A kind of extreme specification hot-rolled weathering steel and its manufacturing method and application

Abstract

The present invention provides a high-spec hot-rolled weathering steel, its manufacturing method, and application. The steel comprises: C 0.05% to 0.07%, Si 0.26% to 0.35%, Mn 0.8% to 1.2%, P ≤ 0.090%, S ≤ 0.002%, Cr 0.5% to 0.8%, Ni 0.05% to 0.09%, Cu 0.15% to 0.20%, Alt 0.020% to 0.045%, Ti 0.010% to 0.020%, and Nb 0.020% to 0.060%, with the remainder being Fe and unavoidable inclusions. Through the above composition design and combined production process, the present invention produces high-performance, uniform, and high-temperature toughness hot-rolled weathering steel sheets with a thickness of 20 to 25.4 mm and a width of 2000 to 2130 mm. The steel sheets exhibit excellent coil shape and surface quality, with no convolution or loose coils when coiled.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel materials, and in particular relates to an extreme specification hot-rolled weathering steel and a manufacturing method and application thereof. Background Art

[0002] Hot rolling production lines produce ultra-wide and ultra-thick extreme-specification weathering steel, mainly referring to weathering steel with a thickness range of 20 to 25.4 mm and a width range of 2000 to 2130 mm, which is used in railway freight cars, large mining cars, bridges and other fields. Although its usage is less than that of similar-specification weathering medium plates, it has better economic benefits and product added value due to its advantages such as convenient transportation in coils and good cooling control. However, the production of ultra-wide and ultra-thick extreme-specification weathering steel on hot rolling production lines is technically difficult. The main problems are low temperature hit rate and poor stability, poor low-temperature toughness, and easy occurrence of towering and loose coils. It is difficult to achieve stable batch production of such products on hot rolling production lines. Therefore, this extreme-specification weathering steel plate is mostly produced on medium and thick plate production lines. Therefore, how to stably produce an extreme-specification weathering steel coil on a hot rolling production line is a key technical difficulty.

[0003] A Chinese invention patent, publication number CN 114657479 A, ​​published on June 24, 2022, discloses a thick-gauge, high-strength, and excellent low-temperature toughness hot-rolled corrosion-resistant steel, its manufacturing method, and its application. The steel has a chemical composition of C: 0.03-0.05%; Si: <0.25%; Mn: 0.50-0.75%; P: ≤0.015%; S: ≤0.005%; Cr: 1.3-1.6%; Ni: 0.05-0.10%; Cu: 0.10-0.19%; Alt: 0.020-0.045%; V: 0.06-0.10%; N: 0.012-0.025%, with a V / N ratio of 4-5, the remainder being Fe and unavoidable inclusions. The steel has a thickness of 18-25 mm. However, it is not the limit specification of the hot rolling production line, nor is it an ultra-wide specification. It also does not propose methods for stabilizing production during the product manufacturing process and preventing defects such as overflow and loose coils.

[0004] Chinese invention patent CN 106521352A, published on March 22, 2017, discloses a thick-gauge niobium-containing weathering steel and its rolling method. The chemical composition is C: ≤0.08%, Si: ≤0.50%, Mn: ≤1.50%, P: ≤0.02%, S: ≤0.008%, Nb: ≤0.05%, Cu: 0.20%-0.55%, Cr: 0.30%-1.25%, Ni: 0.10%-0.65%, with the remainder being Fe and unavoidable impurities. The patent utilizes a low-P, high-Mn, low-Cr, and single-Nb design, suitable for thicknesses ≥16mm. The examples specifically note that the steel was rolled at Panzhihua Iron and Steel 2050, indicating that the actual width is mostly under 1950mm, not an ultra-wide specification. The steel is coiled at a medium-temperature temperature of 555-585°C. Although the yield strength reaches 450MPa in the mechanical performance indicators, the stabilization control of the mechanical properties of the hot coil in the length and width directions during the rolling process of the ultra-wide and ultra-thick limit specifications, as well as the prevention and control of defects such as deviation, overflow, and loose coiling that often occur in limit specifications are not disclosed. Summary of the Invention

[0005] The present invention aims to provide a high-spec hot-rolled weathering steel and its manufacturing method. By focusing on key component design, steelmaking, and rolling process parameter control, this steel achieves stable production of high-spec weathering steel with a thickness of 20 to 25.4 mm and a width of 2000 to 2130 mm on a hot-rolled production line. The resulting steel exhibits high performance, stability, and high and low-temperature toughness, free of defects such as conical coiling and loose coiling.

[0006] Another object of the present invention is to provide an application of extreme specification hot-rolled weathering steel for the manufacture of railway freight cars, large mining cars, bridges, etc.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A hot-rolled weathering steel with extreme specifications comprises the following components in percentage by mass: C: 0.05% to 0.07%; Si: 0.26% to 0.35%; Mn: 0.8% to 1.2%; P: ≤0.090%; S: ≤0.002%; Cr: 0.5% to 0.8%; Ni: 0.05% to 0.09%; Cu: 0.15% to 0.20%; Als: 0.040% to 0.060%; Ti: 0.010% to 0.020%, Nb 0.020% to 0.060%; the remainder being Fe and unavoidable inclusions.

[0009] For the extreme specification hot-rolled weathering steel, if the yield strength is ≥355 MPa, Nb is 0.020-0.040%; if the yield strength is ≥450 MPa, Nb is 0.041-0.060%;

[0010] The microstructure of the extreme specification hot-rolled weathering steel is ferrite+fine pearlite, wherein the volume of fine pearlite accounts for 8-10%, and the grain size is 9-10.

[0011] The extreme specification hot-rolled weathering steel has a thickness of 20 to 25.4 mm and a width of 2000 to 2130 mm.

[0012] When the Nb content of the extreme specification hot-rolled weathering steel is 0.020-0.040%, R eL ≥355MPa, Rm≥480MPa, A≥25%; when Nb is 0.041~0.060%, R eL ≥450MPa, Rm≥550MPa, and A≥25%.

[0013] The yield strength fluctuation of the extreme specification hot-rolled weathering steel in the length direction is less than 50 MPa; the yield strength fluctuation in the width direction is less than 30 MPa.

[0014] The extreme specification hot-rolled weathering steel has high and low temperature toughness: -40℃ KV2 (55×10×10mm) ≥150J; -60℃ KV2 (55×10×10mm) ≥120J, and the ductile-brittle transition temperature is <-60℃. It has good low-temperature toughness and uniformity, and meets the low-temperature service requirements of weathering steel plates for railway freight cars, mine cars, and bridges.

[0015] The extreme specification hot-rolled weathering steel has good coil shape and surface quality: there is no tower-shaped overflow ≤20mm when coiled, and there is no defect such as loose coil.

[0016] The present invention provides a method for manufacturing extreme specification hot-rolled weathering steel, which is produced using a traditional hot-rolled plate and strip process. The manufacturing method includes the following process flow:

[0017] Hot metal pretreatment → converter smelting → LF refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling → unrolling.

[0018] In the LF refining, the sulfur target is ≤0.002% at the end of the LF furnace.

[0019] In order to reduce center porosity and segregation, electromagnetic rollers and dynamic soft reduction are used during the continuous casting process. The thickness of the slab is 250 mm. In order to prevent laminar flow deviation and reduce tower shape, the slab length is ≥ 7 m.

[0020] The slab heating: The slab heating can be carried out by hot charging or cold charging into the furnace.

[0021] Slab heating: To suppress abnormal coarsening of austenite grains, a low tapping temperature of 1140-1180°C is used to improve toughness. To improve temperature uniformity of the slab, the soaking zone temperature is 1160-1200°C, and the soaking zone time is >35 minutes.

[0022] The controlled rolling process involves rough rolling and finishing rolling of heated steel slabs into hot-rolled plates with a thickness of 20-25.4 mm. The final rough rolling temperature is 1020-1080°C, and the finishing reduction is 60-70%. The intermediate bar is 65 mm thick, and medium-frequency electromagnetic induction heating is used to compensate the temperature at the edges of the intermediate bar. The compensation heating value is to increase the temperature 30 mm from the edge by 30-50°C relative to the pre-heating temperature, ensuring a temperature difference of less than 20°C between the edge and the center of the width. The finishing temperature of the finishing rolling is controlled at 800-860°C.

[0023] Multi-stage cooling is carried out after rolling: in order to achieve the ultimate specifications and smoothly coiling in the next process, the first section adopts no cooling for the first 5m, and the coiling temperature is 795-855℃; the second section adopts ultra-fast cooling, with a cooling rate of 50-70℃ / s and a coiling temperature of 500-550℃; the third section adopts tail temperature compensation, and the coiling temperature of the last 30m of the tail is increased by 45-65℃ relative to the second section.

[0024] In order to reduce the tower overflow and loose coiling, strong coiling is adopted, and the relationship between the coiling torque W and the thickness h is as follows: W = W h＝20mm ×(h / 20), where W h＝20mm =180~220kN·m;

[0025] The unit of the winding torque W is kN·m, and the unit of the thickness h is mm.

[0026] The above composition design and controlled rolling and cooling of the present invention are mainly aimed at producing a weathering steel with a thickness of 20-25.4mm and a width of 2000-2130mm on a hot rolling production line. To achieve a good balance of strength and toughness, the main design is "low C + ultra-low S + medium Mn + medium Cr + Nb-Ti composite microalloying". While achieving high strength through precipitation strengthening of a large amount of Nb (C, N) in the austenite region; low-temperature heating, large intermediate billet thickness and high pressure reduction in finishing rolling further reduce the coarsening of austenite grain size, increase deformation in the unrecrystallized austenite region, and refine ferrite grains with Nb (C, N) as nucleation particles; low carbon, high cooling rate and low-temperature coiling are used to further obtain a fine-grained ferrite + fine pearlite structure.

[0027] Measures such as strictly controlling the temperature and time of the soaking section, edge heating compensation, adopting multi-stage cooling and strong coiling, and limiting the lower limit of billet length are all aimed at achieving stable production of extreme-specification weather-resistant coils under the above-mentioned composition and controlled rolling and cooling processes on the hot rolling production line, and reducing technical risks that often occur in extreme-specification coils such as deviation, tower shape, and loose coils.

[0028] The invention provides an application of extreme specification hot-rolled weathering steel for use in the manufacture of railway freight cars, large mining cars, bridges, and the like.

[0029] The design ideas of the present invention are as follows:

[0030] C: The matching and balance of high strength and high toughness of thick-gauge weathering steel is closely related to the C content. In the present invention, firstly, the solid solution strengthening effect of an appropriate content of C ensures its strength; secondly, the overall design concept is based on low carbon, and the low-temperature toughness is improved by the fine grain strengthening and precipitation strengthening of a large amount of Nb (C, N); thirdly, the proportion of pearlite structure is closely related to the C content. The present invention takes ferrite + fine pearlite as the target structure, and the proportion of pearlite should not exceed 10%, so the C content needs to be strictly controlled. Based on the above three reasons, the C content of the present invention is strictly controlled at 0.05-0.07%;

[0031] Si: Si can improve strength through solid solution strengthening and is also an economical element for improving corrosion resistance. However, a high content of Si can easily lead to strip-shaped oxygen defects on the surface of corrosion-resistant steel plates. Therefore, control

[0032] Si: 0.26%~0.35%;

[0033] Mn: Mn significantly improves the strength of thick-gauge weathering steel through solid solution strengthening. However, high Mn content will cause banded structure in the microstructure. This unevenly distributed banded structure is one of the reasons for the decrease in low-temperature toughness. At the same time, a higher Mn content will form MnS inclusions at the center of the ingot thickness, thereby deteriorating impact toughness. In order to reduce the generation of banded structure and MnS inclusions, a medium Mn design is adopted, and the Mn content is controlled at 0.80-1.2%.

[0034] P: P is the most economical element to improve the atmospheric corrosion resistance of steel. When combined with Cu and a small amount of Cr and Ni, excellent corrosion resistance can be achieved. In addition, P also has a strong solid solution strengthening effect. However, a high P content can easily segregate at the grain boundaries, sharply reducing the toughness of the steel, especially the low-temperature toughness, causing "cold brittleness" and increasing the sensitivity of welding cracks. The present invention can add P to improve atmospheric corrosion resistance, so the P content is designed to be P: ≤ 0.090%

[0035] S: S has a significant impact on the low-temperature impact toughness of thick-gauge weathering steel, which is mainly closely related to the formation of pancake-shaped MnS. Therefore, the present invention adopts an ultra-low S design to reduce the formation of MnS inclusions, so S≤0.002%.

[0036] Als: In addition to being a strong deoxidizing element, the main purpose of adopting a higher Als content in the present invention is to refine the austenite grains to obtain better grain refinement strengthening, thereby improving the low-temperature impact toughness under the limit specification and low reduction ratio. Therefore, Als is controlled to be 0.040-0.060%.

[0037] Cr, Ni, and Cu are added in combination: Cr: 0.5-0.8%; Ni: 0.05-0.09%; Cu: 0.15-0.20%. Through the synergistic effect of the three corrosion-resistant elements, a dense and stable rust layer is enriched on the surface, preventing the corrosive medium from diffusing into the matrix and improving the corrosion resistance of the material. On the other hand, the addition of a higher content (0.5-0.8%) of Cr not only helps to improve the stability of austenite before water cooling after final rolling, but also inhibits the formation of large-scale pro-eutectoid ferrite under conditions of low compression ratio and low cooling rate in the core of thick-gauge steel plates; at the same time, the higher Cr content significantly enhances its hardenability, thereby improving the uniformity and stability of the microstructure and performance in the full-thickness direction; Ni is an element that significantly improves low-temperature toughness and inhibits the precipitation of low-melting-point Cu. A higher content of Cu will cause the segregation of Cu-containing phases, resulting in blocky or strip-shaped precipitation, resulting in uneven distribution of the precipitated phase, which in turn leads to unstable impact energy. Therefore, Ni: 0.05-0.09%; Cu: 0.15-0.20%.

[0038] Selective addition of Nb and Ti: Niobium and titanium are mainly combined with C and N elements to form carbonitrides, which improve the strength through two strengthening effects: grain refinement and precipitation. The present invention can achieve flexible selection of 355MPa and 450MPa grades according to the amount of Nb added. ① When Nb is 0.020-0.040%, R eL ≥355, Rm≥480MPa;②When Nb is 0.041~0.060%, R eL ≥450MPa, Rm≥550MPa. At the same time, this extreme specification weathering steel is mostly formed by welding, so weldability is extremely important. Therefore, the design of 0.010-0.020% Ti is also to inhibit the coarsening of austenite grains during welding through TiN.

[0039] Compared with the prior art, the present invention, through the above composition design and production process, obtains the extreme specification hot-rolled corrosion-resistant steel plate with high low temperature toughness and high performance uniformity with a thickness of 20 to 25.4 mm and a width of 2000 to 2130 mm. It has the following advantages: high strength and plasticity and good mechanical property stability; flexible adjustment is achieved according to the addition of Nb: when the Nb content is 0.020 to 0.040%, R eL ≥355MPa, Rm≥480MPa, A≥25%; when Nb is 0.041~0.060%, R eL≥450MPa, Rm ≥550MPa, and A ≥25%; yield strength fluctuation along the coil length is less than 50MPa; yield strength fluctuation along the width is less than 30MPa. High and low-temperature toughness: -40°C KV2 (55×10×10mm) ≥150J; -60°C KV2 (55×10×10mm) ≥120J. The ductile-brittle transition temperature is <-60°C, demonstrating excellent low-temperature toughness and stability, meeting the low-temperature service requirements of weathering steel plate for railway vehicles and mining cars. Excellent coil shape and surface quality: no concavity (overflow ≤20mm) or loose coils. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the surface microstructure morphology of Example 1;

[0041] Figure 2 This is the microstructure morphology of Example 1 at 1 / 4 thickness;

[0042] Figure 3 This is the microstructure morphology of Example 1 at 1 / 2 thickness;

[0043] Figure 4 The roll shape of Example 1;

[0044] Figure 5 Comparative Example 5 roll shape;

[0045] Figure 6 This is a photo of the comparative example 2 where the steel was not coiled successfully due to deviation caused by the billet being too short;

[0046] Figure 7 It is the roll shape of comparative example 8. DETAILED DESCRIPTION

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0048] The present invention provides a hot-rolled weathering steel with an extreme specification, wherein the main chemical components and their weight percentage contents (wt%) of the hot-rolled weathering steel with an extreme specification are: C: 0.05% to 0.07%; Si: 0.26% to 0.35%; Mn: 0.8% to 1.2%; P: ≤0.090%; S: ≤0.002%; Cr: 0.5% to 0.8%; Ni: 0.05% to 0.09%; Cu: 0.15% to 0.20%; Als: 0.040% to 0.060%; Ti: 0.010% to 0.020%, Nb is selectively added, if the yield strength is ≥355MPa, Nb is 0.020% to 0.040%, if the yield strength is ≥450MPa, then Nb is 0.041% to 0.060%; the balance is Fe and unavoidable inclusions.

[0049] A method for manufacturing extreme specification hot-rolled weathering steel has the following process flow: molten iron pretreatment → converter smelting → LF refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling → flattening.

[0050] 1) Smelting, refining and continuous casting processes

[0051] Molten steel is smelted according to the above chemical composition, and attention is paid to desulfurization: at the end of the LF furnace, the sulfur target is ≤0.002%.

[0052] To reduce center porosity and segregation, electromagnetic rollers and dynamic soft reduction are used during continuous casting. The thickness of the slab is 250mm. To prevent laminar flow deviation and reduce tower shape, the slab length is ≥7m.

[0053] 2) Slab heating, controlled rolling and controlled cooling processes

[0054] The slab can be reheated by hot or cold charging into the furnace. To suppress abnormal coarsening of austenite grains, a furnace discharge temperature of 1140-1180°C is used to improve toughness. However, to improve slab temperature uniformity, the soaking zone temperature is 1160-1200°C, and the soaking zone time is >35 minutes.

[0055] The heated steel slab undergoes rough rolling and finish rolling to produce hot-rolled plates with a thickness of 20 to 25.4 mm. The final rough rolling temperature is 1020 to 1080°C; the finishing reduction is 60 to 70%, and the intermediate bar thickness is 65 mm. A medium-frequency electromagnetic induction edge heater is used to compensate for the temperature of the intermediate bar edge. The compensation heating value is to increase the temperature 30 mm from the edge by 30 to 50°C relative to the pre-heating temperature, so that the temperature difference between the edge and the center of the width is less than 20°C. The finishing temperature is controlled at 800 to 860°C.

[0056] Multi-stage cooling is carried out after rolling: in order to achieve the ultimate specifications and smoothly coiling in the next process, the first section adopts no cooling for the first 5m, and the coiling temperature is 795-855℃; the second section adopts ultra-fast cooling, with a cooling rate of 50-70℃ / s and a coiling temperature of 500-550℃; the third section adopts tail temperature compensation, and the coiling temperature of the last 30m of the tail is increased by 45-65℃ on the basis of the second section.

[0057] In order to reduce loose coiling, strong coiling is adopted, and the relationship between the coiling torque W and the thickness h is as follows: W = W h＝20mm ×

[0058] (h / 20). Where W h＝20mm =180~220kN·m;

[0059] The unit of the winding torque W is kN·m, and the unit of the thickness h is mm.

[0060] The present invention obtains a hot-rolled corrosion-resistant steel plate with extreme specifications, high low-temperature toughness and high performance uniformity, with a thickness of 20 to 25.4 mm and a width of 2000 to 2130 mm through the above component design and coordinated production process.

[0061] Several specific embodiments and comparative examples of the present invention are as follows:

[0062] Example 1-Example 2

[0063] A limit specification hot-rolled weathering steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0064] Comparative Example 1-Comparative Example 8

[0065] A limit specification hot-rolled weathering steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0066] Table 1 Chemical compositions of the embodiments of the present invention and comparative examples

[0067]

[0068] The manufacturing method of the extreme specification hot-rolled weathering steel of the above embodiments and comparative examples has the following process flow: molten iron pretreatment → converter smelting → LF refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling → unrolling.

[0069] 1) Smelting, refining and continuous casting processes

[0070] Molten steel is smelted according to the above chemical composition, with particular attention to desulfurization. At the end of the LF furnace, the sulfur target is ≤ 0.002%.

[0071] To reduce center porosity and segregation, electromagnetic rollers and dynamic soft reduction are used during continuous casting. The thickness of the slab is 250mm. To prevent laminar flow deviation and reduce tower shape, the slab length is ≥7m.

[0072] 2) Slab heating, controlled rolling and controlled cooling processes

[0073] The slab can be reheated by hot or cold charging into the furnace. To suppress abnormal coarsening of austenite grains, a tapping temperature of 1140-1180°C is used to improve toughness. However, to improve slab temperature uniformity, the soaking zone temperature is 1160-1200°C, and the soaking zone time is >35 minutes.

[0074] The heated steel slab is rolled into hot-rolled plates with a thickness of 20 to 25.4 mm through rough rolling and finishing rolling. The final rough rolling temperature is 1020 to 1080°C; the finishing rolling reduction is 60 to 70%, and the intermediate bar thickness is 65 mm. A medium-frequency electromagnetic induction edge heater is used to compensate the temperature of the intermediate bar edge. The heating value is to increase the temperature by 30 to 50°C at 30 mm from the edge, so that the temperature difference between the edge and the center of the width is less than 20°C. The finishing rolling temperature is 800 to 860°C.

[0075] Multi-stage cooling is carried out after rolling: in order to achieve the ultimate specifications and smoothly coiling in the next process, the first section adopts no cooling for the first 5m, and the coiling temperature is 795-855℃; the second section adopts ultra-fast cooling, with a cooling rate of 50-70℃ / s and a coiling temperature of 500-550℃; the third section adopts tail temperature compensation, and the coiling temperature of the last 30m of the tail is increased by 45-65℃ relative to the second section.

[0076] In order to reduce loose coiling, strong coiling is adopted, and the relationship between the coiling torque W and the thickness h is as follows: W = W h＝20mm ×

[0077] (h / 20). Where W h＝20mm =180~220kN·m;

[0078] The unit of the winding torque W is kN·m, and the unit of the thickness h is mm.

[0079] The main rolling process parameters of each embodiment and comparative example are shown in Table 2.

[0080] Table 2 Main production process parameters of each embodiment and comparative example

[0081]

[0082]

[0083] The mechanical properties of the embodiments and comparative examples are shown in Table 3. The tensile test method was in accordance with GB / T 228, and the impact test was in accordance with GB / T 229.

[0084] Table 3 Mechanical properties of examples and comparative examples

[0085]

[0086] Figures 1 to 3 This is the microstructure of an example of the present invention under an optical microscope. The microstructure of the steel plate is primarily composed of ferrite and fine pearlite, with a grain size of 10. This invention achieves uniform and refined F+P through a controlled rolling and cooling process combining low-temperature coiling with "low C + ultra-low S + medium Mn + medium Cr," resulting in high plasticity and excellent low-temperature toughness.

[0087] Figure 4 and Figure 5 The roll-shaped photos of the embodiments of the present invention and the comparative examples are shown in FIG1. Figure 4 As shown, the comparative example 5 with overflow of 78mm is shown Figure 5 shown. Figure 6 The deviation and steel piling were caused by the short length of the slab (the length of the slab in Comparative Example 2 was 6.5 m).

[0088] The C content of Comparative Example 1 is relatively high. Even though it is produced according to the process of the present invention, its plasticity is relatively low and its low-temperature toughness is poor.

[0089] Comparative Example 2 has a high Mn content, and even when produced according to the process of the present invention, the resulting finished product has poor low-temperature toughness. Furthermore, due to the short ingot length in Comparative Example 2, the rolled strip is only 80-90 meters long, while the length from the F7 finishing mill to the No. 1 coiler exceeds 130 meters. After the tail of the strip exits F7, the head of the strip does not enter the coiler for stretching, relying solely on the friction of the rollers. This short, wide strip can severely deviate, increasing the risk of steel pile-up.

[0090] The S content in Comparative Example 3 is relatively high, and even if produced according to the process of the present invention, the obtained finished product has poor low-temperature toughness.

[0091] The Nb and Ti contents of Comparative Example 4 are relatively low. Even if produced according to the process of the present invention, the obtained finished product has low tensile strength and poor low-temperature toughness.

[0092] The ingredients of Comparative Example 5 meet the requirements of the present invention, but the soaking temperature is high and the soaking time is short during production, resulting in a coiling overflow of 78 mm and poor low-temperature toughness.

[0093] The composition of Comparative Example 6 meets the requirements of the present invention, but edge heating is not used during production, and the coiling temperature in the middle section is relatively high, resulting in a coiling overflow of 66 mm, poor low-temperature toughness, and large fluctuations in yield strength in the width direction of the coil.

[0094] The composition of Comparative Example 7 meets the requirements of the present invention, but the finishing rolling temperature is low during production, and the head and tail coiling temperatures are also low, resulting in large fluctuations in the yield strength along the length of the coil.

[0095] The composition of Comparative Example 8 meets the requirements of the present invention, but insufficient torque is used for strong winding, resulting in loose coils, poor coil shape, and overflow of 24 mm.

[0096] The above embodiments are described to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A hot-rolled weathering steel with extreme specifications, characterized in that: The extreme specification hot-rolled weathering steel comprises the following mass percentage components: C: 0.05% to 0.07%; Si: 0.26% to 0.35%; Mn: 0.8% to 1.2%; P：≤0.090％； S: ≤0.002%; Cr: 0.5%~0.8%; Ni: 0.05%~0.09%; Cu: 0.15%~0.20%; Als: 0.040%~0.060%; Ti: 0.010%~0.020%, Nb 0.020%~0.060%; the balance is Fe and unavoidable inclusions; The method for manufacturing the extreme specification hot-rolled weathering steel includes the following process flow: Hot metal pretreatment → converter smelting → LF refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling → flattening; The continuous casting has a billet length of ≥7m; The slab is heated with a soaking zone temperature of 1160-1200°C and a soaking zone time of >35 minutes; The controlled rolling process includes: a finishing intermediate billet with a thickness of 65 mm, temperature compensation is performed on the edge of the intermediate billet, the compensation heating value is 30-50°C higher than that before heating at the edge 30 mm, and the temperature difference between the edge 30 mm and the center in the width direction is ensured to be less than 20°C, and the finishing rolling temperature is controlled to be 800-860°C; The controlled cooling method is to perform multi-stage cooling after rolling: the first stage adopts no cooling for the first 5m, with a coiling temperature of 795-855°C; the second stage adopts ultra-fast cooling with a cooling rate of 50-70°C / s and a coiling temperature of 500-550°C; the third stage adopts tail temperature compensation, with the coiling temperature of the last 30m of the tail increased by 45-65°C relative to the second stage; The relationship between the winding torque W and the thickness h is as follows: W=W h=20mm ×(h / 20), where W h=20mm =180~220 kN▪m; The unit of coiling torque W is kN▪m, and the unit of thickness h is mm.

2. The extreme specification hot-rolled weathering steel according to claim 1, characterized in that: The extreme specification hot-rolled weathering steel has a thickness of 20~25.4mm and a width of 2000~2130mm.

3. The extreme specification hot-rolled weathering steel according to claim 1 or 2, characterized in that: For the above-mentioned extreme specification hot-rolled weathering steel, when Nb is 0.020~0.040%, R eL ≥355MPa, Rm≥480MPa, A≥25%; or, when Nb is 0.041~0.060%, R eL ≥450MPa, Rm≥550MPa, and A≥25%.

4. The extreme specification hot-rolled weathering steel according to claim 1, characterized in that: The yield strength fluctuation of the extreme specification hot-rolled weathering steel in the longitudinal direction is less than 50MPa; the yield strength fluctuation in the width direction is less than 30MPa; the KV2 of the extreme specification hot-rolled weathering steel at -40℃ is ≥150J; and the KV2 at -60℃ is ≥120J.

5. The extreme specification hot-rolled weathering steel according to claim 1, characterized in that: Overflow when rolling ≤20mm.

6. A method for manufacturing the extreme specification hot-rolled weathering steel according to any one of claims 1 to 5, characterized in that: The manufacturing method includes the following process flow: Hot metal pretreatment → converter smelting → LF refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling → flattening; The continuous casting has a billet length of ≥7m; The slab is heated with a soaking zone temperature of 1160-1200°C and a soaking zone time of >35 minutes; The controlled rolling process includes: a finishing intermediate billet with a thickness of 65 mm, temperature compensation is performed on the edge of the intermediate billet, the compensation heating value is 30-50°C higher than that before heating at the edge 30 mm, and the temperature difference between the edge 30 mm and the center in the width direction is ensured to be less than 20°C, and the finishing rolling temperature is controlled to be 800-860°C; The controlled cooling method is to perform multi-stage cooling after rolling: the first stage adopts no cooling for the first 5m, with a coiling temperature of 795-855°C; the second stage adopts ultra-fast cooling with a cooling rate of 50-70°C / s and a coiling temperature of 500-550°C; the third stage adopts tail temperature compensation, with the coiling temperature of the last 30m of the tail increased by 45-65°C relative to the second stage; The relationship between the winding torque W and the thickness h is as follows: W=W h=20mm ×(h / 20), where W h=20mm =180~220 kN▪m; The unit of coiling torque W is kN▪m, and the unit of thickness h is mm.

7. An application of the extreme specification hot-rolled weathering steel according to any one of claims 1 to 5, characterized in that: Used in the manufacture of railway freight cars, large mining cars and bridges.

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