JPH01258894A - Submerged arc welding method for 9cr-1mo steel - Google Patents

Abstract

PURPOSE:To prevent the generation of the intercrystalline cracking of a weld metal by limiting the contents of Cr, Mo, Si, O, etc., in a wire to specific weight % and incorporating an Li compd., Al2O3, SiO2, etc., at prescribed weight % into a flux. CONSTITUTION:The components in the wire are limited, by weight %, to 0.01-0.15% C, 0.4-2.5% Mn, 8.0-11.0% Cr, 0.5-1.2% Mo, 0.05-1.3% Ni, 0.1-0.5% V, 0.02-0.12% Nb, 0.02-0.10% N, <=0.15% Si, and <=0.01% O. The components in the flux are limited to 25-75% CaF2, 8-30% CaO, etc., 2-30% Al2O3, etc., 1-10% Li compd., and <=15% SiO2 and the total Al contents in both the wire and the flux is limited to 1-5%. Since the Li compd. in the flux prevents the reaction of the Si with the Ni and Mo, the generation of the intercrystalline cracking is prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a submerged arc welding method used for welding 9 Cr-I Moti4 used in boilers and pressure vessels of thermal power generation and nuclear power generation, and furthermore, Specifically, by combining wire and flux with specified components, weld metal properties such as high-temperature strength, toughness, and crack resistance are improved, as well as welding workability such as bead shape and slag removability, and weld defects are eliminated. The present invention relates to a submerged arc welding method that provides excellent weld metal free of oxidation.

(Conventional technology) In recent years, as thermal power plants have become larger, the environment in which boilers and pressure vessels are used has become increasingly harsh, and boilers have come to be used at higher temperatures and pressures. .

Conventionally, in the submerged arc welding method of 9Cr-IMo steel, a matching welding material is selected according to the steel type from the viewpoint of high temperature strength, oxidation resistance, and toughness.
-I Mo, 9 Cr -I Mo -Nb -V or 9 Cr -2Mo -Nb -V steel wire and molten or sintered flux are used in combination.

For example, JP-A-59-82189 discloses CaO.

5in2. Specific amounts of C, Si, Mn, Cr, Mo, Ni combined with submerged arc welding flux consisting of Al203, Boo□, etc.
JP-A-60-231591 discloses a wire containing CaCO3°CaF2. CaO, MgO, 5in
2. A specific amount of Cr, Mo, N combined with a submerged arc welding flux consisting of A120s etc.
A wire containing , Ni, and REM was disclosed in Japanese Patent Application Laid-open No. 61-15
No. 4789 discloses 5in2°CaF2. CaO, ^
A specific amount of C, St, M combined with a submerged arc welding flux consisting of 1tos, MgO, etc.
n, Cr, Mo, Ni, Nb, V
A wire is disclosed. Also, JP-A-61-14
Publication No. 97 contains specific amounts of TI, REM, C, and C.
r.

0 in the weld metal using a welding material containing Mo and Nb.
A submerged arc welding method is disclosed in which the amounts of , N, St, and Mn are specified.

However, the welding materials and welding methods described above have been variously studied from the viewpoint of basic properties such as high temperature strength, oxidation resistance, toughness, etc., or from the viewpoint of cracking resistance; This method has not been sufficiently studied from the viewpoint of preventing minute cracks that occur in the process, and is not fully satisfactory in this respect. The present invention is disclosed in Japanese Patent Application No. 62-53716, in which specific amounts of C, Mn, Cr, Mo, Nl,
A wire containing V, Nb, A1, N and with a limited amount of Si and O, and a specific amount of CaF2. Can,
We have proposed a method for improving microcracks that occur at the grain boundaries of weld metal by combining a submerged arc welding flux containing Autos, An, and limited Sin, Si, Si. However, limiting 5102 in the flux, which is harmful, requires careful selection of raw materials and strict production control.Also, due to restrictions on raw materials, welding workability is not fully satisfactory, resulting in welding defects. There is a risk that this may occur, and there remains a problem in terms of the integrity of the weld metal.

[Problems to be Solved by the Invention] Japanese Patent Application No. 62-53716 discloses that St reduced from Si in the wire and Sin in the flux forms a low melting point eutectic between Mo and the As a countermeasure, strict restrictions are placed on the content of St and Sin in the welding material.This invention is based on the patent application filed in 1982. This is a further development of No. 53711i, and as a result of various studies, it has been found that adding Li compounds to flux will cause cracks to occur in weld metal without severely restricting 5102, which has an adverse effect on intergranular cracks in weld metal. We found that this can be prevented.

The effects of St and O in the weld metal and Li compounds in the flux on intergranular cracking in the weld metal were investigated. As shown in Figure 1, if a Li compound is added to the flux, the St in the weld metal will be 0.75%, and the 0 will be 0.02%.
If it is within 5%, no grain boundary cracking is observed. By adding Li compounds, the effect of Si, 0 on grain boundary cracks in weld metal is alleviated, and even without severely restricting 5i02 in the flux, microcracks that occur at grain boundaries in weld metal can be prevented and good welding can be achieved. This was done based on the knowledge that it is easier to work with and produces sound weld metal. Based on this knowledge, we have developed a method to prevent cracks that tend to occur at the grain boundaries of weld metal with a mixed structure of martensite + ferrite or a single structure of martensite using 9Cr-I Mo steel wire, and to achieve excellent high-temperature strength. 9. It is possible to obtain a sound weld metal with high toughness, good welding workability, and no welding defects such as slag entrainment and blowholes.
The object of the present invention is to provide a submerged arc welding method for Cr-I MowI.

[Means for solving the problem] The gist of the present invention is C, 0.01 to 0.15%
, Mn; 0.4-2.5%, Cr; 8.0-11.
0%, Mo; 0.5-1.2%, Ni; 0.05-
1.3%, V; 0.1-0.5%, Nb; 0.02-
0.12%, N, 0.02-0.10%,
and Si, wire limited to 0.15% or less, 0; wire limited to 0.01% or less, CaF2; 25-70%, CaO and/or Mg0.8-30%, A4203 and/or Z
Using a bond flux containing rO2: 2 to 35%, Li compound: 1 to 10%, and limited to 5iO2: 15% or less, Ai added from the wire and/or flux (Al in the wire + 0.7 This is a submerged arc welding method for 9Cr-IMo steel, characterized in that a wire and flux are combined so that the Au content in the flux is 1 to 5%.

(Function) The present invention is achieved by combining a wire with specified components and a flux with specified components,
C, Mn, Cr in the wire.

Mo, Ni, V, Nb, and N are essential components for obtaining the basic characteristics of high-temperature strength and toughness as a 9Cr-IMom wire. In addition, the St, 0 in the wire, the Li compound in the flux, 5in2, and the identification of shoulders in the wire and/or flux prevent microcracks occurring at the grain boundaries of molten metal, which is the object of the present invention, and improve welding workability. This is an important requirement for improving the weld metal and obtaining sound weld metal.

First, the components of the wire will be sequentially explained below.

C, 0.01-0.15% C is a necessary component to maintain the strength of the weld metal, and if it is less than 0.01%, it has no effect, and if it exceeds 0.15%, the cracking resistance of the weld metal is reduced. deteriorate. Therefore, the range of C is set to 0.01 to 0.15%.

Mn; Q, 4-2.5% Mn is a necessary component not only for deoxidation but also for maintaining the strength of the weld metal, and if it is less than 0.4%, it has no effect, and 2.
．． If it exceeds 5%, the toughness of the weld metal will decrease. Therefore M
The range of n is 0.4 to 2.5%.

Cr: 8.0-11.0% C is a basic component for ensuring oxidation resistance and high-temperature strength, and is required in an amount of 8.0-11.0%.

Mo; 0.5 to 1.2% MO is an essential component for increasing the high temperature strength and high temperature creep strength of weld metal, and if it is less than 0.5%, it has no effect, and if it exceeds 1.2%, it will deteriorate the weld metal. Deteriorates cracking resistance. Therefore, the Mo content should be in the range of 0.5 to 1.2%.

Ni, 0.05 to 1.3%Nl is an effective component for reducing embrittlement during use, and is an essential component for applications such as the welding material of the present invention, which is used for long periods of time at high temperatures and high pressures. It is.

If it is less than 0.05%, it has no effect, and if it exceeds 1.3%, it deteriorates the creep characteristics of the weld metal. Therefore, the range of Ni is set to 0.05 to 1.3%.

V, 0.1 to 0.5% (1) is a component that significantly increases high temperature strength; if it is less than 0.1%, it has no effect, and if it exceeds 0.5%, it deteriorates the toughness of the weld metal. Therefore, the range of V is set to 0.1 to 0.5%.

Nb, 0.02-0.12% Nb increases high-temperature strength and is effective in improving creep rupture strength at high temperatures and long periods of time, but less than 0.02% has no effect, and more than 0.12% and the toughness of the weld metal deteriorates. Therefore, the range of Nb is set to 0.02 to 0.12%.

N'; 0.02 to 0.1% N is effective in improving the strength of weld metal, but
．． If it is less than 0.02%, there is no effect, and if it exceeds 0.1%, welding workability deteriorates and blow poles occur. Therefore, the range of N is set to 0.02 to 0.1%.

St, 0.15% or less Si tends to form a low melting point eutectic with MO and Ni, and also combines with 0 in the weld metal to precipitate as an oxide, causing intergranular cracking. As mentioned above, intergranular cracking can be prevented by reducing the amount of Sl in the weld metal to 0.75% or less, and 0 to 0.025% or less. will also be returned. In order to reduce the St content in the weld metal to 0.75% or less, the St content in the wire should be reduced to 0.75%, taking into account the Si reduced from the flux.
It is necessary to keep it below 15%. Therefore, the Sl should be 0.15%
Limited to:

0; 0.01% or less 0 produces oxides with Mo, Nl, St, etc. in the weld metal and precipitates at grain boundaries, causing intergranular cracks. To prevent cracking, as mentioned above, it is necessary to reduce the amount of zero in the weld metal to 0.025% or less.
It is necessary to keep it below 1%. Therefore, 0 is limited to 0.01% or less.

The above are the components and contents of the wire specifically defined in the present invention, but in addition, P, S, etc. are included in amounts as unavoidable impurities.

Next, the components of the flux will be explained.

CaF2; 25 to 70% (: aF2 has the effect of increasing the basicity of slag, significantly reducing zero in the weld metal, and improving toughness, and as in the present invention, it reduces the zero in the weld metal and improves the grain size.) It is an essential component to prevent interfacial cracking. It also lowers the melting point of the slag, makes the penetration shallower, improves the peelability of the slag, and improves the bead shape and appearance. Less than 25% However, if it exceeds 70%, the fluidity of the slag becomes excessive and the bead shape and appearance deteriorate.
Limit it to 5-70%.

Ca'0 and/or MgO; 8-30% CaO and Mg
All of O is a strong basic component, and together with CaF2, it is effective in reducing zero in the weld metal. In addition, CaO and MgO are highly refractory components and have a low melting point (: They are effective in adjusting the melting characteristics of flux containing a large amount of aF2 and shaping the bead shape. If it is less than 8%, the effect is Not 30
%, the flux is difficult to melt, the bead surface loses its smoothness, and welding defects such as undercuts occur.

Therefore, CaO and/or MgO is limited to 8-30%.

AM20s and/or z "02:2~30% A12os
and ZrO□ have a high melting point and adjust the fluidity of the slag,
Effective for adjusting the bead shape. This effect is particularly important when used in multi-layer welding; when the basic flux is CaF2-CaO-+TGO, the overlapping portions of the beads are not smooth and uneven, but when Al2O
Addition of 5 and/or Z'02 improves bead alignment and prevents defects such as slug-in and undercut.If it is less than 2%, it is ineffective, and if it exceeds 30%, it may cause slag entrainment or undercut. Therefore, the content of hexagonal as TjL and/or ZrO is limited to 2 to 30%.

Li compound (decomposition temperature 800°C or higher); l~10% Li
Addition of the compound is the most important requirement in the present invention,
510 in flux. is reduced, reducing the amount of Si remaining in the weld metal, and has the effect of alleviating the influence of St on intergranular cracking. If it is less than 1%, there is no effect, and if it exceeds 10%, the slag releasability deteriorates. Therefore, the Li compound is limited to 1 to 10%. However, if the Li compound has a decomposition temperature of less than 800°C, it will decompose during welding and will not be effective.
2Li20・5i02. LizO-CaO-2SiO
, etc. shall be used.

5i02; 5in2 below 15% is effective in adjusting the slag viscosity and improving the bead appearance, but on the other hand, it is reduced in the arc atmosphere,
Increase Si in the weld metal to promote intergranular cracking. As mentioned above, in order to reduce the St content in the weld metal to 0.75% or less, the limit is 15%. Therefore, SlO□ is limited to 15% or less.

A1 added from wire and/or flux; 1 to 5% AM has the effect of significantly reducing 0 in the weld metal, assisting the aforementioned Li compound and preventing intergranular cracking, and prevents intergranular cracking of the weld metal. It is an essential ingredient for prevention. It is also effective in preventing the occurrence of blowholes and obtaining sound weld metal. If it is less than 1%, there is no effect, and if it exceeds 5%, the toughness of the weld metal deteriorates, and slag seize increases, resulting in poor releasability. Therefore, limit AU to 1-5%. There is a method of adding from wire and/or flux, and the effect is greater when adding from wire, but if Al in the wire exceeds 1.5%, hot forgeability deteriorates, so adding from wire When added, the limit is 1.5%. The effect of addition from flux is 7 for wires.
It is 0%.

The essential components of the flux of the present invention have been described above, but the additive raw materials for these components can be added in the form of individual substances, compounds, ores, or molten flux containing the above components. For example, as a raw material to be used, Ca
F2; Fluorite, molten flux, etc., Can; Lime carbonate, molten flux, etc., MgO, magnesia clinker, spinel, molten flux, etc., AjJzO3;
Alumina, spinel, molten flux, etc.; Metal A2. Fe-Al, etc.

In addition to the essential components, metal powders and alloy powders can be added to adjust the synthetic components.

The effects of the welding method of the present invention will be explained below using examples.

(Example) The wire used in the experiment was melted in a vacuum melting furnace, forged, rolled, and wire-drawn to have a diameter of 4.0 mm. The wire compositions are shown in Table 1, W1 to W5 are wires used in the present invention, and W6 to Wll are wires used in comparative examples.

The bonded flux used in the experiment was prepared by mixing ore powder, composite compounds, etc., which are commonly used as raw materials for flux, stirring, granulating using water glass, and firing at 500° C. for about 1 hour. The composition of the flux is shown in Table 2, and F
1 to F6 are fluxes used for the present invention, F7 to F12
was used as a comparative example.

Combine the wire in Table 1 and the flux in Table 2, and
Using the steel plates shown in Table 4, submerged arc welding was performed with a welding length of 2 m under the welding conditions shown in Table 4 and the lamination procedure shown in FIG. 2, and post-heat treatment was performed at 740° C. for 2 hours. Table 5 shows combinations of wire and flux and their accuracy test results.

Accuracy is determined by welding workability test, X-ray transmission test (JISZ 3
104), the grain boundary cracks were investigated by microstructural observation, and high-temperature tensile test pieces (JIS Z051117 diameter: 6 mmφ), impact test pieces (JIS Z 22024), and side bending test pieces (JIS Z 31223) were carried out. were sampled to investigate the basic weld metal performance. The high temperature tensile test was conducted at 550°C, the impact test at 0°C, and the side bending test at R=2t.

Examples No. 1-No. 20 of the present invention have excellent welding workability,
Although weld metal was obtained, No. 21. No. 23 has too much 5102 in the flux, No. 22. No. 24
No. 25 has too much CaF2 in the flux and the sum of CaO and MgO is insufficient. No. 26 has no Li compound in the flux, No. , 27 has too much wire and flux, No. 28 has Li in the flux.
There is no compound and there is too much Ai in the wire or flux, No.
, 29 is in flux ^ and 20. The sum of A4203 and ZrO in the flux is insufficient, resulting in too much Li compound. No. 30 has too much sum of A4203 and z"02 in the flux, resulting in insufficient Al in the wire and flux. No. 31 has C, Nb in the wire. No. 32 has too much C and Nl in the wire and Mo is insufficient. No. 33 has Si and Cr in the wire.
is too much and N is insufficient, No. 34 is insufficient Mn in the wire and V, Nb, and N are too much, No. 35 is Mn in the wire,
There are problems such as poor welding workability, deterioration of mechanical properties, and occurrence of intergranular cracks due to the individual reasons of excessive O content and insufficient Cr, V, and Ni in the wire for No. 38.

(Effect of the invention) As described above, the present invention provides 9 Cr-I Mo1l
A welding method that produces weld metal with excellent mechanical performance such as high temperature strength, impact value, and bending performance without causing intergranular cracks in submerged arc welding, and has excellent welding workability without welding defects. It is. If submerged arc welding of 9 Cr-I Mo steel used in various power generation boilers, pressure vessels, etc. is performed by the method of the present invention, the reliability of welded joints can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between St, O, and Li compounds in the weld metal and intergranular cracking in the weld metal. 'Second
The figure is a sectional view showing the groove shape and lamination procedure used in the example.

Claims (1)

[Claims] C: 0.01 to 0.15% Mn; 0.4 to 2.5% Cr; 8.0 to 11.0% Mo; 0.5 to 1.2% Ni ; 0.05-1.3% V; 0.1-0.5% Nb; 0.02-0.12% N; 0.02-0.10%, and Si; 0.15% The following O: Limited to 0.01% or less, the balance consisting of Fe and unavoidable impurities; CaF_2: 25-70%; one or two of CaO, MgO; 8-30%; one or two of Al_2O_3, ZrO_2 Seed: 2-30%, L with a decomposition temperature of 800°C or higher
Using a bond flux containing one or more of i compounds; 1 to 10% and limited to SiO_2; 15% or less, and further adding Al from one or both of the wire and flux shown in parentheses below. Submerged arc welding method for 9Cr-1Mo steel characterized by combining wire and flux so that the ratio is 1 to 5% (Al in wire + 0.7 x Al in flux)