JP6914182B2 - Shielded metal arc welding rod - Google Patents

Description

The present invention relates to a shielded metal arc welding rod, and more particularly to a shielded metal arc welding rod preferably used for welding 13Cr martensitic stainless steel used for structures such as line pipes.

One of the materials for line pipes used for transporting petroleum and natural gas is 13Cr martensitic steel sheet. The 13Cr martensitic steel sheet has poor weldability as compared with the Cr—Ni steel sheet. Therefore, as a shielded metal arc welding rod used for welding 13Cr martensitic steel sheets, a welding rod to which Nb, Ti, Al, etc. have been added as elements that suppress the precipitation of martensite and contribute to grain refinement has been developed. It is being advanced.
For example, in Patent Document 1, in a Cr-containing arc welding rod containing Nb, Ti, and Al, Ni and V are contained in one or both of the core wire and the coating agent in appropriate amounts, and Ni and V are contained in the molten metal. By adding a small amount, the high temperature strength of 200 to 400 ° C. is enhanced.

In addition, the 13Cr martensitic steel sheet has been improved, and the development of a material having high corrosion resistance, high strength, and high toughness as a steel sheet, and also having good stress corrosion cracking resistance due to low hardness has been promoted. ing. In Patent Document 2, for the steel sheet, by adopting a specific chemical composition in the welding rod, a welded joint having high corrosion resistance, high strength and high toughness, low hardness and improved stress corrosion cracking sensitivity is formed. A 13Cr-based stainless steel welding rod that can be made is disclosed.

Japanese Unexamined Patent Publication No. 05-111790 Japanese Unexamined Patent Publication No. 08-1038887

However, when welding a 13Cr martensitic steel sheet using a shielded metal arc welding rod, not only mechanical properties such as tensile strength and toughness but also good welding workability are important as the performance required for the welding rod. .. Further, while Nb, Ti and Al contribute to the refinement of crystal grains, when they are added to the welding rod, the cost increases.

In view of the above circumstances, the present invention is excellent in weldability it is possible to obtain an excellent weld metal machine械的characteristics, further an object to provide a covered electrode obtained at low cost ..
More specifically, in the present invention, it is a shielded metal arc welding rod preferably used in shielded metal arc welding of a 13Cr martensite-based steel plate, and has various mechanical properties such as 0.2% strength, tensile strength, elongation and toughness. the it is possible to obtain an excellent weld metal, spatter, superior in weldability such bead appearance and slag removability, Nb, Ti and Al essentially the coating obtained at a low cost arc welding without the The purpose is to provide a stick.

The present inventors have result of extensive research, Nb, without substantially free of Ti and Al, by a chemical composition constituting the welding rod and specific ones, the weld metal having excellent opportunity械的characteristics We have found that excellent welding workability can be obtained as well as the above, and have completed the present invention.

That is, the shielded metal arc welding rod of the present invention is a shielded metal arc welding rod containing a core wire and a coating agent, and at least a part of the core wire is covered with the coating agent, with respect to the total mass of the welding rod. , C: 0.01 to 0.13% by mass, Si: 0.1 to 1.1% by mass, Mn: 0.1 to 1.2% by mass, Ni: 0.01 to 0.8% by mass, Mo : 0.01 to 0.8% by mass and Cr: 9.0 to 11.4% by mass, substantially free of Nb, Ti and Al, and the content of each component is (Cr + Mo + 1.5) × Si) / (Ni + 30 × C + 0.5 × Mn) ≦ 6.5
Satisfy the relational expression of.

_{In one aspect, in the shielded metal arc welding rod, the coating agent contains TiO 2} : 5.0 to 40.0% by mass, SiO ₂ : 5.0 to 20.0% by mass, and carbonate with respect to the total mass of the coating agent. It may contain salt: 19.0 to 46.0% by mass and CaF ₂ : 5.0 to 20.0% by mass, and the coverage of the entire welding rod by the coating agent may be 20 to 40% by mass. ..

Further, in one embodiment, the shielded metal arc welding rod may further contain Cu: 0.001 to 0.3% by mass with respect to the total mass of the welding rod.

According to the shielded metal arc welding rod according to the present invention, in the shielded metal arc welding of a 13Cr martensite-based steel plate, welding workability such as spatter generation amount, bead appearance and slag peeling property is excellent, and further, 0.2% proof stress and tensile strength are obtained. Welded metal excellent in various mechanical properties such as elongation and proof stress can be obtained at no cost.

FIG. 1 is a schematic view for showing the structure of a welded metal test piece used for evaluating the welding workability and mechanical properties of the obtained shielded metal arc welding rod.

Hereinafter, embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the embodiments described below. Further, in the present specification, "~" indicating a numerical range is used to mean that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.

The shielded metal arc welding rod (hereinafter, may be simply referred to as “welding rod”) according to the present embodiment includes a core wire and a coating agent, and at least a part of the core wire is covered with the coating agent. , C: 0.01 to 0.13% by mass, Si: 0.1 to 1.1% by mass, Mn: 0.1 to 1.2% by mass, Ni: 0.01 with respect to the total mass of the welding rod. Contains ~ 0.8% by mass, Mo: 0.01 to 0.8% by mass, and Cr: 9.0 to 11.4% by mass, substantially free of Nb, Ti, and Al, and each component. Content satisfies the following relational expression.
(Cr + Mo + 1.5 × Si) / (Ni + 30 × C + 0.5 × Mn) ≦ 6.5

Hereinafter, the content of each component of the shielded metal arc welding rod according to the present embodiment with respect to the total mass of the welding rod will be described. In the present specification, the total mass of the welding rod means the total mass of the core wire constituting the welding rod and the mass of the coating agent.

<C: 0.01 to 0.13% by mass>
C is an element that improves the tensile strength of the weld metal. Therefore, the C content with respect to the total mass of the welding rod is 0.01% by mass or more, preferably 0.03% by mass or more, and more preferably 0.04% by mass or more.
On the other hand, if C is excessively contained, the tensile strength becomes too high, which causes deterioration of toughness and low temperature cracking in welding. Therefore, the C content is 0.13% by mass or less, preferably 0.11% by mass or less, and more preferably 0.09% by mass or less.

<Si: 0.1 to 1.1% by mass>
Si is an element that improves deoxidation and fluidity of the molten pool during welding. Therefore, the Si content with respect to the total mass of the welding rod is 0.1% by mass or more, preferably 0.3% by mass or more, and more preferably 0.4% by mass or more.
On the other hand, the addition of Si increases the δ-ferrite phase and deteriorates the toughness. Therefore, the Si content is 1.1% by mass or less, preferably 1.0% by mass or less, and more preferably 0.9% by mass or less.

<Mn: 0.1 to 1.2% by mass>
Mn has the effect of deoxidizing and desulfurizing during welding, and has the effect of suppressing blowholes (BH) due to oxygen-based gas. Further, Mn is also an element that forms an austenite phase, stabilizes the austenite structure, and suppresses a decrease in the toughness of the weld metal. Therefore, the Mn content with respect to the total mass of the welding rod is 0.1% by mass or more, preferably 0.3% by mass or more, and more preferably 0.5% by mass or more.
On the other hand, if Mn is excessively contained, the tensile strength decreases as the δ-ferrite phase decreases. Therefore, the Mn content is 1.2% by mass or less, preferably 1.0% by mass or less, and more preferably 0.9% by mass or less.

<Ni: 0.01 to 0.8% by mass>
Ni is an element that is effective for improving corrosion resistance and stabilizes the austenite phase to prevent the formation of the δ-ferrite phase. Therefore, the Ni content with respect to the entire welding rod is 0.01% by mass or more, preferably 0.05% by mass or more, and more preferably 0.07% by mass or more.
On the other hand, if Ni is excessively contained, the tensile strength decreases as the δ-ferrite phase decreases. Therefore, the Ni content is 0.8% by mass or less, preferably 0.7% by mass or less, and more preferably 0.5% by mass or less.

<Mo: 0.01 to 0.8% by mass>
Mo is effective for improving corrosion resistance. Therefore, the Mo content with respect to the entire welding rod is 0.01% by mass or more, preferably 0.03% by mass or more, and more preferably 0.04% by mass or more.
On the other hand, since Mo is also a strong element forming a ferrite phase, if the content of Mo is too large, the amount of δ-ferrite phase present in the weld metal increases, and the toughness decreases. Therefore, the Mo content is 0.8% by mass or less, preferably 0.6% by mass or less, and more preferably 0.5% by mass or less.

<Cr: 9.0 to 11.4% by mass>
Cr is a basic element for obtaining corrosion resistance as stainless steel. Therefore, the Cr content with respect to the entire welding rod is 9.0% by mass or more, preferably 9.2% by mass or more, and more preferably 9.4% by mass or more.
On the other hand, since Cr is also a strong element forming a ferrite phase, if the content of Cr is too large, the amount of δ-ferrite phase present in the weld metal increases, and the toughness decreases. Therefore, the Cr content is 11.4% by mass or less, preferably 11.1% by mass or less, and more preferably 11.0% by mass or less.

<Nb, Ti and Al>
Nb, Ti and Al are all elements that contribute to the refinement of crystal grains and can improve toughness. However, in order to obtain the above-mentioned effects of Nb, Ti and Al, it is necessary to add a certain amount or more, which causes an increase in cost. Therefore, the welding rod according to the present embodiment does not substantially contain Nb, Ti and Al. In the present specification, "substantially free" means that the raw material is not positively added, and is not excluded when mixed as an unavoidable impurity of other raw materials.
Specifically, the total content (Nb + Ti + Al) of Nb, Ti and Al with respect to the entire welding rod is preferably 0.05% by mass or less.

<Cu>
If Cu is excessively contained, the tensile strength decreases as the δ-ferrite phase decreases. Further, Cu is an expensive component among metals and causes an increase in cost. Therefore, Cu is not an essential component of the welding rod and does not have to be positively added as a raw material.
On the other hand, Cu is an element that is effective for improving corrosion resistance and stabilizes the austenite phase to prevent the formation of the δ-ferrite phase. When Cu is contained, the Cu content with respect to the entire welding rod is preferably 0.001% by mass or more, more preferably 0.01% by mass or more. Further, 0.3% by mass or less is preferable, and 0.2% by mass or less is more preferable.

<P, S and N>
P, S and N are not essential constituents of the welding rod and do not have to be positively added as raw materials. On the other hand, since N is an element that affects the decrease in toughness and P and S are elements that affect weld cracking, it is desirable that their contents be limited. The P content with respect to the entire welding rod is preferably 0.030% by mass or less, more preferably 0.020% by mass or less. The S content is preferably 0.020% by mass or less, more preferably 0.010% by mass or less. The N content is preferably 0.10% by mass or less, more preferably 0.05% by mass or less.

Among the above components, C, Si, Mn, Ni, Mo and Cr have good mechanical properties when their contents satisfy the following relational expression.
(Cr + Mo + 1.5 × Si) / (Ni + 30 × C + 0.5 × Mn) ≦ 6.5
The element symbol in the formula means the content (mass%) of each component with respect to the total mass of the welding rod.
In the relational expression, (Cr + Mo + 1.5 × Si) means the Cr equivalent in the Chefler structure diagram, and (Ni + 30 × C + 0.5 × Mn) means the Ni equivalent in the Chefler structure diagram. That is, good mechanical properties can be obtained when the value represented by (Cr equivalent / Ni equivalent) is 6.5 or less.
The value of (Cr equivalent / Ni equivalent) represented by the above relational expression is preferably 6.0 or less, more preferably 5.0 or less.
The Cr equivalent in the structure diagram of Scheffler is generally represented by (Cr + Mo + 1.5 × Si + 0.5 × Nb), but since Nb is not substantially contained in the present embodiment, the Cr equivalent is (Cr + Mo + 1). It is represented by .5 × Si).

The coating agent in the shielded metal arc welding rod according to the present embodiment will be described below.
In the shielded metal arc welding rod according to the present embodiment, at least a part of the core wire serving as the core material is covered with a coating agent. The coverage (%) of the entire welding rod with the coating agent can be calculated by the following formula.
(Mass of dressing / Mass of the entire shielded metal arc welding rod) x 100 (%)

From the viewpoint of lowering the toughness and crack resistance of the weld metal due to insufficient shield, the coverage is preferably 20% by mass or more, more preferably 24% by mass or more. Further, in order to maintain arc stability and maintain a good bead shape, the coverage is preferably 40% by mass or less, more preferably 36% by mass or less.

The material of the outer skin used as the coating agent in the present embodiment can be used without particular limitation such as steel type. Above all, the preferable content of each component in the coating agent with respect to the total mass of the coating agent will be described below.
<TiO ₂ : 5.0 to 40.0% by mass>
TiO ₂ is a component that facilitates arc start and improves arc stability during welding. Furthermore, TiO ₂ is the main component of the slag forming agent, and has the effect of raising the melting point of the slag and adjusting the bead shape. _{Therefore, the TiO 2} content with respect to the total mass of the coating agent is preferably 5.0% by mass or more, more preferably 5.5% by mass or more, and further preferably 6.0% by mass or more.
On the other hand, _{if the content of TiO 2} is too large, a stable bead appearance may not be obtained. Therefore, the _{content of TiO 2} is preferably 40.0% by mass or less, more preferably 39.0% by mass or less, and 38. More preferably, it is 0.0% by mass or less.

<SiO ₂ : 5.0 to 20.0% by mass>
SiO ₂ is a component that acts as a slag forming agent and adjusts the shape of the bead. _{Therefore, the SiO 2} content with respect to the total mass of the coating agent is preferably 5.0% by mass or more, more preferably 7.0% by mass or more, and further preferably 8.0% by mass or more.
On the other hand, _{if the content of SiO 2} is too large, the appearance of the bead may be impaired. Therefore, the _{content of SiO 2} is preferably 20.0% by mass or less, more preferably 18.0% by mass or less, and 17.0% by mass. The following is more preferable.

<Carbonate: 19.0-46.0% by mass>
Carbonate is _{a component that protects the weld metal by generating CO 2} gas during welding, blocking the mixing of atmospheric components into the weld metal, and at the same time forming basic slag. Therefore, the content of carbonate with respect to the total mass of the coating agent is preferably 19.0% by mass or more.
On the other hand, if the carbonate content is too high, spatter may occur. Therefore, the carbonate content is preferably 46.0% by mass or less, more preferably 45.0% by mass or less, and 44.0% by mass. % Or less is more preferable.
The _carbonate, CaCO _3, BaCO 3, but MgCO ₃ or the like of the metal carbonate salts, they may comprise two or more include only one kind.

<CaF ₂ : 5.0 to 20.0% by mass>
Since CaF ₂ is a component that lowers the melting point and viscosity of slag and forms slag with good fluidity, it is possible to form a bead with a very good appearance. It is also a component that improves slag peelability. _{Therefore, the content of CaF 2} with respect to the total mass of the coating agent is preferably 5.0% by mass or more, more preferably 6.0% by mass or more, and further preferably 7.0% by mass or more.
On the other hand, if the CaF ₂ content is too large, sputtering may occur. Therefore, the CaF ₂ content is preferably 20.0% by mass or less, more preferably 19.0% by mass or less, and 18.0% by mass. The following is more preferable.

<Remaining part of shielded metal arc welding rod>
The rest of the shielded metal arc welding rod according to the present embodiment is not particularly limited as long as it has a component and content that does not interfere with the effects of the present invention. The component may be contained in either the core wire or the coating agent constituting the welding rod, or may be contained in both the core wire and the coating agent.
Examples of the remaining components include Fe, other metal components (including metalloid components) constituting the entire shielded metal arc welding rod, other oxides and fluorides, and unavoidable impurities. The unavoidable impurities are components that are unavoidably contained with the addition of other components without being positively added as a raw material.

As an example of the remaining portion, Fe constituting the entire shielded metal arc welding rod is preferably contained in an amount of 70 to 95% by mass with respect to the total mass of the welding rod.
Examples of other metal components include W, V, Zr, Bi, Sn, Sb, Pb, Mg, alkali metal, alkaline earth metal, B, Co, As and the like. These may be positively added as a raw material or may not be substantially contained (including the case where they are contained as an unavoidable component).
Other oxides / fluorides include Al ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, MgO, BaO, SnO, ZrO ₂ , Nb ₂ O ₅ , LiF, NaF, BaF ₂ , MgF ₂ , Examples thereof include _{SrF 2} and AlF _3. These components may also be positively added as raw materials or may not be substantially contained (including cases where they are contained as unavoidable components).

The method for manufacturing the shielded metal arc welding rod according to the present embodiment is not particularly limited, and it may be manufactured by a general manufacturing process. The coating agent can be coated on the core wire, for example, by applying a muddy coating agent, which is a mixture of powdery metal powder or the like and water glass, to the surface of the core wire, drying and solidifying.
The amount of water glass added (before drying) to the total mass of the coating agent (including water glass) is preferably 10% by mass or more, more preferably 13% by mass or more from the viewpoint of workability. Similarly, from the viewpoint of workability, 25% by mass or less is preferable, and 20% by mass or less is more preferable.

The shielded metal arc welding rod according to this embodiment is preferably used in shielded metal arc welding of a 13Cr martensitic steel sheet.
The mechanical properties of the welded product welded using the shielded metal arc welding rod according to the present embodiment are evaluated by a tensile test and a Charpy impact test. Further, good welding workability at the time of welding means that the amount of spatter generated is small, the bead shape (waves of the bead) is beautiful and smooth, and slag peeling is easy.

<Mechanical properties: Tensile test>
To evaluate 0.2% proof stress, tensile strength and elongation by performing a tensile test according to JIS Z 2241 (2011) on a welded object welded using the shielded metal arc welding rod according to the present embodiment. Can be done.
The 0.2% proof stress is a stress value at which the permanent strain at the time of unloading becomes 0.2%. The 0.2% proof stress of the welded product is preferably 450 MPa or more, more preferably 480 MPa or more.
The tensile strength TS of the welded product is preferably 620 MPa or more, more preferably 650 MPa or more. On the other hand, if the tensile strength is too high, it becomes difficult to secure toughness. Therefore, 760 MPa or less is preferable, and 740 MPa or less is more preferable.
The elongation El of the welded product is preferably 18% or more, more preferably 20% or more.

<Mechanical characteristics: Charpy impact test @ 20 ° C>
The toughness can be evaluated by determining the absorbed energy of the welded product welded using the shielded metal arc welding rod according to the present embodiment by the Charpy impact test according to JIS Z 2242 (2005).
The absorbed energy by the test at 20 ° C. is preferably 20 J or more, and more preferably 30 J or more.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples, and the present invention is modified to the extent that it can be adapted to the gist of the present invention. It is possible, and all of them are included in the technical scope of the present invention.

<Examples 1 to 17 and Comparative Examples 1 to 8>
A shielded metal arc welding rod having the chemical composition shown in Table 1 was prepared. Of the components in Table 1, the balance is Fe and unavoidable impurities. Further, the component of less than 0.03% by mass is not a component positively added, but an unavoidable impurity.
The coating agent on the core wire was coated by applying a muddy coating agent, which is a mixture of powdery metal powder or the like and water glass, to the surface of the core wire, and drying and solidifying the core wire.
The ratio of the amount of added water glass (before drying) is as shown in Table 2. The diameter of the core wire of the obtained shielded metal arc welding rod was 5.0 mm, and the coverage of the shielded metal arc welding rod with the coating agent was 27% by mass in each example.

Welding was performed using the obtained shielded metal arc welding rod under the following conditions.
Welding uses a shielded metal arc welding rod with a rod diameter of 5.0 mmφ and a length of 400 mm, and a groove shape test is performed in a downward position under the conditions of a welding current of 140 A (AC), an arc voltage of 25 V, and a preheating pass temperature of 250 to 300 ° C. By performing plate welding, a welded metal test piece 5 as shown in FIG. 1 was obtained.
As the base material (steel material to be welded) 1, a steel plate of SM490A specified in JIS G3106 (2015) was used. Further, the groove surfaces of the base material 1 and the backing steel material 2 to be joints were surfaced to provide a three-layer buttering layer 3 made of a test material, and then welding was performed in the groove.

Welding workability at the time of welding and mechanical properties using the obtained welded metal test piece 5 were evaluated. The results are shown in Table 2.
Welding workability is that the amount of spatter generated during welding is small, the bead shape (waves of the bead) of the weld metal 4 after welding is beautiful and smooth, and slag is performed with a force less than the degree of lightly hitting a hammer. The "welding workability" in Table 2 is marked with a circle for those that satisfy all of the conditions of peeling and can be welded without any problem.

The welded metal test piece obtained by using each shielded metal arc welding rod was subjected to a post-welding heat treatment (PWHT; 710 ° C. for 5 hours, furnace cooling), and a tensile test and a Charpy impact test were performed on the welded metal.
In the tensile test, a No. A2 round bar test piece (6 mmφ, reference point distance 30 mm) specified in JIS Z3111 (2005) was collected from the center of the welded metal, and the temperature was 20 ° C. in accordance with JIS Z 2241 (2011). It was carried out at. By this tensile test, 0.2% proof stress (MPa), tensile strength TS (MPa) and elongation El (%) at 20 ° C. were determined.
Good values of each evaluation are 0.2% proof stress: 450 MPa or more, tensile strength TS: 620 MPa or more and 760 MPa or less, and elongation El: 18% or more.

In the Charpy impact test, test pieces (10 x 10 mm) were sampled at three locations so that the notch was located at the center of the thickness of the weld metal, and the notch shape was 2 mmV, in accordance with JIS Z 2242 (2005). It was carried out at 20 ° C. By this impact test, the absorbed energy νE (J) at 20 ° C. was determined, and the toughness was evaluated. A good value of absorbed energy νE at 20 ° C. is 20 J or more.

From the results in Table 2, it can be seen that the shielded metal arc welding rod according to the present embodiment is excellent in welding workability and also excellent in mechanical properties of the obtained welded product even if it does not contain Nb, Ti and Al. Do you get it.
On the other hand, when C was excessively contained in the chemical composition of the shielded metal arc welding rod, the tensile strength became too high, and when the Cr equivalent was too large, the tensile strength became low (Comparative Examples 1 and 8). The toughness deteriorated when the chemical composition contained an excess of Si, Cr and / or Mo (Comparative Examples 2, 5, 7 and 8). Further, when the chemical composition contains Mn and / or Ni in excess, the proof stress decreases by 0.2%, and even if the Cr equivalent is large, the proof stress decreases by 0.2% (Comparative Examples 3, 4 and 8). When the chemical composition had too little Cr, the elongation of the welded product became poor (Comparative Example 6).

1 Base material (steel to be welded)
2 Backing steel 3 Buttering layer 4 Welded metal 5 Welded metal test piece

Claims (1)

A shielded metal arc welding rod containing a core wire and a coating agent, wherein at least a part of the core wire is covered with the coating agent.
For the total mass of the welding rod
C: 0.01 to 0.13% by mass,
Si: 0.1 to 1.1% by mass,
Mn: 0.1 to 1.2% by mass,
Ni: 0.01 to 0.8% by mass,
Mo: 0.01-0.8% by mass,
Cr: 9.0 to 11.4% by mass,
Cu: 0.001 to 0.3% by mass,
And contains Fe as the main component,
Substantially free of Nb, Ti and Al
The content of each component is (Cr + Mo + 1.5 × Si) / (Ni + 30 × C + 0.5 × Mn) ≦ 6.5
Satisfy the relational expression of
The coating agent is used with respect to the total mass of the coating agent.
TiO ₂ : 5.0 to 40.0% by mass,
SiO ₂ : 5.0 to 20.0% by mass,
Contains 19.0-46.0% by mass of carbonate and CaF ₂ : 5.0 to 20.0% by mass of CaF.
The coverage by the coating agent, characterized in that from 20 to 40 wt%, covered electrode which is excellent in welding workability it is possible to obtain an excellent weld metal to the machine械的characteristics throughout the welding rod.

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