JPH07171695A - Submerged arc welding method for 960 MPa high strength steel - Google Patents

Abstract

PURPOSE:To provide a weld zone with excellent weldability, crack resistance, and low temperature toughness in the submerged arc welding method of 960MPa high tensile steel. CONSTITUTION:Welding is executed by combining wires where SiO2, CaF2, metallic carbonate, Li compound and one or two or more kinds of Mn, Ti, and Mg are contained, and the bond flux containing approximate amount of Si and Al, and Mn, Ni, Cr, Mo or the like are contained, the content of Si and N is limited, and the carbon equivalent (Ceq) by the prescribed formula is appropriate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a submerged arc welding method for 960 MPa high-strength steel, and more particularly to a submerged arc welding method for obtaining a weld metal having high toughness at low temperatures when thick plates are multi-layer welded. .

[0002]

2. Description of the Related Art Recently, HT960 TM has been used in place of conventional HT780 steel for large penstocks in connection with equipment at hydroelectric power plants.
The application of CP steel is being considered. In designing such a structure that becomes larger and thicker, a structure with high safety is considered, and steel and welds have good fracture toughness characteristics such as CTOD value in addition to Charpy impact value at low temperature. Is required. In general, the toughness of steel materials and welds tends to deteriorate as the strength increases, and it is becoming more and more difficult to satisfy the recent severe requirements. When such severe toughness is required, a composition of a bond flux is easier to design because a highly basic composition is obtained in submerged arc welding as compared with a molten flux.

Further, in submerged arc welding of 780 MPa high-strength steel, cold cracking due to hydrogen is likely to occur, and in order to prevent this, it is important to reduce the amount of diffusible hydrogen in the weld metal as much as possible. . From this point of view, bond fluxes, which can contain a large amount of metal carbonate, have been used. Therefore, even in the submerged arc welding method of 960 MPa high-strength steel having higher strength, it is important to reduce the amount of diffusible hydrogen in the weld metal as much as possible in order to prevent cold cracking.

The inventors of the present invention disclosed in Japanese Patent Laid-Open No. 3-52796 a method of submerged arc welding of high-strength steel of 780 MPa, in which SiO ₂ , CaF ₂ , and metal carbonate are added in appropriate ranges and Si, Mn, Al, and Ti are added. A welding method was proposed in which a limited bond flux and a wire having sufficiently low Si and N and a carbon equivalent (Ceq) within a proper range are combined.

Further, the present inventors have further disclosed in JP-A-6-21.
No. 2583, the composition of the wire and the flux was examined from the both sides, the metal carbonate and the deoxidizer were contained in a relatively large amount, SiO ₂ and CaF ₂ were restricted, and further, one of MgF ₂ and MnF ₂ as a fluoride or By combining two kinds of bond flux and a wire containing an alloy amount capable of obtaining a strength of 780 MPa and combining Si and N as low as possible, and welding them to obtain a low Si-low N-low oxygen weld metal, We proposed a welding method with low diffusible hydrogen content and high toughness at a low temperature, which produces a good quality weld.

[0006] Further, it is disclosed in, for example, JP-A-60-17 that a proper amount of Cr, Ni and Mo is contained in the wire.
A large number of wires for so-called Cr-Mo steels, including 7966, have been disclosed. Also, containing a proper amount of a large amount of Ni and Mo in a wire is a low-temperature wire, for example, JP-A-62-40996. Is disclosed in.

[0007]

However, Japanese Unexamined Patent Publication (Kokai) No. 3-5.
The submerged arc welding method proposed in Japanese Patent No. 2796 and Japanese Patent Laid-Open No. 6-212583 is for 780 MPa steel, and when it is used for 960 MPa steel as it is, problems such as insufficient strength occur.

All of the wires for Cr-Mo steel, such as JP-A-60-177966, are premised on heat treatment after welding, and do not undergo heat treatment after welding and have high strength of 960 MPa. In the submerged arc welding method for tensile steel, toughness and strength are not always compatible. From the viewpoint of ensuring toughness after heat treatment, Cr-
The wire for Mo steel does not substantially contain Ni, or even if it contains Ni, the amount is limited to a small amount, and the toughness is not always satisfied in the submerged arc welding method of 960 MPa high-strength steel without heat treatment after welding. Absent.

The wire disclosed in Japanese Patent Laid-Open No. 62-40996 is for low temperature and has high strength of 960MP.
a High-strength steel weld metal does not always have both toughness and strength.

As described above, 780 MPa steel, Cr-M
Although the method of welding o steel and low temperature steel has been studied, the fact is that it has not been sufficiently investigated for 960 MPa steel. Therefore, the present invention is 960MP
The purpose is to obtain good welding workability and good mechanical performance in welding of a steel.

[0011]

In order to achieve these objects, the present inventors have made detailed studies on both the composition of the wire and the flux based on the weld metal for 780 MPa steel. As a result, Si containing a relatively large amount of metal carbonate,
It regulates O ₂ , CaO, MgO, Al ₂ O ₃ and CaF ₂ , and further contains MgF ₂ , MnF ₂ and LiF as fluorides, and a relatively small amount of Si, Al, M as a deoxidizing agent.
bond flux to which n, Ti, Mg, etc. are added, and M
960MP containing a relatively large amount of n, Ni, Cr, Mo
a wire containing an alloy amount that can obtain the strength of a and having Si and N lowered as much as possible is welded to obtain a low Si-low N-
It was found that by using a low-oxygen weld metal, it is possible to obtain a high-quality weld that has a low amount of diffusible hydrogen and high toughness at low temperatures.

That is, the gist of the present invention is 960.
In the submerged arc welding method of MPa high strength steel,
By weight%, SiO ₂ is 8 to 16% and CaF ₂ is 9 to 21.
%, 5 to 10% in terms of CO _{2 of} metal carbonate, 0.02 to 1% in terms of Li carbonate or Li fluoride.
0%, Si 0.8-2.5%, Al 0.1-1.0
%, And one or two or more of Mn, Ti, and Mg, which is 1.5 to 4.5% in total including Si and Al, and Si is 0.06% or less. , N
Is 0.0050% or less and the carbon equivalent (Ce
It is a submerged arc welding method for 960 MPa high-strength steel, which comprises welding with a wire having a q) of 0.58 to 0.70% in combination. Ceq = C + 0.09Si + 0.08Mn + 0.06Ni + 0.11Cr + 0.14Mo (however, each component is% by weight)

Further, in this case, the bond flux is further wt%, CaO: 8 to 16%, MgO: 12 to 3
_{0%, Al 2 O 3:} 12~30% of one or containing two or more, and in addition weight%, MgF _2, Mn
It is also characterized by containing 2 to 10% of one or _two of F ₂ . Further, the wire has a further weight% of Mn: 1.0 to
2.2%, Ni: 1.5 to 4.5%, Cr: 0.85
It is also characterized by containing one or more of 1.60% and Mo: 0.55 to 1.20%.

[0014]

The function of the present invention will be described in detail below.
Needless to say, the component limitation of the present invention is basically based on the synergistic effect and the coexistence effect of the components of the flux and the wire, but the limitation including other factors will be described below.

The present inventors set the Ceq of the wire for 780 MPa steel to an appropriate value, and further set the Mn, Ni, Cr, and Mo of the wire to appropriate amounts as needed, and further, if necessary, CaO in the flux. , MgO, and A
Weld metal with good workability, low diffusible hydrogen and low temperature toughness in submerged arc welding of 960 MPa steel by adding 1 ₂ O ₃ and adding 1 or 2 types of MgF ₂ and MnF ₂ to the flux. It was found that

First, the SiO ₂ of the flux of the present invention must be 8 to 16% of the total weight of the flux. SiO
₂ is an extremely effective component for increasing the viscosity of the slag and forming a weld bead with a well-fitted toe, and also has a tendency to make the slag vitreous, which makes it easy to break. It is possible to generate a good slag of Such an effect of SiO ₂ can be obtained by adding 8% or more with respect to the total weight of the flux.
If added in excess of%, the melting point of the slag is lowered, the surface of the weld bead is disturbed, the oxygen content in the weld metal is increased, and the toughness of the weld metal deteriorates.

CaF ₂ is 9 to ₂ with respect to the total weight of the flux.
Must be 1%. CaF ₂ is intended to reduce the amount of oxygen in the weld metal, but reducing the amount of oxygen in the weld metal is extremely important and indispensable for improving the toughness of the weld metal. That is, the reduction of the oxygen amount greatly contributes to the improvement of the Charpy impact value and the CTOD value at low temperature, and in order to satisfy these characteristics, the oxygen amount in the weld metal should be about 230 ppm or less. is necessary.
The effect of such CaF ₂ is 9 with respect to the total weight of the flux.
%, But if added in excess of 21%, the amount of oxygen in the weld metal will be low, but the arc will be unstable, and pockmarks will occur, resulting in poor beads.

Metal carbonates such as CaCO ₃ and BaCO ₃ are converted into CO ₂ and are 5 to 10% based on the total weight of the flux.
Must be included. That is, the metal carbonate dissociates into CO ₂ gas in the arc cavity during welding, lowers the hydrogen partial pressure in the arc cavity, lowers the amount of hydrogen transferred to the weld metal, and reduces the diffusible hydrogen amount. Have. When the metal carbonate is less than 5% based on the total weight of the flux in terms of CO ₂ , the amount of diffusible hydrogen in the weld metal does not decrease and cold cracking due to hydrogen easily occurs. On the other hand, if it exceeds 10%, the gas generation amount becomes excessive, and the arc blows up, resulting in a defective bead shape.

Further, the flux of the present invention contains 0.02 to 1.0% of Li carbonate or Li fluoride in terms of Li based on the total weight of the flux.
Combines with OH groups, suppresses reaction with moisture and reduces moisture absorption,
Further reduce the amount of diffusible hydrogen in the weld metal. Such an effect can be obtained when Li carbonate or Li fluoride is converted to Li in an amount of 0.02% or more. However, when it exceeds 1.0%, the particle strength of the flux becomes small and the flux becomes powder during welding. And become a pock mark.

Further, the flux of the present invention must contain 1.5 to 4.5% in total of one kind or two kinds or more of Si, Mn, Al, Ti and Mg with respect to the total weight of the flux. Si and Mn act as a deoxidizing agent and improve the familiarity of the bead and the smoothness of the bead surface. Also,
As described above, metal carbonate is added for the purpose of reducing the amount of diffusible hydrogen, but the reaction of CO ₂ → CO + O occurs in the arc cavity, and this O (oxygen) increases the amount of oxygen in the weld metal. , Deteriorates low temperature toughness such as Charpy impact value and CTOD value. Therefore, as a strong deoxidizer, Al, T
i and Mg are required.

If the total amount of Si, Mn, Al, Ti and Mg is less than 1.5%, these effects cannot be sufficiently obtained. If it exceeds 4.5%, the amount of oxygen in the weld metal will decrease,
The arc cavity becomes an excessively reducing atmosphere, and SiO _{2 in} the flux moves as Si as it is into the weld metal,
On the contrary, the low temperature toughness such as the Charpy impact value and the CTOD value decreases. In addition, among these, Si is 0.
It needs to be limited to 8-2.5%. If Si is less than 0.8%, not only the deoxidizing effect is not sufficient, but also the alignment of the toes of the beads becomes poor. On the other hand, if it exceeds 2.5%, the amount of Si in the weld metal becomes excessive and the low temperature toughness deteriorates.
Further, Al needs to be limited to 0.1 to 1.0%. Al is particularly effective in reducing oxygen. If it is less than 0.1%, this effect cannot be obtained, and if it exceeds 1.0%, the amount of Al oxide in the weld metal increases, and the toughness decreases.

The form of addition of the deoxidizer to the flux is as follows: Si is metal Si, Fe-Si, Ca-Si, Mn is metal Mn, Fe-Mn, Al is metal Al, Fe-Al,
Al-Mg, Ti is metallic Ti (low N), Mg is Al-M
g, metal powder such as metal Mg, particle size is 0.15 mm
The following are preferred.

The CaO added as required is preferably 8 to 16% with respect to the total weight of the flux. C
aO is a component that increases the basicity, and when 8% or more is added, this effect is remarkably exhibited. On the other hand, when it exceeds 16%, the bead wave becomes rough and the toes become uneven, and the bead shape is somewhat poor. Becomes

Similarly, MgO is 1 with respect to the total weight of the flux.
It is preferably 2 to 30%. MgO has a high melting point and imparts fire resistance to the flux, and stabilizes the bead shape with a relatively large heat input. Although such an effect is remarkably exhibited at 12% or more, on the other hand, if added in a large amount, hard crystals are generated in the slag, and it tends to be difficult to remove it because it is not easily crushed. Therefore, the MgO content in the flux is preferably 30% or less.

Similarly, it is preferable to add 12 to 30% of Al ₂ O ₃ to the total weight of the flux. Al ₂ O
₃ has a high melting point and provides fire resistance to the flux, and stabilizes the bead shape under a relatively large heat input. Further, the slag is made vitreous to produce a slag that is easily broken and has a good peeling property.
Such an effect is remarkably exhibited when added in an amount of 12% or more. On the other hand, when it exceeds 30%, the bead width tends to be narrow and a convex bead tends to be formed.

Further, MgF ₂ , Mn added as necessary
At least one of F ₂ is 2 to 1 with respect to the total weight of the flux.
It is preferably 0%. As mentioned above, with the aim of making the amount of oxygen in the weld metal extremely low, CaF ₂ is contained in a relatively large amount, which may cause arc instability and bead disturbance, but MgF ₂ and MnF ₂ are appropriate amounts. The inclusion improves these. Such Mg
The effect of F ₂ and MnF ₂ can be obtained by adding 2% or more in total of the total weight of the flux.
If added in excess of 0%, the bead shape will be convex.

Further, the flux used in the present invention needs to be a bond flux, which is a metal carbonate or Si, M in the flux used in the present invention.
Since metal powders such as n, Al, Ti, Al-Mg, and Mg are added, these components are decomposed or oxidized and consumed in the sinter flux that is fired at a high temperature or in the melt flux that is melted during production, and This is because it is difficult to secure it. From this point, it is necessary that the bond flux be fired at about 550 ° C. or less.

Further, in the present invention, it is necessary to limit Si of the wire to 0.06% or less. In order to improve the low temperature toughness of the weld metal, it is effective to reduce the Si content in the weld metal as much as possible, and in order to obtain good low temperature toughness, the Si content in the weld metal should be 0.20% or less. Is preferred. From the viewpoint of welding workability, the flux of the present invention contains Si and SiO ₂ , and the Si content of the wire is 0.06.
If it exceeds 0.1%, the amount of Si in the weld metal becomes excessive and the low temperature toughness such as the Charpy impact value and CTOD value decreases.

Further, in the present invention, N of the wire is 0.
It is necessary to limit it to 0050% or less. In order to improve the low temperature toughness of the weld metal, it is extremely important to reduce the amount of N in the weld metal, as with Si described above. Particularly, in order to obtain high strength and low temperature and high toughness as in the present invention, low N is effective. If N exceeds 0.0050%, good low temperature toughness cannot be obtained.

Furthermore, the carbon equivalent (Ceq) of the wire expressed by the following formula must be 0.58 to 0.70%. If the carbon equivalent (Ceq) of the wire is less than 0.58%, the target strength cannot be obtained, and if it exceeds 0.70%, the strength becomes too high and the low temperature toughness deteriorates, and the target value cannot be obtained. Therefore, the carbon equivalent (Ceq) of the wire is 0.58-
It is necessary to be 0.70%. The formula of carbon equivalent (Ceq) is a formula experimentally obtained by the present inventors from the contribution of each alloy to the weld metal yield and strength. Ceq = C + 0.09Si + 0.08Mn + 0.06Ni + 0.11Cr + 0.14Mo (however, each component is% by weight)

Further, in the present invention, Mn, Ni, Cr, and Mo, which are added as necessary to secure appropriate strength and toughness for 960 MPa steel, have Mn of 1.0 to 2.2% and Ni, respectively. Is preferably 1.5 to 4.5%, Cr is 0.85 to 1.60%, and Mo is preferably 0.55 to 1.20%. Mn is 1.0% or more, and Ni is 1.
Sufficient toughness is obtained at 5 or more, but Mn exceeds 2.2%,
If Ni exceeds 4.5%, the strength becomes too high. If the Cr content is 0.85% or more and the Mo content is 0.55% or more, sufficient strength can be obtained, but if the Cr content exceeds 1.60% and the Mo content exceeds 1.20%, the strength becomes too high and the low temperature toughness is rather deteriorated. The target value cannot be obtained due to deterioration.

The wire components other than those defined in the present invention include C of 0.06 to 0.12%, P of 0.015% or less,
It is preferable that S is 0.010% or less, Cu is 0.3% or less, and Ti is 0.10% or less.

[0033]

EXAMPLES The effects of the present invention will be more specifically shown by the following examples. Wires having 16 compositions of W1 to W16 shown in Table 1 were produced. Of these, W1 to W12 are wires of the present invention, and W13 to W16 are wires of comparative examples for clarifying the effects of the present invention. All wire diameters are 4.0
mm.

[0034]

[Table 1]

Next, fluxes of 15 kinds of compositions F1 to F15 shown in Table 2 were prepared. F1 to F7 in Table 2
Is a flux of the present invention, and F8 to F15 are fluxes of comparative examples for clarifying the effect of the present invention. The manufacturing method is a bond flux prepared by first mixing and mixing the flux raw materials, then granulating with water glass as a binder, then constructing under conditions of 530 ° C. for 2 hours, and sizing to 12 to 100 mesh. is there.

[0036]

[Table 2]

As shown in Table 3, the steel sheet has a chemical composition and a thickness of 5
It is 0 mm 960 MPa steel. The steel sheet was processed into a U-shaped groove as shown in FIG. 1 and provided for welding. Welding conditions are welding current 550A, welding voltage 31V, welding speed 300mm / mi
n, the preheating temperature of 100 ° C., and the interpass temperature of 150 ° C. were used for multi-pass welding. Note that θ ₁ and θ ₂ = 4 in FIG.
°, R = 10 mm, t ₁ = 40 mm, t ₂ = 10 mm,
t ₃ = 15 mm.

[0038]

[Table 3]

After 48 hours or more have passed from the end of welding, the presence or absence of cracks in the welded portion was examined by an ultrasonic flaw detection test. For samples without defects, JIS A1 tensile test pieces and JIS were obtained from the welded portion 15 mm below the plate surface. No. 4 V
Notch Charpy test pieces were collected and tested.
Table 4 shows the combination of the wire and the flux and various test results. In Table 4, No. 1-No.
No. 16 is an embodiment of the present invention. 17-No. 28 is a comparative example.

[0040]

[Table 4]

As a result of these, No. 1 of the present invention was used. 1-No.
No. 16 had a good bead appearance and no cracking, and both the tensile strength and the Charpy absorbed energy value at -40 ° C showed good values.

No. 4 among the comparative examples. No. 17 had excessive Si in the wire, and No. 17 In No. 18, the N content of the wire was excessive and the toughness deteriorated. Of the comparative examples, No. In No. 19, the Ceq of the wire was excessive and the tensile strength was excessive. No. In No. 20, the Ceq of the wire was too small and the tensile strength was insufficient. In addition, No. In No. 21, the SiO ₂ of the flux was excessive and the bead surface was disordered, but as a result of continuing the subsequent tests, the toughness was deteriorated due to the insufficient deoxidizing agent.

No. 4 among the comparative examples. 22 is S of flux
Since iO ₂ was too small, the bead alignment was poor, and when Al ₂ O ₃ was too large, a convex bead was formed, and the familiarity was also poor. Therefore, the subsequent tests were stopped. In addition, No. 23 is flux CaF
_{Since 2} was excessive and a pock mark was generated and the bead appearance was poor, the subsequent tests were stopped.

Among the comparative examples, No. Sample No. 24 had an excessive amount of CaO in the flux and had a rough bead wave, but as a result of continuing the subsequent tests, the amount of CaF ₂ was too small and the toughness was deteriorated. Of the comparative examples, No. In No. 25, since the CO ₂ component of the flux was excessive and a pock mark was generated, the subsequent tests were stopped.

Of the comparative examples, No. 26 is the flux M
Although the slag was poorly peeled off due to excessive gO and excessive Al ₂ O ₃ , cracks occurred due to insufficient CO ₂ component when ultrasonic flaw detection was performed, so the subsequent tests were stopped. In addition, No. In No. 27, since Li in the flux was excessive and a pock mark was generated, No. In No. 28, MgF ₂ and MnF ₂ in the flux were excessive and the beads were convex and the shape was defective, so that the subsequent tests were stopped.

[0046]

As described above, by using the present invention,
As shown in the examples, in the submerged arc welding method for 960 MPa steel, a welded portion having good welding workability, no welding cracks and good toughness at low temperature is obtained, which contributes to welding of a large structure. Is large.

[Brief description of drawings]

FIG. 1 is a sectional view showing a groove shape of a welding test plate used in an example of the present invention.

Claims (4)

[Claims] 1. A submerged arc welding method for 960 MPa high-strength steel, wherein SiO ₂ is 8-16 in weight%.
%, CaF ₂ is 9 to 21%, metal carbonate is 5 to 10% in terms of CO ₂ , Li carbonate or Li fluoride is 0.02 to 1.0% in terms of Li, and Si is 0. 8 to 2.5
%, Al 0.1-1.0%, and Mn, T
i, a bond flux containing one or more of Mg and a total of 1.5 to 4.5% including Si and Al, and Si of 0.06% or less and N of 0.0050% or less. And the carbon equivalent (Ceq) represented by the following formula is 0.58 to 0.70.
% Of the wire and welding in combination with the 960 MPa high strength steel submerged arc welding method. Ceq = C + 0.09Si + 0.08Mn + 0.06Ni + 0.11Cr + 0.14Mo (however, each component is% by weight) 2. The bond flux further comprises C by weight.
aO: 8-16%, MgO: 12-30%, Al ₂ O
₃ : 12-30% of 1 type (s) or 2 or more types are contained, The submerged arc welding method of the 960 MPa high strength steel of Claim 1 characterized by the above-mentioned. 3. The bond flux further comprises, by weight%, M
960M according to claim 1 or 2, characterized by containing 2 to 10% of one or _two of gF ₂ and MnF _2.
Submerged arc welding method for high-tensile steel. 4. The wire further comprises Mn: 1.0% by weight.
~ 2.2%, Ni: 1.5-4.5%, Cr: 0.85
-1.60%, Mo: 0.55 to 1.20% of 1 type (s) or 2 or more types, The submerged arc welding method of the 960 MPa high strength steel of Claim 1 thru | or 3 characterized by the above-mentioned.