A rare earth heat-resistant steel and a method for manufacturing the same

Abstract

The present invention relates to a rare earth heat-resistant steel and a manufacturing method thereof, and belongs to the technical field of heat-resistant steel. The rare earth heat-resistant steel comprises C: 0.08-0.12%, Si: 0.2-0.4%, Mn: 0.3-0.5%, Cr: 8.2-9.2%, Mo: 0.90-1.05%, V: 0.18-0.22%, Nb: 0.06-0.10%, Al≤0.012%, rare earth: 0.02-0.08%, O≤0.0020%, N: 0.045-0.055%, and the rare earth is Ce and Y, and the content of Ce is not less than 0.01%. The present invention simultaneously adds rare earth Y and Ce to the heat-resistant steel, and controls the ratio thereof to be not less than 1:2, thereby improving the dispersion strengthening effect, significantly reducing the inclusion level, and significantly improving the performance.

Description

Technical Field

[0001] The present invention relates to the technical field of heat-resistant alloys, and in particular to rare earth heat-resistant steel and a manufacturing method thereof. Background Art

[0002] Heat-resistant steel has been widely used in the new generation of high-parameter thermal power or fourth-generation nuclear power due to its excellent high-temperature strength and creep resistance. In order to further improve the oxidation resistance and durability of heat-resistant steel, both domestic and foreign countries are exploring strengthening through rare earth alloying, using rare earth to purify molten steel, modify inclusions, solid solution strengthening and improve oxidation resistance in heat-resistant steel to improve the mechanical properties, oxidation resistance and long-term creep strength of heat-resistant steel. However, during the engineering trial production of rare earth heat-resistant steel, there are problems such as large fluctuations in rare earth yield and deterioration of performance due to excessive inclusions, which cannot achieve the desired strengthening effect.

[0003] In order to further improve the oxidation resistance and durability of steel, some studies have added Ce and Ca during the RH refining process, in order to make full use of the excellent effects of rare earth Ce in heat-resistant steel in purifying molten steel, modifying inclusions, solid solution strengthening and improving oxidation resistance. However, this method has limited improvement on the performance of heat-resistant steel, and in the smelting process, rare earths are easily formed into oxide inclusions after being added to molten steel, and the density of inclusions is similar to that of molten steel, making it difficult to completely remove them by floating. Therefore, during the engineering trial production of rare earth heat-resistant steel, there are problems such as large fluctuations in rare earth yield and deterioration of performance due to excessive inclusions, which affect the performance of heat-resistant steel.

[0004] Therefore, there is an urgent need for a heat-resistant steel with better performance and rare earth content that meets the requirements. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a rare earth heat-resistant steel and a method for manufacturing the same, so as to ensure the rare earth yield and improve the performance of the rare earth heat-resistant steel.

[0006] On the one hand, the present invention provides a rare earth heat-resistant steel, which comprises, by mass percentage, C: 0.08-0.12%, Si: 0.2-0.4%, Mn: 0.3-0.5%, Cr: 8.2-9.2%, Mo: 0.90-1.05%, V: 0.18-0.22%, Nb: 0.06-0.10%, Al: ≤0.012%, rare earth: 0.02-0.08%, O: ≤0.0020%, N: 0.045-0.055%, and the rest is Fe;

[0007] The rare earths are Ce and Y, and the content of Ce is not less than 0.01%.

[0008] Furthermore, the mass ratio of Y to Ce is not less than 1:2.

[0009] Furthermore, various types of inclusions in the heat-resistant steel do not exceed level 0.5.

[0010] Furthermore, at room temperature, the tensile strength is above 720 MPa, the yield strength is above 530 MPa, and the impact energy is above 190 J.

[0011] In another aspect, the present invention provides a method for preparing rare earth heat-resistant steel, comprising the following steps:

[0012] S1: Vacuum induction melting, the raw materials are melted into molten steel, and after high vacuum refining and adjusting the content of other elements except rare earth, N, and Mn to meet the requirements, a mixed gas of 15000~25000Pa is filled in. The mixed gas is N 2 and Ar, after the molten steel fully absorbs nitrogen, add metallic manganese, ferrochromium nitride and rare earth iron alloy, stir, sample and tap within 30 minutes, and cast into electrode ingots;

[0013] S2: electroslag remelting, remelting the electrode ingot to obtain an electroslag ingot;

[0014] S3: forging, forging the obtained electroslag ingot to obtain a forged rod;

[0015] S4: heat treatment, heat treatment of the obtained forged rod, normalizing and tempering, to obtain rare earth heat-resistant steel.

[0016] Furthermore, using N 2 Together with ferrochrome nitride, nitrogen is added to meet , where [N] is the target N content; P N2 N 2 Partial pressure, Pa; [N] N-CrFe The N content brought into the molten steel by ferrochromium nitride, and 0.005%≤[N] N-CrFe ≤0.010%.

[0017] Furthermore, the rare earth iron alloy composition is: Ce+Y content 25~35%, Si content 8~12%, C content 0.05~0.1%, Zr content 0.1~1.0%, and the balance is Fe.

[0018] Furthermore, in electroslag remelting, the slag system is: CaF 2 :35~45%;Al 2 O 3 :11~15%;CaO:22~27%;Ce 2 O 3 :8~12%;Y 2 O 3 :15~18%,SiO 2 ≤0.3%,FeO≤0.5%.

[0019] Furthermore, the normalizing temperature is 1050-1080°C, and the tempering temperature is 760-790°C.

[0020] Furthermore, the rare earth recovery rate is above 50%.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] 1. The present invention adds rare earth Y and Ce to the heat-resistant steel at the same time, and controls the ratio to be not less than 1:2, so as to modify the inclusions in the molten steel into Y 2 O 3 During the solidification process, avoid using magnesium aluminum spinel or Ce 2 O 3 Inclusions act as nucleation cores to form large-sized angular carbonitrides, which improve the dispersion strengthening effect. The inclusion level in the resulting rare earth heat-resistant steel is significantly reduced, and the performance is significantly improved.

[0023] 2. The present invention optimizes the N addition process of heat-resistant steel and adopts N 2 Alloying is carried out by combining diffusion nitrogen filling with a small amount of ferrochromium nitride, and a special rare earth alloy and electroslag remelting slag system are designed. The yield and stability of rare earth elements are significantly improved, which can be stabilized at more than 50%, and has a prospect for engineering production.

[0024] 3. The present invention combines component design, manufacturing method and heat treatment process, and the performance of the rare earth heat-resistant steel obtained is significantly improved. At room temperature, the present invention combines component design, manufacturing method and heat treatment process, and the performance of the rare earth heat-resistant steel obtained is significantly improved. At room temperature, the tensile strength is above 720MPa, the yield strength is above 530MPa, and the impact energy is above 190J. The performance is also improved in high temperature environment.

[0025] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0027] Figure 1 This is the metallographic diagram of the rare earth heat-resistant steel obtained in Example 1;

[0028] Figure 2 This is the metallographic image of the rare earth heat-resistant steel obtained in Comparative Example 1;

[0029] Figure 3 The morphology of inclusions under a metallographic microscope in Example 1;

[0030] Figure 4 This is the inclusion morphology under the metallographic microscope of Comparative Example 1. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0032] Heat-resistant steel has received extensive attention and application in the new generation of high-parameter thermal power or nuclear power due to its excellent high-temperature strength and creep resistance. However, heat-resistant steel contains inclusions and has poor cleanliness, which in turn affects its performance.

[0033] In order to reduce inclusions and improve the performance of heat-resistant steel, studies have shown that adding Ce and Ca elements during RH refining can purify the molten steel, reduce inclusions and improve oxidation resistance to improve the performance of heat-resistant steel. However, when the above method is used for preparation, the performance improvement is relatively limited and the yield of rare earth is low.

[0034] Therefore, the present invention provides a rare earth heat-resistant steel, which comprises, by mass percentage, C: 0.08-0.12%, Si: 0.2-0.4%, Mn: 0.3-0.5%, Cr: 8.2-9.2%, Mo: 0.90-1.05%, V: 0.18-0.22%, Nb: 0.06-0.10%, Al: ≤0.012%, rare earth: 0.02-0.08%, O: ≤0.0020%, N: 0.045-0.055%, and the rest is Fe;

[0035] The rare earths are Ce and Y, and the content of Ce is not less than 0.01%.

[0036] Compared with the prior art, the rare earth heat-resistant steel provided by the present invention changes the size, morphology and distribution of inclusions through the mutual compounding of chemical elements. Only by strictly controlling the content of rare earth elements can the rare earth solid solution strengthening effect be fully exerted to improve the performance of heat-resistant steel. In the present invention, the rare earth content should be greater than 0.02%, otherwise the rare earth mainly exists in the form of inclusions; when the content exceeds 0.08%, it is easy to form a low melting point eutectic at the grain boundary, resulting in deterioration of plasticity.

[0037] Specifically, the rare earths are Ce and Y, the Ce content is not less than 0.01%, and the mass ratio of Y to Ce is not less than 1:2.

[0038] It should be noted that a certain amount of Nb and V elements are usually added to heat-resistant steel to form MX phase with N element, which plays a role of dispersion strengthening. Rare earth Y and Ce are added to heat-resistant steel at the same time, and their ratio is controlled to be not less than 1:2, so that inclusions in the molten steel are modified into Y 2 O 3 , while Ce element combines with O to form Ce 2 O 3 , Ce 2 O 3 It is very easy to become the nucleus of MX phase, and precipitate large size at once during solidification, consuming the dispersion strengthening effect of MX phase. Rare earth Y has a stronger ability to combine with O than Ce in molten steel. When Y / Ce is greater than 0.5, the inclusions are mainly Y 2 O 3 、Ce 2 O 2 The existence of S can effectively avoid the precipitation of large-sized primary MX, purify the S element deviation at the grain boundary, and improve the thermoplasticity and creep properties.

[0039] Specifically, the various inclusions in the heat-resistant steel do not exceed level 0.5.

[0040] It should be noted that, since Ce and Y have very strong binding ability with S and O in steel, the addition of Ce and Y limits the combination of O with Mg and Al, reduces the irregular and angular Mg-Al-O inclusions, and transforms them into spherical rare earth oxides, sulfides and oxysulfides, and the size is also refined to below 0.5 level. In addition, after adding rare earth elements Ce and Y, the dispersion of inclusions in steel is increased, and at the same time, the grain structure is significantly refined, with an average grain size of 7-10 levels, which enhances the fine grain strengthening effect.

[0041] The present invention provides a method for preparing rare earth heat-resistant steel, comprising the following steps:

[0042] S1: Vacuum induction melting, the raw materials are melted into molten steel, and after high vacuum refining and adjusting the content of other elements except rare earth, N, and Mn to meet the requirements, a mixed gas of 15000~25000Pa is filled in. The mixed gas is N 2 and Ar, after the molten steel fully absorbs nitrogen, add metallic manganese, ferrochromium nitride and rare earth iron alloy, stir and tap the steel within 30 minutes, and cast it into electrode ingots;

[0043] S2: electroslag remelting, remelting the electrode ingot to obtain an electroslag ingot;

[0044] S3: forging, forging the obtained electroslag ingot to obtain a forged rod;

[0045] S4: heat treatment, heat treatment of the obtained forged rod, normalizing and tempering, to obtain rare earth heat-resistant steel.

[0046] Compared with the existing technology, since rare earth heat-resistant steel has extremely high purity requirements, a vacuum induction furnace is used for smelting, and the vacuum C removal O reaction is used to obtain a purity far higher than that of refining outside the furnace. In addition, there is no protective slag or covering agent in the vacuum induction process, and the rare earth recovery rate is more stable. At the same time, electroslag remelting helps to further filter inclusions, ensure that large-sized inclusions that are not easy to float are removed, and improve purity. Finally, after forging and heat treatment, the comprehensive performance of heat-resistant steel is guaranteed.

[0047] Specifically, in the vacuum induction melting process, N 2 Together with ferrochrome nitride, nitrogen is added to meet , where [N] is the target N content; P N2 N 2 Partial pressure, Pa; [N] N-CrFe The N content brought into the molten steel by ferrochromium nitride, and 0.005%≤[N] N-CrFe ≤0.010%.

[0048] It should be noted that as active metals, rare earths should be added to molten steel to reduce the content of impurities such as O and S in the molten steel as much as possible. However, the Al content in heat-resistant steel is relatively low, and it is difficult to reduce the O content to a sufficiently low level by refining outside the furnace. At the same time, during the smelting process, rare earths will react with refractory materials, electroslag remelting slag systems, etc., resulting in a significant reduction in the yield. Steel must be tapped within 30 minutes. In addition, considering the Mn and N 2 The yield fluctuated due to evaporation under vacuum. 2 and Ar mixed mode, while playing the role of N 2 It has the function of diffusing nitrogen into the molten steel and inhibiting element burning loss.

[0049] The O content in ferrochromium nitride is high, and the molten steel is added after the vacuum induction furnace is filled with inert gas. The O introduced into the molten steel cannot be effectively removed, which is not conducive to rare earth alloying. 2 It takes a long time for the diffusion nitrogen filling to reach equilibrium, and a small amount of ferrochrome nitride is also needed. 2 Nitrogen is added together with ferrochrome nitride, and the nitrogen content brought into the molten steel by ferrochrome nitride satisfies 0.005≤[%N] N-CrFe ≤0.010.

[0050] Specifically, the rare earth iron alloy composition is: Ce+Y content 25-35%, Si content 8-12%, C content 0.05-0.1%, Zr content 0.1-1.0%, and the balance is Fe.

[0051] It should be noted that rare earth Ce and Y have low melting points, but they will oxidize rapidly when placed in the air. By refining into ferrosilicon alloy, the oxidation rate can be effectively slowed down, the strength can be improved and it is not easy to pulverize, which helps to stabilize the yield rate, and the rare earth yield rate is above 50%. At the same time, adding a small amount of C plays a deoxidation role during the smelting process, further reducing the O content in the alloy. Zr can protect rare earth from oxidation and burning due to its stronger ability to combine with O than rare earth, and its content is low, so it can be completely removed after electroslag.

[0052] Specifically, in electroslag remelting, the slag system is: CaF 2 :35~45%;Al 2 O 3 :11~15%;CaO:22~27%;Ce 2 O 3 :8~12%;Y 2 O 3 :15~18%,SiO 2 ≤0.3%,FeO≤0.5%.

[0053] It should be noted that in the present invention, in order to ensure the yield of Ce and Y elements, it is necessary to use a Ce-containing 2 O 3 , Y 2 O 3 Special slag system, improving CaO / Al 2 O 3 ratio, inhibiting Al 2 O 3 activity, avoiding the occurrence of 2[Ce]+(Al 2 O 3 )=2[Al]+(Ce 2 O 3 ) or 2[Y]+(Al 2 O 3 )=2[Al]+(Y 2 O 3 ) reaction, resulting in fluctuations in rare earth yield and excessive Al content.

[0054] Specifically, the normalizing temperature is 1050-1080°C, and the tempering temperature is 760-790°C.

[0055] It should be noted that rare earths can significantly refine the solidification structure and inhibit grain coarsening and precipitate phase coarsening through solute drag and inclusion pinning effects, which helps to appropriately increase the normalizing temperature and tempering temperature, obtain a suitable grain size, and improve strength and organizational stability.

[0056] It should be noted that the heat-resistant steel obtained by the present invention has a lath martensite structure, which is characterized by a large number of slender parallel lath structures distributed in clusters. At the same time, it can be observed that a large number of second phases are precipitated, and a large number of precipitated fine carbides are mostly distributed on the original austenite grain boundaries and martensite laths, which can play a role in precipitation strengthening.

[0057] The refinement effect of rare earth elements on the structure: First, with the addition of surface active rare earth elements, the heterogeneous nucleation work is reduced, thereby promoting the nucleation process; second, rare earth inclusions have a significant nucleation effect on the heterogeneous nucleation of δ-Fe and γ-Fe, promoting the heterogeneous nucleation of molten steel; third, due to the large radius of rare earth atoms, their solid solubility in the matrix is ​​low, and they tend to segregate on the grain boundaries, which reduces the interfacial tension and grain boundary energy, limiting the driving force of grain growth. Due to the inheritance of the organization, there is a fine solidification structure before forging, which provides favorable conditions for the further refinement of martensite during heat treatment. In addition, during the normalizing process, the fine rare earth inclusions with high melting points and dispersed distribution have a strong drag and pinning effect on the migration of grain boundaries and subsequent grain growth, achieving the effect of fine grain strengthening.

[0058] After adding rare earth elements Ce and Y, most inclusions are spherical inclusions, which have a lower stress concentration tendency than angular inclusions. When cracks initiate, the tiny rare earth inclusions are tightly combined with the matrix and are not easy to fall off, and the crack propagation process will be hindered by the tiny spherical inclusions.

[0059] In addition, the elastic modulus and linear expansion coefficient of rare earth inclusions are basically the same as those of the iron matrix, with good compatibility, less effect on the continuity of the organization after forging deformation, and beneficial to the relevant performance of the product. Therefore, the addition of rare earth effectively reduces the number of large-sized inclusions with high hardness and edges, which is beneficial to improving the mechanical properties of heat-resistant steel, not only improving the performance at room temperature, but also improving the performance at high temperature. At room temperature, the present invention combines component design, manufacturing method and heat treatment process, and the performance of the obtained rare earth heat-resistant steel is significantly improved. At room temperature, the tensile strength is above 720MPa, the yield strength is above 530MPa, and the impact energy is above 190J.

[0060] In order to more clearly describe the present invention, it is further illustrated by the following examples and comparative examples.

[0061] Example 1

[0062] The preparation of rare earth heat-resistant steel includes the following steps:

[0063] S1: Vacuum induction melting, the raw materials are melted into molten steel, after high vacuum refining and adjusting the content of other elements except rare earth, N and Mn to meet the requirements, 8000Pa N 2+12000Pa Ar, after stirring for 30 minutes, add chromium nitride, rare earth iron alloy and metal manganese, stir for 10 minutes, tap the steel within 30 minutes, and cast it into electrode ingots;

[0064] Among them, the nitrided chromium iron brings in 0.006% N content;

[0065] Among them, the rare earth iron alloy composition: Ce+Y content 30%, of which Ce content 12%, Y content 18%, Si content 10%, C content 0.07%, Zr content 0.2%, and the balance is Fe;

[0066] S2: The obtained electrode ingot is electroslag remelted, and the slag system used is CaF 2 :41%;Al 2 O 3 :12%;CaO:24%;Ce 2 O 3 :8.5%;Y 2 O 3 :16%,SiO 2 : 0.12%, FeO: 0.2%, and the rest are inevitable impurities;

[0067] Among them, the composition of the electroslag ingot is C: 0.09%, Si: 0.3%, Mn: 0.35%, Cr: 8.70%, Mo: 1.00%, V: 0.20%, Nb: 0.08%, Al: 0.005%, Ce: 0.025%, Y: 0.039%, O: 0.0009%, N: 0.052%, and the rest is Fe;

[0068] S3: forging, forging the obtained electroslag ingot to obtain a forged rod;

[0069] S4: heat treatment, heat treatment of the obtained forged rod, with a normalizing temperature of 1060°C and a tempering temperature of 780°C, to obtain rare earth heat-resistant steel.

[0070] Example 2

[0071] The preparation process of Example 2 is substantially the same as that of Example 1, except that the rare earth iron alloy composition in Example 2 is as follows: Ce+Y content is 28%, wherein Ce content is 15%, Y content is 13%, Si content is 11%, C content is 0.07%, Zr content is 0.2%, and the balance is Fe;

[0072] The obtained electroslag ingot has a Ce content of 0.015% and a Y content of 0.012%.

[0073] Example 3

[0074] The preparation process of Example 3 is substantially the same as that of Example 1, except that the rare earth iron alloy composition in Example 3 is as follows: Ce+Y content is 33%, wherein Ce content is 23%, Y content is 10%, Si content is 10%, C content is 0.06%, Zr content is 0.2%, and the balance is Fe;

[0075] 9000Pa N 2 +11000Pa Ar;

[0076] The content of N brought by chromium nitride is 0.010%;

[0077] The obtained electroslag ingot has a Ce content of 0.042% and a Y content of 0.021%.

[0078] Example 4

[0079] The preparation process of Example 4 is substantially the same as that of Example 1, except that the slag used in Example 4 is CaF 2 :37%;Al 2 O 3 :11.3%;CaO:22.5%;Ce 2 O 3 :11%;Y 2 O 3 :17.5%,SiO 2 : 0.12%, FeO: 0.2%, and the rest are inevitable impurities.

[0080] Comparative Example 1

[0081] The preparation process of Comparative Example 1 is substantially the same as that of Example 1, except that the content of Ce and Y in Comparative Example 1 is 0%.

[0082] Comparative Example 2

[0083] The preparation process of Comparative Example 2 is substantially the same as that of Example 1, except that commercially pure rare earth Ce and pure rare earth Y are directly added in Comparative Example 2;

[0084] Rare earth content of electroslag ingot: Ce: 0.011%, Y: 0.014%.

[0085] Comparative Example 3

[0086] The preparation process of Comparative Example 3 is substantially the same as that of Example 1, except that, after vacuum refining in Comparative Example 3, Ar is charged, and chromium iron nitride plus N is used completely;

[0087] The obtained electroslag ingot contains 0.0011% Ce and 0.0009% Y.

[0088] Comparative Example 4

[0089] The preparation process of Comparative Example 4 is substantially the same as that of Example 1, except that conventional 60% CaF 2 -20%Al 2 O 3 -20%CaO slag system;

[0090] The obtained electroslag ingot contains 0.008% Ce and 0.011% Y.

[0091] Comparative Example 5

[0092] The preparation process of Comparative Example 5 is substantially the same as that of Example 1, except that in Comparative Example 5, the steel is tapped 1.5 hours after rare earth is added by vacuum induction;

[0093] The obtained electroslag ingot contains: Ce: 0.0006%, Y: 0.0008%.

[0094] Comparative Example 6

[0095] The preparation process of Comparative Example 6 is substantially the same as that of Example 1, except that Ce iron alloy is added in Comparative Example 6, wherein the Ce iron alloy comprises Ce: 29%, Si: 11%, C: 0.07%, Zr: 0.2%, and the balance is Fe;

[0096] The obtained electroslag ingot contains: Ce: 0.0525%.

[0097] Comparative Example 7

[0098] The preparation process of Comparative Example 7 is substantially the same as that of Example 1, except that no ferrochromium nitride is added in Comparative Example 7;

[0099] The obtained electroslag ingot contains: Ce: 0.025%, Y: 0.041%.

[0100] Comparative Example 8

[0101] The preparation process of Comparative Example 8 is substantially the same as that of Example 1, except that the normalizing temperature in Comparative Example 8 is 1030°C;

[0102] The obtained electroslag ingot contains: Ce: 0.021%, Y: 0.039%.

[0103] Performance Testing

[0104] The above Examples 1-4 and Comparative Examples 1-8 were subjected to component testing, performance testing and inclusion testing. The specific test results are shown in Tables 1 and 2.

[0105]

[0106] Combined with Examples 1-4 and Comparative Examples 1-8 and referring to Tables 1 and Figure 3 and Figure 4It can be seen that the preparation method provided by the present invention is used to prepare rare earth heat-resistant steel, which significantly improves the yield and stability of rare earth elements. The contents of Ce and Y in the obtained rare earth heat-resistant steel meet the requirements, and the yield of Ce and Y can be stabilized at more than 50%, and the inclusion D is finer than level 0.5.

[0107]

[0108] Combining Examples 1-4 and Comparative Examples 1-8 and referring to Table 2, it can be seen that the rare earth heat-resistant steel obtained by combining the composition design, manufacturing method and heat treatment process of the present invention has significantly improved performance. At room temperature, the rare earth heat-resistant steel obtained by combining the composition design, manufacturing method and heat treatment process of the present invention has significantly improved performance. At room temperature, the tensile strength is above 720MPa, the yield strength is above 530MPa, and the impact energy is above 190J. At 550°C, the tensile strength is above 430MPa and the yield strength is above 370MPa.

[0109] Combination Figure 1 (Example 1) and Figure 2 (Comparative Example 1) It can be seen that both show typical lath martensite structure, characterized by a large number of slender parallel lath structures, and distributed in clusters. After rare earth elements Ce and Y are added to the heat-resistant steel obtained in Example 1, the dispersion of inclusions in the steel is increased, and at the same time, the grain structure is significantly refined, with an average grain size of 7-10, which enhances the fine grain strengthening effect.

[0110] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A rare earth heat-resistant steel, characterized in that: According to mass percentage, it includes C: 0.08~0.12%, Si: 0.2~0.4%, Mn: 0.3~0.5%, Cr: 8.2~9.2%, Mo: 0.90~1.05%, V: 0.18~0.22%, Nb: 0.06~0.10%, Al: ≤0.012%, rare earth: 0.02~0.08%, O: ≤0.0020%, N: 0.045~0.055%, and the rest is Fe; The rare earths are Ce and Y, and the content of Ce is not less than 0.01%; the mass ratio of Y to Ce is not less than 1:2; The heat-resistant steel is prepared by the following steps: S1: Vacuum induction melting, melting the prepared raw materials into molten steel, after high vacuum refining and adjusting the content of other elements except rare earth, N, and Mn to meet the requirements, filling with 15000~25000Pa of mixed gas, the mixed gas is N2 and Ar, after the molten steel fully absorbs nitrogen, adding metallic manganese, ferrochrome nitride and rare earth iron alloy, stirring, sampling and tapping within 30 minutes, and casting into electrode ingots; S2: electroslag remelting, remelting the electrode ingot to obtain an electroslag ingot; S3: forging, forging the obtained electroslag ingot to obtain a forged rod; S4: heat treatment, heat treating the obtained forged rod by normalizing and tempering to obtain rare earth heat-resistant steel; The heat-resistant steel has various inclusions not exceeding 0.5 level, and the average grain size is 7-10 level, and the heat-resistant steel has a lath martensite structure.

2. The rare earth heat-resistant steel according to claim 1, characterized in that: At room temperature, the tensile strength is above 720MPa, the yield strength is above 530MPa, and the impact energy is above 190J.

3. A method for preparing the rare earth heat-resistant steel according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1: Vacuum induction melting, melting the prepared raw materials into molten steel, after high vacuum refining and adjusting the content of other elements except rare earth, N, and Mn to meet the requirements, filling with 15000~25000Pa of mixed gas, the mixed gas is N2 and Ar, after the molten steel fully absorbs nitrogen, adding metallic manganese, ferrochrome nitride and rare earth iron alloy, stirring, sampling and tapping within 30 minutes, and casting into electrode ingots; S2: electroslag remelting, remelting the electrode ingot to obtain an electroslag ingot; S3: forging, forging the obtained electroslag ingot to obtain a forged rod; S4: heat treatment, heat treatment of the obtained forged rod, normalizing and tempering, to obtain rare earth heat-resistant steel.

4. The method for preparing rare earth heat-resistant steel according to claim 3, characterized in that: The rare earth iron alloy composition is: Ce+Y content 25-35%, Si content 8-12%, C content 0.05-0.1%, Zr content 0.1-1.0%, and the balance is Fe.

5. The method for preparing rare earth heat-resistant steel according to claim 3, characterized in that: In electroslag remelting, the slag system is: CaF2: 35~45%; Al2O3: 11~15%; CaO: 22~27%; Ce2O3: 8~12%; Y2O3: 15~18%, SiO2≤0.3%, FeO≤0.5%.

6. The method for preparing rare earth heat-resistant steel according to claim 3, characterized in that: The normalizing temperature is 1050-1080°C, and the tempering temperature is 760-790°C.

7. The method for preparing rare earth heat-resistant steel according to claim 3, characterized in that: The rare earth recovery rate is over 50%.

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