A 700MPa grade hot-rolled high-strength high-weathering steel and its preparation method and application

Abstract

The present application relates to the field of weathering steel materials, and in particular to a 700MPa grade hot-rolled high-strength high-weathering steel and a preparation method and application thereof; the chemical composition of the hot-rolled high-strength high-weathering steel comprises, by mass fraction, C: 0.043% to 0.048%, Si: 0.51% to 0.59%, Mn: 0.61% to 0.68%, P: 0.041% to 0.049%, S: 0.0031% to 0.0038%, Al: 0.071% to 0.079%, Ti: 0.092% to 0.099%, Cu: 0.251% to 0.259%, Cr: 1 .81%~1.98%, N: 0.0031%~0.0034%, and the rest are Fe and unavoidable impurities; adopt micro-alloying design with low C content, low Mn content and high Ti content to improve the overall strength of high weathering steel, reduce the deformation resistance during rolling process, and have good rolling stability. Composite weathering resistance design is carried out for Si, P, Cu and Cr elements to give full play to the contribution of cheap weathering elements such as Si and P to weathering resistance and solid solution strengthening, and then utilize Cu to reduce the adverse effects of chromium carbide on weather resistance and toughness, so as to achieve simultaneous improvement of weather resistance and strength and toughness, while also reducing rolling difficulty and alloy cost.

Description

Technical Field

[0001] The present application relates to the field of weathering steel materials, and in particular to a 700MPa grade hot-rolled high-strength high-weathering steel and a preparation method and application thereof. Background Art

[0002] As a functional structural steel with good atmospheric corrosion resistance, weathering steel has been widely used in containers, railway vehicles, bridges, buildings, towers, photovoltaic brackets and other fields. However, there are generally problems of light weight, insufficient corrosion resistance and low service life. Potential solutions also have problems such as excessive addition of precious alloys, high cost and deviation in welding performance, which have restricted the green and high-quality development of the steel structure industry. At present, the highest strength grade weathering steel is the yield strength of 700MPa, and thin-gauge high-strength weathering steel of 700MPa and above can be divided into Cr-Ni-Cu system, Cr-Ni-Cu-P system and Cr-Cu-P system according to weathering alloy elements. At present, the Cr-Ni-Cu system is the main one. However, there are the following disadvantages:

[0003] 1) Cr-Ni-Cu weathering alloy system: A large amount of precious alloy Ni element is added to the main system, the cost is high, and the economy is not strong. Some systems have high alloy content, difficult smelting and rolling, and there is a problem of welding formability deviation;

[0004] 2) Cr-Ni-Cu-P weather-resistant alloy system: This system is mainly used in thin slab continuous casting and rolling production lines and thin strip casting and rolling production lines, but it has the problems of high micro-alloying cost, containing precious alloy Ni elements, high deformation resistance of thin strip rolling, and insufficient contribution of economic phosphorus elements to weather resistance;

[0005] 3) Cr-Cu-P weather-resistant alloy system: This system has poor weather resistance and is difficult to meet high weather resistance requirements.

[0006] Therefore, how to provide a hot-rolled high-strength and high-weathering steel that contains no or a small amount of precious metal elements to reduce the rolling difficulty and alloy cost is a technical problem that urgently needs to be solved. Summary of the invention

[0007] The present application provides a 700MPa grade hot-rolled high-strength high-weathering steel and a preparation method and application thereof, in order to solve the technical problems in the prior art that excessive addition of precious alloys in high-weathering steel leads to excessive rolling difficulty and excessive alloy cost.

[0008] In the first aspect, the present application provides a 700MPa grade hot-rolled high-strength and high-weathering steel. The chemical composition of the hot-rolled high-strength and high-weathering steel includes, by mass fraction: C: 0.043%~0.048%, Si: 0.51%~0.59%, Mn: 0.61%~0.68%, P: 0.041%~0.049%, S: 0.0031%~0.0038%, Al: 0.071%~0.079%, Ti: 0.092%~0.099%, Cu: 0.251%~0.259%, Cr: 1.81%~1.98%, N: 0.0031%~0.0034%, and the rest is Fe and unavoidable impurities.

[0009] Optionally, the microstructure of the hot-rolled high-strength and high-weathering steel includes ferrite and TiC nano-scale precipitates, wherein the nano-scale precipitates with a particle size of 2nm to 5nm in the ferrite account for more than 88% of the TiC nano-scale precipitates.

[0010] Optionally, the thickness h of the hot-rolled high-strength and high-weathering steel is 1.2 mm to 8.0 mm.

[0011] In a second aspect, the present application provides a method for preparing the hot-rolled high-strength and high-weathering steel according to the first aspect, the method comprising:

[0012] Obtaining a cast billet having the same chemical composition as the hot-rolled high-strength and high-weathering steel described in the first aspect;

[0013] The ingot is heated, and then roughly descaled and roughly rolled in sequence to obtain an intermediate slab;

[0014] The intermediate slab is subjected to fine descaling, fine rolling, ultra-fast cooling, laminar cooling, and coiling to obtain hot-rolled high-strength and high-weathering steel.

[0015] Optionally, the heating includes a preheating section, a first heating section, a second heating section and a soaking section, wherein the heating rate of the preheating section is 16°C / min to 19°C / min, and the end temperature of the preheating section is ≥850°C;

[0016] The end temperature T1 of the heating stage satisfies:

[0017] T1=T*(0.936-0.013h+0.0020h 2 );

[0018] Wherein, h is the thickness of the hot-rolled high-strength high-weathering steel, mm; T is the heating furnace temperature; and / or,

[0019] The end temperature T2 of the second heating stage satisfies:

[0020] T2=T*(1.016-0.015h+0.0018h 2 );

[0021] Wherein, h is the thickness of the hot-rolled high-strength high-weathering steel, mm; T is the heating furnace temperature; and / or,

[0022] The end temperature T of the soaking section satisfies:

[0023] T = 1262-8.33h;

[0024] Wherein, h is the thickness of hot-rolled high-strength and high-weathering steel, mm; T is the heated furnace temperature.

[0025] Optionally, the atmosphere of the preheating section is a strong oxidizing atmosphere, and the air excess coefficient α of the preheating section is 1.40 to 1.50; and / or,

[0026] The atmosphere of the heating stage is a weak oxidizing atmosphere, and the air excess coefficient α1 of the heating stage satisfies:

[0027] α1=1.15-0.025h,

[0028] Wherein, h is the thickness of hot-rolled high-strength high-weathering steel, mm; and / or,

[0029] The atmosphere of the second heating stage is a weak oxidizing atmosphere, and the air excess coefficient α2 of the second heating stage satisfies:

[0030] α2=1.13-0.027h,

[0031] Where, h is the thickness of hot-rolled high-strength and high-weathering steel, mm;

[0032] The atmosphere in the soaking section is a weakly oxidizing atmosphere, and the excess air coefficient α3 in the soaking section satisfies:

[0033] α3=1.11-0.029×h,

[0034] Where h is the thickness of hot-rolled high-strength and high-weathering steel, mm.

[0035] Optionally, the heating further comprises heating at a temperature above 1100° C. in a manner of controlling the total heating time to be ≥110 min, wherein the total heating time t satisfies:

[0036] t=135-3.10h,

[0037] Wherein, h is the thickness of hot-rolled high-strength high-weathering steel, mm; and / or,

[0038] The duration of the soaking period is 51 to 59 minutes.

[0039] Optionally, the rough rolling includes a first rough rolling and a second rough rolling.

[0040] The total reduction ratio of the first rough rolling is 32.2% to 34.9%, the total reduction ratio of the second rough rolling is 49.3% to 51.9%, and the outlet temperature of the second rough rolling is 1061° C. to 1079° C.; and / or,

[0041] The finishing rolling includes finishing rolling in a continuous finishing rolling manner, and the outlet temperature of the finishing rolling is 826° C. to 848° C.

[0042] Optionally, the ultrafast cooling includes cooling by ultrafast water cooling, the pressure of the ultrafast cooling is 0.37MPa-0.39MPa, the outlet temperature of the ultrafast cooling is 625°C-639°C, and the speed of the ultrafast cooling is 51°C / s-79°C / s; and / or,

[0043] The laminar cooling is performed by shielding the hot-rolled strip at the edge, and the width of the edge shielding is 210 mm to 240 mm; and / or,

[0044] The coiling includes coiling in a stepped U-shaped temperature manner to control the temperature of the strip body and the head and tail of the strip after finish rolling, wherein the coiling temperature of the strip body is 555° C. to 575° C.; and / or,

[0045] The coiling temperature at a distance of 0 to 15 m from the head and tail of the strip is 585°C to 605°C; and / or,

[0046] The coiling temperature at a distance of 16m to 30m from the head and tail of the strip is 575°C to 595°C; and / or,

[0047] The coiling temperature at a distance of 31m to 45m from the head and tail of the strip is 565℃ to 585℃.

[0048] In a third aspect, the present application provides an application of the hot-rolled high-strength and high-weathering steel described in the first aspect, and the application includes: using the hot-rolled high-strength and high-weathering steel described in the first aspect in a paint-free steel structure under a C1 to C3 atmospheric environment.

[0049] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0050] A 700MPa grade hot-rolled high-strength and high-weathering steel provided in an embodiment of the present application adopts a micro-alloying design with low C content, low Mn content and high Ti content compared to the traditional weathering steel system. The precipitated micro-alloy precipitates are used to improve the overall strength of the high-weathering steel, while reducing the deformation resistance during the rolling process, so that the rolling stability is good. At the same time, a composite weathering resistance design is carried out for Si, P, Cu and Cr elements, and the contribution of cheap weathering elements such as Si and P to weathering resistance and solid solution strengthening is fully utilized. The addition of Cu can effectively reduce the amount of Cr element added, reduce the formation of chromium carbide precipitates between Cr elements and C, and thereby reduce the adverse effects of chromium carbide on weather resistance and toughness, thereby achieving simultaneous improvement of weather resistance and strength and toughness. At the same time, the addition of precious alloying elements such as Ni, Nb, V and Mo can be avoided, thereby reducing the difficulty of rolling and the cost of alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0052] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0053] Figure 1 A schematic diagram of the metallographic structure of the hot-rolled high-strength and high-weathering steel provided in an embodiment of the present application;

[0054] Figure 2 A schematic diagram of the process for preparing hot-rolled high-strength and high-weathering steel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0056] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0057] The creative thinking of this application is:

[0058] At present, thin-gauge high-strength weathering steels of 700MPa and above can be divided into Cr-Ni-Cu system, Cr-Ni-Cu-P system and Cr-Cu-P system according to weathering alloy elements. At present, the above systems have the following problems:

[0059] 1) Cr-Ni-Cu weathering alloy system: The main system includes: Cr content range 0.30% ~ 1.25%, Ni content range 0.03% ~ 0.80%, Cu content range 0.10% ~ 0.60%, such as patent application numbers CN200610123458, CN200710031548, CN201010246778, CN107365940B, CN109402508B, etc. Although compared with carbon steel, its weathering performance is increased by about 1 times, which can meet the relative corrosion rate of ≤ 55% in pastoral and industrial atmospheric environments. The high weather resistance requirement is achieved, but the relative corrosion rate ≤ 37% cannot be achieved, and the precious alloy Ni element is added in large quantities, the cost is high, and the economy is not strong; some use high Cr-high Ni-Cu weather-resistant alloy systems, such as in the patent application number CN200910056602 "Weathering steel with a yield strength above 700MPa and its manufacturing method", 2.50%~10.00% Cr, 0.20%~1.00% Ni and 0.20%~0.50% Cu are used, which has good weather resistance, but there are problems such as high alloy content, great difficulty in smelting and rolling, and deviation in welding formability.

[0060] 2) Cr-Ni-Cu-P weathering alloy system: This composition system is mainly used in thin slab continuous casting and rolling production lines and thin strip casting and rolling production lines. For example, in patent application number CN200610035800.2 "A method for producing 700MPa grade VN microalloyed high-strength atmospheric corrosion-resistant steel based on thin slab continuous casting and rolling process", 0.05% to 0.20% vanadium is used, and vanadium-nitrogen microalloying is used; in patent application number CN201911108607.0 "A 700MPa grade high-strength weathering steel strip and its CSP process production method", 0.03% to 0.05% Ti and 0.25% to 0.45% Mo composite microalloying is used. Metallization; for example, in patent application number CN201810587493.1 "A thin strip cast and rolled 700MPa grade weathering steel and its production method", 0.05%~0.20% Nb and 0.05%~0.20% V composite microalloying is adopted; for example, in patent application number CN201210066986.3 "A thin strip continuous casting 700MPa grade high-strength weathering steel manufacturing method", Nb, V, Ti and Mo elements composite microalloying is adopted; however, this series of patents have the problems of high microalloying cost, containing precious alloy Ni elements, large deformation resistance of thin strip steel rolling, and insufficient contribution of economic phosphorus element to weathering resistance.

[0061] 3) Cr-Cu-P weather-resistant alloy system: In patent application number CN202010362920.3 "Weathering steel for wide width 700MPa grade hot-rolled containers and its manufacturing method", a low weather-resistant alloy design of 0.22% to 0.29% Cr, 0.11% to 0.19% Cu and 0.035% to 0.045% P is adopted. The weather resistance index is low and cannot meet the high weather resistance requirements.

[0062] Therefore, how to provide a hot-rolled high-strength and high-weathering steel that contains no or a small amount of precious metal elements to reduce the rolling difficulty and alloy cost is a technical problem that urgently needs to be solved.

[0063] An embodiment of the present application provides a 700MPa grade hot-rolled high-strength and high-weathering steel. The chemical composition of the hot-rolled high-strength and high-weathering steel includes, by mass fraction: C: 0.043%~0.048%, Si: 0.51%~0.59%, Mn: 0.61%~0.68%, P: 0.041%~0.049%, S: 0.0031%~0.0038%, Al: 0.071%~0.079%, Ti: 0.092%~0.099%, Cu: 0.251%~0.259%, Cr: 1.81%~1.98%, N: 0.0031%~0.0034%, and the rest is Fe and unavoidable impurities.

[0064] In the embodiments of the present application, the positive effect of limiting the mass fraction of C to 0.043% to 0.048% is due to the fact that C improves the strength of the steel through solid solution strengthening and precipitation strengthening through interaction with micro-alloying elements. However, when the C content is too high, the formability and weldability of the steel will deteriorate, and the uniformity of the structure will deteriorate, resulting in micro-area galvanic corrosion and reduced weather resistance. When the C content is too low, the solid solution strengthening and precipitation strengthening effects are insufficient, resulting in low strength of the steel. Therefore, the C content is controlled to be between 0.043% and 0.048%.

[0065] The positive effect of Si mass fraction of 0.51% to 0.59% is that Si mainly plays a role in solid solution strengthening. At the same time, increasing the Si content can refine the α FeOOH in the rust layer of weathering steel, increase the resistance of the rust layer, and is beneficial to improving the weather resistance of steel. While increasing the Si content, increasing the P content, through the synergistic effect of the two, on the one hand, it can effectively inhibit the red rust defects on the surface of the steel, and on the other hand, it can inhibit the enrichment of Cu elements in the low temperature section during the heating process of the slab and promote the diffusion of Cu elements in the high temperature section, so as to reduce the amount of Cu enriched per unit interface between the iron sheet and the steel matrix, thereby inhibiting the effect of copper embrittlement. However, if the Si content is too high, it will be detrimental to the plasticity, toughness and weldability of the strip steel, so the Si content is controlled to 0.51% to 0.59%.

[0066] The positive effect of Mn mass fraction of 0.61% to 0.68% is due to the fact that Mn mainly plays the role of solid solution strengthening and grain refinement strengthening, but Mn is an element that easily segregates. Too high a content of Mn will lead to an increase in banded structure, obvious anisotropy of steel, poor formability and weldability, and reduced weather resistance. Therefore, the Mn content is controlled to 0.61% to 0.68%.

[0067] The positive effect of P mass fraction of 0.041% to 0.049% is due to the fact that P is an important solid solution strengthening element and the most economical and effective element for improving the weather resistance of steel. It can also work synergistically with Si element to reduce the red rust defect on the surface of steel with high Si content and can synergistically inhibit the copper brittle defect of Cu-containing steel. However, if its content is too high, it will lead to deterioration of cold brittleness, weldability and plastic toughness. Therefore, the P content needs to be controlled to 0.041% to 0.049%.

[0068] The positive effect of S mass fraction of 0.0031% to 0.0038% is that S will form sulfide inclusions, which will reduce the plastic toughness of steel, and will also cause poor weather resistance as a source of pitting corrosion; for Ti micro-alloyed steel, large-particle carbon sulfide Ti4C2S2 will be formed, which can reduce the effective Ti content; but if the S content is controlled too low, it will significantly increase the refining and desulfurization burden and increase the desulfurization cost, so the S content is controlled to 0.0031% to 0.0038%.

[0069] The positive effect of Al's mass fraction of 0.071% to 0.079% is due to the fact that Al is an important deoxidizing element and fine grain strengthening element. It is also an element that improves the density of the rust layer of weathering steel. However, because Al is an extremely active element, special protective slag is required when its content is high, which increases the continuous casting cost.

[0070] The positive effect of Ti's mass fraction of 0.092% to 0.099% is due to the fact that Ti is a strong carbonitride-forming element and is also the most economical and effective grain refinement and precipitation strengthening element. At the same time, the composite addition of Ti and P elements can form a certain amount of iron-titanium-phosphorus phase, reduce the grain boundary segregation of P elements, and promote the role of P elements in improving weather resistance. However, if the Ti content is too high, coarse TiN or TiC particles will be formed, which will deteriorate the plasticity and toughness of the steel. Therefore, the Ti content is controlled to be 0.092% to 0.099%.

[0071] The positive effect of Cu's mass fraction of 0.251% to 0.259% is due to the fact that Cu has the function of activating the cathode and promoting the passivation of the anode in steel. It is an important element for improving the weather resistance of steel. Adding an appropriate amount can significantly improve the weather resistance. When adding more, the increase in weather resistance is small, and the risk of Cu brittle defects is significantly increased. Therefore, the Cu content is controlled to be 0.251% to 0.259%.

[0072] The positive effect of Cr mass fraction of 1.81% to 1.98% is because Cr is an important solid solution strengthening element. When added in small amounts, it can enrich the rust layer in the steel to improve weather resistance, while when added in large amounts, it can form a passivation film on the steel surface, which will further improve weather resistance. However, when the Cr content is too high, a large amount of CrxCy will be formed in the steel, deteriorating the plasticity, toughness, formability and welding performance of the steel. Therefore, the Cr content is controlled to 1.81% to 1.98%.

[0073] The positive effect of N mass fraction of 0.0031% to 0.0034% is due to the fact that N is easily combined with Ti element to form large particles of TiN, which will consume a part of Ti, thereby reducing the effective Ti content and also deteriorating the plasticity and toughness of the steel. However, if the N content is controlled too low, the degassing cost of the refining process will be significantly increased. From the perspective of improving product performance stability, the N content should be controlled in a narrow range, so the N content is controlled to be 0.0031% to 0.0034%.

[0074] like Figure 1 As shown, in some optional embodiments, the structure of the hot-rolled high-strength and high-weathering steel includes ferrite and TiC nano-scale precipitates, wherein the nano-scale precipitates with a particle size of 2nm to 5nm in the ferrite account for more than 88% of the TiC nano-scale precipitates.

[0075] In the embodiments of the present application, the precipitates with a particle size of 2nm to 5nm in the ferrite are limited as the main precipitation form, indicating that the high-strength and high-weathering resistant steel obtained in the present application has excellent performance, thereby obtaining a product with a yield strength ≥700MPa, a tensile strength ≥800MPa, an elongation after fracture ≥18%, an impact energy at -40℃ ≥47J, and a through-roll yield strength fluctuation ≤65MPa.

[0076] In some optional embodiments, the thickness h of the hot-rolled high-strength and high-weathering steel is 1.2 mm to 8.0 mm.

[0077] In the embodiments of the present application, the specific thickness of the hot-rolled high-strength and high-weathering steel is limited to ensure the excellent performance of the high-strength and high-weathering steel, thereby obtaining a product with a yield strength ≥700MPa, a tensile strength ≥800MPa, an elongation after fracture ≥18%, an impact energy at -40°C ≥47J, and a yield strength fluctuation through the coil ≤65MPa.

[0078] like Figure 2 As shown, based on a general inventive concept, the present application provides a method for preparing the hot-rolled high-strength and high-weathering steel, the method comprising:

[0079] S1. Obtaining a slab containing the same chemical composition as the hot-rolled high-strength high-weathering steel;

[0080] S2. The ingot is heated, and then subjected to rough descaling and rough rolling to obtain an intermediate slab;

[0081] S3. The intermediate slab is subjected to fine descaling, fine rolling, ultra-fast cooling, laminar cooling, and coiling to obtain hot-rolled high-strength and high-weathering steel.

[0082] In the embodiment of the present application, the high-strength and high-weathering-resistant steel raw materials with target chemical composition are processed according to the general process of smelting → continuous casting → continuous casting ingot heating → rough descaling → fixed-width press → rough rolling → flying shear → fine descaling → fine rolling → ultra-fast cooling + laminar cooling → coiling into steel coils, so that steel products that meet the expected strength and weathering resistance can be obtained.

[0083] This method is a method for preparing the above-mentioned hot-rolled high-strength and high-weathering steel. The specific composition of the hot-rolled high-strength and high-weathering steel can refer to the above-mentioned embodiment. Since this method adopts part or all of the technical solutions of the above-mentioned embodiment, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiment, which will not be repeated here one by one.

[0084] In some optional embodiments, the heating includes a preheating section, a first heating section, a second heating section and a soaking section, wherein the heating rate of the preheating section is 16°C / min to 19°C / min, and the end temperature of the preheating section is ≥850°C;

[0085] The end temperature T1 of the heating stage satisfies:

[0086] T1=T*(0.936-0.013h+0.0020h 2 );

[0087] Where, h is the thickness of the hot-rolled high-strength high-weathering steel, mm; T is the heating furnace temperature, °C; and / or,

[0088] The end temperature T2 of the second heating stage satisfies:

[0089] T2=T*(1.016-0.015h+0.0018h 2 );

[0090] Where, h is the thickness of the hot-rolled high-strength high-weathering steel, mm; T is the heating furnace temperature, °C; and / or,

[0091] The end temperature T of the soaking section satisfies:

[0092] T = 1262-8.33h;

[0093] Wherein, h is the thickness of hot-rolled high-strength and high-weathering steel, mm; T is the heated furnace temperature, ℃.

[0094] In the embodiments of the present application, the temperatures of the preheating section, the first heating section, the second heating section and the soaking section in the heating process are limited to vary with the thickness of the final strip product, thereby reducing the oxidation enrichment of copper elements at the interface between the iron sheet and the steel matrix in the low-temperature stage through rapid heating at low temperature, reducing the amount of copper element enrichment at the interface, and reducing the copper brittleness hazard of the liquid copper-rich phase in the subsequent rolling process, thereby avoiding the "copper brittleness" quality problem of the strip surface caused by the nickel-free low-cost design of the designed chemical composition system.

[0095] In some optional embodiments, the atmosphere of the preheating section is a strong oxidizing atmosphere, and the air excess coefficient α of the preheating section is 1.40 to 1.50; and / or,

[0096] The atmosphere of the heating stage is a weak oxidizing atmosphere, and the air excess coefficient α1 of the heating stage satisfies:

[0097] α1=1.15-0.025h,

[0098] Wherein, h is the thickness of hot-rolled high-strength high-weathering steel, mm; and / or,

[0099] The atmosphere of the second heating stage is a weak oxidizing atmosphere, and the air excess coefficient α2 of the second heating stage satisfies:

[0100] α2=1.13-0.027h,

[0101] Where, h is the thickness of hot-rolled high-strength and high-weathering steel, mm;

[0102] The atmosphere in the soaking section is a weakly oxidizing atmosphere, and the excess air coefficient α3 in the soaking section satisfies:

[0103] α3=1.11-0.029×h,

[0104] Where h is the thickness of hot-rolled high-strength and high-weathering steel, mm.

[0105] In the embodiments of the present application, the specific atmosphere and excess air coefficient of each stage in the heating process are defined, and the weakly oxidizing atmosphere is used for long-term heat preservation to accelerate the diffusion of copper elements enriched at the interface between the iron sheet and the steel matrix into the interior of the iron sheet and the steel matrix, thereby effectively reducing the amount of copper elements enriched at the interface and reducing the copper embrittlement hazard of the liquid copper-rich phase in the subsequent rolling process.

[0106] In summary, by adopting the refined heating process system design of "high-temperature rapid burning in a strong oxidizing atmosphere in the front stage of heating + long-term insulation in a weak oxidizing atmosphere in the middle and rear stages of heating" of the present application, the oxidation enrichment of copper elements at the interface between the iron sheet and the steel matrix in the low-temperature stage is reduced by rapid heating at low temperature; by long-term insulation in a weak oxidizing atmosphere, the diffusion of copper elements enriched at the interface between the iron sheet and the steel matrix into the interior of the iron sheet and the steel matrix is ​​accelerated, the amount of copper element enrichment at the interface is effectively reduced, and the copper embrittlement hazard of the liquid copper-rich phase in the subsequent rolling process is reduced.

[0107] In some optional embodiments, the heating further comprises controlling the total heating time at a temperature above 1100°C.

[0108] ≥110min, where the total heating time t satisfies:

[0109] t=135-3.10h,

[0110] Wherein, h is the thickness of hot-rolled high-strength high-weathering steel, mm; and / or,

[0111] The duration of the soaking period is 51 to 59 minutes.

[0112] In the embodiment of the present application, the specific time for heating to above 1000°C is limited in relationship to the thickness of the strip, and the time of the equalization period is further limited, so as to ensure that the heating process meets the requirements of "high temperature and fast burning in a strong oxidizing atmosphere in the front stage of heating + long-term heat preservation in a weak oxidizing atmosphere in the middle and rear stages of heating", thereby avoiding the "copper brittleness" quality problem on the strip surface caused by the low-cost nickel-free design of 700MPa hot-rolled high-strength and high-weathering steel.

[0113] In some optional embodiments, the rough rolling includes a first rough rolling and a second rough rolling.

[0114] The total reduction ratio of the first rough rolling is 32.2% to 34.9%, the total reduction ratio of the second rough rolling is 49.3% to 51.9%, and the outlet temperature of the second rough rolling is 1061° C. to 1079° C.; and / or,

[0115] The finishing rolling includes finishing rolling in a continuous finishing rolling manner, and the outlet temperature of the finishing rolling is 826° C. to 848° C.

[0116] In the embodiment of the present application, rough rolling is carried out sequentially by two rough rolling mills (R1 and R2), and a 3+3 mode is adopted. Rough rolling R1 and rough rolling R2 both adopt three-pass rolling, and rough rolling R1 adopts the first, second and third passes for descaling, and rough rolling R2 adopts the first and third passes for descaling. By increasing the number of rough rolling descaling passes, the liquid copper-rich phase at the interface between the iron sheet and the steel matrix is ​​removed along with the iron sheet.

[0117] The specific total rolling reduction ratio of rough rolling and finish rolling is limited, and a reduction strategy is adopted to reduce the reduction ratio of the first three passes of rough rolling and increase the reduction ratio of the last three passes of rough rolling, so as to reduce the harmful effect of the liquid copper-rich phase at the austenite grain boundary on the surface of the steel matrix.

[0118] The positive effect of the outlet temperature of the second rough rolling being 1061°C to 1079°C is that within this temperature range, the outlet temperature of the strip after the rough rolling R2 can be controlled below the melting point of the liquid copper-rich phase, 1085°C;

[0119] The continuous finishing rolling adopts the method of continuous rolling of 6 to 7 stands, and the outlet temperature of the finishing rolling is 826℃~848℃. In this way, within the lower finishing rolling outlet temperature range, the finishing rolling stability, controlled rolling fine grain and post-rolling cooling effect are taken into account to achieve the purpose of refining the grain size of the deformed austenite before phase transformation.

[0120] In some optional embodiments, the ultrafast cooling includes cooling by ultrafast water cooling, the pressure of the ultrafast cooling is 0.37MPa to 0.39MPa, the outlet temperature of the ultrafast cooling is 625°C to 639°C, and the speed of the ultrafast cooling is 51°C / s to 79°C / s; and / or,

[0121] The laminar cooling is performed by shielding the hot-rolled strip at the edge, and the width of the edge shielding is 210 mm to 240 mm; and / or,

[0122] The coiling includes coiling in a stepped U-shaped temperature manner to control the temperature of the strip body and the head and tail of the strip after finish rolling, wherein the coiling temperature of the strip body is 555° C. to 575° C.; and / or,

[0123] The coiling temperature at a distance of 0 to 15 m from the head and tail of the strip is 585°C to 605°C; and / or,

[0124] The coiling temperature at a distance of 16m to 30m from the head and tail of the strip is 575°C to 595°C; and / or,

[0125] The coiling temperature at a distance of 31m to 45m from the head and tail of the strip is 565℃ to 585℃.

[0126] In the embodiment of the present application, a cooling mode of ultra-fast cooling + laminar cooling is adopted after rolling, and the ultra-fast cooling pressure is controlled to be 0.37MPa~0.39MPa, the ultra-fast cooling outlet temperature is 625℃~639℃, and the ultra-fast cooling speed is 51℃ / s~79℃ / s, thereby taking into account the precipitation strengthening contribution and fine grain strengthening contribution of Ti microalloying, ensuring that the 700MPa grade finished strip steel has a good strength and toughness match.

[0127] The specific form of laminar cooling is limited, and edge shielding and stepped U-shaped coiling are used to ensure that the performance of the coiled strip is controlled in a narrow range, avoiding insufficient precipitation and low strength due to low temperature at the edges and heads and tails of the strip.

[0128] Based on a general inventive concept, the present application provides an application of the hot-rolled high-strength and high-weathering steel, and the application includes: using the hot-rolled high-strength and high-weathering steel in a paint-free steel structure under a C1 to C3 atmospheric environment.

[0129] Based on the excellent performance of the hot-rolled high-strength and high-weathering steel obtained in this application, it can be used to manufacture railway vehicles, containers, photovoltaic brackets, highway guardrails, and building scaffolding. The products produced can be applied to photovoltaic brackets, highway guardrails, building scaffolding and other fields without painting under C1-C3 atmospheric environment.

[0130] This application is realized based on the above-mentioned hot-rolled high-strength and high-weathering steel. The specific composition of the hot-rolled high-strength and high-weathering steel can refer to the above-mentioned embodiment. Since this application adopts part or all of the technical solutions of the above-mentioned embodiment, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiment, which will not be repeated here one by one.

[0131] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0132] In the actual production process, the specific preparation process of hot-rolled high-strength and high-weathering steel is as follows:

[0133] The chemical composition ratio shown in Table 1 is adopted, and the specific process is as follows: smelting → continuous casting → continuous casting billet heating → rough descaling → fixed width press → rough rolling → flying shear → fine descaling → fine rolling → ultra-fast cooling + laminar cooling → coiling into steel coils.

[0134] (1) Smelting and continuous casting: Molten steel is smelted according to the set composition and cast into billets. The chemical elements are shown in Table 1 in terms of mass percentage.

[0135] Table 1 Chemical composition of high strength and high weathering steel of different groups (%)

[0136]

[0137]

[0138] In Table 1, the calculation formula of the weather resistance index I is as follows:

[0139] I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(%Ni)(%P)-33.39(%Cu) 2 ,

[0140] Wherein, (%Cu) is the Cu content, (%Ni) is the Ni content, (%Cr) is the Cr content, (%Si) is the Si content, and (%P) is the P content.

[0141] The calculation result of the weather resistance index I is I≥8.0.

[0142] The calculation formula of the comprehensive factor index T is as follows:

[0143] T=[5(%P)+(%Cu)+(%Cr) / 3+0.1(%Si)+0.1(%Al)] / [4(%C)+0.5(%Mn)],

[0144] Wherein, (%P) is the content of P, (%Cu) is the content of Cu, (%Cr) is the content of Cr, (%Si) is the content of Si, (%Al) is the content of Al, (%C) is the content of C, and (%Mn) is the content of Mn.

[0145] The calculation result of the comprehensive factor index T is T≥2.3.

[0146] (2) Slab heating: In the preheating section, a strong oxidizing atmosphere with an excess air coefficient α of 1.40 to 1.50 is used, and the slab is rapidly heated to ≥850°C at a heating rate of 16°C / min to 19°C / min;

[0147] In the heating stage, a weak oxidizing atmosphere with an excess air coefficient α1 of (1.15-0.025h) is used to quickly heat to a temperature T1 = furnace temperature * (0.936-0.013h + 0.0020h 2 );

[0148] In the second heating stage, a weak oxidizing atmosphere with an excess air coefficient α2 of (1.13-0.027h) is used to quickly heat to a temperature T2 = furnace exit temperature * (1.016-0.015h + 0.0018h 2 );

[0149] In the soaking section, a weak oxidizing atmosphere with an excess air coefficient α3 of (1.11-0.029h) is used, and the steel is rapidly heated to the furnace temperature T = (1262-8.33h) ° C. The soaking time is 51min to 59min, where h is the thickness of the hot-rolled high-strength and high-weathering steel, mm, and the total heating time t above 1100 ° C is required to be (135-3.10h)min and ≥110min, so as to fully austenitize, ensure the dissolution of micro-alloying elements and the full diffusion of the liquid copper-rich phase at the interface between the iron sheet and the steel matrix. The heating process is shown in Table 2.

[0150] Table 2 Heating process parameters

[0151]

[0152] (3) Hot rolling: In order to reduce the harmful effects of the liquid copper-rich phase at the austenite grain boundary on the steel matrix surface, the rough rolling adopts the 3+3 mode. The rough rolling R1 adopts three passes, and the rough rolling R2 adopts three passes. The total reduction rate of the three passes of R1 accounts for 32.2% to 34.9%. R1 adopts the first, second and third passes for descaling, and the total reduction rate of the three passes of R2 accounts for

[0153] 49.3%~51.9% and R2 adopts the first and third passes for descaling; at the same time, the outlet temperature of rough rolling R2 is controlled below the melting point of liquid copper-rich phase 1085℃, that is, 1061℃~1079℃; finishing rolling adopts 6-7 stands continuous rolling, and adopts a lower finishing temperature of 826℃~848℃. The hot rolling process is shown in Table 3.

[0154] Table 3. Soaking and rolling process parameters

[0155]

[0156] (4) Post-rolling cooling: After rolling, ultra-fast cooling + laminar cooling mode is adopted, the cooling water pressure is 0.37MPa~0.39MPa, the ultra-fast cooling outlet temperature is 625℃~639℃, and the ultra-fast cooling rate range is 51℃ / s~79℃ / s; after ultra-fast cooling, laminar cooling is carried out and edge shielding and U-shaped coiling are adopted. The edge shielding width is 210mm~240mm, and the coiling temperature of the strip body is controlled at 555℃~575℃. The coiling temperature of the strip head and tail 0~15m is 30℃ higher than that of the strip body, the coiling temperature of the strip head and tail 16m~30m is 20℃ higher than that of the strip body, and the coiling temperature of the strip head and tail 31m~45m is 10℃ higher than that of the strip body. The specific post-rolling cooling process parameters are shown in Table 4.

[0157] Table 4 Post-rolling cooling process parameters

[0158]

[0159] Related experiments and effect data:

[0160] The mechanical properties and corrosion properties of the hot-rolled high-strength and high-weathering steel obtained in each group were tested respectively. The corrosion performance is the relative corrosion rate of the ordinary carbon steel Q345B in a 0.01 mol / L NaHSO3 environment for 72 h of immersion corrosion, as shown in Table 5.

[0161] Table 5 Mechanical properties and corrosion resistance of each group of hot-rolled high-strength and high-weathering steel

[0162]

[0163] In Table 5, the steel plates of Examples 1 / 2 and 3 are too thin to be suitable for impact tests, so only the steel plate of Example 4 is subjected to impact tests.

[0164] It can be seen from Table 5 that the yield strength of the hot-rolled high-strength and high-weathering steel of the present application is greater than 700MPa, and the highest reaches 754MPa; and the tensile strength is greater than 800MPa, and the highest reaches 879MPa; the elongation after fracture is greater than or equal to 18.0%, and the highest can reach 24.0%; at the same time, the 180°d=a transverse and longitudinal cold bending tests are qualified; -40℃ impact energy (specimen size 5*10*55mm) ≥47J, and the corrosion rate relative to ordinary structural steel Q345B is ≤37%; and the hot-rolled high-strength and high-weathering steels obtained in Examples 1-4 all have a metallographic structure with quasi-polygonal ferrite + dispersed TiC nano-precipitates, and the nano-precipitation phase in the ferrite is mainly precipitates with a particle size distribution of 2nm~5nm, accounting for as much as 88%.

[0165] One or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages: (1) The present application provides a 700MPa grade hot-rolled high-strength and high-weathering resistant steel, which has a quasi-polygonal ferrite + dispersed TiC nano-precipitate microstructure, and the nano-precipitate phase in the ferrite is mainly precipitates with a particle size distribution of 2 to 5nm, accounting for up to 88%; its yield strength can reach more than 700MPa, the tensile strength can reach more than 800MPa, the elongation after fracture can reach more than 18%, the 180°d=a transverse bending is qualified, the -40℃ impact energy is ≥47J, the through-roll yield strength fluctuation is ≤65MPa, and the corrosion rate relative to the ordinary structural steel Q345B is ≤37%.

[0166] (2) The present application provides a 700MPa grade hot-rolled high-strength and high-weathering steel having good plate shape, surface quality, cold formability, weldability and weather resistance, and can be applied to the processing and performance requirements of steel structures.

[0167] (3) The present application provides a 700MPa grade hot-rolled high-strength and high-weathering steel. Railway vehicles, containers, photovoltaic brackets, highway guardrails, building scaffolding, etc. made of this high-strength and high-weathering steel have excellent cold forming performance, welding performance and corrosion resistance. It can be applied to photovoltaic brackets, highway guardrails, building scaffolding and other fields without painting in C1-C3 atmospheric environment, and its service life is more than 23 years.

[0168] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0169] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0170] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A 700MPa grade hot-rolled high-strength high-weathering steel, characterized in that: The chemical composition of the hot-rolled high-strength and high-weathering steel includes, by mass fraction, C: 0.043% to 0.048%, Si: 0.51% to 0.59%, Mn: 0.61% to 0.68%, P: 0.041% to 0.049%, S: 0.0031% to 0.0038%, Al: 0.071% to 0.079%, Ti: 0.092% to 0.099%, Cu: 0.251% to 0.259%, Cr: 1.81% to 1.98%, N: 0.0031% to 0.0034%, and the rest is Fe and unavoidable impurities. The structure of the hot-rolled high-strength and high-weathering steel includes ferrite and TiC nanoscale precipitates, wherein the nanoscale precipitates with a particle size of 2nm to 5nm in the ferrite account for more than 88% of the TiC nanoscale precipitates; The preparation method of the hot-rolled high-strength high-weathering steel comprises: Obtaining a casting billet; The ingot is heated, and then roughly descaled and roughly rolled in sequence to obtain an intermediate slab; The intermediate slab is subjected to fine descaling, fine rolling, ultra-fast cooling, laminar cooling, and coiling to obtain hot-rolled high-strength and high-weathering steel; The heating includes a preheating section, a first heating section, a second heating section and a soaking section, wherein the heating rate of the preheating section is 16°C / min to 19°C / min, and the end temperature of the preheating section is ≥850°C; The end temperature T1 of the heating stage satisfies: T1=T*(0.936-0.013h+0.0020h 2 ); Where, h is the thickness of the hot-rolled high-strength high-weathering steel, mm; T is the heating furnace temperature, °C; and / or, The end temperature T2 of the second heating stage satisfies: T2=T*(1.016-0.015h+0.0018h 2 ); Where, h is the thickness of the hot-rolled high-strength high-weathering steel, mm; T is the heating furnace temperature, °C; and / or, The end temperature T of the soaking section satisfies: T = 1262-8.33h; Where, h is the thickness of hot-rolled high-strength and high-weathering steel, mm; T is the heating furnace temperature, °C; The atmosphere of the preheating section is a strong oxidizing atmosphere, and the air excess coefficient α of the preheating section is 1.40 to 1.50; The atmosphere of the heating stage is a weak oxidizing atmosphere, and the air excess coefficient α1 of the heating stage satisfies: α1=1.15-0.025h， Where, h is the thickness of hot-rolled high-strength and high-weathering steel, mm; The atmosphere of the second heating stage is a weak oxidizing atmosphere, and the air excess coefficient α2 of the second heating stage satisfies: α2=1.13-0.027h， Where, h is the thickness of hot-rolled high-strength and high-weathering steel, mm; The atmosphere in the soaking section is a weakly oxidizing atmosphere, and the excess air coefficient α3 in the soaking section satisfies: α3=1.11-0.029×h， Where, h is the thickness of hot-rolled high-strength and high-weathering steel, mm; The ultra-fast cooling includes cooling by high-pressure cooling water, the pressure of the ultra-fast cooling is 0.37MPa-0.39MPa, the outlet temperature of the ultra-fast cooling is 625°C-639°C, and the speed of the ultra-fast cooling is 51°C / s-79°C / s; The laminar cooling is performed by shielding the hot-rolled strip at the edge, and the width of the edge shielding is 210 mm to 240 mm; The coiling includes coiling in a stepped U-shaped temperature manner to control the temperature of the strip body and the head and tail of the strip after finish rolling, wherein the coiling temperature of the strip body is 555° C. to 575° C.; The coiling temperature at a distance of 0 to 15 m from the head and tail of the strip is 585°C to 605°C; The coiling temperature at a distance of 16m to 30m from the head and tail of the strip is 575℃ to 595℃; The coiling temperature at a distance of 31m to 45m from the head and tail of the strip is 565℃ to 585℃.

2. The hot-rolled high-strength and high-weathering steel according to claim 1, characterized in that: The thickness h of the hot-rolled high-strength and high-weathering steel is 1.2 mm to 8.0 mm.

3. The hot-rolled high-strength and high-weathering steel according to claim 1, characterized in that: The heating further comprises heating at a temperature of 1100° C. or higher in a manner of controlling the total heating time to be ≥110 min, wherein the total heating time t satisfies: t = 135-3.10h, Wherein, h is the thickness of hot-rolled high-strength high-weathering steel, mm; and / or, The duration of the soaking period is 51 to 59 minutes.

4. The hot-rolled high-strength and high-weathering steel according to claim 1, characterized in that: The rough rolling includes a first rough rolling and a second rough rolling. The total reduction ratio of the first rough rolling is 32.2% to 34.9%, the total reduction ratio of the second rough rolling is 49.3% to 51.9%, and the outlet temperature of the second rough rolling is 1061° C. to 1079° C.; and / or, The finishing rolling includes finishing rolling in a continuous finishing rolling manner, and the outlet temperature of the finishing rolling is 826° C. to 848° C.

5. An application of the hot-rolled high-strength and high-weathering steel according to any one of claims 1 to 4, characterized in that: The application includes: using the hot-rolled high-strength and high-weathering steel as described in any one of claims 1 to 4 in a paint-free steel structure in a C1 to C3 atmospheric environment.

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