Limit specification hot continuous rolling weathering steel and manufacturing method and application thereof

Abstract

The invention provides limit specification hot continuous rolling weathering steel as well as a manufacturing method and application thereof. The component C is 0.05-0.07%; 0.26%-0.35% of Si; 0.8% to 1.2% of Mn; p is less than or equal to 0.090%; s < = 0.002%; 0.5%-0.8% of Cr; 0.05%-0.09% of Ni; 0.15% to 0.20% of Cu; 0.020% to 0.045% of Al < t >; 0.010% to 0.020% of Ti, and 0.020% to 0.060% of Nb; and the balance of Fe and inevitable inclusions. According to the hot continuous rolling weather-resistant steel plate and the preparation method thereof, the hot continuous rolling weather-resistant steel plate which is 20-25.4 mm in thickness, 2000-2130 mm in width, high in low-temperature toughness and high in performance uniformity in limit specification, good in coil shape and surface quality and free of tower shape and coil loosening in the coiling process is obtained through component design in cooperation with process production.

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] The hot rolling production line produces ultra-wide and ultra-thick extreme specifications of 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 trucks, large mining cars, bridges and other fields. Although its usage is less than that of similar specifications of weathering medium plates, it has good economic benefits and product added value due to its advantages such as convenient transportation of coils and good cooling control. However, the technology of producing ultra-wide and ultra-thick extreme specifications of weathering steel on the hot rolling production line is difficult. The main problems are low temperature hit rate and poor stability, poor low-temperature toughness, and easy occurrence of tower and loose coils. It is difficult to achieve stable batch production of such products on the hot rolling production line, so this extreme specification weathering steel plate is mostly produced by medium and thick plate production lines. Therefore, how to stably produce an extreme specification weathering steel coil on the hot rolling production line is a key technical difficulty.

[0003] The Chinese invention patent with publication number CN 114657479 A published on June 24, 2022, discloses a thick-gauge, high-strength, and low-temperature toughness hot-rolled corrosion-resistant steel and its manufacturing method and application, with 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%, and V / N = 4-5, the remainder is Fe and unavoidable inclusions. Thickness 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] The Chinese invention patent with the publication number CN 106521352A published on March 22, 2017, discloses a niobium-containing thick-gauge weathering steel and its rolling method, with chemical composition of 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%, and the rest is Fe and unavoidable impurities. The patent adopts low P+high Mn+low Cr+single Nb design, and is suitable for thickness ≥16mm. The embodiment specifically states that it is rolled at Panzhihua 2050, indicating that the actual width is mostly below 1950mm, not an ultra-wide specification. It adopts medium-temperature coiling, and the coiling temperature is 555~585℃. Although the yield strength of the mechanical properties index reaches 450MPa, there is no disclosure of the stabilization control of the mechanical properties in the length and width directions of the hot coil 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. Summary of the invention

[0005] The purpose of the present invention is to provide an extreme specification hot-rolled weathering steel and a manufacturing method thereof, which realizes the stable production of extreme specification weathering steel with a thickness of 20 to 25.4 mm and a width of 2000 to 2130 mm in a hot-rolled production line from the technical points of key component design, steelmaking and rolling process parameter control. The steel has no defects such as tower shape and loose coil when rolled and has the advantages of high performance stability, high and low temperature toughness, etc.

[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 is Fe and unavoidable inclusions.

[0009] For the extreme specification hot-rolled weathering steel, if the yield strength is ≥355MPa, Nb is 0.020-0.040%; if the yield strength is ≥450MPa, then Nb: 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 50MPa; the yield strength fluctuation in the width direction is less than 30MPa.

[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 are no defects such as loose coils.

[0016] The present invention provides a method for manufacturing extreme specification hot-rolled weathering steel, which is produced by a conventional 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 → opening.

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

[0019] In order to reduce the center looseness and segregation, electromagnetic rollers and dynamic soft pressure are used in the continuous casting process. The thickness of the ingot is 250mm. In order to prevent the laminar flow from running off and reduce the tower type, the ingot length is ≥7m.

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

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

[0022] The controlled rolling process: the heated steel billet is rolled into a hot-rolled plate with a thickness of 20 to 25.4 mm in two stages of rough rolling and finish rolling. The rough rolling final rolling temperature is 1020 to 1080°C; the finish rolling reduction rate is 60 to 70%. The intermediate billet thickness is 65 mm, and the intermediate billet edge is temperature compensated by medium-frequency electromagnetic induction heating. The compensation heating value is 30 to 50°C higher than before heating at the edge 30 mm, so that the temperature difference between the edge 30 mm and the center in the width direction is less than 20°C. The finish rolling final rolling temperature is controlled to be 800 to 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 the head 5m without cooling, 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 increases 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 controlled cooling of the present invention are mainly to obtain an extreme specification weathering steel with a thickness of 20 to 25.4 mm and a width of 2000 to 2130 mm in the hot rolling production line. In order to obtain a good match of strength and toughness, the main design is "low C + ultra-low S + medium Mn + medium Cr + Nb-Ti composite microalloying". By strengthening the precipitation of a large amount of Nb (C, N) in the austenite region to achieve high strength; low temperature heating, large intermediate billet thickness and high pressure reduction in finishing rolling further reduce the coarsening of austenite grain size, increase the deformation of the austenite non-recrystallization zone and Nb (C, N) as nucleation particles to refine the ferrite grains; low carbon, high cooling rate and low temperature coiling are to further obtain fine-grained ferrite + fine pearlite structure.

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

[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 the 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-compression 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, but high Mn 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 content of Mn will form MnS inclusions at the center of the ingot thickness, thereby deteriorating the impact toughness. In order to reduce the generation of banded structure and MnS inclusions, a medium Mn design is adopted to control the Mn content at 0.80-1.2%.

[0034] P: P is the most economical element to improve the atmospheric corrosion resistance of steel. It can obtain excellent corrosion resistance by adding a small amount of Cr and Ni in combination with Cu. In addition, P also has a strong solid solution strengthening effect. However, if the P content is high, it is easy to segregate at the grain boundary, which will sharply reduce the toughness of the steel, especially the low-temperature toughness, causing the "cold brittleness" phenomenon, and increase the sensitivity of welding cracks. The present invention can add P to improve the atmospheric corrosion resistance, so the P content is designed to be P: ≤0.090%

[0035] S: S has a great influence on the low-temperature impact toughness of thick-gauge weathering steel, which is mainly 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 effect, thereby improving the low-temperature impact toughness under the limit specification and low reduction ratio, so Als is controlled to be 0.040-0.060%.

[0037] Cr, Ni, Cu composite addition: 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 to prevent the corrosion medium from diffusing into the matrix and improve the corrosion resistance of the material. On the other hand, the addition of a higher content (0.5-0.8%) of Cr is not only beneficial to improve the stability of austenite before water cooling after final rolling, but also inhibits the formation of large-sized pro-eutectoid ferrite under the conditions of small compression ratio and low cooling rate in the core of thick-gauge steel plates; at the same time, higher Cr significantly enhances its hardenability, thereby improving the uniformity and stability of the microstructure in the full thickness direction; Ni is an element that significantly improves low-temperature toughness, while inhibiting the precipitation of low-temperature melting point Cu. A higher content of Cu will cause the segregation of Cu-containing phases, causing block or strip precipitation, resulting in uneven distribution of precipitation phases, which leads to unstable impact energy. Therefore, Ni is controlled to be 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 can improve strength through two strengthening effects: fine grain and precipitation. The present invention can achieve flexible selection of 355MPa and 450MPa levels 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, most of this extreme specification weathering steel is formed by welding, so welding performance is extremely important. Therefore, the use 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 adopts the above composition design and production process to obtain the hot-rolled corrosion-resistant steel plate with extreme specifications of high and 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 plasticity and good mechanical property stability; flexible adjustment according to Nb addition: when Nb 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%; the yield strength fluctuation in the length direction of the coil is less than 50MPa; the yield strength fluctuation in the width direction is less than 30MPa. It has high and low temperature toughness: -40℃KV2(55×10×10mm)≥150J; -60℃KV2(55×10×10mm)≥120J, the tough-brittle transition temperature is less than -60℃, and it has good low temperature toughness and stability, meeting the low temperature service requirements of weathering steel plates for railway vehicles and mine cars. It has good coil shape and surface quality: no tower shape (overflow ≤20mm) and no loose coil when coiled. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The surface microstructure of Example 1;

[0041] Figure 2 The microstructure morphology of Example 1 at 1 / 4 thickness;

[0042] Figure 3 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 physical picture of the comparative example 2 in which the steel pile failed to be successfully coiled due to the billet being too short;

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

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are 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 are within the scope of protection of the present invention.

[0048] The present invention provides a kind of extreme specification hot-rolled weathering steel, and the main chemical components and weight percentage contents (wt%) of the extreme specification hot-rolled weathering steel are: C: 0.05%-0.07%; Si: 0.26%-0.35%; Mn: 0.8%-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 is selectively added, if the yield strength is ≥355MPa, Nb is 0.020-0.040%, if the yield strength is ≥450MPa, then Nb: 0.041-0.060%; the balance is Fe and unavoidable inclusions.

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

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

[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] In order to reduce center looseness and segregation, electromagnetic rollers and dynamic soft pressure are used in the continuous casting process. The thickness of the slab is 250mm. In order to prevent laminar deviation and reduce tower type, the length of the slab is ≥7m.

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

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

[0055] The heated steel billet is rolled into a hot-rolled plate with a thickness of 20 to 25.4 mm in two stages of rough rolling and finish rolling. The rough rolling final rolling temperature is 1020 to 1080°C; the finish rolling reduction rate is 60 to 70%, the intermediate billet thickness is 65 mm, and the intermediate billet edge is temperature compensated by a medium-frequency electromagnetic induction edge heater. The compensation heating value is 30 to 50°C higher than before heating at the edge 30 mm, so that the temperature difference between the edge 30 mm and the center of the width direction is less than 20°C. The finish rolling final rolling 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 stage adopts the head 5m without cooling, and the coiling temperature is 795-855℃; the second stage adopts ultra-fast cooling, with a cooling rate of 50-70℃ / s and a coiling temperature of 500-550℃; the third stage 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 stage.

[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 of high and 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 process production.

[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 the comparative examples

[0067]

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

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

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

[0071] In order to reduce center looseness and segregation, electromagnetic rollers and dynamic soft pressure are used in the continuous casting process. The thickness of the slab is 250mm. In order to prevent laminar deviation and reduce tower type, the length of the slab is ≥7m.

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

[0073] The billet can be reheated by hot or cold charging into the furnace. In order to suppress the abnormal coarsening of austenite grains, the furnace discharge temperature of 1140-1180°C is used to improve toughness. However, in order to improve the temperature uniformity of the billet, the soaking section temperature is 1160-1200°C. The soaking section time is >35min.

[0074] The heated steel billet is rolled into a hot-rolled plate with a thickness of 20 to 25.4 mm in two stages of rough rolling and finish rolling. The rough rolling final rolling temperature is 1020 to 1080°C; the finish rolling reduction rate is 60 to 70%, the intermediate billet thickness is 65 mm, and the intermediate billet edge is temperature compensated by a medium-frequency electromagnetic induction edge heater. The heating value is 30 to 50°C at 30 mm from the edge, so that the temperature difference between the edge 30 mm and the center of the width direction is less than 20°C, and the finish rolling final 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 the head 5m without cooling, 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 increases 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 each embodiment and comparative example are shown in Table 3. The tensile test method is in accordance with GB / T 228, and the impact test is performed in accordance with GB / T 229.

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

[0085]

[0086] Figure 1 to Figure 3 The microstructure morphology of the embodiment of the present invention under an optical microscope shows that the microstructure of the steel plate is mainly ferrite + fine pearlite, and the grain size is level 10. The present invention obtains uniform and refined F+P through the controlled rolling and controlled cooling process of "low C + ultra-low S + medium Mn + medium Cr" combined with low-temperature coiling, and has good low-temperature toughness on the basis of high plasticity.

[0087] Figure 4 and Figure 5 The roll-shaped photos of the embodiments of the present invention and the comparative examples are shown in Example 1 with overflow less than 20 mm. Figure 4 As shown, the comparative example 5 with overflow of 78 mm is shown in Figure 5 shown. Figure 6 The deviation and steel piling were caused by the short length of the ingot (the ingot length of 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] The Mn content of Comparative Example 2 is relatively high, and even if it is produced according to the process of the present invention, the low-temperature toughness of the finished product is poor. At the same time, due to the short length of the ingot in Comparative Example 2, the length of the strip after rolling is only 80-90m, while the length from the F7 finishing mill to the 1# coiler exceeds 130m. After the tail of the strip exits F7, the head of the strip has not yet entered the coiler for sheeting, and can only move forward by relying on the friction of the roller. The short and wide steel strip deviates seriously, resulting in an increased risk of steel pile-up.

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

[0091] The contents of Nb and Ti in 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 time is short during production, resulting in a coiling overflow of 78 mm and poor low-temperature toughness.

[0093] The ingredients of Comparative Example 6 meet the requirements of the present invention, but edge heating is not used in 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 ingredients of Comparative Example 7 meet 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 ingredients of Comparative Example 8 meet the requirements of the present invention, but the strong winding is not carried out with a sufficiently large torque, resulting in loose winding, poor winding shape, and overflow of 24 mm.

[0096] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 protection scope 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 inevitable inclusions.

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 to 25.4 mm and a width of 2000 to 2130 mm.

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 limit specification hot-rolled weathering steel has a yield strength fluctuation of less than 50MPa in the length direction of the coil; the yield strength fluctuation in the width direction is less than 30MPa; the limit specification hot-rolled weathering steel has a KV2≥150J at -40℃; and a KV2≥120J at -60℃.

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 comprises the following process flow: Hot metal pretreatment → converter smelting → LF refining → continuous casting → slab heating → controlled rolling → controlled cooling → coiling → opening.

7. The manufacturing method according to claim 6, characterized in that: In the continuous casting, the length of the ingot is ≥7m.

8. The manufacturing method according to claim 6, characterized in that: The slab is heated, the soaking zone temperature is 1160-1200° C., and the soaking zone time is greater than 35 minutes.

9. The manufacturing method according to claim 6, characterized in that: The controlled rolling: the thickness of the intermediate billet for finishing rolling is 65mm, and the edge of the intermediate billet is temperature compensated. The compensation heating value is 30-50°C higher than that before heating at 30mm of the edge, ensuring that the temperature difference between 30mm of the edge and the center in the width direction is less than 20°C, and the finishing rolling final rolling temperature is controlled to be 800-860°C.

10. The manufacturing method according to claim 6, characterized in that: The controlled cooling is performed in multiple stages after rolling: the first stage adopts no cooling for the head 5m, and the coiling temperature is 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, and the coiling temperature of the last 30m of the tail is increased by 45-65°C relative to the second stage.

11. The manufacturing method according to claim 6, characterized in that: The relationship between the winding torque W and the thickness h is as follows: W = W h＝20mm ×(h / 20), where W h＝20mm =180~220kN·m; the unit of winding torque W is kN·m, and the unit of thickness h is mm.

12. 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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