JPH09194987A - Low alloy heat resistant steel and steam turbine rotor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low alloy heat resistant steel for a steam turbine rotor high in toughness and furthermore excellent in high temp. strength at a low cost by using specified metals by specified weight ratios. SOLUTION: This low alloy heat resistant steel is the one having a compsn. contg., by weight, 0.005 to <0.15% carbon, 0.005 to 0.3% silicon, 0.01 to 1.0% manganese, 0.8 to <1.5% chromium, 0.1 to 2.0% nickel, 0.05 to 0.3% vanadium, 0.1 to 1.5% molybdenum and 0.1 to 2.5% tungsten and iron. Or, it is the one in which a part of the above iron is substituted by one or more kinds among, by weight, 0.01 to 0.15% niobium, 0.01 to 0.15% tantalum, 0.01 to 0.1% nitrogen and 0.001 to 0.03% boron. Or, it is the one in which the above nickel is substituted by iron and contg. no nickel except for the one contained as impurities. The steam turbine rotor composed of the above any low alloy heat resistant steel is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low alloy heat-resistant steel having high toughness and excellent high-temperature strength properties, and is suitable for use in a heat-resistant structural member for thermal power generation, particularly in a steam turbine rotor.

[0002]

2. Description of the Related Art Generally, as a high temperature rotor material used in a steam turbine plant for thermal power generation, a low alloy type C is used.
Examples thereof include rMoV steel and high Cr-based 12Cr steel. Among them, CrMoV steel is limited to a plant having a steam temperature of up to 566 ° C. from the limit of high temperature strength, and depending on the steam temperature, the rotor needs to be cooled and the structure becomes complicated.

On the other hand, a rotor material made of 12Cr steel (for example, JP-A-60-165359 and JP-A-62-1033).
Since the high temperature strength (see Japanese Patent Publication No. 45) is superior to that of CrMoV steel, it can be applied to a plant having a steam temperature of up to about 600 ° C., but it is difficult to manufacture the material and the cost is high.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention is a low alloy heat resistant steel which is easy to manufacture and inexpensive, and which is a conventional material such as CrM.
The present invention provides a new low-alloy heat-resistant steel that has higher toughness and excellent high-temperature strength characteristics than oV steel, and a high-temperature steam turbine rotor composed of this new heat-resistant steel.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventor has conducted extensive studies, and as a result, the following low-alloy heat-resistant steels and excellent heat-resistant steels having The present invention has been completed by finding that a turbine rotor having a structure is obtained.

The present invention based on such knowledge is specified by the following matters.

<Invention of Claim 1> The low alloy heat-resisting steel according to claim 1 has a weight ratio of carbon: 0.05 to 0.15% (0.1
5% not included), Silicon: 0.005 to 0.3%, Manganese: 0.01 to 1.0%, Chromium: 0.8 to 1.5% (1.5% not included), Nickel: 0 .1 to 2.0%, vanadium: 0.05
~ 0.3%, molybdenum: 0.1-1.5%, tungsten:
It is characterized in that it comprises 0.1 to 2.5% and the balance iron and unavoidable impurities.

<Invention of Claim 2> The low alloy heat resistant steel according to claim 2 is the low alloy heat resistant steel according to claim 1,
Part of iron is replaced with at least one of niobium, tantalum, nitrogen or boron, and the weight ratio is niobium: 0.01 to 0.15.
%, Tantalum: 0.01 to 0.15%, nitrogen: 0.01 to 0.1
%, Boron: 0.001 to 0.03%.

<Invention of Claim 3> The low alloy heat-resistant steel according to claim 3 is the low alloy heat-resistant steel according to claim 1 or 2, except that nickel is replaced by iron to contain impurities. Is characterized by not containing nickel.

<Invention of Claim 4> A steam turbine rotor according to claim 4 is characterized in that the steam turbine rotor is formed of the low alloy heat resistant steel of claims 1 to 3.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in order from the invention of claim 1.

First, the contents of the low alloy heat resistant steel according to claim 1 will be described.

The low alloy heat resistant steel according to claim 1 has a composition of carbon, silicon, manganese, chromium, nickel, vanadium, molybdenum, tungsten and the balance iron and inevitable impurities, and the weight ratio thereof is carbon: 0. 0.05
0.15% (however, 0.15% is not included), Silicon: 0.0
05-0.3%, manganese: 0.01-1.0%, chromium: 0.0.
8-1.5% (but not including 1.5%), nickel: 0.1
~ 2.0%, vanadium: 0.05-0.3%, molybdenum:
0.1 to 1.5%, Tungsten: 0.1 to 2.5%, and the balance consisting of iron and inevitable impurities are proposed. Further, the present invention proposes a steam turbine rotor made of a low alloy heat resistant steel having this specific composition.

[Operation] The present inventors have made a careful selection of alloying elements using CrMoV steel as a basic component to earnestly improve high temperature strength, and are a low alloy that can be applied to a new high temperature steam turbine rotor having excellent high temperature characteristics. We came to obtain heat-resistant steel.

The reasons for limiting the components in the material of the present invention will be described below.

Carbon (C): weight ratio is 0.05 to 0.15%
(However, 0.15% is not included). Where carbon is
It has the effects of ensuring hardenability during heat treatment and increasing the material strength. In addition, it forms carbides and contributes to improvement in creep rupture strength at high temperatures. However, in this alloy system, a sufficient effect cannot be obtained if the addition amount is less than 0.05%. On the other hand, if the added amount of carbon is too large, the toughness is reduced, and the carbonitrides are agglomerated and coarsened during use at a high temperature, thereby deteriorating the high-temperature long-time creep rupture strength. Therefore, the upper limit of the added amount is 0.15% (however, 0.15% is not included). Therefore, the addition range is preferably 0.05 to 0.15% (however, 0.15% is not included), but a particularly desirable range is 0.10 to 0.10 in order to have both strength characteristics and excellent toughness. 13%.

Silicon (Si): weight ratio is 0.005 to 0.
3%. Here, silicon has an effect as a deoxidizer, but on the other hand, it is an element that embrittles the matrix. When the deoxidizing effect is sufficiently expected, the addition of up to 0.3% is allowed, but when the vacuum carbon deoxidizing method is applied in the steelmaking process in the production of the material of the present invention, the deoxidizing effect by silicon is particularly high. It is not necessary to expect so much, and the addition amount can be minimized. However, this alloy system is 0.00
If it is less than 5%, a sufficient effect cannot be obtained. Therefore,
The addition range is preferably 0.005 to 0.3%. However, if it is assumed that the vacuum carbon deoxidizing method is adopted, the desirable range is 0.005 to 0.05%.

Manganese (Mg): weight ratio is 0.01 to 1.0
%. Here, manganese is an element which acts as a deoxidizer and is useful for preventing hot cracking during forging. In addition, it has the effect of increasing the hardenability during heat treatment. However, when manganese is added, the creep rupture strength deteriorates depending on the amount, and it is also an element that essentially promotes embrittlement of steel, so the maximum amount of addition was set to 1.0%. Further, especially when the content is suppressed to 0.15% or less, the creep rupture strength is further improved. Therefore, it is necessary to suppress the addition to 0.15% or less as needed. However, in order to control to 0.01% or less, it is necessary to carefully select the raw material steel and excessive refining process, which leads to high cost, so the minimum amount is set to 0.01%. Therefore, the addition range is preferably 0.01 to 1.0%, and the more desirable component range is 0.01 to 0.15%.

Chromium (Cr): Weight ratio is 0.8 to 1.5%
(However, it does not include 1.5%). Where chrome is
It enhances the hardenability during heat treatment, forms carbides, contributes to the improvement of creep rupture strength, and dissolves in the matrix to improve the oxidation resistance. Further, strengthening the matrix itself also contributes to the improvement of creep rupture strength. If the addition amount is less than 0.8%, the effect is not sufficient, and if the addition amount exceeds 1.5% (however, 1.5% is not included), the creep rupture strength decreases in this alloy system. Tend to do. Therefore, the range of addition is 0.8% to 1.5% (however,
Does not include 1.5%. ) Is desirable, but the more desirable range is
It is 1.2% to 1.45%.

Nickel (Ni): Weight ratio is 0.1 to 2.0%
It is. Here, nickel is effective in enhancing hardenability during heat treatment, improving tensile strength and proof stress, and particularly enhancing toughness. If the addition amount is 0.1% or less, no remarkable effect is expected, so the lower limit value is made 0.1%. On the other hand, the long-term creep rupture strength decreases with the addition of nickel, so the upper limit of the addition amount is limited to 2.0%. Therefore, the addition range is preferably 0.1% to 2.0%, but when the creep rupture strength is important, the preferable addition amount is 0.1 to 0.5.
%, And when the tensile strength, proof stress and toughness are emphasized, the desirable addition amount is 1.5 to 2.0%.

Vanadium (V): weight ratio of 0.05 to 0.3
%. Here, vanadium enhances the hardenability at the time of heat treatment and becomes a carbonitride to improve the creep rupture strength. If it is less than 0.05%, a sufficient effect cannot be obtained. On the contrary, if the amount exceeds 0.3%, the creep rupture strength is rather lowered. Therefore, the addition range is 0.0
5 to 0.3 is preferable.

Molybdenum (Mo): Weight ratio is 0.1 to 1.5
%. Here, molybdenum enhances the hardenability during heat treatment, and forms a solid solution in the matrix or carbonitride to improve the creep rupture strength. If the added amount is 0.1% or less, no remarkable effect is expected. On the other hand, the addition of a large amount increases unstable precipitates and promotes the formation of ferrite, so the upper limit of the addition amount is limited to 1.5%. Therefore, the addition range is preferably 0.1 to 1.5%.

Tungsten (W): weight ratio is 0.1 to 2.5
%. Here, tungsten dissolves in the matrix or carbonitride to improve the creep rupture strength. If the added amount is 0.1% or less, no remarkable effect is expected. On the other hand, if added excessively, the ferrite phase appears and increases, so the upper limit of the addition amount is limited to 2.5%. Therefore, the addition range is preferably 1.2% to 2.0%.

[Examples] The present invention will be described below based on examples.

"Table 1" shows the chemical components of the materials used in the test. Here, in "Table 1," sample numbers 1 to 7 correspond to the material of the present invention, and sample numbers 8 to 12 correspond to the comparative material. All materials are melted in a 50kg vacuum high frequency melting furnace and heating temperature: 1
Forging was performed at 200 ° C. The heat treatment of the test materials used in various tests was a quenching process simulating the center part of a 1200 dia. Rotor with oil cooling, followed by tempering of 0.2.
The tempering temperature of each material was determined so that the% proof stress was about 65 ± 3 kgf / mm ² .

[0026]

[Table 1]

Table 2 shows the mechanical properties and creep rupture properties of the material of the present invention and the comparative material.

[0028]

[Table 2] As shown in "Table 2", among the materials of the present invention, steel grades 1, 2 and 5 have the same creep rupture strength as CrMoV steel (steel grades 8 and 9 of the comparative material) and significantly increase toughness. The steel types 3, 4, 6 and 7 are intended for
This is a steel type aiming at improving both the creep rupture strength and toughness of CrMoV steel.

The Charpy impact absorbed energies (normal temperature test) of the materials of the present invention all show high values of 7 kgf-m or more, which shows that a sufficiently high impact value can be secured. In particular, the steel types 1, 2 and 5 show dramatically high values of 15 kgf-m or more.

Focusing on the creep rupture time when a load of 15 kgf / mm ² was applied at 600 ° C., the steel types 1, 2 and 5 were slightly shorter than the steel types 8 and 9 of the comparative material, but were almost the same. It can be judged that they have creep rupture properties, and it is understood that the steel types 3, 4, 6 and 7 have a significantly longer rupture time than the comparative material. The above is
It is suggested that proper compositional design of various elements is effective in improving toughness and creep rupture strength.

[Effects] As described above, the low alloy heat resistant steel of the present invention has excellent high temperature strength and toughness, and is therefore useful as a high temperature steam turbine rotor material. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to construct a power plant with low cost and high efficiency, which contributes to the saving of fossil fuel and is useful in suppressing the amount of carbon dioxide generated.

Next, the claim (2) will be described.

[Means] Next, the contents of the low alloy heat resistant steel of claim 2 will be described.

The low alloy heat-resistant steel according to claim 2 is the low alloy heat-resistant steel according to claim 1, in which a part of iron is replaced with niobium, tantalum,
Substituted with at least one of nitrogen and boron, and weight ratio of niobium: 0.01 to 0.15%, tantalum: 0.01 to 0.15
%, Nitrogen: 0.01 to 0.1%, boron: 0.001 to 0.03
It is proposed that one containing at least one kind of%. Further, the present invention proposes a steam turbine rotor made of a low alloy heat resistant steel having this specific composition.

[Operation] The inventors of the present invention have proposed the low alloy heat-resistant steel of claim (1) by carefully selecting alloying elements using CrMoV steel as a basic component and making an earnest effort to improve high temperature strength.
Furthermore, we have obtained a low alloy heat resistant steel material that can be applied to a new high temperature steam turbine rotor material having high toughness and excellent high temperature characteristics.

The reasons for limiting the components in the material of the present invention will be described below. The components already described in the above-mentioned claim (1) have the same reason for limitation, and therefore, only the new components niobium, tantalum, nitrogen and boron will be described here.

Niobium (Nb): weight ratio is 0.01 to 0.15
%. Here, niobium forms a carbonitride and contributes to improvement of high temperature strength. Further, the carbide or carbonitride (M ₂₃ C ₆ ) which precipitates at a high temperature is made fine and contributes to improvement of long-term creep rupture strength. If the addition amount is less than 0.01%, there is no effect, and if the addition amount exceeds 0.15%, the niobium carbide or carbonitride produced during the steel ingot production is sufficient for the matrix during heat treatment (solution treatment). However, it does not form a solid solution and coarsens during use to reduce long-term creep rupture strength. Therefore, the range of addition is 0.01% to 0.1
5% is desirable.

Tantalum (Ta): weight ratio is 0.01 to 0.1
5%. Here, tantalum forms carbonitrides like niobium and contributes to improvement of high temperature strength. Further, the carbide or carbonitride (M ₂₃ C ₆ ) which precipitates at a high temperature is made fine and contributes to improvement of long-term creep rupture strength. If the addition amount is less than 0.01%, there is no effect, and if the addition amount is more than 0.15%, the tantalum carbide or carbonitride produced during steel ingot production is sufficient for the matrix during heat treatment (solution treatment). However, it does not form a solid solution and coarsens during use to reduce long-term creep rupture strength. Therefore, the addition range is preferably 0.01% to 0.15%.

The nitrogen (N): weight ratio is 0.01 to 0.1%. Here, nitrogen forms carbonitrides together with carbon and alloy elements and contributes to improvement of high temperature strength. If it is less than 0.01%, sufficient carbonitride cannot be formed,
A sufficient contribution to creep rupture strength cannot be obtained. Also,
If the amount exceeds 0.1%, carbonitrides aggregate and grow over a long period of time, making it impossible to obtain sufficient creep rupture strength. It also causes a decrease in toughness. Therefore, the range of addition is preferably 0.01 to 0.1%.

Boron (B): weight ratio is 0.001 to 0.03
%. Here, boron has the effect of increasing the grain boundary strength. This contributes to improvement in creep rupture strength. However, if added in a large amount, the hot workability deteriorates and the toughness decreases. Therefore. The lower limit of 0.001% of the minimum amount that can actually control the addition amount is set as the lower limit value, and the upper limit value is set as 0.03% at which no adverse effect appears. Therefore, the addition range is preferably 0.001 to 0.03%, and the particularly preferable range is 0.005 to 0.02% in order to contribute to the improvement of creep rupture strength while considering the decrease in toughness.

[Examples] The present invention will be described below based on Examples.

"Table 3" shows the chemical components of the materials used in the test. Samples Nos. 13 to 15 were prepared by improving the creep rupture strength while maintaining the very high toughness at the same level as the steel type 2 by adding various elements using the steel type 2 shown in claim (1) as a base material. It is a steel grade. Sample Nos. 16 to 18 are steel grades in which the creep rupture strength is further improved while maintaining good toughness at the same level as the steel grade 2 by adding various elements using the steel grade 6 shown in claim (1) as a base material. Is. All materials were melted in a vacuum high-frequency melting furnace of 50 kg and forged at a heating temperature of 1200 ° C. Test material heat treatment using the various test performs simulating the quenching the heart when the oil cooling of the rotor of the trunk diameter 1200Fai, then tempering, as a 0.2% yield strength of approximately a 65 kgf / mm ² The tempering temperature of each material was decided.

[0043]

[Table 3]

Table 4 shows the mechanical properties and creep rupture properties of the material of the present invention.

[0045]

[Table 4]

As shown in "Table 4", the characteristics of the steel types 13 to 15 are compared with the characteristics of the steel type 2 shown in "Table 2".
Charpy impact absorption energy (normal temperature test) is the same as Steel Type 2 or 17
It maintains a very high level of kgf-m and is 600
The creep rupture time when a load of 15 kgf / mm ^{2 at} ℃ was also extended.

Comparing the characteristics of the steel types 16 to 18 with the steel type 6, the Charpy impact absorbed energy (at room temperature test) is the same as that of the steel type 6 or 6.5 kgf-m for the lowered steel types.
Keeps good level and 15kg at 600 ℃
The creep rupture time when a load of f / mm ² is applied is certainly extended.

As described above, adding an appropriate element to the component system of claim (1) improves creep rupture strength while maintaining toughness or suppressing deterioration of toughness as much as possible. It is suggested to be effective.

[Effects] As described above, the low alloy heat-resistant steel of the present invention exhibits excellent high-temperature strength while maintaining the toughness comparable to that of the low-alloy heat-resistant steel according to claim 1. It is useful as a rotor material. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to construct a power plant with low cost and high efficiency, which contributes to the saving of fossil fuel and is useful in suppressing the amount of carbon dioxide generated.

[Means] Next, the contents of the low alloy heat resistant steel of claim 3 will be described.

It is proposed that the low alloy heat-resistant steel according to claim 3 does not contain nickel except that nickel is replaced by iron and that it is contained as an impurity. Further, the present invention proposes a steam turbine rotor made of a low alloy heat resistant steel having this specific composition.

That is, the material of the present invention excludes all nickel contained in the invention materials of the above-mentioned claims (1) and (2) (however, those which are unavoidably contained as impurities are excluded). , Is characterized by replacing it with iron.

The reasons for limiting the components will be described below, but since elements other than nickel are the same as those of the invention materials of claims 1 and 2, they are omitted here and only the purpose and action of eliminating nickel will be described.

Nickel is effective in enhancing the hardenability during heat treatment, improving the tensile strength and proof stress, and particularly enhancing the toughness. Therefore, mainly for the purpose of ensuring toughness,
At least 0.5% for heat-resistant steel for ordinary turbine rotors
Some nickel has been added. On the other hand, nickel has an adverse effect on the long-term creep rupture strength, and the rupture strength decreases with the addition amount. Therefore, the novelty of the present invention lies in the point that the first goal is to further improve the creep rupture property, and the improvement of the toughness due to the addition of nickel is not expected, and this is eliminated.

A description will be given below according to an embodiment.

[Example] "Table 5" shows the chemical components of the materials used in the test. All materials were melted in a vacuum high-frequency melting furnace of 50 kg and forged at a heating temperature of 1200 ° C. The heat treatment of the test material used for various tests is a body diameter of 1200φ
The rotor is oil-cooled, and the quenching process is performed to simulate the central part, and then the tempering is performed with 0.2% proof stress of about 65 kgf /
The tempering temperature of each material was determined so as to be mm ² . Sample No. 19 is based on the composition of Steel Type 2 used in the embodiment of claim 1, the present invention material excluding nickel, Sample No. 20 is based on the composition of Steel Type 7 used in the embodiment of Claim 1, The present invention material excluding nickel, Sample No. 21 is the present invention material excluding nickel based on the composition of the steel type 14 used in the embodiment of Claim 2, and Sample No. 22 is the embodiment of Claim 2. It is the material of the present invention in which nickel is excluded, based on the composition of the steel type 18 used in 1.

[0057]

[Table 5]

Table 6 shows the mechanical properties and creep rupture properties of the material of the present invention.

[0059]

[Table 6]

As shown in "Table 6", the Charpy impact value absorbed energy of the material of the present invention (normal temperature test) is lower than that of the base material, but it is still CrMoV steel (shown as a comparative material in claim (1)). The value is sufficiently higher than that of steel grades 8 and 9). Focusing on the creep rupture time when a load of 15 kgf / mm ² was applied at 600 ° C., it can be seen that the rupture time of the material of the present invention is certainly longer than that of the base material. The above suggests that the elimination of nickel of the low alloy heat resistant steels according to claims 1 and 2 slightly lowers the toughness but further improves the creep rupture strength.

[Effects] As described above, the low alloy heat-resistant steel of the present invention exhibits slightly higher toughness than the low alloy heat-resistant steel of claim 1 or 2, but exhibits excellent high-temperature strength. Therefore, it is useful as a high temperature steam turbine rotor material. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to construct a power plant with low cost and high efficiency, which contributes to the saving of fossil fuel and is useful in suppressing the amount of carbon dioxide generated.

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[Procedure amendment]

[Submission date] May 21, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

Silicon (Si): weight ratio is 0.005 to 0.
3%. Here, silicon has an effect as a deoxidizer, but on the other hand, it is an element that embrittles the matrix. When the deoxidizing effect is sufficiently expected, the addition of up to 0.3% is allowed, but when the vacuum carbon deoxidizing method is applied in the steelmaking process in the production of the material of the present invention, the deoxidizing effect by silicon is particularly high. It is not necessary to expect so much, and the addition amount can be minimized. However, the amount of silicon
If it is too low, the raw materials must be carefully selected and the cost will increase
Therefore, the lower limit is set to 0.005%. Therefore, the addition range is 0.
It is desirable to set it to 005 to 0.3%. However, if it is assumed that the vacuum carbon deoxidizing method is adopted, the desirable range is 0.005 to 0.05%.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

Manganese (M n ): weight ratio is 0.01 to 1.0
%. Here, manganese is an element which acts as a deoxidizer and is useful for preventing hot cracking during forging. In addition, it has the effect of increasing the hardenability during heat treatment. However, when manganese is added, the creep rupture strength deteriorates depending on the amount, and it is also an element that essentially promotes embrittlement of steel, so the maximum amount of addition was set to 1.0%. Further, especially when the content is suppressed to 0.15% or less, the creep rupture strength is further improved. Therefore, it is necessary to suppress the addition to 0.15% or less as needed. However, in order to control to 0.01% or less, it is necessary to carefully select the raw material steel and excessive refining process, which leads to high cost, so the minimum amount is set to 0.01%. Therefore, the addition range is preferably 0.01 to 1.0%, and the more desirable component range is 0.01 to 0.15%.

Claims (4)

[Claims] 1. Carbon to weight ratio: 0.05 to 0.15% (0.1
5% not included), Silicon: 0.005 to 0.3%, Manganese: 0.01 to 1.0%, Chromium: 0.8 to 1.5% (1.5% not included), Nickel: 0 .1 to 2.0%, vanadium: 0.05
~ 0.3%, molybdenum: 0.1-1.5%, tungsten:
A low alloy heat resistant steel characterized by comprising 0.1 to 2.5% and iron. 2. The low alloy heat-resistant steel according to claim 1, wherein a part of iron is replaced by at least one of niobium, tantalum, nitrogen or boron, and the weight ratio is niobium: 0.01 to 0.15.
%, Tantalum: 0.01 to 0.15%, nitrogen: 0.01 to 0.1
%, Boron: 0.001 to 0.03%, a low alloy heat resistant steel. 3. The low alloy heat resistant steel according to claim 1 or 2, wherein nickel is replaced by iron and does not contain nickel except those contained as impurities. 4. A steam turbine rotor comprising a low alloy heat resistant steel according to any one of claims 1 to 3.