阅读说明：本技术 装配式钢结构用钢及其制备方法 (Steel for assembly type steel structure and preparation method thereof ) 是由 崔凯禹 李正荣 汪创伟 熊雪刚 陈述 高爱芳 于 2020-06-29 设计创作，主要内容包括：本发明属于热连轧板带生产技术领域,具体涉及装配式钢结构用钢及其制备方法。本发明提供了具有良好焊接性能、抗震性能和耐大气腐蚀性能的装配式钢结构用钢。由如下重量百分比的成分组成：C：0.06～0.08％,Si：0.30～0.40％,Mn：0.85～1.00％,P≤0.018％,S≤0.007％,Cu：0.30～0.40％,Cr：0.40～0.50％,Ni：0.20～0.30％,V：0.04～0.05％,Nb：0.020～0.030％,Als：0.015～0.050％,N：0.0025～0.0035％,余量为Fe及不可避免的杂质。本发明装配式钢结构用钢具有良好的焊接性能、抗震性能和耐大气腐蚀性能。(The invention belongs to the technical field of hot continuous rolling strip production, and particularly relates to steel for an assembly steel structure and a preparation method thereof. The invention provides steel for an assembly steel structure, which has good welding performance, shock resistance and atmospheric corrosion resistance. The composite material comprises the following components in percentage by weight: c: 0.06-0.08%, Si: 0.30-0.40%, Mn: 0.85-1.00%, P is less than or equal to 0.018%, S is less than or equal to 0.007%, Cu: 0.30-0.40%, Cr: 0.40 to 0.50%, Ni: 0.20-0.30%, V: 0.04-0.05%, Nb: 0.020-0.030%, Als: 0.015-0.050%, N: 0.0025 to 0.0035% and the balance of Fe and inevitable impurities. The steel for the assembly steel structure has good welding performance, shock resistance and atmospheric corrosion resistance.)

1. The steel for the assembly type steel structure is characterized in that: the composite material comprises the following components in percentage by weight: c: 0.06-0.08%, Si: 0.30-0.40%, Mn: 0.85-1.00%, P is less than or equal to 0.018%, S is less than or equal to 0.007%, Cu: 0.30-0.40%, Cr: 0.40 to 0.50%, Ni: 0.20-0.30%, V: 0.04-0.05%, Nb: 0.020-0.030%, Als: 0.015-0.050%, N: 0.0025 to 0.0035% and the balance of Fe and inevitable impurities.

2. The steel for assembly steel structure according to claim 1, characterized in that: the carbon equivalent CEV of the steel for the assembly steel structure is less than or equal to 0.42 percent; the welding crack sensitivity index Pcm is less than or equal to 0.20 percent; the atmospheric corrosion resistance index I is more than or equal to 6.0.

3. A method for producing a steel for assembly steel structures according to claim 1 or 2, characterized in that: the method comprises the following steps: smelting the steel into a steel billet according to the components of the steel for the assembled steel structure, and carrying out hot continuous rolling, laminar cooling and coiling to obtain the steel billet; the laminar cooling process adopts front-stage cooling.

4. The method for producing a steel for assembly steel structures according to claim 3, characterized in that: in the hot continuous rolling procedure, the heating temperature of the steel billet is 1220-1260 ℃.

5. The method for producing a steel for assembly steel structures according to claim 3 or 4, characterized in that: in the hot continuous rolling procedure, the rough rolling is carried out for 5 times of rolling, the deformation of each time is more than or equal to 20 percent, and the whole scale is removed; the initial rolling temperature of finish rolling is not more than 1040 ℃, and the final rolling temperature is 850-890 ℃.

6. The method for producing a steel for assembly steel structures according to any one of claims 3 to 5, characterized in that: in the laminar cooling process, the number of the cooling water openings between the racks is more than or equal to 5.

7. The method for producing a steel for assembly steel structures according to any one of claims 3 to 6, characterized in that: the coiling temperature is 560-600 ℃.

Technical Field

The invention belongs to the technical field of hot continuous rolling strip production, and particularly relates to steel for an assembly steel structure and a preparation method thereof.

Background

Because the assembled steel structure system has the characteristics of greenization, industrialization, informatization, lightness, quickness, goodness, province and the like, and the practical requirements of resolving the serious excess contradiction of steel productivity, strategic decision of steel hiding in people and the like, at present, the assembled steel structure building is vigorously popularized by the nation, and the traditional and laggard production and construction mode is fundamentally changed. However, traditional steel structure materials such as carbon structural steel, low-alloy high-strength steel and the like are not corrosion-resistant, and rust removal and coating are needed in steel structure construction, so that the cost of the steel structure construction is increased, and the problem of environmental pollution also exists. In addition, the seismic performance is also a disadvantage of the traditional steel structure material.

The weathering steel is also named as atmospheric corrosion resistant steel, and is a low alloy steel with good corrosion resistance in the atmosphere. Through a large amount of research at home and abroad, at present, it is generally believed that after long-time exposure to the atmosphere, a layer of compact and good-adhesion oxidation product is generated on the surface of the weathering steel, so that a steel matrix is isolated from external corrosive substances, and the corrosion resistance of the weathering steel is obviously improved. The domestic weathering steel is mainly used for railway vehicles, containers and the like, and in developed countries such as the United states, Japan and the like, the weathering steel is widely and naked and used in the fields of steel structure buildings and municipal facilities. In the united states, the largest use of weathering steel is to construct bridges and expand the use of bare forms, with buildings using bare weathering steel reaching over 500. In japan, from 1965, exterior members such as building roofs, blinds, steel ribs, exterior panel lights, and the like have been exposed to weathering steel. Therefore, the application of the weathering steel in the field of fabricated steel structures can effectively solve the problem that the traditional steel structure material is not corrosion-resistant.

Patent document CN102839323A discloses a steel for building structure and a production method thereof, wherein the steel comprises the following smelting process components: c: 0.012-0.015%, Si: 0.018-0.022%, Mn: 0.50-0.60%, P is less than or equal to 0.025%, S is less than or equal to 0.015%, N: 0.0024-0.0026%, Nb: 0.010-0020%, Ti: 0.025-0.045%, residual elements Cu, Ni and Cr are respectively less than or equal to 0.10%, V is less than or equal to 0.008%, and Mo is less than or equal to 0.050%. The control range of C, N element in the steel for the building structure is small, and the smelting difficulty is improved; contains residual elements of Cu, Ni and Cr, so that the atmospheric corrosion resistance of the product is poor; the earthquake-resistant performance such as yield ratio, yield platform length and the like is not described.

Patent document CN103866188B discloses a fire-resistant corrosion-resistant earthquake-resistant steel with yield strength of 460MPa grade and a production method thereof, wherein the steel comprises the following components: 0.095-0.180%, Si: 0.28 to 0.55%, Mn: 1.40-1.60%, P is less than or equal to 0.008%, S is less than or equal to 0.002%, Nb: 0.014 to 0.045%, Ti: 0.004-0.030%, V: 0.034-0.044%, Mo: 0.09-0.29%, W: 0.06-0.12%, Mg: 0.0080-0.0100%, Sn: 0.08-0.13 percent of iron, less than or equal to 0.0016 percent of oxygen, and the balance of Fe and inevitable impurities. The content of C in the steel for construction is basically in a peritectic region, and a casting blank is easy to crack; p, S content is controlled to be low, thus improving smelting difficulty; elements such as Mg, Sn and W are added to improve the corrosion resistance, the influence of the addition of the elements on the quality of molten steel and the quality of steel plates needs to be evaluated, and the actual industrial production has difficulty.

Disclosure of Invention

The invention aims to provide steel for an assembly type steel structure with good welding performance, shock resistance and atmospheric corrosion resistance and a preparation method thereof.

The technical scheme adopted by the invention for solving the technical problems is to provide the steel for the assembly steel structure. The steel comprises the following components in percentage by weight: c: 0.06-0.08%, Si: 0.30-0.40%, Mn: 0.85-1.00%, P is less than or equal to 0.018%, S is less than or equal to 0.007%, Cu: 0.30-0.40%, Cr: 0.40 to 0.50%, Ni: 0.20-0.30%, V: 0.04-0.05%, Nb: 0.020-0.030%, Als: 0.015-0.050%, N: 0.0025 to 0.0035% and the balance of Fe and inevitable impurities.

Further, the carbon equivalent CEV of the steel for the assembly steel structure is less than or equal to 0.42 percent; the welding crack sensitivity index Pcm is less than or equal to 0.20 percent; the atmospheric corrosion resistance index I is more than or equal to 6.0.

The invention also provides a preparation method of the steel for the assembly type steel structure, which comprises the following steps: smelting the steel into a steel billet according to the components of the steel for the assembled steel structure, and carrying out hot continuous rolling, laminar cooling and coiling to obtain the steel billet; the laminar cooling process adopts front-stage cooling.

Further, in the hot continuous rolling procedure, the heating temperature of the steel billet is 1220-1260 ℃.

Further, in the hot continuous rolling procedure, rough rolling is carried out for 5 times of rolling, the deformation of each time is more than or equal to 20%, and the whole scale is removed in the whole length; the initial rolling temperature of finish rolling is not more than 1040 ℃, and the final rolling temperature is 850-890 ℃.

Furthermore, in the laminar cooling process, the number of the cooling water openings between the racks is more than or equal to 5.

Further, the coiling temperature is 560-600 ℃.

The invention has the beneficial effects that:

according to the invention, the content of C, Si and Mn elements is controlled, the carbon equivalent and the welding crack sensitivity index are reduced, a certain amount of V element is added, the fine grain strengthening and precipitation strengthening effects are exerted, and a proper amount of Cu, Cr and Ni elements are added, so that the atmospheric corrosion resistance of the steel for the assembly steel structure is improved. The yield strength of the steel for the assembled steel structure is more than or equal to 450MPa, the tensile strength is more than or equal to 550MPa, the yield ratio is less than or equal to 0.85, the elongation is more than or equal to 20%, the yield point elongation Ae is more than or equal to 2.0%, D (thickness is less than or equal to 6mm) or D (thickness is more than 6mm) in a 180-degree cold bending test, the impact power at 40 ℃ is more than or equal to 60J (full size), and the relative corrosion rate (relative to Q355B) is less than or equal to 55%. By adopting the hot continuous rolling and cooling process, the production of the steel for the assembled steel structure on the hot continuous rolling unit is realized, and the obtained product has good welding performance, shock resistance and atmospheric corrosion resistance.

Drawings

FIG. 1 is a tensile curve of examples and comparative examples.

FIG. 2 shows the metallographic structure (1000X) at 1/4 in the thickness direction of the example.

FIG. 3 shows the metallographic structure (1000X) at 1/4 in the thickness direction of comparative example 1.

FIG. 4 shows the metallographic structure (1000X) at 1/4 in the thickness direction of comparative example 2.

FIG. 5 shows the metallographic structure (1000X) of comparative example 3 at 1/4 in the thickness direction.

Detailed Description

Specifically, the invention provides steel for an assembly steel structure, which comprises the following components in percentage by weight: c: 0.06-0.08%, Si: 0.30-0.40%, Mn: 0.85-1.00%, P is less than or equal to 0.018%, S is less than or equal to 0.007%, Cu: 0.30-0.40%, Cr: 0.40 to 0.50%, Ni: 0.20-0.30%, V: 0.04-0.05%, Nb: 0.020-0.030%, Als: 0.015-0.050%, N: 0.0025 to 0.0035% and the balance of Fe and inevitable impurities.

C is an effective strengthening element in steel, can be dissolved into a matrix to play a role in solid solution strengthening, can be combined with V, Nb to form carbide precipitated particles to play a role in fine grain strengthening and precipitation strengthening, improves the carbon content, and is favorable for improving the strength, but too high carbon content can form more large and thick brittle carbide particles in the steel, is unfavorable for plasticity and toughness, too high carbon content can also form a segregation zone in the center of the steel plate, is unfavorable for bending property formability, and meanwhile, too high carbon content increases welding carbon equivalent, and is unfavorable for welding processing. Thus, design C of the present invention: 0.06-0.08%.

Si has higher solid solubility in steel, is beneficial to thinning rust layer tissues, reduces the integral corrosion rate of the steel and improves the toughness, but the scale removal is difficult during rolling due to the over-high content, and the welding performance is reduced. Therefore, the invention designs Si: 0.30 to 0.40 percent.

Mn has a strong solid solution strengthening effect, can obviously reduce the phase transition temperature of steel, refines the microstructure of the steel, is an important toughening element, but easily produces casting blank cracks in the continuous casting process when the content of Mn is excessive, and simultaneously can reduce the welding performance of the steel. Therefore, the invention designs Mn: 0.85 to 1.00 percent.

P can effectively improve the atmospheric corrosion resistance of steel, and when P and Cu are jointly added into the steel, a better composite effect can be displayed, but the plasticity and the low-temperature toughness of the steel are obviously reduced when the content of P is too high. Therefore, the design P is less than or equal to 0.018 percent.

S can form sulfide inclusions to deteriorate the performance of steel, and meanwhile, pitting corrosion expansion is easy to form in the corrosion process, and the corrosion performance is adversely affected. Therefore, S is less than or equal to 0.007 percent in the design.

The addition of Cu is favorable for forming a compact amorphous oxide (alkyl oxide) protective layer with good adhesion on the surface of steel, and the corrosion resistance is more obvious. In addition, Cu forms insoluble sulfides with S, thereby counteracting the deleterious effects of S on steel corrosion resistance. However, if the Cu content is too high, cracks are likely to occur during heating or hot rolling. Therefore, the present invention designs Cu: 0.30 to 0.40 percent.

Cr has an obvious effect of improving the passivation capability of steel, can promote the surface of the steel to carry out a compact passivation film or a protective rust layer, and the enrichment of Cr in the rust layer can effectively improve the selective permeability of the rust layer to corrosive media. However, too high Cr content increases the production cost. Therefore, the invention designs Cr: 0.40 to 0.50 percent.

While Ni can significantly improve the low-temperature toughness of steel and effectively prevent the hot brittleness of Cu, Ni is a precious metal element, and too high Ni increases the adhesion of scale, and hot rolling defects are formed on the surface when pressed into steel. Therefore, the present invention designs Ni: 0.20 to 0.30 percent.

V is added to form VN precipitation in a hot rolling stage, so that a certain grain refining effect is achieved, and V (C, N) is precipitated in a large amount in ferrite, so that a remarkable precipitation strengthening effect is achieved. However, too high a V content increases production costs. Thus, the present invention design V: 0.04-0.05%.

Nb can pin austenite grain boundaries to prevent grain growth, and finally refine grains, which is beneficial to improving impact toughness, but fine grain strengthening enables yield strength to rise more obviously, resulting in yield ratio rise, and the production cost is increased due to overhigh Nb content. The present invention therefore designs Nb: 0.020-0.030%.

Al plays a role in deoxidation when added into steel, but the content of Al is too high, and nitrogen oxides are easy to precipitate at austenite grain boundaries to cause casting blank cracks to be generated. Therefore, the invention designs Als: 0.015-0.050%.

The carbon equivalent CEV of the steel for the assembly steel structure is less than or equal to 0.42 percent, the welding crack sensitivity index Pcm is less than or equal to 0.20 percent, the atmospheric corrosion resistance index I is more than or equal to 6.0, and the steel has good welding performance and atmospheric corrosion resistance.

The invention also provides a preparation method of the steel for the assembly type steel structure, which comprises the following steps: smelting the steel into a steel billet according to the components of the steel for the assembled steel structure, and carrying out hot continuous rolling, laminar cooling and coiling to obtain the steel billet; the laminar cooling process adopts front-stage cooling.

In the hot continuous rolling procedure, the heating temperature of a steel billet is 1220-1260 ℃; carrying out 5-pass rolling on the rough rolling, wherein the deformation of each pass is more than or equal to 20 percent, and carrying out full-length descaling; the initial rolling temperature of finish rolling is not more than 1040 ℃, and the final rolling temperature is 850-890 ℃. In the laminar cooling process, the opening quantity of cooling water between the racks is more than or equal to 5. The coiling temperature is 560-600 ℃.

In the hot continuous rolling process, the composition segregation of the cast structure can be homogenized by adopting a higher heating temperature, but the problems of burning loss, overheating, overburning and the like can occur when the heating temperature is too high. Therefore, the heating temperature of the billet in the hot continuous rolling procedure is 1220-1260 ℃.

The rough rolling needs to reach enough deformation to ensure austenite recrystallization, refine austenite grains and prevent mixed grain tissues, and the rough rolling is carried out for 5 passes, wherein the deformation of each pass is more than or equal to 20 percent; and 4, rough rolling is carried out, and the scale is removed in a full-length full-line manner so as to fully remove the scale and avoid the surface quality problem caused by pressing the scale into the steel plate.

If the initial rolling temperature of finish rolling is too high, the deformation of the non-recrystallization region of austenite in the finish rolling process is insufficient, and the structure is not refined, so the initial rolling temperature of finish rolling is less than or equal to 1040 ℃.

If the finish rolling temperature is too low, the difference between the finish rolling temperature and the initial rolling temperature is too large, so that the cooling speed in the finish rolling process is too high, the risk of rolling of a plurality of racks in a two-phase region after finish rolling exists, and the comprehensive performance of a product is poor; if the finish rolling temperature is too high, the cooling speed in the laminar cooling process is too high, so that abnormal structures are generated, and therefore, the finish rolling temperature of the finish rolling is 850-890 ℃.

The cooling water between the racks is opened, so that the cooling speed of the strip steel in the finish rolling process can be increased, the rolling speed is increased on the basis of ensuring the start rolling temperature and the finish rolling temperature of finish rolling, the difference between the finish cooling temperature and the coiling temperature of a laminar cooling section is reduced, the product performance is ensured, and the opening number of the cooling water between the racks is more than or equal to 5.

In the coiling process, the coiling temperature is controlled to be 560-600 ℃, if the coiling temperature is too low, the cooling speed in the laminar cooling process is too high, so that abnormal structures are generated, and if the coiling temperature is too high, grains are coarse, so that the comprehensive performance of a finished product is poor.

In the cooling procedure, the front section cooling is adopted, so that the sufficient cooling speed is ensured to refine the final structure, and simultaneously, the separation of a fine and dispersed second phase is facilitated, and the formation of an obvious yield effect is facilitated.

For the requirement of earthquake resistance of construction steel, section 6 of structural steel: the yield ratio of steel for the anti-seismic structure is required to be less than or equal to 0.85 in the technical conditions for delivery of anti-seismic building structural steel (GB/T34560.6-2017), and the steel for the anti-seismic structure is required to have an obvious yield platform and good impact toughness in the building anti-seismic design code (GB 50011-2010).

The yield effect of the low-carbon steel is that because the Coriolis gas mass formed by the interstitial atoms C, N and the precipitated phase are equal to the pinning of the dislocation, the stress must be increased to a certain degree during deformation to enable the dislocation to get rid of the pinning, and an upper yield point is formed on a tensile curve at the moment; once the dislocations are free of pinning, they can continue to move under less stress, at which point a lower yield point is formed on the stress-strain curve.

The research shows that the microstructure type is a main factor influencing the yield platform length of the steel, and the original movable dislocation density in the equiaxed polygonal ferrite is low, so that the obvious yield platform is easily generated. It has been found that the yield point elongation Ae of a material, which is the percentage of the ratio of the extension of the extensometer gauge length from the onset of yielding to the onset of uniform work hardening to the extensometer gauge length, increases with ferrite grain refinement, and that the yield point elongation Ae of a material, which is the percentage of a metallic material exhibiting a pronounced yielding behavior, increases with the increase in Ae.

The microstructure of the steel for the assembled steel structure prepared by the components and the method is polygonal ferrite and pearlite, a proper amount of V element is added into the steel, and the grain of the ferrite is refined by the precipitation of V (C, N), so that the elongation after fracture and low-temperature impact toughness are improved, and an obvious yield platform is generated; meanwhile, due to the adoption of a front-section cooling mode, V (C, N) is dispersed and precipitated in the ferrite at a lower temperature, the growth of precipitated phases is inhibited, and the fine dispersed precipitates are strengthened relative to the pinning effect of dislocation. Therefore, the steel for a fabricated steel structure has a long yield plateau length and a large yield elongation Ae value.

The yield strength of the steel for the assembled steel structure is more than or equal to 450MPa, the tensile strength is more than or equal to 550MPa, the yield ratio is less than or equal to 0.85, the elongation is more than or equal to 20%, the yield point elongation Ae is more than or equal to 2.0%, D (thickness is less than or equal to 6mm) or D (thickness is more than 6mm) in a 180-degree cold bending test, the impact power at 40 ℃ is more than or equal to 60J (full size), and the relative corrosion rate (relative to Q355B) is less than or equal to 55%.