JPH05113106A - High purity heat resistant steel and manufacture of high and low pressure integrated type turbine rotor made of high purity heat resistant steel - Google Patents

Abstract

PURPOSE:To provide both of high temperature creep strength and tenacity by forging-forming a steel ingot, which consists of a high purity heat resistant steel, into a turbine rotor body of a desired shape, heating the turbine rotor body for quenching, and tempering the quenched turbine rotor body once or more times. CONSTITUTION:High purity heat resistant steel contains C: 0.05-0.2weight%, Ni: 0.5-1.5weight%, Cr: 8-12weight%, Mo: 0.5-2weight%, V: 0.1-0.5weight%, and N: 0.01-0.08weight%, and the remained consists of Fe and unavoidable impurity. Allowable content among the unavoidable impurity is Si: less than 0.1weght%, Mn: less than 0.1weight%, P: less than 0.01weight%, and S: less than 0.005weight%. A lump of steel which consists of high purity heat resistant steel is heated up to 980-1,120 deg.C to be hardened and tempered at 550-700 deg.C more than once to produce a high and low pressure integrated type turbine rotor. It is thus possible to provide the high and low pressure integrated type turbine rotor with excellent high temperature creep strength and excellent tenacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent high temperature creep strength and toughness and is used for a rotor shaft of a steam turbine in which a high pressure part and a low pressure part are integrated, and a high purity heat resistant steel. The present invention relates to a method of manufacturing a high-low pressure integrated turbine rotor using high-purity heat-resistant steel.

[0002]

2. Description of the Related Art Generally, toughness and high temperature creep strength are
It is known that they have contradictory properties and it is difficult to satisfy both at the same time. However, for example, a heat resistant material such as a high and low pressure integrated rotor shaft needs to have both properties. Conventionally, CrMoV heat-resisting steel has been used for high- and low-pressure integrated rotors. In recent years,
An improved material of CrMoV steel is being applied (for example, Japanese Patent Publication No. 54-19370). Then, in the manufacturing process, all the materials are uniformly heated and quenched.

[0003]

However, when it is attempted to obtain sufficient high temperature creep strength with any of the materials, the fracture surface transition temperature is 0 ° C. or less in the shaft core of the low pressure part which requires high toughness. Has not been achieved. Further, although the 12Cr heat resistant steel is excellent in high temperature creep strength, but lacks in toughness, it has been used only as a material for a high pressure rotor or a medium pressure rotor. Therefore, when the 12Cr heat resistant steel is used, for example, as a material for a high / low pressure integral type rotor, the high temperature creep strength required in the high pressure portion is excellent, but sufficient toughness is not obtained in the low pressure portion. The present invention maintains excellent high temperature creep strength in 12Cr heat resistant steel,
Providing 12Cr heat resistant steel that also has excellent toughness,
Further, it is an object of the present invention to provide a method for manufacturing a high / low pressure integrated turbine rotor having both excellent high temperature creep strength and excellent toughness.

[0004]

According to the present invention, in order to significantly improve the toughness of a 12Cr-based heat-resistant steel without lowering the high temperature creep strength, the Ni content is set higher than that of the conventional 12Cr-based heat-resistant steel. It is a new heat-resisting steel with increased content and reduced content of Si, Mn, and other unavoidable impurities. Its specific composition is C:
0.05-0.2%, Ni: 0.5-1.5%, Cr:
8-12%, Mo: 0.5-2%, V: 0.1-0.5
%, N: 0.01 to 0.08%, the balance consisting of Fe and unavoidable impurities. Of these unavoidable impurities, Si: 0.1% or less and Mn: 0.1% by weight. Hereinafter, P: 0.01% or less and S: 0.005% or less are high-purity heat-resistant steels with allowable contents. And 2nd invention is Nb: 0.01-0.15 by weight% in the said composition.
%, Ta: 0.01 to 0.15%, B: 0.005% to
It is characterized by containing 0.03% of one kind or two or more kinds.

Furthermore, a third aspect of the present invention, which is a method for producing a high-low pressure integrated turbine rotor made of high-purity heat-resistant steel, comprises the steps of melting, refining, and agglomerating raw materials; A step of forging a turbine rotor body of a desired shape from a steel ingot made of high-purity heat-resistant steel having the composition described in 1 or 2, and a step of heating the turbine rotor body to 980 to 1120 ° C. and quenching it. ,
550 ° C. to 70 ° C. on the quenched turbine rotor body
And a step of performing tempering at 0 ° C. once or more.

According to a fourth aspect of the present invention, there is provided a method for manufacturing a high-low pressure integrated turbine rotor made of high-purity heat-resistant steel, wherein the turbine rotor body has portions 980 to 980 corresponding to a high pressure portion and an intermediate pressure portion in an operating environment of a steam turbine. 1150 ° C., a portion corresponding to the low pressure portion is heated to 950 to 1120 ° C. and a temperature difference between the low pressure portion and the high pressure portion is 30 to 80 ° C. ..

[0007]

Next, the action of each element contained in the steel of the present invention,
The reason for the limitation will be described. C: 0.05 to 0.2% C promotes martensitic transformation, and at the same time alloys
Carbides by combining with Fe, Cr, Mo, V, Nb, etc.
Form and improve room temperature tensile strength and high temperature creep strength
Let However, if the C content is less than 0.05%, a sufficient amount of
Warm tensile strength and high temperature creep strength were not obtained, and 0.
If the content exceeds 2%, the low temperature toughness deteriorates, and
In addition, coarsening of carbides easily occurs and high temperature creep strength increases.
Since it also deteriorates, its content should be 0.05-0.2%.
Limited

Ni: 0.5 to 1.5% Ni improves the toughness of the steel of the present invention, but has the effect of lowering the high temperature creep strength. However, if the content is less than 0.5%, no improvement in toughness is observed,
Further, if the content exceeds 1.5%, it becomes difficult to maintain the high temperature creep strength equivalent to that of the conventional material, so the content is limited to 0.5% to 1.5%.

Cr: 8-12% Cr is a main constituent component of the steel of the present invention, which enhances the oxidation resistance and the high temperature corrosion resistance, and further forms a solid solution in the alloy to improve the strength of the alloy. When the content is less than 8%, sufficient oxidation resistance and strength cannot be obtained, and when the content exceeds 12%, harmful delta ferrite is formed, and ductility at low temperature, toughness, and creep strength at high temperature are reduced. Therefore, the content is limited to 8 to 12%. Mo: 0.5 to 2% Mo forms a solid solution in the alloy, enhances the strength at low temperature and high temperature, forms fine carbides, and improves high temperature creep strength. It is also an element that contributes to the suppression of temper embrittlement. If its content is less than 0.5%, its action and effect are small, and if it exceeds 2%, the creep strength decreases conversely, so its content was limited to 0.5-2%.

V: 0.1 to 0.5% V forms fine carbides and carbonitrides and improves high temperature creep strength, but if its content is less than 0.1%, its action and effect are insufficient. And the lower limit was made 0.1%. Also,
If the content exceeds 0.5%, delta ferrite is formed and the high temperature creep strength decreases, so the upper limit is 0.5.
%. N: 0.01 to 0.08% N combines with Nb, V, etc. to form a nitride and improves high temperature creep strength, but if its content is less than 0.01%, sufficient strength, And high temperature creep strength cannot be obtained, and if the content exceeds 0.08%, it becomes difficult to manufacture a steel ingot and the hot workability deteriorates, so the content is set to 0.01 to 0. It was limited to 0.08%.

Nb: 0.01 to 0.15% Nb forms fine carbides and carbonitrides, improves high-temperature creep strength, and promotes grain refinement.
It is an element necessary for improving the low temperature toughness and is added if desired. In order to obtain the effect, it is necessary to contain at least 0.01%. But 0.15
%, Coarse carbides and carbonitrides precipitate and the toughness decreases, so the upper limit is 0.15.
%. Ta: 0.01 to 0.15% Ta has the same action as Nb and improves the high temperature creep strength and contributes to the improvement of the low temperature toughness, so it is added if desired. If the content is less than 0.01%,
The above-described effects are insufficient, and if the content exceeds 0.15%, coarse carbides and carbonitrides precipitate and the toughness decreases, so the content is 0.01 to 0.15%.
Limited to. When Nb is added in combination, Nb
It is desirable that the content of + Ta is 0.15% or less.

B: 0.005% to 0.03% B is added in a small amount to increase hardenability, improve toughness, suppress precipitation and agglomeration of carbides at grain boundaries, and contribute to improvement in high temperature creep strength. Therefore, it is added if desired. If the content is less than 0.005%, the above effect is insufficient, and if it exceeds 0.03%, the high temperature creep ductility is remarkably reduced, so the content was limited to 0.005 to 0.03%.

Inevitable impurities (Si: 0.1% or less, M
n: 0.1% or less, P: 0.01% or less, S: 0.00
5% or less) Si is usually used as a deoxidizing material, but if the Si content is high, segregation inside the steel ingot increases, and the temper embrittlement susceptibility becomes extremely large, and the notch toughness is impaired. It is desirable to reduce it as much as possible. At present, the Si content is reduced by applying a vacuum carbon deoxidation method or the like, but the allowable content is limited to 0.1% or less in consideration of the limits of industrially possible refining technology. Mn is generally used as a deoxidizing and desulfurizing agent during dissolution. However, Mn combines with S to form non-metallic inclusions, lowers toughness, and has the effect of increasing temper embrittlement susceptibility like Si. Currently, refining techniques such as out-of-furnace refining make it easy to reduce the amount of S, and it is no longer necessary to add Mn as an alloy component. In the present invention, Mn is an unavoidable impurity, and its allowable content is 0.
It was limited to 1% or less.

P is an element that increases temper embrittlement susceptibility, and it is desirable to reduce P as much as possible in order to reduce aging deterioration and improve reliability. The allowable content of P is taken into consideration in the limit of refining technology. To 0.01% or less. Furthermore, it is desirable that the content be 0.005% or less. S
Promotes the tendency of V segregation and reverse V segregation in large steel ingots, and also forms sulfides with Mn, Nb, V, Fe, etc., which deteriorates toughness, so it should be reduced as much as possible by ladle refining. However, the allowable content is set to 0.005% or less in consideration of the limits of the current refining technology.

As other unavoidable impurities, A
Examples include s, Sn and Sb. Similar to P, these impurities are elements that increase temper embrittlement susceptibility, and it is desirable to reduce them as much as possible. However, these impurity elements are inevitably mixed with the raw materials,
It is difficult to remove by refining. Therefore,
This is largely due to careful selection of raw materials. From the standpoint of reducing temper embrittlement susceptibility, As: 0.008% or less, Sn: 0.0
It is desirable that the content be 1% or less and Sb: 0.005% or less.

When a turbine rotor is manufactured by the manufacturing method of the present invention using the above steel types, the structure of the steel ingot is austenitized by the heating at the time of quenching, and the martensite transformation by quenching causes sufficient strength. Further, the toughness is improved by tempering. The heating temperature at the time of quenching is different between the high and medium pressure parts and the low pressure part,
In the high and medium pressure parts, the effect of improving the high temperature creep strength is large, and in the low pressure part, the effect of improving the toughness is large, and the mechanical properties suitable for the operating environment are obtained.

Next, the reason for limiting the heating temperature during the quenching will be described. Quenching heating temperature (when heating uniformly) Heating temperature : 980 to 1120 ° C. In heat treatment when manufacturing a high-low pressure integrated turbine rotor, when heating the whole uniformly, the austenitizing temperature during quenching is 980 ° C. If it is less than 1, the sufficient high temperature creep strength cannot be obtained, and if it exceeds 1120 ° C., the low temperature toughness decreases, so the above range is set.

(When providing a difference in heating temperature between the high-middle pressure portion and the low-pressure portion) Heating temperature : high-middle pressure portion 980 to 1150 ° C., low-pressure portion 95
0 to 1120 ° C, high intermediate pressure part temperature-low pressure part temperature 30 to 8
0 ℃ In case of providing a difference in heating temperature between high and medium pressure parts and low pressure part,
If the austenitizing temperature of the high-medium pressure portion is less than 980 ° C, sufficient high temperature creep strength cannot be obtained, and 1150
When the temperature exceeds ℃, notch weakening at high temperature is recognized, so the range is set to this range. When the austenitizing temperature of the low pressure part is less than 950 ° C, a ferrite phase is easily generated,
If the strength at low temperature is not sufficiently obtained, and if it exceeds 1120 ° C., the austenite crystal grains become coarse,
Since the low temperature toughness decreases, it is set to this range.

The austenitizing temperature of the high and medium pressure parts is 30 to 80 higher than the austenitizing temperature of the low pressure part.
Although it is selected in a temperature range higher by ° C, it is necessary to make a temperature difference of 30 ° C or more in order to obtain the effect. Further, if the temperature difference exceeds 80 ° C., the production is difficult, so the temperature range is limited to 30 to 80 ° C. Tempering temperature: 550 to 700 ° C. If the tempering temperature is lower than 550 ° C., a sufficient tempering effect cannot be obtained, and therefore good toughness cannot be obtained. Further, at a tempering temperature exceeding 700 ° C, the desired strength cannot be obtained, so the tempering temperature was limited to 550 to 700 ° C.

[0020]

【Example】

(Example 1) Using a vacuum induction heating furnace, 50 kg of ingots of the invention steel and the comparative steel having the compositions shown in Table 1 were melted, and then heated to 1150 ° C and forged into a rotor shaft material shape.
From these forged materials, test piece materials were cut out and subjected to heat treatment by simulating a thermal history corresponding to the actual shaft core of the rotor shaft material. That is, after holding at 1025 ° C. for 10 hours,
After gradually cooling at a constant rate and quenching, the first tempering was performed at 600 ° C., and the second tempering was further performed at 650 ° C. to obtain a test material. Specimen No. Nos. 1 to 8 are the steels of the present invention, and the test steel Nos. 9 to 12 are comparative steels. Among them, the sample steel No. 9 is a conventional 12Cr steel component. Table 2 shows the material test results of these test materials. As is clear from the material test results, the invention steel was excellent in both high temperature creep strength and toughness. In contrast, the comparative steel could not satisfy both the high temperature creep strength and the toughness.

[0021]

[Table 1]

[0022]

[Table 2]

Example 2 The invention steel and comparative steel shown in Example 1 were melted and forged in the same manner as in Example 1 to obtain a high-low pressure integral type rotor shaft material body. During use, the parts to be the high-pressure part and the intermediate-pressure part during use were heated to 1060 ° C., and the parts to be the low-pressure part were heated to 1010 ° C. for quenching. Then, the first tempering was performed at 600 ° C., and further the second tempering was performed at 650 ° C. to obtain a test material. This test material was subjected to a test for evaluating the mechanical properties of each of the high and medium pressure parts and the low pressure part, and the results are shown in Table 3. As is clear from the results in Table 3,
The high and medium pressure parts had excellent high temperature creep strength and toughness, and the low pressure part obtained more excellent toughness.

[0024]

[Table 3]

[0025]

As described above, according to the high-purity heat-resistant steel of the present invention, such characteristics are required as a high-purity heat-resistant steel excellent in high-temperature creep strength and having extremely good toughness. It can be applied as a heat-resistant material such as a turbine rotor shaft material that integrates the low pressure part and the low pressure part. Further, further reliability can be obtained by reducing the content of the impurity element that affects the susceptibility to temper embrittlement. In addition, since this steel provides superior high-temperature creep strength than conventional steel, this steel type is not only for rotor shaft materials of high and low pressure integrated type, but also for medium-pressure, high-pressure, and ultra-high-pressure rotors that do not require relatively high toughness. It also has the effect of expanding the range of applications for shaft materials. Furthermore, if a high-low pressure integrated turbine rotor is manufactured using the above steel types, a rotor having excellent high temperature creep strength and toughness can be obtained. Then, by making the quenching temperature different between the high and medium pressure parts and the low pressure part, there is an effect that suitable mechanical properties (high temperature creep strength, toughness) can be obtained depending on the part.

[Procedure amendment]

[Submission date] December 11, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: High-purity heat-resistant steel, high-low pressure integrated turbine rotor made of high-purity heat-resistant steel, and method of manufacturing high-low pressure integrated turbine rotor made of high-purity heat-resistant steel

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

4. dissolving raw materials, refining, comprising the steps of ingot making,
980 to 1120 for a step of forging a turbine rotor body of a desired shape from a steel ingot made of high-purity heat-resistant steel having the composition according to claim 1 or 2 obtained by the ingot casting, and the turbine rotor body. A high-pressure low-pressure one made of high-purity heat-resistant steel, characterized by comprising: a step of heating and quenching at 0 ° C .; and a step of subjecting the quenched turbine rotor body to tempering at 550 ° C. to 700 ° C. one or more times. Method for manufacturing body turbine rotor

5. In a turbine rotor body, a portion corresponding to a high pressure portion and an intermediate pressure portion in an operating environment of a steam turbine is 980 to 1150 ° C., and a portion corresponding to a low pressure portion is 9 parts.
The high-purity heat-resistant steel according to claim 4, which has a step of heating and quenching at 50 to 1120 ° C and a temperature difference between the low pressure portion and the high pressure portion of 30 to 80 ° C, respectively. Method for manufacturing high and low pressure integrated turbine rotor

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction content]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent high temperature creep strength and toughness and is used for a rotor shaft of a steam turbine in which a high pressure part and a low pressure part are integrated, and a high purity heat resistant steel. The present invention relates to a high-low pressure integrated turbine rotor using high-purity heat-resistant steel and a method for manufacturing the high-low pressure integrated turbine rotor .

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

[0003]

However, when it is attempted to obtain sufficient high temperature creep strength with any of the materials, the fracture surface transition temperature is 0 ° C. or less in the shaft core of the low pressure part which requires high toughness. Has not been achieved. Further, although the 12Cr heat resistant steel is excellent in high temperature creep strength, but lacks in toughness, it has been used only as a material for a high pressure rotor or a medium pressure rotor. Therefore, when the 12Cr heat resistant steel is used, for example, as a material for a high / low pressure integral type rotor, the high temperature creep strength required in the high pressure portion is excellent, but sufficient toughness is not obtained in the low pressure portion. The present invention maintains excellent high temperature creep strength in 12Cr heat resistant steel,
Providing 12Cr heat resistant steel that also has excellent toughness,
Furthermore, it is an object to provide a high-low pressure integrated type turbine rotor having both excellent and excellent high-temperature creep strength toughness and a method of manufacturing the same.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction content]

High and low pressure integrated turbine rotor of the second invention
Is composed of the high-purity heat-resistant steel of the present invention.
Characterize. Furthermore, the method for producing a high-low pressure integrated turbine rotor made of high-purity heat-resistant steel according to a fourth aspect of the invention is a step of melting, refining, and ingot raw materials, and claim 1 or 2 obtained by the ingot A step of forging a turbine rotor body of a desired shape from a steel ingot made of high-purity heat-resistant steel having the composition described above, and a step of heating the turbine rotor body to 980 to 1120 ° C. and hardening it.
550 ° C. to 70 ° C. on the quenched turbine rotor body
And a step of performing tempering at 0 ° C. once or more.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

According to a fifth aspect of the present invention, there is provided a method of manufacturing a high-low pressure integrated turbine rotor made of high-purity heat-resistant steel, wherein the turbine rotor body has portions 980 to 980 corresponding to a high-pressure portion and an intermediate-pressure portion in an operating environment of a steam turbine. 1150 ° C., a portion corresponding to the low pressure portion is heated to 950 to 1120 ° C. and a temperature difference between the low pressure portion and the high pressure portion is 30 to 80 ° C. ..

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // B21K 3/04 6921-4E

Claims (4)

[Claims] 1. By weight%, C: 0.05-0.2%, N
i: 0.5 to 1.5%, Cr: 8 to 12%, Mo: 0.
5-2%, V: 0.1-0.5%, N: 0.01-0.
The content of Fe is 0.08% and the balance is Fe and unavoidable impurities. Of these unavoidable impurities, Si: 0.1% by weight.
% Or less, Mn: 0.1% or less, P: 0.01% or less,
S: High-purity heat-resistant steel with an allowable content of 0.005% or less 2. The composition according to claim 1, further comprising Nb: 0.01 to 0.15% and Ta: 0.01 to 0.1% by weight.
High purity heat resistant steel containing 5%, B: 0.005% to 0.03% of one kind or two or more kinds. 3. A step of melting, refining and agglomerating raw materials,
980 to 1120 for a step of forging a turbine rotor body of a desired shape from a steel ingot made of high-purity heat-resistant steel having the composition according to claim 1 or 2 obtained by the ingot casting, and the turbine rotor body. A high-pressure low-pressure one made of high-purity heat-resistant steel, characterized by comprising: a step of heating and quenching at 0 ° C .; and a step of subjecting the quenched turbine rotor body to tempering at 550 ° C. to 700 ° C. one or more times. Method for manufacturing body turbine rotor 4. In the turbine rotor body, a portion corresponding to a high pressure portion and an intermediate pressure portion in an operating environment of a steam turbine is 980 to 1150 ° C., and a portion corresponding to a low pressure portion is 9 parts.
The high-purity heat-resistant steel according to claim 3, further comprising a step of heating and quenching at a temperature of 50 to 1120 ° C and a temperature difference between the low pressure portion and the high pressure portion of 30 to 80 ° C. Method for manufacturing high and low pressure integrated turbine rotor