JP3442563B2 - Flux-cored wire for gas shielded arc welding of 690 MPa class high tensile steel - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding 690 MPa class high-strength steel by as-weld and post-weld heat treatment (hereinafter also referred to as PWHT). The present invention relates to a flux-cored wire capable of satisfying both performance, particularly high-temperature strength and low-temperature toughness. 2. Description of the Related Art In recent years, pressure vessels and penstocks used in petrochemical plants and power generation facilities have been required to operate at higher pressures for the purpose of improving the operation efficiency. 690 MPa
The application of high-grade high-strength steel is increasing. Conventionally, Mn-Mo steel or Mn-Mo-Ni steel has been used for these steel materials. However, the high-temperature strength and low-temperature toughness of the weld after PWHT, particularly the toughness below the freezing point depending on the installation area of the equipment. In consideration of the above, a steel type of a type containing less than 0.5% of Cr, Ni, Cu and a small amount of Nb or V based on a low-temperature Mn-Ni steel is also used. In an apparatus using these steel materials, as an example of the strength requirement of the welded portion, for example, the high temperature strength at 350 ° C after PWHT of 620 ° C x 12 hours is 600 MPa and the toughness of the welded portion after PWHT is -30 ° C. 47J or more, and very strict requirements have been met for conventional flux cored wire technology. On the other hand, gas welding arc welding using a flux-cored wire has been increasingly used as a welding method because it is more efficient than a welding rod and has a good weld bead shape in posture welding. ing. In particular, for members used at high temperatures and pressures, the demand for toughness at low temperatures is becoming more sophisticated from the viewpoint of preventing brittle fracture of the weld at the same time as having sufficient high-temperature strength, and a balance between high strength and high toughness is great. It has become a challenge. In such welding of high strength members,
In general, PWHT is performed on a welded portion for the purpose of relaxing residual stress in the welded portion, softening the affected zone, and diffusing and releasing hydrogen in the weld metal. However, when the PWHT extends for a long time at a high temperature, the toughness of the weld metal may deteriorate. Particularly in gas shielded arc welds constructed using flux cored wires, the oxygen level in the weld metal is higher and the behavior of toughness degradation due to PWHT is different compared to solid wires, welding rods and submerged arc welding. There has been a demand for the development of a flux-cored wire having an optimum component design, which can obtain good weld metal performance after welding and after PWHT. [0005] Regarding the weld metal performance of a flux-cored wire for Ni-based low alloy steel after PWHT, for example, Japanese Patent Application Laid-Open No. 52-65736 discloses a technique relating to a flux-cored wire for submerged arc welding of Mn-Ni-Cu steel. However, with the flux-cored wire of the present invention, it is difficult to perform vertical or upward welding by gas-shielded arc welding, and it is not possible to achieve both high-temperature strength and low-temperature toughness of a weld after PWHT. [0006] The present invention relates to the above-mentioned 690
In welding of high-strength steels of the MPa class, a good bead shape, workability and work efficiency are secured in all positions of welding, and a flux cored wire with good high-temperature strength and low-temperature toughness of the weld after long-time PWHT. It is intended to provide. SUMMARY OF THE INVENTION The present invention has been completed as a result of various studies on wire components for this purpose. The gist of the present invention is to fill a steel sheath with powder. In a flux-cored wire for gas shielded arc welding, TiO ₂ : 3.0 was used in terms of% by weight based on the total weight of the wire.
6.0%, metal fluoride all amount 1.0 to 2.0%, the essential and slag agent and C: 0.15% or less, Si: 0.3
-1.2%, Mn: 0.5-2.5%, Ni: 1.0-
3.0%, Cr: 0.3% or less, Mo: 0.2% or less,
Cu: 0.5% or less, Mg: 0.4 to 1.2% below the metal deoxidizing components or alloy components essentially containing (1) the carbon equivalent CeqFCW wires of the formula is from 0.43 to 0 .5
0, and as an alloy component, the entire wire
By weight% with respect to weight, Ti: 0.01 to 0.20%,
B: containing 0.005 to 0.015%, further ratio 0.4 ≦ a Mg amount and the metal fluoride all amounts in the wire (Mg amount / metal fluoride all amount) ≦ 0.8 Der Other, iron powder, arc
It is a flux-cored wire for gas shielded arc welding for 690 MPa class high-tensile steel, which is a stabilizer, a slag agent and inevitable impurities . CeqFCW = C + 0.08Si + 0.07Mn + 0.
05Ni + 0.07Cr + 0.15Mo + 0.02Cu
+ 0.08Mg (1) As described above, the welded portion of a high-temperature and high-pressure device using 690 MPa class high-strength steel needs to have both high-temperature strength and low-temperature toughness after PWHT. It is. In a conventional welded part using a flux-cored wire, there is a problem that high-temperature strength is obtained but toughness is insufficient, or good low-temperature toughness is obtained but high-temperature strength is insufficient.
A flux-cored wire having a strength of 90 MPa, a strength of 600 MPa at 350 ° C., and a low-temperature toughness at a temperature below the freezing point has not been studied.
The present inventors have studied the effects of the alloy components and slag composition on the weld metal in order to achieve these objects, and have obtained the following findings. [0009] By combining a small amount of Cr, Mo, Cu, Ti, and B into a wire composition based on the Si-Mn-Ni system so as to be an appropriate combination component, it is possible to achieve both high-temperature strength and low-temperature toughness. It is. In order to obtain stable low-temperature toughness and high-temperature ductility in all-position welding, the viscosity of the slag and the weld metal is adjusted by adjusting the viscosity of the slag and the weld metal by adjusting the composition of the slag agent and the amount of Mg added appropriately. It is necessary to reduce nonmetallic inclusions that inhibit toughness. Based on the above findings, the present invention is effective only by appropriately combining the components of the wire. The reasons for limiting the components of the wire and the amounts of the individual added components are described below. . TiO ₂ : 3.0 to 6.0% TiO ₂ is an arc stabilizer and constitutes a main component of a slag agent together with a metal fluoride described later. In addition to encapsulating the weld metal during welding and shielding it from the atmosphere, the appropriate viscosity affects the shape of the weld bead, and particularly in attitude welding, the balance with other metal components greatly affects the sag of the metal. On the other hand, it also causes the formation of a non-metallic inclusion component of a melting type or a non-melting type, which affects weld metal performance.
If the content of TiO ₂ is less than 3.0%, the slag is not sufficiently covered and the position welding is difficult. On the other hand, if it exceeds 6.0%, the amount of slag becomes excessive in combination with the metal fluoride, making it difficult to hold the weld metal by posture welding and forming a non-melting non-metallic inclusion. The toughness deteriorates. Total amount of metal fluorides: 1.0 to 2.0% CaF ₂ , NaF, MgF ₂ , BaF ₂ , K ₂ ZrF _6, etc.
Metal fluoride is effective in deoxidizing the weld metal by the action of fluorine gas generated by decomposition by the welding arc,
It greatly affects the basicity and viscosity of slag. M to be described later
An appropriate component amount is determined by the balance with g, but if the total metal fluoride content is less than 1.0%, the deoxidation of the weld metal becomes insufficient, and the toughness of the weld metal deteriorates. 2.0%
If it exceeds, the amount of slag becomes excessive, the arc becomes unstable, and the position weldability deteriorates. C: 0.15% or less In the flux-cored wire for a 690 MPa class steel according to the present invention, the wire component of the alloy or metal deoxidizer having a balance in which the high-temperature strength and low-temperature toughness of the weld metal is optimized is CeqFCW described later. However, it is necessary to limit the upper limit or the appropriate component range for each component. C not only strengthens the solid solution of the weld metal, but also affects the toughness of the weld metal by an optimum balance amount. Also PW
When HT is performed, Cr, Mn, Cr, Mo, Nb, V
Interaction with a component that easily forms carbide with the like deteriorates toughness. When the amount of C in the wire exceeds 0.15%, the low-temperature toughness is deteriorated, and a large amount of spatter is generated at the time of welding, and welding workability is also deteriorated. Also,
As long as CeqFCW described later is secured, the lower limit value of C may be the value of a normal steel outer skin component, and is not particularly specified. Si: 0.3 to 1.2% Si is a component for deoxidizing and strengthening solid solution of a weld metal. If the content of Si is less than 0.3%, the strength of the weld metal cannot be secured. On the other hand, if it is less than 0.3%, the deoxidation of the weld metal becomes insufficient, so that sufficient high-temperature strength and low-temperature toughness cannot be ensured, the arc becomes unstable, and SiO ₂ formed as a deoxidation product is formed. Insufficient amount, and the balance of slag viscosity is lost, and good welding workability cannot be obtained. If it exceeds 1.2%, the low-temperature toughness of the weld metal deteriorates. Mn: 0.5 to 2.5% Mn also acts as a deoxidizer and a solid solution strengthener for the weld metal similarly to Si. If it is less than 0.5%, the low-temperature toughness deteriorates due to insufficient deoxidation. On the other hand, if it exceeds 2.5%, the strength of the weld metal increases and the low-temperature toughness deteriorates due to PWHT. Ni: 1.0 to 3.0% Ni improves the strength of the weld metal by solid solution strengthening and significantly improves the corrosion resistance and low-temperature toughness. Also Ni
Has a lower degree of embrittlement on low-temperature toughness due to PWHT than other alloy components. In the present invention, the effect of improving high-temperature strength and low-temperature toughness can be obtained by adding 1.0% or more in terms of balance with other components. Cracks easily occur. Cr: 0.3% or less, Mo: 0.2% or less Cr and Mo, like Mn, are components that increase the high-temperature strength of the weld metal. However, if added excessively, PWH
Since the weld metal is embrittled by T, in the present invention, Cr: 0.3% or less, Mo:
It must be limited to 0.2% or less. Cu: 0.5% or less Cu exerts the strength of the weld metal and improves the corrosion resistance by being added simultaneously with Ni. Further, by applying Cu plating to the surface of the wire, the electrical conductivity and the feeding property of the wire are stabilized. The appropriate amount of Cu added to the wire is determined by the balance with other components.
If it exceeds 5%, hot cracking occurs. Mg: 0.4 to 1.2% Mg reacts in a high-temperature welding arc and acts as a strong deoxidizer. In the wire of the present invention,
Since the viscosity of the molten metal and the MgO generated by the deoxidation reaction greatly affect the slag composition and slag viscosity,
As will be described later, it is necessary to add an appropriate amount depending on the balance with the total amount of the metal fluoride. In order to obtain the effect of deoxidation, it is necessary to add 0.4 % or more. In addition, 1.2%
If it exceeds, the viscosity of the slag becomes excessive, and the welding workability in posture welding is deteriorated. Ti: 0.01 to 0.20% Ti makes the crystal grains finer by adding a small amount, and improves the low temperature toughness by adding 0.01% or more. But,
If it is added in excess of 0.20%, the strength becomes excessive and the toughness deteriorates. Since the components from C to Ti mainly act as a metal deoxidizing agent or alloying agent, they are added to the steel shell or the filling flux in the form of a simple metal or an alloy. B: 0.005 to 0.015% B enhances the hardenability of the weld metal with a small amount of addition, and improves the strength and low-temperature toughness of the weld metal. 0.005
%, There is no effect, and if it exceeds 0.015%, the strength becomes excessive and the toughness is deteriorated. Since the effect of B can be exhibited by any of simple metals, alloys, and addition by oxidation, the form of addition to the flux is free. In the present invention, C, Si, Mn, Ni,
For Cr, Mo, Cu and Mg, the carbon equivalent CeqFCW represented by the formula (1) needs to be 0.43 to 0.50 . If CeqFCW is less than 0.43 , P
The strength at which the tensile strength of the weld metal after WHT is 690 MPa at room temperature and the high-temperature tensile strength at 350 ° C. is 600 MPa or more cannot be obtained. On the other hand, if it exceeds 0.50 , the strength becomes excessive and the low-temperature toughness deteriorates. In order to improve the high-temperature ductility, low-temperature toughness, and welding workability of the weld metal after PWHT, the ratio of the amount of Mg to the amount of metal fluoride is set within a certain range. Keeping is one of its features. Generally, in a welding position in which a weld metal is apt to hang down, such as in vertical and upward welding, slag must hold the weld metal by interfacial tension. However, as in the present invention, slag is mainly composed of TiO ₂ and metal fluoride. The slag flux cored wire described above is characterized in that the slag has a relatively low viscosity due to the addition of fluoride. As a deoxidizing agent, Mg rapidly undergoes an oxidation reaction at the tip of a wire or in a droplet in an arc atmosphere to form MgO.
When a large amount of Mg is added, the MgO solid-dissolves in the molten slag, thereby increasing the viscosity of the slag and improving the welding workability. The relationship between the Mg content / metal fluoride all amounts and definitive <br/> the vertical welding sagging of the metal is shown in Figure 1, the metal by the Mg quantity / metal fluoride all amount 0.4 more The dripping property is improved. However, when the amount of Mg / the total amount of metal fluoride is excessive, the viscosity of the slag becomes excessive,
Mg amount / metal fluoride all amount for the amount of occurrence of spatter becomes no longer be stable welding often has to be 0.8 or less. When Mg is added from the flux, metal M
g may be added alone or in an alloy with another metal element. In general, Nb and V are inevitably present in the wire as impurities of TiO ₂ and fluoride as a slag agent, but these Nb and V tend to form carbides by PWHT. Deteriorates low-temperature toughness after PWHT. In the flux-cored wire of the present invention, these N
The values of b and V are not specified, but are preferably limited to 0.015% or less. The flux-cored wire of the present invention includes:
Addition of iron powder, a small amount of an arc stabilizer, a small amount of a slag, etc. other than the above components does not affect the effect. The filling rate of the flux may be within the range of 8 to 25% applied to the ordinary flux-cored wire, but is preferably 12% or more from the viewpoint of arc stability. Further applied to the shielding gases CO _2, Ar and CO ₂ and a small amount of O ₂ added ones such conventional MA gas mixture further to these gases
Any shielding gas used for G welding can be used. Next, the present invention will be described more specifically with reference to examples. Using a mild steel pipe sheath, the hollow portion of the sheath was filled with flux, drawn, and finished to 1.2 mmφ to produce a flux-cored wire. The fluoride is CaF ₂ ,
MgF ₂ and K ₂ ZrF ₆ were combined and added at a fixed ratio of 1: 2: 1. The flux filling rate was 16%.
Table 1 shows the component composition of the wire. In Table 1, no. 1-6
No. is an example of the present invention. 7 to 26 are comparative examples. Using the above wires, vertical welding was performed under the conditions shown in Table 2, and the welding workability was evaluated by observing the arc state and measuring the upper limit voltage at which metal sagging occurred. FIG. 2 is a schematic diagram showing a welding operation test method, in which reference numeral 1 denotes a test piece, and 2 denotes a welding torch. Except those having particularly poor welding workability, welding was performed under the conditions shown in Table 3 and a weld metal performance test was performed. FIG. 3 is a sectional view showing a groove shape in a weld metal test. Specimen after welding is 620 ° C x 12 hours P
After performing WHT, JIS Z
3111 A1 tensile test piece and JIS G056
7 A type II-10 high temperature tensile test was taken and a tensile test of the deposited metal was performed. A 2 mm V notch Charpy impact test at -30 ° C was performed using a JIS Z31114 test piece. The tensile test was performed at room temperature and 350 ° C.
The test was carried out at 2 ° C. [Table 1] [Table 2] [Table 3] Table 4 shows the test results. Here, the results of the impact test were shown as an average of three test pieces. As is clear from Table 4, No. 3 having less than 3% TiO ₂ . 7. Conversely, TiO ₂
Exceeds 6%. No. 8 and No. 8 in which the amount of fluoride exceeds 2%. Regarding the wire of No. 10, the slag amount was inappropriate, the arc was unstable, the amount of spatter generated was large,
Posture was difficult. In addition, No. 3 having less than 0.3% of Si. As for No. 12, the viscosity of the slag was insufficient and stable vertical welding was difficult. Further, in the case of No. 3 in which Cu was added in excess of 0.5%. In No. 20, a vertical crack considered to be a hot crack occurred at the center of the weld bead. [0029] C. When C exceeds 0.15%. 11, Si
Exceeds 1.2%. 13, No. 13 in which Ni exceeds 3.0%. No. 17, Mg exceeding 1.2%. In all of the wires of No. 22, the CeqFCW exceeded 0.50 , the strength of the weld metal was excessive, and good low-temperature toughness was not obtained.
Further, in the case of No. Nos. 24 and B exceed 0.015%. Also for wire No. 26, the strength of the weld metal was excessive and good toughness could not be obtained. On the other hand, No. 3 having Mn of less than 0.5%. 1
No. 4 and Ni containing less than 1.0%. 16 is Ce
Although qFCW was also less than 0.43, the strength of the weld metal was less than 690 MPa in any of the wires. Mn is 2.5
%. No. 15, Cr containing more than 0.3%.
No. 18, Mo exceeds 0.2%. In 19 wires, insufficient toughness due to PWHT embrittlement was observed. Ti is 0.
No. less than 01%. No. 23 and B containing less than 0.005%. With No. 25, good toughness was not obtained. No. 3 having less than 1.0% of fluoride. 9, M
g with less than 0.4%. In the case of No. 21, low impact values originating from nonmetallic inclusions considered to be caused by insufficient deoxidation of the weld metal were observed, and good toughness was not obtained on average. Compared to the comparative example described above, the present invention N
o. 1 to No. Wire 6 has good values for both high-temperature strength and low-temperature toughness. [Table 4] As described in detail above, according to the sixth aspect of the present invention,
With the flux-cored wire for gas shielded arc welding for 90 MPa class high tensile strength steel, it is possible to obtain a well-balanced weld metal having good room temperature strength, high temperature strength and low temperature toughness after PWHT.

Diagram showing the relationship between BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] Mg amount / metal fluoride all amounts and limit voltage in UeSusumu welding in the wire, FIG. 2 is a schematic diagram showing the weldability test method [ FIG. 3 is a sectional view showing a groove shape in a weld metal test.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-224094 (JP, A) JP-A-2-217195 (JP, A) JP-A 8-10982 (JP, A) JP-A 8- 174267 (JP, A) JP-A-63-252694 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 35/00-35/368

Claims (1)

(57) [Claims 1] In a flux cored wire for gas shielded arc welding in which powder is filled in a steel sheath, TiO ₂ : 3 is used in a weight% with respect to the total weight of the wire. 0.0-6.0% Total amount of metal fluoride: 1.0-2.0% Slag agent and C: 0.15% or less Si: 0.3-1.2% Mn: 0.5- 2.5% Ni: 1.0 to 3.0% Cr: 0.3% or less Mo: 0.2% or less Cu: 0.5% or less Mg: 0.4 to 1.2% The deoxidizing component or alloy component is as follows (1)
The carbon equivalent CeqFCW of the wire represented by the formula is 0.43
０．５0.50, and further contains, as an alloying component, by weight% with respect to the total weight of the wire : Ti: 0.01 to 0.20% B: 0.005 to 0.015% ratio 0.4 ≦ (Mg amount / metal fluoride all amount) ≦ 0.8 der the Mg content and the metal fluoride all amount of is, other iron powder, arc stabilizer, the slag agent and No
A flux-cored wire for gas shielded arc welding of 690 MPa class high-tensile steel, which is an evasive impurity . CeqFCW = C + 0.08Si + 0.07Mn + 0.
05Ni + 0.07Cr + 0.15Mo + 0.02Cu
+ 0.08Mg (1) (However, each component is% by weight)