Rare earth high-strength steel, its preparation methods, and applications

Abstract

This invention discloses a rare-earth high-strength steel, its preparation method, and its applications, relating to the field of iron and steel smelting technology. By controlling the alloy composition of the high-strength steel, using appropriate carbon and manganese content, low P and S content, and adding Cr, Nb, and Ti metal composite alloying, combined with the effects of rare-earth solid solution strengthening, grain refinement strengthening, and inclusion modification, the strength and toughness of the steel are rationally matched. Furthermore, to obtain higher strength while reducing the production cost of the steel, the steel of this invention adopts a high B content composition design, which can reduce the addition of Mn, Nb, and Ti elements, while still maintaining good strengthening effects, further reducing alloy costs.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, and more specifically, to a rare earth high-strength steel, its preparation method, and its application. Background Technology

[0002] As steel equipment develops towards lighter weight, larger size, and stronger and tougher properties, the requirements for the strength and toughness of steel are becoming increasingly higher. When the weight of steel is reduced, its strength is increased, and its toughness is excellent, it can reduce the production cost of products, increase the effective load of equipment, and improve product competitiveness.

[0003] The most common method to improve the strength of steel is to increase the content of carbon and manganese. However, excessive addition of carbon and manganese can affect the toughness and weldability of the steel. Some solutions use precious alloys to improve the toughness and weldability of steel, but this requires a large amount of precious metals, increasing the production cost. Therefore, how to improve the toughness and weldability of steel while reducing its production cost is one of the most pressing problems to be solved in this field.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a rare earth high-strength steel, its preparation method, and its application.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a rare earth high-strength steel, the elemental composition of which, by weight percentage, comprises: C: 0.06-0.15%, Mn: 1.45-1.6%, S≤0.015%, P≤0.022%, Si: 0.1-0.2%, Cr: 0.22-0.32%, Ti: 0.010-0.018%, Nb: 0.026-0.03%, B: 0.003-0.004%, Als: 0.010-0.030%, rare earth: 0.0042-0.0060%, Mo≤0.010%, Ni≤0.020%, As≤0.014%, Sn≤0.0050%, Cu≤0.05%, V≤0.004%, Ca≤0.0005%, with the balance being Fe and unavoidable impurities.

[0008] Secondly, the present invention provides a method for preparing rare earth high-strength steel as described in any of the foregoing embodiments, comprising smelting raw materials to obtain castings, hot rolling the castings, and tempering after hot rolling.

[0009] Thirdly, the present invention provides the application of rare earth high-strength steel as described in any of the foregoing embodiments or the preparation method as described in any of the foregoing embodiments in the field of iron and steel smelting.

[0010] The present invention has the following beneficial effects:

[0011] This invention provides a rare-earth high-strength steel, its preparation method, and its applications. By controlling the alloy composition of the high-strength steel, using appropriate carbon and manganese content, low P and S content, and adding Cr, Nb, and Ti metal composite alloying, combined with the effects of rare-earth solid solution strengthening, grain refinement strengthening, and inclusion modification, the strength and toughness of the steel are rationally matched. Furthermore, to obtain higher strength while reducing the production cost of the steel, the steel of this invention adopts a high B content composition design, which can reduce the addition of Mn, Nb, and Ti elements, while still maintaining good strengthening effects, further reducing alloy costs. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a 100x scanning electron microscope image of the rare earth high-strength steel provided in Embodiment 1 of the present invention;

[0014] Figure 2 This is a 200x scanning electron microscope image of the rare earth high-strength steel provided in Embodiment 1 of the present invention;

[0015] Figure 3 This is a 500x scanning electron microscope image of the rare earth high-strength steel provided in Embodiment 1 of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0018] In a first aspect, the present invention provides a rare earth high-strength steel, the elemental composition of which, by weight percentage, comprises: C: 0.06-0.15%, Mn: 1.45-1.6%, S≤0.015%, P≤0.022%, Si: 0.1-0.2%, Cr: 0.22-0.32%, Ti: 0.010-0.018%, Nb: 0.026-0.03%, B: 0.003-0.004%, Als: 0.010-0.030%, rare earth: 0.0042-0.0060%, Mo≤0.010%, Ni≤0.020%, As≤0.014%, Sn≤0.0050%, Cu≤0.05%, V≤0.004%, Ca≤0.0005%, with the balance being Fe and unavoidable impurities.

[0019] By controlling the alloy composition of high-strength steel, using moderate carbon and manganese content, low P and S content, and adding Cr, Nb, and Ti metal composite alloying, combined with rare earth solid solution strengthening, grain refinement strengthening, and inclusion modification, the strength and toughness of the steel are rationally matched. Furthermore, to obtain higher strength while reducing the production cost of the steel, the steel of this invention adopts a high B content composition design, which can reduce the amount of Mn, Nb, and Ti elements added, while still maintaining good strengthening effects, further reducing alloy costs.

[0020] The functions of the above-mentioned main elements are as follows:

[0021] Carbon: The carbon content is controlled between 0.06% and 0.15%. As the carbon content in steel increases, the strength and hardness will increase, but the plasticity, impact toughness and weldability will decrease. Using a moderate carbon content, strength can be obtained while maintaining good toughness and weldability.

[0022] Silicon: When the silicon content is controlled between 0.1% and 0.2%, it can strengthen ferrite, improve the strength and hardness of steel, reduce the critical cooling rate of steel, and improve the hardenability of steel. When the content is ≤0.40%, it can improve the tendency of hot cracking. Excessive content will deteriorate the weldability of steel.

[0023] Manganese: The manganese content should be controlled between 1.45% and 1.6%. A moderately high manganese content can achieve higher strength, hardness, and wear resistance, reduce the critical cooling rate of the steel, improve its hardenability, and enhance its hot working properties. It can also reduce the size of precipitated carbides and promote precipitation strengthening. However, excessive manganese content will reduce weldability, weaken the steel's corrosion resistance, cause significant temper brittleness, and promote grain growth. Therefore, the inventors controlled the manganese content within the above-mentioned range and added grain-refining elements such as niobium, titanium, and aluminum to effectively control the steel's microstructure.

[0024] Chromium: The chromium content should be controlled between 0.22% and 0.32%. It has a great strengthening effect on low alloy steel, which can improve strength, hardness and wear resistance, reduce the critical cooling rate of steel and improve hardenability. Excessive chromium content will increase the brittle transition temperature of steel and increase temper brittleness.

[0025] Niobium: The manganese content should be controlled between 0.026% and 0.03%. Niobium has a strong binding force with carbon, nitrogen, and oxygen, and forms corresponding stable compounds with them. It plays a role in refining grains and precipitation strengthening, reducing the overheating sensitivity and temper brittleness of steel, and is conducive to improving low-temperature impact toughness. Niobium can increase the recrystallization temperature. Through controlled rolling and controlled cooling, the grains can be further refined, improving the reduction in toughness caused by precipitation strengthening, and improving welding performance, thereby enabling the steel plate to obtain comprehensive properties of high strength and high toughness.

[0026] Titanium: The titanium content should be controlled between 0.01% and 0.018%. Titanium is a low-cost alloying element that can make the internal structure of steel dense and refine the grains. Through the precipitation of titanium carbide particles in the ferrite body after phase transformation or phase transition, a strong precipitation strengthening effect can be produced, which can significantly improve the strength. At the same time, it can effectively reduce aging sensitivity and cold brittleness and improve welding performance.

[0027] Niobium, titanium and other alloying elements are beneficial to increasing the solid solubility of rare earth elements in steel. Solidly dissolved rare earths tend to accumulate at grain boundaries, which can significantly delay the recrystallization process and refine the recrystallized grains. At the same time, rare earths can effectively increase the dissolution of alloying elements such as niobium and titanium in steel. Through controlled cooling, the dispersion precipitation of alloying phases such as niobium and titanium can be promoted, thereby enhancing the strengthening effect of alloying elements.

[0028] Boron: Boron readily adsorbs on austenite grain boundaries and accumulates there, effectively delaying the transformation of austenite to ferrite, increasing the solubility of alloying elements, and postponing the aging effect. After rolling, it can be further strengthened due to the aging effect. Boron segregation at grain boundaries can reduce the diffusion coefficient of alloying elements such as niobium and titanium at grain boundaries, increase the force of niobium and titanium on grain boundaries, reduce the interface migration rate and recrystallization driving force, refine grains, and improve strength.

[0029] Aluminum: The aluminum content should be controlled between 0.010% and 0.030%. Adding an appropriate amount of aluminum to steel can refine the grains and improve impact toughness. Aluminum also has antioxidant and anti-corrosion properties. Excessive content has an adverse effect on the hot working performance, welding performance and cutting performance of steel.

[0030] Rare earth: The rare earth content should be controlled between 0.0042% and 0.0060%. Rare earth elements easily react with oxygen and sulfur to form oxides, sulfides, and sulfur oxides with high melting points and low plasticity at high temperatures. By adding an appropriate amount of rare earth, the desulfurization, deoxidation, and inclusion modification effects of rare earth can be fully utilized, the steel grains can be refined, the as-cast structure can be improved, the normal and low temperature toughness and fracture resistance of steel can be improved, the hot brittleness of steel can be reduced, and the hot workability and weldability can be improved.

[0031] Rare earth elements can purify molten steel, causing carbides such as niobium and titanium to precipitate more finely and disperse, fully leveraging their strengthening effect as alloying elements. Simultaneously, the modifying effect of rare earth elements on inclusions effectively reduces their harmful effects, further improving plasticity and toughness. Rare earth elements dissolved in steel accumulate at grain boundaries, reducing the segregation of impurity elements at these boundaries, strengthening them, and effectively mitigating the harmful effects of segregated elements such as phosphorus and sulfur, further improving the steel's microstructure and properties.

[0032] In an optional implementation, rare earth elements include La and / or Ce.

[0033] Preferably, the amount of La added is 30-40%, and the amount of Ce added is 60-70%. More preferably, the amount of La added is 35%, and the amount of Ce added is 65%.

[0034] In an optional implementation, the contents of C, N, Cr, Nb, Ti and B in the elemental composition have the following relationships: 2≤Ti / N≤5; 6≤(Ti+Nb) / N≤12; 1.5≤Cr / C≤2.3. By controlling the content ratio of the above elements within the above range, titanium has a lower solid solution temperature, making it easier to form fine and stable TiN, which can effectively prevent austenite grain growth, refine grains and microstructure. Excess titanium can suppress recrystallization in the form of solid solution titanium or TiC, playing a role in precipitation and strengthening. Appropriate amount of titanium can also promote the formation of niobium carbide. Niobium carbide pins grain boundaries during rolling, preventing grain growth. During recrystallization, the pinning of dislocations and the prevention of subgrain boundary migration greatly prolong the recrystallization time, effectively suppressing recrystallization nucleation, thereby obtaining more solid solution niobium. The precipitation of solid solution niobium can further produce a strengthening effect. Chromium has a great strengthening effect on microalloyed steel, which can reduce the critical cooling rate of steel, expand the cooling rate range, refine the microstructure, improve the hardenability of steel, and make the steel have better comprehensive mechanical properties after quenching and tempering.

[0035] In an optional implementation, the carbon equivalent Ceq ≤ 0.45% and Pcm ≤ 0.25%. The carbon equivalent Ceq is calculated using the following formula: Ceq = C + Mn / 6 + (Cr + V + Mo) / 5 + (Cu + Ni) / 15. The Pcm is calculated using the following formula: Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B. Controlling the carbon equivalent within the above range can prevent adverse effects on the toughness and weldability of the steel.

[0036] Secondly, the present invention provides a method for preparing rare earth high-strength steel as described in any of the foregoing embodiments, comprising smelting raw materials to obtain castings, hot rolling the castings, and tempering after hot rolling.

[0037] In an optional embodiment, hot rolling includes heating the casting in a heating furnace and then rolling it, followed by cooling the rolled piece after each rolling cycle. By controlling the hot rolling temperature, the alloy structure of the steel reaches the phase transformation temperature, and then by controlling the cooling process, the morphology of the alloy structure is fixed, thereby improving the strength of the steel while reducing its production cost.

[0038] Preferably, when a thinner steel is required, the hot rolling is performed twice: first, the casting is hot rolled to a thickness of 40-45 mm, and then hot rolled to a thickness of 10-12 mm.

[0039] Preferably, the heating rate of the furnace for the first hot rolling is 5–10 °C / min, the furnace temperature is 1200–1250 °C, the holding time is 90–120 min, the initial rolling temperature is 1100–1150 °C, and the final rolling temperature is 850–900 °C. The rolling passes are 5–7, with a reduction of 20–30% in the first two passes and 15–25% in the remaining passes. By controlling the hot rolling parameters within the above range, higher strength high-strength steel can be obtained.

[0040] Preferably, the heating rate of the furnace for the second hot rolling is 8–12 °C / min, the furnace temperature is 1200–1250 °C, the holding time is 60–90 min, the initial rolling temperature is 1100–1130 °C, and the final rolling temperature is 870–900 °C. The rolling passes are 6–8, with a reduction of 20–25% in the first two passes and 15–20% in the remaining passes.

[0041] In an optional embodiment, the cooling medium during the first hot rolling process is air. The temperature of the rolled piece entering the cooling section after hot rolling is 1050–1060°C, and the temperature of the rolled piece exiting the cooling section is 1000–1050°C. The speed of the rollers in the cooling section is 0.1–0.3 m / s. The primary goal of the first hot rolling is to reduce the thickness of the steel while simultaneously allowing the alloying materials in the steel to be fully dissolved, thereby increasing the strength of the steel and refining the grain size.

[0042] In an optional embodiment, water is used as the cooling medium during the second hot rolling process, and laminar flow cooling is employed. The temperature of the rolled piece entering the cooling section after hot rolling is 780–990°C. The speed of the rollers in the cooling section is 0.2–0.4 m / s, the cooling rate is 35–45°C / s, the final cooling temperature is 120–150°C, the water temperature in the cooling section is 22–26°C, and the water pressure is 50–60 kPa. The rolled piece obtained from the second hot rolling can be directly used for subsequent processing. Therefore, using water cooling to control the temperature after the second hot rolling ensures that the steel microstructure is refined, the phase transformation is complete, and the steel has high strength.

[0043] In an optional implementation, tempering is performed to obtain comprehensive mechanical properties with good strength, plasticity and toughness. Therefore, the tempering temperature is 600-650°C and the holding time is 40-60 minutes.

[0044] In optional embodiments, the raw material smelting method includes smelting in a vacuum induction furnace. In other embodiments, smelting can also be carried out using equipment such as converters, LF furnaces, or RH furnaces.

[0045] Preferably, the parameters for vacuum induction furnace smelting include: compressed air pressure 0.4–0.5 MPa, argon pressure 1.1–1.2 MPa, cooling water pressure 0.2–0.3 MPa; secondary vacuum pump opening vacuum degree ≤450 Pa, secondary vacuum pump ultimate vacuum degree ≤4 Pa; medium frequency power supply power 15–16 KW, melting power 50–60 KW, clearing power 100–110 KW; alloy steel molten temperature 1590–1600 °C, and casting temperature 1560–1570 °C.

[0046] Preferably, the order of adding each raw material is as follows: chromium, niobium and scrap steel are added to the crucible together; aluminum granules, ferrosilicon, metallic manganese, ferrotitanium, ferroboron and rare earth are added from the silo; aluminum granules are added after the scrap steel begins to melt; after the scrap steel is completely melted, protective gas is introduced into the furnace at a pressure of 10,000 to 11,000 Pa; ferrosilicon, ferrotitanium, metallic manganese, ferroboron and rare earth are added in sequence, with an interval of 1 to 2 minutes between each alloy addition.

[0047] Thirdly, the present invention provides the application of rare earth high-strength steel as described in any of the foregoing embodiments or the preparation method as described in any of the foregoing embodiments in the field of iron and steel smelting.

[0048] Example 1

[0049] This embodiment provides a rare earth high-strength steel, the elemental composition of which, by weight percentage, includes: C: 0.13%, Mn: 1.47%, S: 0.013%, P: 0.021%, Si: 0.3%, Cr: 0.34%, Ti: 0.018%, Nb: 0.026%, B: 0.0031%, Als: 0.024%, rare earth: 0.0042%, Mo: 0.010%, Ni: 0.020%, As: 0.012%, Sn: 0.0028%, Cu: 0.03%, V: 0.003%, Ca≤0.0005%, with the balance being Fe and unavoidable impurities.

[0050] The rare earth element content is 35% La and 65% Ce.

[0051] In this embodiment, the carbon equivalent of the rare earth high-strength steel is Ceq = 0.448% and Pcm = 0.248%.

[0052] This embodiment also provides a method for preparing rare earth high-strength steel, including the following steps:

[0053] S01, Vacuum Induction Furnace Steelmaking

[0054] Chromium, niobium, and scrap steel are added to the crucible together. Aluminum granules, ferrosilicon, metallic manganese, ferrotitanium, ferroboron, and rare earth elements are added from the hopper. Aluminum granules are added after the scrap steel begins to melt. After the scrap steel is completely melted, protective gas is introduced into the furnace at a pressure of 10080 Pa. Ferrosilicon, ferrotitanium, metallic manganese, ferroboron, and rare earth elements are added in sequence, with a 1-minute interval between each alloy addition. Steel is poured 1.5 minutes after all alloys have been added.

[0055] During the steelmaking process, the compressed air pressure is controlled at 0.43 MPa, the argon pressure at 1.2 MPa, the cooling water pressure at 0.22 MPa, and the hydraulic station oil pressure at 6 MPa; the secondary vacuum pump is opened at a vacuum degree of 445 Pa, and the ultimate vacuum degree of the secondary vacuum pump is 3 Pa; the medium frequency power supply has a power output of 15.6 KW, a melting power of 50.4 KW, and a cleaning power of 100 KW; the alloy steel liquid is added at a temperature of 1590℃, and the steel casting temperature is 1560℃, after which steel is cast to obtain the casting.

[0056] S02, First Hot Rolling

[0057] The casting obtained in step S01 was placed in a heating furnace for its first hot rolling, which was performed to a thickness of 40 mm. The casting was heated to 1230°C in the heating furnace at a heating rate of 6°C / min, held at that temperature for 100 min, and then hot rolling began. The initial rolling temperature was 1100°C, and the final rolling temperature was 870°C. The rolling process consisted of 5 passes, with a reduction rate of 24% in the first two passes and 20% in the remaining passes.

[0058] After the first hot rolling, the workpiece is sent to the cooling section for air cooling. The temperature of the workpiece entering the cooling section after hot rolling is 1054℃, and the temperature of the workpiece exiting the cooling section is 1016℃. The speed of the roller conveyor in the cooling section is 0.2m / s.

[0059] S03, Second Hot Rolling

[0060] The rolled piece obtained in step S02 is fed back into the heating furnace for a second hot rolling process, rolling it to a thickness of 12 mm. The casting is heated to 1230°C in the heating furnace at a rate of 8°C / min, held at that temperature for 60 min, and then hot rolling begins. The initial rolling temperature is 1078°C, and the final rolling temperature is 876°C; the rolling passes are 6, with a reduction of 24.5% in the first two passes and 18% in the remaining passes.

[0061] After the second hot rolling, the roll is sent to the cooling section for laminar flow cooling at a rate of 45℃ / s and a final cooling temperature of 125℃. The temperature of the rolled piece entering the cooling section after hot rolling is 816℃, the speed of the cooling section rollers is 0.3m / s, the water temperature in the cooling section is 23.9℃, and the water pressure is 57.6KPa.

[0062] S04, Tempering

[0063] The 10mm thick rolled piece obtained by cooling in step S03 was tempered at 620℃ for 60 minutes.

[0064] The rare earth high-strength steel provided in Example 1 was observed under a scanning electron microscope as follows: Figures 1-3 The results are shown. According to... Figures 1 to 3 By magnifying the microstructure of rare earth high-strength steel, it can be found that the microstructure of rare earth high-strength steel is tempered sorbite.

[0065] Example 2

[0066] This embodiment provides a rare earth high-strength steel, the elemental composition of which, by weight percentage, includes: C: 0.12%, Mn: 1.5%, S: 0.013%, P: 0.021%, Si: 0.3%, Cr: 0.30%, Ti: 0.020%, Nb: 0.025%, B: 0.0030%, Als: 0.025%, rare earth: 0.0045%, Mo: 0.010%, Ni: 0.020%, As: 0.012%, Sn: 0.0028%, Cu: 0.03%, V: 0.003%, Ca≤0.0005%, with the balance being Fe and unavoidable impurities.

[0067] The rare earth element content is 35% La and 65% Ce.

[0068] In this embodiment, the carbon equivalent Ceq of the rare earth high-strength steel is 0.436%, and Pcm is ≤0.238%.

[0069] The rare earth high-strength steel provided in this embodiment is prepared by the same method as in Example 1.

[0070] Example 3

[0071] This embodiment provides a rare earth high-strength steel with the same elemental composition and preparation method as in Example 1, the only difference being that the cooling rate is 35℃ / s.

[0072] Comparative Example 1

[0073] This comparative example provides a high-strength steel, which is prepared in the same way as in Example 1. The elemental composition by weight includes: C: 0.11%, Mn: 1.53%, S: 0.004%, P: 0.022%, Si: 0.29%, Cr: 0.07%, Ti: 0.012%, Nb: 0.031%, B: 0.0002%, Als: 0.024%, Mo: 0.011%, Ni: 0.02%, As: 0.0125%, Sn: 0.0055%, Cu: 0.03%, V: 0.036%, Ca: 0.0011%, with the balance being Fe and unavoidable impurities.

[0074] Comparative Example 2

[0075] This comparative example provides a rare earth high-strength steel with the same elemental composition as Example 1. The difference in preparation method between Example 1 and Example 1 is that the cooling rate of the laminar flow cooling of the rolled piece is 20-30℃ / s.

[0076] Experimental Example 1

[0077] The rare earth high-strength steels prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to tensile and impact tests. The tensile test method was GB / T228.1, and the impact test method was GB / T229. The results are shown in Table 1.

[0078] Table 1 Tensile properties of rare earth high-strength steel

[0079]

[0080] As shown in Table 1, the overall performance of rare earth high-strength steel is better than that of conventional high-strength steel. This is mainly due to the full utilization of the composite strengthening effect of Cr, Nb, Ti, B and rare earth. At the same time, the rare earth has the effect of modifying inclusions and purifying molten steel, which can improve the comprehensive properties such as plasticity and toughness while increasing the strength of the steel.

[0081] The rare earth high-strength steel, its preparation method, and its application provided by this invention have at least the following advantages:

[0082] By controlling the alloy composition of high-strength steel, using moderate carbon and manganese content, low P and S content, and adding Cr, Nb, and Ti metal composite alloying, combined with rare earth solid solution strengthening, grain refinement strengthening, and inclusion modification, the strength and toughness of the steel are rationally matched. Furthermore, to obtain higher strength while reducing the production cost of the steel, the steel of this invention adopts a high B content composition design, which can reduce the amount of Mn, Nb, and Ti elements added, while still maintaining good strengthening effects, further reducing alloy costs.

[0083] Titanium has a lower solution temperature, making it easier to form fine and stable TiN, which can effectively prevent austenite grain growth and refine grains and microstructure. Excess titanium can suppress recrystallization in the form of titanium solution or TiC, playing a role in precipitation and strengthening. Appropriate amounts of titanium can also promote the formation of niobium carbide. Niobium carbide pins grain boundaries during rolling, preventing grain growth. During recrystallization, the pinning of dislocations and the prevention of subgrain boundary migration greatly prolong the recrystallization time, effectively suppressing recrystallization nucleation, thereby obtaining more niobium in solid solution. The precipitation of niobium in solid solution can further produce a strengthening effect. Chromium has a significant strengthening effect on microalloyed steel, which can reduce the critical cooling rate of steel, expand the cooling rate range, refine the microstructure, improve the hardenability of steel, and give the steel better comprehensive mechanical properties after quenching and tempering.

[0084] Rare earth elements can purify molten steel, causing carbides such as niobium and titanium to precipitate more finely and disperse, fully leveraging their strengthening effect as alloying elements. Simultaneously, the modifying effect of rare earth elements on inclusions effectively reduces their harmful effects, further improving plasticity and toughness. Rare earth elements dissolved in steel accumulate at grain boundaries, reducing the segregation of impurity elements at these boundaries, strengthening them, and effectively mitigating the harmful effects of segregated elements such as phosphorus and sulfur, further improving the steel's microstructure and properties.

[0085] The rare earth high-strength steel provided by this invention, after rolling, has good comprehensive mechanical properties, cold and hot working properties and welding properties, and can be used in ships, bridges, vehicles, engineering and other welded structural components.

[0086] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rare-earth high-strength steel, characterized by, The element composition includes, in percentage by weight: C: 0.06-0.15%, Mn: 1.45-1.6%, S≤0.015%, P≤0.022%, Si: 0.1-0.2%, Cr: 0.22-0.32%, Ti: 0.010-0.018%, Nb: 0.026-0.03%, B: 0.003-0.004%, Als: 0.010-0.030%, rare earth: 0.0042-0.0060%, Mo≤0.010%, Ni≤0.020%, As≤0.014%, Sn≤0.0050%, Cu≤0.05%, V≤0.004%, Ca≤0.0005%, the balance being Fe and inevitable impurities; The rare earth includes La and / or Ce; The content of C, N, Cr, Nb and Ti in the element composition satisfies the following relationships: 2≤Ti / N≤5; 6≤(Ti+Nb) / N≤12; 1.5≤Cr / C≤2.3; The preparation method of the rare earth high-strength steel includes smelting raw materials to obtain a casting, hot-rolling the casting, and tempering after the hot-rolling is completed, wherein the tempering temperature is 600-650℃, and the holding time is 40-60min; The hot-rolling includes heating the casting in a heating furnace and then rolling, and the rolled piece obtained by rolling is cooled after each rolling is completed; The hot-rolling is performed twice, including first hot-rolling and second hot-rolling, wherein the first hot-rolling is to hot-roll the casting to a rolled piece with a thickness of 35-40mm, and the second hot-rolling is to hot-roll the rolled piece obtained by the first hot-rolling to a rolled piece with a thickness of 10-12mm; The heating furnace for the first hot-rolling has a heating rate of 5-10℃ / min, a heating temperature of 1200-1250℃, a holding time of 90-120min, a starting rolling temperature of 1100-1150℃, and a final rolling temperature of 850-900℃; The heating furnace for the second hot-rolling has a heating rate of 8-12℃ / min, a heating temperature of 1200-1250℃, a holding time of 60-90min, a starting rolling temperature of 1100-1130℃, and a final rolling temperature of 870-900℃; The cooling medium in the first hot-rolling is air, the temperature of the rolled piece entering the cooling section after the hot-rolling is completed is 1050-1060℃, the temperature of the rolled piece exiting the cooling section is 1000-1050℃, and the speed of the cooling section roller is 0.1-0.3m / s; The cooling medium in the second hot-rolling is water, the cooling mode is laminar flow cooling, the temperature of the rolled piece entering the cooling section after the hot-rolling is completed is 780-990℃, the speed of the cooling section roller is 0.2-0.4m / s, the cooling speed is 35-45℃ / s, the final cooling temperature is 120-150℃, the water temperature of the cooling section is 22-26℃, and the water pressure is 50-60KPa.

2. The rare-earth high-strength steel according to claim 1, characterized in that, The addition amount of La is 30-40%, and the addition amount of Ce is 60-70%.

3. The rare-earth high-strength steel according to claim 1, characterized in that, The carbon equivalent Ceq is ≤0.45%, and Pcm is ≤0.25%. Wherein, the calculation formula of carbon equivalent Ceq is as follows: Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Cu+Ni) / 15; The calculation formula of Pcm is as follows: Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

4. The application of the rare earth high-strength steel in the field of steel smelting according to any one of claims 1-3.

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