JPH10272592A - TIG welding wire for heat resistant steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a TIG welding wire for heat-resistant steel capable of obtaining a weld metal having good room temperature strength, toughness and creep strength after heat treatment in welding of heat-resistant steel to which W is added. . SOLUTION: The TIG welding wire for heat resistant steel is weight%.
C: 0.05 to 0.15%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, S: 0.001
To 0.01%, Cr: 1.7 to 3%, Mo: 0.4
5 to 1%, W: 0.1 to 1.2%, and V: 0.1 to 0.5%, P is 0.01% or less, and Ni is 0.1 to 0.2%.
25% or less, Al is 0.01% or less, O is 0.02% or less, N is 0.015% or less, and the balance is F.
e and unavoidable impurities. When the content of W is [W] by weight% and the content of Mo is [Mo] by weight%, [W] / [Mo] is 0.2 to 2.6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TIG welding wire used for welding a high-temperature member such as a super-supercritical boiler in the field of a thermal power plant, and in particular, it can improve the properties of the obtained weld metal. The present invention relates to a TIG welding wire for heat-resistant steel.

[0002]

2. Description of the Related Art In recent years, in the field of thermal power plants, the operating environment tends to be further increased in temperature and pressure in order to operate equipment efficiently, and the material of the structure is selected according to the operating conditions. Have been. For example, under low temperature and low pressure conditions, 2.25% Cr-1% Mo steel is mainly used, and under high temperature and high pressure conditions, a carbide forming element such as V is added to increase the strength. ~ 12% Cr
Steel or stainless steel is used.

However, 9 to 12% Cr steel has a high raw material cost as a steel material for a medium temperature region.
A heat-resistant steel in which the creep strength is improved by adding W to 2.25% Cr-1% Mo steel has been disclosed (JP-A-2-217438). This heat-resistant steel
Due to the combined effect of Mo and W, creep strength equal to or higher than that of 9 to 12% Cr steel can be obtained, and the raw material cost is lower than that of 9 to 12% Cr steel. Therefore, such heat-resistant steel is expected to be applied as a member for medium to high temperatures of a supercritical boiler in the field of thermal power plants in the future.

On the other hand, as a welding material for welding heat-resistant steel to which W is added, a welding material for heat-resistant steel having excellent creep strength has been proposed (JP-A-5-269590). This welding material contains 1.3 to 2.5% by weight of W in order to increase the creep strength of the obtained weld metal.

[0005]

However, when a heat-resistant steel is welded using a TIG welding wire described in Japanese Patent Application Laid-Open No. 5-269590, the resulting weld metal has a high Ni content, so that a heat treatment ( After SR), there is a problem that excellent creep strength cannot be obtained. Further, since the added amount of W is excessive, there arises a problem that the toughness is lowered and the material tends to be unstable.

As described above, in the past, welding materials capable of obtaining a weld metal having high performance in welding of heat-resistant steel to which W has been added have not yet been developed.

The present invention has been made in view of the above problems, and it is an object of the present invention to obtain a weld metal having good room temperature strength, toughness and creep strength after heat treatment in welding of heat-resistant steel to which W is added. It is an object of the present invention to provide a TIG welding wire for heat resistant steel that can be used.

[0008]

According to the present invention, a T for heat-resistant steel according to the present invention is provided.
IG welding wire, C: 0.05 to 0.15% by weight,
Si: 0.1 to 1.0% by weight, Mn: 0.3 to 1.
5% by weight, S: 0.001 to 0.01% by weight, Cr:
1.7 to 3% by weight, Mo: 0.45 to 1% by weight,
W: 0.1 to 1.2% by weight and V: 0.1 to 0.5
% Of P, 0.01% by weight or less of P, and 0.2% of Ni.
25 wt% or less, Al 0.01 wt% or less, O
The content of N is regulated to not more than 02% by weight and the content of N is set to 0.015% by weight or less, and the balance is composed of Fe and unavoidable impurities. When the amount is [Mo] in weight%, [W] / [M
o] is 0.2 to 2.6.

[0009] The TIG welding wire further comprises B: 0.
It is preferable to contain 0005 to 0.01% by weight. Further, Nb: 0.05% by weight or less and Ti: 0.0
It is desirable to contain at least one element selected from the group consisting of 5% by weight or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive experiments and studies in order to solve the problems of the present invention. As a result, by defining the composition of a TIG welding wire within an appropriate range, this TI
It has been found that when welding heat resistant steel using a G welding wire, a weld metal having excellent properties can be obtained.

That is, in the present invention, the creep strength of the obtained weld metal is improved by adjusting the contents of C and Cr in the wire and controlling the Ni content. In addition, Mo and W are added as a wire component in a complex manner, and Nb, Ti and B are also added.

Further, while the upper limit of the W content in the wire is regulated, the ratio of the W content to the Mo content is regulated, and B is contained in the wire to improve the toughness of the weld metal. Is being planned. As described above, since the composition of the TIG welding wire is adjusted in the present invention, when the heat-resistant steel to which W is added is welded using this TIG welding wire, good room-temperature strength, toughness, and creep are obtained. A weld metal having strength can be obtained.

Hereinafter, the reasons for limiting the composition of the TIG welding wire for heat-resistant steel according to the present invention will be described.

C: 0.05 to 0.15% by weight C is an element that greatly affects the hardenability, and is added to secure the room temperature strength and toughness of the weld metal. It is also a component necessary for forming carbides in the weld metal to increase the creep strength of the weld metal.
If the C content in the wire is less than 0.05% by weight, these properties will deteriorate. On the other hand, when the C content in the wire exceeds 0.15% by weight, the room temperature strength is improved, but the toughness is reduced. In addition, the creep strength also decreases due to the aggregation and coarsening of the carbides in the weld metal.
Therefore, the C content in the wire is set to 0.05 to 0.15% by weight. Preferably, the C content is between 0.08 and 0.5.
11% by weight.

Si: 0.1 to 1.0% by weight Si has an effect of improving bead conformability. When the Si content in the wire is less than 0.1% by weight, the effect of improving the bead conformability is reduced, and particularly, the welding workability is reduced during backwash welding. On the other hand, Si in the wire
If the content exceeds 1.0% by weight, segregation of P, which is an impurity, to the grain boundary is promoted, so that the toughness and temper embrittlement resistance of the weld metal deteriorate. Therefore, the Si content in the wire is set to 0.1 to 1.0% by weight. Preferably, Si
The content is between 0.20 and 0.50% by weight.

Mn: 0.3 to 1.5% by weight Mn has the effect of improving the toughness of the weld metal. If the Mn content in the wire is less than 0.3% by weight, the effect is reduced and the toughness cannot be sufficiently improved. On the other hand, if the Mn content in the wire exceeds 1.5% by weight, the creep strength of the weld metal is reduced, and segregation of P, which is an impurity, to the grain boundary is promoted. descend. Therefore, the Mn content in the wire is 0.3
To 1.5% by weight. Preferably, the Mn content is between 0.5 and 1.0% by weight.

S: 0.001 to 0.01% by weight S has an effect of improving the conformability of a bead like Si. If the S content in the wire is less than 0.001% by weight, the effect cannot be sufficiently obtained. On the other hand, if the S content in the wire exceeds 0.01% by weight, the toughness and hot crack resistance of the weld metal decrease. Therefore, the S content in the wire is set to 0.001 to 0.01% by weight.
Preferably, the S content is between 0.003 and 0.007% by weight.

Cr: 1.7 to 3% by weight Cr has the effect of improving the room temperature strength, oxidation resistance and high temperature corrosion resistance of the weld metal. Cr content in the wire is 1.
If the amount is less than 7% by weight, the effect cannot be sufficiently obtained. On the other hand, if a large amount of Cr is added to the wire in excess of 3% by weight, relatively large Cr carbides will agglomerate and coarsen in the weld metal, and the creep strength of the weld metal will decrease. Therefore, the Cr content in the wire is set to 1.7 to 3% by weight.

Mo: 0.45 to 1% by weight, W: 0.1
To 1.2 wt% Mo and W have the effect of strengthening the matrix by solid solution strengthening effect. In addition, since the tendency of carbide formation is larger than that of Cr and Fe, by adding both to the wire in a composite manner, the precipitation of relatively large Cr carbide and cementite is suppressed, and the carbide is precipitated as fine carbide in the weld metal, Thereby, the creep strength of the weld metal can be significantly improved. Mo content in the wire is 0.45% by weight
Or less than 0.1% by weight of W in the wire
If it is less than the above, the above-mentioned effects cannot be sufficiently obtained. On the other hand, if the Mo content in the wire exceeds 1% by weight or the W content in the wire exceeds 1.2% by weight, the toughness of the weld metal is significantly reduced. Therefore, the Mo content in the wire is set to 0.45 to 1% by weight, and the W content is set to 0.1 to 1.2% by weight. Preferably, the Mo content is 0.5 to 0.7% by weight, and the W content is 0.1% by weight.
3 to 0.7% by weight.

V: 0.1 to 0.5% by weight V is a component that contributes to the improvement of the creep strength of the weld metal because V precipitates in the weld metal as fine carbide. If the V content in the wire is less than 0.1% by weight, the effect cannot be sufficiently obtained. On the other hand, when the V content in the wire exceeds 0.5% by weight, the toughness of the weld metal is significantly reduced. Therefore, the V content in the wire is set to 0.1 to 0.5% by weight. Preferably, the V content is between 0.3 and 0.4% by weight.

P: not more than 0.01% by weight P is an element that segregates at the grain boundary and deteriorates the toughness and temper embrittlement resistance of the weld metal. If the P content in the wire exceeds 0.01% by weight, a weld metal having desired properties cannot be obtained. Therefore, the P content in the wire is restricted to 0.01% by weight or less. Preferably, the P content is regulated to be 0.005% by weight or less.

Ni: 0.25% by weight or less The present inventors have found that if Ni is added to the wire in an amount exceeding 0.25% by weight, the creep strength of the obtained weld metal is significantly reduced. . Therefore, the Ni content in the wire is restricted to 0.25% by weight or less. Preferably, the Ni content is regulated to be 0.1% by weight or less.

Al: not more than 0.01% by weight The present inventors have found that if Al is added to the wire in an amount exceeding 0.01% by weight, the resulting weld metal will have increased room temperature strength and reduced toughness. I found something to do. Therefore, the Al content in the wire is restricted to 0.01% by weight or less. Preferably, the Al content is regulated to be 0.005% by weight or less.

O: not more than 0.02% by weight The present inventors have found that when O is added to the wire in an amount exceeding 0.02% by weight, nonmetallic inclusions increase in the obtained weld metal, It has been found that the room temperature strength, the toughness, and the creep strength of the weld metal all significantly decrease due to the decrease in the yield of other components. Therefore, the O content in the wire is restricted to 0.02% by weight or less. Preferably, the O content is regulated to be 0.01% by weight or less.

N: not more than 0.015% by weight The present inventors have found that when N is added to the wire in an amount exceeding 0.015% by weight, the room temperature strength and creep strength of the obtained weld metal are improved. It was found that the toughness was significantly reduced. Therefore, the N content in the wire is 0.01
Regulate to 5% by weight or less. Preferably, the N content is 0.1.
It is regulated to be not more than 01% by weight.

[W] / [Mo]: 0.2 to 2.6 As described above, in the present invention, Mo and W are contained in the wire.
, The creep strength of the weld metal is significantly improved. However, in order to obtain this effect, W
It is necessary to appropriately regulate the ratio between the content and the Mo content. When the W content in the wire is [W] in weight% and the Mo content in the wire is [Mo] in weight%, [W]
If / [Mo] is less than 0.2, the effect of improving the creep strength of the weld metal cannot be obtained. on the other hand,
If [W] / [Mo] exceeds 2.6, the strength of the weld metal becomes too high, and the toughness is significantly reduced. Therefore,
[W] / [Mo] is 0.2 to 2.6. Preferably, [W] / [Mo] is 0.5 to 1.5.

In the present invention, a weld metal having excellent properties can be obtained by appropriately regulating the content of the above elements and the ratio of the W content to the Mo content in the wire. By containing B in the wire, or adding one or both of Nb and Ti in an appropriate amount, the properties of the obtained weld metal can be further improved. Hereinafter, the reasons for limiting the preferable ranges of the contents of these elements will be described.

B: 0.0005 to 0.01% by weight B is an element having the effect of improving the hardenability and making the structure of the weld metal finer, thereby improving the toughness of the weld metal. B also precipitates in the weld metal as fine carbonitrides, thereby contributing to the improvement of the room temperature strength and creep strength of the weld metal. When adding B to the wire,
If the content is less than 0.0005% by weight, the effect of addition cannot be sufficiently obtained. On the other hand, when the B content in the wire exceeds 0.01% by weight, the strength of the weld metal is significantly increased, the toughness is reduced, and the hot cracking resistance is also reduced. Therefore, when B is contained in the wire, the content is preferably 0.0005 to 0.01% by weight. More preferably, the B content in the wire is 0.1.
002 to 0.006% by weight.

Nb: 0.05% by weight or less, Ti: 0.0
By adding one or both of Nb and Ti to the wire in an amount of 5% by weight or less , even if the amount is very small, these are precipitated as fine carbonitrides in the weld metal. Room temperature strength and creep strength can be further improved. When Nb or Ti is contained in the wire, the Nb content exceeds 0.05% by weight or Ti
If the content exceeds 0.05% by weight, the strength becomes too high and the toughness is remarkably reduced. Therefore, Nb
When one or both of Ti and Ti are contained, the Nb content in the wire is preferably 0.05% by weight or less, and the Ti content in the wire is preferably 0.05% by weight or less. More preferably, the Nb content is between 0.005 and 0.5.
03% by weight, and the Ti content is 0.005 to 0.0
3% by weight.

The TIG welding wire of the present invention may be plated without plating or may be plated with Cu for imparting rust prevention. When performing Cu plating for rust prevention on the wire surface, the total amount of the Cu content and the Cu plating amount in the wire is set to 0.4% by weight or less.

[0031]

EXAMPLES Examples of the TIG welding wire for heat-resistant steel according to the present invention will be specifically described below in comparison with comparative examples.

FIG. 1 is a sectional view showing the shape of a welding base metal used in this embodiment. As shown in FIG. 1, in this example, a welding test was performed according to JIS Z3316. That is, as shown in FIG. 1, the welding base material 1 has a V-shaped groove, and a backing metal 2 having the same chemical composition as the welding base material 1 is provided on the back surface of the V-shaped groove. Is arranged. In the present embodiment, the groove angle of this V shape is 4
5 °, the gap width of the portion where the backing metal is arranged was 6 mm. Further, the plate thickness of the welding base material 1 was set to 16 mm.

First, a solid wire having a chemical composition shown in the following Tables 1 and 2 and having a diameter of 1.6 mm was used.
The welding base metal having the chemical composition shown in Tables 3 and 4 below is shown in FIG.
Automatic TIG shown in Table 5 below
The weld metal was formed at the groove by welding under the welding conditions. However, during TIG welding, the polarity was set to DCEN, and 100% Ar gas was used as a shielding gas. In addition, solid wire has C
u plating was applied. The total amount of Cu and Cu plating in the wire was about 0.15% by weight.

Next, after the obtained weld metal is subjected to a heat treatment at a temperature of 740 ° C. for 1 hour, test pieces for various mechanical tests are collected from the weld metal, and the room temperature strength is evaluated. Three types of mechanical tests were performed: a room temperature tensile test, a Charpy impact test for evaluating toughness, and a creep rupture test for evaluating creep strength. These test pieces had the shapes shown in Table 6 below, and were all taken from the center of the thickness of the formed weld metal.

The evaluation results of these mechanical tests are shown in Table 7 below.
Shown in However, in Table 7 below, when the room temperature tensile strength was 600 (N / mm ² ) or more, it was judged to be good. Regarding toughness, the case where the absorbed energy at 0 ° C. was 250 J or more was judged to be good. Further, regarding the creep rupture strength, the applied stress was set to 196.
(N / mm ² ), a creep rupture test was conducted at a test temperature of 600 ° C., and a case where the rupture time was 1000 hours or more was judged to be good.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

[Table 6]

[0042]

[Table 7]

As shown in Tables 1, 2 and 7 above, Example No. 1 to 8 are the chemical composition and W content of the wire and M
Since the ratio to the o content was appropriately regulated, all of the weld metals had excellent room-temperature tensile strength, toughness, and creep strength.

On the other hand, in Comparative Example No. No. 9 shows that the content of C and Cr in the wire is less than the lower limit of the range of the present invention,
Since the content exceeds the upper limit of the range of the present invention, all of the tensile strength, toughness and creep strength of the weld metal decreased.
Comparative Example No. In No. 10, since the content of Si and S in the wire was less than the lower limit of the range of the present invention, the bead shape and conformability of the bead became extremely poor, and undercut frequently occurred.
Therefore, no mechanical tests were performed. Comparative Example No. 1
In No. 1, since the Mn content in the wire is less than the lower limit of the range of the present invention and the Al and N contents are more than the upper limit of the range of the present invention, the strength of the weld metal is excessively increased and the toughness is remarkably increased. Dropped.

Comparative Example No. 12 is Si, M in the wire
Since the contents of n, P, S and Cr exceed the upper limit of the range of the present invention, the toughness of the weld metal is significantly reduced,
The creep strength was also low. Comparative Example No. In No. 13, the Ni content in the wire exceeded the upper limit of the range of the present invention, and the contents of Mo, W, and V were less than the lower limit of the range of the present invention, so that the creep strength of the weld metal was significantly reduced. Comparative Example No. In No. 14, since the contents of C and Mo in the wire exceeded the upper limit of the range of the present invention, the strength of the weld metal was excessively increased and the toughness was significantly reduced.

Comparative Example No. In No. 15, since the contents of W and V in the wire exceeded the upper limit of the range of the present invention, the strength of the weld metal was excessively increased and the toughness was significantly reduced. Comparative Example No. In No. 16, Nb, Ti and B were added to the wire beyond the preferred range of the present invention, so that the strength of the weld metal was excessively increased and the toughness was significantly reduced. Comparative Example No. In No. 17, since [W] / [Mo] exceeded the upper limit of the range of the present invention, the strength of the weld metal was excessively increased, and the toughness was significantly reduced. Comparative Example No. 18 is [W] / [M
o] is less than the lower limit of the range of the present invention, so that the creep strength of the weld metal is reduced.

[0047]

As described in detail above, according to the present invention,
Since the composition of the TIG welding wire for heat-resistant steel is properly specified and the ratio of the W content to the Mo content in the wire is specified, the heat-resistant steel to which W is added using this TIG welding wire is used. When welding steel, room temperature strength after heat treatment,
A weld metal having good toughness and creep strength can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a shape of a welding base material used in the present embodiment.

[Explanation of symbols]

 1: welding base metal 2: backing metal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Nakagawa 100-1 Urakawachi, Miyama-ji, Fujisawa-shi, Kanagawa Prefecture Inside the Kobe Steel Fujisawa Plant (72) Inventor Akinobu Goto 100 Urakawachi, Miyamae, Fujisawa-shi, Kanagawa No. 1 Kobe Steel Ltd. Fujisawa Works

Claims (3)

[Claims] 1. C: 0.05 to 0.15% by weight, S
i: 0.1 to 1.0% by weight, Mn: 0.3 to 1.5
% By weight, S: 0.001 to 0.01% by weight, Cr:
1.7 to 3% by weight, Mo: 0.45 to 1% by weight,
W: 0.1 to 1.2% by weight and V: 0.1 to 0.5
% Of P, 0.01% by weight or less of P, and 0.2% of Ni.
25 wt% or less, Al 0.01 wt% or less, O
The content of N is regulated to not more than 02% by weight and the content of N is set to 0.015% by weight or less, and the balance is composed of Fe and unavoidable impurities. When the amount is [Mo] in weight%, [W] / [M
o] is 0.2 to 2.6. 2. The TIG welding wire according to claim 1, further comprising B: 0.0005 to 0.01% by weight. 3. Nb: 0.05% by weight or less and T
2. The composition according to claim 1, further comprising at least one element selected from the group consisting of i: 0.05% by weight or less.
Or the TIG welding wire for heat-resistant steel according to 2.