A weathering-resistant steel modified by rare earth La and a preparation method thereof

Abstract

The application discloses a rare earth La modified weather-resistant steel and a preparation method thereof, and belongs to the technical field of Q500qenh weather-resistant steel preparation. The weather-resistant steel comprises the following raw material components: C, Si, Mn, Cr, Ni, Cu, Mo, V, Ti, Nb, Al, 0.001-0.04wt% La, and the balance of Fe and inevitable impurities. Through precise regulation and control of the La element addition amount and the preparation process, the inherent problems of the Q500qenh steel, such as uneven as-cast grains, inclusion hazards and performance fluctuation, are solved.

Description

Technical Field

[0001] This invention belongs to the field of Q500qenh weathering steel preparation technology, specifically relating to a rare earth La-modified weathering steel and its preparation method. Background Technology

[0002] Q500qenh weathering steel, a type of high-performance weathering structural steel for bridges, is widely used in outdoor exposed engineering structures such as large bridges, port and wharf facilities, and rail transit bearings due to its excellent atmospheric corrosion resistance, moderate strength, and good weldability. This type of steel, by adding corrosion-resistant alloying elements such as Cu, Cr, Ni, and P to low-carbon steel, forms a dense and strongly adhering protective rust layer on its surface during service. This effectively blocks external corrosive media from contacting the substrate, significantly extending the service life of the structure and reducing subsequent maintenance costs.

[0003] As engineering projects extend to complex conditions such as cross-sea and high-corrosion environments, Q500qenh weathering steel is gradually exhibiting its specific performance bottlenecks: uneven development of bainitic ferrite grains in the cast billet easily leads to stress concentration, making it difficult to meet the stringent requirements of long-span bridges for a balance of strength and toughness; irregular inclusions in the molten steel not only weaken mechanical properties but also disrupt the continuity of the rust layer, exacerbating localized corrosion; and the difficulty in controlling the microstructure evolution during heat treatment leads to performance fluctuations in the same batch of materials, affecting project quality control. Rare earth element La, due to its strong deoxidation and desulfurization capabilities and grain boundary segregation characteristics, provides a technological possibility for overcoming these bottlenecks. However, in existing technologies, the La addition amount is mostly within a wide range, without precise design for the specific composition system and performance requirements of Q500qenh steel, resulting in the inability to fully realize the modification effect of La.

[0004] The response of weathering steels with different strength grades and composition systems to La exhibits fundamental differences. While Chinese patent CN117182259A targets Q500qenh steel, it uses Ce to replace La at a dosage of only 0.0004~0.0015 wt%, which only improves weld toughness and cannot solve the problem of uneven as-cast microstructure (bainite lath width 1.8~2.5μm). Chinese patent CN117051334A discloses a 235 MPa grade La~Ce composite rare earth weathering steel with a Mn content of 0.80~1.00% and no Mo, exhibiting a polygonal ferrite microstructure. The 0.02 wt% composite rare earth only reduces cost and cannot achieve bainite refinement. Therefore, developing a precise La modification scheme suitable for Q500qenh weathering steel is of great significance for improving its engineering applicability. Summary of the Invention

[0005] To address the aforementioned shortcomings in the existing technology, this invention provides a rare earth La-modified weathering steel and its preparation method. This invention addresses the inherent problems of Q500qenh steel, such as uneven grain size in the as-cast state, inclusion hazards, and performance fluctuations, by precisely controlling the amount of La added and the preparation process.

[0006] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows: The purpose of this invention is to provide a rare earth La-modified weathering steel, which comprises the following raw material components by weight percentage: 0.015~0.020wt% C, 0.22~0.28wt% Si, 1.35~1.49wt% Mn, 0.26~0.32wt% Cr, 0.35~0.42wt% Ni, 0.35~0.41wt% Cu, 0.12~0.18wt% Mo, V≤0.02wt%, 0.010~0.015wt% Ti, 0.010~0.015wt% Nb, 0.050~0.070wt% Al, 0.001~0.04wt% La, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, it includes the following raw material components by weight percentage: 0.015~0.080wt% C, 0.22~0.26wt% Si, 1.35~1.49wt% Mn, 0.26~0.30wt% Cr, 0.35~0.40wt% Ni, 0.35~0.40wt% Cu, 0.12~0.15wt% Mo, V≤0.02wt%, 0.010~0.015wt% Ti, 0.010~0.015wt% Nb, 0.050~0.070wt% Al, 0.01~0.03wt% La, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the rare earth La-modified weathering steel is Q500qenh weathering steel.

[0009] Another object of the present invention is to provide a method for preparing the above-mentioned rare earth La-modified weathering steel, which includes the following steps: S1. Weigh each ingredient according to the formula, remove impurities and set aside; S2. Place the processed raw material in a vacuum environment, introduce protective gas to isolate the influence of air, and maintain the pressure at 0.05~0.07MPa. S3, furnace charge pre-melting An electric arc torch is used to ignite the arc with a current of 200-300 A and a voltage of 20-25 V, so that the added furnace charge pure iron is pre-melted for 1-2 minutes to remove residual gas and impurities from the surface of the raw materials. S4, Full melting of furnace charge Adjust the current to 300~400 A and the voltage to 25~30 V, and melt for 3~5 minutes until the furnace charge is completely melted; S5, alloying elements and La addition After the furnace charge is fully melted, Mo, Nb, and Ti are added first. After the temperature is raised and they melt, Cr and Ni are added. After they melt, Cu, Al, and La elements are melted and diffused into the alloy liquid by utilizing the high temperature and convection of the melted alloy liquid itself. S6. Adjust the current to 350~450 A and the voltage to 22~28 V, refine for 3~5 min to ensure uniform dissolution of alloying elements, then cast into shape and cool to room temperature to obtain a pre-molten cast steel ingot. S7. After flipping the initially melted cast steel ingot, repeat the above S3~S6 processes 5~6 times to obtain rare earth La modified weathering steel.

[0010] Further, the process of step S1 is as follows: take raw materials with a purity of ≥99.5%, grind to remove oxide scale, remove oil stains with anhydrous ethanol, and dry at 120~150℃ for 2~3 hours to ensure that there are no impurities remaining in the raw materials.

[0011] Furthermore, the pressure in step S2 is 0.05~0.06MPa.

[0012] Furthermore, in step S3, the current is 200~240A, the voltage is 20~24V, and the pre-melting time is 2min.

[0013] Furthermore, in step S4, the current is 400A, the voltage is 28~30V, and the melting time is 3 minutes.

[0014] The beneficial effects of this invention are: 1. This invention uses metallic La particles as additives, combined with vacuum arc melting protection, to precisely control the amount of La added, ensuring uniform distribution of La in the molten steel. This is better suited to the requirements of Q500qenh steel for precise composition and uniform distribution, eliminating the need for additional complex steps such as calcium treatment.

[0015] 2. In the La-containing Q500qenh weathering steel prepared by this invention, La particles combine with O in the molten steel to form fine, dispersed inclusions, replacing traditional coarse oxides, improving the purity of the molten steel, and reducing the number of harmful inclusions. La segregates at the as-cast grain boundaries, inhibiting the enrichment of harmful elements, purifying the grain boundary structure, and laying the foundation for subsequent improvement of the material's corrosion resistance.

[0016] 3. Through six repeated melting processes, the La is evenly distributed with other alloying elements, which inhibits abnormal growth of as-cast grains and reduces casting defects (such as porosity and segregation). This results in the yield strength and tensile strength of the same batch of materials fluctuating within ±3%. The La particles inhibit abnormal growth of as-cast grains, making the microstructure more uniform and dense, reducing casting defects, and improving the consistency of material performance.

[0017] 4. This invention discovers that in the 'low carbon-high Mo-bainite' system of Q500qenh steel, the optimal addition amount of La is 0.02 wt%. Through synergistic cooperation with Mo-Ni-Cu, the bainitic ferrite laths can be refined to 0.8~1.2μm, achieving optimal uniformity. This effect cannot be achieved in other existing technologies. Attached Figure Description

[0018] Figure 1 The XRD patterns of each alloy sample in the test examples are shown below. Figure 2 The images show the metallographic morphology of the alloy samples in the test examples, where (a) is Comparative Example 1; (b) is Example 1; (c) is Example 2; and (d) is Example 3. Figure 3 The following are SEM images of the microstructure of each alloy sample in the test examples: (a) Comparative Example 1; (b) Example 1; (c) Example 2; (d) Example 3; Figure 4 The figures show the room temperature tensile stress-strain curves of each alloy specimen in the test examples. Detailed Implementation

[0019] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0020] Example 1 A rare earth La-modified weathering steel comprising the following raw material components by weight percentage: C: 0.015wt%, Si: 0.22wt%, Mn: 1.35wt%, Cr: 0.26wt%, Ni: 0.35wt%, Cu: 0.35wt%, Mo: 0.12wt%, V: 0.01wt%, Ti: 0.010wt%, Nb: 0.010wt%, Al: 0.050wt%, La: 0.005%, with the balance being Fe and unavoidable impurity elements.

[0021] Its preparation method is as follows: S1. Raw material preparation and pretreatment Prepare pure iron, metallic manganese, Cr, Ni, Cu, Mo, V, Ti, Nb, Al, La, and silicon carbide according to the predetermined ratio; the purity of the raw materials is ≥99.5%, polish to remove oxide scale, remove oil stains with anhydrous ethanol, and dry at 120℃ for 3 hours.

[0022] S2, Melting Chamber Atmosphere Control Pure iron, used as furnace charge, is charged into the electric arc furnace melting chamber, and a vacuum of 6×10⁻⁶ is drawn. -4 Pa, purge with high-purity argon gas to 0.05 MPa, repeat vacuuming and argon purging 3~5 times, finally argon pressure 0.05~0.07 MPa.

[0023] S3, furnace charge pre-melting The electric arc torch is used to ignite the arc with a current of 200A and a voltage of 20V. The pre-melting time is 2 minutes to remove residual gas and impurities from the surface of the raw materials.

[0024] S4, The furnace charge is completely melted. Adjust the current to 400A and the voltage to 30V, and melt for 3 minutes to ensure that the furnace charge is completely melted.

[0025] S5, alloying elements and La addition After the furnace charge is fully melted, add the alloys in the following order: first add Mo, Nb, and Ti, then add Cr and Ni, and finally add Cu and Al; place pure La metal particles at the bottom of the crucible to ensure uniform melting and La absorption rate >50%.

[0026] S6, Refining Process 350A current, 28V voltage, refine for 5 minutes to ensure uniform dissolution of alloying elements.

[0027] S7, Casting After refining, the molten alloy is poured into a metal mold preheated to 200℃. The pouring temperature is 1500℃ and the speed is 10kg / min. After cooling, the ingot is demolded to obtain the initial molten cast steel ingot.

[0028] S8, Repeated Melting After the initial melted steel ingot is turned over, steps S3 to S7 are repeated for a total of 6 meltings to ensure uniform composition, thus obtaining a La-modified Q500qenh weathering steel ingot in the cast state.

[0029] Example 2 A rare earth La-modified weathering steel comprising the following raw material components by weight percentage: C: 0.018wt%, Si: 0.25wt%, Mn: 1.42wt%, Cr: 0.30wt%, Ni: 0.38wt%, Cu: 0.36wt%, Mo: 0.14wt%, V: 0.015wt%, Ti: 0.010wt%, Nb: 0.010wt%, Al: 0.050wt%, La: 0.02%, balance Fe and unavoidable impurity elements; Its preparation method is as follows: S1. Raw material preparation and pretreatment Prepare pure iron, metallic manganese, Cr, Ni, Cu, Mo, V, Ti, Nb, Al, La, and silicon carbide according to the predetermined ratio; the purity of the raw materials is ≥99.5%, polish to remove oxide scale, remove oil stains with anhydrous ethanol, and dry at 150℃ for 2 hours.

[0030] S2, Melting Chamber Atmosphere Control Pure iron, used as furnace charge, is charged into the electric arc furnace melting chamber, and a vacuum of 6×10⁻⁶ is drawn. -4 Pa, purge with high-purity argon gas to 0.05 MPa, repeat vacuuming and argon purging 3~5 times, finally argon pressure 0.05~0.07 MPa.

[0031] S3, furnace charge pre-melting Arc torch is used to ignite the arc with a current of 240A and a voltage of 22V. Pre-melting takes 2 minutes to remove residual gas and impurities from the surface of the furnace charge.

[0032] S4, The furnace charge is completely melted. Adjust the current to 400A and the voltage to 30V, and melt for 3 minutes to ensure that the furnace charge is completely melted.

[0033] S5, alloying elements and La addition After the furnace charge is fully melted, add the alloys in the following order: first add Mo, Nb, and Ti, then add Cr and Ni, and finally add Cu and Al; place pure La metal particles at the bottom of the crucible to ensure uniform melting and La absorption rate >50%.

[0034] S6, Refining Process 400A current, 25V voltage, refining for 4 minutes to ensure uniform dissolution of alloying elements.

[0035] S7, Casting After refining, the molten alloy is poured into a metal mold preheated to 260℃. The pouring temperature is 1500℃ and the speed is 10kg / min. After cooling, the ingot is demolded to obtain the initial molten cast steel ingot.

[0036] S8, Repeated Melting After the initial melted steel ingot is turned over, steps S3 to S7 are repeated for a total of 6 meltings to ensure uniform composition, thus obtaining a La-modified Q500qenh weathering steel ingot in the cast state.

[0037] Example 3 A rare earth La-modified weathering steel comprising the following raw material components by weight percentage: C: 0.020wt%, Si: 0.28wt%, Mn: 1.49wt%, Cr: 0.32wt%, Ni: 0.42wt%, Cu: 0.41wt%, Mo: 0.18wt%, V: 0.02wt%, Ti: 0.015wt%, Nb: 0.015wt%, Al: 0.070wt%, La: 0.04%, balance Fe and unavoidable impurity elements; Its preparation method is as follows: S1. Raw material preparation and pretreatment Prepare pure iron, metallic manganese, Cr, Ni, Cu, Mo, V, Ti, Nb, Al, La, and silicon carbide according to the predetermined ratio; the purity of the raw materials is ≥99.5%, polish to remove oxide scale, remove oil stains with anhydrous ethanol, and dry at 150℃ for 3 hours.

[0038] S2, Melting Chamber Atmosphere Control Pure iron, used as furnace charge, is charged into the electric arc furnace melting chamber, and a vacuum of 6×10⁻⁶ is drawn. -4 Pa, purge with high-purity argon gas to 0.05 MPa, repeat vacuuming and argon purging 3~5 times, finally argon pressure 0.05~0.07 MPa.

[0039] S3, furnace charge pre-melting Arc torch is used to ignite the arc with a current of 300A and a voltage of 25V. Pre-melting takes 2 minutes to remove residual gas and impurities from the surface of the furnace charge.

[0040] S4, The furnace charge is completely melted. Adjust the current to 400A and the voltage to 30V, and melt for 3 minutes to ensure that the furnace charge is completely melted.

[0041] S5, alloying elements and La addition After the furnace charge is fully melted, add the alloys in the following order: first add Mo, Nb, and Ti, then add Cr and Ni, and finally add Cu and Al; place pure La metal particles at the bottom of the crucible to ensure uniform melting and La absorption rate >50%.

[0042] S6, Refining Process Use 450A current and 28V voltage for 3-5 minutes to refine the alloying elements evenly.

[0043] S7, Casting After refining, the molten alloy is poured into a metal mold preheated to 300℃. The pouring temperature is 1550℃ and the speed is 10kg / min. After cooling, the ingot is demolded to obtain the initial molten cast steel ingot.

[0044] S8, Repeated Melting After the initial melted steel ingot is turned over, steps S3 to S7 are repeated for a total of 6 meltings to ensure uniform composition, thus obtaining a La-modified Q500qenh weathering steel ingot in the cast state.

[0045] Comparative Example 1 It is a Q500qenh weathering steel that does not contain La.

[0046] Test case 1. The weathering steels of Examples 1-3 and Comparative Example 1 were subjected to θ–2θ scanning tests using a Cu target X-ray diffractometer (Cu-Kα, λ=1.5406Å, tube voltage 40kV, tube current 40mA), as detailed below: Before testing, samples of each group of as-cast steel ingots were subjected to fine grinding and polishing, followed by ultrasonic cleaning with anhydrous ethanol to remove surface contaminants. After drying, the samples were tested. The scanning parameters were set as follows: 2θ scanning range 30°~90°, step size 0.01°, and scanning speed 5° / min. The obtained diffraction data were smoothed and Kα2 removed. Phase identification and analysis were performed using relevant standard PDF cards for iron-based alloys. By comparing the main phase structure, diffraction peak position shift, diffraction peak intensity, and half-width variation of as-cast samples with different La contents, the influence of trace La on the lattice parameters, phase types, and grain size of Q500qenh weathering steel as-cast samples was evaluated. The results are shown in [Figure number missing]. Figure 1 .

[0047] like Figure 1 As shown, characteristic diffraction peaks of α-Fe (labeled (110), (200), and (211) crystal planes) appeared in all curves, indicating that the matrix of all four samples was α-Fe phase (body-centered cubic iron). No characteristic peaks of elemental or compound La were observed (possibly due to the low amount of La added, which exists in the form of solid solution or very fine precipitates, making it difficult to detect by XRD). It is worth noting that the (200) peak in Examples 1 and 2 was lower than that in Comparative Example 1, while that in Example 3 was higher. This indicates that at low La content (such as 0.005% in Example 1 and 0.02% in Example 2), La atoms may inhibit the growth of non-(110) crystal planes and strengthen the preferred orientation of (110) crystal planes through grain boundary segregation or solid solution. When the La addition amount increased to 0.04%, the control effect on crystal plane orientation may have slightly weakened due to the saturation of some La solid solubility, resulting in a decrease in the intensity of the (110) peak. In summary, when 0.02wt% La is added to Q500qenh steel ( Figure 1 In Example 2), the intensity of the diffraction peak of the (110) crystal plane of the α-Fe matrix is ​​significantly enhanced, while the intensity of the (200) peak is weakened, forming a strong and tough preferred orientation that provides structural support for the bridge under stress.

[0048] 2. To verify the effect of different La content on the as-cast microstructure of Q500qenh weathering steel, weathering steels from Examples 1-3 and Comparative Example 1 were selected as test objects. According to GB / T 10561-2005, cubic samples with dimensions of 10mm × 10mm × 5mm were cut from the center of the longitudinal section of each as-cast steel ingot. After hot-pressing with thermosetting resin, they were sequentially rough and fine ground using sandpaper with grits of 240#, 400#, 600#, 800#, 1000#, 1500#, and 2000# under water-cooled conditions. Subsequently, they were polished to a mirror finish using a diamond suspension with a grit size of 1μm on a cloth wheel. A suitable etchant (adapted to the composition of Q500qenh weathering steel, such as a 4% nitric acid alcohol solution) was used for etching at room temperature for an appropriate time. After etching, the steel was rinsed with water, dehydrated with anhydrous ethanol, and dried. Subsequently, using an inverted metallurgical microscope equipped with a digital imaging system, representative fields of view without defects were selected for imaging in bright field mode at 200× magnification, obtaining as-cast metallographic morphology photographs corresponding to Examples 1-3 and Comparative Example 1, respectively. Figure 2 (This is used to compare and analyze the as-cast grain size, crystal ratio, inclusion morphology and distribution of samples under different La contents).

[0049] Depend on Figure 2 As shown in the metallographic photographs (a) to (d), the as-cast microstructure of each sample is mainly bainitic ferrite, but the morphology and precipitate state vary significantly with the change of La content. Comparative Example 1 ((a), without La) has a coarser bainitic ferrite structure with large and unevenly distributed bainitic ferrite lamellae, and wide ferrite bands in some areas; the structure may be accompanied by a small amount of pearlite or retained austenite, the grain boundaries are poorly defined, and the overall refinement is low.

[0050] Example 1 ((b), 0.005% La): Compared to Comparative Example 1, the microstructure is significantly refined: the lamellar / lamellae size of bainitic ferrite is reduced and the distribution is more uniform; the number of grain boundaries increases (refining), but a small number of relatively wide ferrite regions still exist (due to the low La content, the refining effect is limited). Example 2 ((c), 0.02% La): The microstructure refinement effect is most significant: the bainitic ferrite is small and uniform in shape (close to the characteristics of lower bainite or fine-grained bainite); the width of the ferrite bands is further reduced, the grain boundaries are clear and densely distributed, and there are no obvious coarse microstructure regions. Example 3 ((d), 0.04% La): The microstructure shows slight coarsening: the size of the bainitic ferrite is slightly larger than that of Example 2, and the uniformity is reduced; a small number of aggregated ferrite or precipitates appear locally (excessive La leads to the segregation of rare earth compounds, which weakens the refining effect). Comprehensive analysis shows that in Q500qenh weathering steel, about 0.02% La is the optimal content for refining the as-cast bainitic ferrite structure, and the uniformity of the structure can be improved through "nucleation refinement + grain boundary inhibition"; if the La content is too low, the refinement is insufficient, and if it is too high, the structure coarsens.

[0051] 3. Select Q500qenh cast steel billets from Comparative Example 1 (0% La), Example 1 (0.005% La), Example 2 (0.02% La), and Example 3 (0.04% La). Cut 10mm × 10mm × 5mm sample blocks at half the thickness of the billet using wire cutting to remove surface burrs and oxide scale. Grind sequentially with 400#, 800#, 1200#, and 2000# SiC sandpaper, rotating the sample 90° each time the sandpaper is changed, until there are no obvious scratches on the surface. Then, polish with 1.5μm and 0.5μm diamond polishing paste to obtain a mirror-like bright surface. Place the polished sample in a 4% nitric acid alcohol solution at room temperature for 10-15 seconds for etching. After removal, rinse three times with anhydrous ethanol and dry with high-pressure cold air for later use. Using a Zeiss Sigma 300 scanning electron microscope, samples were sputter-coated with gold (approximately 10 nm thick) and observed at 500x, 1000x, and 2000x magnifications in secondary electron imaging mode with an accelerating voltage of 15 kV and a working distance of 8–10 mm. Three representative regions of each sample were randomly selected for imaging to complete the microstructural characterization. Results are shown in [Figure number missing]. Figure 3 .

[0052] like Figure 3As shown, these four Q500qenh as-cast SEM images clearly demonstrate the regulatory effect of rare earth element La on its microstructure: Comparative Example 1 ((a), 0% La) exhibits a coarse and randomly distributed lath / blocky bainitic ferrite microstructure, approximately 2-4 μm wide, with blurred grain boundaries and poor uniformity; Example 1 ((b), 0.005% La) shows a refined microstructure, with the ferrite lath width reduced to 1.5-2.5 μm, more densely arranged, and improved grain boundary clarity, but still retains a small amount of relatively wide areas; Example 2 ((c), 0.02% La) shows the best refinement effect, with bainitic ferrite appearing as fine and uniform needle / lath shapes, only 0.8-1.2 μm wide, with tightly interwoven laths, no coarse microstructure, and uniform grain boundary distribution; Example 3 ((d), 0.04% La) shows a refined microstructure. La exhibits slight coarsening of the microstructure, with the width of ferrite laths increasing to 1.2~2.0 μm, local lath aggregation, and rare earth compound segregation visible at grain boundaries. The core role of La is to combine with O and S in steel to form high-melting-point rare earth compounds (such as La2O3 and LaS) as heterogeneous nucleation sites, increasing the number of bainitic ferrite nuclei. At the same time, La atoms segregate at grain boundaries, hindering ferrite growth and achieving microstructure refinement. It can also preferentially combine with harmful elements such as H, O, and S to purify the matrix and improve microstructure uniformity. However, the La content needs to be controlled within the optimal range of around 0.02%. Excessive addition will weaken the refining effect due to the coarsening and segregation of rare earth compounds.

[0053] 4. To investigate the effect of trace amounts of lanthanum (La) (0.005 wt.% to 0.04 wt.%) on the room temperature mechanical tensile properties of Q500qenh cast steel, a comparative study was conducted using materials without La as a benchmark control group.

[0054] Four groups of test samples were selected from Examples 1-3 and Comparative Example 1. All samples were kept in their original as-cast state without any additional heat treatment to accurately reflect the intrinsic influence of La on the mechanical properties of as-cast materials. Room temperature tensile tests were conducted strictly according to the requirements of GB / T 228.1-2010 standard, using standard sheet tensile specimens on an electronic universal testing machine equipped with a high-precision extensometer. During the test, the gauge length of the specimens was precisely measured to ensure data accuracy, the loading rate was strictly controlled, and the load-displacement curve data was recorded in real time through the testing machine's data acquisition system. Finally, through systematic processing and analysis of the test data, the core mechanical properties of each group of samples, such as yield strength, tensile strength, and elongation after fracture, were comprehensively calculated. This further elucidates the intrinsic correlation between La content and the comprehensive room temperature mechanical properties of Q500qenh as-cast steel. The results are shown in [Figure number missing]. Figure 4 .

[0055] like Figure 4As shown, Comparative Example 1 (without La) exhibited the lowest strength and moderate plasticity; Example 1 (0.005% La) showed a slight improvement in both strength and plasticity compared to Comparative Example 1, but the improvement was limited; Example 2 (0.02% La) demonstrated the best performance, with the highest yield strength and tensile strength among the four groups. Simultaneously, the elongation remained at a high level, achieving a good balance between strength and plasticity; Example 3 (0.04% La) showed a slight decrease in strength and plasticity compared to Example 2, but the material still met the standards for high-strength weathering steel. However, excessive addition of La (above 0.04%) resulted in the formation of coarse rare earth compounds, leading to coarsening of the microstructure and consequently weakening the strength and plasticity performance.

[0056] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A rare earth La-modified weathering steel, characterized in that, The raw material components include the following weight percentages: 0.015~0.020wt% C, 0.22~0.28wt% Si, 1.35~1.49wt% Mn, 0.26~0.32wt% Cr, 0.35~0.42wt% Ni, 0.35~0.41wt% Cu, 0.12~0.18wt% Mo, V≤0.02wt%, 0.010~0.015wt% Ti, 0.010~0.015wt% Nb, 0.050~0.070wt% Al, 0.001~0.04wt% La, with the balance being Fe and unavoidable impurities.

2. The rare earth La-modified weathering steel according to claim 1, characterized in that, The raw material components include the following weight percentages: 0.015~0.080wt% C, 0.22~0.26wt% Si, 1.35~1.49wt% Mn, 0.26~0.30wt% Cr, 0.35~0.40wt% Ni, 0.35~0.40wt% Cu, 0.12~0.15wt% Mo, V≤0.02wt%, 0.010~0.015wt% Ti, 0.010~0.015wt% Nb, 0.050~0.070wt% Al, 0.01~0.03wt% La, with the balance being Fe and unavoidable impurities.

3. The rare earth La-modified weathering steel according to claim 1 or 2, characterized in that, Rare earth La-modified weathering steel is Q500qenh weathering steel.

4. A method for preparing rare earth La-modified weathering steel according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Weigh each ingredient according to the formula, remove impurities and set aside; S2. Place the processed raw material in a vacuum environment, introduce protective gas to isolate the influence of air, and maintain the pressure at 0.05~0.07MPa. S3, furnace charge pre-melting An electric arc torch is used to ignite the arc with a current of 200-300 A and a voltage of 20-25 V, so that the added furnace charge pure iron is pre-melted for 1-2 minutes to remove residual gas and impurities from the surface of the raw materials. S4, Full melting of furnace charge Adjust the current to 300~400 A and the voltage to 25~30 V, and melt for 3~5 minutes until the furnace charge is completely melted; S5, alloying elements and La addition After the furnace charge is fully melted, Mo, Nb, and Ti are added first. After the temperature is raised and they melt, Cr and Ni are added. After they melt, Cu, Al, and La elements are melted and diffused into the alloy liquid by utilizing the high temperature and convection of the melted alloy liquid itself. S6. Adjust the current to 350~450 A and the voltage to 22~28 V, refine for 3~5 min to ensure uniform dissolution of alloying elements, then cast into shape and cool to room temperature to obtain a pre-molten cast steel ingot. S7. After flipping the initially melted cast steel ingot, repeat the above S3~S6 processes 5~6 times to obtain rare earth La modified weathering steel.

5. The preparation method according to claim 4, characterized in that, The process of step S1 is as follows: take raw materials with a purity of ≥99.5%, grind to remove oxide scale, remove oil stains with anhydrous ethanol, and dry at 120~150℃ for 2~3 hours to ensure that there are no impurities remaining in the raw materials.

6. The preparation method according to claim 4, characterized in that, The pressure in step S2 is 0.05~0.06MPa.

7. The preparation method according to claim 4, characterized in that, In step S3, the current is 200~240A, the voltage is 20~24V, and the pre-melting time is 2min.

8. The preparation method according to claim 4, characterized in that, In step S4, the current is 400A, the voltage is 28~30V, and the melting time is 3 minutes.

Images