A CO 2 Heat-resistant F91 steel ingot for medium supercritical power generation and preparation method thereof

Abstract

The present invention provides a heat-resistant F91 steel ingot for CO2 medium supercritical power generation and a preparation method thereof, belonging to the field of metallurgical technology. The present invention can improve the heat resistance of steel by reasonably matching alloy components; wherein Ni has high strength under high temperature environment, and by optimizing the content of Mn and Ni, the heat resistance of steel can be improved while reducing the content of Mo and Nb and omitting V; W is a high melting point metal, and by optimizing its content with Ni, the heat resistance can be further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a heat-resistant F91 steel ingot for CO2 medium supercritical power generation and a preparation method thereof. Background Art

[0002] At present, under the development of new energy, my country is undergoing tremendous changes in energy structure and equipment innovation and creation. Upstream main engine design and manufacturing plants are transforming their power generation equipment from "steam" to "gas" medium, and from the original "steam" turbine equipment that has been developed for a hundred years to supercritical units with "CO2, H2, and air" as the medium for power generation. This transformation requires that the steel used in this equipment has excellent heat resistance.

[0003] At present, the chemical composition of F91 steel includes, by mass percentage: C: 0.08-0.12%, Mn: 0.30-0.60%, P≤0.020%, S≤0.010%, Si: 0.20-0.50%, Ni: ≤0.40%, Cr: 8.00-9.50%, Mo: 0.85-1.05%, Nb: 0.06-0.10%, N: 0.030-0.070%, Al≤0.020%, V: 0.18-0.25% and the balance of Fe, but the heat resistance of this steel is difficult to meet the performance requirements. Therefore, how to improve the heat resistance of F91 steel has become a technical problem to be solved in this field. Summary of the invention

[0004] The object of the present invention is to provide a heat-resistant F91 steel ingot for CO2 medium supercritical power generation and a preparation method thereof. The F91 steel provided by the present invention has excellent heat resistance.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a heat-resistant F91 steel ingot for CO2 medium supercritical power generation, wherein the chemical composition comprises, by mass percentage, C 0.08-0.12%, Mn 0.35-0.45%, P≤0.008%, S≤0.008%, Si 0.30-0.45%, Ni0.10-0.30%, Cr 7.00-7.50%, Mo 0.50-0.75%, Nb0.02-0.06%, N 0.03-0.07%, Al0.01-0.03%, W 0.1-0.5% and the balance Fe;

[0007] The total content of W and Ni is 0.35-0.45wt%;

[0008] The total content of Mn and Ni is 0.51-0.61 wt %.

[0009] Preferably, the chemical composition includes, by mass percentage, C 0.09-0.11%, Mn 0.36-0.42%, P≤0.005%, S≤0.005%, Si 0.35-0.42%, Ni 0.15-0.25%, Cr 7.10-7.40%, Mo 0.55-0.70%, Nb 0.03-0.05%, N 0.04-0.06%, Al 0.015-0.025%, W0.2-0.4% and the balance Fe.

[0010] Preferably, the chemical composition includes, by mass percentage, C 0.10-0.11%, Mn 0.38-0.40%, P≤0.005%, S≤0.005%, Si 0.38-0.40%, Ni 0.16-0.22%, Cr 7.20-7.30%, Mo 0.60-0.65%, Nb 0.04-0.045%, N 0.045-0.05%, Al 0.020-0.025%, W0.25-0.3% and the balance Fe.

[0011] Preferably, the total content of W and Ni is 0.36-0.42 wt%.

[0012] Preferably, the total content of Mn and Ni is 0.53-0.60 wt%.

[0013] The present invention also provides a method for preparing the heat-resistant F91 steel ingot for CO2 medium supercritical power generation described in the above technical solution, comprising the following steps:

[0014] (1) subjecting the alloy raw materials to electric arc furnace smelting and vacuum refining furnace refining in sequence to obtain molten steel;

[0015] (2) The molten steel obtained in step (1) is sequentially cast and annealed to obtain a heat-resistant F91 steel ingot for CO2 medium supercritical power generation.

[0016] Preferably, the vacuum refining furnace refining in step (1) comprises a VOD stage, a VCD stage, a VOH stage and a VD stage which are performed in sequence.

[0017] Preferably, the process parameters of the VOD stage include: vacuum degree 50-150 mbar, oxygen flow rate 450-550 mbar 3 / h, vacuum time 1~1.5h, argon flow rate 1~5m 3 / h.

[0018] Preferably, the process parameters of the VCD stage include: vacuum degree ≤ 1 mbar, vacuum pumping time 10-15 min, argon flow rate 1-5 m 3 / h.

[0019] Preferably, the process parameters of the VOH stage include: temperature 1650-1670°C, oxygen flow rate 500-650m 3 / h, vacuum degree 360~420mbar, argon flow rate 1~5m 3 / h; the process parameters of the VD stage include: vacuum degree ≤1.0mbar, vacuum time 10-20min, argon flow rate 1-5m 3 / h.

[0020] The invention provides a heat-resistant F91 steel ingot for CO2 medium supercritical power generation. The chemical composition comprises, by mass percentage, C 0.08-0.12%, Mn 0.35-0.45%, P≤0.008%, S≤0.008%, Si 0.30-0.45%, Ni0.10-0.30%, Cr 7.00-7.50%, Mo 0.50-0.75%, Nb0.02-0.06%, N 0.03-0.07%, Al0.01-0.03%, W 0.1-0.5% and the balance Fe; the total content of W and Ni is 0.35-0.45wt%; the total content of Mn and Ni is 0.51-0.61wt%. The present invention can improve the heat resistance of steel by reasonably matching alloy components; among them, Ni has high strength in high temperature environment, and by optimizing the content of Mn and Ni, the heat resistance of steel can be improved while reducing the content of Mo and Nb and omitting V; W is a high melting point metal, and by optimizing its content with Ni, the heat resistance can be further improved. Experimental results show that the mechanical properties of the steel ingot prepared into forgings at room temperature are: R p0.2 500~565MPa, Rm 680~735MPa, A 25~35%, Z 50~65%, KV2 88.5~110J, HBW 206~245; High temperature mechanical properties: R at 500℃ p0.2 480~510MPa, at 600℃ R p0.2 The endurance strength at 620°C is 98-110MPa, and the endurance strength at 640°C is 81-95MPa. DETAILED DESCRIPTION

[0021] The invention provides a heat-resistant F91 steel ingot for CO2 medium supercritical power generation. The chemical composition comprises, by mass percentage, C 0.08-0.12%, Mn 0.35-0.45%, P≤0.008%, S≤0.008%, Si 0.30-0.45%, Ni0.10-0.30%, Cr 7.00-7.50%, Mo 0.50-0.75%, Nb0.02-0.06%, N 0.03-0.07%, Al0.01-0.03%, W 0.1-0.5% and the balance Fe.

[0022] In terms of mass percentage, the heat-resistant F91 steel ingot for CO2 medium supercritical power generation provided by the present invention comprises 0.08-0.12% C, preferably 0.09-0.11%, and more preferably 0.10-0.11% C. In the present invention, the purity of the steel can be improved and the crack sensitivity can be improved by controlling the carbon element.

[0023] The heat-resistant F91 steel ingot for CO2 supercritical power generation provided by the present invention further comprises Mn 0.35-0.45%, preferably 0.36-0.42%, more preferably 0.38-0.40%, and most preferably 0.39%, by mass percentage. In the present invention, the manganese element can refine carbides and prevent grain growth, thereby improving the strength of the steel.

[0024] In terms of mass percentage, the heat-resistant F91 steel ingot for CO2 medium supercritical power generation provided by the present invention also includes P≤0.008%, preferably ≤0.005%. In the present invention, the phosphorus element is a harmful element, and by reducing its content, the performance of the steel can be further improved.

[0025] In terms of mass percentage, the heat-resistant F91 steel ingot for CO2 medium supercritical power generation provided by the present invention also includes S≤0.008%, preferably ≤0.005%. In the present invention, the sulfur element is a harmful element, and by reducing its content, the performance of the steel can be further improved.

[0026] The heat-resistant F91 steel ingot for CO2 supercritical power generation provided by the present invention further comprises Si0.30-0.45%, preferably 0.35-0.42%, more preferably 0.38-0.40%, and most preferably 0.39%, by mass percentage. In the present invention, the silicon element is combined with Al to significantly improve the oxidation resistance of the steel, promote the formation of an oxide film on the metal surface, prevent further oxidation, and thus improve the corrosion resistance.

[0027] In terms of mass percentage, the heat-resistant F91 steel ingot for CO2 medium supercritical power generation provided by the present invention further comprises Ni 0.10-0.30%, preferably 0.15-0.25%, more preferably 0.16-0.22%, and more preferably 0.20-0.22%. In the present invention, the nickel has high strength under high temperature environment and can improve the heat resistance of steel.

[0028] In terms of mass percentage, the heat-resistant F91 steel ingot for CO2 medium supercritical power generation provided by the present invention further comprises 7.00-7.50% Cr, preferably 7.10-7.40%, and more preferably 7.20-7.30%. In the present invention, the chromium element can increase the thermal strength of the steel and improve the high-temperature mechanical properties of the steel.

[0029] The heat-resistant F91 steel ingot for CO2 supercritical power generation provided by the present invention further comprises 0.50-0.75% Mo, preferably 0.55-0.70%, more preferably 0.60-0.65%. In the present invention, the molybdenum element can improve the hardenability and heat strength of the steel.

[0030] The heat-resistant F91 steel ingot for CO2 medium supercritical power generation provided by the present invention further comprises Nb 0.02-0.06%, preferably 0.03-0.05%, and more preferably 0.04-0.045%. In the present invention, the Nb is a strong carbide-forming element, and a small amount of addition can refine the grains through the precipitation of nano-carbides, thereby improving the strength and toughness of the steel.

[0031] The heat-resistant F91 steel ingot for CO2 supercritical power generation provided by the present invention further comprises 0.03-0.07% N, preferably 0.04-0.06%, and more preferably 0.045-0.05%. In the present invention, the nitrogen element has the effects of solid solution strengthening and improving hardenability, and nitrides precipitate on grain boundaries, which can improve the high-temperature strength of grain boundaries and increase the creep strength of steel.

[0032] The heat-resistant F91 steel ingot for CO2 supercritical power generation provided by the present invention further comprises 0.01-0.03% Al, preferably 0.015-0.025%, and more preferably 0.020-0.025% Al by mass percentage. In the present invention, the aluminum element has a solid solution strengthening effect in the steel, improving the mechanical properties such as wear resistance and fatigue strength of the carburized steel.

[0033] By mass percentage, the heat-resistant F91 steel ingot for CO2 medium supercritical power generation provided by the present invention further comprises 0.1-0.5%, preferably 0.2-0.4%, and more preferably 0.25-0.3% W. In the present invention, the W is a high melting point metal that can improve the high temperature performance of the steel.

[0034] The heat-resistant F91 steel ingot for CO2 supercritical power generation provided by the present invention further comprises a balance of Fe in terms of mass percentage. In the present invention, the Fe is a matrix element.

[0035] In the present invention, the total content of W and Ni is 0.35-0.45wt%, preferably 0.36-0.42wt%, more preferably 0.38-0.40wt%. The present invention can further improve the high temperature mechanical properties of steel by controlling the contents of tungsten and nickel.

[0036] In the present invention, the total content of Mn and Ni is 0.51-0.61wt%, preferably 0.53-0.60wt%, more preferably 0.55-0.58wt%. The present invention can further improve the high temperature mechanical properties of steel by controlling the contents of manganese and nickel.

[0037] The present invention can improve the heat resistance of steel by reasonably matching alloy components; among them, Ni has high strength in a high temperature environment, and by optimizing the content of Mn and Ni, the heat resistance of steel can be improved while reducing the content of Mo and Nb and omitting V; W is a high melting point metal, and by optimizing its content with Ni, the heat resistance can be further improved.

[0038] The steel ingot provided by the invention also has excellent corrosion resistance.

[0039] The present invention also provides a method for preparing the heat-resistant F91 steel ingot for CO2 medium supercritical power generation described in the above technical solution, comprising the following steps:

[0040] (1) subjecting the alloy raw materials to electric arc furnace smelting and vacuum refining furnace refining in sequence to obtain molten steel;

[0041] (2) The molten steel obtained in step (1) is sequentially cast and annealed to obtain a heat-resistant F91 steel ingot for CO2 medium supercritical power generation.

[0042] The present invention has no particular limitation on the sources of the raw materials, and the raw materials may be prepared using commercially available products or well-known preparation methods known to those skilled in the art.

[0043] The invention sequentially performs electric arc furnace smelting and vacuum refining furnace refining on alloy raw materials to obtain molten steel.

[0044] In the present invention, the alloy raw materials are preferably scrap steel and alloy; the mass content of P in the scrap steel is preferably ≤0.030%; the mass content of S in the scrap steel is preferably ≤0.030%. The present invention selects pure scrap steel with both S and P ≤0.030% to improve the purity of molten steel.

[0045] In the present invention, iron ore and lime are preferably laid on the bottom of the electric arc furnace before the start of the electric arc furnace smelting; the content of the iron ore is preferably 1-2% of the mass of the scrap steel; the content of the lime is preferably 2% of the mass of the scrap steel. In the present invention, adding an appropriate amount of lime and iron ore can adjust the slag to remove S and O in the steel.

[0046] In the present invention, the electric arc furnace smelting preferably includes a melting period, an oxidation period and a reduction period performed in sequence.

[0047] The present invention has no particular limitation on the operation of the melting period, and operations well known to those skilled in the art may be adopted.

[0048] The present invention has no special limitation on the operation of the oxidation period. The operation well known to those skilled in the art is adopted to make the carbon removal amount of the molten steel ≥ 0.40% and the phosphorus removal amount to 0.002-0.003%.

[0049] In the present invention, when the temperature of the molten steel in the oxidation period is 1540-1560°C, FeO and lime are preferably added to the molten steel; the mass of the FeO is preferably 2.0-2.5% of the mass of the molten steel; the mass of the lime is preferably 1.8-2.5% of the mass of the molten steel. The present invention can make the basicity of the molten steel within the range of 2-2.5 by adding FeO and lime to the molten steel.

[0050] The present invention has no particular limitation on the operation of the reduction period, and operations well known to those skilled in the art may be used.

[0051] After the arc furnace smelting is completed, the present invention preferably transfers the molten steel obtained by the arc furnace smelting into a tundish, and then removes the slag in the tundish.

[0052] The present invention has no special limitation on the operations of transferring into the tundish and deslagging in the tundish. The slag can be cleaned by operations well known to those skilled in the art to prevent P from returning during smelting in the VODC refining furnace.

[0053] In the present invention, the vacuum refining furnace refining preferably includes a VOD stage, a VCD stage, a VOH stage and a VD stage performed in sequence.

[0054] In the present invention, the process parameters of the VOD stage preferably include: vacuum degree 50-150 mbar, oxygen flow rate 450-550 mbar, 3 / h, vacuum time 1~1.5h, argon flow rate 1~5m 3 / h; more preferably: vacuum degree 80-120mbar, oxygen flow rate 480-520m 3 / h, vacuum time 1.2~1.4h, argon flow rate 3~4m 3 / h.

[0055] In the present invention, the VOD stage preferably removes C to below 0.10 wt%.

[0056] In the present invention, the process parameters of the VCD stage preferably include: vacuum degree ≤ 1 mbar, vacuum pumping time 10 to 15 min, argon flow rate 1 to 5 m 3 / h; more preferably: vacuum degree ≤ 1mbar, vacuum time 12-14min, argon flow rate 3-4m 3 / h.

[0057] In the present invention, the process parameters of the VOH stage preferably include: temperature 1650-1670°C, oxygen flow rate 500-650m 3 / h, vacuum degree 360~420mbar, argon flow rate 1~5m 3 / h; more preferably: temperature 1655 ~ 1665 ° C, oxygen flow 550 ~ 600m 3 / h, vacuum degree 380~400mbar, argon flow rate 3~4m 3 / h.

[0058] In the present invention, the process parameters of the VD stage preferably include: vacuum degree ≤ 1.0 mbar, vacuum pumping time 10 to 20 min, argon flow rate 1 to 5 m 3 / h; more preferably: vacuum degree ≤ 1.0 mbar, vacuum time 12 to 18 min, argon flow rate 3 to 4 m 3 / h.

[0059] The present invention can further improve the mechanical properties of steel by controlling the refining process parameters of the vacuum refining furnace.

[0060] After the refining in the vacuum refining furnace is completed, the present invention preferably transfers the molten steel obtained by the vacuum refining furnace into a ladle, and then calms it to obtain the molten steel.

[0061] In the present invention, the temperature of the molten steel when transferred into the ladle is preferably 1600-1650°C; a silicon-calcium deoxidizer is preferably added to the ladle; and the amount of the silicon-calcium deoxidizer is preferably 1.5-2.5 Kg / t. The present invention uses a silicon-calcium deoxidizer to further deoxidize.

[0062] In the present invention, the sedation time is preferably greater than 4 minutes, more preferably 7 to 10 minutes.

[0063] After obtaining the molten steel, the present invention sequentially casts and anneals the molten steel to obtain a heat-resistant F91 steel ingot for CO2 medium supercritical power generation.

[0064] In the present invention, the pouring is preferably carried out in an argon protective atmosphere; the pouring temperature is preferably 1500-1600° C.; and the pouring speed is preferably 6-7 mm / s.

[0065] After the pouring is completed, the present invention preferably performs mold cooling and demolding on the product obtained by the pouring.

[0066] The present invention has no particular limitation on the mold cooling and demolding operations, and operations well known to those skilled in the art may be used.

[0067] In the present invention, the annealing holding temperature is preferably 700-750°C, more preferably 730°C; the annealing speed is preferably 2.5-3.00 min / mm; the annealing cooling method is preferably first furnace cooling to 300°C and then air cooling out of the furnace.

[0068] The present invention has no particular limitation on other operations of the preparation method, and operations familiar to those skilled in the art may be adopted.

[0069] The preparation method provided by the invention is simple in process

[0070] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] Example 1

[0072] The chemical composition of the heat-resistant F91 steel ingot for CO2 medium supercritical power generation is calculated by mass percentage: C0.08%, Mn0.45%, P 0.008%, S 0.008%, Si 0.30%, Ni 0.16%, Cr 7.00%, Mo 0.75%, Nb 0.02%, N 0.07%, Al 0.01%, W 0.2% and the balance Fe;

[0073] The total content of W and Ni is 0.36wt%;

[0074] The total content of Mn and Ni is 0.61wt%;

[0075] The preparation method of the heat-resistant F91 steel ingot for CO2 medium supercritical power generation comprises the following steps:

[0076] (1) Adding 1.8% of iron ore by weight of scrap steel and 2% of lime by weight of scrap steel as furnace bottom materials in an electric arc furnace, and then smelting scrap steel and alloy with S≤0.030% and P≤0.030% in an electric arc furnace, first entering a melting period, and then entering an oxidation period. When the temperature of the molten steel is 1550°C, adding 2.35% of FeO by weight of the molten steel and 2.25% of lime by weight of the molten steel to make the molten steel basicity between 2 and 2.5, the decarbonization amount ≥0.40%, and the P removal to within the range of 0.002 to 0.003%, and then entering a reduction period, and then the steel is The molten steel is transferred to the tundish, and the slag is scraped off in the tundish, and then it enters the VODC vacuum refining furnace for refining. Then, when the molten steel temperature reaches 1600℃, it is transferred to the ladle, and 2.25kg / t of silicon-calcium deoxidizer is added to the ladle for final deoxidation. The N is adjusted to the range of 0.03-0.07%, and then calmed for 10 minutes to obtain molten steel. Among them, the refining in the VODC vacuum refining furnace is carried out in sequence as VOD stage, VCD stage, VOH stage and VD stage; the process parameters of the VOD stage are: vacuum degree 135mbar, oxygen flow rate 535m 3 / h, vacuum time 1.5h, argon flow rate 4.5m 3 / h, and remove C to below 0.10wt%; the process parameters of the VCD stage are: vacuum degree 0.8mbar, vacuum time 13min, argon flow rate 4.5m 3 / h, adjust the components to the specified requirements; the process parameters of the VOH stage are: add 1wt% aluminum by weight of molten steel to increase the temperature by 250℃, raise the temperature to 1665℃, oxygen flow rate 535m 3 / h, vacuum degree 415mbar, argon flow rate 4.5m 3 / h; the process parameters of the VD stage are: vacuum degree 0.8mbar, vacuum time 18min, argon flow rate 4.5m 3 / h;

[0077] (2) The molten steel obtained in the step (1) is first poured in an argon atmosphere, then mold cooled and demolded, and finally annealed at 730° C., then furnace cooled to 300° C., and then air cooled to obtain a heat-resistant F91 steel ingot for CO2 medium supercritical power generation; wherein the pouring temperature is 1580° C., the pouring speed is 6.5 mm / s; and the annealing speed is 2.8 min / mm.

[0078] Example 2

[0079] The chemical composition of the heat-resistant F91 steel ingot for CO2 medium supercritical power generation is calculated by mass percentage as follows: C0.12%, Mn0.35%, P 0.008%, S 0.008%, Si 0.45%, Ni 0.21%, Cr7.50%, Mo 0.50%, Nb 0.06%, N0.03%, Al 0.03%, W 0.15% and the balance Fe;

[0080] The total content of W and Ni is 0.36wt%;

[0081] The total content of Mn and Ni is 0.56wt%; the preparation method is the same as that of Example 1.

[0082] Example 3

[0083] The chemical composition of the heat-resistant F91 steel ingot for CO2 medium supercritical power generation is calculated by mass percentage as follows: C0.09%, Mn0.42%, P 0.005%, S 0.005%, Si 0.35%, Ni 0.18%, Cr7.10%, Mo 0.70%, Nb 0.03%, N0.06%, Al 0.015%, W 0.22% and the balance Fe;

[0084] The total content of W and Ni is 0.4wt%;

[0085] The total content of Mn and Ni is 0.6wt%; the preparation method is the same as that of Example 1.

[0086] Example 4

[0087] The chemical composition of the heat-resistant F91 steel ingot for CO2 medium supercritical power generation is calculated by mass percentage: C0.11%, Mn0.36%, P 0.005%, S 0.005%, Si 0.42%, Ni 0.20%, Cr 7.40%, Mo 0.55%, Nb 0.05%, N 0.04%, Al 0.025%, W 0.2% and the balance Fe;

[0088] The total content of W and Ni is 0.4wt%;

[0089] The total content of Mn and Ni is 0.56wt%; the preparation method is the same as that of Example 1.

[0090] Comparative Example 1

[0091] The contents of W, Ni, Mn and Fe were changed on the basis of Example 4, while other conditions remained unchanged, wherein W was 0.5%, Ni was 0.30%, and Mn was 0.45%;

[0092] The total content of W and Ni is 0.8wt%;

[0093] The total content of Mn and Ni is 0.75 wt %.

[0094] Comparative Example 2

[0095] The contents of W, Ni, Mn and Fe were changed on the basis of Example 4, while other conditions remained unchanged, wherein W was 0.1%, Ni was 0.10%, and Mn was 0.35%;

[0096] The total content of W and Ni is 0.2wt%;

[0097] The total content of Mn and Ni is 0.45 wt %.

[0098] Comparative Example 3

[0099] The chemical composition of the F91 steel ingot is, by mass percentage, C 0.092%, Mn 0.44%, Si 0.26%, S0.0072%, P 0.006%, Cr 9.13%, Ni 0.28%, Mo 0.97%, V 0.21%, Nb 0.087%, N0.038%, Al 0.022% and the balance Fe, and other conditions are the same as in Example 1.

[0100] The F91 steel ingots prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were prepared into forgings in the following steps:

[0101] (1) performing a first heat treatment on the steel ingot after cutting to obtain a pretreated workpiece; the heating procedure of the first heat treatment is: heating to 650°C at a heating rate of 55°C / h for a first heat treatment of 8h; continuing to heat to 970°C at a heating rate of 55°C / h for a second heat treatment of 8h; continuing to heat to 1180°C at a heating rate of 35°C / h for a third heat treatment of 9h, followed by air cooling;

[0102] (2) subjecting the pretreated workpiece to forging deformation treatment, wherein the initial forging temperature is controlled at: 1150° C. for forging to obtain a forging blank, and then cooling to 850° C. (furnace cooling rate 35° C. / h) for final forging to obtain a casting;

[0103] (3) The casting is subjected to rough machining and a second heat treatment in sequence to obtain a forging; the procedure of the second heat treatment is: tempering temperature: 1050° C. air cooling, tempering temperature: 760° C. air cooling.

[0104] The forgings were subjected to mechanical properties and high-temperature creep tests, and the results are shown in Tables 1 and 2 (the room temperature tensile test adopts GB / T228.1; the impact property adopts the Charpy pendulum impact test method for metal materials in GB / T 229-2020; the hardness test HBW adopts GB / T231.1 standard; the high-temperature mechanical properties compressive strength and endurance strength MPa test adopts GB5310-2008 standard).

[0105] Table 1 Room temperature mechanical properties of forgings made from steel ingots of Examples 1 to 4 and Comparative Examples 1 to 3

[0106] project <![CDATA[R p0.2 / MPa]]> Rm / MPa A / ％ Z / ％ <![CDATA[KV2 / J]]> HBW standard 440 620 20 45 68 197～269 Example 1 500 680 25 50 88.5 206 Example 2 530 710 26 52 101.5 215 Example 3 545 725 29 55 105.5 220 Example 4 565 735 35 65 110 245 Comparative Example 1 538 708 26 53 95 209 Comparative Example 2 535 705 24 50 90 203 Comparative Example 3 480 655 23 45 81 198

[0107] Table 2 High temperature mechanical properties of forgings made from steel ingots of Examples 1 to 4 and Comparative Examples 1 to 3

[0108]

[0109]

[0110] The following conclusions can be drawn from Tables 1 and 2: It can be seen from Examples 1 to 4 and Comparative Example 3 that the present invention can improve the room temperature and high temperature mechanical properties of steel by a reasonable combination of alloy components; It can be seen from Example 4 and Comparative Examples 1 to 2 that the present invention can further improve the room temperature and high temperature mechanical properties of steel by controlling the contents of tungsten and nickel, and can further improve the room temperature and high temperature mechanical properties of steel by controlling the contents of manganese and nickel.

[0111] It can be seen from the above embodiments and comparative examples that the stainless steel provided by the present invention has excellent room temperature and high temperature mechanical properties.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A heat-resistant F91 steel ingot for CO2 medium supercritical power generation, the chemical composition of which is as follows by mass percentage: C 0.08-0.12%, Mn 0.35-0.45%, P≤0.008%, S≤0.008%, Si 0.30-0.45%, Ni 0.10-0.30%, Cr 7.00-7.50%, Mo 0.50-0.75%, Nb 0.02-0.06%, N0.03-0.07%, Al 0.01-0.03%, W 0.1-0.5% and the balance Fe; The total content of W and Ni is 0.35-0.45wt%; The total content of Mn and Ni is 0.51-0.61 wt %.

2. The heat-resistant F91 steel ingot for CO2 medium supercritical power generation according to claim 1, characterized in that: The chemical composition by mass percentage is: C 0.09-0.11%, Mn 0.36-0.42%, P≤0.005%, S≤0.005%, Si 0.35-0.42%, Ni 0.15-0.25%, Cr 7.10-7.40%, Mo 0.55-0.70%, Nb 0.03-0.05%, N 0.04-0.06%, Al 0.015-0.025%, W 0.2-0.4% and the balance Fe.

3. The heat-resistant F91 steel ingot for CO2 medium supercritical power generation according to claim 2, characterized in that: The chemical composition by mass percentage is: C 0.10-0.11%, Mn 0.38-0.40%, P≤0.005%, S≤0.005%, Si 0.38-0.40%, Ni 0.16-0.22%, Cr 7.20-7.30%, Mo 0.60-0.65%, Nb 0.04-0.045%, N0.045-0.05%, Al 0.020-0.025%, W 0.25-0.3% and the balance Fe.

4. The heat-resistant F91 steel ingot for CO2 medium supercritical power generation according to any one of claims 1 to 3, characterized in that: The total content of W and Ni is 0.36-0.42 wt %.

5. The heat-resistant F91 steel ingot for CO2 medium supercritical power generation according to any one of claims 1 to 3, characterized in that: The total content of Mn and Ni is 0.53-0.60 wt %.

6. The method for preparing the heat-resistant F91 steel ingot for CO2 medium supercritical power generation according to any one of claims 1 to 5, comprising the following steps: (1) subjecting the alloy raw materials to electric arc furnace smelting and vacuum refining furnace refining in sequence to obtain molten steel; (2) The molten steel obtained in step (1) is sequentially cast and annealed to obtain a heat-resistant F91 steel ingot for CO2 medium supercritical power generation.

7. The preparation method according to claim 6, characterized in that: The vacuum refining furnace refining in step (1) includes a VOD stage, a VCD stage, a VOH stage and a VD stage which are performed in sequence.

8. The preparation method according to claim 7, characterized in that: The process parameters of the VOD stage include: vacuum degree 50-150 mbar, oxygen flow rate 450-550 m 3 / h, vacuum time 1~1.5h, argon flow rate 1~5m 3 / h.

9. The preparation method according to claim 7, characterized in that: The process parameters of the VCD stage include: vacuum degree ≤ 1 mbar, vacuum pumping time 10 to 15 min, argon flow rate 1 to 5 m 3 / h.

10. The preparation method according to claim 7, characterized in that: The process parameters of the VOH stage include: temperature 1650-1670°C, oxygen flow rate 500-650m 3 / h, vacuum degree 360~420mbar, argon flow rate 1~5m 3 / h; the process parameters of the VD stage include: vacuum degree ≤ 1.0mbar, vacuum time 10-20min, argon flow rate 1-5m 3 / h.

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