Rare earth Er-doped CrMo steel and thermodynamic-based preparation method thereof

Abstract

The invention discloses rare earth Er-doped CrMo steel and a thermodynamic-based preparation method thereof, and relates to the technical field of alloy materials. According to thermodynamic calculation of a phase diagram, the range of the adding amount of Er is obtained through phase change, the mechanical property of the iron-based alloy is improved by controlling the change of the Er element content and through the phase change, and refining of the structure and synergistic enhancement of the performance are achieved by adopting a non-consumable electric arc furnace for smelting and controlling the cooling rate and the annealing / tempering treatment process. And through molten steel purification and grain refinement of rare earth Er, an action mechanism of a dispersion phase is formed, and the tensile strength, microhardness and corrosion resistance of the material are remarkably improved. Experimental results show that when the Er content is 0.1%, the tensile strength of the alloy steel is improved by about 44.6%, the hardness is improved by about 10.7%, the corrosion potential is improved by 10%, the corrosion current density is reduced by 81.8%, and the performance is optimal. The method is simple, components are controllable, and the method is suitable for large-scale industrial preparation of the structural steel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy materials, in particular to a rare earth Er doped CrMo steel and a preparation method thereof based on thermodynamics. BACKGROUND

[0002] In the prior art, 42CrMo, 35CrMo and 40Cr steel, as typical medium-carbon alloy structural steel, are widely used in the fields of mechanical transmission, high-load components, heavy-load connecting components, etc., and have high strength, good hardenability and strong fatigue performance. However, with the development of industrial equipment towards high strength, long service life and corrosion resistance, the above-mentioned alloy steel still has room for improvement in terms of comprehensive performance, especially in complex working conditions, its corrosion resistance and service life are still insufficient.

[0003] Optimizing the performance of alloy steel through micro-alloying has become one of the main means of current research and engineering application. In the prior art, the addition of vanadium, titanium, zirconium, rare earth elements and other elements has been proven to effectively improve the mechanical properties and corrosion resistance of steel through mechanisms such as grain refinement, liquid purification and inclusions modification. Among them, rare earth elements have strong deoxidation and desulfurization ability due to their unique 4f orbital structure and high chemical activity, and can react with harmful elements (such as O, S, P, As, Sn, etc.) in the liquid steel to form high-melting-point compounds, achieving deep purification of the liquid steel. Such rare earth inclusions have the characteristics of high stability, small size and regular morphology, which can effectively induce grain refinement and reduce the probability of crack initiation, thereby improving the overall strength and toughness of the material.

[0004] In addition, the micro-solid solution of rare earth elements in steel can strengthen the grain boundary through lattice distortion, hinder the enrichment and migration of harmful elements, and improve the crack resistance and ductility of the steel. At present, most of the related research focuses on the application of Ce, La and other rare earth elements in steel, which has achieved remarkable results in inclusion spheroidization, carbide regulation and microstructure homogenization. However, the systematic doping and performance regulation of rare earth Er (erbium) in medium-carbon alloy steel are still relatively blank.

[0005] Therefore, it is urgent to develop a method of doping rare earth Er elements in 42CrMo, 35CrMo, 40Cr and other alloy structural steels, so as to comprehensively improve the mechanical properties (such as tensile strength, yield strength, elongation, hardness) and corrosion resistance of the steel by accurately controlling the content of Er without significantly changing the original composition system of the steel, thereby expanding the engineering application range of such steel in extreme load and complex service environment. SUMMARY

[0006] The application aims to provide a rare earth Er doped CrMo steel and a thermodynamic preparation method thereof, based on phase diagram thermodynamic calculation, the range of Er addition amount is obtained according to phase change, the phase change process is controlled by accurately controlling the content of Er, the mechanical properties of the iron-based alloy are improved, and the method for doping rare earth element Er in the alloy structural steel to improve the comprehensive performance of the material is provided. The steel material comprises CrMo steel; the method comprises adding 0.03-0.15% of rare earth Er element to the steel in the steel smelting stage or the refining stage, and utilizing the purification of the molten steel, modification of inclusions and micro-alloying effect to significantly improve the mechanical properties and corrosion resistance of the steel material.

[0007] The application discloses a rare earth Er doped CrMo steel, and the expression is CrMo 0.2 Fe 98-x-x Er, wherein x=0.03-0.15, that is, the doping mass fraction of rare earth Er in the CrMo steel is 0.03%-0.15%;

[0008] The CrMo steel comprises the following components in terms of weight percentage: C: 0.38-0.45%, Si: 0.17-0.37%, Mn: 0.50-0.80%, Cr: 0.90-1.20%, Mo: 0.15-0.25%, and Fe is the balance.

[0009] Preferably, the doping mass fraction of rare earth Er in the CrMo steel is 0.10%, and the expression of the rare earth Er doped CrMo steel is CrMo 0.2 Fe 97.9-0.1 Er, the tensile strength of the rare earth Er doped CrMo steel is greater than or equal to 1600 N / mm 2 , and the hardness is greater than or equal to 346 HV.

[0010] Preferably, the structure of the rare earth Er doped CrMo steel is a refined alpha-Fe matrix, and a second phase of Fe 17 Er2 is dispersedly distributed.

[0011] Preferably, the corrosion potential of the rare earth Er doped CrMo steel is less than or equal to-0.736 V (vs SCE), and the corrosion current density is less than or equal to 10 -3.86 A / cm 2 .

[0012] The application further provides a thermodynamic preparation method of the rare earth Er doped CrMo steel, comprising the following steps:

[0013] (1) screening alloy components based on thermodynamics

[0014] The Scheil module of Thermo-Calc software is used to calculate the phase change path under non-equilibrium solidification conditions of different Er contents by inputting the thermodynamic database of Fe-Er binary phase diagram.

[0015] (2) Melting and casting

[0016] Different Er contents are doped in CrMo steel for melting, and the rapid cooling process of melting is set based on the Scheil solidification curve, so that the actual solidification process is close to the non-equilibrium condition, and the phase composition is consistent with the thermodynamic prediction;

[0017] (3) Cast structure characterization and performance detection

[0018] The alloy is subjected to microscopic analysis and performance detection.

[0019] Preferably, in step (1), the Er content is 0.03%, 0.05%, 0.10%, 0.15%;

[0020] According to the thermodynamic analysis result: when Er≤0.10%, the main phase of the cast state is ɑ-Fe, and there is no harmful second phase;

[0021] When Er=0.15%, the main phase of the cast state is ɑ-Fe, and a small amount of Fe 17 Er2 second phase exists.

[0022] Preferably, in step (2), the melting method is non-consumable vacuum arc furnace melting, and the vacuum degree is controlled to be ≤3×10 -3 Pa during the melting process, the melting times are 3-4 times, and each time is turned over to ensure uniform composition; the rapid cooling rate is 80℃ / s.

[0023] Preferably, in step (2), the following heat treatment process is adopted after melting: first, 800℃ annealing for 30 minutes, then furnace cooling to 550℃, taking out and air cooling, and then tempering treatment at 500℃ for 2 hours.

[0024] Therefore, the rare earth Er doped CrMo steel and the thermodynamic-based preparation method thereof have the following beneficial effects:

[0025] (1) The present application realizes the synergistic jump of mechanics and corrosion resistance by thermodynamic-guided precise doping of rare earth Er (0.03%-0.10%) on the basis of retaining the original high strength and toughness of CrMo steel. Er element significantly optimizes the microstructure of the material through three mechanisms: ① deep purification of molten steel (formation of high melting point Er-O / S compound), ② induction of grain refinement (inhibition of grain boundary segregation), ③ formation of nanoscale Er-Cr / Mo dispersed phase. Experiments have proved that when the content of Er is 0.1%, the tensile strength of the alloy is increased by 44.6% (attributed to fine-grain strengthening and dispersion strengthening), the microhardness is increased by 10.7% (solid solution distortion and phase interface strengthening), at the same time, the corrosion potential is positively shifted by 10%, the corrosion current density is reduced by 81.8% (dense oxide film and impurity passivation), the Er inclusions are spherical or ellipsoidal in distribution, replacing irregular oxide and sulfide inclusions, and improving the stress concentration phenomenon, which is beneficial to improve the fatigue life and cutting performance. The composition design breaks through the performance bottleneck of traditional CrMo steel under complex working conditions, and provides a new generation of material solution for high-load corrosion-resistant structural parts.

[0026] (2) Based on the preparation method of thermodynamic calculation-process control-organization verification, the industrialization problem of rare earth doped steel is solved. The Scheil module of Thermo-Calc software is used to predict the non-equilibrium solidification phase change path, avoiding the brittle Fe 17 Er2 phase generation, from the source to optimize the composition design; secondly, through the non-consumable arc furnace smelting combined with controllable cooling rate (matching Scheil non-equilibrium condition), to ensure that the as-cast structure is mainly α-Fe phase, supplemented by annealing / tempering process to further refine the grain and dispersed phase distribution; finally, SEM verification and performance test form a feedback cycle. This method only needs to adjust a single variable (Er content), without complex equipment modification, with strong composition controllability and high process stability. Therefore, under the condition of low rare earth addition and controllable smelting process, the present process does not change the basic composition system of the steel, and can adapt to the existing smelting and heat treatment process, and has the basis for industrialization.

[0027] The technical solutions of the present application will be further described in detail below through the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the alloy tensile specimen drawing;

[0029] Figure 2 is the Fe-Er binary phase diagram;

[0030] Figure 3 is the Scheil solidification curve when the Er doping amount is 0.03%-0.10%;

[0031] Figure 4Scheil solidification curve of the CrMo steel doped with Er with an Er doping amount of 0.15%;

[0032] Figure 5 XRD diffraction patterns of the CrMo steel doped with rare earth Er with Er doping amounts of 0.03%, 0.05%, 0.10% and 0.15%;

[0033] Figure 6 SEM surface scanning electron images and EDS backscattering electron images of the CrMo steel doped with rare earth Er with an Er doping amount of 0.10%;

[0034] Figure 7 SEM surface scanning electron images and EDS backscattering electron images of the CrMo steel doped with rare earth Er with an Er doping amount of 0.15%;

[0035] Figure 8 SEM microstructure of the corrosion treated alloy, wherein (a) is the CrMo 0.2 Fe 98.77-0.03 Er; (b) is the CrMo 0.2 Fe 98.75-0.05 Er; (c) is the CrMo 0.2 Fe 98.70-0.10 Er; (d) is the CrMo 0.2 Fe 98.65-0.15 Er;

[0036] Figure 9 Tafel polarization curve diagrams of the CrMo steel doped with rare earth Er with Er doping amounts of 0.03%, 0.05%, 0.10% and 0.15%;

[0037] Figure 10 Tensile strength change curve diagrams of the CrMo steel doped with rare earth Er with Er doping amounts of 0.03%, 0.05%, 0.10% and 0.15%;

[0038] Figure 11 Hardness change curve diagrams of the CrMo steel doped with rare earth Er with Er doping amounts of 0.03%, 0.05%, 0.10% and 0.15%. DETAILED DESCRIPTION

[0039] Unless otherwise defined, technical or scientific terms used in the present application shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0040] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that those skilled in the art can understand. These other embodiments are also covered within the protection scope of the present application.

[0041] The present application discloses a rare earth Er doped CrMo steel, the expression is CrMo 0.2 Fe 98-x-x Er wherein x = 0.03 ~ 0.15, that is, the doping mass fraction of rare earth Er in CrMo steel is 0.03% ~ 0.15%; CrMo steel includes the following weight fractions of components: C: 0.38 ~ 0.45%, Si: 0.17 ~ 0.37%, Mn: 0.50 ~ 0.80%, Cr: 0.90 ~ 1.20%, Mo: 0.15 ~ 0.25%, and Fe is the balance.

[0042] The microstructure of the rare earth Er doped CrMo steel is a refined α-Fe matrix, and the second phase of Fe 17 Er2 is dispersedly distributed, the grain boundary is well combined, the inclusion size is reduced and tends to be spheroidized.

[0043] The corrosion potential of the rare earth Er doped CrMo steel is ≤-0.736V (vs SCE), and the corrosion current density is ≤10 -3.86 A / cm 2 , and exhibits excellent corrosion resistance and stability in a 3.5% NaCl simulated seawater environment.

[0044] The optimal doping mass fraction of rare earth Er in CrMo steel is 0.10%, and at this time the expression of the rare earth Er doped CrMo steel is CrMo 0.2 Fe 97.9-0.1 Er, the tensile strength of the obtained material is not less than 1600N / mm 2 , the hardness is not less than 346HV, the corrosion potential is increased by more than 80mV, and the corrosion current density is reduced by more than 80%.

[0045] The application also provides the preparation method of the rare earth Er doped CrMo steel based on thermodynamics, the phase transition behavior is analyzed according to the phase diagram thermodynamic calculation, and the addition amount range of the Er element is determined; the phase transition process is controlled by accurately controlling the Er content, and the mechanical property of the iron-based alloy is improved. The non-consumable arc furnace smelting process is adopted, combined with the controllable cooling rate and annealing / tempering treatment, the organization is refined and the comprehensive performance is enhanced. The rare earth Er significantly improves the tensile strength, microhardness and corrosion resistance of the material through the triple action mechanism of purifying the molten steel (deoxidizing and desulfurizing), refining the grains (suppressing segregation) and forming the dispersion strengthening phase (such as Er-Cr / Mo compound).

[0046] Wherein, the Er content is 0.03%, 0.05%, 0.10%, 0.15%; according to the thermodynamic analysis result: when Er≤0.10%, the main phase of the as-cast is α-Fe, and there is no harmful second phase; when Er=0.15%, the main phase of the as-cast is α-Fe, and there is a small amount of Fe 17 Er2second phase.

[0047] The smelting mode is non-consumable vacuum arc furnace smelting, and the vacuum degree is controlled to be ≤3×10 -3 Pa during the smelting process, the smelting frequency is 3-4 times, and each time is turned over to ensure the uniformity of the composition; the rapid cooling rate is 80℃ / s.

[0048] After smelting, the following heat treatment process is adopted: first, 800℃ annealing for 30 minutes, then furnace cooling to 550℃, taking out and air cooling, and then 500℃ tempering treatment for 2 hours.

[0049] The technical solutions of the application are further described below through the drawings and examples.

[0050] Unless otherwise defined, the technical terms or scientific terms used in the application should be understood as the usual meaning understood by those skilled in the art to which the application belongs.

[0051] In addition, it should be understood that although the present specification is described in terms of embodiments, each embodiment does not contain only one independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each example can also be appropriately combined to form other embodiments that those skilled in the art can understand. These other embodiments are also covered by the protection scope of the present application.

[0052] Examples

[0053] Step (1) pre-screening alloy composition based on thermodynamics

[0054] The Scheil module in Thermo-Calc software is used to analyze the phase transition behavior of the alloy composition in the application Figure 2The Fe-Er binary phase diagram thermodynamic data shown are used to calculate the composition of the main and secondary phases in the as-cast microstructure of the alloy during non-equilibrium solidification. The composition and changes of the intermediate phase in the as-cast state of the ingot are calculated using the Scheil module and verified by SEM observation.

[0055] 1. Using the Scheil module, the as-cast non-equilibrium solidification curves of the Fe-Er phase diagram composition were obtained when Er was 0.03%, 0.05%, 0.10%, and 0.15%. The Scheil solidification curves for Er doping amounts of 0.03%–0.10% are shown below. Figure 3 As shown, the Scheil solidification curves reveal that the main phase in the as-cast state of Er (0.03%-0.10%) within this range is α-Fe (BCC-A2).

[0056] 2. When the Er doping concentration is 0.15%, the Scheil solidification curve is as follows: Figure 4 As shown, within this range, the main phase in the as-cast state is α-Fe(BCC-A2), forming Fe. 17 The second phase of Er2. Because the Er content is low, the generated Fe... 17 The second phase of Er2 is also rare; the main phase α-Fe (BCC-A2) still dominates.

[0057] 3. Using CrMo steel as the matrix, the basic composition range of this matrix is ​​C: 0.38–0.45%, Si: 0.17–0.37%, Mn: 0.50–0.80%, Cr: 0.90–1.20%, Mo: 0.15–0.25%, with Fe as the balance. Rare earth Er elements with doping amounts of 0.03%, 0.05%, 0.1%, and 0.15% were added to the CrMo steel, respectively, with the following formulas: CrMo 0.2 Fe 98.77-0.03 Er,CrMo 0.2 Fe 98.75-0.05 Er,CrMo 0.2 Fe 98.7-0.10 Er,CrMo 0.2 Fe 98.65-0.15 Er, named A1, A2, A3, A4 respectively.

[0058] The correspondence is shown in Table 1:

[0059] Table 1. Rare Earth Er-Doped CrMo Steel Numbers with Different Doping Ratios

[0060] Ingredients (wt. %) FE Er No. CrMo 0.2 Fe 98.77-0.03 Er]]> 98.77 0.03 A1 CrMo 0.2 Fe 98.75-0.05 Er]]> 98.75 0.05 A2 CrMo 0.2 Fe 98.7-0.10 Er]]> 98.70 0.10 A3 CrMo 0.2 Fe 98.65-0.15 Er]]> 98.65 0.15 A4

[0061] Step (2) Smelting and Casting

[0062] 1. Preparation of CrMo0.2 Fe 98-x-x Er iron alloy materials

[0063] According to the molecular formula CrMo 0.2 Fe 98-x-x Weigh out 100g each of CrMo steel with a purity of 99.99%, and 0.030g, 0.050g, 0.10g, and 0.15g of metallic Er with a purity of 99.99%. Place them in a non-consumable vacuum melting furnace for melting, and achieve a furnace vacuum of 3.0 × 10⁻⁶. -3 After Pa, argon gas is introduced for protection, and the melting current is 70-80A. The melting is repeated 3-4 times to obtain the sample.

[0064] 2. The metal ingot is cut to the desired shape using a mechanical wire cutter. Figure 1 The standard sample size shown was used to grind the sample sequentially with 600#, 800#, 1000#, 1200#, 1500# and 2000# SiC sandpaper, polish it with a polishing cloth until the surface roughness was below 1μm, and then clean it in anhydrous ethanol for 15 minutes. Figure 1 The dimensions of the tensile specimens conform to the design principles for miniature specimens in GB / T 228.1-2021.

[0065] 3. After adding, stir evenly and cool to room temperature by controlling the cooling rate (80℃ / s). Then, perform annealing treatment in a muffle furnace at 800℃ for 30 minutes. When the furnace is cooled to 550℃, remove it and air cool it to allow it to cool quickly to prevent it from staying in the brittle temperature range for too long, which would cause temper brittleness. Then, temper it at 500℃ for 2 hours to obtain a dense structure and refined grains.

[0066] The above sample was ultrasonically cleaned and dried to obtain rare earth Er-doped CrMo steel, denoted as CrMo. 0.2 Fe 98-x- x Er, respectively CrMo 0.2 Fe 98.77-0.03 Er,CrMo 0.2 Fe 98.75-0.05 Er,CrMo 0.2 Fe 98.7-0.10 Er,CrMo 0.2 Fe 98.65- 0.15 Er corresponds to numbers A1-A4 in Table 1.

[0067] Step (3) Characterization of the as-cast structure

[0068] 1. XRD characterization

[0069] XRD characterization of A1-A4 was performed, and the results are as follows: Figure 5As shown, with the gradual increase of the rare earth element Er doping amount, the main diffraction peak of the α-Fe matrix in the XRD diffraction pattern appears a significant shift trend. Specifically, the main peak shifts to low angle in the 2θ direction, indicating that the lattice spacing has expanded. This change can be reasonably explained by the fact that the atomic radius of Er element is significantly larger than that of Fe (Er≈0.176 nm, Fe≈0.124 nm): when Er atoms enter the Fe matrix lattice in solid solution, it will cause lattice distortion and local strain field, thereby increasing the lattice constant. According to Bragg's law 2dsinθ=nλ, the increase of lattice spacing d makes the diffraction angle θ decrease, resulting in the XRD peak position shifting to low angle direction.

[0070] In addition, with the further increase of Er content, the second phase such as Fe17Er2 is precipitated in the local area, which changes the degree of lattice distortion of the main phase, and the main peak will slightly shift to the left in the XRD pattern.

[0071] This doping-induced lattice micro-strain and grain boundary strengthening effect helps to explain the synergistic improvement of the alloy in mechanical properties and corrosion resistance.

[0072] This phenomenon is consistent with the XRD peak shift behavior observed in the existing research of rare earth doped Fe-based alloy, NdFeB magnet and Fe-Cr high-entropy alloy, further confirming that Er element plays a key role in regulating the lattice structure during micro-alloying.

[0073] 2、SEM characterization

[0074] (1) The sample A1 was characterized by SEM and EDS, and the results are shown in Figure 6 The image shows that the black is α-Fe, and the face scanning of SEM can prove that Scheil solidification Er (0.03%-0.10%) in this range is α-Fe (BCC-A2) in the as-cast main phase, the grain distribution is relatively uniform, and there is no obvious macrosegregation or serious agglomeration phenomenon, which indicates that the rare earth element Er is well distributed in the smelting and solidification process, and the surface morphology is relatively dense, and there is no obvious hole or crack, indicating that Er helps to improve the grain boundary bonding ability and improve the overall density. Small granular precipitated phase (bright white area) is uniformly distributed, which may inhibit grain growth and is beneficial to refining the structure.

[0075] (2) By observing SEM and EDS, when the Er addition amount increases to 0.15%, as shown in Figure 7 , the Er content in the system exceeds the solid solution limit of the Fe matrix, and part of Er reacts with Fe to form Fe 17 Er2 second phase. This phase is in the form of coarse block in the microstructure, which destroys the original grain boundary continuity and becomes the stress concentration and crack initiation position. In addition, the coarse Fe 17Er2 cannot effectively participate in the dislocation strengthening mechanism, but weakens the overall deformation coordination, resulting in a decrease in tensile properties and hardness compared with the 0.1% sample. Therefore, Fe 17 The formation of Er2 marks the critical transition of the Er addition amount from "intentional strengthening" to "organizational deterioration".

[0076] (3) After the corrosion treatment of samples A1-A4, the microstructure of the alloy was observed by SEM, and the results are shown in Figure 8 By comparison, Figure 8 (c) The CrMo 0.2 Fe 98.70-0.10 Er grain profile is clearer, the internal structure is more uniform, the grain size is smaller and uniformly distributed, it is dense but orderly, and it is likely to be fine tempered martensite or tempered sorbite, the grain is obviously refined, and the rare earth element plays a good grain refinement and second phase dispersion strengthening effect; The uniformity of the structure is good, which indicates that Er is mainly distributed in the grain boundary and plays a "pinning" effect on the grain rather than segregation and deposition; Uniform corrosion indicates that a more dense passivation film is formed on the surface, improving corrosion resistance.

[0077] 3. Corrosion resistance

[0078] In this experiment, the corrosion of alloys with different Er contents in simulated seawater (3.5wt% NaCl solution) was analyzed by electrochemical polarization curve (Tafel), and the electrochemical polarization characterization of the experimental surface was obtained. A series of dynamic point polarization curves were obtained, as shown in Figure 9 , to obtain the corrosion situation of the designed alloy in simulated seawater.

[0079] By comparing the Tafel curves of CrMo 0.2 Fe 98.77-0.03 Er, CrMo 0.2 Fe 98.75-0.05 Er, CrMo 0.2 Fe 98.70-0.10 Er, CrMo 0.2 Fe 98.65-0.15 Er, the corrosion potential of the Tafel curve of CrMo 0.2 Fe 98.70-0.10 Er is the most positive (-0.736V, i.e. the most difficult to occur corrosion reaction), the corrosion current density is the lowest (-3.86A / cm 2 , indicating the slowest corrosion rate), the corrosion potential increases by 10%, the corrosion current decreases by 81.8%, and the corrosion resistance is the best. It may be because Er is easy to form a dense and stable oxide film (such as Er2O3) on the surface, which is well combined with the matrix and can block the penetration of water molecules and Cl － and other corrosion media.

[0080] 4. Tensile properties

[0081] The test method used an LD26.105 microcomputer-controlled electronic universal testing machine to perform tensile tests on samples A1-A4 alloys, obtaining the strength data of the doped ferroalloy materials. The tensile properties of CrMo steel and Cr steel alloys with different Er contents are shown in the figure below. Figure 10 As shown.

[0082] As shown in the figure, the tensile strength of the alloy reaches its maximum (1631 N / mm) at an Er content of 0.1%. 2 Compared to the original iron alloy (1128 N / mm) 2 The tensile strength was increased by 44.59%, while the elongation remained essentially unchanged while maintaining high tensile strength, ensuring both high strength and good plasticity. Appropriate Er doping (especially 0.10%) significantly improved the tensile strength and overall mechanical properties of CrMo steel. This may be because Er's purification effect refines non-metallic inclusions, and under appropriate conditions, promotes the synergistic effect of grain refinement and dislocation strengthening mechanisms. However, when the Er content increased to 0.15%, the material showed a trend of decreasing peak stress and fracture strain, indicating that at this point, Fe... 17 The precipitation of second phases such as Er2 and severe Er enrichment induce grain boundary embrittlement and unstable fracture, thereby reducing the overall performance. This result indicates that 0.10% is the optimal doping range for Er to enhance the performance of CrMo steel.

[0083] 5. Hardness Measurement

[0084] Measurement method: An HVS-1000Z microhardness tester was used, and the HV1 Vickers scale was selected to test the hardness of samples A1-A4 alloy. The microhardness of the doped titanium alloy surface was obtained as follows: Figure 11 As shown, the hardness increases and then decreases with increasing rare earth element Er. The maximum hardness of the doped alloy is 346.5076 HV, which is 10.75% higher than the original alloy hardness (312.8731 HV).

[0085] Therefore, this invention provides a rare-earth Er-doped CrMo steel and its thermodynamic preparation method. Based on phase diagram thermodynamic calculations, the range of Er addition amount is determined according to phase changes. By precisely controlling the Er content to regulate the phase transformation process, the mechanical properties of the iron-based alloy are improved. This method involves doping rare-earth element erbium (Er) into alloy structural steel to enhance the overall material performance. The steel includes CrMo steel. The method involves adding 0.03% to 0.15% by mass of rare-earth Er element to the steel during the smelting or refining stage. Err's effects on purifying the molten steel, modifying inclusions, and microalloying significantly improve the mechanical properties and corrosion resistance of the steel.

[0086] The above specific embodiments further explain the purposes, technical solutions and beneficial effects of the present application. It should be understood that the above specific embodiments only serve as the specific embodiments of the present application and do not limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A rare earth Er doped CrMo steel, characterized in that, The rare earth Er doped CrMo steel is expressed as CrMo 0.2 Fe 98-x-x Er, wherein x = 0.03 to 0.15; The CrMo steel comprises the following components in weight fraction: C: 0.38-0.45%, Si: 0.17-0.37%, Mn: 0.50-0.80%, Cr: 0.90-1.20%, Mo: 0.15-0.25%, and Fe as the balance.

2. The rare earth Er doped CrMo steel according to claim 1, characterized in that, The doping mass fraction of rare earth Er in CrMo steel is 0.10%, and the expression of the rare earth Er doped CrMo steel is CrMo 0.2 Fe 97.9-0.1 Er, the tensile strength of the rare earth Er doped CrMo steel is greater than or equal to 1600 N / mm 2 , and the hardness is greater than or equal to 346 HV.

3. The rare earth Er doped CrMo steel according to claim 1, characterized in that, The microstructure of the rare earth Er doped CrMo steel is a refined α-Fe matrix, with a second phase of Fe 17 Er2.

4. The rare earth Er doped CrMo steel according to claim 1, characterized in that, The corrosion potential of the rare earth Er-doped CrMo steel is ≤-0.736 V (vs SCE), and the corrosion current density is ≤10 -3.86 A / cm 2 .

5. A thermodynamic-based method of producing a rare earth Er-doped CrMo steel as claimed in any one of the preceding claims 1 to 4, characterized in that, The method comprises the following steps: (1) Pre-screening alloy components based on thermodynamics The Scheil module of Thermo-Calc software is used to input the thermodynamic database of Fe-Er binary phase diagram, and the phase transformation path under non-equilibrium solidification conditions of different Er contents is calculated; (2) Melting and casting Different Er contents are doped in the CrMo steel for melting, and based on the Scheil solidification curve, the rapid cooling process of melting is set to ensure that the actual solidification process is close to the non-equilibrium condition, so that the phase composition is consistent with the thermodynamic prediction; (3) Characterization of as-cast structure and performance detection Microscopic analysis and performance detection are performed on the alloy.

6. The thermodynamic-based method of producing a rare earth Er-doped CrMo steel according to claim 5, characterized in that, In step (1), the Er content is 0.03%, 0.05%, 0.10%, 0.15%; According to the thermodynamic analysis results: when Er≤0.10%, the main phase of the as-cast state is ɑ-Fe, and there is no harmful second phase; Er = 0.15%: as-cast main phase is a-Fe, with a small amount of Fe 17 second phase of Er2.

7. The thermodynamic-based method of producing a rare earth Er-doped CrMo steel according to claim 5, characterized in that, In step (2), the melting method is non-consumable vacuum arc furnace melting, and the vacuum degree is controlled at ≤3×10 -3 Pa during the melting process. The melting frequency is 3-4 times, and each time is turned over to ensure uniform composition; the rapid cooling rate is 80℃ / s.

8. The thermodynamic-based method of producing a rare earth Er-doped CrMo steel according to claim 5, characterized in that, In step (2), the following heat treatment process is adopted after melting: first, annealing at 800℃ for 30 minutes, then furnace cooling to 550℃, taking out and air cooling, and then tempering treatment at 500℃ for 2 hours.

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