A 690MPa grade low temperature corrosion resistant steel for frozen soil highway and its preparation method

Abstract

The present invention relates to a 690MPa grade low temperature corrosion resistant steel for frozen soil roads, which belongs to the technical field of corrosion resistant steel and solves the problem that high strength steel in the prior art cannot meet the low cost and high performance requirements of high strength frozen soil road steel. The low temperature corrosion resistant steel comprises: C: 0.05-0.12%, Si: 0.30-0.50%, Mn: 1.50-1.80%, P: 0.002-0.02%, S: ≤0.005%, Cu: 0.05-0.55%, Cr: 0.1-0.8%, Ni: 0.5-3.0%, V: 0.02-0.08%, Nb: 0.010-0.02%, N: 0.003-0.020%, Al≥0.015%, La+Ce≤0.05%, and the balance is Fe and unavoidable impurities. The 690MPa grade low temperature corrosion resistant steel for frozen soil roads of the present invention is suitable for high strength frozen soil road steel.

Description

Technical Field

[0001] The present invention relates to the technical field of corrosion-resistant steel, and in particular to a 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof. Background Art

[0002] During the construction of frozen soil highways, due to the problems of frozen soil thawing, low temperature, corrosion resistance, and service life, frozen soil highway steel is not only required to have high strength, but also has higher and higher requirements for plasticity, low temperature toughness, corrosion resistance, and welding performance. At present, researchers are studying and tackling key issues in the brittle transition temperature, corrosion resistance service life, economical preparation process, and high-rigidity highway steel structure of frozen soil highway steel.

[0003] At present, the main grades used in frozen soil roads are 420 and 460 MPa. In order to further improve the freeze-thaw resistance of frozen soil roads, 690 MPa low-temperature corrosion-resistant steel is usually used in the main load-bearing positions. However, the existing 690 MPa corrosion-resistant steel cannot have low-temperature toughness, corrosion resistance, shear resistance and low cost. For example, the existing Q690E, the -45℃ A KV2 It is 80 J, and its low-temperature toughness is poor, which cannot meet the user's requirements for low-temperature performance ≥150J; the existing high-nickel corrosion-resistant steel (nickel weight percentage is 5%), although it has high low-temperature toughness, its corrosion resistance and mechanical properties are not well matched, and the cost is very high.

[0004] The existing 690 MPa grade corrosion-resistant steel mainly has the following problems:

[0005] (1) Due to the strict requirements for high-strength steel for frozen soil roads, there are few high-strength steels that have both corrosion resistance and low-temperature performance, and the alloy cost is high, which is not conducive to large-scale promotion and application; (2) Due to the temperature difference between the center and the surface and element segregation, the uniformity and stability of mechanical properties, welding properties, corrosion resistance, and low-temperature impact performance need to be improved; (3) The environment of high-strength steel for frozen soil roads involves -45℃~-50℃, while the standard E-grade plate (-40℃) only stipulates -40℃A KV2 ≥47J, which cannot meet actual needs. The cost of using standard medium F grade plate (-60℃) is too high and the manufacturing process is complicated. The production of steel with good low-temperature toughness is difficult. Summary of the invention

[0006] In view of the above analysis, the embodiments of the present invention aim to provide a 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof, so as to solve the problem that existing high-strength steel is not suitable for high-strength frozen soil road steel.

[0007] On the one hand, an embodiment of the present invention provides a 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads, and the chemical composition of the 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads includes, by weight percentage: C: 0.05-0.12%, Si: 0.30-0.50%, Mn: 1.50-1.80%, P: 0.002-0.02%, S: ≤0.005%, Cu: 0.05-0.55%, Cr: 0.1-0.8%, Ni: 0.5-3.0%, V: 0.02-0.08%, Nb: 0.010-0.02%, N: 0.003-0.020%, Al≥0.015%, La+Ce≤0.05%, and the remainder is Fe and unavoidable impurities; wherein the atomic ratio of nitrogen to vanadium is 0.5-0.9.

[0008] Preferably, the hot-rolled microstructure of the 690 MPa grade low-temperature corrosion-resistant steel for frozen soil roads is one of a mixed structure of bainite and 5-30% lath martensite, entirely acicular ferrite, and entirely lath bainite.

[0009] On the other hand, the present invention also provides a method for preparing the above-mentioned 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads, the preparation method comprising:

[0010] Step (1): smelting and continuous casting to obtain continuous casting billet.

[0011] Step (2): performing a uniform heat treatment on the continuous casting billet.

[0012] Step (3): rolling the continuous casting billet, wherein the rolling process includes rough rolling and finish rolling.

[0013] Step (4): After rolling to the target thickness, the continuous casting billet is subjected to laminar cooling, wherein the laminar cooling method is a method of coupling uniform cooling and differentiated shielding.

[0014] Step (5): coiling.

[0015] Preferably, the coupling manner of uniform cooling and differentiated shielding includes: in the first 1 / 3 section of the total cooling line length, 5-10% of the width are respectively shielded on both sides of the continuous casting billet, and only the area located in the middle of the continuous casting billet and 80-90% of the width is spray cooled; in the second 1 / 3 section of the total cooling line length, 10-20% of the width are respectively shielded on both sides of the continuous casting billet, and only the area located in the middle of the continuous casting billet and 60-80% of the width is spray cooled; in the third 1 / 3 section of the total cooling line length, 20-30% of the width are respectively shielded on both sides of the continuous casting billet, and only the area located in the middle of the continuous casting billet and 40-60% of the width is spray cooled.

[0016] Preferably, in the first 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water streams is 100-400mm; in the second 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water streams is 500-800mm; in the third 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water streams is 900-1200mm.

[0017] Preferably, the cooling rate of the laminar cooling is 30-50° C. / s.

[0018] Preferably, in step (2), the temperature of the heat treatment is 1130-1200°C.

[0019] Preferably, in step (3), the starting rolling temperature of the rough rolling is 1050-1180°C, and the deformation amount of the first pass is greater than 40%.

[0020] Preferably, in step (3), the finish rolling adopts low-temperature rolling in the non-recrystallization zone, and the cumulative deformation of 7 passes is greater than 30%.

[0021] Preferably, in step (5), the coiling temperature is 430-600°C.

[0022] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0023] 1. The 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention contains Nb, V, and N at the same time, and the nitrogen-vanadium atomic ratio is 0.5-0.9 (the nitrogen-vanadium atomic ratio of conventional steel is <0.5). The composite addition can obtain fine Nb (N, C) + V (N, C) composite precipitates, which is beneficial to the improvement of low-temperature toughness; the high manganese-sulfur ratio Mn: S ≥ 300 (Mn: 1.50-1.80%, S: ≤ 0.005%) is beneficial to the uniformity of microstructure and performance, and can reduce the influence of sulfur on RE elements; considering the addition of La+Ce+Al at the same time under low oxygen, low sulfur and phosphorus conditions, and without adding Ti, fine oxides can be obtained within a suitable temperature range, and at the same time, fine oxides + carbides + sulfides can be obtained with low carbon. Composite precipitates , reducing large inclusions, which is beneficial to the refinement of grains and the substantial improvement of low-temperature toughness, and has excellent welding performance; adding La+Ce+Ni+Cr+Cu+Al at the same time under low sulfur and phosphorus conditions, combined with the iron oxide scale structure control process, is different from the conventional reliance on Ni+Cr+Cu or Ni+Cr+Cu+P single iron oxide scale structure to improve corrosion resistance. The present invention can obtain a dense iron oxide (Ni+Cr+Cu) + rare earth element oxide + passivated oxide film on the surface while increasing the matrix potential and reducing the internal potential difference, effectively improving the corrosion resistance, especially the corrosion in saline-alkali, salt, atmospheric and other environments under freeze-thaw conditions; high Ni, low Cu, high Al, high N combined with the addition of Nb+V is beneficial to the improvement of surface quality and the improvement of comprehensive mechanical properties.

[0024] 2. The 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention has a low alloy content, and a small amount of Ni, Cr, Cu, rare earth RE, Nb, and V are added, with a total amount of ≤4%, and the alloy cost is low.

[0025] 3. The 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention mainly considers obtaining a structure with both good mechanical properties and corrosion resistance, such as acicular ferrite, lath bainite, and lath martensite. The fine needle structure and lath structure are beneficial to grain boundary strengthening and avoid grain boundary corrosion, which in turn helps to improve low-temperature toughness, improve resistance to freeze-thaw alternating stress corrosion, and resistance to low-temperature saline-alkali environment corrosion.

[0026] 4. The mechanical properties, low-temperature impact toughness and corrosion resistance of the 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention are far superior to those of conventional products (Q235 steel). The tensile strength is about 200MPa higher than that of conventional products, the yield strength ratio is less than 0.8, and the -45℃A KV2 ≥150J, relative corrosion rate to Q235 steel is <50%, which can meet the corrosion resistance requirements of frozen soil steel in different environments.

[0027] 5. In the preparation method of the present invention, high-strength plastic corrosion-resistant steel for frozen soil roads with good mechanical properties, corrosion resistance and low-temperature properties is obtained through high-permeability rolling deformation process, cooling path design, uniform cooling and differentiated shielding coupling process, and online heat treatment process optimization.

[0028] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0030] Figure 1 It is the microstructure morphology of Example 1 of the present invention;

[0031] Figure 2 It is the microstructure morphology of Example 2 of the present invention;

[0032] Figure 3 It is the microstructure morphology of Example 3 of the present invention;

[0033] Figure 4 It is the microstructure morphology of Comparative Example 2 of the present invention;

[0034] Figure 5 This is the impact fracture morphology of Example 3 of the present invention;

[0035] Figure 6 It is the impact fracture morphology of comparative example 1 of the present invention;

[0036] Figure 7 It is a comparison chart of relative corrosion rates of the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0038] On the one hand, the present invention provides a 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads, wherein the chemical composition of the 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads comprises, by weight percentage: C: 0.05-0.12% (e.g., 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%), Si: 0.30-0.50% (e.g., 0.35%, 0.40%, 0.45%), Mn: 1.50-1.80% (e.g., 1.60%, 1.70%), P: 0.002-0.02% (e.g., 0.005%, 0.010%, 0.015%), S: ≤ 0.005%, Cu: 0.05~0.55%, Cr: 0.1~0.8%, Ni: 0.5~3.0% (for example 1.0%, 1.5%, 2.0%, 2.5%), V: 0.02~0.08% (for example 0.03%, 0.04%, 0.05%, 0.06%, 0.07%), Nb: 0.01~0.02%, N: 0.003~0.020% (for example 0.005%, 0.010%, 0.015%), Al≥0.015%, La+Ce≤0.05%, the balance is Fe and unavoidable impurities; among which, the atomic ratio of nitrogen to vanadium is 0.5~0.9.

[0039] Carbon (C): The steel of the present invention has a mixed structure of bainite and a small amount of lath martensite, acicular ferrite or lath bainite as the final structure, and the range of C content needs to be strictly controlled; the addition of an appropriate amount of C can play a role in solid solution strengthening in the steel and improve the strength of the matrix; strictly controlling the C content can effectively reduce the sensitivity of the Mn / S ratio of the continuous casting billet and reduce the probability of continuous casting longitudinal cracking. A relatively low C content can improve the uniform elongation of the steel, so the carbon content of the steel of the present invention is controlled to be 0.05-0.12%.

[0040] Silicon (Si): The Si element can not only play a role in solid solution strengthening, but also improve the corrosion resistance of steel. Too high a silicon content will have an adverse effect on the plasticity and toughness of the steel, so the Si content is controlled within the range of 0.3-0.5%.

[0041] Manganese (Mn): Mn is the most effective element for expanding the austenite phase, refining grains and ensuring the comprehensive performance of steel. 0.1% Mn can increase the tensile strength of the matrix by 10 MPa. Taking all factors into consideration, the Mn content in steel should be controlled in the range of 1.5-1.8%.

[0042] Phosphorus (P) and sulfur (S): Phosphorus and sulfur elements have a great influence on the low-temperature toughness of steel. The enrichment or segregation of phosphorus and sulfur elements will seriously reduce the low-temperature toughness of steel. Therefore, the phosphorus and sulfur content in steel needs to be strictly controlled. The control range of P element is 0.002-0.02%, and the control range of S element is ≤0.005%.

[0043] Copper (Cu): Cu is a solid solution strengthening element that can improve the strength of the steel matrix. The addition of Cu can enhance the corrosion resistance of steel and make it more durable in corrosive environments such as acid, alkali, and salt. However, when the Cu content increases, it is easy to produce hot brittleness during hot processing. When the Cu content exceeds 0.5%, the plasticity is significantly reduced. Therefore, the Cu content in steel is controlled in the range of 0.05-0.55%.

[0044] Chromium (Cr): Chromium can reduce the γ phase area and form a γ phase ring. It is infinitely soluble in α iron and is a carbide-forming element. As the Cr content increases, (Fe, Cr) 3C and 7-3 type 23-6 type can be formed. When the chromium content is too high, δ phase and temper brittleness are prone to occur, and it will affect the welding performance. Therefore, the Cr content in steel is controlled in the range of 0.1-0.8%.

[0045] Nickel (Ni): Nickel can improve the strength and toughness of steel and improve hardenability. When the content is high, it can significantly change some physical properties of steel and alloys and improve the corrosion resistance of steel. However, considering economic efficiency, it is controlled at 0.5~3.0%.

[0046] Lanthanum (La), cerium (Ce): La and Ce can effectively improve the characteristics of inclusions in steel, purify molten steel, refine grains, improve the corrosion resistance and oxidation resistance of steel, and effectively resist plateau soil corrosion. Therefore, La+Ce≤0.05%, wherein the La content range is controlled at 0-0.05%, more preferably 0.001-0.05% (for example, 0.01%, 0.02%, 0.03%, 0.04%), and the Ce content range is controlled at 0-0.05%, more preferably 0.001-0.05% (for example, 0.01%, 0.02%, 0.03%, 0.04%).

[0047] Vanadium (V), niobium (Nb): V and Nb are strong carbonitride forming elements. They can reduce the γ phase area and improve the strength of steel through grain refinement, precipitation strengthening and solid solution strengthening. Increasing the V element can reduce the ductile-brittle transition temperature of steel; trace amounts of Nb can increase the strength of steel without affecting the plasticity or toughness of steel. The addition of Nb can fix the carbon in the steel and precipitation hardening effect. Its precipitates can effectively pin the austenite grain boundaries and play a role in refining the grains. It can improve the low-temperature toughness of the steel matrix and the heat-affected zone of welding and reduce its brittle transition temperature.

[0048] Nitrogen (N): N forms nitrides with V and Nb, which can play a role in precipitation strengthening, better play the role of microalloy strengthening in steel, and increase the strength and corrosion resistance of the steel matrix. Therefore, the nitrogen content in steel is controlled in the range of 0.003-0.020%.

[0049] Aluminum (Al): The Al element contributes to inclusion control, corrosion resistance and welding performance optimization.

[0050] Furthermore, the oxygen content of the 690MPa grade low temperature corrosion resistant steel for frozen soil highway of the present invention is ≤30ppm. The O content in the steel mainly exists in the form of oxide inclusions, which seriously affects the low temperature toughness of the steel. In order to better exert the purification effect of rare earth elements on molten steel and the corrosion resistance effect of solid solution rare earth, it is necessary to strictly control the oxygen content in low carbon steel. Therefore, the control range of oxygen content in steel is ≤30ppm.

[0051] Exemplarily, the total amount of Ni, Cr, Cu, La+Ce, Nb, and V is ≤4%.

[0052] Exemplarily, the hot-rolled microstructure of the 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads is a mixed structure of bainite and a small amount of lath martensite, acicular ferrite and one of lath bainite. These structures are conducive to obtaining good mechanical properties and corrosion resistance, but too much martensite content is not conducive to improving toughness, and its content needs to be limited. At the same time, the fine needle structure and lath structure are conducive to grain boundary strengthening and avoiding grain boundary corrosion, which is beneficial to improving low-temperature toughness, improving resistance to freeze-thaw alternating stress corrosion, and resistance to low-temperature saline-alkali environment corrosion.

[0053] It should be noted that when the hot-rolled microstructure of 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads is bainite + a small amount of lath martensite, considering the matching of strength, plasticity and toughness, the content of bainite is 70-100%, and the content of lath martensite is 0-30%. Furthermore, the content of bainite is 70-95%, and the content of lath martensite is 5-30%.

[0054] For example, the grain size of 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads is 10 to 11 levels.

[0055] For example, the yield strength of the 690MPa grade low temperature corrosion resistant steel for frozen soil roads is ≥690MPa, the tensile strength is ≥1000MPa, the yield strength ratio is <0.8, the elongation A is ≥20%, and the -45℃A KV2 ≥150J, relative corrosion rate to Q235B steel is <50% (corrosion method see relevant national standards).

[0056] Exemplarily, the 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads has a thickness of 0.6 to 20 mm and a width of 900 to 2200 mm.

[0057] On the other hand, the present invention also provides a method for preparing the above-mentioned 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads, the preparation method comprising:

[0058] Step (1): smelting and continuous casting to obtain continuous casting billet.

[0059] Step (2): performing a uniform heat treatment on the continuous casting billet.

[0060] Step (3): rolling the continuous casting billet, wherein the rolling process includes rough rolling and finish rolling.

[0061] Step (4): After rolling to the target thickness, the continuous casting billet is subjected to laminar cooling, wherein the laminar cooling method is a method of coupling uniform cooling and differentiated shielding.

[0062] Step (5): coiling.

[0063] Illustratively, in step (1), smelting and continuous casting include converter or electric furnace smelting, LF refining, RH / VD vacuum treatment and continuous casting process. In this process, the mass percentage of the following elements is controlled: P: 0.002-0.02%, S≤0.005%, O≤30ppm, H≤3ppm. Moderate nitrogen addition is beneficial to promote the precipitation of fine nitrides, but the plasticization level is taken into account, and the N content is controlled to be 0.003-0.020%.

[0064] Exemplarily, in step (2), the soaking treatment temperature is 1130-1200° C., mainly considering the severe oxidation of low-temperature corrosion-resistant steel, in order to reduce oxidation and improve surface quality.

[0065] For example, in step (3), the starting rolling temperature of the rough rolling is 1050-1180°C, and the first deformation is greater than 40%. The rough rolling adopts a high temperature and large reduction process with a reduction rate of ≥50%, which can significantly refine the austenite grains in the recrystallization zone.

[0066] Exemplarily, in step (3), the finish rolling adopts low-temperature rolling in the non-recrystallization zone to ensure a certain cumulative compression ratio, and the cumulative deformation of 7 passes is set to be greater than 30%, so as to achieve microstructure refinement in the non-recrystallization zone.

[0067] For example, the continuous casting billet is kept warm for 2 to 4 minutes before entering the finishing rolling entrance. Considering that low-temperature rolling is beneficial to improving toughness, the finishing rolling entrance temperature is set at 800 to 830°C, and the final rolling temperature is set at 750-830°C.

[0068] It should be noted that laminar cooling refers to the post-rolling online controlled cooling process of hot-rolled steel plates or strips using laminar water flow. Several laminar flow headers are installed above the output roller of the finishing mill to form a cooling belt. After hot rolling, the steel plates (strips) pass through the cooling belt for accelerated cooling. Multiple rows of water flow are set in the cooling belt, and each row of water flow is parallel to the width direction of the steel plate. The steel plate moves through the cooling belt along its length direction in the cooling belt.

[0069] The laminar cooling method of the present invention is a coupling of uniform cooling method and differential shielding. Because the temperature of the edge area of ​​the continuous casting billet after rolling is lower than the temperature of the middle area, the temperature difference is controlled at 10-30°C.

[0070] Specifically, the uniform cooling method and the differentiated shielding are coupled to include: in the first 1 / 3 section of the total cooling line length, 5-10% of the width are respectively shielded on both sides of the continuous casting billet, and only the area in the middle of the continuous casting billet and 80-90% of the width is spray cooled; in the second 1 / 3 section of the total cooling line length, 10-20% of the width are respectively shielded on both sides of the continuous casting billet, and only the area in the middle of the continuous casting billet and 60-80% of the width is spray cooled; in the third 1 / 3 section of the total cooling line length, 20-30% of the width are respectively shielded on both sides of the continuous casting billet, and only the area in the middle of the continuous casting billet and 40-60% of the width is spray cooled, which is conducive to obtaining a uniform microstructure, and further conducive to improving the stress corrosion resistance and low-temperature impact toughness of the grain boundaries and intragranular regions.

[0071] It should be noted that the “shielding” can be achieved by closing the water flow in the area to be shielded or using a baffle to prevent the water flow from spraying to the area to be shielded.

[0072] Exemplarily, in the first 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water streams is 100-400mm; in the second 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water streams is 500-800mm; in the third 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water streams is 900-1200mm. This is mainly due to the fact that as the cooling temperature decreases, the temperature drop at the edge increases. In order to obtain a uniform cooling effect, the cooling spacing between adjacent spray water streams is gradually extended.

[0073] Exemplarily, the cooling rate of the laminar cooling is 30-50°C / s, which avoids the appearance of ferrite and pearlite due to too low cooling rate, and also avoids the appearance of too much martensite due to too fast cooling rate, which is not conducive to the matching of low-temperature corrosion resistance and mechanical properties.

[0074] Exemplarily, in step (5), the coiling temperature is 430-600° C. Conventional coiling temperature is above 650° C. The present invention adopts a low-temperature coiling process, and the coiling temperature is 430-600° C.

[0075] The following is a detailed description of the 690MPa grade low temperature corrosion resistant steel for frozen soil roads and its preparation method through specific examples.

[0076] Embodiment 1:

[0077] This embodiment provides a 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof.

[0078] The chemical composition of the 690MPa grade low temperature corrosion resistant steel for frozen soil roads in this embodiment is shown in Table 1.

[0079] The preparation method of the 690MPa grade low temperature corrosion resistant steel for frozen soil highway comprises:

[0080] Step (1): steelmaking is performed by using a converter + LF + RH + continuous casting process for smelting and continuous casting. During the process, the mass percentage of the following elements is controlled: P ≤ 0.02%, S ≤ 0.005%, O ≤ 30ppm, H ≤ 3ppm, and nitrogen is appropriately increased, N ≤ 100ppm;

[0081] Step (2): performing a soaking treatment on the continuous casting billet at a temperature of 1150°C and a heating time of 2.5 hours;

[0082] Step (3): rolling the continuous casting billet, the rolling process includes rough rolling and finishing rolling; the rough rolling adopts a high temperature and large reduction process, the rough rolling start temperature is 1100°C, and the first pass deformation is 45%; the finishing rolling stage adopts low temperature rolling in the non-recrystallization zone, the cumulative deformation of 7 passes is 55%, and the temperature is kept for 2 minutes before entering the finishing rolling entrance, the finishing rolling entrance temperature is 820°C, and the final rolling temperature is 770°C.

[0083] Step (4): After rolling to the target thickness, the continuous casting billet is subjected to laminar cooling, wherein the laminar cooling method is a uniform cooling method. In the first 1 / 3 section of the total cooling line length, 5% of the width of the two sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 90% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 200 mm; in the second 1 / 3 section of the total cooling line length, 10% of the width of the two sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 80% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 500 mm; in the third 1 / 3 section of the total cooling line length, 30% of the width of the two sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 40% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 1000 mm. The cooling rate of the laminar cooling is 45°C / s.

[0084] Step (5): adopt a low-temperature coiling process and control the coiling temperature to 450°C.

[0085] The 690MPa grade low temperature corrosion resistant steel for frozen soil highway has a thickness range of 0.6mm and a width of 900mm. The hot rolled structure is lath bainite and the grain size is 10-11. The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Table Figure 7 .

[0086] Embodiment 2:

[0087] This embodiment provides a 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof.

[0088] The chemical composition of the 690MPa grade low temperature corrosion resistant steel for frozen soil roads in this embodiment is shown in Table 1.

[0089] The preparation method of the 690MPa grade low temperature corrosion resistant steel for frozen soil highway comprises:

[0090] Step (1): The steel is smelted and continuously casted by using a converter + LF + RH + continuous casting process. During the process, the mass percentage of the following elements is controlled: P ≤ 0.02%, S ≤ 0.005%, O ≤ 30ppm, H ≤ 3ppm, and nitrogen is appropriately increased, N ≤ 200ppm.

[0091] Step (2): The continuous casting slab is subjected to a uniform heat treatment at a temperature of 1150° C. and a heating time of 2.5 h.

[0092] Step (3): rolling the continuous casting billet, the rolling process includes rough rolling and finishing rolling; the rough rolling adopts a high temperature and large reduction process, the rough rolling start temperature is 1100°C, and the first pass deformation is 45%; the finishing rolling stage adopts low temperature rolling in the non-recrystallization zone, the cumulative deformation of 7 passes is 55%, and the billet is kept warm for 2 minutes before entering the finishing rolling entrance, the finishing rolling entrance temperature is 820°C, and the final rolling temperature is 760°C.

[0093] Step (4): After rolling to the target thickness, the continuous casting billet is subjected to laminar cooling, wherein the laminar cooling method is a uniform cooling method. In the first 1 / 3 section of the total cooling line length, 10% of the width of both sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 80% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 400 mm; in the second 1 / 3 section of the total cooling line length, 20% of the width of both sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 60% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 800 mm; in the third 1 / 3 section of the total cooling line length, 30% of the width of both sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 40% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 1200 mm. The cooling rate of the laminar cooling is 35°C / s.

[0094] Step (5): adopt a low-temperature coiling process and control the coiling temperature to 550°C.

[0095] The 690MPa grade low temperature corrosion resistant steel for frozen soil highway has a thickness range of 4mm and a width of 2100mm. The hot rolled structure is bainite and the grain size is 10-11. The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Table Figure 7 .

[0096] Embodiment 3:

[0097] This embodiment provides a 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads and a preparation method thereof.

[0098] The chemical composition of the 690MPa grade low temperature corrosion resistant steel for frozen soil roads in this embodiment is shown in Table 1.

[0099] The preparation method of the 690MPa grade low temperature corrosion resistant steel for frozen soil highway comprises:

[0100] Step (1): The steel is smelted and continuously cast by using a converter + LF + RH + continuous casting process. During the process, the mass percentage of the following elements is controlled: P ≤ 0.02%, S ≤ 0.005%, O ≤ 30ppm, H ≤ 3ppm, and nitrogen is appropriately increased, N ≤ 120ppm.

[0101] Step (2): The continuous casting billet is subjected to a uniform heat treatment at a temperature of 1200° C. and a heating time of 3 h.

[0102] Step (3): rolling the continuous casting billet, the rolling process includes rough rolling and finishing rolling; the rough rolling adopts a high temperature and large reduction process, the rough rolling start temperature is 1100°C, and the first pass deformation is 45%; the finishing rolling stage adopts low temperature rolling in the non-recrystallization zone, the cumulative deformation of 7 passes is 65%, and the temperature is kept for 3 minutes before entering the finishing rolling entrance. The finishing rolling entrance temperature is 820°C and the final rolling temperature is 820°C.

[0103] Step (4): After rolling to the target thickness, the continuous casting billet is subjected to laminar cooling, wherein the laminar cooling method is a uniform cooling method. In the first 1 / 3 section of the total cooling line length, 5% of the width of the two sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 90% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 300 mm; in the second 1 / 3 section of the total cooling line length, 20% of the width of the two sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 60% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 600 mm; in the third 1 / 3 section of the total cooling line length, 20% of the width of the two sides of the continuous casting billet are respectively shielded, and only the area in the middle of the continuous casting billet and 20% of the width is sprayed for cooling; the spacing between two adjacent rows of spray water flows is 1000 mm. The cooling rate of the laminar cooling is 30°C / s.

[0104] Step (5): adopt a low-temperature coiling process and control the coiling temperature to 570°C.

[0105] The 690MPa grade low temperature corrosion resistant steel for frozen soil highway has a thickness range of 18mm and a width of 1800mm. The hot rolled structure is bainite (content 95%) + lath martensite (content 5%), and the grain size is 10-11. The mechanical properties and low temperature toughness of the low temperature corrosion resistant steel are shown in Table 2, and the corrosion resistance is shown in Figure 7 .

[0106] Comparative Example 1 and Comparative Example 2

[0107] The chemical compositions of the corrosion-resistant steels of Comparative Example 1 and Comparative Example 2 are shown in Table 1. The preparation methods are conventional methods, including:

[0108] Step (1): conventional smelting and continuous casting to obtain qualified continuous casting billets.

[0109] Step (2): heating and heat-treating the continuous casting ingot.

[0110] Step (3): rolling the continuous casting billet, wherein the rolling process includes rough rolling and finish rolling.

[0111] Step (4): After rolling to the target thickness, the continuous casting billet is subjected to laminar cooling, wherein the laminar cooling method is a continuous cooling method without considering edge shielding and uniform cooling path design.

[0112] Step (5): high temperature coiling at 670°C.

[0113] The mechanical properties and low temperature toughness of the corrosion resistant steels of Comparative Examples 1 and 2 are shown in Table 2, and the corrosion resistance is shown in Table Figure 7 .

[0114] Comparative Example 3

[0115] This comparative example provides a low-temperature corrosion-resistant steel and a preparation method thereof similar to Example 1, except that a uniform cooling method is not used during laminar cooling, and a shielding process and a change in water flow density are not performed. The mechanical properties and low-temperature toughness of the corrosion-resistant steel of Comparative Example 3 are shown in Table 2, and the relative corrosion rate is 53.47%.

[0116] Table 1 Chemical composition wt% of Examples and Comparative Examples

[0117]

[0118] Table 2

[0119]

[0120] It can be seen from Table 1 and Table 2 that compared with the existing 690MPa grade corrosion-resistant steel Q690E, the 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention has a comparable elongation A and a higher yield strength R el or R p0.2and tensile strength R m , the yield strength is relatively small, with higher section shrinkage Z and higher -45℃A KV2 The value indicates that the low-temperature corrosion-resistant steel of the present invention has high low-temperature toughness; Figure 7 It can be seen that, relative to Q235 steel, the relative corrosion rate of the 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention is less than 50%, which is lower than the relative corrosion rate of Q690E. Therefore, the 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention has good mechanical properties, low-temperature properties and corrosion resistance at the same time, and meets the requirements of high-strength frozen soil road steel.

[0121] It can be seen from Tables 1 and 2 that, compared with the corrosion-resistant steel of Comparative Example 1, the 690MPa-grade low-temperature corrosion-resistant steel for frozen soil roads of the present invention has comparable mechanical properties, but its composition is reduced by at least 2% Ni, and the alloy cost is saved by more than 100 yuan.

[0122] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A 690MPa grade low temperature corrosion resistant steel for frozen soil roads, characterized in that: The chemical composition of the 690MPa grade low temperature corrosion resistant steel for frozen soil roads includes, by weight percentage: C: 0.05-0.12%, Si: 0.30-0.50%, Mn: 1.50-1.80%, P: 0.002-0.02%, S: ≤0.005%, Cu: 0.05-0.55%, Cr: 0.1-0.8%, Ni: 0.5-3.0%, V: 0.02-0.08%, Nb:

0. : 0.010~0.02%, N: 0.003~0.020%, Al≥0.015%, La+Ce≤0.05%, and the balance is Fe and inevitable impurities; wherein the atomic ratio of nitrogen to vanadium is 0.5~0.9; the hot-rolled microstructure of the 690MPa grade low-temperature corrosion-resistant steel for frozen soil roads is a mixed microstructure of bainite and 5~30% lath martensite, all acicular ferrite, and all lath bainite.

2. A method for preparing 690MPa grade low temperature corrosion resistant steel for frozen soil roads as claimed in claim 1, characterized in that: The preparation method comprises: Step (1): smelting and continuous casting to obtain a continuous casting billet; Step (2): performing a soaking treatment on the continuous casting slab; Step (3): rolling the continuous casting billet, wherein the rolling process includes rough rolling and finish rolling; Step (4): after rolling to the target thickness, laminar cooling is performed on the continuous casting billet, wherein the laminar cooling method is a method of coupling uniform cooling and differential shielding; Step (5): coiling.

3. The preparation method according to claim 2, characterized in that: The coupling method of uniform cooling and differentiated shielding includes: in the first 1 / 3 section of the total cooling line length, 5-10% of the width are respectively shielded on both sides of the continuous casting billet, and only the area in the middle of the continuous casting billet and 80-90% of the width is spray cooled; in the second 1 / 3 section of the total cooling line length, 10-20% of the width are respectively shielded on both sides of the continuous casting billet, and only the area in the middle of the continuous casting billet and 60-80% of the width is spray cooled; in the third 1 / 3 section of the total cooling line length, 20-30% of the width are respectively shielded on both sides of the continuous casting billet, and only the area in the middle of the continuous casting billet and 40-60% of the width is spray cooled.

4. The preparation method according to claim 3, characterized in that: In the first 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water flows is 100-400mm; in the second 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water flows is 500-800mm; in the third 1 / 3 of the total cooling line length, the spacing between two adjacent rows of spray water flows is 900-1200mm.

5. The preparation method according to claim 2, characterized in that: The cooling rate of the laminar cooling is 30-50°C / s.

6. The preparation method according to claim 2, characterized in that: In step (2), the temperature of the heat treatment is 1130-1200°C.

7. The preparation method according to claim 2, characterized in that: In step (3), the starting rolling temperature of the rough rolling is 1050-1180°C, and the deformation amount of the first pass is greater than 40%.

8. The preparation method according to claim 2, characterized in that: In step (3), the finish rolling adopts low-temperature rolling in the non-recrystallization zone, and the cumulative deformation of 7 passes is greater than 30%.

9. The preparation method according to claim 2, characterized in that: In step (5), the coiling temperature is 430-600°C.

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