A high-strength and high-toughness steel with high-temperature strength endurance, its manufacturing method and application

Abstract

The present invention belongs to the technical field of metal materials, and particularly relates to a high-strength and high-toughness steel with excellent high-temperature strength retention, and a manufacturing method and application thereof. The composition of the high-temperature strength retention refractory steel is as follows by weight percentage: 0.011% ≤ C ≤ 0.049%, 0.11% ≤ Si ≤ 0.19%, 1.41% ≤ Mn ≤ 1.51%, S ≤ 0.0005%, P ≤ 0.020%, 1.1% ≤ Ni ≤ 1.3%, 0.1% ≤ Mo ≤ 0.3%, 0.02% ≤ Al ≤ 0.04%, 300×10⁻⁴% ≤ O ≤ 400×10⁻⁴%, 400×10⁻⁴% ≤ Zr + Ti + Mg ≤ 600×10⁻⁴%, and the contents of Zr, Ti, and Mg satisfy the following formula: Ti / Zr = 50 - 70, Zr / Mg = 2 - 4, and the balance is Fe. Its high-temperature mechanical properties are stable and excellent, and it can be widely used in applications such as refractory materials and high-temperature aging-resistant structures.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and particularly relates to a high-strength and high-toughness steel with excellent high-temperature strength retention, and its manufacturing method and application. Background Art

[0002] As an important structural form of modern buildings, steel structures have received increasing favor and attention from the construction industry and users. However, steel structure buildings have a fatal flaw, which is poor fire resistance. To prevent fires from causing catastrophic damage to steel structure buildings and ensure the safety of personnel and property, new requirements have been put forward for structural steel used in buildings. Fire-resistant steel has emerged to meet this development trend.

[0003] Fire-resistant steel is a low-alloy high-strength structural steel that is alloyed on the basis of ordinary C and Mn steels, and is subjected to controlled rolling and controlled cooling processes during processing, and has fire-resistant properties. The fire resistance of fire-resistant steel is evaluated by the high-temperature yield strength of the steel. According to the provisions of the national standard GB / T 28415-2012, it is mainly used in steel structures of high-rise or super-high-rise buildings. When the steel is designed for use, it is required to meet the following conditions: the high-temperature yield strength at 600 °C remains above 2 / 3 of the room temperature; the mechanical properties at room temperature and other quality indicators meet the requirements of ordinary building steel. Fire-resistant steel generally bears load at room temperature. After being exposed to a fire of about 600 °C for (1 - 3 h), its strength is not lower than 2 / 3 of the room temperature strength to ensure the safety of the building structure.

[0004] The yield strength of ordinary steel drops steeply above 350 °C and cannot meet the strength requirements specified by building standards [Sakumoto, Y., Keira, K., Furumura. F. and Ave, T., Tests of fire resistant bolts and joints, Joumal of strucural Engineering, 1993, 11(119): 3131 - 3150]. The thermal activation of ordinary steel at high temperatures increases the dislocation activity, resulting in a decrease in the matrix strength. In addition, the weakening of the Peierls force, dislocation climb or slip, coarsening of precipitates, detachment of pinning atoms from dislocations, detachment of inclusion particles from the matrix, and generation of new vacancies are all factors affecting the reduction of high-temperature strength.

[0005] To improve the refractory performance, Nb, V, Ti, B, Mo, and Ni are usually used for microalloying or alloying to achieve dispersed and fine precipitation phases and solid solution of alloying elements, thereby obtaining good high-temperature performance. Additionally, through reasonable alloy and process design, the controlled rolling and controlled cooling process is adopted to obtain a duplex structure, such as a mixed microstructure of ferrite + a small amount of pearlite + granular bainite, to achieve good high-temperature performance. This is because, compared with grain boundaries, the phase boundaries of this mixed structure have a stronger hindering effect on the movement of dislocations. At the same time, at high temperatures, the phase boundaries of the mixed structure have different hindering effects on the diffusion of alloying elements and carbon, which is beneficial to hindering the growth of ferrite grains and inhibiting the coarsening of precipitation phases, and can more effectively improve the high-temperature strength of steel. In summary, the high-temperature strength can be improved by means of solid solution strengthening, precipitation strengthening, and fine grain strengthening.

[0006] CN114875329A reports a corrosion-resistant refractory steel with excellent high-temperature creep performance under uniaxial tension and its production method, mainly using the precipitation of carbonitrides of microalloying elements such as Mo, Nb, and V to improve the refractory performance. CN114959451A also reports a weather-resistant refractory structural steel for the South China Sea marine environment, similarly using the precipitation of carbonitrides of microalloying elements such as Mo and Nb to improve the refractory performance. CN115572913A reports a refractory high-strength steel and its production method, which uses expensive alloying elements Ni 5-6%, Cr 19-21.2%, and Mo 10-19% to improve the refractory performance.

[0007] CN115369318A reports a low-cost high-strength refractory building structure steel and its production method, using the tissue control method of bainitic ferrite + martensite-austenite island to improve the refractory performance. 11763881A reports a high-strength low-carbon bainitic refractory steel and its preparation method, which, while using the precipitation strengthening of carbonitrides of microalloying elements such as Mo, Nb, and V, uses the bainite structure to improve the refractory performance. 202010570427.0 reports a similar high-strength low-carbon bainitic refractory steel and its preparation method.

[0008] From the above analysis, it can be seen that the main ways to achieve high-temperature strength are as follows: (1) Using Mo, Nb, V, etc. for microalloying to improve the refractory performance; (2) Using expensive Ni, Cr, Mo for alloying to improve the refractory performance; (3) Improving the refractory performance through tissue control methods such as ferrite + martensite-austenite island and low-carbon bainite. The above methods have high alloy costs, complex manufacturing processes or tissue control methods, increasing the manufacturing cost. Summary of the Invention

[0009] To address the deficiencies of the prior art, the present invention provides a high-strength and high-toughness steel with excellent high-temperature strength retention, as well as its manufacturing method and applications. The present invention can solve the problems of insufficient high-temperature strength duration of traditional high-strength steels and high alloy costs.

[0010] The technical solution provided by the present invention is as follows:

[0011] The high-strength and high-toughness steel with excellent high-temperature strength retention provided by the present invention has the following chemical composition by weight percentage: 0.011% ≤ C ≤ 0.049%, 0.11% ≤ Si ≤ 0.19%, 1.41% ≤ Mn ≤ 1.51%, 0 < S ≤ 0.0005%, 0 < P ≤ 0.020%, 1.1% ≤ Ni ≤ 1.3%, 0.1% ≤ Mo ≤ 0.3%, 0.02% ≤ Al ≤ 0.04%, 300×10 -4 ≤ O ≤ 400×10 -4 、400×10 -4 % ≤ Zr + Ti + Mg ≤ 600×10 -4 %, and the contents of Zr, Ti, and Mg satisfy the following formula: Ti / Zr = 50 - 70, Zr / Mg = 2 - 4, and the balance is Fe.

[0012] The preparation process of the above high-strength and high-toughness steel with excellent high-temperature strength retention is simple. It can be obtained by using common raw materials through common methods, and is easy for industrial production.

[0013] Specifically, the ingredients can be prepared according to the chemical composition and content of the above high-temperature strength retention refractory steel. Medium-frequency induction furnace is used for melting. During the melting process, a refining agent is used for covering. The composition of the molten steel is adjusted by metals, alloys, and oxides. After the melting composition is qualified, it is poured into steel billets. The obtained steel billets are forged or hot-rolled and air-cooled or water-cooled to obtain high-strength steel with stable and excellent high-temperature mechanical properties, which can be widely used in refractory structures and other applications.

[0014] Specifically, the steel billets are forged by means of free forging. Before forging, the specimens are heated to 850 - 1050°C, the forging ratio is 2.0 - 5.0, the forging time is 25 - 50 min, and the thickness of the specimens after forging is 20 - 100 mm.

[0015] Specifically, the condition parameters for hot rolling are: controlling the reduction per pass to be 5 - 15 mm, the reduction ratio to be 2 - 3, and air-cooling at room temperature.

[0016] The functions of each element in the high-strength and high-toughness steel with excellent high-temperature strength retention are as follows:

[0017] Carbon: When C is dissolved in the α-Fe matrix by occupying the tetrahedral interstitial positions of the α-Fe lattice, the strength of the α-Fe matrix is increased due to the distortion of the α-Fe lattice. 1% of C can increase the strength of the α-Fe matrix by 5000 MPa. However, the solubility of C in the α-Fe matrix is very limited (the maximum saturation solubility of C is 0.02%), and excessive C will precipitate. The C precipitated from the Fe matrix exists in the form of precipitate phase particles, strengthening the α-Fe matrix by hindering the movement of dislocations. These precipitate phase particles also play a strengthening role by refining the microstructure. C also strengthens the steel by forming bainite or martensite structures. However, a higher carbon content will seriously damage the welding performance of the steel. Therefore, the C content is controlled below 0.05%.

[0018] Silicon: Si can promote the formation of ferrite and has a solid solution strengthening effect. It hinders the coarsening of cementite and is beneficial to the high-temperature strength. In weldable steels, Si can be used as a deoxidizer. However, if the content is higher than 0.3%, it is not conducive to the welding performance. Generally, the silicon content is controlled at about 0.15%.

[0019] Manganese: The main function of Mn is deoxidation. At the same time, it can react with S to form MnS to prevent the hot brittleness of the steel. In addition, Mn has a strain interaction with N at about 450°C, which is beneficial to the high-temperature tensile strength but will cause temper brittleness and is not conducive to the high-temperature ductility. Increasing the Mn content can reduce the carbon diffusion rate, thereby obtaining fine carbides and improving the performance. In addition, Mn can promote the dissolution of VN and VC and reduce the solution temperature of VC. However, too high a Mn content will reduce the plasticity of the steel. In refractory steels, the Mn content generally does not exceed 1.6%.

[0020] Molybdenum: Mo is mainly dissolved in ferrite, strengthening the ferrite matrix and ensuring good room-temperature strength. Mo2C and MoC precipitate phases begin to form at 500°C, and the Mo2C precipitate phase increases significantly after 550°C. The increase in the precipitate phase of Mo at high temperatures is a major reason for the refractory steel to maintain good high-temperature performance. Mo plays a better role in the performance of refractory steels through the interaction with other alloying elements. Due to the good dispersion of Mo, M(C, N) particles and the high lattice friction strength generated by the solid solution of Mo, the movement of dislocations is hindered, resulting in good high-temperature strength and creep properties. It can be considered that Mo is an effective alloying element for refractory steels to maintain good high-temperature performance.

[0021] Titanium: The Ti element can effectively inhibit the growth of austenite grains in steel, especially the inhibition effect on the growth of austenite grains in the high-temperature region is more obvious. The nitrides of Ti are difficult to dissolve in austenite, have high stability and low growth rate, and can control the grain size during the heating process of the steel. However, adding too high a Ti content will produce large TiN particles and cannot play the role of inhibiting the growth of austenite grains.

[0022] Nickel: The addition of nickel can hinder the formation of δ-ferrite, promote the formation of the austenite region and maintain the stability of the austenite region. At the same time, it can also improve the mechanical properties of the steel. However, nickel is a precious metal element, and minimizing its use can reduce costs.

[0023] Zirconium: Zr is a strong carbide-forming element, a strong deoxidizing element, and a complex oxygen sulfide-forming element. Adding a small amount of zirconium has the effects of degassing, purifying, and refining grains, which is beneficial to improving the low-temperature performance of stainless steel, improving stamping performance, and significantly increasing the hardenability of the steel when dissolved in austenite. Due to the effects of fixing carbon and precipitation hardening, it can improve the high-temperature performance of heat-resistant steel, such as high-temperature strength, etc.

[0024] Magnesium: Magnesium is a strong deoxidizing element and a complex oxygen sulfide-forming element. Magnesium can reduce the number, size, and make the distribution uniform and improve the morphology of inclusions in the steel. Trace amounts of magnesium can improve the size and distribution of carbides in stainless steel. The carbide particles are fine and uniform, and the formed MgO inclusions have the effect of pinning the austenite grain boundaries, providing good control over the grain size.

[0025] Phosphorus / Sulfur: The effects of phosphorus and sulfur in steel materials are complex, but they are generally regarded as harmful elements. While considering both product performance and cost in this invention, the upper limit of the phosphorus content is controlled at 0.020 wt%, and the upper limit of the sulfur content is controlled at 0.0005 wt%.

[0026] Aluminum: Aluminum is one of the main anti-oxidation elements in heat-resistant steel. It can form a dense and protective Al2O3 oxide film on the matrix of heat-resistant steel to protect the underlying heat-resistant steel from further oxidation. The Al2O3 oxide film has good stability even at temperatures exceeding 1250 °C and can adhere firmly to the matrix without falling off. This is not only beneficial to improving the high-temperature oxidation resistance of heat-resistant steel but also can protect chromium elements and reduce the degree of formation of volatile substances. In this invention, the aluminum content is controlled at 0.02 - 0.04 wt%, significantly improving the high-temperature oxidation resistance of the prepared low-cost aluminum-containing heat-resistant steel. Description of the Drawings

[0027] Figure 1 Optical micrographs of the high-strength and high-toughness steel obtained in Example 1 before and after tempering at different temperatures, where: (a) before tempering; (b) tempered at 580 °C for 10 h; (c) tempered at 610 °C for 10 h; (d) tempered at 640 °C for 10 h.

[0028] Figure 2 Scanning electron microscope photos of the high-strength and high-toughness steel obtained in Example 1 before and after tempering at different temperatures, where: (a) before tempering; (b) tempered at 580 °C for 10 h; (c) tempered at 610 °C for 10 h; (d) tempered at 640 °C for 10 h.

[0029] Figure 3 Transmission morphology and selected area diffraction patterns of the high-strength and high-toughness steel obtained in Example 1 before tempering and after tempering at 580 °C for 12 h, where: (a) and (b) are morphology diagrams, and (c) and (d) are selected area diffraction patterns at the circles in (a) and (b), respectively.

[0030] Figure 4 Electron backscattering diffraction (EBSD) results of the high-strength and high-toughness steel obtained in Example 1 before tempering and after tempering at different temperatures for 12 h. Among them, a-d are grain orientation maps, and e-h are grain boundary type distribution maps.

[0031] Figure 5 Variation of the tensile strength of the high-strength and high-toughness steel obtained in Example 1 with time at different tempering temperatures.

[0032] Figure 6 Variation of the yield strength of the high-strength and high-toughness steel obtained in Example 1 with time at different tempering temperatures.

[0033] Figure 7 Variation of the impact toughness of the high-strength and high-toughness steel obtained in Example 1 with time at different tempering temperatures Specific implementation mode

[0034] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0035] Example 1

[0036] A high-strength and high-toughness steel with high-temperature strength endurance and its manufacturing method, the composition of which is by weight percentage: C 0.048%, Si 0.11%, Mn 1.51%, S 0.0005%, P 0.018%, Ni 1.19%, Mo 0.14%, Al 0.033%, O 0.035%, Ti 0.049%, Zr 0.0008%, Mg 0.0004%, and the balance is Fe.

[0037] The specific manufacturing process is as follows:

[0038] Using lumpy or granular Si, Mn, Mo, Ti, Zr, Fe ferroalloys, Ni, Fe, Al, Mg pure metals, and graphite C (the purity of pure metals and graphite C is not less than 99.9%), proportion the ingredients according to the above mass percentages, and use an intermediate frequency induction furnace for melting. The specific melting condition parameters are as follows: conduct induction melting in an argon protective atmosphere, and carry out melting under the conditions of a melting furnace frequency of 400HZ and a power of 500kW to improve the purity and tissue uniformity of the refractory steel and minimize segregation to the greatest extent. During the melting process, use a refining agent for covering, and the refining agent is a CaO-based basic refining agent. After the melting is completed, use the bottom casting method for pouring to obtain an ingot;

[0039] Forged the steel billet by means of free forging. Before forging, heat the specimen to 1000°C, with a forging ratio of 2.5 and a forging time of 30 minutes. After forging, the thickness of the specimen is 40mm;

[0040] Carry out hot rolling on the obtained ingot by using a hot rolling process. The hot rolling parameters are as follows: control the reduction per pass to be 6mm, with a reduction ratio of 2, and air cool at room temperature. Obtain a refractory steel with high-temperature strength and long-term durability.

[0041] Example 2

[0042] A high-strength and high-toughness steel with high-temperature strength and long-term durability and its manufacturing method. Its composition by weight percentage is: C 0.045%, Si 0.19%, Mn 1.46%, S 0.0004%, P 0.015%, Ni 1.15%, Mo 0.3%, Al 0.04%, O 0.04%, Ti 0.045%, Zr 0.0007%, Mg 0.0035%, and Fe 96.71%.

[0043] The specific manufacturing process is as follows:

[0044] Using lumpy or granular Si, Mn, Mo, Ti, Zr, Fe ferroalloys, Ni, Fe, Al, Mg pure metals, and graphite C (the purity of pure metals and graphite C is not less than 99.9%), proportion the ingredients according to the above mass percentages, and use an intermediate frequency induction furnace for melting. The specific melting condition parameters are as follows: conduct induction melting in an argon protective atmosphere, and carry out melting under the conditions of a melting furnace frequency of 400HZ and a power of 500kW to improve the purity and tissue uniformity of the refractory steel and minimize segregation to the greatest extent. During the melting process, use a refining agent for covering, and the refining agent is a CaO-based basic refining agent. After the melting is completed, use the bottom casting method for pouring to obtain an ingot;

[0045] Forged the steel billet by means of free forging. Before forging, heat the specimen to 1050°C, with a forging ratio of 3 and a forging time of 48 minutes. After forging, the thickness of the specimen is 90mm;

[0046] The obtained ingot is hot-rolled by a hot-rolling process. The hot-rolling parameters are as follows: the reduction per pass is controlled at 15 mm, the reduction ratio is 3, and it is air-cooled at room temperature. A refractory steel with high-temperature strength retention is obtained.

[0047] Example 3

[0048] A high-strength and high-toughness steel with high-temperature strength retention and its manufacturing method. Its composition by weight percentage is: C 0.01%, Si 0.15%, Mn 1.41%, S 0.0003%, P 0.010%, Ni 1.1%, Mo 0.1%, Al 0.02%, O 0.03%, Ti 0.040%, Zr 0.0006%, Mg 0.0002%, and Fe 97.13%.

[0049] Si, Mn, Mo, Ti, Zr, Fe ferroalloys, Ni, Fe, Al, Mg pure metals, and graphite C (the purity of pure metals and graphite C is not less than 99.9%) in block or granular form are proportioned according to the above mass percentages and melted in an intermediate-frequency induction furnace. The specific melting condition parameters are as follows: induction melting is carried out in an argon protection atmosphere, and melting is carried out under the conditions of a melting furnace frequency of 400 HZ and a power of 500 kW to improve the purity and tissue uniformity of the refractory steel and minimize segregation to the greatest extent. During the melting process, a refining agent is used for covering, and the refining agent is a CaO-based basic refining agent. After melting, casting is carried out by the bottom-pouring method to obtain an ingot;

[0050] The steel billet is forged by a free forging method. Before forging, the sample is heated to 880 °C, the forging ratio is 2, the forging time is 26 min, and the thickness of the sample after forging is 40 mm;

[0051] The obtained ingot is hot-rolled by a hot-rolling process. The hot-rolling parameters are as follows: the reduction per pass is controlled at 5 mm, the reduction ratio is 2, and it is air-cooled at room temperature. A refractory steel with high-temperature strength retention is obtained.

[0052] The materials prepared in Example 1 are selected for various tests, and the results are as follows:

[0053] Figure 1 It is an optical micrograph after tempering at different temperatures and for a long time. It can be seen that the microstructure before tempering and after tempering at each temperature for 10 h is not significantly different, and there is no obvious coarsening phenomenon. It is composed of a large amount of acicular ferrite (AF) and a small part of grain boundary ferrite (GBF), etc. The volume fraction of acicular ferrite is as high as about 90%, and it grows radially with micron-sized inclusions as the core. It shows that after the material has been tempered for 10 hours, the main tissue phases, acicular ferrite and grain boundary ferrite, are very stable.

[0054] Figure 2It is the microstructure diagram of the material under scanning electron microscopy. Compared with the tissue observed under optical microscope, the tissue under scanning electron microscopy is basically the same, both composed of a large amount of acicular ferrite and a small part of grain boundary ferrite. In addition, there is a very small amount of MA island tissue in the sample tissue before tempering.

[0055] Figure 3 To obtain the transmission morphology and selected area diffraction patterns of the material before tempering and after tempering at 580 °C for 12 h, (a) and (b) are morphology diagrams, and (c) and (d) are the selected area diffraction patterns at the circles in (a) and (b) respectively. It is further confirmed that the matrix structure of the material prepared by the above method before tempering is mainly acicular ferrite, and the acicular ferrite grains contain a high density of dislocations. Comparing Figure 3 parts (a) and (b) in, it can be seen that after tempering at 580 °C for 12 h, the fine and dispersed precipitates in the matrix do not increase significantly. Point scanning is performed on the possible nano-sized black dots, and no precipitate energy spectrum is found, indicating that it is difficult to form effective precipitation at this time. There are a small amount of particles precipitated at the grain boundary, and the dislocation density basically remains unchanged without obvious decrease. Diffraction calibration shows a relatively pure and bright set of spots, and no accompanying second-phase diffraction spots are found, indicating that the main structure ferrite has not changed significantly. The calibration results are all ferrite with a BCC structure, and the transmission results at 610 °C are similar to those at 580 °C.

[0056] Figure 4 It is the electron backscattering diffraction (EBSD) results before tempering and after tempering at different temperatures for 12 h. a - d are grain orientation maps, and e - h are grain boundary type distribution maps. Table 1 is the statistical value of the test results. It can be seen from the test results that the grain size of the sample remains basically unchanged before and after tempering and after tempering at different temperatures and times, about 4 μm, and the proportion of large-angle grain boundaries is also basically unchanged compared with that before tempering, about 71%. The EBSD test results are consistent with the optical microstructure and scanning microstructure. Comparative statistical results show that the microstructure basically does not change before and after tempering, and still mainly consists of acicular ferrite, reaching about 90%. It can be considered that the high-temperature strength is mainly determined by acicular ferrite with very excellent high-temperature stability.

[0057] Table 1 Statistics of grain size and large and small angle grain boundaries before tempering and after tempering for 12 hours

[0058]

[0059] The yield strength of the material measured before tempering (As-received) is 503 MPa, and the tensile strength is 606 MPa. Figure 5 and Figure 6They are the tensile strength and yield strength after tempering at 580°C, 610°C, and 640°C for different times respectively. It can be seen from the figure that as the tempering time prolongs, both the tensile strength and yield strength first increase to the maximum value and then slowly decrease, and finally remain stable, without large fluctuations. After tempering at 580°C, 610°C, and 640°C for 1 hour, the tensile strength reaches the maximum level, and then decreases slightly with the prolonging of the tempering time and finally remains unchanged. At the same time, after tempering at 640°C for different times, the tensile and yield strengths are significantly higher than those at 580°C and 610°C, but there are also no large fluctuations. Combining the previous observation and analysis of the microstructure, it shows that although the matrix microstructure does not change after tempering at 640°C, a large amount of precipitates precipitate, improving the mechanical properties of the microstructure.

[0060] From the above test analysis results and analysis, it can be seen that when the material fluctuates at high temperature (600°C) and the upper and lower ranges (20 - 40°C), the yield strength is above 477 MPa, with almost no yield strength loss, and most of them even increase by dozens of MPa. The high-temperature yield strength is mostly more than 1 times the room-temperature yield strength, far exceeding the requirement of 2 / 3 for refractory steel; most of the tensile strengths not only do not decrease, but increase by dozens to hundreds of MPa.

[0061] Figure 7 It is the change diagram of V-notch impact specimens at -45°C measured before and after tempering at 580°C, 610°C, and 640°C for different times. It can be seen from the figure that as the tempering time prolongs, the low-temperature impact toughness significantly increases at 580 and 600°C, and slightly decreases at 640°C. Thus, it can be seen that the material maintains high toughness during long-term high-temperature tempering.

[0062] This is mainly because in the above material composition, there are a large number of metal elements Ti, Zr, and Mg with a large affinity for oxygen. After composite deoxidation and microalloying, a large number of non-metallic oxides with very good high-temperature stability are formed. They provide a large number of ready-made nucleation sites for the nucleation of acicular ferrite, and a main microstructure with acicular ferrite as the absolute dominant is obtained.

[0063] As is well known, like Ti, Zr and Mg are also strong oxide-forming elements. The composite deoxidation of titanium and zirconium is beneficial to the formation of uniformly distributed composite oxides. The densities of Ti2O3 and ZrO2 are 4.486 g / cm 3 and 5.68 g / cm 3 , respectively, which are greater than the density of Al2O3 (3.97 g / cm 3 ), and the density of molten steel (7.15 g / cm 3) Close, so once the oxides are formed, Ti2O3 and ZrO2 can float uniformly in the molten steel while Al2O3 will float on the surface of the molten steel and become a component of the steel slag. The electrical conductivity of the oxides is the key factor for particle movement. According to the electrical conductivities of the three oxides, it can be concluded that the driving force for the movement of Al2O3 in the molten steel is greater than that of Ti2O3 and ZrO2. During the electroslag refining process, Ti2O3 and ZrO2 particles tend to repel each other and are difficult to agglomerate, while Al2O3 is prone to form large particles and thus float to the surface of the molten steel and be absorbed by the surface covering agent. Therefore, a large number of fine titanium and zirconium composite oxide particles are uniformly distributed in the matrix of the steel.

[0064] The existence of the manganese-depleted zone can promote the formation of acicular ferrite. There are two formation mechanisms for the manganese-depleted zone. For cation vacancy oxides (Ti2O3), Mn can diffuse into the cation vacancies of Ti2O3, and a manganese-depleted zone is formed around Ti2O3 due to the decrease in Mn content. For anion vacancy oxides (ZrO2), S elements can occupy the anion vacancies, and S and Mn have a very strong affinity. By absorbing Mn around the oxides, MnS is formed to obtain the manganese-depleted zone. There are literature reports that MnS and ZrO2 have extremely similar lattice constants, and the specific data are shown in Table 2. Therefore, MnS and ZrO2 have a good lattice matching relationship, which will reduce the interfacial energy between the two. The lower interfacial energy will result in better adhesion between grains of different interfaces. This is the reason why MnS tends to form on the pre-formed ZrO2 particles, which further promotes the formation of acicular ferrite. For the anion oxide Al2O3, the formation energy of Al4O5S is too large, S cannot enter the anion vacancies of Al2O3, and the lattice constants of MnS and Al2O3 differ too much to achieve good lattice matching. Therefore, a manganese-depleted zone cannot be formed, and the formation of ferrite cannot be promoted.

[0065] Table 2 Lattice Constants of MnS and ZrO2

[0066]

[0067] Liu Qingchun et al. invented a fire-resistant steel (CN101748336A). The structure of this fire-resistant steel is mainly composed of bainite and ferrite, and the volume fractions of bainite and ferrite are 20-40% and 40-60% respectively. The component mass percentages of this fire-resistant steel are as follows: C 0.05-0.12%, Si 0.1-0.5%, Mn 0.3-1.6%, V 0.05-0.12%, Cr 0.1-0.6%, Mo 0.2-0.4%, B 0.0005-0.002%, N 0.003-0.015%, P≤0.02%, S≤0.01%, and Fe 97.0-99.1%. Obviously, there are significant differences in composition from the invention of this patent. The mechanical properties measured at room temperature of Example 1 and Example 2 (named Comparative Example 1 and Comparative Example 2 in sequence) of the patent invention of Liu Qingchun et al. were compared with the strength of the high-strength and high-toughness steel with high-temperature strength endurance of this patent invention after tempering at 580°C, 610°C, and 640°C for 10 hours (named Example 1). The results are shown in Table 2 below.

[0068] Table 3 Performance Comparison between the Invention and Comparative Invention Examples

[0069]

[0070] As can be seen from Table 3, different from conventional fire-resistant steels, the high-temperature strength endurance fire-resistant steel of this patent invention has significantly good high-temperature endurance fire-resistant performance. Even after undergoing high-temperature long-term fire-resistant treatment, its strength does not decrease but increases instead. Both the tensile strength and yield strength are basically higher than those before the fire-resistant treatment, and with the tempering temperature rising to 640°C, the increase is more obvious. This provides great guarantee for the safety of actual industrial implementation and is a creative invention with remarkable distinguishing features. In addition, its composition is simple, the amount of precious metals used is very small, the process is concise, and the material and manufacturing costs are low.

[0071] The following are the positive effects of this specific implementation manner compared with the prior art:

[0072] 1) For the invented material, when it fluctuates at high temperature (600°C) and within the upper and lower ranges (20-40°C), the yield strength is above 460 MPa. There is no yield strength loss, but instead it increases by dozens of MPa. The high-temperature yield strength is more than 1 times that of the room-temperature yield strength, far exceeding 2 / 3 of the requirements for fire-resistant steels; the tensile strength not only does not decrease, but instead increases by dozens to hundreds of MPa.

[0073] 2) After the invented material is subjected to compound deoxidation with Ti, Zr, and Mg, a large number of non-metallic oxides with very excellent high-temperature stability are formed. They provide a large number of ready-made nucleation sites for the nucleation of acicular ferrite, and a main structure with acicular ferrite as the absolute dominant is obtained.

[0074] 3) Acicular ferrite is a microstructure with excellent high-temperature stability compared to martensite, bainite, and pearlite. It can resist long-term high-temperature retention and is very suitable as the main microstructure of refractory steel. Compared with the aforementioned microstructures, its refractory performance is more superior. In addition, the precipitation of carbonitrides further strengthens the matrix, so it exhibits a higher high-temperature yield strength than at room temperature.

[0075] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-strength and high-toughness steel with high-temperature strength retention, characterized in that, Its components are by weight percentage: 0.045% ≤ C ≤ 0.049%, 0.11% ≤ Si ≤ 0.19%, 1.41% ≤ Mn ≤ 1.51%, S ≤ 0.0005%, P ≤ 0.020%, 1.1% ≤ Ni ≤ 1.3%, 0.1% ≤ Mo ≤ 0.3%, 0.02% ≤ Al ≤ 0.04%, 300×10 -4 % ≤ O ≤ 400×10 -4 %, 400×10 -4 % ≤ Zr + Ti + Mg ≤ 600×10 -4 %, and the contents of Zr, Ti, and Mg satisfy the following formula: Ti / Zr = 50 - 70, Zr / Mg = 2 - 4, and the balance is Fe.

2. A preparation method of a high-strength and high-toughness steel with excellent high-temperature strength and creep resistance according to claim 1, characterized in that, It includes the following steps: 1) Melting is carried out by using an intermediate frequency induction furnace. During the melting process, a refining agent is used for covering, and the composition of the molten steel is adjusted by metal, alloy or oxide raw materials. After the melting composition meets the requirements of the refractory steel with high temperature strength and endurance described in claim 1, it is poured into a steel billet. 2) The obtained steel billet is forged or hot-rolled and air-cooled or water-cooled to obtain the refractory steel with high temperature strength and endurance.

3. The preparation method of the high-strength and high-toughness steel with excellent high-temperature strength retention according to claim 2, characterized in that, The condition parameters for forging are: the steel billet is forged by using the open-die forging method. Before forging, the specimen is heated to 850 - 1050 °C, the forging ratio is 2.0 - 5.0, the forging time is 25 - 50 min, and the thickness of the specimen after forging is 20 - 100 mm.

4. The preparation method of the high-strength and high-toughness steel with excellent high-temperature strength retention according to claim 2, characterized in that, The condition parameters for hot rolling are: controlling the reduction per pass to be 5 - 15 mm, the reduction ratio to be 2 - 3, and air-cooling at room temperature.

5. Use of a high-strength and high-toughness steel with excellent high-temperature strength retention according to claim 1, characterized in that: It is used for preparing refractory and high-temperature aging-resistant structural materials.

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