JP2000271785A - WELDING MATERIAL FOR HIGH Cr FERRITIC BASE HEAT RESISTANT STEEL, TIG WELDING ROD COMPOSED OF THIS MATERIAL, SUBMERGED ARC WELDING ROD, WIRE FOR WELDING AND COATED ARC WELDING ROD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding material, with which the sound welding part is obtd. while keeping the high temp. strength corresponding to 9.Cr-2.W steel and the welding of pressure resistant parts of a boiler tube, piping and devices usable in the steam condition of >=600 deg.C, such as an extra supper critical power plant is suitably executed. SOLUTION: The welding material for high ferritic base heat resistant steel has the chemical components contained by wt.% of 0.01-0.12 C, 0.25-0.50 Si, 0.10-<0.30 Mn, 8.0-9.5 Cr, 0.30-<0.50 Mo, 1.50-2.00 W, 0.15-0.25 V, 0.04-0.09 Nb, 0.001-0.006 B, 0.030-0.050 N, 0.40-0.60 Ni, 0.25-1.50 Co, <=0.04 Al and in the case the above chemical components except Cr, C and Co become the average value in each range, the Cr, C and Co are to satisfy the formula 14Cr-220C-7 Co<=100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding material used for welding equipment such as boiler tubes, pipes and valves used in an ultra-supercritical power plant.

[0002]

2. Description of the Related Art The temperature and pressure of steam in a power plant greatly affect the thermal efficiency of the power plant. In Japan, the pressure of a power plant of 450,000 KW or more constructed after 1967 is 246 kg / cm. ^2. Supercritical pressure steam conditions of temperature: 538-566 ° C have been adopted. However, since the oil crisis, since 1970, ultra-supercritical power plants have been constructed to further increase the steam pressure and temperature conditions and improve power generation efficiency. This became possible because
Like 9Cr-2Mo steel and improved 9Cr-1Mo steel,
This is because expensive ferritic heat-resistant steel containing no Ni was developed.

[0003] The steam conditions of an ultra-supercritical power plant are as follows: first step: 316 Kg / cm ² × 566 ° C, second step: 316 Kg / cm ² × 593 ° C, third step:
It is planned to gradually increase the temperature and pressure to 352 Kg / cm ² × 649 ° C. However, in reality, the second
In the process of shifting from the step to the third step, for example,
It is tempting to adopt intermediate temperature conditions such as the 621 ° C level.

In response to the high temperature and high pressure of these steam conditions, an improved 9Cr-1Mo steel (forged steel: American Society for Testing and Materials [ASTM] standard: F91, cast steel standard: C1) is now available.
By applying 2A), a power plant up to the second step has been constructed. However, since the use limit temperature of this 9Cr-1Mo steel is about 600 ° C., in an ultra-supercritical power plant, this steel must be used in a temperature range of 600 ° C. or less. Research and development of ferritic steels that can be used under the above steam conditions are underway.

As a result of this study, it has been found that to improve the creep strength required to use the improved 9Cr-1Mo steel at a temperature level of 600 ° C. or higher, the improved 9Cr-1M
It has been found that the steel in which the Mo content of the Mo steel in the o steel is reduced to about 0.5% by weight and W is added to about 1.8% by weight instead is excellent.

[0006] This ferritic steel is SUS316H
Compared to an austenitic steel such as (JIS standard), it has a high temperature strength up to 650 ° C. and is inexpensive because it does not contain Ni.
This steel grade is the American Society of Mechanical Engineers (hereinafter referred to as "ASME").
The chemical composition of Seamless 9Cr-2W steel is standardized in the code case 2179 of
And C: 0.07 to 0.13, Mn: 0.30 to 0.6
0, Si ≦ 0.50, P ≦ 0, 020, S ≦ 0.01
0, Cr: 8.50 to 9.50, Mo: 0.30 to 0.
60, W: 1.50 to 2.00, Ni ≤ 0.40, V:
0.15 to 0.25, Nb: 0.04 to 0.09, N:
0.03 to 0.07, Al ≦ 0.040, B: 0.00
1 to 0.006. This steel type is defined for seamless tube and pipe materials, and contains N up to 0.07% by weight in the chemical composition.

On the other hand, as a welding material for steel as described above, at present, generally, a high Mn-based steel material in which Mn and Ni are increased is used, and its chemical composition is expressed by weight%.
And C: 0.08, Mn: 1.63, Si: 0.32,
P: 0.007, S: 0.002, Cr: 8.99, M
o: 0.49, W: 1.41, Ni: 0.56, V:
0.31, Nb: 0.06.

[0008]

However, this high Mn steel has a creep strength of 9Cr-
There was a disadvantage that it was inferior to 2W steel.

On the other hand, in the development of welding materials for high-temperature and high-pressure equipment, 1) Among high-temperature strengths, there is a demand for mechanical properties such that creep strength is equivalent to that of a base material and ductility and toughness are high. In addition, 2) it is necessary to solve the problem of manufacturability that is excellent in welding workability.

Therefore, in the development of a welding material of this steel type, in order to maintain good mechanical properties, it is necessary to add an appropriate element for preventing the formation of δ ferrite in the welded portion and increasing the creep strength. In addition, in order to maintain good weldability, it is necessary to prevent the occurrence of defects such as cracks at the time of welding and to limit appropriate elements in order to prevent the occurrence of blowholes (bubbles). . .

Accordingly, the present invention has been made in order to solve the above-mentioned problems, and it has been found that a sound welding portion can be obtained while maintaining a high-temperature strength corresponding to 9Cr-2W steel, such as an ultra-supercritical power plant.
Boiler tubes that can be used under steam conditions of 00 ° C or higher,
An object of the present invention is to provide a welding material used for welding pressure-resistant parts of piping and equipment.

[0012]

According to a main aspect of the present invention, a welding material for a high Cr ferritic heat-resistant steel has a chemical composition in weight% and C: 0.0%.
6-0.12, Si: 0.25-0.50, Mn: 0.
10 to less than 0.30, Cr: 8.0 to 9.5, Mo:
0.30 to less than 0.50, W: 1.50 to 2.00,
V: 0.15 to 0.25, Nb: 0.04 to 0.09,
B: 0.001 to 0.006, N: 0.030 to 0.0
50, Ni: 0.40 to 0.60, Co: 0.25 to
1.50, Al: 0.04 or less, and when the chemical components other than Cr, C, and Co have average values within the respective ranges, the Cr, C, and Co are 14Cr-220C-7Co. ≦ 100.

The welding material for high Cr ferritic heat resistant steel may further contain, by weight%, a chemical component Ce: 0.02-0.
Preferably, it contains 10. In addition, the above-mentioned welding materials for high Cr ferritic heat resistant steel can be applied to a welding rod, a submerged arc welding rod, a welding wire, and the like.

[0014] Further, a coating material containing at least one of an arc stabilizer, a slag forming agent, and a binder other than the above-mentioned chemical components is added to the welding material for high Cr ferritic heat resistant steel. It is also preferable to apply to a covered arc welding rod and the like.

[0015]

When the high Cr ferritic heat-resistant steel welding material has the above-mentioned chemical composition, δ ferrite is suppressed in the material forming process, the creep strength and the like are not reduced, and the generation of cracks and blow holes is prevented. A sound weld can be obtained while maintaining high-temperature strength.

Further, by adding Ce to each of the above-mentioned cast steel materials for the pressure-resistant part, oxides generated on the surface of the welded part can be fixed and hardly peeled off. Therefore, it is also possible to prevent the erosion of the welded part and the equipment by the thin pieces formed by peeling.

Further, a TIG welding rod and a submerged arc welding rod used for welding such a welding material for high Cr ferritic heat-resistant steel to a pressure-resistant part used under high-temperature and high-pressure conditions such as an ultra-supercritical power plant. If a coating material such as an arc stabilizer is further added to a welding wire or a welding material and applied to a coated arc welding rod, the high-temperature strength and pressure resistance are excellent, so that highly reliable welded parts and devices are used. Is obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a high Cr
The basis for selecting the ratio of each chemical component in the welding material for ferritic heat-resistant steel is described.

The inventor of the present invention melted steel having various chemical components by using a high-frequency electric melting furnace having a capacity of 1 ton to obtain Φ310
A disk-shaped specimen of × 110 mm was cast, and the relationship between the chemical composition of 9Cr-2W steel and the amount of δ ferrite and the occurrence of blowholes were examined. If δ ferrite can be suppressed, the creep strength and the like will not be reduced, and a material excellent in pressure resistance while maintaining high temperature strength can be obtained.

Next, based on the results, a welding material having extremely low δ ferrite and high creep strength was manufactured, and a welding work test and a creep test as a basis for determining the high temperature strength of the steel material were performed. Thus, the welding material for high Cr ferritic heat resistant steel according to the present invention was completed.

First, suppression of δ ferrite will be described. The amount of δ ferrite of 9Cr-based steel is generally expressed by Cr equivalent (Creq). The Cr equivalent is obtained by classifying the chemical components of steel into ferrite-forming elements and austenite-forming elements. Various empirical formulas have been proposed in which the generating abilities are expressed in a fixed ratio, and in the present test, the following formula (1) was applied as the Cr equivalent. Creq% = (14Cr + 6Si + 5Mo10W + 18V + 90Nb + 54Al) −220 (C + N) −20Ni−6Mn−7Co−146 (1) In this equation (1), the element in parentheses before is a ferrite forming element, The element with the symbol (-symbol) is an austenite-forming element.

Next, the δ ferrite and the chemical composition of Cr
The relationship between the equivalent% and 9Cr-2W steel and 9Cr-2W-
The test results obtained for Co cast steel are shown in FIG. As shown in this figure, the relationship between the Cr equivalent and the δ ferrite is well represented by equation (2).

Δ% = 170 exp 0.107 Creq (2) As shown in FIG. 1, the chromium equivalent (δ ferrite: δ ferrite: δ ferrite of these steels does not actually deteriorate the mechanical properties)
3% or less) is calculated by using equation (2).
It turns out that it is 37.7% or less.

On the other hand, since the welded portion solidifies after welding and is not subjected to forging such as rolling, if a defect such as a blowhole occurs during welding, the defect remains in the product as it is. Therefore, for the welding material, the N content in the steel needs to be particularly strictly controlled. This is because if the content of N is large, blow holes are likely to occur. FIG.
Indicates the allowable amount of N when the molten steel of the Cr-containing steel solidifies. As shown in this figure, the upper limit of the N content at which 9% Cr steel can be solidified without generating blowholes is 0.05%.

Therefore, in consideration of the above points, the ratio of chemical components was selected as follows in order to manufacture the steel for welding material for high Cr ferritic heat resistant steel according to the present invention.

N (nitrogen) mainly combines with V to form VN
(Vanadium nitride) and NbN (niobium nitride), which are elements that increase the creep strength at 600 to 650 ° C. When N is 0.01%, VN is not sufficiently generated, so that the creep strength is not improved. However, even when N is 0.02%, if V is 0.15 to 0.25%, the creep strength is improved. On the other hand, as mentioned above,
From the viewpoint of preventing blowholes, the maximum content of N in the welding material needs to be 0.05%. For this reason, the range of the content of N is 0.03 to 0.0
5%.

Cr (chromium) enhances the oxidation resistance of the present steel to enable its use at 600 ° C. or higher, and converts the matrix (hereinafter, referred to as “base”) into martensite to form C. Is an important element from the viewpoint of forming a strong carbide by combining with and increasing the high-temperature strength. On the other hand, in the welding material, in order to prevent the generation of air bubbles, the content of Si is set at 0.25%.
Add above. Since this Si has an oxidation resistance like Cr, even if the amount of Cr is reduced by an amount corresponding to the amount of Si, the oxidation resistance can be maintained. For example, Si: 0.1%, Cr: 9
% Steel has an oxidation resistance of 0.3% for Si and 8.0% for Cr.
Is equivalent to steel. For this reason, the lower limit of Cr is set to 8.0%.
And the upper limit is 9.5%. Therefore, the component range of Cr is set to 8.0 to 9.5%.

Mo (molybdenum) and W (tungsten) are effective for improving the creep strength by forming a solid solution in the present steel. The effect is as follows: Mo equivalent = Mo + ／.
In W, the best results are obtained when the Mo equivalent is 1.5%. However, even if W is added at 2% or more, the creep strength does not increase any more, so Mo: 0.30 to 0.50%
, W: 1.50 to 2.00%.

V (vanadium) combines with N to form VN
(Vanadium nitride) and significantly improve creep strength. However, when the V amount is 0.15% or less, precipitation of VN is small, and Cr ₂ N precipitates, and the creep strength is not improved. On the other hand, when the V amount is 0.25%, N
When the amount is up to 0.06%, the creep strength is improved due to bonding as VN, but the strength is not increased by adding more. Therefore, the added amount of V is set to 0.15 to 0.25%.

When Nb (niobium) is contained in a small amount in the steel, fine Nb (C, N) (carbonitride of niobium) is generated, and the creep strength is improved by a synergistic effect with VN. However, when it is contained in a large amount, Nb (C, N) which does not form a solid solution in the steel is generated to reduce the precipitation amount of VN, or Nb (N, C) becomes coarse and coarse. Decreases creep strength. Therefore, the Nb content is set to 0.1.
04 to 0.09%.

C (carbon) combines with Cr to form a martensitic structure, and combines with Cr, Mo, V and Nb to form carbides, and is important in increasing the high-temperature strength of the steel. However, when contained in a large amount, the ductility decreases and the weldability also decreases. However, as shown in equation (1), C is an element having the greatest ability to generate austenite at a high temperature equal to or higher than the A _C3 transformation point.
12%, and the lower limit is 0.06%. That is, in the formula (1), when the chemical components other than Cr, C, and Co take an average value, the conditional expression in which the δ ferrite is 3% or less is represented by the formula (3).

14Cr-220C-7Co ≦ 100 (3) In the formula (3), Cr: 8.75% (average value),
When Co: 1.50 (maximum value), C ≧ 0.0
Since it is 55%, the lower limit of C is set to 0.06%. Therefore, the C content is set to 0.06 to 0.12%.

[0033] Si (silicon) is used as a deoxidizing agent for molten steel during steelmaking, is an essential element for preventing the occurrence of blowholes, and prevents high-temperature oxidation of products when used. Here, in order to prevent the occurrence of blowholes in the welding material, the lower limit of the amount of Si is set to 0.25%.
And On the other hand, Si increases the hardness of the base of the welded portion, so that if a large amount of Si is added, the weldability is reduced. In addition, Si promotes the decomposition and aggregation of carbides when the product is used, and lowers the creep strength. Therefore, the amount of Si is
0.25 to 0.50%.

Mn (manganese) has the effect of removing oxygen during the steelmaking process, and also combines with S (sulfur) to form a compound called MnS, thereby preventing S from adversely affecting the strength of the steel. However, Mn is also an austenite forming element and suppresses the formation of δ ferrite. However, when Mn is contained in a large amount, it promotes the decomposition and agglomeration of carbides and lowers the creep strength. Therefore, Mn is
0.10 to less than 0.30%.

Since Ni (nickel) is an element having a large austenite forming ability, it suppresses the formation of δ ferrite. However, when this element is added, the A _C1 transformation point, which is the temperature at which austenitization starts, per 1% of Ni content Decreases by 30 ° C. The A _C1 transformation point of 9Cr steel containing about 0.1% of C amount is 820 to 840 ° C., and the tempering temperature is set to be lower than the A _C1 transformation point. Tempering temperature is too low. Also, the Ni content is 1%
Addition of the above promotes decomposition and aggregation of carbides and lowers creep strength. Regarding the weldability, when the Ni content is 0.6% or more, cracking during welding is promoted.
Therefore, the component range of Ni is set to 0.40 to 0.60%.

Co (cobalt) is represented by the following formula (1):
It is an austenite forming element. When Co is added, the δ ferrite decreases according to the equation (1), and thus the lower limit of C can be reduced. The effect of Co on the A _C1 transformation point is to decrease by 5 ° C. per 1% of Co content.
Much smaller than i. In addition, Co combines with carbon to form carbides, thereby improving the creep strength of steel. However, when Co is added in a large amount, on the contrary, the decomposition and agglomeration of carbides are promoted to lower the creep strength. Therefore, the component range of Co is 0.25 to 1.50%.
And

B (boron) is an element that enhances the hardenability of a steel material and promotes the formation of martensite in a welded portion. However, if contained in a large amount, the weldability is reduced. Therefore, the B content is set to 0.001 to 0.006%.

Al (aluminum) is the most excellent element as a deoxidizing material in steel making. However, if contained in a large amount, it promotes the decomposition and aggregation of carbides and lowers the creep strength. %.

Ce (cerium) is a rare earth metal, but is a metal that is easily oxidized like Al, and also acts as a deoxidizer. However, this Ce oxide is mainly present at the crystal grain boundaries, and has the effect of fixing the oxide mainly composed of Cr, which is an oxide generated on the surface of the product, and making it difficult to peel off. For this reason, the oxides on the product surface are less likely to be separated due to the stoppage of the start-up of the plant, and it is also possible to prevent the erosion of the equipment due to the flakes formed by the separation. Also, by fixing Cr oxide, C
Increase the oxidation resistance effect of r. Such an effect of Ce appears from 0.02% by weight%, but if contained in a large amount in the material, Ce itself promotes oxidation, so the upper limit is set to 0.10%. As a result, the component range of Ce is set to 0.02 to 0.10%.

From the above considerations, it can be seen that the high Cr
The chemical composition of the 9Cr-2W welding material steel as a welding material for ferritic heat-resistant steel is expressed in terms of% by weight, C: 0.06-
0.12, Si: 0.25 to 0.50, Mn: 0.10
Less than 0.30, Cr: 8.0 to 9.5, Mo: 0.3
0 to less than 0.50, W: 1.50 to 2.00, V: 0.
15 to 0.25, Nb: 0.04 to 0.09, B: 0.
001 to 0.006, N: 0.030 to 0.050, N
i: 0.40 to 0.60, Co: 0.25 to 1.50,
Al: 0.04 or less was selected.

A welding material for high Cr ferritic heat-resistant steel was also selected in which Ce was added to the above chemical composition at 0.02 to 0.10% by weight.

The inventor of the present invention has found that, as a welding material for high Cr ferritic heat-resistant steel, a steel material having the chemical composition clarified from the above description is obtained by using a high-frequency electric furnace having a capacity of 1 ton and a single material of 100 kg of φ310 mm × 120 mm. Was melted by four heats of A, B, C, and D, and a 3.2 to 4Φ Tail welding rod was produced from this test piece. In addition, Table 1 attached at the end of the detailed description of the invention of this specification shows the chemical composition of the manufactured welding rod.

Using these prepared welding rods, FIG.
9Cr of 150 width x 150 length x 20 thickness as shown in
-2W steel base material is welded, and the tensile test specimen, impact test specimen, and weldability test specimen (Weld Procedu) of the welded joint specified in ASME Chapter 9 Article 2 (Sec IX, Article 2)
re Qualification Tests) were processed to conduct a weldability test.

The test results are shown in Tables 2 to 4 attached at the end of the detailed description of the invention in this specification. As can be seen from these tables, the test pieces welded with the welding rods produced from each heat satisfied all the standard values. That is, it was proved that the weldability and mechanical properties of the present invention were good.

Next, a creep test was performed by processing the creep test piece from the deposited metal. FIG. 4 shows a comparison of the creep rupture strength between the conventionally used high Mn welding rod and the material of the present invention. Show. In FIG. 4, the horizontal axis is a Larson-Miller parameter,
Is the absolute temperature (° K) of the creep test temperature, and t is the rupture time (h). The vertical axis indicates the creep rupture stress (MPa), and the higher the line segment is, the higher the creep rupture strength is.

As shown in FIG. 4, the creep rupture strength of the welding material of the present invention is equivalent to that of the base material of 9Cr-2W, and the above-described high Mn which has been conventionally applied to welding of this steel type. The value was much larger than that of the base steel welding material.

In the oxidation test at 650 ° C., the effect of Ce was that the peeling of the oxide when 0.04% of Ce was added was significantly reduced as compared with the case where Ce was not contained.

[0048]

The welding material for high Cr ferritic heat resistant steel according to the present invention having the chemical composition as described above suppresses δ ferrite in the material forming process, does not reduce creep strength and the like, and also has cracks and blowholes. By preventing the occurrence of cracks, a sound welding material and a welded part having excellent pressure resistance while maintaining high-temperature strength can be obtained.

Also, by adding Ce to the above-mentioned pressure-resistant part cast steel material, oxides generated on the product surface are fixed,
It can be hard to peel off. Therefore, it is possible to prevent the erosion of the welded part and the equipment by the thin pieces formed by peeling.

Further, a TIG welding rod or a submerged arc welding rod used for welding such a welding material for high Cr ferritic heat-resistant steel to a pressure-resistant portion used under high-temperature and high-pressure conditions such as an ultra-supercritical power plant. If a coating material such as an arc stabilizer is further added to a welding wire or a welding material and applied to a coated arc welding rod, the high-temperature strength and pressure resistance are excellent, so that highly reliable welded parts and devices are used. Is obtained.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Brief description of the drawings]

FIG. 1 Cr equivalent (Creq%) determined from test results
FIG. 4 is a diagram showing the relationship between and δ ferrite.

FIG. 2 is a graph showing the solubility of N in a Cr-based steel.

FIG. 3 is a view showing the shape and dimensions of a 9Cr-2W welding base material.

FIG. 4 is a diagram comparing creep rupture strengths of the welding rod according to the present invention, a 9Cr-2W base metal, and a conventional high Mn welding rod.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsumi Hirano 1-14 Nakamachi, Moji-ku, Kitakyushu City, Fukuoka Prefecture Inside Okano Valve Manufacturing Co., Ltd. (72) Kazuhiro Takemoto 1-14 Nakamachi, Moji-ku, Kitakyushu City, Fukuoka Okano Valve Manufacturing Co., Ltd.

Claims (6)

[Claims] 1. The chemical component in weight%, C: 0.06 to
0.12, Si: 0.25 to 0.50, Mn: 0.10
Less than 0.30, Cr: 8.0 to 9.5, Mo: 0.3
0 to less than 0.50, W: 1.50 to 2.00, V: 0.
15 to 0.25, Nb: 0.04 to 0.09, B: 0.
001 to 0.006, N: 0.030 to 0.050, N
i: 0.40 to 0.60, Co: 0.25 to 1.50,
Al: not more than 0.04, and when the chemical components other than Cr, C, and Co have average values within the respective ranges, the Cr, C, and Co are in the relationship of 14Cr-220C-7Co ≦ 100. Welding material for high Cr ferritic heat resistant steel that satisfies the formula. 2. The chemical component Ce: 0.0% by weight.
The welding material for high Cr ferritic heat-resistant steel according to claim 1, which contains 2 to 0.10. 3. High Cr according to claim 1 or claim 2.
Tail welding rod made of welding material for heat resistant ferritic steel. 4. High Cr according to claim 1 or claim 2.
Submerged arc welding rod made of welding material for ferritic heat resistant steel. 5. High Cr according to claim 1 or claim 2.
Welding wire made of welding material for heat resistant ferritic steel. 6. High Cr according to claim 1 or claim 2.
A coated arc welding rod further comprising a welding material for heat-resistant ferritic steel, further comprising a coating agent containing at least one of an arc stabilizer, a slag forming agent, and a binder other than the above chemical components.