JP3281685B2 - Hot bolt material for steam turbine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-temperature bolt material for a steam turbine for thermal power generation. More specifically, the present invention provides:
The present invention relates to a bolt material suitable for use under a high temperature condition, which constitutes a bolt for fastening a cabin constituting a steam turbine.

[0002]

2. Description of the Related Art Bolt materials used in steam turbine plants for thermal power generation are mainly 12Cr steel used in a low temperature range (500 ° C. or lower), and superalloy refractoalloy 26 (37Ni-20Co) used in a high temperature range. -18Cr) or nickel-based superalloy Nimonic 80A. Of these, 12Cr steel for low temperature is difficult to use at a temperature of 500 ° C or higher, and as a bolt material used at a high temperature exceeding 500 ° C, the superalloy refracto alloy 26 or Nimonic 80A shown here is used. Limited.

[0003] Of these, refracto alloy 26 has been widely used as a high-temperature bolt material because it has excellent high-temperature strength and high-temperature ductility. However, when used for tightening the casing of a steam turbine, this material has a large coefficient of thermal expansion, so the difference in thermal expansion between the material and the casing material reduces the tightening force of the casing and causes steam leakage. It has become. Refractoalloy 26 is a high cost material because it contains a large amount of cobalt (about 20%).

On the other hand, Nimonic 80A is a nickel-based superalloy, has good high-temperature strength, and has a thermal expansion coefficient not so large as that of Refract Alloy 26, and therefore has a small difference in thermal expansion coefficient from that of the casing material ( As a result, the tightening force of the passenger compartment is not reduced), and since it does not contain cobalt, there is an advantage that the cost is lower than that of the refract alloy 26. However, this material has low ductility at high temperatures and is liable to crack during use.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a high-temperature strength and high-ductility ductile material having a small difference in the coefficient of thermal expansion from a ferrite (CrMo, 12Cr, etc.) or martensitic casing material. It is intended to provide a high-temperature bolt material which can be used at a high temperature of not less than ° C.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found an excellent high-temperature bolt material which can satisfy the above-mentioned characteristics required particularly for use in a steam turbine for thermal power generation. Reached.

[0007] The high-temperature bolt material for a steam turbine of the present invention comprises:
0.04 to 0.10% carbon and 1% or less silicon by weight percentage
Bottom, manganese 1% or less, chromium 18-21%, aluminum
0.7-1.3%, titanium 1.3-1.8%, iron
1,5% or less and inevitable impurities and nickel residue
After hot forging after melting, 1000-112
Solution treatment at 0 ° C, first stage aging at 820-880 ° C
Treatment, second stage aging treatment at 700-750 ° C., and 60
It is characterized by being subjected to the third stage aging treatment at 0 to 650 ° C.
I do .

Further , a high-temperature bolt material for a steam turbine according to the present invention.
Is 0.04 to 0.10% carbon by weight, silicon 1
%, Manganese 1% or less, Chromium 18-21%, Al
0.7-1.3% of minium, 1.3-1.8% of titanium,
Iron 1.5% or less, phosphorus 0.01% or less, sulfur 0.00
Less than 5% and composed of unavoidable impurities and nickel residue
After hot forging after melting, 1000-1120
Solution treatment at 820 ° C., first stage aging at 820-880 ° C.
Aging at 700 to 750 ° C., and 600
Characterized by being subjected to a third stage aging treatment at ~ 650 ° C.
You .

Further, a third object of the present invention is to provide the above-mentioned high-temperature bolt material, which is subjected to hot forging after melting and then to 1000
Solution treatment at ~ 1120 ° C, first stage aging at 820-880 ° C, second stage aging at 700-750 ° C, and third stage aging at 600-650 ° C To provide a high-temperature bolt material.

[0010]

The present inventors have obtained a high-temperature bolt material having excellent characteristics by limiting the components and further limiting the heat treatment using Nimonic 80A as a basic component.

The reasons for limiting the composition ratio of each constituent element in the bolt material of the present invention will be described below. Carbon: C forms carbides and contributes to improvement in high-temperature strength. However, if it is less than 0.04%, a sufficient effect cannot be obtained, and if it exceeds 0.10%, excessive carbides are formed and the toughness is reduced, so that the content is made 0.04 to 0.10%. Silicon: Si is an element necessary as a deoxidizing material. But,
Since excessive addition of Si causes creep embrittlement and the like, the content is set to 1% or less. Manganese: Mn is also an element useful as a deoxidizer. If this element is added more than necessary, the toughness is reduced, so that the content is set to 1% or less. Chromium: Cr forms carbides and contributes to improvement in high-temperature strength, and also dissolves in the matrix to improve oxidation resistance. If it is less than 18%, the effect is not enough, and 21%
If exceeding the value, embrittlement is caused. Aluminum: Al forms a γ '[Ni ₃ (Al, Ti)] phase which is an intermetallic compound with Ni and Ti in the matrix, and contributes to improvement in high-temperature strength. For this reason, from the viewpoint of high-temperature strength, it is better to have more. If it is less than 0.7%, the precipitation amount of the γ 'phase is small, and sufficient high-temperature strength cannot be obtained. Meanwhile, 1.3%
If it exceeds, ductility in creep rupture decreases. Therefore, the content is set to 0.7 to 1.3%. Titanium: Ti forms a γ '[Ni ₃ (Al, Ti)] phase with Al and Ni. The content of Ti greatly affects high-temperature strength and ductility. That is, when the Ti content increases, the temperature is from room temperature to
Strength up to high temperatures is improved. However, ductility decreases with increasing Ti content. In the material of the present invention in which the amount of Al is lower than the conventional material to improve the creep rupture ductility,
If the Ti content is less than 1.3% from the balance with Al, sufficient strength cannot be obtained. When added in an amount exceeding 1.8%, the creep ductility decreases. Therefore, it was set to 1.3 to 1.8%. Phosphorus and sulfur: P and S are impurities mixed from scrap during the steel making stage. These elements are low-melting elements and preferably appear at the grain boundaries and reduce the grain boundary strength. Therefore, when a creep rupture test is performed on a material rich in P and S, the creep rupture strength is inferior due to fragile grain boundaries, and sufficient creep rupture ductility cannot be obtained. P is 0.01% or less,
When S is set to 0.005% or less, the adverse effect hardly appears. Therefore, it is preferable that P is 0.01% or less and S is 0.005% or less.

Next, the reasons for limiting the heat treatment will be described.

When a bolt material is manufactured with the composition according to the present invention, the form of the precipitate such as the γ 'phase changes depending on the heat treatment method, which greatly affects the mechanical properties and creep rupture characteristics. Therefore, the present inventors have conducted intensive studies on the heat treatment conditions. As a result, after performing the solution treatment, a three-stage aging treatment is performed to sufficiently stabilize the precipitates, so that stable ductility without deteriorating high-temperature strength can be obtained. The knowledge that it can be obtained was obtained. Details will be described in Examples.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

The bolt material of the present invention is based on Nimonic 80A, a nickel-base superalloy, and by changing its components, it is possible to produce a high-strength bolt material having excellent creep ductility.

Table 1 summarizes the chemical components of the materials subjected to the test. All materials were melted in a 50 Kg vacuum high-frequency melting furnace, then forged at high temperatures, and subjected to various tests. Table 2 shows the mechanical properties of each test material at room temperature.

[0017]

[Table 1]

[0018]

[Table 2]

From these results, the material of the present invention is stable in strength and satisfies 60 kgf / mm ² or more with 0.2% proof stress. Also, there is little variation in ductility and toughness, and stable values are obtained. On the other hand, the comparative material has sufficient strength, but is inferior in ductility and toughness (material numbers 7, 12, 13), and has insufficient mechanical strength (material numbers 8, 9, 10). Has become.

Table 3 shows the results of the creep rupture test at 600 ° C.

[0021]

[Table 3]

It can be seen that the material of the present invention has a longer rupture time than the comparative material and has a high creep rupture strength. Some of the comparative materials show high creep rupture strength, such as material No. 7, but have low creep rupture ductility (material Nos. 7, 12, 13) and are judged to be unsuitable as high-temperature structural materials. You.

Further, when the ductility at break is compared, the three-stage aging material shows higher breaking elongation and reduction than the two-stage aging material, and the above-mentioned three-stage aging treatment is more preferable as the heat treatment. It can be seen that it is.

[0024]

The bolt material according to the present invention has excellent high-temperature strength and good ductility and toughness.
Highly reliable high-temperature bolt material that can be used at temperatures exceeding According to the present invention, in addition to contributing to the production of an ultra-high-temperature steam turbine that is to be produced in large numbers in the future,
It is also industrially beneficial from the viewpoint of ensuring high reliability of the bolt material of a normal steam turbine.

Continuation of the front page (56) References JP-A-4-187363 (JP, A) JP-A-63-86841 (JP, A) JP-A-4-198444 (JP, A) JP-A-61-69954 (JP, A) , A) JP-A-55-31130 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 19/05 C22F 1/10 F16B 35/00

Claims (2)

(57) [Claims] (1) a carbon content of 0.04 to 0.10% by weight;
Silicon 1% or less, manganese 1% or less, chromium 18-21
%, Aluminum 0.7-1.3%, titanium 1.3-
It consists of 1.8%, iron 1,5% or less, inevitable impurities and nickel residue, and after hot forging after melting, 10 %
Solution treatment at 00 to 1120 ° C, 820 to 880 ° C
First-stage aging treatment, second-stage aging treatment at 700 to 750 ° C.
And a third stage aging treatment at 600 to 650 ° C.
A high-temperature bolt material for a steam turbine, comprising: 2. A carbon content of 0.04 to 0.10% by weight,
Silicon 1% or less, manganese 1% or less, chromium 18-21
%, Aluminum 0.7-1.3%, titanium 1.3-
1.8%, 1.5% iron or less, 0.01% phosphorus less, 0.005% sulfur or less and consists unavoidable impurities and nickel balance, after performing a dissolution after hot forging, 1000
Solution treatment at 1120 ° C., first at 820-880 ° C.
Stage aging, second stage aging at 700 to 750 ° C, and
Steam turbine high temperature bolt member, characterized in that subjected to a 3-stage aging treatment at beauty 600 to 650 ° C..