CN114622132A - Heat-resistant steel for ultra-supercritical steam turbine casting with temperature of above 630 ℃ and preparation method thereof - Google Patents
Heat-resistant steel for ultra-supercritical steam turbine casting with temperature of above 630 ℃ and preparation method thereof Download PDFInfo
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Abstract
The invention discloses heat-resistant steel for an ultra supercritical steam turbine casting with the temperature of above 630 ℃ and a preparation method thereof, belongs to the technical field of metal materials, and aims to solve the problem of poor comprehensive performance of the existing heat-resistant steel. The heat-resistant steel comprises the following components in percentage by mass: c: 0.04 to 0.08 percent; mn: 0.2% -0.5%; si: 0.6% -1.0%; cr: 8.5% -9.2%; v: 0.15% -0.35%; w: 2.0 to 2.45 percent; co: 3% -3.4%; cu: 0.01% -0.5%, Nb: 0.01% -0.15%, Ta: 0.01% -0.15%, Nb + Ta: 0.09% -0.3%, B: 0.012% -0.02%; n: 0.004% -0.008%; al is less than or equal to 0.01 percent, Ti is less than or equal to 0.01 percent, rare earth: 0.01% -0.3%; p is less than or equal to 0.008 percent; s is less than or equal to 0.005 percent; the balance of Fe and inevitable impurities, and the rare earth is more than two mixed rare earths consisting of Ce, Y, Nd, La and Pr. The heat-resistant steel has good comprehensive performance and is suitable for steam turbine castings with the working temperature of 630 ℃ or above.
Description
Technical Field
The invention belongs to the technical field of metal materials, and particularly relates to heat-resistant steel for an ultra-supercritical steam turbine casting with the temperature of above 630 ℃ and a preparation method thereof.
Background
As the largest coal consumption country in the world, coal-fired thermal power generation is the most important energy supply mode in China, and the coal-fired power generation technology is still the important development direction of the power industry in China for a long time in the future. For a thermal power generating unit, the heat efficiency of the unit can be obviously improved by improving steam parameters, and the coal consumption and the greenhouse gas emission are reduced. Under the condition that a thermodynamic system is not changed, the initial parameters of the current unit are improved from 31MPa/600 ℃/620 ℃/620 ℃ to 35MPa/615 ℃/630 ℃/630 ℃, and the coal consumption for power generation can be reduced by about 3 g/kWh; the initial parameters of the unit are further improved to 35MPa/630 ℃/650 ℃/650 ℃, and the coal consumption for power generation can be reduced by about 2 g/kWh. At present, the maximum steam inlet temperature of a unit which is put into commercial operation reaches 620 ℃, thermal power units below 620 ℃ are not approved any more in China, and the future development direction is thermal power units above 630 ℃, 650 ℃ and 700 ℃.
However, the preparation of key parts of clean and efficient ultra-supercritical thermal generator sets in China is still limited by people, corresponding key heat-resistant materials need to be imported, and the localization of high-performance and high-reliability heat-resistant steel materials and products is urgent for overcoming key core technologies. The improvement of the unit parameters further improves the requirements on the material performance, and particularly has more strict requirements on the obdurability and the durability under the conditions of high stress and high temperature. Precipitation strengthening is an important strengthening method of 9Cr heat-resistant steel, and the main strengthening phase is M23C6And MX-type particles, and with increasing time of service, M23C6The size of the type carbide will grow, resulting in a large reduction of the strengthening effect. Among the existing high-temperature casting materials, ZG12Cr10Mo1W1VNbN, ZG12Cr9Mo1W1VNb and the like can be selected and used in the JB/T11018 standard. The ZG12Cr10Mo1W1VNbN steel has good room temperature performance, but the highest working temperature cannot exceed 610 ℃, the creep rupture strength cannot meet the requirement after being higher than 610 ℃, and the corrosion resistance and the high-temperature oxidation resistance are slightly poor; the material of large castings for steam turbines with higher service temperature is not reliable at present.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a heat-resistant steel for ultra supercritical steam turbine castings of 630 ℃ or higher, which has good comprehensive properties such as high-temperature strength, impact resistance, high-temperature durability, and the like, and is suitable for steam turbine castings of 630 ℃ or higher in operating temperature, and a preparation method thereof.
The purpose of the invention is mainly realized by the following technical scheme:
the invention provides heat-resistant steel for an ultra-supercritical steam turbine casting with the temperature of above 630 ℃, which comprises the following components in percentage by mass: c: 0.04 to 0.08 percent; mn: 0.2 to 0.5 percent; si: 0.6% -1.0%; cr: 8.5% -9.2%; v: 0.15% -0.35%; w: 2.0% -2.45%; co: 3% -3.4%; cu: 0.01% -0.5%, Nb: 0.01% -0.15%, Ta: 0.01% -0.15%, Nb + Ta: 0.09% -0.3%, B: 0.012% -0.02%; n: 0.004% -0.008%; al is less than or equal to 0.01 percent, Ti is less than or equal to 0.01 percent, rare earth: 0.01% -0.3%; p is less than or equal to 0.008 percent; s is less than or equal to 0.005 percent; the balance of Fe and inevitable impurities, and the rare earth is more than two mixed rare earths consisting of Ce, Y, Nd, La and Pr.
Further, the composition comprises the following components in percentage by mass: c: 0.077% -0.08%; mn: 0.45% -0.5%; si: 0.7% -1.0%; cr: 8.9% -9.0%; v: 0.21% -0.26%; w: 2.35% -2.45%; co: 3% -3.21%; cu: 0.3% -0.4%, Nb: 0.02% -0.06%, Ta: 0.07% -0.11%, Nb + Ta: 0.09% -0.3%, B: 0.014% -0.017%; n: 0.005% -0.008% of Al: 0.005-0.007%, Ti is less than or equal to 0.01%, rare earth: 0.01% -0.3%; p is less than or equal to 0.008 percent; s is less than or equal to 0.005 percent; the balance of Fe and inevitable impurities.
Furthermore, the microstructure of the heat-resistant steel is tempered martensite, fine dispersed second phase particles and a very small amount of dispersed spherical M3B2The second phase particles comprise M23C6Type carbide and MX particles.
The invention also provides a preparation method of the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃, which comprises the following steps:
step S1: determining the proportion of the raw materials according to the content of each component in the component proportion, smelting the raw materials, refining, and carrying out casting forming to obtain an ingot;
step S2: and (3) carrying out high-temperature homogenization and normalizing heat treatment on the cast ingot, and then carrying out tempering heat treatment to obtain the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃.
Further, the specific step of step S2 includes:
step S201: heating the ingot to 1050-;
step S202: normalizing, wherein the normalizing process comprises the steps of heating the cast ingot to 1000-1200 ℃, preserving heat and then cooling to room temperature;
step S203: and tempering, wherein the tempering process comprises the steps of heating the cast ingot to 700-800 ℃, preserving heat, and then cooling the cast ingot to room temperature along with the furnace to obtain the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃.
Further, in the step S201, the holding time T1 of the high temperature homogenization treatment and the ingot thickness H1 satisfy the following relationship:
h1/60 is not less than T1 is not less than H1/40, wherein the unit of H1 is mm, and the unit of T1 is H.
Further, in the step S202, before the heating is carried out to the normalizing temperature, the heating speed in the range of 800-950 ℃ is 50-80 ℃/h.
Further, in the step S202, the holding time T2 for the normalizing and the ingot thickness H2 satisfy the following relationship:
h2/60 is not less than T2 is not less than H2/40, wherein the unit of H2 is mm, and the unit of T2 is H.
Further, in step S202, the cooling method after heat preservation is as follows: air cooling is carried out to 300 ℃ and then air cooling is carried out.
Further, in the step S202, the cooling speed of air cooling is 30-50 ℃/h.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
a) the heat-resistant steel for the ultra supercritical steam turbine casting with the temperature of above 630 ℃ provided by the invention can promote the sufficient formation of MX type carbonitride nano reinforced phase by controlling the carbon content at a lower level, not containing Mo and Ni elements and controlling the W, V and Nb element contents, and can avoid the formation of coarse carbonitride and high-temperature delta ferrite, thereby ensuring the uniform structure and the performance to meet the use requirements.
b) A certain amount of Cu element is added to inhibit the formation of high-temperature delta ferrite, and meanwhile, the phenomenon that the creep rupture strength is reduced due to overhigh Cu content is avoided; more than two mixed rare earths of Ce, Y, Nd, La and Pr are also added to purify molten steel and refine cast structure, and multiple rare earth elements can play a synergistic effect to improve the processing performance and further improve the high-temperature mechanical property, oxidation resistance and corrosion resistance of the heat-resistant steel.
c) The invention provides a method for preparing heat-resistant steel for an ultra-supercritical steam turbine casting with temperature of above 630 DEG CIn the process, the process parameters such as time and temperature of high-temperature homogenization treatment, normalizing temperature and time, tempering temperature and time and the like are accurately controlled to ensure that the obtained microstructure is tempered martensite, fine dispersed second phase particles and a very small amount of dispersed spherical M3B2The second phase particles comprise M in face centered cubic (fcc) structure23C6The size of the type carbide is about 20nm-150nm, M is mainly Cr, Fe, W, Co and a small amount of Mo and V, the second phase particles also comprise a nano-scale precipitation phase (MX type precipitation phase) with the size of 5-20nm, M is mainly V, Nb, Ta, Ce and the like, and X is mainly N, C. Ensures the excellent room temperature strength, the excellent high temperature strength, the high temperature oxidation resistance and the corrosion resistance of the heat-resistant steel, and is suitable for castings of 650 ℃ steam turbine cylinder bodies, valve bodies and the like.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description.
Drawings
The drawings are only for purposes of illustrating the particular invention and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout the figures.
FIG. 1A tempered martensite structure of a heat-resistant steel in example 1;
FIG. 2 example 1 after tempering M23C6Forming a precipitated phase;
FIG. 3 MX-type precipitated phases after tempering in example 1.
Detailed Description
The invention provides heat-resistant steel for an ultra supercritical steam turbine casting with the temperature of above 630 ℃, which comprises the following components in percentage by mass: c: 0.04 to 0.08 percent; mn: 0.2% -0.5%; si: 0.6% -1.0%; cr: 8.5% -9.2%; v: 0.15% -0.35%; w: 2.0% -2.45%; co: 3% -3.4%; cu: 0.01% -0.5%, Nb: 0.01% -0.15%, Ta: 0.01% -0.15%, Nb + Ta: 0.09% -0.3%, B: 0.012% -0.02%; n: 0.004% -0.008%; al is less than or equal to 0.01 percent, Ti is less than or equal to 0.01 percent, rare earth: 0.01% -0.3%; p is less than or equal to 0.008 percent; s is less than or equal to 0.005 percent; the balance of Fe and inevitable impurities, and the rare earth is more than two mixed rare earths consisting of Ce, Y, Nd, La and Pr.
Compared with the prior art, the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃ has the characteristics of excellent high-temperature mechanical property, oxidation resistance, corrosion resistance and the like. The invention controls the carbon content at a lower level, does not contain Mo and Ni elements, controls the W, V and Nb element content, can promote the sufficient formation of MX-type carbonitride nano reinforced phase, avoids the formation of coarse carbonitride and high-temperature delta ferrite, and ensures the uniform structure and the performance to meet the use requirements; a certain amount of Cu element is added to inhibit the formation of high-temperature delta ferrite, and the phenomenon that the creep rupture strength is reduced due to overhigh Cu content is avoided; the invention also adds more than two mixed rare earths of Ce, Y, Nd, La and Pr for purifying molten steel and refining cast structure, and multiple rare earth elements can play a synergistic effect to improve the processing performance and the high-temperature mechanical property, oxidation resistance and corrosion resistance of the heat-resistant steel.
Specifically, the heat-resistant steel for the ultra supercritical steam turbine casting with the temperature of above 630 ℃ has the following functions of the components:
c: form a main dispersion strengthening phase, M, in heat-resistant steel23C6Form and MX carbonitride particles; c is also an austenite forming element and can inhibit the formation of harmful phase high-temperature delta ferrite; since too high a carbon content results in coarse reinforcing phase particles, the mass percentage of C in the present invention is controlled to 0.04% to 0.08%.
Mn: the hot working performance can be improved, the formation of high-temperature delta ferrite is inhibited, the effect is not obvious when the content is lower than 0.2 percent, and the creep rupture strength is reduced when the content is too high, so that the Mn content is 0.2 to 0.5 percent in the invention.
Si: effective deoxidizer in steel can improve oxidation resistance. However, Si promotes the precipitation of Laves phase and promotes the formation of high-temperature ferrite, and thermodynamic calculation shows that when the Si content is more than 1.0%, the precipitation temperature of the high-temperature ferrite is reduced to 1170 ℃, and the temperature is in the temperature range of the heat treatment process, so that the performance is easily adversely affected; when the Si content is more than 0.6%, the oxidation resistance of the steel can be improved to a certain degree, so that the Si content is controlled to be 0.6-1.0%.
Cr: improve the corrosion resistance and oxidation resistance of steel to form Cr23C6The type strengthening phase can promote the precipitation of the Z phase when the Cr content exceeds 9.2 percent and damage the high-temperature service performance of the material, so the Cr content is controlled to be 8.5 to 9.2 percent in the invention.
V: the method is mainly used for forming MX type vanadium carbonitride strengthening phases, the quantity of the strengthening phases is insufficient when the V content is too low, and the thick vanadium carbonitride is formed when the V content is too high, so that the creep strength is reduced. In the invention, the content of V is controlled to be 0.15-0.35%.
W: inhibition of M23C6The shape particles are coarsened, a proper amount of W element can ensure the creep strength of the heat-resistant steel to be at the best level, excessive W is easy to generate segregation, and a harmful Laves phase is formed. Test research shows that when W is more than 2.5%, component segregation can be caused, the casting process performance of the material is damaged, a large amount of Laves phases are locally formed, and the high-temperature service performance is reduced; when the W content is less than 2.0%, the strengthening effect on the material in the invention is not obvious, so that the W content is controlled to be 2.0-2.45% in the invention.
Co: the formation of delta ferrite in the high-temperature heat treatment process is inhibited, the solid solution strengthening effect of W is fully exerted, the toughness of steel is improved, the creep rupture strength is improved effectively, and the cost is increased, so that the content of Co is controlled to be 3.0-3.4%.
Cu: solid solution in the matrix can restrict dislocation movement to reduce creep rate, can inhibit high-temperature delta ferrite from forming, can precipitate and strengthen and improve corrosion resistance, but the impact toughness of steel is reduced when the content of copper is too high, and the content of Cu is controlled to be 0.01-0.5 percent in the invention.
Nb: has strong solid solution strengthening effect at normal temperature and high temperature, can improve the high-temperature yield strength of the heat-resistant steel, form MX-type niobium carbonitride strengthening phase, refine grains, improve high-temperature corrosion resistance, simultaneously form CrNbN phase in the crystal and form Cr at lower temperature23C6The coating adheres to the surface of the steel sheet, thereby improving the grain boundary corrosion resistance, suppressing VN grain boundary segregation, and strengthening the grain boundary. The compatibility of Nb and Cu elements can improve the creep resistance of the heat-resistant steelCan be used. Since too high Nb content tends to cause segregation, the Nb content of the present invention is controlled to 0.01% to 0.15%.
Ta: similar to Nb element, MX type tantalum carbonitride strengthening phase is formed, and CrTaN phase which is finer than CrNbN phase and not easy to grow is easier to form in the heat treatment process, so that the effect of precipitation strengthening is achieved, and the content of Ta in the invention is controlled to be 0.01-0.15%.
B: can stabilize precipitated phase, strengthen grain boundary and lath boundary and obviously improve creep rupture strength. However, too high a content of B forms a BN phase with N element in the steel, is hardly eliminated by heat treatment, and forms M3B2Boride reduces the effective boron content, has adverse effect on creep property and hot working, and the B content is controlled to be 0.012-0.02 percent in the invention.
N: and an MX-type carbonitride strengthening phase is formed, so that the heat strength of the heat-resistant steel is ensured, and the high content of the carbonitride strengthening phase can be combined with B to form BN, so that the toughness of the steel is seriously damaged, B elements are consumed, and the high-temperature durable strength of the steel is damaged. The content of N and B is controlled in a proper proportioning range, the proportion of N to B is 0.5-0.8 (such as 0.5-0.66), the generation of boron nitride particles can be avoided, and the lasting strength is greatly improved, so that the content of N element is controlled to be 0.005% -0.008% in the invention.
Al: the oxidation resistance of the ferritic heat-resistant steel can be improved, but since it has a strong tendency to bond with N, and it is not favorable for N to exert its effective action, the Al content is controlled to 0.01% or less in the present invention.
Ti: the Ti element has strong combination tendency with the N element, the size can not be controlled and eliminated by heat treatment after TiN is formed, the N element is influenced to play a role, and the performance is damaged, and the content of the Ti element is controlled to be below 0.01 percent.
Rare earth elements: can improve the high-temperature mechanical property and the corrosion resistance of the heat-resistant steel. The addition of the mixed rare earth elements can play a synergistic role, purify the crystal boundary and control the quantity and the form of inclusions, and the comprehensive addition amount of the rare earth elements is 0.01-0.3%.
In addition, the lower the harmful elements such as P, S, the better, and the P is less than or equal to 0.008 percent in the invention; s is less than or equal to 0.005 percent.
In order to further improve the overall performance of the heat-resistant steel, the composition of the heat-resistant steel may be further adjusted. Illustratively, the components comprise the following components in percentage by mass: c: 0.077% -0.08%; mn: 0.45% -0.5%; si: 0.7% -1.0%; cr: 8.9% -9.0%; v: 0.21% -0.26%; w: 2.35% -2.45%; co: 3% -3.21%; cu: 0.3% -0.4%, Nb: 0.02% -0.06%, Ta: 0.07-0.11%, Nb + Ta: 0.09% -0.3%, B: 0.014% -0.017%; n: 0.005% -0.008% of Al: 0.005-0.007%, Ti is less than or equal to 0.01%, rare earth: 0.01% -0.3%; p is less than or equal to 0.008 percent; s is less than or equal to 0.005 percent; the balance of Fe and inevitable impurities, and the rare earth is more than two mixed rare earths consisting of Ce, Y, Nd, La and Pr.
The invention also provides a preparation method of the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃, which comprises the following steps:
step S1: determining the proportion of the raw materials according to the content of each component in the component proportion, smelting the raw materials, refining, and carrying out casting forming to obtain an ingot;
step S2: and (3) carrying out high-temperature homogenization and normalizing heat treatment on the cast ingot, and then carrying out tempering heat treatment to obtain the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃.
Specifically, the step S2 includes the following steps:
step S201: heating the ingot to 1050-;
step S202: normalizing, wherein the normalizing process comprises the steps of heating the cast ingot to 1000-1200 ℃, preserving heat and then cooling to room temperature;
step S203: and tempering, wherein the tempering process comprises the steps of heating the cast ingot to 700-800 ℃, preserving heat, and then cooling the cast ingot to room temperature along with a furnace to obtain the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃.
Specifically, in step S201, the high temperature homogenization treatment is performed to eliminate the element segregation in the as-cast structure, to homogenize the elements in the steel, and to eliminate the portion M3B2Phase and delta ferrite generated in a relatively slow solidification process during casting. High temperature homogenizationToo high temperature can cause more high temperature delta ferrite to be formed in the structure, damage the strength of the steel and be not beneficial to the durability; too low high homogenization temperature results in poor segregation elimination effect and failure to eliminate the skeletal M3B2Therefore, the temperature fluctuation in the actual working condition is considered, and the high temperature homogenization temperature is controlled to 1050-.
Specifically, in step S201, the holding time for the high-temperature homogenization treatment is determined according to the size of the ingot; specifically, the holding time T1 after the workpiece reaches the temperature (i.e. the workpiece is completely hot, and the workpiece is completely hot hereinafter) and the thickness H1 of the cast ingot conform to the following relationship:
h1/60 is not less than T1 is not less than H1/40. Wherein the unit of H1 is mm, and the unit of T1 is H.
Preferably, T1 ═ H1/50.
Specifically, in step S202, too high normalizing temperature causes high-temperature δ ferrite to be precipitated, the structure is too coarse, the solid solution strengthening effect of B and other metal elements is weakened, the casting strength is insufficient and is not favorable for durability, too low segregation elimination effect is poor, and M is3B2The phase dissolution effect is not good, which is not beneficial to the B and other alloy elements to play the role, therefore, the normalizing temperature range is controlled to be 1000-1200 ℃. In addition, when the steel plate is heated under the condition of fully considering the actual working condition, the steel plate can pass through a critical zone (800-950 ℃) as fast as possible, and spherical austenite can be obtained in the austenitizing process so as to obtain a more uniform structure, so that the heating speed in the 800-950 ℃ range is 50-80 ℃/h.
Specifically, in step S202, the holding time for normalizing is determined according to the size of the ingot; specifically, the holding time T2 of the workpiece after reaching the temperature and the thickness H2 of the cast ingot accord with the following relationship:
h2/60 is not less than T2 is not less than H2/40. Wherein the unit of H2 is mm, and the unit of T2 is H.
Preferably, T2 ═ H2/50.
Specifically, in step S202, the cooling method after heat preservation is as follows: air cooling is carried out after air cooling is carried out to 300 ℃, the cooling speed of the air cooling is 30-50 ℃/h, a tempered martensite structure with good mechanical property can be obtained under the air cooling condition, a blocky Laves phase which is not beneficial to performance can appear in the slow cooling process when the cooling speed is too slow, the structure stress is too large when the cooling speed is too fast, and the risk of generating cracks is caused, so the cooling speed is selected to be 30-50 ℃/h.
Specifically, in step S203, the holding time for tempering is determined according to the ingot size, and specifically, the holding time T3 after the workpiece is heated and the ingot thickness H3 satisfy the following relationship:
h3/50 is not less than T3 is not less than H3/30. Wherein the unit of H3 is mm, and the unit of T3 is H.
Preferably, T3 ═ 3H 3/100.
In step S203, the microstructure of the tempered heat-resistant steel is tempered martensite + second phase particles, and has a grain size of 0 grade, and specifically, the microstructure is lath martensite + high-density dislocations and dispersedly distributed second phase particles + a very small amount of dispersedly spherical M3B2(ii) a The second phase particles comprise M of face centered cubic (fcc) structure23C6The size of the type carbide is about 20nm-150nm, M is mainly Cr, Fe, W, Co and a small amount of Mo and V, the second phase particles also comprise a nano-scale precipitation phase with the size of 5-20nm, the nano-scale precipitation phase is subjected to high-resolution observation, is calibrated after Fourier transform and is determined to be an MX type precipitation phase with a face-centered cubic structure by combining an energy spectrum result, M is mainly V, Nb, Ta, Ce and the like, and X is mainly N, C.
It should be noted that the room temperature yield strength of the heat resistant steel after tempering treatment is above 650Mpa (650-; the yield strength at 650 ℃ is more than 260MPa (e.g. 266-286MPa), the tensile strength is more than 360MPa (e.g. 367-388MPa), the elongation is more than or equal to 23 percent (e.g. 23.5-24 percent), and the reduction of area is more than or equal to 85 percent (e.g. 85-88 percent); the creep rupture time of 650 ℃ and 150MPa is more than 4416 h; resisting 650 deg.C water vapor weight gain (1000h)17mg/m2The following (e.g., 12-17 mg/m)2) (ii) a Resisting 650 deg.C oxidation weight gain (400h) of 0.5mg/m2The following. Excellent comprehensive performance and is suitable for castings of cylinder bodies, valve bodies and the like of 650 ℃ steam turbines。
The advantages of the invention of the precise control of the composition and process parameters of the heat-resistant steel will be shown in the following by specific examples and comparative examples.
Example 1
The embodiment provides heat-resistant steel for an ultra-supercritical steam turbine casting with the temperature of above 630 ℃ and a preparation method thereof.
The chemical components and ingredients of embodiment 1 of the invention, in percentage by weight (%), comprise: c: 0.08 percent; mn: 0.5 percent; si: 1 percent; cr: 9.0 percent; v: 0.26 percent; w: 2.35 percent; co: 3.0 percent; cu: 0.3%, Nb + Ta: 0.16%, Nb: 0.04%, Ta: 0.12 percent; b: 0.014%; n: 0.005 percent; al is less than or equal to 0.01 percent, Ti is less than or equal to 0.01 percent, Ce: 0.02%, Y: 0.001%, La: 0.01%, Nd: 0.02 percent; pr: 0.01 percent; p: 0.005 percent; s: 0.0013 percent; the balance of Fe and inevitable impurities.
Smelting 40kg of small steel ingots by adopting a vacuum induction furnace in the embodiment 1, wherein the thickness of the steel ingots is 100mm, casting and molding are carried out after uniform smelting is ensured, and the steel ingots are cooled to room temperature along with the furnace; then the following heat treatment is carried out: the homogenization temperature is 1140 and 1160 ℃, and the temperature is kept for 6 hours and then the furnace is cooled to the room temperature; keeping the normalizing temperature of 1120-; and (4) keeping the tempering temperature of 750/770 ℃ for 8/16h, and then cooling along with the furnace.
The chemical compositions of the steels of examples 1-4 and comparative examples 1-2 are shown in Table 1, the process steps are the same as those of example 1, the specific process parameters are shown in Table 2, the properties of examples 1-4 and comparative examples 1-2 are shown in tables 3 and 4, and the metallographic structures of examples 1-4 and comparative examples 1-2 are shown in Table 5.
TABLE 1 chemical composition wt% of examples and comparative examples
TABLE 1 chemical composition wt% (continue) of examples and comparative examples
| Numbering | Nb | Ta | Ce | Y | Nd | La | Pr |
| Example 1 | 0.05 | 0.11 | 0.02 | 0.001 | 0.02 | 0.01 | 0.01 |
| Example 2 | 0.02 | 0.07 | 0.01 | 0.001 | - | - | - |
| Example 3 | 0.06 | 0.09 | 0.02 | 0.002 | - | 0.01 | - |
| Example 4 | 0.04 | 0.15 | 0.02 | - | 0.07 | - | - |
| Comparative example 1 | 0.05 | 0.12 | - | - | - | - | - |
| Comparative example 2 | - | - | - | - | - | - | - |
TABLE 2 specific Process parameters of the examples and comparative examples
TABLE 3 Room temperature Properties of examples and comparative examples
TABLE 4 650 ℃ Performance of examples and comparative examples
TABLE 5 metallographic structure of examples and comparative examples
Remarking: in this table, a very small amount means a volume fraction of 3% or less, and a small amount means a volume fraction of 5% to 15%.
As can be seen from tables 3 to 4, the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of more than 630 ℃ provided by the invention has good comprehensive properties such as high-temperature strength, impact resistance, high-temperature durability, corrosion resistance, high-temperature oxidation resistance and the like, and is suitable for steam turbine castings with the working temperature of more than 630 ℃. As can be seen from table 3, lowering the tempering temperature can improve the strength of the heat-resistant steel, but the plasticity is lowered, and therefore, the tempering process can be controlled according to the use requirements during the actual use.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. The heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃ is characterized by comprising the following components in percentage by mass: c: 0.04 to 0.08 percent; mn: 0.2% -0.5%; si: 0.6% -1.0%; cr: 8.5% -9.2%; v: 0.15% -0.35%; w: 2.0% -2.45%; co: 3% -3.4%; cu: 0.01% -0.5%, Nb: 0.01% -0.15%, Ta: 0.01% -0.15%, Nb + Ta: 0.09% -0.3%, B: 0.012% -0.02%; n: 0.004% -0.008%; less than or equal to 0.01 percent of Al, less than or equal to 0.01 percent of Ti, rare earth: 0.01% -0.3%; p is less than or equal to 0.008 percent; s is less than or equal to 0.005 percent; the balance of Fe and inevitable impurities, and the rare earth is more than two mixed rare earths consisting of Ce, Y, Nd, La and Pr.
2. The heat-resistant steel for ultra supercritical steam turbine casting at above 630 ℃ according to claim 1, characterized by comprising, in mass percent: c: 0.077% -0.08%; mn: 0.45% -0.5%; si: 0.7% -1.0%; cr: 8.9% -9.0%; v: 0.21% -0.26%; w: 2.35 to 2.45 percent; co: 3% -3.21%; cu: 0.3% -0.4%, Nb: 0.02% -0.06%, Ta: 0.07% -0.11%, Nb + Ta: 0.09% -0.3%, B: 0.014% -0.017%; n: 0.005% -0.008% of Al: 0.005-0.007%, Ti is less than or equal to 0.01%, rare earth: 0.01% -0.3%; p is less than or equal to 0.008 percent; s is less than or equal to 0.005 percent; the balance of Fe and inevitable impurities.
3. The heat-resistant steel for ultra supercritical steam turbine casting at a temperature of 630 ℃ or higher according to claim 1, wherein the microstructure of the heat-resistant steel is tempered martensite, finely dispersed second phase particles, and a very small amount of dispersed spherical M3B2The second phase particles include M23C6Type carbide and MX particles.
4. A method for producing a heat-resistant steel for ultra supercritical steam turbine castings of 630 ℃ or higher according to claims 1 to 3, characterized by comprising the steps of:
step S1: determining the proportion of the raw materials according to the content of each component in the component proportion, smelting the raw materials, refining, and carrying out casting forming to obtain an ingot;
step S2: and (3) carrying out high-temperature homogenization and normalizing heat treatment on the cast ingot, and then carrying out tempering heat treatment to obtain the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃.
5. The preparation method according to claim 4, wherein the specific step of step S2 includes:
step S201: heating the ingot to 1050-;
step S202: normalizing, wherein the normalizing process comprises the steps of heating the cast ingot to 1000-1200 ℃, preserving heat and then cooling to room temperature;
step S203: and tempering, wherein the tempering process comprises the steps of heating the cast ingot to 700-800 ℃, preserving heat, and then cooling the cast ingot to room temperature along with a furnace to obtain the heat-resistant steel for the ultra-supercritical steam turbine casting with the temperature of above 630 ℃.
6. The method of claim 5, wherein in the step S201, the holding time T1 of the high-temperature homogenization treatment and the ingot thickness H1 satisfy the following relationship:
h1/60 is not less than T1 is not less than H1/40, wherein the unit of H1 is mm, and the unit of T1 is H.
7. The method according to claim 5, wherein in step S202, the heating rate is 50-80 ℃/h within the range of 800-950 ℃ before the normalizing temperature is reached.
8. The method of claim 5, wherein in the step S202, the holding time T2 of the normalizing and the thickness H2 of the ingot satisfy the following relationship:
h2/60 is not less than T2 is not less than H2/40, wherein the unit of H2 is mm, and the unit of T2 is H.
9. The method according to claim 5, wherein in step S202, the cooling method after the heat preservation is as follows: air cooling is carried out to 300 ℃ and then air cooling is carried out.
10. The method as claimed in claim 9, wherein the cooling rate of the air-cooling is 30-50 ℃/h in the step S202.
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| CN104561839A (en) * | 2015-02-09 | 2015-04-29 | 中国第一重型机械股份公司 | Novel rare-earth modified 9% Cr martensitic heat resisting cast steel and manufacturing method thereof |
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