A 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine and a preparation method thereof

Abstract

The present invention provides a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650℃ grade ultra-supercritical steam turbine and a preparation method thereof, belonging to the field of metallurgy technology. The present invention improves the heat resistance, strength and fatigue resistance of the steel ingot by optimizing the content of Si and Co, adding Mo, and cooperating with other components. Experimental results show that the mechanical properties of the steel provided by the present invention at room temperature are: yield strength R p0.2 ≥520N / mm 2 , tensile strength Rm is 680~850N / mm 2 , elongation A (L0 = 5d0) ≥ 15%, section shrinkage Z ≥ 40%, impact energy KV2 ≥ 30J; high temperature creep performance: 650 ° C, endurance time up to 100h.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine and a preparation method thereof. Background Art

[0002] In order to vigorously develop my country's efficient, energy-saving, clean, high-power coal-fired power generation steam turbine equipment with a capacity of more than one million kilowatts, the operating temperature of steam turbine steam has been increased from the original subcritical 540℃, supercritical 570℃, ultra-supercritical 600-610℃, and secondary reheating ultra-supercritical 620-630℃ to the new ultra-supercritical 630-650℃, and the coal consumption of coal-fired power generation steam turbine equipment has been reduced from the original 350g per hour to the secondary reheating ultra-supercritical 257.2g and then to 247g, and energy conservation and emission reduction have reached a new high. However, the original 1Cr12Mo, 1Cr12MoV, X12CrMoWVNbN10-1-1, CB2 and other martensitic heat-resistant steels are no longer applicable. It is necessary to develop more heat-resistant, higher strength, and high fatigue resistance martensitic heat-resistant steels to replace them in order to meet the performance of forging materials such as high-pressure valve forgings and rotors of key components of new ultra-supercritical gas turbines with a capacity of one million kilowatts. Therefore, how to improve the heat resistance, strength and fatigue resistance of heat-resistant steel has become a difficult problem to be solved urgently in this field. Summary of the invention

[0003] The purpose of the present invention is to provide a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine and a preparation method thereof. The heat-resistant steel ingot provided by the present invention has higher heat resistance, strength and fatigue resistance, and can be used to manufacture a new type of million-kilowatt ultra-supercritical steam turbine unit with an operating temperature of 650°C.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine, wherein the chemical composition comprises, by mass percentage, C 0.06-0.10%, Si 0.20-0.40%, Mn 0.40-0.80%, P ≤ 0.015%, S ≤ 0.010%, Ni 0.10-0.20%, Cr 8.50-9.50%, Mo 0. .50~0.55%, Co2.9~3.1%, W2.70~2.90%, V0.18~0.25%, Nb0.05~0.08%, N0.006~0.010%, Al≤0.015%, B0.011~0.015%, Sn≤0.02%, Ti≤0.02%, Cu≤0.25%, RE0.001~0.008% and the balance of Fe.

[0006] Preferably, the chemical composition includes, by mass percentage, C0.07-0.09%, Si0.25-0.35%, Mn0.50-0.70%, P≤0.015%, S≤0.010%, Ni0.15-0.18%, Cr8.80-9.20%, Mo0.52-0.53%, Co3.0-3.1%, W2.75-2.85%, V0.20-0.23%, Nb0.06-0.07%, N0.007-0.009%, Al0.005-0.010%, B0.012-0.014%, Sn≤0.01%, Ti≤0.01%, Cu0.10-0.20%, RE0.003-0.005% and the balance Fe.

[0007] Preferably, the RE comprises cerium and / or lanthanum.

[0008] The present invention also provides a method for preparing the 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine as described in the above technical solution, comprising the following steps:

[0009] (1) subjecting the alloy raw materials to electric arc furnace smelting and VODC vacuum refining in sequence to obtain molten steel;

[0010] (2) pouring the molten steel obtained in step (1) to obtain a cast part;

[0011] (3) The cast part obtained in step (2) is annealed to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine.

[0012] Preferably, the electric arc furnace smelting in step (1) comprises a melting period, an oxidation period and a reduction period which are performed in sequence.

[0013] Preferably, the VODC vacuum refining in step (1) comprises a VOD stage, a VCD stage and a VD stage which are performed in sequence.

[0014] Preferably, the process parameters of the VOD stage are: vacuum degree 80-120 mbar, vacuum time 0.5-2.0 h, oxygen blowing speed 550-650 m 3 / h, Ar flow rate 2~5m 3 / h.

[0015] Preferably, the process parameters of the VCD stage are: vacuum degree ≤ 2 mbar, vacuum pumping time 5 to 20 min, Ar flow rate 1 to 5 m 3 / h.

[0016] Preferably, the process parameters of the VD stage are: vacuum degree ≤ 1.5 mbar, and vacuuming time 10 to 20 min.

[0017] Preferably, the pouring temperature in step (2) is 1570-1590°C.

[0018] The present invention provides a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine, wherein the chemical composition comprises, by mass percentage, C 0.06-0.10%, Si 0.20-0.40%, Mn 0.40-0.80%, P ≤ 0.015%, S ≤ 0.010%, Ni 0.10-0.20%, Cr 8.50-9.50%, Mo 0. .50~0.55%, Co2.9~3.1%, W2.70~2.90%, V0.18~0.25%, Nb0.05~0.08%, N0.006~0.010%, Al≤0.015%, B0.011~0.015%, Sn≤0.02%, Ti≤0.02%, Cu≤0.25%, RE0.001~0.008% and the balance of Fe. The present invention improves the heat resistance, strength and fatigue resistance of the steel ingot by optimizing the content of Si and Co, adding Mo, and cooperating with other ingredients. Experimental results show that the mechanical properties of the steel provided by the present invention at room temperature are: yield strength R p0.2 ≥520N / mm 2 , tensile strength Rm is 680~850N / mm 2 , elongation A (L0 = 5d0) ≥ 15%, section shrinkage Z ≥ 40%, impact energy KV2: ≥ 30J; high temperature short-time creep test, 650 ° C for 100h. DETAILED DESCRIPTION

[0019] The present invention provides a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine, wherein the chemical composition comprises, by mass percentage, C 0.06-0.10%, Si 0.20-0.40%, Mn 0.40-0.80%, P ≤ 0.015%, S ≤ 0.010%, Ni 0.10-0.20%, Cr 8.50-9.50%, Mo 0. .50~0.55%, Co2.9~3.1%, W2.70~2.90%, V0.18~0.25%, Nb0.05~0.08%, N0.006~0.010%, Al≤0.015%, B0.011~0.015%, Sn≤0.02%, Ti≤0.02%, Cu≤0.25%, RE0.001~0.008% and the balance of Fe.

[0020] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention comprises 0.06-0.10% C, preferably 0.07-0.09%, and more preferably 0.08-0.09%. In the present invention, the C element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0021] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises Si0.20-0.40%, preferably 0.25-0.35%, and more preferably 0.30%. In the present invention, the Si element is beneficial to improving the strength, heat resistance and fatigue resistance of the material matrix, and combining it with other components can further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0022] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises 0.40-0.80% Mn, preferably 0.50-0.70%, and more preferably 0.55-0.60%. In the present invention, the Mn element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0023] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises P≤0.015%, preferably ≤0.010%. In the present invention, the P is a harmful element, and the heat resistance, strength and fatigue resistance of the steel ingot can be further improved by strictly controlling its content.

[0024] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention also includes S≤0.010%. In the present invention, the S is a harmful element, and the heat resistance, strength and fatigue resistance of the steel ingot can be further improved by strictly controlling its content.

[0025] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises 0.10-0.20% Ni, preferably 0.15-0.18%, and more preferably 0.16-0.17%. In the present invention, the Ni element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0026] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises 8.50-9.50% Cr, preferably 8.80-9.20%, and more preferably 8.90-9.10% Cr by mass percentage. In the present invention, the Cr element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0027] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises 0.50-0.55% Mo, preferably 0.52-0.53%. In the present invention, the Mo element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0028] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises 2.9-3.1% Co, preferably 3.0-3.1%. In the present invention, the combination of the Co element and other components can further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0029] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises W2.70-2.90%, preferably 2.75-2.85%, and more preferably 2.80-2.85%. In the present invention, the W element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0030] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises V0.18-0.25%, preferably 0.20-0.23%, and more preferably 0.21-0.22%. In the present invention, the V element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0031] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises Nb 0.05-0.08%, preferably 0.06-0.07%. In the present invention, the Nb element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0032] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises 0.006-0.010% N, preferably 0.007-0.009%, and more preferably 0.008-0.009%. In the present invention, the N element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0033] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises Al≤0.015%, preferably 0.005-0.010%. In the present invention, the Al element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0034] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises B 0.011-0.015%, preferably 0.012-0.014%, and more preferably 0.012-0.013%. In the present invention, the B element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0035] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises Sn≤0.02%, preferably ≤0.01%. In the present invention, the Sn element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0036] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises Ti≤0.02%, preferably ≤0.01%. In the present invention, the combination of the Ti element and other components can further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0037] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises Cu≤0.25%, preferably 0.10-0.20%. In the present invention, the Cu element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0038] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine provided by the present invention further comprises RE 0.001-0.008%, preferably 0.003-0.005%, by mass percentage; the RE preferably comprises cerium and / or lanthanum. In the present invention, the rare earth element is combined with other components to further improve the heat resistance, strength and fatigue resistance of the steel ingot.

[0039] The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine 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.

[0040] The invention improves the heat resistance, strength and fatigue resistance of the steel ingot by optimizing the contents of Si and Co, adding Mo and coordinating with other components.

[0041] The present invention also provides a method for preparing the 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine as described in the above technical solution, comprising the following steps:

[0042] (1) subjecting the alloy raw materials to electric arc furnace smelting and VODC vacuum refining in sequence to obtain molten steel;

[0043] (2) pouring the molten steel obtained in step (1) to obtain a cast part;

[0044] (3) The cast part obtained in step (2) is annealed to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine.

[0045] 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.

[0046] The invention sequentially performs electric arc furnace smelting and VODC vacuum refining on alloy raw materials to obtain molten steel.

[0047] 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.

[0048] The present invention has no particular limitation on the source of the alloy, and any high-purity alloy material well known to those skilled in the art may be used.

[0049] 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 2% of the mass of the scrap steel; the content of the lime is preferably 2-2.5% of the mass of the scrap steel. The present invention can adjust the slag by adding an appropriate amount of lime and iron ore to remove S and O in the steel.

[0050] In the present invention, the electric arc furnace smelting preferably includes a melting period, an oxidation period and a reduction period performed in sequence.

[0051] In the present invention, the temperature of the melting period is preferably 1500-1600°C; the oxygen pressure of the melting period is preferably 0.1-0.5 mPa; the basicity of the molten steel in the melting period is preferably 2-2.5. The present invention has no special limitation on the time of the melting period, as long as the P is removed to ≤0.006%.

[0052] In the present invention, the process parameters of the oxidation period are preferably: oxygen pressure 1.0-1.5 mPa, molten pool temperature 1600-1700° C. The present invention has no special limitation on the time of the oxidation period, as long as the carbon removal amount is guaranteed to be 0.39-0.59%.

[0053] In the present invention, when the C content in the molten steel is 0.8-1.0% and the molten pool temperature is greater than 1640-1650°C, it is preferred to stop blowing oxygen.

[0054] In the present invention, a reducing agent is preferably added during the reduction period; the reducing agent is preferably ferrosilicon powder; and the amount of the reducing agent is preferably 1-10 Kg / t.

[0055] The present invention has no special limitation on the time of the reduction period, as long as C is ensured to be between 0.8% and 1.0%, P≤0.010%, S≤0.008%, and the remaining components are adjusted to the specified requirements.

[0056] 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.

[0057] The present invention has no special limitation on the operations of transferring into the tundish and deslagging in the tundish, and operations well known to those skilled in the art may be adopted.

[0058] In the present invention, the VODC vacuum refining preferably includes a VOD stage, a VCD stage and a VD stage which are performed in sequence.

[0059] In the present invention, the process parameters of the VOD stage are preferably: vacuum degree 80-120 mbar, vacuum time 0.5-2.0 h, oxygen blowing speed 550-650 m 3 / h, Ar flow rate 2~5m 3 / h; more preferably: vacuum degree 80-100mbar, vacuum time 1.0-2.0h, oxygen blowing speed 600-650m 3 / h, Ar flow rate 3~5m 3 / h.

[0060] In the present invention, the process parameters of the VCD stage are preferably: vacuum degree ≤ 2 mbar, vacuum pumping time 5 to 20 min, Ar flow rate 1 to 5 m 3 / h; more preferably: vacuum degree ≤ 2mbar, vacuum time 10-15min, Ar flow rate 3-5m 3 / h.

[0061] In the present invention, 1-2 kg / t of calcium silicate deoxidizer is preferably added in the VCD stage. The present invention can adjust various elements within a specified range through the VCD stage.

[0062] In the present invention, the process parameters of the VD stage are preferably: vacuum degree ≤ 1.5 mbar, and vacuuming time 10 to 20 min.

[0063] After the VODC vacuum refining is completed, the present invention preferably transfers the molten steel obtained by the VODC vacuum refining into a ladle, and then calms it to obtain the molten steel.

[0064] In the present invention, the temperature of the molten steel when transferred into the ladle is preferably 1600-1650°C; the bottom of the ladle is preferably paved with a silicon-calcium deoxidizer; the amount of the silicon-calcium deoxidizer is preferably 1-5 Kg / t. The present invention uses a silicon-calcium deoxidizer to further deoxidize.

[0065] In the present invention, the sedation time is preferably 6 to 7 minutes.

[0066] After obtaining the molten steel, the present invention pours the molten steel to obtain a casting.

[0067] In the present invention, the pouring temperature is preferably 1570-1590° C.; the pouring is preferably performed in an argon protective atmosphere; and the pouring speed is preferably 1-10 mm / s.

[0068] After the pouring is completed, the present invention preferably demoulds the product obtained by pouring to obtain a cast part.

[0069] The present invention has no particular limitation on the demoulding operation, and any operation well known to those skilled in the art may be used.

[0070] After the casting is obtained, the invention performs annealing treatment on the casting to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine.

[0071] In the present invention, the holding temperature of the annealing treatment is preferably 770-790°C; the holding time of the annealing treatment is preferably 30h; and the cooling method of the annealing treatment is preferably first furnace cooling to 550°C and then air cooling out of the furnace.

[0072] 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.

[0073] The preparation method provided by the invention has simple process.

[0074] 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.

[0075] Example 1

[0076] The chemical composition of 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650℃ grade ultra-supercritical steam turbine is as follows by mass percentage: C0.06%, Si0.40%, Mn0.40%, P0.015%, S0.010%, Ni0.20%, Cr8.80%, Mo0.55%, Co2.9%, W2.90%, V0.18%, Nb0.08%, N0.006%, Al0.015%, B0.011%, Sn0.02%, Ti0.02%, Cu0.25%, Ce0.008% and the balance of Fe;

[0077] The preparation method of the 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine comprises the following steps:

[0078] (1) Laying iron ore and lime on the bottom of an electric arc furnace, then smelting the alloy raw materials in an electric arc furnace, then transferring them to a tundish, slagging the tundish, then performing VODC vacuum refining, then transferring them to a ladle, and quenching for 7 minutes to obtain molten steel; wherein the content of iron ore is 2% of the mass of the scrap steel, and the content of lime is 2.5% of the mass of the scrap steel;

[0079] Electric arc furnace smelting consists of a melting period, an oxidation period, and a reduction period that are carried out in sequence;

[0080] The process parameters during the melting period are: temperature of 1500°C, oxygen pressure of 0.5mPa; basicity of molten steel of 2.5, P removal to ≤0.006% to enter the oxidation period;

[0081] The process parameters of the oxidation period are: oxygen pressure 1.5mPa, molten pool temperature 1600℃, carbon removal ≥ 0.45%, when the carbon content in the molten steel is 0.8-1.0% and the molten pool temperature is greater than 1640-1650℃, stop blowing oxygen;

[0082] Add reducing agent during the reduction period; the reducing agent is ferrosilicon powder, the dosage is 5Kg / t, C is 0.8-1.0%, P≤0.010%, S≤0.008%, and the remaining ingredients are adjusted to the specified requirements;

[0083] VODC vacuum refining consists of the VOD stage, VCD stage and VD stage which are carried out in sequence;

[0084] The process parameters of the VOD stage are: vacuum degree 120mbar, vacuum time 0.5h, oxygen blowing speed 650m 3 / h, Ar flow rate 5m 3 / h;

[0085] The process parameters of the VCD stage are: vacuum degree 2 mbar, vacuum time 20 min, Ar flow rate 1 m 3 / h; add 2Kg / t silicon calcium deoxidizer;

[0086] The process parameters of the VD stage are: vacuum degree 1.5 mbar, vacuum time 15 min;

[0087] The temperature of the molten steel when transferred into the ladle is 1650℃; the bottom of the ladle is paved with silicon calcium deoxidizer; the dosage of silicon calcium deoxidizer is 5Kg / t;

[0088] (2) pouring the molten steel obtained in step (1) in an argon protective atmosphere, and obtaining a casting after demolding; wherein the pouring temperature is 1570° C. and the pouring speed is 10 mm / s;

[0089] (3) The cast part obtained in step (2) is annealed to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine; wherein the holding temperature for the annealing treatment is 780°C and the holding time is 30 hours; and the cooling method is first furnace cooling to 550°C and then air cooling after being taken out of the furnace.

[0090] Example 2

[0091] The chemical composition of 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650℃ grade ultra-supercritical steam turbine is as follows by mass percentage: C0.07%, Si0.20%, Mn0.50%, P0.010%, S0.005%, Ni0.10%, Cr9.30%, Mo0.50%, Co3.1%, W2.75%, V0.20%, Nb0.05%, N0.010%, Al0.010%, B0.015%, Sn0.01%, Ti0.01%, Cu0.20%, Ce0.001% and the balance of Fe;

[0092] The preparation method of the 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine comprises the following steps:

[0093] (1) Laying iron ore and lime on the bottom of an electric arc furnace, then smelting the alloy raw materials in an electric arc furnace, then transferring them to a tundish, slagging the tundish, then performing VODC vacuum refining, then transferring them to a ladle, and quenching them for 6 minutes to obtain molten steel; wherein the content of iron ore is 2% of the mass of the scrap steel, and the content of lime is 2% of the mass of the scrap steel;

[0094] Electric arc furnace smelting consists of a melting period, an oxidation period, and a reduction period that are carried out in sequence;

[0095] The process parameters during the melting period are: temperature of 1600°C, oxygen pressure of 0.1mPa; basicity of molten steel of 2, P removal to ≤0.006% to enter the oxidation period;

[0096] The process parameters of the oxidation period are: oxygen pressure 1.00mPa, molten pool temperature 1700℃, carbon removal ≥ 0.45%, when the carbon content in the molten steel is 0.8-1.0% and the molten pool temperature is greater than 1640-1650℃, stop blowing oxygen;

[0097] Add reducing agent during the reduction period; the reducing agent is ferrosilicon powder, the dosage is 10Kg / t, C is 0.8-1.0%, P≤0.010%, S≤0.008%, and the remaining ingredients are adjusted to the specified requirements;

[0098] VODC vacuum refining consists of the VOD stage, VCD stage and VD stage which are carried out in sequence;

[0099] The process parameters of the VOD stage are: vacuum degree 80mbar, vacuum time 2.0h, oxygen blowing speed 550m 3 / h, Ar flow rate 2m 3 / h;

[0100] The process parameters of the VCD stage are: vacuum degree 1 mbar, vacuum time 5 min, Ar flow rate 5 m 3 / h; add 1Kg / t silicon calcium deoxidizer;

[0101] The process parameters of the VD stage are: vacuum degree 1.0 mbar, vacuum time 20 min;

[0102] The temperature of the molten steel when transferred into the ladle is 1600℃; the bottom of the ladle is paved with silicon calcium deoxidizer; the dosage of silicon calcium deoxidizer is 1Kg / t;

[0103] (2) pouring the molten steel obtained in step (1) in an argon protective atmosphere, and obtaining a cast part after demolding; wherein the pouring temperature is 1580° C. and the pouring speed is 1 mm / s;

[0104] (3) The cast part obtained in step (2) is annealed to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine; wherein the holding temperature for the annealing treatment is 780°C and the holding time is 30 hours; and the cooling method is first furnace cooling to 550°C and then air cooling after being taken out of the furnace.

[0105] Example 3

[0106] The chemical composition of 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650℃ grade ultra-supercritical steam turbine is as follows by mass percentage: C0.08%, Si0.30%, Mn0.60%, P0.015%, S0.010%, Ni0.15%, Cr9.20%, Mo0.52%, Co3.0%, W2.85%, V0.25%, Nb0.06%, N0.008%, Al0.005%, B0.013%, Ce0.005% and the balance of Fe;

[0107] The preparation method of the 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine comprises the following steps:

[0108] (1) Laying iron ore and lime on the bottom of an electric arc furnace, then smelting the alloy raw materials in an electric arc furnace, then transferring them to a tundish, deslagging the tundish, then performing VODC vacuum refining, then transferring them to a ladle, and quenching them for 6.5 minutes to obtain molten steel; wherein the content of iron ore is 2% of the mass of the scrap steel, and the content of lime is 2.3% of the mass of the scrap steel;

[0109] Electric arc furnace smelting consists of a melting period, an oxidation period, and a reduction period that are carried out in sequence;

[0110] The process parameters during the melting period are: temperature of 1550°C, oxygen pressure of 0.3mPa; basicity of molten steel of 2.3, P removal to ≤0.006% to enter the oxidation period;

[0111] The process parameters of the oxidation period are: oxygen pressure 1.2mPa, molten pool temperature 1650℃, carbon removal amount ≥0.45%, when the carbon content in the molten steel is 0.8-1.0% and the molten pool temperature is greater than 1640-1650℃, stop blowing oxygen;

[0112] Add reducing agent during the reduction period; the reducing agent is ferrosilicon powder, the dosage is 1Kg / t, C is 0.8-1.0%, P≤0.010%, S≤0.008%, and the remaining ingredients are adjusted to the specified requirements;

[0113] VODC vacuum refining consists of the VOD stage, VCD stage and VD stage which are carried out in sequence;

[0114] The process parameters of the VOD stage are: vacuum degree 100mbar, vacuum time 1.5h, oxygen blowing speed 600m 3 / h, Ar flow rate 3m 3 / h;

[0115] The process parameters of the VCD stage are: vacuum degree 0.5 mbar, vacuum time 10 min, Ar flow rate 3 m 3 / h; add 1.5Kg / t silicon calcium deoxidizer;

[0116] The process parameters of the VD stage are: vacuum degree 0.5 mbar, vacuum time 15 min;

[0117] The temperature of the molten steel when transferred into the ladle is 1630℃; the bottom of the ladle is paved with silicon calcium deoxidizer; the dosage of silicon calcium deoxidizer is 3Kg / t;

[0118] (2) pouring the molten steel obtained in step (1) in an argon protective atmosphere, and obtaining a cast part after demolding; wherein the pouring temperature is 1580° C. and the pouring speed is 5 mm / s;

[0119] (3) The cast part obtained in step (2) is annealed to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine; wherein the holding temperature for the annealing treatment is 780°C and the holding time is 30 hours; and the cooling method is first furnace cooling to 550°C and then air cooling after being taken out of the furnace.

[0120] The heat-resistant steel ingots prepared in Examples 1 to 3 are prepared into forgings in the following steps:

[0121] (1) performing a first heat treatment on the steel ingot after cutting to obtain a pretreated workpiece; the procedure of the first heat treatment is: heating to 640°C at a heating rate of 50°C / h for a first heat treatment of 7h; continuing to heat to 960°C at a heating rate of 50°C / h for a second heat treatment of 7h; continuing to heat to 1170°C at a heating rate of 30°C / h for a third heat treatment of 7h, followed by air cooling;

[0122] (2) subjecting the pretreated workpiece to forging deformation treatment to obtain a forging blank;

[0123] (3) The forging blank is subjected to rough machining and a second heat treatment in sequence to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel forging; the procedure of the second heat treatment is as follows: annealing: heating to 830°C at a heating rate of 70°C / h, furnace cooling, tempering: 1020°C, oil cooling, ≥650°C air cooling.

[0124] The mechanical properties of the forgings were tested, and the results are shown in Table 1 (the room temperature tensile test used a Φ5mm standard specimen, using a WE-300 tensile testing machine, the test temperature was 25°C, and the tensile strength Rm and yield strength R P0.2 , elongation after fracture A and section shrinkage rate Z; the impact performance adopts GB / T229-2020 Metal Material Charpy Pendulum Impact Test Method); the forgings are subjected to high temperature creep test, and the results are shown in Table 2; the forgings are subjected to metallographic test, and the results are shown in Table 3.

[0125] Table 1 Room temperature mechanical properties of forgings prepared from steel ingots of Examples 1 to 3

[0126]

[0127] Table 2 High temperature creep properties of forgings made from steel ingots of Examples 1 to 3

[0128] Test temperature Test stress Test time Example 1 650℃ 30KN 100 hours Example 2 650℃ 30KN 100 hours Example 3 650℃ 30KN 100 hours

[0129] Table 3 Metallographic test results

[0130]

[0131] It can be seen from Tables 1 and 2 that the heat-resistant steel ingot provided by the present invention has higher heat resistance, strength and fatigue resistance, and can be used to manufacture a new type of million-kilowatt ultra-supercritical steam turbine unit with an operating temperature of 650°C; it can be seen from Table 3 that the intrinsic quality of its forging material meets the requirements of the material specification.

[0132] 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 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine, the chemical composition of which is as follows by mass percentage: C 0.06-0.08%, Si 0.20-0.40%, Mn 0.40-0.80%, P≤0.015%, S≤0.010%, Ni 0.10-0.20%, Cr 8.50-9.50%, Mo0.50-0.55%, Co 2.9-3.1%, W 2.70-2.90%, V 0.18-0.25%, Nb 0.05-0.08%, N 0.006-0.010%, Al≤0.015%, B 0.011~0.015%, Sn≤0.02%, Ti≤0.02%, Cu≤0.25%, RE 0.001~0.008% and the balance Fe; The method for preparing the 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine comprises the following steps: (1) subjecting the alloy raw materials to electric arc furnace smelting and VODC vacuum refining in sequence to obtain molten steel; (2) pouring the molten steel obtained in step (1) to obtain a cast part; (3) The cast part obtained in step (2) is annealed to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine; the holding temperature of the annealing treatment is 770-790°C; the holding time of the annealing treatment is 30 hours; the cooling method of the annealing treatment is first furnace cooling to 550°C and then air cooling after being taken out of the furnace.

2. The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine according to claim 1, characterized in that: The chemical composition is calculated by mass percentage: C 0.07-0.08%, Si 0.25-0.35%, Mn 0.50-0.70%, P≤0.015%, S≤0.010%, Ni 0.15-0.18%, Cr 8.80-9.20%, Mo 0.52-0.53%, Co 3.0-3.1%, W 2.75-2.85%, V 0.20-0.23%, Nb 0.06-0.07%, N 0.007-0.009%, Al 0.005-0.010%, B0.012-0.014%, Sn≤0.01%, Ti≤0.01%, Cu 0.10-0.20%, RE 0.003-0.005% and the balance Fe.

3. The 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine according to claim 1, characterized in that: The RE includes cerium and / or lanthanum.

4. The method for preparing the 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for 650°C grade ultra-supercritical steam turbine according to any one of claims 1 to 3, comprising the following steps: (1) subjecting the alloy raw materials to electric arc furnace smelting and VODC vacuum refining in sequence to obtain molten steel; (2) pouring the molten steel obtained in step (1) to obtain a cast part; (3) The cast part obtained in step (2) is annealed to obtain a 08Cr9Co3W3VNbNB martensitic heat-resistant steel ingot for a 650°C grade ultra-supercritical steam turbine; the holding temperature of the annealing treatment is 770-790°C; the holding time of the annealing treatment is 30 hours; the cooling method of the annealing treatment is first furnace cooling to 550°C and then air cooling after being taken out of the furnace.

5. The preparation method according to claim 4, characterized in that: The electric arc furnace smelting in step (1) includes a melting period, an oxidation period and a reduction period which are carried out in sequence.

6. The preparation method according to claim 4, characterized in that: The VODC vacuum refining in step (1) comprises a VOD stage, a VCD stage and a VD stage which are performed in sequence.

7. The preparation method according to claim 6, characterized in that: The process parameters of the VOD stage are: vacuum degree 80-120 mbar, vacuum time 0.5-2.0 h, oxygen blowing speed 550-650 m 3 / h, Ar flow rate 2~5m 3 / h.

8. The preparation method according to claim 6, characterized in that: The process parameters of the VCD stage are: vacuum degree ≤ 2 mbar, vacuum pumping time 5 to 20 min, Ar flow rate 1 to 5 m 3 / h.

9. The preparation method according to claim 6, characterized in that: The process parameters of the VD stage are: vacuum degree ≤ 1.5 mbar, and vacuuming time 10 to 20 min.

10. The preparation method according to claim 4, characterized in that: The pouring temperature in step (2) is 1570-1590°C.

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