Weathering resistant steel with high toughness and low yield ratio and preparation method thereof

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to high-toughness and low-yield-ratio weathering steel and a preparation method thereof. The weathering steel comprises the following chemical elements in percentage by weight: 0.05%-0.07% of C, 0.20%-0.40% of Si, 1.0%-1.20% of Mn, 0.013% < = P < = 0.018%, 0.003% < = S, 0.01%-0.03% of Al, 0.045% < = Nb, 0.025% < = Ti, 0.30%-0.45% of Cu, 0.70% < = Cr, 0.35% < = Ni and the balance of Fe and inevitable impurities. And the contents of the chemical elements simultaneously meet the following relations: the value range of a corrosion resistant factor xi is more than or equal to 6.5 and less than or equal to 9.0, and the value range of a through quenching factor phi is more than or equal to 0.17 and less than or equal to 0.2. The weathering resistant steel provided by the invention is good in microstructure uniformity, low in yield ratio and high in toughness.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a weathering steel with high toughness and low yield ratio and a preparation method thereof. Background Art

[0002] Steel plates are exposed to the air for a long time and are easily corroded and worn out. If the steel plates have excellent corrosion resistance, the maintenance cost of the steel structure can be greatly reduced. Weathering steel is made by adding a small amount of corrosion-resistant elements such as copper and nickel to ordinary carbon steel. It has the characteristics of saving labor and energy, resisting corrosion and extending life. Therefore, weathering steel has more advantages than ordinary steel in the application of large-scale steel structure projects such as bridges and building structures. As large-scale steel structures / buildings develop towards all-welded structures and high parameters, the safety and reliability requirements of the structures are becoming more and more stringent, especially for the quality of medium and thick weathering steel plates, which should not only have high strength to meet the requirements of lightweight structures, but also have excellent low-temperature toughness.

[0003] In theory, as the thickness of weathering steel increases during the preparation process, its mechanical properties such as compression, bending and shear resistance will increase. However, in reality, the thicker the weathering steel plate, the more difficult it is to control the internal grain size, and defects such as inclusions and sand inclusions are prone to occur. These defects will cause the mechanical properties of the weathering steel plate to deteriorate, and adjusting the production process is a test of the research and development capabilities of technical personnel. CN109161793A discloses a low yield ratio high-strength weathering steel and a method for manufacturing the same. The yield strength is only 428 to 444 MPa, the finished product specification is 6 to 12 mm, and the product is a hot-rolled coil, the steel strength is low, and the thickness specification is thin. CN102080192A discloses a low yield ratio high plasticity ultrafine grain high-strength steel and a method for manufacturing the same. It adopts two-phase quenching + two-phase tempering, has a long production cycle, difficult organization, and high cost. Summary of the invention

[0004] In view of the technical problem that thick weathering steel has poor mechanical properties during the preparation process, the present invention provides a weathering steel with high toughness and low yield ratio and a preparation method thereof. The weathering steel has a simple composition design, good microstructure uniformity, low yield ratio, high toughness, and strong corrosion resistance. The thickness can reach 10 to 60 mm.

[0005] In a first aspect, the present invention provides a weathering steel with high toughness and low yield ratio, wherein the chemical element composition is, by weight percentage: C 0.05% to 0.07%, Si 0.20% to 0.40%, Mn 1.0% to 1.20%, 0.013%≤P≤0.018%, S≤0.003%, Al 0.01% to 0.03%, Nb≤0.045%, Ti≤0.025%, Cu 0.30% to 0.45%, Cr≤0.70%, Ni≤0.35%, and the balance is Fe and unavoidable impurities; And the contents of the above chemical elements satisfy the following relationship at the same time: The range of corrosion resistance factor ξ is 6.5≤ ξ ≤9.0, and the range of hardenability factor Ф is 0.17≤ ф ≤0.21; in,

[0006]

[0007] The thickness of weathering steel is 10mm~60mm.

[0008] Furthermore, the microstructure of the weathering steel is bainite + ferrite + pearlite or bainite + polygonal ferrite.

[0009] Furthermore, the elongation after fracture of weathering steel is ≥26.5%, the yield strength ratio is ≤0.75, the impact resistance at -60℃ is ≥360J, the corrosion potential is ≥ -451mV, and the corrosion weight loss after 144h is ≤0.658mg / m 2 •h, 72h corrosion weight loss ≤ 0.452mg / m 2 •h, relative corrosion rate ≤11.48%.

[0010] Chemical element composition is one of the important factors affecting the comprehensive performance of weathering steel. The chemical composition of the present invention is limited as follows: C: The main solid solution strengthening element in steel, which can significantly improve the strength of steel plates, but a high carbon content is not good for steel plate welding, toughness and plasticity. In order to effectively reduce segregation, improve microstructural uniformity, avoid galvanic corrosion caused by potential difference between different phases, improve the corrosion resistance of steel, and consider economic efficiency, its mass percentage content is limited to 0.05% to 0.07%.

[0011] Si: Silicon is one of the effective deoxidizing and exothermic elements in the steelmaking process. It has a certain solid solution strengthening effect, is conducive to the formation of a dense rust layer, and can improve the atmospheric corrosion resistance of steel. However, too high silicon content will reduce the surface quality, welding performance and low-temperature toughness of the steel. The mass percentage content is limited to 0.20%~0.40%.

[0012] Mn: Manganese has a strong solid solution strengthening effect, can significantly reduce the phase transition temperature of steel, refine the microstructure of steel, and is low in cost. It is an effective element for improving strength. In order to achieve sufficiently high tensile strength and obtain a low yield ratio, the content should not be less than 0.80%. However, too high a content can easily cause segregation of the ingot and form a banded structure, reducing the weldability of the steel plate and the toughness of the heat affected zone of the weld, as well as the corrosion resistance. The mass percentage content is limited to 1.0% to 1.20%.

[0013] P: It can effectively improve the atmospheric corrosion resistance of steel. When P and Cu are added to steel together, it can show a better composite effect. However, too high P content will significantly reduce the plasticity and low-temperature toughness of steel, increase the cold brittleness of steel, and deteriorate welding performance. Its mass percentage content is limited to 0.013%~0.018%.

[0014] S: Sulfur makes steel hot brittle, reduces its ductility and toughness, and promotes the anisotropy of steel plates. Sulfide inclusions also significantly reduce the corrosion resistance of steel. The sulfur content in steel should be strictly controlled, and its mass percentage should be limited to ≤0.003%.

[0015] Al: Aluminum is one of the effective deoxidizing elements in the steelmaking process. It can effectively reduce the inclusion content in steel and refine the grains. However, if the content is too high, it is easy to cause cracks on the surface of the ingot. The mass percentage content is limited to 0.01% to 0.03%.

[0016] Cr: It is not only an element that improves the hardenability of steel, but also one of the effective elements to improve the weather resistance of steel. It has a significant effect on improving the passivation ability of steel and can promote the formation of a dense passivation film or protective rust layer on the steel surface. Its enrichment in the rust layer can effectively improve the selective permeability of the rust layer to corrosive media. However, too high a Cr content will increase production costs and reduce the toughness and weldability of steel. Its mass percentage content is limited to ≤0.70%.

[0017] Cu: Copper is one of the effective elements to improve the weather resistance of steel. It has a high electrochemical potential ratio, which can densify the rust on the surface of the steel plate and promote the formation of a stable rust layer. The addition of copper to steel is conducive to the formation of a dense, well-adhesive amorphous oxide (hydrocarbon-based oxide) protective layer on the surface of the steel, which has a significant corrosion resistance. In addition, Cu and S form insoluble sulfides, thereby offsetting the harmful effects of S on the corrosion resistance of steel. However, when the Cu content is too high, due to the low melting point of Cu, which is lower than the heating temperature of the steel billet, the precipitated Cu is in liquid and aggregates at the austenite grain boundary. When the precipitated Cu content reaches a certain level, it is easy to produce cracks during heating or hot rolling, and its mass percentage content is limited to 0.30% to 0.45%.

[0018] Ni: Adding nickel to steel will significantly improve the corrosion resistance of the steel. At the same time, Ni and Cu elements form a Cu-rich phase containing Ni, and are retained in the outer oxide layer in a solid state, reducing the enrichment of Cu in the matrix and the chance of forming a liquid Cu-rich phase, thereby avoiding hot brittle defects and reducing the sensitivity to hot cracks during casting, hot rolling and welding. In addition, nickel is also an indispensable alloying element for steel plates to obtain excellent low-temperature toughness, so Ni / Cu in steel is generally controlled to be ≥1 / 2. However, too high Ni will increase the adhesion of the oxide scale, and pressing it into the steel will form hot rolling defects on the surface. Ni is a precious metal, and too high Ni content will significantly increase the alloy cost of the steel, so its mass percentage content is limited to ≤0.35%.

[0019] Nb: Niobium is one of the important elements for grain refinement strengthening. It increases the recrystallization temperature of austenite, prevents austenite recrystallization and inhibits grain growth, and refines austenite grains. Its carbonitrides precipitate on dislocations and segregate at austenite grain boundaries, improving strength and toughness. However, if the niobium content is too high, surface cracks are likely to occur in the ingot and the welding performance is deteriorated. Therefore, its mass percentage content is limited to ≤0.045%.

[0020] Ti: produces strong precipitation strengthening and moderate grain refinement. A trace amount of titanium is added to the steel to combine with nitrogen in the steel to generate highly stable titanium nitride particles, inhibit the growth of austenite grains in the HAZ zone, change the secondary phase transformation products, and improve the low-temperature toughness of high-energy input welding. The titanium content added to the steel must match the nitrogen content in the steel. When the titanium content is too little, the number of titanium nitride particles formed is insufficient to inhibit the growth of austenite grains in the HAZ and change the secondary phase transformation products to improve the low-temperature toughness of the HAZ in high-energy input welding. When too much titanium is added, large-sized titanium nitride particles are precipitated during the solidification of the molten steel. Such large-sized particles not only cannot inhibit the growth of austenite grains in the HAZ, but instead become the starting point for crack initiation. The mass percentage content is limited to ≤0.025%.

[0021] Elements such as copper, nickel, chromium, silicon, and phosphorus all have the effect of increasing the corrosion resistance of steel materials. Different component compositions generate different copper, chromium, nickel and other element compounds, which have different effects on the corrosion resistance of materials. The corrosion resistance factor designed by the present invention is closely related to the ratio of chemical elements, and the corrosion resistance factor is required to be controlled at 6.5 to 9.0; this is one of the key technologies of the present invention.

[0022] The hardenability factor controls the hardenability of the material. In the subsequent rolling and controlled cooling process, the steel structure type and proportion are guaranteed, and the proportion of bainite and ferrite is controlled, so as to obtain excellent comprehensive mechanical properties, such as a lower yield strength ratio, good plasticity and toughness. The hardenability factor designed in the present invention is closely related to the ratio of chemical elements, and the hardenability factor is controlled at 0.17-0.21. This is one of the key technologies of the present invention.

[0023] In a second aspect, the present invention provides a method for preparing weathering steel with high toughness and low yield ratio, wherein molten iron is pretreated, smelted, refined and continuously cast to obtain a casting, and the casting is subjected to slow cooling, heating, rolling and water cooling to obtain weathering steel with high toughness and low yield ratio; The rolling is a two-stage rolling process, the second stage rolling temperature is T1- (10-30) °C, and the third to last rolling temperature is T2+ (30-50) °C; The final cooling temperature of water cooling is T3±40℃; Wherein, T1=910-320×[%C]-14×[%Ni]-12×[%Cu]-10×[%Mn]+5×[%Cr]+18×[%Si]; T2=723-10.7×[%Mn]-16.9×[%Ni]+29.1×[%Si]+16.9×[%Cr]; T3=529-423×[%C]-30.4×[%Mn]-20×[%Si]-12.1×[%Cr]-17.7×[%Ni].

[0024] The settings of T1- (10 ~ 30) ℃ and T2 + (30 ~ 50) ℃ are to ensure that the microstructure of the thick weathering steel plate is uniform and fine and has a two-phase structure with a reasonable number, size and reasonable distribution. T3 ± 40 ℃ is to ensure that the microstructure size of the steel plate is further refined and uniform, while the proportion, morphology and distribution of the ferrite and bainite two-phase structures are reasonable, so that the steel plate has a lower yield strength ratio and high toughness; and T1, T2 and T3 are closely related to the ratio of chemical elements, which is one of the key technologies of the present invention.

[0025] Furthermore, the final S content in the molten iron after pretreatment is 0.0025%~0.001%; ​​the smelting adopts converter smelting, and the final phosphorus content is 0.008%~0.009%; the refining adopts LF / RH refining for micro-alloying, the RH vacuum degree is 100~110Pa, the vacuum time is 13~15min, and the molten steel calming time before tapping is 29~35min; the continuous casting is full-process protected casting, electromagnetic stirring, and heavy pressure reduction technology is adopted at the end of casting, and the reduction ratio is 12%~13%.

[0026] Furthermore, the temperature of the ingot during slow cooling is ≥500°C, and the temperature of the ingot after the slow cooling is ≤150°C; the temperature of the ingot out of the furnace during heating is 1100-1140°C, and the thickness of the ingot is 150-300mm.

[0027] Furthermore, the temperature of the ingot during slow cooling is ≥680°C, and the temperature of the ingot after the slow cooling is ≤135°C; the temperature of the ingot out of the furnace during heating is 1118-1130°C.

[0028] Furthermore, during rolling, the starting temperature of the first stage rolling is 1046-1068°C, the starting temperature of the second stage rolling is 850-860°C, and the starting temperature of the third to last rolling is 745-765°C.

[0029] Furthermore, during water cooling, the final cooling temperature is 430-486°C, the cooling rate is 13-16°C / s, and stack cooling is prohibited after the steel plate is water-cooled.

[0030] The beneficial effects of the present invention are: The present invention provides a weathering steel with high toughness and low yield strength ratio. The finished weathering steel plate has a thickness of 10 to 60 mm, a simple composition design, a fine microstructure, and good uniformity. The microstructure is mainly bainite + ferrite + pearlite or bainite + polygonal ferrite. The yield strength is ≥408 MPa, the tensile strength is ≥575 MPa, the elongation after fracture is ≥26.5%, the yield strength ratio is ≤0.75, the AKV is ≥360 J at -60 ° C, the corrosion potential is ≥ -451 mV, and the corrosion weight loss for 144 hours is ≤0.658 mg / m 2 •h, 72h corrosion weight loss ≤ 0.452mg / m 2 •h, relative corrosion rate ≤11.48%, atmospheric corrosion resistance is more than 5 times that of ordinary low-alloy structural steel, with excellent welding performance, low-temperature toughness, low yield ratio, high corrosion resistance and other properties, which can meet the requirements of corrosion resistance, low yield ratio and high toughness for building structures and engineering structures in coastal atmospheric environment. It adopts low-carbon + micro-alloy composition design and is produced through TMCP process. The preparation method is simple, the production cycle is short, the production cost is low, it is suitable for stable production in large-scale industry, and is conducive to promotion and application. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0032] The formula used in the embodiments and comparative examples is as follows: Corrosion resistance factor ξ=15.5×[%Cu]+4×[%Ni]+2×[%Cr]+0.89×[%Si]+6.3×[%P]+1.3×[%Cu] ×[%Ni]+1.1×[%Cu]×[%Cr]; Hardening factor Ф = [%C] + 0.1 × [%Mn] + 0.03 × [%Cu] + 0.008 × [%Ni] + 0.07 × [%Cr] - 0.04 × [%Cr]×[%Mn]-0.18×[%Cu]×[%Ni]×[%Cr]; T1=910-320×[%C]-14×[%Ni]-12×[%Cu]-10×[%Mn]+5×[%Cr]+18×[%Si]; T2=723-10.7×[%Mn]-16.9×[%Ni]+29.1×[%Si]+16.9×[%Cr]; T3=529-423×[%C]-30.4×[%Mn]-20×[%Si]-12.1×[%Cr]-17.7×[%Ni].

[0033] Example 1 A weathering steel with high toughness and low yield ratio. The chemical element composition is shown in Table 1.

[0034] According to the formula, the corrosion resistance factor ξ=7.0 and the hardening factor Ф=0.183.

[0035] The specific steps include: (1) Hot metal pretreatment: The hot metal is pretreated, and the final S content in the hot metal is 0.0025%; (2) Smelting: Use converter smelting, top and bottom double blowing, full decarburization and dephosphorization, the final phosphorus content is 0.009%, argon blowing throughout the process, weak stirring, the slag surface is slightly turned over without exposing, and lime and fluorite are used to make white slag; (3) Refining: LF / RH refining is used for microalloying to reduce the content of harmful elements / impurities to obtain molten steel, wherein the RH vacuum degree is 100 Pa, the vacuum time is 13 min, and the molten steel calming time before tapping is 29 min; (4) Continuous casting: full protection casting, electromagnetic stirring, heavy pressure reduction technology at the end of casting, and a pressure reduction ratio of 12%; (5) Slow cooling: After the billet is cut, it is placed in a slow cooling pit. The billet temperature at the beginning of slow cooling is 680°C and the billet temperature at the end of slow cooling is 102°C. (6) Heating: The billet out of the furnace temperature is 1130°C, the time in the furnace is 189 min, and the billet thickness is 150 mm; (7) Rolling: After the ingot is removed from the furnace and descaled by 21MPa high-pressure water, the second-stage rolling begins. The first-stage rolling temperature is 1046°C, the intermediate billet thickness is 43mm, T1 is calculated to be 875°C, and the second-stage rolling temperature is 855°C; T2 is calculated to be 713°C, and the third-to-last rolling temperature is 745°C. (8) Water cooling: T3 is calculated to be 460°C, the final cooling temperature is 483°C, the cooling rate is 13°C / s, and stack cooling is prohibited after the steel plate is water-cooled.

[0036] Example 2 A weathering steel with high toughness and low yield ratio. The chemical element composition is shown in Table 1. According to the formula, the corrosion resistance factor ξ=8.70 and the hardenability factor Ф=0.190 can be obtained.

[0037] The specific steps include: (1) Hot metal pretreatment: The hot metal is pretreated and the final S content in the hot metal is 0.001%; (2) Smelting: Use converter smelting, top and bottom double blowing, full decarburization and dephosphorization, the final phosphorus content is 0.008%, argon blowing throughout the process, weak stirring, the slag surface is slightly turned over without exposing, and lime and fluorite are used to make white slag; (3) Refining: LF / RH refining is used for microalloying to reduce the content of harmful elements / impurities to obtain molten steel, wherein the RH vacuum degree is 100 Pa, the vacuum time is 15 min, and the molten steel calming time before tapping is 31 min; (4) Continuous casting: full protection casting, electromagnetic stirring, heavy pressure reduction technology at the end of casting, and a pressure reduction ratio of 12%; (5) Slow cooling: After the billet is cut, it is placed in a slow cooling pit. The billet temperature at the beginning of slow cooling is 692°C and the billet temperature at the end of slow cooling is 112°C. (6) Heating: The billet out of the furnace temperature is 1128°C, the time in the furnace is 325 min, and the billet thickness is 200 mm; (7) Rolling: After the ingot is removed from the furnace and descaled by 21 MPa high-pressure water, the second-stage rolling begins. The first-stage rolling temperature is 1054°C, the intermediate billet thickness is 96 mm, T1 is calculated to be 878°C, the second-stage rolling temperature is 855°C, T2 is calculated to be 723°C, and the third-to-last rolling temperature is 765°C. (8) Water cooling: T3 is calculated to be 451°C, the final cooling temperature is 486°C, the cooling rate is 16°C / s, and stack cooling is prohibited after the steel plate is water-cooled.

[0038] Example 3 A weathering steel with high toughness and low yield ratio. The chemical element composition is shown in Table 1. According to the formula, the corrosion resistance factor ξ=7.44 and the hardenability factor Ф=0.201 can be obtained.

[0039] The specific steps include: (1) Hot metal pretreatment: The hot metal is pretreated and the final S content in the hot metal is 0.001%; (2) Smelting: Use converter smelting, top and bottom double blowing, full decarburization and dephosphorization, the final phosphorus content is 0.009%, argon blowing throughout the process, weak stirring, the slag surface is slightly turned over without exposing, and lime and fluorite are used to make white slag; (3) Refining: LF / RH refining is used for microalloying to reduce the content of harmful elements / impurities to obtain molten steel, wherein the RH vacuum degree is 100 Pa, the vacuum time is 15 min, and the molten steel calming time before tapping is 35 min; (4) Continuous casting: full protection casting, electromagnetic stirring, heavy pressure reduction technology at the end of casting, and a pressure reduction ratio of 12%; (5) Slow cooling: After the billet is cut, it is placed in a slow cooling pit. The billet temperature at the beginning of slow cooling is 696°C and the billet temperature at the end of slow cooling is 135°C. (6) Heating: The billet out-of-furnace temperature is 1118°C, the time in the furnace is 396 min, and the billet thickness is 300 mm; (7) Rolling: After the cast billet is descaled by 21MPa high-pressure water, the second-stage rolling begins. The first-stage rolling temperature is 1068°C, the intermediate billet thickness is 150mm, T1 is calculated to be 883°C, the second-stage rolling temperature is 860°C, T2 is calculated to be 729°C, and the third-to-last rolling temperature is 765°C. (8) Water cooling: T3 is calculated to be 455°C, the final cooling temperature is 430°C, the cooling rate is 13°C / s, and stack cooling is prohibited after the steel plate is water-cooled.

[0040] Comparative Example 1 A weathering steel with high toughness and low yield ratio. The chemical element composition is shown in Table 1. According to the formula, the corrosion resistance factor ξ=10.0 and the hardenability factor Ф=0.222 can be obtained.

[0041] The specific steps include: (1) Hot metal pretreatment: The hot metal is pretreated and the final S content in the hot metal is 0.001%; (2) Smelting: Use converter smelting, top and bottom double blowing, full decarburization and dephosphorization, the final phosphorus content is 0.009%, argon blowing throughout the process, weak stirring, the slag surface is slightly turned over without exposing, and lime and fluorite are used to make white slag; (3) Refining: LF / RH refining is used for microalloying to reduce the content of harmful elements / impurities to obtain molten steel, wherein the RH vacuum degree is 100 Pa, the vacuum time is 15 min, and the molten steel calming time before tapping is 35 min; (4) Continuous casting: full protection casting, electromagnetic stirring, heavy pressure reduction technology at the end of casting, and a pressure reduction ratio of 12%; (5) Slow cooling: After the billet is cut, it is placed in a slow cooling pit. The billet temperature at the beginning of slow cooling is 690°C and the billet temperature at the end of slow cooling is 130°C. (6) Heating: The billet out-of-furnace temperature is 1123°C, the time in the furnace is 323 min, and the billet thickness is 200 mm; (7) Rolling: After the cast slab is removed from the furnace and descaled by 21 MPa high-pressure water, the second-stage rolling begins. The first-stage rolling temperature is 1054°C, the intermediate slab thickness is 96 mm, T1 is calculated to be 870°C, the second-stage rolling temperature is 850°C, T2 is calculated to be 719°C, and the third-to-last rolling temperature is 765°C. (8) Water cooling: T3 is calculated to be 433°C, the final cooling temperature is 486°C, the cooling rate is 16°C / s, and stack cooling is prohibited after the steel plate is water-cooled.

[0042] Comparative Example 2 A weathering steel with high toughness and low yield ratio, the chemical element composition of which is the same as that of comparative example 1 in Table 1, and the corrosion resistance factor ξ=10.0 and the hardenability factor Ф=0.222 are calculated according to the formula.

[0043] The specific steps include: Steps (1) to (6) are the same as those in Comparative Example 1; (7) Rolling: After the ingot is removed from the furnace and descaled by 21 MPa high-pressure water, the second-stage rolling begins. The first-stage rolling temperature is 1054°C, the intermediate billet thickness is 96 mm, T1 is calculated to be 870°C, and the second-stage rolling temperature is 890°C. (8) Water cooling: T3 is calculated to be 433°C, the final cooling temperature is 350°C, the cooling rate is 18°C / s, and stack cooling is prohibited after the steel plate is water-cooled.

[0044] Table 1 Chemical element composition of the example steel plate and the comparative example steel plate (excluding Fe and unavoidable impurities)

[0045] Experimental Example 1 Tensile Properties Test The tensile properties of the weathering steel plates of Examples 1 to 3 and Comparative Examples 1 to 2 were tested. The test results are shown in Table 2.

[0046] Table 2 Tensile performance test results of the example steel plate and the comparative example steel plate

[0047] The microstructure of the weathering steel in Examples 1 to 3 is bainite + ferrite + a small amount of pearlite or bainite + polygonal ferrite, with an elongation after fracture ≥ 26.5, a yield ratio ≤ 0.75, and an impact performance at -60°C ≥ 360J, which meets the high toughness, low yield ratio, and easy welding high safety requirements of large structural parts.

[0048] Compared with Examples 1 to 3, the corrosion resistance factor and hardenability factor of Examples 1 to 2 are too high, the temperature range during the preparation process is inappropriate, a large amount of lath bainite appears on the weathering steel, the material strength increases significantly, but the yield ratio, plasticity, and toughness index values ​​decrease significantly, and the comprehensive performance of the steel plate deteriorates.

[0049] Experimental Example 2 Corrosion Performance Test 1. Electrochemical corrosion potential test The electrochemical test uses a three-electrode system: the working electrodes are 10×10mm 2 The bare plate electrode and the rusted electrode prepared after 30 dry-wet alternating cycles of corrosion, the reference electrode is a saturated calomel electrode (SCE), and the auxiliary electrode is a 9 cm 2 The platinum sheet was used, and the working electrode and the reference electrode were connected by a salt bridge. The working temperature was room temperature 25°C, and all potential values ​​were relative to the potential of the saturated calomel electrode (SCE). The polarization curve was scanned by Solartron1287 dynamic potential, with a scanning potential range of ±0.2V vs.Ecorr (relative to the self-corrosion potential) and a scanning speed of 0.1667mV / s. The experiment was carried out at room temperature, and the results are shown in Table 3: Table 3 Electrochemical corrosion potential measurement results of the example steel plate and Q345D

[0050] 2. Cyclic immersion test The example steel plates were processed into standard specimens according to "TB 2375-1993 Test Method for Periodic Immersion Corrosion of Weathering Steel for Railway Use" and compared with Q345D steel. 72h and 144h periodic immersion tests were carried out. The test results are shown in Table 4.

[0051] Table 4 Cyclic immersion test results of example steel plates and Q345D

[0052] It can be seen from the comparison with Q345D that, relative to ordinary low-alloy structural steel Q345D, the weathering steel plates of Examples 1 to 3 have a small micro-area electrode potential difference, a large electrochemical corrosion potential, a small corrosion weight loss, a low relative corrosion rate, and an excellent corrosion resistance. The weathering resistance is improved by more than 5 times, and can replace low-alloy steel and be applied in buildings, bridges, outdoor towers and other fields without painting to reduce the use and maintenance costs of the steel plates.

[0053] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A weathering steel with high toughness and low yield ratio, characterized in that: The chemical element composition by weight percentage is: C 0.05% to 0.07%, Si 0.20% to 0.40%, Mn 1.0% to 1.20%, 0.013% ≤ P ≤ 0.018%, S ≤ 0.003%, Al 0.01% to 0.03%, Nb ≤ 0.045%, Ti ≤ 0.025%, Cu 0.30% to 0.45%, Cr ≤ 0.70%, Ni ≤ 0.35%, the balance is Fe and unavoidable impurities; And the contents of the above chemical elements satisfy the following relationship at the same time: The range of corrosion resistance factor ξ is 6.5≤ ξ ≤9.0, and the range of hardenability factor Ф is 0.17≤ ф ≤0.21; in, The thickness of weathering steel is 10mm~60mm.

2. A weathering steel with high toughness and low yield ratio as claimed in claim 1, characterized in that: The microstructure of weathering steel is bainite + ferrite + pearlite or bainite + polygonal ferrite.

3. The high toughness and low yield ratio weathering steel according to claim 1, characterized in that: The elongation after fracture of weathering steel is ≥26.5%, the yield strength ratio is ≤0.75, the impact resistance at -60℃ is ≥360J, the corrosion potential is ≥ -451mV, and the corrosion weight loss for 144h is ≤0.658mg / m 2 •h, 72h corrosion weight loss ≤ 0.452mg / m 2 •h, relative corrosion rate ≤11.48%.

4. A method for preparing weathering steel with high toughness and low yield ratio as claimed in claim 1, characterized in that: The molten iron is pretreated, smelted, refined and continuously cast to obtain a casting billet, and the casting billet is slowly cooled, heated, rolled and water-cooled to obtain a weathering steel with high toughness and low yield strength ratio; The rolling is a two-stage rolling process, the second stage rolling temperature is T1- (10-30) °C, and the third to last rolling temperature is T2+ (30-50) °C; The final cooling temperature of water cooling is T3±40℃; Wherein, T1=910-320×[%C]-14×[%Ni]-12×[%Cu]-10×[%Mn]+5×[%Cr]+18×[%Si]; T2=723-10.7×[%Mn]-16.9×[%Ni]+29.1×[%Si]+16.9×[%Cr]; T3=529-423×[%C]-30.4×[%Mn]-20×[%Si]-12.1×[%Cr]-17.7×[%Ni].

5. The method for preparing weathering steel with high toughness and low yield ratio as claimed in claim 4, characterized in that: The final S content in the molten iron after pretreatment is 0.0025%~0.001%; ​​the smelting adopts converter smelting, and the final phosphorus content is 0.008%~0.009%; the refining adopts LF / RH refining for micro-alloying, the RH vacuum degree is 100~110Pa, the vacuum time is 13~15min, and the molten steel calming time before tapping is 29~35min; the continuous casting is full-process protected casting, electromagnetic stirring, and heavy pressure reduction technology is adopted at the end of casting, and the reduction ratio is 12%~13%.

6. The method for preparing weathering steel with high toughness and low yield ratio according to claim 4, characterized in that: The temperature of the ingot during slow cooling is ≥500°C, and the temperature of the ingot after the slow cooling is ≤150°C; the temperature of the ingot out of the furnace during heating is 1100-1140°C, and the thickness of the ingot is 150-300mm.

7. The method for preparing a weathering steel with high toughness and low yield ratio as claimed in claim 6, characterized in that: The temperature of the ingot during slow cooling is ≥680°C, and the temperature of the ingot after the slow cooling is ≤135°C; the temperature of the ingot out of the furnace during heating is 1118-1130°C.

8. The method for preparing weathering steel with high toughness and low yield ratio as claimed in claim 4, characterized in that: During rolling, the starting temperature of the first stage rolling is 1046-1068°C, the starting temperature of the second stage rolling is 850-860°C, and the starting temperature of the third to last rolling is 745-765°C.

9. The method for preparing weathering steel with high toughness and low yield ratio according to claim 4, characterized in that: During water cooling, the final cooling temperature is 430-486°C, the cooling rate is 13-16°C / s, and stack cooling is prohibited after the steel plate is water-cooled.

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