Rare earth microalloyed plateau weather-resistant high-performance structural steel plate and preparation method thereof

Abstract

The invention belongs to the field of ferrous metallurgy, and relates to a rare earth microalloyed plateau weather-resistant high-performance structural steel plate and a preparation method thereof. The steel comprises the following components in percentage by weight: 0.03%-0.05% of C, 0.15%-0.25% of Si, 1.30%-1.60% of Mn, less than or equal to 0.013% of P, less than or equal to 0.005% of S, 0.020%-0.045% of Nb, 0.006%-0.020% of Ti, 0.5%-1.0% of Ni, 0.15%-0.20% of Cr, 0.10%-0.30% of Cu, 0.001%-0.003% of Zr, 0.001%-0.010% of RE and the balance of Fe and inevitable impurities. The preparation method comprises the steps of molten steel converter smelting, RH and LF refining, continuous casting, casting blank heating, rolling and the like. According to the high-performance structural steel plate, ReH is larger than or equal to 420 MPa, Rm is larger than or equal to 525 MPa, the ductility is larger than or equal to 30%, the yield ratio is smaller than or equal to 0.80, the longitudinal impact energy at the temperature of-60 DEG C is larger than or equal to 250 J, the comprehensive mechanical property is excellent, the relative corrosion rate is smaller than or equal to 50% compared with traditional Q355 carbon steel, and the high-performance structural steel plate has the advantages of being resistant to low-temperature freezing and thawing, resistant to corrosion and resistant to environment-sensitive fracture.

Description

Technical Field

[0001] The invention belongs to the field of iron and steel metallurgy, and relates to a rare earth micro-alloyed plateau weather-resistant high-performance structural steel plate and a preparation method thereof. Background Art

[0002] With the continuous advancement of economic development and highway construction, the demand for highway construction in plateau permafrost areas has increased year by year. Against the backdrop of global warming, the response of plateau permafrost has accelerated. In the past 20 years, the average temperature of permafrost has risen by 0.2℃ to 0.3℃, island permafrost has disappeared faster, high-temperature permafrost has degraded more, and low-temperature permafrost has warmed up significantly, resulting in a significant increase in highway engineering diseases in permafrost areas. Therefore, overcoming plateau permafrost diseases has become a problem that must be faced and solved in highway construction.

[0003] Concrete is the main material used in key projects such as highway bridges and tunnels, but the special environment of plateau permafrost areas causes concrete to undergo long freeze-thaw cycles, which induces concrete cracking and reduces its service life. Due to the excellent strength and toughness and low-temperature performance of low-alloy steel, steel structure bridges are an ideal choice to replace steel-concrete structure bridges in plateau permafrost environments. However, due to the annual increase in permafrost temperature, in relatively high temperature and high ice content permafrost areas, structural steel not only faces low temperature environments, but also undergoes soil freeze-thaw and electrochemical corrosion processes. It is very easy to fail due to environmentally sensitive fractures (low-temperature brittle fractures, corrosion fatigue) under the coupling of low temperature, mechanics and electrochemistry, threatening the service safety of bridges.

[0004] Therefore, there is an urgent need to develop low-alloy steels that are resistant to low-temperature freeze-thaw, corrosion, and environmentally sensitive fracture to meet the needs of the plateau permafrost service environment. Summary of the invention

[0005] In view of the development status of the existing technology, the purpose of the present invention is to provide a rare earth micro-alloyed high-altitude weather-resistant high-performance structural steel plate and a preparation method thereof, which can achieve a yield strength ≥420MPa, a tensile strength ≥525MPa, an elongation ≥30%, an impact energy of -60℃ ≥250J, a yield strength ratio ≤0.8, and a relative corrosion rate of ≤50% compared to traditional Q355 carbon steel, and has good freeze-thaw resistance.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A rare earth microalloyed plateau weather-resistant high-performance structural steel plate, comprising the following components by weight percentage:

[0008] C: 0.03% ~ 0.05%, Si: 0.15% ~ 0.25%, Mn: 1.30% ~ 1.60%, P ≤ 0.013%, S ≤ 0.005%, Nb: 0.020% ~ 0.045%, Ti: 0.006% ~ 0.020%, Ni: 0.5% ~ 1.0%, Cr: 0.15% ~ 0.20%, Cu: 0.10% ~ 0.30%, Zr: 0.001% ~ 0.003%, RE (rare earth): 0.001% ~ 0.010%, and the rest are Fe and unavoidable impurities.

[0009] The present invention optimizes the chemical composition of the steel:

[0010] Carbon (C): Carbon is one of the most important alloying elements in steel. It has a direct impact on the hardness and strength of steel. As the carbon content increases, the hardness and strength of the steel will increase, but the plasticity and toughness will decrease. When the carbon content exceeds 0.23%, the welding performance of the steel deteriorates, so the carbon content of low-alloy structural steel used for welding generally does not exceed 0.20%. High carbon content will also reduce the steel's resistance to atmospheric corrosion and increase the steel's cold brittleness and aging sensitivity. Considering the strength and toughness factors required for the steel plate, the present invention sets the carbon content in the steel to be controlled at 0.03% to 0.05%.

[0011] Silicon (Si): Silicon is mainly used as a deoxidizer in steel. It can dissolve in ferrite and austenite to improve the hardness and strength of steel. Its effect is second only to phosphorus and is stronger than elements such as manganese, nickel, chromium, tungsten, molybdenum, and vanadium. When the silicon content is too high, such as more than 3%, the plasticity and toughness of the steel will be significantly reduced. Silicon can reduce the welding performance of steel. Because silicon has a stronger ability to combine with oxygen than iron, low-melting-point silicates are easily generated during welding, which increases the fluidity of slag and molten metal, causes splashing, and affects the welding quality. The silicon content of the present invention is designed to be 0.15% to 0.25%.

[0012] Manganese (Mn): Manganese is a good deoxidizer and desulfurizer. Steel generally contains a certain amount of manganese, which can eliminate or weaken the hot brittleness of steel caused by sulfur, thereby improving the hot processing performance of steel. The solid solution formed by manganese and iron can improve the hardness and strength of ferrite and austenite in steel; at the same time, it is also a carbide-forming element, entering the cementite to replace a part of the iron atoms. Manganese in steel reduces the critical transformation temperature, plays a role in refining pearlite, and indirectly plays a role in improving the strength of pearlite steel. The manganese content of the present invention is 1.30% to 1.60%.

[0013] Phosphorus (P): It is generally considered a harmful element because it can form a brittle phase at the grain boundary of steel, which can significantly reduce the toughness of steel, especially at low temperatures. Phosphorus is sometimes also used to improve the strength and weather resistance of steel. The present invention controls P≤0.013%.

[0014] Sulfur (S): Sulfur is generally regarded as a harmful element in steel because it can form brittle sulfide inclusions, resulting in a decrease in the hot working properties of steel. The present invention controls S to ≤ 0.005%.

[0015] Niobium (Nb): Niobium has a solid solution strengthening effect. A trace amount of niobium can improve the strength of steel without affecting the plasticity or toughness of steel. Because it has the effect of refining grains, it can improve the impact toughness of steel and reduce its brittle transition temperature, which is beneficial to welding performance. When the content is greater than 8 times that of carbon, it can almost fix all the carbon in the steel, making the steel have good hydrogen resistance. In austenitic steel, it can prevent intergranular corrosion of steel by oxidizing media. The niobium content of the present invention is 0.020% to 0.045%.

[0016] Titanium (Ti): Titanium has a strong affinity with nitrogen, oxygen, and carbon, and its affinity with sulfur is stronger than that of iron. Therefore, titanium is a good deoxidizing and degassing agent and an effective element for fixing nitrogen and carbon. Although titanium is a strong carbide-forming element, it does not form a composite compound with other elements. Titanium carbide is stable and not easy to decompose. It can only be slowly dissolved into a solid solution in steel when heated to above 1000°C. Before being dissolved, titanium carbide particles have the effect of preventing grain growth, thereby refining the grains and improving the low-temperature toughness of the steel plate. At the same time, elements such as Ti and N can precipitate near the welding molten pool and the heat-affected zone to form a fine and dispersed nitride second phase, which can effectively promote the nucleation and growth of intracrystalline ferrite, inhibit the growth of original austenite grains, and thus significantly improve the performance of the heat-affected zone of steel plate welding. The titanium content in the present invention is 0.006% to 0.020%.

[0017] Nickel (Ni): Nickel can be dissolved in the iron lattice to form a solid solution strengthening effect, thereby increasing the strength of steel without significantly reducing its toughness. Nickel can reduce the low-temperature brittle transition temperature of steel, allowing the steel to maintain good toughness in a low-temperature environment. Nickel can improve the corrosion resistance of steel, especially in acidic and alkaline environments. Nickel can increase the resistance of steel to fatigue and reduce the sensitivity of steel to notches. The nickel content in the present invention is 0.5% to 1.0%.

[0018] Chromium (Cr): Chromium can increase the strength and hardness of steel, but at the same time it may reduce plasticity and toughness. This is because chromium can be dissolved in the iron lattice to form a solid solution strengthening effect, thereby improving the mechanical properties of steel. The presence of chromium helps to reduce cracks generated during welding and improve the quality of welds. Chromium can also form alloy carbides with carbon, which have high hardness and wear resistance, and can further enhance the surface properties of steel. Chromium can increase the hardenability of steel, and when the content exceeds a certain proportion, it can give steel good corrosion resistance. The Cr content in the present invention is 0.15% to 0.20%.

[0019] Copper (Cu): Copper can improve the atmospheric corrosion resistance of steel, especially in a humid environment, copper helps to form a protective layer and slow down the corrosion rate of steel. The addition of an appropriate amount of copper can improve the strength of steel, and can also increase the plasticity and ductility of steel, making it easier to process and shape. Excessive copper may cause hot brittleness problems, that is, cracks appear during forging, rolling and other processing at high temperatures. In addition, the presence of copper may affect the welding performance of steel. Therefore, the copper content in the present invention is 0.10% to 0.30%.

[0020] Zirconium (Zr): Zirconium is a strong carbide-forming element, a strong deoxidizing element and a composite oxysulfide-forming element. Adding a small amount of zirconium has the functions of degassing, purifying and refining grains, which is beneficial to improving the low-temperature performance of low-alloy high-strength steel, improving the stamping performance, and significantly improving the hardenability of steel when dissolved in austenite. The Zr content in the present invention is 0.001% to 0.003%.

[0021] Rare earth (RE): The role of rare earth in steel: (1) Purify molten steel. Rare earth elements can react with oxygen and sulfur in steel to form stable oxides and sulfides, thereby reducing the oxygen and sulfur content in the molten steel and improving the purity of the steel. This reduces the number of non-metallic inclusions and improves the mechanical properties of the steel. (2) Improve the morphology of inclusions. Rare earth elements can react with sulfur and oxygen in steel to form spherical or chain-shaped rare earth sulfides or sulfur oxides, replacing the original long strip-shaped manganese sulfide inclusions. The morphology of these new inclusions is more conducive to the toughness of steel and reduces the risk of brittle fracture. (3) Microalloying effect. Rare earth elements interact with iron atoms in molten steel. Due to the large radius of rare earth atoms, they can strengthen the solid solution, thereby improving the strength of steel. (4) In addition to the above effects, rare earth elements can also improve the corrosion resistance of steel. For example, the corrosion resistance of rare earth low alloy steel is nearly 10 times higher than that of ordinary steel. However, when the rare earth content exceeds the critical content, the rare earth will be concentrated at the grain boundary, destroying the pearlite orientation relationship, resulting in an increase in the pearlite interlamellar spacing and a decrease in impact toughness. Therefore, the mass percentage of the rare earth in the present invention is 0.001% to 0.010%.

[0022] Preferably, 0.008%≤Zr+Ti+RE≤0.030%.

[0023] A method for preparing a rare earth microalloyed plateau weather-resistant high-performance structural steel plate, comprising molten steel converter smelting → LF+RH refining → continuous casting → heating of the ingot → rolling, and the specific steps are:

[0024] (1) Converter smelting

[0025] Use low sulfur and low phosphorus hot metal, with S≤0.010%, P≤0.013%, and S≤0.005% after KR treatment. Strictly control the loading amount, and do not add pig iron. Use low carbon and low phosphorus silicon manganese, metal manganese, nickel plate, low carbon ferrochrome, ferroniobium, and silicon zirconium alloy for alloying. Add the alloy when 1 / 4 of the steel is put in, and add it when 3 / 4 is finished. Add the alloy to the impact zone of the steel flow. Use aluminum manganese iron for deoxidation, and the amount of aluminum manganese iron added is 2.0-3.5kg / t steel.

[0026] The low-carbon and low-phosphorus silicon manganese has main element contents of 0.15% to 0.17% carbon, ≤0.028% phosphorus, 68.10% to 69.7% manganese and 15.65% to 17.19% silicon.

[0027] The main element content of the metal manganese is 96.80-97.50%.

[0028] The main element content of the nickel plate is Ni+Co≥99.9%, wherein Co≤0.08%.

[0029] The main element contents of the low-carbon ferrochromium alloy are 0.18% to 0.21% carbon and 58.30% to 58.80% chromium.

[0030] The main element content of the niobium-iron alloy is 64.25% to 66.75% of niobium.

[0031] The silicon-zirconium alloy is Si 50 Zr 35 , that is, the silicon content is 46.83%~49.63%, the Zr content is 34.85%~35.10%, and the rest are unavoidable impurities.

[0032] (2) LF refining operation

[0033] The whole process is bottom blown with argon for stirring. The argon pressure and flow rate are suitable for slightly turning the slag surface without exposing the molten steel. The argon pressure can be appropriately increased according to the situation in the early stage. A small pressure weak blow is used before leaving the station to ensure that the inclusions float up and the refining soft blowing argon is ≥5min. The "high-low-low-high" method is adopted during heating, that is, high voltage, low current long arc operation is adopted at the beginning of power-on, and low voltage, high current submerged arc operation is adopted after the slag is well melted. Aluminum particles and calcium carbide are used for slag adjustment during refining, and titanium wire is used to adjust the Ti composition. After the fine-tuning of the composition is completed, the block rare earth alloy is added, and argon is blown to make the rare earth fully melted and evenly distributed and meet RE / (O+S)>0.8, O≤0.01%, S≤0.005%, so as to obtain fine rare earth inclusions. Refining time ≥45min (including soft blowing), soft blowing time ≥10min.

[0034] The aluminum slag is a deoxidation accelerator, and its main elements are 51% to 55% of Al2O3, 12% to 15% of Al, 5% to 7% of SiO2, 8% to 10% of CaO, 4% to 6% of MgO, and the rest are H2O and inevitable impurities.

[0035] The rare earth alloy comprises lanthanum and cerium, wherein the weight percentage of lanthanum and cerium is La:Ce=70:30-60:40, the melting point of La is 920°C, the melting point of Ce is 804°C, and the temperature after fine-tuning the composition is 1400-1600°C, at which time the rare earth alloy can be fully melted.

[0036] (3) RH refining operation

[0037] The main purpose of RH refining is to conduct vacuum degassing, reduce the gas content in steel, reduce the defects caused by gas inside the steel plate, and improve the purity, alloying and homogenization of molten steel. RH refining adopts this treatment mode, the vacuum degree is maintained within 50Pa for more than 15 minutes, the pure degassing time is not less than 5 minutes, and the soft blowing of argon gas is more than 10 minutes to achieve the purpose of degassing, promoting the floating of inclusions and uniform molten steel temperature. After the treatment, feed 100-150m of nano high calcium wire, and the RH smelting cycle is controlled at 40-60 minutes.

[0038] The present treatment mentioned here refers to vacuum circulation degassing treatment, the main purpose of which is dehydrogenation and denitrification to ensure that H≤0.0002% and N≤0.006%.

[0039] The nano high calcium wire is a high calcium wire with a diameter of 9.0-10 mm, coated with a nano layer with a weight of not less than 2 g / m. The high calcium wire is a wire with a calcium core covered with an iron sheet, wherein the calcium content is ≥98%, the calcium core weight is ≥42 g / m, and the core-iron ratio is ≥0.17. Adding nano high calcium wire can remove aluminum oxide inclusions, which is conducive to the floating of inclusions and improves the fluidity of molten steel.

[0040] (4) Continuous casting operation

[0041] The continuous casting process mainly reduces the degree of central segregation of the ingot by controlling the casting superheat, and reduces or avoids surface cracks of the ingot by reasonable control of cooling water and straightening temperature, thereby improving the surface quality of the ingot and providing a strong guarantee for the quality of the final product. During continuous casting, in order to prevent rare earth inclusions from clogging the water inlet, pulse current, i.e. electromagnetic stirring, is added to the crystallizer to fully float the inclusions.

[0042] The casting superheat refers to the value of the molten steel exceeding its solidification temperature during the casting process. Preferably, the superheat is ≤20°C.

[0043] The electromagnetic stirring is a metallurgical technology that uses the magnetic field generated by electric current to stir the metal liquid. Its advantages are: ① By adjusting the current, the stirring intensity can be accurately controlled to achieve effective control of melt temperature, composition and other parameters; ② It can make the flow inside the molten metal more uniform, which helps to improve the uniformity of the alloy composition and thus improve the quality of the casting; ③ Because it does not require physical contact, it can avoid the contamination of the molten metal caused by traditional mechanical stirrers.

[0044] The continuous casting process adopts full-process protection pouring, that is, the ladle to the tundish adopts a long nozzle and argon sealing protection; the tundish is covered with a covering agent combined with carbonized rice husk to ensure good liquid surface coverage, isolate the molten steel from the air, avoid secondary oxidation, and control the liquid level of the tundish. The liquid level height is not less than 600mm when pouring, and the liquid level height during normal pouring is between 800 and 1000mm. Low liquid level pouring is strictly prohibited to prevent slag rolling; the tundish to the crystallizer adopts an immersed nozzle and argon sealing protection. The argon flow rate during the argon sealing protection is 70 to 100L / min.

[0045] In the continuous casting step, the pulling speed is very important and directly affects the quality and production efficiency of the billet. The influence of too fast pulling speed: ① It may lead to poor solidification in the center area of ​​the billet, resulting in central segregation. ② It may cause increased stress inside the billet, especially in the center area, resulting in the generation of central cracks. ③ The surface of the billet may not be cooled sufficiently in the crystallizer, resulting in surface cracks due to excessive temperature gradient after being pulled out. ④ The residence time of the molten metal in the crystallizer is short, and the inclusions have no time to float up and be removed, resulting in an increase in the number of inclusions in the billet, affecting the purity of the billet. The influence of too slow pulling speed: ① The solidification time in the center area of ​​the billet may be too long, resulting in central looseness. ② The long solidification process is likely to cause uneven distribution of chemical composition, resulting in central segregation. ③ The long solidification process makes it difficult for inclusions to float up and be removed, which may cause inclusions to accumulate inside the billet.

[0046] The pulling speed refers to the speed at which the billet is pulled out of the crystallizer. Preferably, for a 175 mm cross section, the pulling speed during continuous casting is 1.25 to 1.35 m / min; for a 200 mm cross section, the pulling speed during continuous casting is 1.3 to 1.4 m / min; for a 250 mm cross section, the pulling speed during continuous casting is 1.1 to 1.3 m / min; for a 300 mm cross section, the pulling speed during continuous casting is 0.8 to 0.9 m / min.

[0047] In the continuous casting step, the crystallizer uses special protective slag, and the crystallizer vibration adopts a non-sinusoidal vibration mode. The crystallizer vibration can ensure that the slab and the crystallizer wall do not stick together during the casting process and obtain good surface quality of the cast billet.

[0048] (5) Billet heating system

[0049] Furnace charging method: cold charging. The specific requirements of the heating system for the slab entering the furnace are shown in Table 1.

[0050] Table 1 Slab heating process

[0051]

[0052] In the above heating process, the preferred soaking zone temperature is 1180-1250°C, the tapping temperature is 1180-1230°C, and the heating rate is 10°C / min / cm.

[0053] (6) Rolling system

[0054] The present invention adopts TMCP process for rolling. TMCP (Thermomechanical Control Process), that is, thermomechanical control process, is an advanced steel manufacturing technology that combines controlled rolling (Controlled Rolling) and controlled cooling (Controlled Cooling). In order to fully refine the original austenite grains and allow the grains with the largest deformation to penetrate into the core of the continuous casting billet to change the structure of the core of the billet, the rough rolling stage should increase the pass reduction as much as possible and reduce the deformation pass. Under the condition that the equipment parameters allow, the rough rolling stage adopts a high-temperature and large-reduction mode to shorten the billet waiting time, at least ensure that the single-pass reduction rate is greater than 18%, and the final pass reduction rate is ≥25%, and is controlled within 3 to 5 passes.

[0055] The number of rolling passes in the finishing rolling stage is controlled at 7 to 9 passes, and the reduction in a single pass is ≥8%. In the early stage of finishing rolling, the austenite structure can be refined by recrystallization rolling of the austenite in the critical temperature range; in the later stage of finishing rolling, the deformation is increased to increase the strain accumulation of the deformed austenite, increase the distortion energy, provide more nucleation sites for the organizational transformation, obtain a fine organizational morphology, and give full play to the fine grain strengthening effect.

[0056] The TMCP process of steel plates is shown in Table 2.

[0057] Table 2 Steel plate rolling process

[0058]

[0059] The mechanical properties of the steel plate are: R eH ≥420MPa, R m ≥525MPa, elongation ≥30%, yield strength ratio ≤0.80, -60℃ longitudinal impact energy ≥250J, excellent comprehensive mechanical properties, relative corrosion rate ≤50% compared with traditional Q355 carbon steel.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) In view of the failure forms and mechanisms of structural steel in plateau permafrost environments, reverse design is carried out to establish an integrated design criterion for component organization and structure oriented towards service performance, and breakthroughs are made in purification and homogenization preparation technologies.

[0062] (2) Based on Zr-Ti-RE composite deoxidation and microalloying, deep deoxidation, inclusion modification and dispersion distribution, rare earth microalloying and other effects of freeze-thaw resistant steel are achieved. Combined with the matching controlled rolling and controlled cooling (TMCP) process flow, breakthroughs are made in the coordinated regulation technology of the composition and structure of freeze-thaw resistant steel, thus achieving controllable preparation of freeze-thaw resistant steel.

[0063] (3) The indicators of prototype steel are: R eH ≥420MPa, R m ≥525MPa, elongation ≥30%, yield strength ratio ≤0.80, -60℃ longitudinal impact energy ≥250J, excellent comprehensive mechanical properties, relative corrosion rate ≤50% compared with traditional Q355 carbon steel.

[0064] (4) Through the implementation of the present invention, considerable social and economic benefits will be created for the national economic growth. It has positive significance and demonstration effect in reducing the diseases of plateau frozen soil roads, avoiding frozen soil degradation, protecting ecological balance, accelerating the economic development of the western region, and promoting the construction and development of frozen soil roads in the world. It will accelerate the new practice of frozen soil road projects and make important contributions to speeding up the solution of world problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is the metallographic structure diagram of rare earth microalloyed plateau weather-resistant high-performance structural steel plate;

[0066] Figure 2 This is a scanning electron micrograph of the rare earth microalloyed plateau weather-resistant high-performance structural steel plate;

[0067] Figure 3 It is the grain boundary distribution map of rare earth microalloyed plateau weather-resistant high-performance structural steel plate;

[0068] Figure 4 It is the IPF grain orientation diagram of rare earth micro-alloyed plateau weather-resistant high-performance structural steel plate. DETAILED DESCRIPTION

[0069] In order to highlight the purpose, technical solutions and advantages of the present invention, the present invention is further described below in conjunction with embodiments, which are described by way of explanation of the present invention but not limiting the present invention. The technical solution of the present invention is not limited to the specific implementation methods listed below, but also includes any combination of the specific implementation methods.

[0070] Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes. Unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0071] Example 1

[0072] The production process of Example 1 of the present invention is: molten steel converter smelting → RH+LF refining → continuous casting → heating of ingot → rolling. The smelting components of Example 1 are shown in Table 3, and each component is within the design range of the present invention.

[0073] Table 3 Melting composition of Example 1

[0074]

[0075] The steel billet rolling process of Example 1 is shown in Table 4, and the rolling processes of steel plates of various specifications are in line with the design scope of the present invention.

[0076] Table 4 Example 1 Billet rolling process

[0077]

[0078]

[0079] Example 1 The mechanical properties of the steel plates after rolling are shown in Table 5. The R eH ≥420MPa, R m ≥525MPa, yield strength ratio ≤0.8, -60℃ average longitudinal impact energy ≥250J (8mm adopts proportional sample).

[0080] Table 5 Mechanical properties of steel plate in Example 1

[0081]

[0082] The microstructure of the steel plate was analyzed. Figure 1-4 As shown, Figure 1 The steel plate is mainly composed of ferrite and pearlite. Figure 2 The grain size of the steel sheet is shown to be about 10 μm. Figure 3 It shows that the grain size of the steel plate is small. Figure 4 It shows that the grain orientation of the steel plate is evenly distributed, which provides a favorable guarantee for obtaining good comprehensive mechanical properties.

[0083] Example 2

[0084] The production process of Example 2 of the present invention is: molten steel converter smelting → RH+LF refining → continuous casting → heating of ingot → rolling. The smelting components of Example 2 are shown in Table 6, and each component is within the design range of the present invention.

[0085] Table 6 Melting composition of Example 2

[0086]

[0087] The steel billet rolling process of Example 2 is shown in Table 7, and the processes for steel plates of various specifications are all within the design scope of the present invention.

[0088] Table 7 Example 2 Billet Rolling Process

[0089]

[0090] The mechanical properties of the steel plates after rolling in Example 2 are shown in Table 8. The ReH of the steel plates of various specifications is ≥420MPa, Rm ≥525MPa, the yield strength ratio is ≤0.8, and the average longitudinal impact energy at -60°C is ≥250J.

[0091] Table 8 Mechanical properties of steel plate in Example 2

[0092]

[0093] Example 1 and Example 2 were selected to conduct salt spray tests for 7 days, 14 days, 21 days, and 28 days, and compared with traditional Q355 carbon steel. The results are shown in Table 9. As can be seen from the table, compared with the traditional Q355 carbon steel, the relative corrosion rate is ≤50%. The elements such as Cu, Cr, and rare earth added in the present invention play a role in corrosion resistance.

[0094] The concentration of the NaCl solution used in the salt spray test is 50 g / L, the pH is between 6.5 and 7.2, and the test temperature is 35±2°C.

[0095] Table 9 Corrosion rate results

[0096]

[0097] The process parameters (such as temperature, time, etc.) of the present invention can realize the method by taking upper and lower limits and interval values, and the embodiments are not listed one by one here.

[0098] Any contents not described in detail in the present invention can be based on the conventional technical knowledge in the art.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A rare earth microalloyed plateau weather-resistant high-performance structural steel plate, characterized in that: In terms of weight percentage, high performance structural steel plates include the following components: C: 0.03% ~ 0.05%, Si: 0.15% ~ 0.25%, Mn: 1.30% ~ 1.60%, P ≤ 0.013%, S ≤ 0.005%, Nb: 0.020% ~ 0.045%, Ti: 0.006% ~ 0.020%, Ni: 0.5% ~ 1.0%, Cr: 0.15% ~ 0.20%, Cu: 0.10% ~ 0.30%, Zr: 0.001% ~ 0.003%, RE: 0.001% ~ 0.010%, the rest are Fe and unavoidable impurities.

2. The rare earth microalloyed plateau weather-resistant high-performance structural steel plate according to claim 1, characterized in that: 0.008%≤Zr+Ti+RE≤0.030%.

3. The rare earth microalloyed plateau weather-resistant high-performance structural steel plate according to claim 1, characterized in that: The steel plate has ReH≥420MPa, Rm≥525MPa, elongation≥30%, yield strength ratio≤0.80, longitudinal impact energy at -60°C≥250J, and a relative corrosion rate of ≤50% compared to traditional Q355 carbon steel.

4. The rare earth microalloyed plateau weather-resistant high-performance structural steel plate according to claim 1, characterized in that: The metallographic structure of high performance structural steel plate is mainly ferrite and pearlite.

5. A method for preparing a rare earth microalloyed plateau weather-resistant high-performance structural steel plate, the method comprising the following steps: (1) Converter smelting Use low-sulfur and low-phosphorus molten iron, with S≤0.010% and P≤0.013%. After KR treatment, the S of the molten iron is ≤0.005%. Strictly control the loading amount and do not add pig iron. Use low-carbon and low-phosphorus silicon-manganese, metallic manganese, nickel plate, low-carbon ferrochrome, ferroniobium and silicon-zirconium alloy for alloying. The alloy is added when 1 / 4 of the steel is put in and is finished when 3 / 4 is put in. The alloy is added to the impact zone of the steel flow. Use aluminum-manganese-iron deoxidation, and the amount of aluminum-manganese-iron added is 2.0-3.5kg / t steel. (2) LF refining operation Blow argon and stir at the bottom throughout the whole process. The argon pressure and flow rate should be such that the slag surface is slightly turned over without exposing the molten steel. The argon pressure can be appropriately increased according to the situation in the early stage. Weak blowing with low pressure is adopted before leaving the station to ensure that the inclusions float up and the refining soft blowing argon is ≥5min. The "high-low-low-high" method is adopted during heating, that is, high voltage, low current and long arc operation is adopted at the beginning of power-on, and low voltage and high current submerged arc operation is adopted after the slag is well melted. Aluminum particles and calcium carbide are used for slag adjustment in refining, and titanium wire is used to adjust the Ti composition. After the fine adjustment of the composition, block rare earth alloy is added, and argon is blown to make the rare earth fully melted and evenly distributed and meet RE / (O+S)>0.8, O≤0.01%, S≤0.005%, so as to obtain fine rare earth inclusions. The refining time including soft blowing is ≥45min, and the soft blowing time is ≥10min. (3) RH refining operation RH refining adopts this treatment mode, the vacuum degree is maintained within 50Pa for more than 15min, the pure degassing time is not less than 5min, and the soft blowing of argon gas is more than 10min to achieve the purpose of degassing, promoting the floating of inclusions and uniforming the temperature of molten steel. After the treatment, feed 100-150m of nano high calcium wire, and the RH smelting cycle is controlled at 40-60min; (4) Continuous casting operation The continuous casting process adopts full-process protection pouring; during continuous casting, in order to prevent rare earth inclusions from clogging the water inlet, pulse current, i.e. electromagnetic stirring, is added to the crystallizer to make the inclusions fully float, and the superheat is ≤20°C; for a 175mm section, the pulling speed during continuous casting is 1.25-1.35m / min; for a 200mm section, the pulling speed during continuous casting is 1.3-1.4m / min; for a 250mm section, the pulling speed during continuous casting is 1.1-1.3m / min; for a 300mm section, the pulling speed during continuous casting is 0.8-0.9m / min; (5) Billet heating system Charging method: cold charging is adopted, and the heating system of the slab entering the furnace is as follows: the finished product thickness specification is 8-40mm, the soaking section temperature is 1170-1260℃, the steel tapping temperature range is 1180-1250℃, the heating rate is 9-10min / cm, and the soaking time is ≥30min; (6) Rolling system The rolling process adopts the TMCP process; the high temperature and large reduction mode is adopted in the rough rolling stage to shorten the waiting time of the steel billet, and at least ensure that the single-pass reduction rate is greater than 18%, the final pass reduction rate is ≥25%, and is controlled within 3 to 5 passes. The rolling passes in the finishing rolling stage are controlled within 7 to 9 passes, and the single-pass reduction is ≥8%.

6. The preparation method according to claim 5, characterized in that: In step (1), the silicon-zirconium alloy is Si 50 Zr 35， That is, the silicon content is 46.83% to 49.63%, the Zr content is 34.85% to 35.10%, and the rest are unavoidable impurities.

7. The preparation method according to claim 5, characterized in that: In step (2), the rare earth alloy includes lanthanum and cerium, wherein the weight percentage of lanthanum and cerium is La:Ce=70:30-60:40, the melting point of La is 920°C, the melting point of Ce is 804°C, and the temperature after fine-tuning the composition is 1400-1600°C.

8. The preparation method according to claim 5, characterized in that: In step (3), the present treatment mode refers to vacuum circulation degassing treatment, the main purpose of which is dehydrogenation and denitrification to ensure that H ≤ 0.0002% and N ≤ 0.006%.

9. The preparation method according to claim 5, characterized in that: In step (4), in the continuous casting step, the crystallizer uses special protective slag, and the crystallizer vibration uses a non-sinusoidal vibration mode. The crystallizer vibration can ensure that the slab and the crystallizer wall do not stick together during the casting process and obtain good surface quality of the cast billet.

10. The preparation method according to claim 5, characterized in that: In step (6), the final rolling temperature is ≥820°C, the final cooling temperature is 590-620°C, and the cooling rate is 12-18°C / s.

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