature was 620 MPa or more. In the evaluation of the tensile test at a high temperature, the tensile strength at a test temperature of 500 ° C. was good at 350 MPa or more. For the evaluation of toughness, a Charpy impact test was carried out at a test temperature of 0 ° C., and the average value of absorbed energy three times each was set to be good at 15 J or more.

For the evaluation of defect resistance, a welded joint was manufactured using the above steel plate with a welding current of 140 A, an X-ray transmission test was carried out according to JIS Z 3106, and the grade 1 was judged to be good.

To evaluate the welding workability, perform horizontal fillet welding using the above steel plate under welding conditions of welding current 140A and welding speed 10cm / min, and visually check the arc stability, spatter generation amount, slag encapsulation property and slag peeling property. I investigated in. The results are summarized in Table 4.

The welding rod symbols 1 to 20 in Table 4 are examples of the present invention, and the welding rod symbols 21 to 40 are comparative examples. The welding rod symbols 1 to 20 which are examples of the present invention are the core wire mass ratios of the core wire made of 9% Cr steel and the core wire of the coating agent, and are C, Si, Mn, Ni, Cr, Mo, Nb, Cu, Al, V. , Mg and N are appropriate, total SiO ₂ conversion value of Si oxide in the coating, total ZrO ₂ conversion value of Zr oxide, total Al ₂ O ₃ conversion value of Al oxide, CaCO ₃ , CaF ₂ , the total Ca conversion value of CaO, the total F conversion value of the metal fluoride, the total Na conversion value and the total K conversion value of MgO, Na compound and K compound, and the D value are all contained as specified in the present invention. Since the amount was within the range, the tensile strength and absorption energy of the weld metal at room temperature were good, the tensile strength at high temperature was also good, and the result of the X-ray transmission test was also good. Further, regarding the welding workability, the arc stability was good, the amount of spatter generated was small, and both the slag encapsulation property and the slag peeling property were good, and the results were extremely satisfactory.

Since the welding rod symbol 21 has a small core wire mass ratio C, the tensile strength of the weld metal at a high temperature is low. In addition, since the core wire mass ratio of Al is small, blow holes are generated and the defect resistance is lowered. Since the welding rod symbol 22 has a large core wire mass ratio C, the absorption energy of the weld metal is low. In addition, since the core wire mass ratio of Al is large, the slag encapsulation property is poor.

Since the welding rod symbol 23 has a small amount of Si in the core mass ratio, blow holes are generated and the defect resistance is lowered. In addition, since the total value of Si oxides in the coating material in terms of SiO ₂ was small, the arc stability was unstable.

Since the welding rod symbol 24 has a large amount of Si in the core mass ratio, the absorption energy of the weld metal is low. In addition, since the total value of Si oxides in the coating material in terms of SiO ₂ is large, the slag encapsulation property is poor.

Since the welding rod symbol 25 has a small Mn of the core wire mass ratio, blow holes are generated and the defect resistance is lowered. In addition, since the total Al ₂ O ₃ conversion value of Al oxide in the coating agent was small, the slag encapsulation property was poor.

Since the welding rod symbol 26 has a large amount of Mn in the core mass ratio, the absorption energy of the weld metal is low. In addition, since the total Al ₂ O ₃ conversion value of the Al oxide in the coating agent was large, the slag peelability was poor.

Since the welding rod symbol 27 has a small amount of Ni in the core mass ratio, the absorption energy of the weld metal is low. Moreover, since the D value was low, the slag peelability was poor.

Since the welding rod symbol 28 has a large amount of Ni in the core mass ratio, the tensile strength of the weld metal at a high temperature was low. Moreover, since the D value was high, the arc stability was unstable.

Since the welding rod symbol 29 has a small amount of Cr in the core mass ratio, the tensile strength of the weld metal at a high temperature is low. Further, since the core wire mass ratio N was small, the tensile strength of the weld metal at room temperature was low.

Since the welding rod symbol 30 has a large amount of Cr in the core mass ratio, the absorption energy of the weld metal is low. Further, since the core wire mass ratio N is large, blow holes are generated and the defect resistance is lowered.

Since the welding rod symbol 31 has a small amount of Mo in the core mass ratio, the tensile strength of the weld metal at room temperature was low. Moreover, since the total F conversion value of the metal fluoride in the coating material was small, the arc stability was unstable.

Since the welding rod symbol 32 has a large amount of Mo in the core mass ratio, the absorption energy of the weld metal is low. In addition, since the total F-converted value of the metal fluoride in the coating agent was large, the slag peelability was poor.

Since the welding rod symbol 33 has a small core wire mass ratio Nb, the tensile strength of the weld metal at a high temperature is low. Further, since the total of the Na-converted value and the K-converted value of the Na compound and the K compound in the coating agent was small, the amount of spatter generated was large.

Since the welding rod symbol 34 has a large Nb of the core wire mass ratio, the absorption energy of the weld metal is low. Further, since the total of the Na-converted value and the K-converted value of the Na compound and the K compound in the coating agent was large, the arc stability was unstable.

Since the welding rod symbol 35 has a small amount of Cu in the core mass ratio, the tensile strength of the weld metal at room temperature was low. In addition, since the total Ca conversion values of CaCO ₃ , CaF ₂ , and CaO in the coating agent were small, the slag encapsulation property was poor.

Since the welding rod symbol 36 has a large amount of Cu in the core mass ratio, the absorption energy of the weld metal is low. In addition, since the total Ca conversion values of CaCO ₃ , CaF ₂ , and CaO in the coating agent were large, the amount of spatter generated was large.

The arc stability of the welding rod symbol 37 was unstable because the total ZrO ₂ conversion value of the Zr oxide in the coating material was small. Further, since the amount of MgO in the coating agent was small, the slag peelability was poor.

The welding rod symbol 38 had a poor slag encapsulation property because the total ZrO ₂ conversion value of the Zr oxide in the coating material was large. Further, since the amount of MgO in the coating material was large, the amount of spatter generated was large.

Since the welding rod symbol 39 has a small V of the core wire mass ratio, the tensile strength of the weld metal at a high temperature is low. In addition, since the amount of Mg in the core mass ratio was small, blowholes were generated and the defect resistance was lowered.

Since the welding rod symbol 40 has a large V of the core wire mass ratio, the absorption energy of the weld metal is low. In addition, the arc stability was unstable due to the large amount of Mg in the core mass ratio.

Claims (1)

In a 9Cr-1Mo steel welding coated arc welding rod, 9% Cr steel is used as the core wire, and the total of one or both of the core wire and the coating agent is the core wire mass ratio shown in the following formula.
C: 0.05 to 0.15%,
Si: 0.1-1.0%,
Mn: 0.7-1.5%,
Ni: 0.1-0.6%,
Cr: 9.0 to 11.0%,
Mo: 0.5-1.5%,
Nb: 0.02 to 0.20%,
Cu: 0.01-0.15%,
Al: 0.1-0.8%,
V: 0.1-0.4%,
Mg: 0.3-1.5%,
N: Containing 0.02 to 0.10%,
The coating agent is in mass% with respect to the total mass of the coating agent.
Total SiO ₂ conversion value of Si oxide: 3-10%,
Total ZrO ₂ conversion value of Zr oxide: 3-8%,
Total Al ₂ O ₃ conversion value of Al oxide: 0.01-0.50%,
Total Ca conversion values of CaCO ₃ , CaF ₂ , and CaO: 15-40%,
Total F conversion value of metal fluoride: 6-17%,
MgO: 0.1-1.0%,
The total of Na conversion value and K conversion value of Na compound and K compound: 1 to 3% is contained.
Moreover, the D value calculated by the total of the Ca conversion values of CaCO ₃ , CaF ₂ , and CaO / the total of the F conversion values of the metal fluoride is 2.0 to 3.0, and the balance is Fe of the core wire. A shielded metal arc welding rod for 9Cr-1Mo steel welding, which comprises a coating agent as a coating agent, Fe content from an iron alloy, and unavoidable impurities.
Core wire mass ratio = content% in core wire + content% in coating agent x coverage rate / 100 ... (Equation)
(However, the content in the core wire is mass% with respect to the total mass of the core wire, the content% in the coating agent is mass% with respect to the total mass of the coating agent, and the coverage is the entire coated arc welding rod for 9Cr-1Mo steel welding. (Mass% of the coating agent by mass)