A martensitic heat-resistant steel and its smelting method

Abstract

The present invention discloses a martensitic heat-resistant steel and its smelting method, relating to the technical field of metallurgy. The smelting method includes the following steps: S1. Design the ingredient composition of the martensitic heat-resistant steel; S2. Add the returned scrap steel into the intermediate frequency furnace according to the ingredient composition requirements in S1, and obtain molten steel after melting. The requirements for the scrap steel added into the intermediate frequency furnace in terms of weight percentage are: C: 1.0% - 1.7%; the superheat of the molten steel ≤ 70°C; S3. Conduct AOD blowing on the molten steel in S2 to adjust the composition; S4. Conduct LF smelting on the molten steel in S3 to adjust the composition and temperature; S5. Conduct VD smelting on the molten steel in S4, degas, adjust the composition, lift the ladle to tap the steel, and cast the ingot by die casting. The present invention provides a martensitic heat-resistant steel using vanadium, molybdenum, and nitrogen as high-temperature creep-resistant elements and its smelting method, realizing the advantages of high purity and uniform solidification structure of the martensitic heat-resistant steel prepared under industrial conditions.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical technology, and particularly to a martensitic heat-resistant steel for aviation and ship gas turbines and a smelting method thereof. Background Art

[0002] Martensitic heat-resistant stainless steels are now widely used in important components such as high-pressure compressor disks and rotor blades of aeroengines, and are also applied to key components of gas turbines. Martensitic heat-resistant steels are alloy steels with relatively high strength and good chemical stability at high temperatures. It includes two categories: oxidation-resistant steels (or high-temperature scale-resistant steels) and heat-resistant steels with high strength. Oxidation-resistant steels generally require good chemical stability but bear relatively low loads. Heat-resistant steels with high strength require relatively high high-temperature strength and corresponding oxidation resistance. Heat-resistant steels are often used to manufacture components that work at high temperatures in industrial sectors such as boilers, steam turbines, power machinery, industrial furnaces, aviation, petrochemicals, etc. In addition to high-temperature strength and resistance to high-temperature oxidation and corrosion, these components also require sufficient toughness, good machinability and weldability, and a certain degree of tissue stability according to different uses. At present, the service life of martensitic heat-resistant steels for ship gas turbines often needs to reach 100,000 h to 200,000 h, which poses extremely high requirements for the purity of the material and the uniformity of the solidification structure.

[0003] The patent with the application number CN202011482339.1 discloses "a smelting method of martensitic heat-resistant steel". The smelting method thereof includes the technological process of EAF electric furnace smelting + LF refining + VD vacuum treatment + ingot casting + forging the ingot into a consumable electrode + electroslag remelting. By precisely controlling the chemical composition of the steel internally, strictly controlling the gas content, improving the purity of the steel, and greatly improving the segregation of W, the produced G115 meets standards such as CSTM 00017-2017, Q / OAPD 2753-2017, and Q / OAPD 2253-2017. It has passed the strict performance evaluation and welding evaluation of relevant users. The G115 produced by this smelting method fully meets the conditions for engineering application in 630°C ultra-supercritical units.

[0004] The patent with the application number CN201910203172.1 discloses "A Steel for High-Temperature, Steam-Resistant and Corrosion-Resistant Boilers and Its Preparation Method". The composition of the steel is as follows by weight percentage: C: 0.07% - 0.14%, Si: 0.20% - 0.45%, Mn: 0.30% - 0.65%, Cr: 10.0% - 11.50%, W: 1.50% - 2.50%, V: 0.15% - 0.3%, Nb: 0.04% - 0.10%, Co: 2.50% - 3.50%, Mo: 0.25% - 0.60%, Ni: 0.20% - 0.50%, N: 0.040% - 0.100%, Cu: 0.30% - 1.70%, B: 0.0005% - 0.005%, P ≤ 0.015%, S ≤ 0.008%, and the rest is Fe and impurities. The preparation method includes the following steps: (1) Ingot casting process; (2) Heating process; (3) Hot rolling process; (4) Heat treatment; (5) Cooling. This method can increase the maximum operating temperature, raise the maximum steam operating temperature, and has excellent strength and toughness, high-temperature creep strength, steam oxidation and corrosion resistance, oxidation resistance, and creep rupture strength, and can meet the performance requirements of high-temperature and high-pressure components such as superheater tubes, main steam pipelines, and reheaters in ultra-supercritical thermal power units under harsh service environments of high temperature and high pressure.

[0005] The patent with the application number CN201910049001.8 discloses "A New Heat-Resistant Steel for Key Hot-End Components of Ultra-High Parameter Steam Turbines". This new heat-resistant steel contains, by weight percentage: C: 0.02% - 0.08%, Cr: 8.00% - 10.00%, Co: 2.0% - 4.0%, W: 2.0% - 4.0%, Mo: 0.10% - 0.80%, V: 0.10% - 0.30%, Ni: 0.30% - 0.70%, Nb: 0.05% - 0.15%, N: 0.010% - 0.050%, B: 0.010% - 0.030%, rare earth elements: 0.1% - 1.0%, Si: ≤ 0.10%, Mn: 0.10% - 1.00%, and the balance is Fe and inevitable impurities. This heat-resistant steel belongs to martensitic heat-resistant steel and has good high-temperature performance and oxidation resistance, thereby increasing the temperature parameters of the steam turbine and helping to improve the power generation efficiency of the steam turbine.

[0006] The patent with the application number CN201210378217.7 discloses "Fe-Cr-Co-W-Mo martensitic heat-resistant steel and its manufacturing method". Its chemical composition is by weight percentage: C: 0.08% - 0.12%, Cr: 11.0% - 16.0%, Co: 3.5% - 10.0%, W: 2.0% - 5.5%, Mo: 0.3% - 1.5%, V: 0.1% - 0.5%, Nb: 0.03% - 0.15%, Cu: 0.5% - 1.5%, Si ≤ 1.0%, Mn ≤ 1.0%, N: 0.04% - 0.06%, B: 0.002% - 0.004%, and the balance is Fe and inevitable impurities. The process parameters are: the ingot blooming temperature is 1150 °C, the final forging temperature ≥ 950 °C, the starting rolling temperature is 1150 °C, the final rolling temperature ≥ 950 °C, and the normalizing temperature is 750 °C - 790 °C. The advantage of this application is that it has excellent high-temperature strength and oxidation resistance in high-temperature gas and steam corrosion environments.

[0007] The patent with the application number CN201910933237.8 discloses "a super-supercritical high-nitrogen martensitic cast steel and its preparation method". The main components of the cast steel by weight percentage are: C: 0.005% - 0.05%; N: 0.04% - 0.65%; Cr: 8.0% - 12.0%; W: 3.5% - 6.5%; Co: 3.5% - 4.5%; Mo: 0.5% - 1.5%; V: 0.4% - 0.8%; Nb: 0.01% - 0.15%; Mn: 0.03% - 0.80%; Si: 0.02% - 0.10%; Ni: 0.005% - 0.04%; Hf: 0.01 - 0.10%; La + Ce: 0.008% - 0.10%; Fe: the balance. It mainly improves the high-temperature performance and oxidation resistance of the heat-resistant cast steel through nitride strengthening by reducing the carbon element and increasing the nitrogen element content; appropriate trace elements Hf and rare earth elements La + Ce improve the structure of the steel and ensure that a complete martensitic structure is finally obtained. The preparation process of pressure vacuum induction combined with pressure electroslag remelting effectively increases the solid solubility of nitrogen in the steel and also makes the ingot structure more uniform and dense.

[0008] In the current smelting technologies of the above-mentioned martensitic heat-resistant steels, most of them add W and Nb as alloying elements to the martensitic heat-resistant steel, and there are many problems in industrial large-scale production and engineering applications. For example, it is difficult to meet the material standards for gas turbines in terms of ferrite control, purity control, and the uniformity of solidification structure. Summary of the Invention

[0009] The object of the present invention is to provide a martensitic heat-resistant steel and its smelting method, specifically to provide a martensitic heat-resistant steel with vanadium, molybdenum, and nitrogen as high-temperature creep-resistant elements and its smelting method, so as to achieve the advantages of high purity and uniform solidification structure of the martensitic heat-resistant steel prepared under industrial conditions.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] The present invention provides a smelting method for a martensitic heat-resistant steel, and the method includes the following steps:

[0012] Step S1: Design the batching composition of the martensitic heat-resistant steel;

[0013] Step S2: Add the returned scrap steel into the medium-frequency furnace according to the requirements of the batching composition in Step S1, and obtain molten steel after melting; the requirements for the scrap steel added into the medium-frequency furnace in terms of weight percentage are: C: 1.0% - 1.7%; the superheat of the molten steel ≤ 70°C;

[0014] Step S3: Conduct AOD blowing on the molten steel in Step S2 to adjust the composition;

[0015] Step S4: Conduct LF smelting on the molten steel in Step S3 to adjust the composition and temperature;

[0016] Step S5: Conduct VD smelting on the molten steel in Step S4, degas, adjust the composition, lift the ladle to tap the steel, and cast it into ingots by die casting.

[0017] In a possible implementation manner, in Step S1, the chemical composition of the batching is as follows in terms of weight percentage: C: 0.07 - 0.14%, Si ≤ 0.2%, Mn: 0.4 - 0.9%, Mo: 1.5 - 2.0%, S ≤ 0.02%, P ≤ 0.02%, Cr: 11.0 - 12.6%, Ni: 2.0 - 3.0%, V: 0.2 - 0.4%, N: 0.025 - 0.04%, B: 0.001 - 0.003%, and the balance is Fe and unavoidable impurities.

[0018] In a possible implementation manner, in Step S1, the chromium-nickel equivalent ratio Cr eq / Ni eq ≤ 2.2; where

[0019] The chromium equivalent calculation formula is: Cr eq = Cr + 1.5Mo + 2Si + 5V;

[0020] The nickel equivalent calculation formula is: Ni eq = Ni + 30C + 0.5Mn + 25N.

[0021] In a possible implementation, in step S2, the scrap steel added into the medium-frequency furnace is required by weight percentage to be: Mo and Ni are configured according to the upper limit of the batching composition in step S1, S ≤ 0.02%, P ≤ 0.02%.

[0022] In a possible implementation, in step S3, the molten steel in step S2 is subjected to AOD blowing to adjust the composition, including:

[0023] The C content of the molten steel in step S2 is blown down to less than 0.07% by AOD, and the temperature of the molten steel shall not be lower than 1650 °C.

[0024] In a possible implementation, step S3 further includes:

[0025] When the temperature of the molten steel is lower than 1650 °C, C is added, and then FeSi is used for deoxidation to reduce the oxygen content to less than 50 ppm;

[0026] After deoxidation, high-purity electrolytic Cr and electrolytic Ni are added in no less than three batches according to the batching composition requirements in step S1. After addition, the temperature of the molten steel shall not be lower than 1500 °C, and then the steel is tapped into the LF furnace.

[0027] In a possible implementation, in step S4, the molten steel in step S3 is subjected to LF smelting to adjust the composition and temperature, including:

[0028] FeV is added to the molten steel in step S3 to adjust the V content to the upper limit requirement of the batching composition in step S1. NiMg alloy is put in for deep deoxidation. After the oxygen content is measured to be ≤ 20 ppm, the steel is tapped, and the tapping temperature is not lower than 1600 °C.

[0029] In a possible implementation, in step S5, the conditions for VD smelting include: the vacuum degree ≤ 50 Pa, and the holding time ≥ 20 min.

[0030] In a possible implementation, in step S5, the argon flow rate during the casting process is 2 - 4 Nm 3 / h.

[0031] The present invention also provides a martensitic heat-resistant steel smelted by the above method.

[0032] The technical effects and advantages of the present invention:

[0033] This patent relates to martensite mainly using V, N, and Mo as strengthening phases for high-temperature creep resistance. At the same time, medium-frequency furnace + AOD + LF + VD are used for smelting. The billets produced by this method have high purity and dense structure. The production cost and smelting time are much lower than those of the VIM + VAR special smelting process. The product quality meets the requirements of materials such as rotor shafts, high-pressure stationary blades, and casings for aviation and ship gas turbines below 500°C in the service environment. Since there are relatively few domestic related manufacturers of this alloy and the demand is large, the market prospect is good, and the added value of this product is high. It is estimated that the economic benefit can reach 3 million per year.

[0034] Other features and advantages of the present invention will be described in the following specification, and in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structure pointed out in the specification and the drawings. Brief Description of the Drawings

[0035] Figure 1 It is a flow chart of a method for smelting a martensitic heat-resistant steel according to an exemplary embodiment of the present invention. Detailed Embodiments

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] To solve the deficiencies of the prior art, the present invention discloses a method for smelting a martensitic heat-resistant steel. Figure 1 It is a flow chart of a method for smelting a martensitic heat-resistant steel according to an exemplary embodiment of the present invention, as Figure 1 shown. The method includes the following steps:

[0038] Step S1: Design the ingredient composition of the martensitic heat-resistant steel;

[0039] Step S2: Add the returned scrap steel into the medium-frequency furnace according to the ingredient composition requirements in Step S1, and obtain molten steel after melting;

[0040] Step S3: Conduct AOD blowing on the molten steel in Step S2 to adjust the composition;

[0041] Step S4: Conduct LF smelting on the molten steel in Step S3 to adjust the composition and temperature;

[0042] Step S5: Conduct VD smelting on the molten steel in Step S4, degas, adjust the composition, lift the ladle to tap the steel, and cast it into ingots by die casting;

[0043] As a preferred solution, in step S1, the chemical composition of the ingredients is as follows by weight percentage: C: 0.07 - 0.14%, Si ≤ 0.2%, Mn: 0.4 - 0.9%, Mo: 1.5 - 2.0%, S ≤ 0.02%, P ≤ 0.02%, Cr: 11.0 - 12.6%, Ni: 2.0 - 3.0%, V: 0.2 - 0.4%, N: 0.025 - 0.04%, B: 0.001 - 0.003%, and the balance is Fe and inevitable impurities.

[0044] As a further preferred solution, in step S1, to avoid the formation of δ-ferrite during solidification and subsequent hot working, the chromium-nickel equivalent ratio needs to be controlled to ≤ 2.2 after the final solidification of the molten steel. The nickel equivalent calculation formula is: Ni eq = Ni + 30C + 0.5Mn + 25N, and the chromium equivalent calculation formula is: Cr eq = Cr + 1.5Mo + 2Si + 5V;

[0045] As a preferred solution, in step S2, the requirements for the scrap steel entering the intermediate frequency furnace are as follows by weight percentage: C: 1.0% - 1.7%, Mo and Ni are configured according to the upper limits of the ingredient composition in step S1 above, S ≤ 0.02%, P ≤ 0.02%, and the addition of other components is strictly prohibited. After the molten steel in the intermediate frequency furnace is melted evenly, it is quickly transferred to an AOD (argon-oxygen decarburization) furnace, and the superheat of the molten steel ≤ 70°C;

[0046] As a preferred solution, in step S3, the C content is blown down to below 0.07% through AOD, and the temperature of the molten steel shall not be lower than 1650°C. If the temperature is insufficient, C is appropriately supplemented, and then FeSi alloy is added for deoxidation to reduce the oxygen content to below 50 ppm;

[0047] As a further preferred solution, after deoxidation in step S3, high-purity electrolytic Cr and electrolytic Ni are added in not less than three batches according to the ingredient composition requirements in step S1 above. After addition, the temperature of the molten steel shall not be lower than 1500°C, and then the steel is tapped into the LF furnace;

[0048] As a preferred solution, in step S4, the composition is measured, and the composition is fine-tuned and FeV alloy is added according to the ingredient composition requirements in step S1 above to adjust its V content to the upper limit requirement of the ingredient composition in step S1 above; NiMg alloy is put in for deep deoxidation. After measuring the oxygen content ≤ 20 ppm, the steel is tapped, and the tapping temperature is not lower than 1600°C, and the [C] content shall not be higher than the upper limit requirement of the ingredient composition in step S1 above;

[0049] As a preferred solution, in the VD vacuum furnace treatment in step S5, control the vacuum degree ≤ 50 Pa and the holding time ≥ 20 min; charge Ar gas to strengthen stirring and determine hydrogen, with H ≤ 1.0 ppm; add ferromanganese alloy, boron nitride and iron nitride to adjust the Mn, B and N components to the ingredient requirements in step S1 above. Before lifting the ladle, control the Ar gas supply pressure to be 0.20 - 0.40 Mpa to prevent the molten steel from being exposed to air; control the ladle temperature to be 1500 ± 10 °C.

[0050] As a preferred solution, to prevent the production of TiN in the later stage, strictly control the entry of Ti element throughout the process, and the Ti content in the molten steel during tapping shall not exceed 25 ppm;

[0051] As a preferred solution, in the ingot casting described in step S5, use a protective cover to protect the casting nozzle, and use argon gas for protection during casting, with the argon gas flow rate being 2 - 4 Nm 3 / h; adopt the bottom-pouring method for casting, and charge Ar into the ingot mold before casting; after pouring, add heat-generating agent and rice husk ash as supplements.

[0052] Using the above method, the present invention also discloses a martensitic heat-resistant steel for aviation and ship gas turbines, and its chemical composition is by weight percentage: C: 0.07 - 0.14%, Si ≤ 0.2%, Mn: 0.4 - 0.9%, Mo: 1.5 - 2.0%, S ≤ 0.02%, P ≤ 0.02%, Cr: 11.0 - 12.6%, Ni: 2.0 - 3.0%, V: 0.2 - 0.4%, N: 0.025 - 0.04%, B: 0.001 - 0.003%, and the balance is Fe and inevitable impurities.

[0053] Example 1:

[0054] A smelting method of a martensitic heat-resistant steel provided by an exemplary embodiment of the present invention, the method includes the following steps:

[0055] Step S1, design the ingredient composition of the martensitic heat-resistant steel;

[0056] The weight percentage of its target chemical composition is: C: 0.13%, Si ≤ 0.2%, Mn: 0.5%, Cr: 12.4%, Mo: 1.9%, Ni: 3.0%, V: 0.3%, N: 0.03%, B: 0.002%, S ≤ 0.02%, P ≤ 0.02%;

[0057] Step S2, add the returned scrap steel into the intermediate frequency furnace according to the ingredient requirements in step S1, and obtain molten steel after melting;

[0058] The scrap steel charged into the intermediate frequency furnace is configured according to the requirements of C: 1.7%, Mo: 2.0% and Ni: 3.0%, where S ≤ 0.02%, P ≤ 0.02%, and the addition of other components is strictly controlled. After the molten steel in the intermediate frequency furnace is melted evenly, it is quickly transferred to the AOD furnace, and the superheat of the molten steel is 40°C;

[0059] Step S3: Blow the molten steel in step S2 in the AOD furnace to adjust the composition;

[0060] Blow the C content down to 0.03% through the AOD. The temperature of the molten steel shall not be lower than 1690°C. Use FeSi for deoxidation to reduce the oxygen content to 50 ppm;

[0061] Add high-purity electrolytic Cr and electrolytic Ni in three batches according to the designed composition. After complete melting, the measured temperature of the molten steel is 1530°C, and then tap the steel to the LF furnace;

[0062] Step S4: Smelt the molten steel in step S3 in the LF furnace to adjust the composition and temperature;

[0063] During the LF smelting process, after the measured composition is qualified, add FeV to adjust its V content to 0.4, and put in NiMg alloy for deep deoxidation until the oxygen content is 20 ppm and then tap the steel. The tapping temperature is 1610°C. At this time, the C content is 0.11%, and then pour the molten steel into the VD furnace;

[0064] Step S5: Smelt the molten steel in step S4 in the VD furnace for degassing, adjusting the composition, and tapping and casting into ingots;

[0065] During the treatment in the VD vacuum furnace, control the vacuum degree to 50 Pa and the holding time to 20 min; fill in Ar gas to strengthen stirring, determine the hydrogen content, H ≤ 1.0 ppm; add ferromanganese alloy, boron nitride and iron nitride to adjust the Mn, B and N components to 0.5%, 0.002% and 0.03% respectively. Before lifting the ladle, control the Ar gas supply pressure to 0.30 Mpa, do not expose the molten steel to the air, and the ladle temperature is 1500°C.

[0066] Use a protective cover to protect the casting nozzle, and use argon gas for protection during casting. The argon gas flow rate is 3 Nm 3 / h; Adopt the bottom-pouring method for casting. First, fill Ar in the ingot mold before casting; after pouring, add heat-generating agent and rice husk ash.

[0067] The chemical composition of the final martensitic heat-resistant steel obtained in this example is shown in Table 1, the macrostructure inspection results are shown in Table 2, and the inclusion rating results are shown in Table 3.

[0068] Example 2:

[0069] A method for smelting a martensitic heat-resistant steel provided by an exemplary embodiment of the present invention, the method comprising the following steps:

[0070] Step S1: Design the ingredient composition of martensitic heat-resistant steel;

[0071] The weight percentages of its target chemical components are as follows: C: 0.14%, Si ≤ 0.2%, Mn: 0.6%, Cr: 11.8%, Mo: 1.9%, Ni: 2.8%, V: 0.3%, N: 0.04%, B: 0.003%, S ≤ 0.02%, P ≤ 0.02%;

[0072] Step S2: Add the returned scrap steel into the intermediate frequency furnace according to the ingredient composition requirements in Step S1, and obtain molten steel after melting;

[0073] The requirements for the scrap steel entering the intermediate frequency furnace are configured with C: 1.5%, Mo: 2.0% and Ni: 3.0%, where S ≤ 0.02%, P ≤ 0.02%, and the addition of other components is strictly prohibited. After the molten steel in the intermediate frequency furnace is melted evenly, it is quickly transferred to the AOD furnace, and the superheat of the molten steel is 50°C;

[0074] Step S3: Conduct AOD blowing on the molten steel in Step S2 to adjust the composition;

[0075] Blow the C content down to 0.05% through AOD, the temperature of the molten steel shall not be lower than 1670°C, use FeSi for deoxidation, and deoxidize the oxygen content to 50 ppm;

[0076] Add high-purity electrolytic Cr and electrolytic Ni in three batches according to the designed composition. After complete melting, the temperature of the molten steel is measured to be 1520°C, and then tap the steel to the LF furnace;

[0077] Step S4: Conduct LF smelting on the molten steel in Step S3 to adjust the composition and temperature;

[0078] During LF smelting, after the measured composition is qualified, add FeV to adjust its V content to 0.4, and put in NiMg alloy for deep deoxidation until the oxygen content is 18 ppm and then tap the steel. The tapping temperature is 1620°C. At this time, the C content is 0.10%, and then pour the molten steel into the VD furnace;

[0079] Step S5: Conduct VD smelting on the molten steel in Step S4 to degas, adjust the composition, and tap the steel to cast ingots;

[0080] During the treatment in the VD vacuum furnace, control the vacuum degree to be 30 Pa and the holding time to be 20 min; charge Ar gas to strengthen stirring, determine hydrogen, H ≤ 1.0 ppm; add ferromanganese alloy, boron nitride and iron nitride to adjust the Mn, B and N components to 0.65%, 0.003% and 0.04% respectively. Before lifting the ladle, control the Ar gas supply pressure to be 0.40 Mpa, do not expose the molten steel to the air, and the ladle temperature is 1510°C.

[0081] The casting nozzle is protected by a protective cover, and argon is used for protection during casting, with an argon flow rate of 2 Nm 3 / h; The downcasting method is adopted for casting. Before casting, Ar is filled in the ingot mold; after pouring, a heat-generating agent and rice husk ash are added as supplements.

[0082] The chemical composition of the martensitic heat-resistant steel obtained in this embodiment is shown in Table 1, the macro-examination results are shown in Table 2, and the inclusion rating results are shown in Table 3.

[0083] Table 1 Chemical composition of the martensitic heat-resistant steel obtained in each embodiment

[0084]

[0085]

[0086] Table 2 Macro-examination results of the martensitic heat-resistant steel obtained in each embodiment

[0087] General looseness Central looseness Spotty segregation Other visually visible defects Example 1 1 0 0 0 Example 2 1 0 0 0

[0088] Table 3 Inclusion rating results of the martensitic heat-resistant steel obtained in each embodiment

[0089]

[0090] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A smelting method for a martensitic heat-resistant steel, characterized in that, The method includes the following steps: Step S1: Design the ingredient composition of the martensitic heat-resistant steel. In the described ingredients, the chromium-nickel equivalent ratio Cr eq / Ni eq ≤ 2.2; among them, The chromium equivalent calculation formula is: Cr eq = Cr + 1.5Mo + 2Si + 5V; The nickel equivalent calculation formula is: Ni eq = Ni + 30C + 0.5Mn + 25N; Step S2: Add the returned scrap steel into the intermediate frequency furnace according to the ingredient composition requirements in Step S1, and obtain molten steel after melting; the requirements for the scrap steel added into the intermediate frequency furnace in terms of weight percentage are: C: 1.0% - 1.7%; the superheat of the molten steel ≤ 70°C. Step S3: Conduct AOD blowing on the molten steel in Step S2 to adjust the composition. Step S4: Conduct LF smelting on the molten steel in Step S3 to adjust the composition and temperature. Step S5: Conduct VD smelting on the molten steel in Step S4, degas, adjust the composition, lift the ladle to tap the steel, and cast it into an ingot by die casting. To prevent the production of TiN in the later stage, strictly control the entry of Ti element throughout the process, and the Ti content in the molten steel during tapping shall not exceed 25 ppm. The chemical composition of the martensitic heat-resistant steel in terms of weight percentage is: C: 0.07 - 0.14%, Si ≤ 0.2%, Mn: 0.4 - 0.9%, Mo: 1.5 - 2.0%, S ≤ 0.02%, P ≤ 0.02%, Cr: 11.0 - 12.6%, Ni: 2.0 - 3.0%, V: 0.2 - 0.4%, N: 0.025 - 0.04%, B: 0.001 - 0.003%, and the balance is Fe and inevitable impurities.

2. The smelting method of the martensitic heat-resistant steel according to claim 1, characterized in that, In Step S2, the requirements for the scrap steel added into the intermediate frequency furnace in terms of weight percentage are: Mo and Ni are configured according to the upper limit of the ingredient composition in Step S1, S ≤ 0.02%, P ≤ 0.02%.

3. The smelting method of the martensitic heat-resistant steel according to claim 1, characterized in that, In Step S3, the conduct of AOD blowing on the molten steel in Step S2 to adjust the composition includes: Blow the C content in the molten steel in Step S2 below 0.07% through AOD, and the temperature of the molten steel shall not be lower than 1650°C.

4. The smelting method of the martensitic heat-resistant steel according to claim 3, characterized in that, Step S3 further includes: When the temperature of the molten steel is lower than 1650°C, add C, and then use FeSi for deoxidation to reduce the oxygen content to below 50 ppm. After deoxidation, add high-purity electrolytic Cr and electrolytic Ni in no less than three batches according to the ingredient composition requirements in Step S1. After adding, the temperature of the molten steel shall not be lower than 1500°C, and then tap the steel to the LF furnace.

5. The smelting method of the martensitic heat-resistant steel according to claim 1, characterized in that, In Step S4, the conduct of LF smelting on the molten steel in Step S3 to adjust the composition and temperature includes: Add FeV to the molten steel in Step S3 to adjust the V content to the upper limit requirement of the ingredient composition in Step S1, put in NiMg alloy for deep deoxidation, and tap the steel after measuring the oxygen content ≤ 20 ppm, and the tapping temperature is not lower than 1600°C.

6. The smelting method of the martensitic heat-resistant steel according to claim 1, characterized in that, In Step S5, the conditions for VD smelting include: the vacuum degree ≤ 50 Pa, and the holding time ≥ 20 min.

7. The smelting method of the martensitic heat-resistant steel according to claim 1, characterized in that, In step S5, the argon flow rate during the casting process is 2 - 4 Nm 3 / h.

8. A martensitic heat-resistant steel, characterized in that, Smelted by the method described in any one of claims 1 - 7.

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