JP4266194B2 - Heat resistant steel, heat treatment method for heat resistant steel, and steam turbine rotor for high temperature - Google Patents

Description

  The present invention relates to a heat-resistant steel, in particular, a heat-resistant steel exhibiting excellent performance as a member of a high-temperature steam turbine rotor material or a steam turbine power generation facility, a heat-treating method for the heat-resistant steel, and a high-temperature steam turbine rotor.

  As high-temperature component materials for thermal power generation facilities, low alloy heat resistant steel typified by 1Cr-1Mo-0.25V steel and high Cr heat resistant steel typified by 12Cr-1Mo-VNbN steel are frequently used. However, in recent thermal power generation facilities, the steam temperature has been rapidly increased, and the use of high Cr heat resistant steel having higher temperature characteristics has been increasing (see, for example, Patent Documents 1-4).

On the other hand, recent thermal power generation facilities are required to have high efficiency and economical efficiency. From this viewpoint, it is expected to use heat-resistant steel that is inexpensive and excellent in characteristics as a constituent material (for example, Patent Document 5- 7).
Japanese Patent Publication No. 60-54385 JP-A-2-149649 JP-A-6-306550 JP-A-8-3697 Japanese Patent No. 3334217 Japanese Patent No. 3439197 JP 2002-348642 A

  The parts constituting the center of the thermal power generation facility are molded from a large material, and it is indispensable to be excellent in manufacturability as a large material and moldability to a desired shape. In addition, the material characteristics are required not to be impaired by the increase in size and to be uniform. However, for example, the conventional heat-resistant steel having the chemical composition disclosed in Japanese Patent No. 3334217 has low hardenability as a large member, and can exhibit desired characteristics in the center of a steel ingot having a large body diameter. Have difficulty. Further, the heat resistant steel having the chemical composition disclosed in Japanese Patent No. 3439197 has a significant component segregation when a large steel ingot is cast, and it is difficult to exhibit uniform material characteristics throughout the steel ingot. Moreover, when the homogeneity of the steel ingot is increased by using special melting, there is a disadvantage that has both advantages and disadvantages such as inferior economy.

  In addition, since conventional heat-resistant steel contains a relatively large amount of ferrite-forming elements such as Cr, Mo, and W as strengthening elements, the tendency to generate a ferrite phase increases. Generally, the ferrite phase generated in the bainite phase is formed by combining the above-mentioned ferrite forming elements with Fe. Therefore, the concentration of these elements added as strengthening elements in the locally generated ferrite reduces the content of these elements in the matrix, and in particular the problem that the high-temperature strength decreases. is there. Furthermore, in heat resistant steel, when the amount of ferrite phase generated increases, the impact properties and toughness of the material may be significantly reduced.

  Therefore, the present invention has been made to solve the above-mentioned problems, and can be stably operated in a high-temperature steam environment, and is heat-resistant steel having a bainite single-phase structure excellent in economy and heat treatment of heat-resistant steel. It is an object to provide a method and a high temperature steam turbine rotor.

In order to achieve the above object, the heat-resisting steel of the present invention is, in mass %, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.00. 3 to 0.6, Cr: 1.6 to 1.9, V: 0.26 to 0.35, Mo: 0.6 to 0.9, W: 0.9 to 1.4, Ti: 0. less than 01, N: 0.001 to 0.007, a total of Mo and W / 2 is 1.3 to 1.4, the balance being Fe and unavoidable impurities, after tempering, in mass% Fe: 1.0 or more, Cr: 0.8 to 0.9, Mo: 0.4 to 0.5, W: 0.3 to 0.5, V: 0.2 or more move into the precipitate. And it consists of a bainite single phase structure which secured 3.5 or more precipitates total quantity.

Moreover, the heat-resisting steel of the present invention is in mass %, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6-1.9, V: 0.26-0.35, Mo: 0.6-0.9, W: 0.9-1.4, Ti: less than 0.01, Mo and W / 2 is 1.3 to 1.4, and the balance consists of Fe and inevitable impurities, and after tempering heat treatment, in mass %, Fe: 1.0 or more, Cr: 0.8-0. 9, Mo: 0.4 to 0.5, W: 0.3 to 0.5, V: 0.2 or more moved into the precipitate, and a bainite single phase in which the total amount of the precipitate was secured 3.5 or more It consists of an organization.

  According to these heat-resisting steels, heat-resisting steels having a bainite single-phase structure can be formed by being configured in the range of the content ratios of the respective components described above. As a result, it is possible to provide a heat-resistant steel excellent in high-temperature characteristics, toughness, embrittlement characteristics, etc., which does not have a ferrite phase or the like that significantly lowers the mechanical properties of the material when the generation amount increases. In addition, you may substitute Ti and / or N which are the above-mentioned composition components with Fe and C.

The heat treatment method of the heat-resistant steel of the present invention is in mass%, C: 0.25 to 0.35, Si: 0.00.
15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9, V: 0.26 to 0.35, Mo: 0.6 to 0 .9, W: 0.9 to 1.4, Ti: less than 0.01, N: 0.001 to 0.007, and the total of Mo and W / 2 is 1.3 to 1.4, After the steel ingot consisting of Fe and unavoidable impurities is heated to 980 to 1030 ° C., the steel ingot is cooled so that the cooling rate at the center of the steel ingot is at least 20 ° C./h to 80 ° C./h , It is characterized by tempering.

Moreover, the heat processing method of the heat-resistant steel of this invention is the mass%, C: 0.25-0.35, Si:
0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9, V: 0.26 to 0.35, Mo: 0.6 -0.9, W: 0.9-1.4, Ti: less than 0.01, the total of Mo and W / 2 is 1.3-1.4, the balance being from Fe and inevitable impurities The resulting steel ingot is heated to 980 to 1030 ° C., then cooled so that the cooling rate at the center of the steel ingot is at least 20 ° C./h to 80 ° C. , and then tempered.

  According to these heat-resistant steel heat treatment methods, for example, at least 20 ° C./h or more is very slow at the center of the steel ingot without using a coolant such as water or oil or forcibly cooling by a blast. Even when quenched at a cooling rate, a heat resistant steel having a bainite single phase structure in which a ferrite phase is not formed can be formed.

The steam turbine rotor for high temperature of the present invention is in mass %, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6 , Cr: 1.6-1.9, V: 0.26-0.35, Mo: 0.6-0.9, W: 0.9-1.4, Ti: less than 0.01, N: 0.001 to 0.007, a total of Mo and W / 2 is 1.3 to 1.4, the balance being Fe and unavoidable impurities, after tempering, by mass%, Fe: 1. 0 or more, Cr: 0.8 to 0.9, Mo: 0.4 to 0.5, W: 0.3 to 0.5, V: 0.2 or more move into the precipitate, and the precipitate It is characterized by being formed of a heat resistant steel having a bainite single phase structure with a total amount of 3.5 or more.

Moreover, the steam turbine rotor for high temperature of this invention is the mass %, C: 0.25-0.35, Si: 0.15 or less, Mn: 0.2-0.8, Ni: 0.3-0 .6, Cr: 1.6 to 1.9, V: 0.26 to 0.35, Mo: 0.6 to 0.9, W: 0.9 to 1.4, Ti: less than 0.01, The sum of Mo and W / 2 is 1.3 to 1.4, and the balance is Fe and inevitable impurities, and after tempering heat treatment, in mass %, Fe: 1.0 or more, Cr: 0.8 To 0.9, Mo: 0.4 to 0.5, W: 0.3 to 0.5, V: 0.2 or more moved into the precipitate, and the total amount of the precipitate was secured to 3.5 or more. It is characterized by being formed of heat resistant steel having a bainite single phase structure.

  According to these high-temperature steam turbine rotors, a high-temperature steam turbine rotor composed of a bainite single-phase structure can be formed by being configured in the range of the content ratios of the respective composition components described above. As a result, it is possible to provide a high-temperature steam turbine rotor excellent in high-temperature characteristics, toughness, embrittlement characteristics, etc., which does not have a ferrite phase or the like that significantly lowers the mechanical properties of the material as the generation amount increases. In addition, you may substitute Ti and / or N which are the above-mentioned composition components with Fe and C. Further, in these high-temperature steam turbine rotors, the total amount of precipitates is ensured to be 2.8% or more after operation for 100,000 hours in the vicinity of the portion of the high-temperature steam turbine rotor that is exposed to the highest temperature steam during steady operation. ing. In addition, the maximum temperature of the vapor | steam at the time of steady operation is about 540-580 degreeC.

  The high-temperature steam turbine rotor is a high-pressure rotor, medium-pressure rotor, or high-medium-pressure rotor. The exhaust temperature at the final stage outlet of the high-pressure portion of the high-pressure or high-medium-pressure rotor is 300 ° C. or higher. It is a rotor of a steam turbine that is operated at an exhaust temperature of the final stage outlet of the intermediate pressure section at 200 ° C. or higher. The exhaust steam is introduced into a boiler or a low-pressure turbine installed separately.

  According to the heat-resistant steel, heat-resistant steel heat treatment method and high-temperature steam turbine rotor of the present invention, it has a bainite single-phase structure, can be stably operated in a high-temperature steam environment, and is excellent in economy.

  Hereinafter, an embodiment of the present invention will be described.

First, the reason for limiting each component range in the alloy used in the present invention will be described. In the following description, “%” representing the composition is “% by mass” unless otherwise specified.

(1) C (carbon)
C is an essential element as a constituent element of various carbides contributing to precipitation strengthening while ensuring hardenability. When the C content is less than 0.25%, the above-described effects are small, and when it exceeds 0.35%, agglomeration of carbides is promoted and the segregation tendency during solidification of the steel ingot is increased. Therefore, the C content is determined to be 0.25 to 0.35%. Moreover, the more preferable range of the content rate of C is 0.27 to 0.33%.

(2) Si (silicon)
Si is useful as a deoxidizer and improves steam oxidation resistance. However, when the content is high, a decrease in toughness and embrittlement are promoted. From this viewpoint, it is desirable to suppress the Si content as much as possible. When the Si content exceeds 0.15%, the above characteristics are remarkably deteriorated. Therefore, the Si content is set to 0.15% or less (0 is not included). A more preferable range of the Si content is 0.1% or less.

(3) Mn (manganese)
Mn is an element useful as a desulfurizing agent, but if the Mn content is less than 0.2%, the desulfurization effect is not observed, and if it exceeds 0.8%, the creep strength is lowered. Therefore, the Mn content is determined to be 0.2 to 0.8%. A more preferable range of the Mn content is 0.4 to 0.8%.

(4) Cr (chrome)
Cr is an indispensable element as a constituent element of carbonitride which is effective for oxidation resistance and corrosion resistance and contributes to precipitation strengthening. In the heat resistant steel according to the present invention, Cr is also useful as an element for improving toughness. When the Cr content is less than 1.6%, the amount of Cr transferred to the carbonitride after the tempering heat treatment is small, so the high temperature stability of the carbonitride cannot be ensured, and when it exceeds 1.9%, the temper softening resistance Decreases, the desired normal temperature strength cannot be ensured, and the creep strength also decreases. Therefore, the Cr content is determined to be 1.6 to 1.9%.

(5) V (Vanadium)
V contributes to solid solution strengthening and formation of fine carbonitrides. When the V content is 0.26% or more, fine precipitates are sufficiently precipitated to suppress the recovery of the parent phase. However, if it exceeds 0.35%, the toughness is lowered and the coarsening of the carbonitride is promoted. . Therefore, the V content is determined to be 0.26 to 0.35%.

(6) W (tungsten)
W becomes a constituent element of solid solution strengthening and carbonitride of the parent phase and contributes to precipitation strengthening. In particular, when combined with Mo, the high-temperature stability of the precipitate can be remarkably enhanced. Since W moves from the parent phase into the precipitate with time during long-time heating at a high temperature, in order to keep the amount of W contributing to solid solution strengthening high for a long time, the W content is set to 0. It should be 9% or more. However, if the W content exceeds 1.4%, the reduction in toughness and the formation of ferrite are promoted, and the component segregation tendency of large steel ingots increases. Therefore, the W content is determined to be 0.9 to 1.4%. A more preferable range of the W content is 0.9 to 1.2%.

(7) Mo (molybdenum)
Mo becomes a constituent element of solid solution strengthening and carbonitride, and contributes to precipitation strengthening. In particular, when combined with W, the high-temperature stability of the precipitate can be remarkably enhanced. Mo moves from the parent phase into the precipitate over time during heating at high temperature for a long time. Therefore, in order to keep the amount of Mo contributing to solid solution strengthening high for a long time, the Mo content is set to 0. It should be 6% or more. However, when the Mo content exceeds 0.9%, the toughness reduction and the formation of ferrite are promoted, and the component segregation tendency of the large steel ingot increases. Therefore, the Mo content is determined to be 0.6 to 0.9%. A more preferable range of the Mo content is 0.7 to 0.9%.

(8) N (nitrogen)
N forms nitrides or carbonitrides and contributes to precipitation strengthening. Furthermore, N remaining in the matrix contributes to solid solution strengthening, but these effects are not observed when the N content is less than 0.001%. On the other hand, when the N content exceeds 0.007%, the coarsening of the nitride or carbonitride is promoted, and the creep strength is lowered. Therefore, the N content is determined to be 0.001 to 0.007%. In the heat-resisting steel according to the present invention, N can be substituted for the formation of carbonitride by increasing the C content within the range of the C content. Further, Fe may be used as an alternative to N.

(9) Ti (titanium)
Ti is useful as a deoxidizer. If the Ti content is less than 0.01%, the remaining Ti dissolves after exhibiting the deoxidation effect, but if it exceeds 0.01%, undissolved coarse Ti carbonitride. As a result, the toughness is reduced and the notch is weakened. Therefore, the Ti content is set to less than 0.01% (0 is not included). Moreover, by containing Ti in this range, the amount of O (oxygen) in the steel ingot can be reduced by the deoxidation effect, and the formation of oxides during the production of the steel ingot can also be prevented. Note that Ti can be substituted by increasing the C content within the range of the C content. Further, Fe may be used as an alternative to Ti.

(10) Ni (nickel)
Ni improves the hardenability and toughness and has the effect of suppressing the formation of ferrite, and the effect is recognized when the Ni content is 0.3% or more. However, if the Ni content exceeds 0.6%, the creep strength is lowered. Therefore, the Ni content is determined to be 0.3 to 0.6%.

  In addition, it is desirable to reduce impurities incidentally mixed when adding the above component and the main component Fe.

  Next, the reason why the total of Mo and W / 2 is limited to 1.3 to 1.4 will be described.

The respective effects of W and Mo in the heat resistant steel of the present invention are as described in (6) and (7) above. However, when these are added in combination, the creep strength is higher than when these are added alone. On the other hand, the segregation tendency of light elements during the production of large steel ingots is significantly increased. In order to exert desired creep strength and avoid segregation, it is necessary to limit the combined amount of W and Mo. For this purpose, it is preferable to use an index generally referred to as Mo equivalent (total content ( mass %) of Mo and W / 2). In the case of the heat resistant steel of the present invention, if the Mo equivalent is less than 1.3, the creep strength decreases, and if the Mo equivalent exceeds 1.4, the component segregation during the production of a large steel ingot becomes remarkable. Therefore, the Mo equivalent (the total content of Mo and W / 2 ( mass %)) was set to 1.3 to 1.4.

Then, after the tempering heat treatment of the heat-resisting steel of the additive element content in the above range, by mass%, Fe: 1.0 or more, Cr: 0.8~0.9, Mo: 0.4~0.5 , W: The reason why 0.3 to 0.5 and V: 0.2 or more are present in the precipitate and the total amount of the precipitate is secured to 3.5 or more will be described.

The heat resistant steel of the present invention is strengthened by solid solution strengthening of the matrix and precipitation of carbonitrides. Carbonitride is intentionally deposited in the tempering heat treatment, and there are four types of precipitates in the heat-resistant steel of the present invention: M ₇ C ₃ type, M ₃ C type, M ₂ C type, and MC type. . M represents a metal element, and M in the M ₇ C ₃ type and M ₃ C type is mainly Fe and Cr, and may contain Mo, W, and the like. Further, M in the M ₂ C type is mainly Mo and W, and may contain V in addition. Further, M in the MC type is mainly V and may contain Mo and W in addition.

Below, the reason for limitation of each component range of Fe, Cr, Mo, W and V described above will be explained. In the following description, “%” representing the composition is “% by mass” unless otherwise specified.
In addition, the measurement and identification of the amount of precipitates were carried out by dissolving the mother phase by electrolysis in a mixed solution of methanol, acetylacetone and tetramethylammonium chloride, washing the residue after filtration, measuring the weight, and before and after dissolution. It was carried out using a value gradually reduced by the weight of Furthermore, the kind of the precipitate was determined using X-ray analysis or the like for the collected residue.

(11) Fe (iron)
Fe in the precipitate is a constituent element of the M ₇ C ₃ type and M ₃ C type precipitates and contributes to precipitation strengthening. If the transfer amount of Fe into the precipitate after the tempering heat treatment is less than 1.0%, the precipitation amount is small and the precipitation strengthening action does not work sufficiently. In order to exhibit the creep strength, it is effective to use the temporal transformation after precipitation as an M ₃ C type precipitate after the tempering heat treatment. If it is less than the range, the amount of precipitation of M ₃ C type precipitates is small, so that it is not expected to increase the creep strength by such a method. For these reasons, the Fe content in the precipitate after the tempering heat treatment was set to 1.0% or more.

(12) Cr (chrome)
Cr in the precipitate mainly serves as a constituent element of the M ₇ C ₃ type and M ₃ C type precipitates and contributes to precipitation strengthening. Since Cr substitutes a part of Fe in these precipitates, it also has an effect of improving the stability of the precipitates. If the amount of Cr transferred into the precipitate after the tempering heat treatment is less than 0.8%, the amount of precipitation is small and the precipitation strengthening action does not work sufficiently. On the other hand, if the amount of Cr transferred into the precipitate after the tempering heat treatment exceeds 0.9%, the disappearance of the Fe ₃ C type precipitate is induced during the tempering heat treatment, and the time-dependent effect described in (11) Cannot be demonstrated. Therefore, the Cr content in the precipitate after the tempering heat treatment is set to 0.8 to 0.9%.

(13) W (tungsten)
W in the precipitate mainly becomes a constituent element of the M ₂ C type precipitate, contributes to precipitation strengthening, and a part of the M ₇ C ₃ type, M ₃ C type and MC type precipitates are also substituted. Therefore, the high temperature stability of these precipitates is remarkably increased. If the amount of movement of W into the precipitate after the tempering heat treatment is less than 0.3%, the stability of these precipitates is low and the desired creep strength cannot be exhibited. On the other hand, if the movement amount of W into the precipitate after the tempering heat treatment exceeds 0.5%, the solid solution amount of W in the matrix phase is lowered, and the solid solution strengthening amount at high temperature is lowered. Therefore, the W content in the precipitate after the tempering heat treatment is set to 0.3 to 0.5%.

(14) Mo (molybdenum)
Mo in the precipitate mainly becomes a constituent element of the M ₂ C type precipitate and contributes to precipitation strengthening, and a part of the M ₇ C ₃ type, M ₃ C type and MC type precipitates are also substituted. Therefore, the high temperature stability of these precipitates is remarkably increased. If the amount of Mo transferred into the precipitate after the tempering heat treatment is less than 0.4%, the stability of these precipitates is so low that the desired creep strength cannot be exhibited. On the other hand, if the amount of Mo moved into the precipitate after the tempering heat treatment exceeds 0.5%, the solid solution amount of Mo in the matrix phase decreases and the solid solution strengthening amount at high temperature decreases. Therefore, the Mo content in the precipitate after the tempering heat treatment is set to 0.4 to 0.5%.

(15) V (Vanadium)
V in the precipitate mainly becomes a constituent element of the fine MC type precipitate, contributes to precipitation strengthening, and partly in the M ₇ C ₃ type, M ₃ C type and M ₂ C type precipitates. Will significantly increase the high temperature stability of these precipitates. If the amount of movement of V into the precipitate after the tempering heat treatment is less than 0.2%, the amount of MC-type precipitates is small, and the stability of other precipitates is low. Therefore, the V content in the precipitate after the tempering heat treatment is set to 0.2% or more.

  In order for the precipitate composed mainly of the above five elements (11) to (15) and C, N, etc. to be finely and uniformly dispersed by the tempering heat treatment, the total amount of the precipitate is required to be 3.5% or more. If it is lower than this, as described in (11) to (15), the strength characteristics and the high-temperature stability of the precipitate itself are lowered. Therefore, the total content of precipitates after tempering heat treatment is set to 3.5% or more.

  Next, the deposits of the above (11) to (15) after the tempering heat treatment of the high-temperature steam turbine rotor formed of the heat-resistant steel composed of each component element in the range of (1) to (10) described above Even if the total amount (3.5%) decreases from the total amount of precipitates after the tempering heat treatment after operation for 100,000 hours in the vicinity of the portion exposed to steam at the highest temperature during steady operation, The reason why it is preferable to secure the above will be described.

The heat-resistant steel constituting the high-temperature steam turbine rotor of the present invention is different from ordinary heat-resistant steel in that the amount of solid solution and the amount of carbonitride deposited changes over time during operation, which itself is excellent in high temperature. This is one of the causes of the characteristics. In this heat-resistant steel, Mo and W dissolved in supersaturation move mainly over time into M ₂ C type precipitates and MC type precipitates, while increasing their high temperature stability, The M ₃ C type precipitate containing Fe as a main constituent element transforms with time into a more stable M ₇ C ₃ type precipitate containing Cr as a main constituent element to maintain the creep strength. In particular, the latter is accompanied by dissolution of Fe in the M ₃ C type precipitate precipitated in a large amount by the tempering heat treatment, so that the total amount of the precipitate is reduced as compared with that after the tempering heat treatment. The remaining M ₃ C type precipitate has an effect in maintaining the creep strength, but when the total amount of the precipitate falls below 2.8%, the M ₃ C type precipitate disappears completely and rapidly The precipitation strengthening action is reduced. Therefore, the total amount of precipitates after operation corresponding to 100,000 hours is set to 2.8% or more.

  The precipitates deposited on the heat-resistant steel constituting the high-temperature steam turbine rotor have different precipitation amounts depending on the type, and the precipitation amount changes with time depending on the operation of the high-temperature steam turbine rotor. However, no new types of precipitates are deposited during operation. Moreover, the maximum temperature of the vapor | steam at the time of steady operation is about 540-580 degreeC.

  Next, the reason why the average austenite crystal grain size is preferably 100 μm or less will be described.

  The prior austenite grain size has a considerable influence on various mechanical properties. When it exceeds 100 μm, ductility is lowered and intergranular cracking is likely to occur, and notch creep strength and toughness are lowered. Therefore, the prior austenite crystal grain size is set to 100 μm or less on average.

  The crystal grain size is finally determined by the heating temperature at the time of quenching. In the heat resistant steel of the present invention, a heating temperature of 980 to 1030 ° C. is suitable. When the heating temperature is less than 980 ° C., a sufficient quenching effect cannot be obtained and desired mechanical properties cannot be exhibited. On the other hand, when the heating temperature exceeds 1030 ° C., the coarsening of the crystal grains becomes remarkable, and the characteristic deterioration due to the above-mentioned coarsening becomes remarkable.

  The heat-resistant steel and high-temperature steam turbine rotor of the present invention contain the elements described in the above (1) to (10) in a predetermined range, the Mo equivalent is in a predetermined range, and the prior austenite grain size is an average. The elements described in (11) to (12) are contained in the precipitate within a predetermined range. In addition, in the vicinity of the high temperature steam turbine rotor that is exposed to the highest temperature steam during steady operation, the total amount of precipitates can be maintained at a predetermined value or more even after operation equivalent to 100,000 hours. It can exhibit properties.

  In addition, when it contains Cr, Mo, W, V etc. which are ferrite forming elements like the heat-resistant steel of this invention, a ferrite may produce | generate in a metal structure depending on the addition amount of each element. Since these elements are concentrated in the ferrite in the low alloy steel and the effects of the respective elements described above cannot be sufficiently exhibited, in the heat-resistant steel of the present invention, each additive element (( The addition range of 1) to (10)) is determined.

  In addition, the generation of the ferrite phase may occur depending on the heating temperature at the time of manufacture and the cooling conditions after heating. In particular, in a steam turbine rotor material that is repeatedly heated and cooled in the manufacturing process and has a large material size, for example, a ferrite phase is generated depending on the cooling rate during quenching. That is, the ferrite phase has a characteristic that it is generated when it is exposed to a certain temperature range for a certain time. For example, when the cooling rate during quenching is low, it passes through this generation region in the cooling process. As a result, a structure in which a ferrite phase is generated in the bainite structure is obtained, leading to deterioration of characteristics.

  Even when carbonitride is precipitated in ferrite, the properties are lower than those of a bainite single-phase structure, and the concentration of components and the structure are inhomogeneous. Adjustment of the cooling rate to obtain a bainite single-phase structure as much as possible is emphasized in the production of heat-resistant steel.

  However, in heat-resistant steel and high-temperature steam turbine rotors within the component range of the present invention, a bainite single-phase structure with good mechanical properties at high temperatures can be obtained without providing such a limitation on the cooling rate. it can.

  Examples of the present invention will be described below.

(First embodiment)
It will be described that the heat resistant steel according to one embodiment of the present invention has excellent characteristics.
The test steel in the first example was prepared by melting about 30 kg of the material in the chemical composition range of the present invention, hot forging the cast ingot, followed by annealing, normalizing, quenching, It was made by tempering. The quenching was performed so that the cooling rate at the center of the ingot was 20 to 80 ° C./h in the ingot after normalizing at 980 to 1030 ° C.

Table 1 shows the chemical composition of the produced test steel. Among the test steels shown in Table 1, steel types P1 to P14 are heat resistant steels in the composition range according to the present invention. On the other hand, steel types C1 to C6 are heat resistant steels whose compositions are not within the chemical composition range described in the present invention, and are comparative examples. Table 1 also shows the remaining amount of oxygen of each steel type. The unit of numerical values shown in Table 1 is mass %.

  As shown in Table 1, the residual oxygen amount of the test steel containing Ti is 10 ppm at the maximum. Since this value is lower than the residual oxygen amount of the test steel not containing Ti, it can be seen that deoxidation by the addition of Ti works effectively. Steel type C2 has a deoxidizing effect, but produces undissolved Ti carbonitride.

  Moreover, as shown in Table 2, each steel type shown in Table 1 is adjusted to a normal temperature 0.02% yield strength of about 660 to 690 MPa suitable for a turbine rotor.

  About each steel type, the JIS4 2mmV notch Charpy impact test piece was produced and the Charpy impact test was done using the test piece. The test results are shown in Table 2. Table 2 also shows the measurement results of the rupture time in the creep rupture test at 600 ° C. to 196 MPa.

  The steel types P1 to P14 of the examples within the chemical composition range of the present invention exhibited an impact absorption energy of 50 to 55 J at 20 ° C. On the other hand, in the steel types C1 to C6 of the comparative examples, the impact absorption energy was at most 40 J at 20 ° C., and the impact absorption energy was generally lower than that of the examples.

  Moreover, the rupture time in the creep rupture test at 600 ° C. and 196 MPa conducted for each steel was the shortest about 1850 hours in the case of the steel types P1 to P14 of the examples. On the other hand, the creep rupture time in the steel types C1 to C6 of the comparative examples was 800 to 1530 hours.

In the steel types of the comparative examples, steel types C1, C3, and C5, which showed relatively long break times, had significantly lower impact absorption energy at 20 ° C. than the respective steel types of the examples. Also, when steel equivalent is Mo equivalent (total content of Mo and W / 2 (% by mass )) is less than 1.3, as in steel grade C4, and when Mo equivalent is above 1.4, as in steel grade C5 Clearly has a short creep rupture time. Furthermore, even when the Mo equivalent is in the range of 1.3 to 1.4, if the amount of other elements added is not within the chemical composition range of the present invention, the creep rupture time is short and the impact absorption energy is low. It was.

  From the above, when the heat resistant steel of this example is adjusted to an equivalent normal temperature of 0.02% proof stress, compared with the heat resistant steel of the comparative example having an additive element amount not in the composition range of the present invention, the impact absorption energy and It was found that both creep rupture times showed excellent values. Moreover, it became clear that the oxygen residual amount in a steel ingot fell by adding Ti.

(Second embodiment)
It will be described that the heat resistant steel within the chemical composition range of the present invention is preferably adjusted to a state in which a predetermined amount of precipitation is secured when tempering heat treatment is performed.

  In the second embodiment, the steel types P1, P6, P11, and P14 shown in Table 1 were quenched so that the cooling rate from 990 ° C. to the center of the test steel was 20 to 80 ° C./h. After performing, tempering heat processing was performed at 630-730 degreeC.

Table 3 shows the contents ( mass %) of Fe, Cr, Mo, W and V, and the total amount ( mass %) of precipitates among the elements contained in the precipitates after tempering heat treatment in these test steels. Show. Table 3 also shows the measurement results of the rupture time in a creep rupture test at 600 ° C. to 196 MPa performed on these test steels.

From the measurement results shown in Table 3, the content of each element contained in the precipitate after the tempering heat treatment, which is shown as a comparative example in each steel type, is included in the precipitate of the present invention described above. When the content is not within the range of the element content, and when the total amount of precipitates is less than the total amount of precipitates of the present invention (3.5% by mass or more), the creep rupture time is significantly shortened. I understand.

On the other hand, the heat resistant steel (Example) that satisfies the range of the content of elements contained in the precipitate of the present invention and whose total amount is equal to or greater than the total amount (3.5% by mass or more) of the precipitate of the present invention is excellent. It can be seen that it exhibits creep rupture characteristics. It should be noted that the heat-resistant steels shown as examples in each of these steel types are not only creep rupture characteristics but also sufficient impact as can be inferred from the results of steel types P1, P6, P11, and P14 in Table 2. It is also possible to ensure the absorbed energy.

(Third embodiment)
When the heat-resistant steel in the chemical composition range of the present invention is subjected to a tempering heat treatment, it is adjusted to a state in which a predetermined amount of precipitation is secured, and in the vicinity of a portion exposed to high-temperature steam at a predetermined temperature for 100,000 hours, It will be explained that it is preferable to ensure that the total amount of precipitates is 2.8% by mass or more.

In the third example, the total amount of precipitates after the tempering heat treatment in the steel types P2, P7, P10 and P13 shown in Table 1 is within the range of the content of elements contained in the precipitates of the present invention. A heat resistant steel satisfying and having a total amount of precipitates equal to or greater than the total amount (3.5% by mass or more) of the precipitates of the present invention was used as a test steel. These test steels were heated at a temperature of 550 to 600 ° C. for 100,000 hours.

  Table 4 shows the total amount of precipitates after tempering heat treatment, the total amount of precipitates after heating equivalent to 100,000 hours, and the measurement results of the rupture time in a creep rupture test at 600 ° C.-196 MPa.

From the measurement results shown in Table 4, when the total amount of precipitates after heating exceeds 2.8% by mass (Example column), the creep rupture time is 1500 hours or more, and the steel type P1 shown in Table 2 With respect to the creep rupture time at ~ P14, a rupture time of at least 80% is secured. On the other hand, when the total amount of precipitates after heating is less than 2.8% (comparative example column), the creep rupture time is about 700 to 825 hours, and the creep rupture time in steel types P1 to P14 shown in Table 2 The rupture time was about 40%.

From the above, when the heat resistant steel in the chemical composition range of the present invention is subjected to tempering heat treatment, the elements described in (11) to (12) are contained in the precipitate within a predetermined range, for example, When the total amount of precipitates after heating at a high temperature of 550 to 600 ° C. for 100,000 hours is 2.8% by mass or more, compared with the comparative example that does not reach the total amount of precipitates. It can be seen that a significantly longer creep rupture time is obtained.

(Fourth embodiment)
It will be described that the heat-resistant steel in the chemical composition range of the present invention is suitable for producing a homogeneous steel ingot with small concentration segregation of components.

  In the fourth example, assuming that steel ingots of 60 tons or more were produced with chemical composition components of steel types P6, P12, C2 and C6 shown in Table 1, a numerical simulation was performed on the segregation tendency. .

  In this numerical simulation, the concentration of the component in the height direction at the center of the ingot after solidification was measured for an ingot produced using a mold having a value obtained by gradually reducing the mold height by the mold diameter. Was analyzed.

  Table 5 shows the analysis results of the component concentrations of C, which is the lightest element, and W, which is the heaviest element, constituting the steel types described above. In addition, the value in Table 5 is a value obtained by gradually grading the component concentration of each part of the steel ingot with the component concentration of the molten metal. Further, a distance of 100% from the bottom of the steel ingot represents the upper end of the steel ingot.

  From the analysis results shown in Table 5, the concentration ratio of C, which is the lightest element in steel types P6 and P12, is in the range of 0.93 to 1.15, and the concentration ratio of W, which is the most heavy element, is approximately 1.0. On the other hand, in the steel types C2 and C6, it can be seen that the concentration ratio of C increases particularly as it goes to the end of the steel ingot, and significant component segregation occurs.

  From the above results, it can be seen that the chemical composition range of the present invention is suitable for producing a homogeneous steel ingot with small concentration segregation of components.

(Fifth embodiment)
The reason why it is preferable that the prior austenite crystal grain size of the heat resistant steel in the chemical composition range of the present invention is adjusted to 100 μm or less on average will be described.

  In the fifth example, the steel types P3, P7, P12 and P13 shown in Table 1 were used as test steels. In this test steel, after adjusting the crystal grain size by hot working, The yield was adjusted to a suitable room temperature of 0.02% proof stress of about 660 to 690 MPa.

  About these test steels, the crystal grain diameter was measured using the test method described in JIS G 0551. Further, the drawing at 300 ° C. was measured based on the tensile test method described in JIS Z 2241. Further, the notch creep rupture strength in the creep rupture test at 300 ° C. was strengthened or weakened compared to the smooth material. Was measured.

Table 6 shows the results of the above measurement.
From the measurement results shown in Table 6, when the prior austenite crystal grain size is 100 μm or less (Example), 50% or more of the tensile drawing and notch strengthening can be exhibited, whereas the prior austenite crystal grain size is 100 μm. In the case of exceeding (comparative example), the tensile drawing was suddenly lowered and the notch was weakened.

  From the above, it is possible to exhibit good tensile properties and creep rupture properties by adjusting the heat resistant steel in the chemical composition range of the present invention to a predetermined precipitation state and further making the crystal grain size 100 μm or less. I understand that.

Claims (11)

    In mass%, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9 , V: 0.26 to 0.35, Mo: 0.6 to 0.9, W: 0.9 to 1.4, Ti: less than 0.01, N: 0.001 to 0.007, Mo and The total of W / 2 is 1.3 to 1.4, and the balance is Fe and inevitable impurities, and after tempering heat treatment, in mass%, Fe: 1.0 or more, Cr: 0.8 to 0 .9, Mo: 0.4 to 0.5, W: 0.3 to 0.5, V: 0.2 or more moved into the precipitate, and the total amount of precipitate was secured to 3.5 or more. A heat-resistant steel comprising a phase structure.     In mass%, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9 , V: 0.26-0.35, Mo: 0.6-0.9, W: 0.9-1.4, Ti: less than 0.01, and the total of Mo and W / 2 is 1.3. -1.4, the balance being Fe and inevitable impurities, and after tempering heat treatment, in mass%, Fe: 1.0 or more, Cr: 0.8-0.9, Mo: 0.4-0 0.5, W: 0.3 to 0.5, V: 0.2 or more move into the precipitate, and the heat resistance is characterized by comprising a bainite single-phase structure in which the total amount of precipitates is secured to 3.5 or more. steel.   The heat-resistant steel according to claim 1 or 2, wherein the Ti and / or N is substituted with Fe and C. The heat resistant steel is
It has a tempered bainite single-phase structure with an average austenite crystal grain size of 100 μm or less on average, and in the bainite single-phase structure, an M ₃ C type precipitate, an M ₇ C ₃ type precipitate, an M ₂ C type precipitate, 4. The heat-resisting steel according to any one of claims 1 to 3, wherein the MC type precipitate is deposited and the type of the precipitate does not change even when exposed to high temperature steam at a predetermined temperature for 100,000 hours. In mass%, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9 , V: 0.26 to 0.35, Mo: 0.6 to 0.9, W: 0.9 to 1.4, Ti: less than 0.01, N: 0.001 to 0.007, Mo and After heating the steel ingot with the sum of W / 2 being 1.3 to 1.4 and the balance being Fe and inevitable impurities to 980 to 1030 ° C., the cooling rate at the center of the steel ingot is A heat-treating method for heat-resistant steel, characterized by cooling at least 20 ° C./h to 80 ° C./h and then tempering. In mass%, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9 , V: 0.26-0.35, Mo: 0.6-0.9, W: 0.9-1.4, Ti: less than 0.01, and the total of Mo and W / 2 is 1.3. After the steel ingot consisting of Fe and unavoidable impurities is heated to 980 to 1030 ° C., the cooling rate at the center of the steel ingot is at least 20 ° C./h or more and 80 ° C./h A heat-treating method for heat-resistant steel, which is cooled to the following and then tempered.   In mass%, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9 , V: 0.26 to 0.35, Mo: 0.6 to 0.9, W: 0.9 to 1.4, Ti: less than 0.01, N: 0.001 to 0.007, Mo and The total of W / 2 is 1.3 to 1.4, the balance is Fe and inevitable impurities, and after tempering heat treatment, in mass%, Fe: 1.0 or more, Cr: 0.8 to 0 .9, Mo: 0.4 to 0.5, W: 0.3 to 0.5, V: 0.2 or more moved into the precipitate, and the total amount of precipitate was secured to 3.5 or more. A high-temperature steam turbine rotor characterized by being formed of heat-resistant steel having a phase structure.   In mass%, C: 0.25 to 0.35, Si: 0.15 or less, Mn: 0.2 to 0.8, Ni: 0.3 to 0.6, Cr: 1.6 to 1.9 , V: 0.26-0.35, Mo: 0.6-0.9, W: 0.9-1.4, Ti: less than 0.01, and the total of Mo and W / 2 is 1.3. -1.4, the balance being Fe and inevitable impurities, and after tempering heat treatment, in mass%, Fe: 1.0 or more, Cr: 0.8-0.9, Mo: 0.4-0 .5, W: 0.3 to 0.5, V: 0.2 or more moved into the precipitate, and was formed of a heat-resistant steel having a bainite single-phase structure in which the total amount of the precipitate was secured 3.5 or more. A high-temperature steam turbine rotor characterized by that. The total amount of precipitates is ensured to be 2.8% or more after 100,000 hours of operation in the portion of the high-temperature steam turbine rotor exposed to the highest temperature steam during steady operation. The high-temperature steam turbine rotor according to claim 8. 10. The high-temperature steam turbine rotor according to claim 7, wherein the Ti and / or N is replaced with Fe and C. 11. The high temperature steam turbine rotor comprises:
It has a tempered bainite single-phase structure with an average austenite crystal grain size of 100 μm or less on average, and in the bainite single-phase structure, an M ₃ C type precipitate, an M ₇ C ₃ type precipitate, an M ₂ C type precipitate, 11. The high temperature use according to any one of 7 to 10, wherein the MC type precipitate is deposited, and the type of the precipitate does not change even if the MC type deposit is exposed to steam at a maximum temperature for 100,000 hours during steady operation. Steam turbine rotor.