A Q235B hot-rolled H-beam and production method thereof

Abstract

The invention discloses a Q235B hot-rolled H-shaped steel and a production method thereof, and relates to the technical field of steel production. The hot-rolled H-shaped steel is composed of the following chemical components by mass percentage: C: 0.12-0.18%, Si: 0.12-0.25%, Mn: 0.32-0.50%, S≤0.040%, P≤0.040%, As%≤0.080%, and no expensive alloys such as V and Nb are added, and the remaining Fe element and inevitable impurity elements are not added. The invention realizes low alloy cost by reasonably allocating alloy components, matching and designing a reasonable heating furnace firing temperature and furnace time, rough rolling start rolling temperature and speed, finishing rolling start rolling temperature and speed, finishing rolling final rolling temperature, and cooling bed cooling, obtains an H-shaped steel with a ferrite + pearlite structure, effectively controls the grain size in the H-shaped steel, and enables the obtained H-shaped steel to have both excellent yield strength, tensile strength, and elongation, and has excellent comprehensive mechanical properties.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a Q235B hot-rolled H-shaped steel and a production method thereof. Background Art

[0002] Advantages of hot-rolled H-shaped steel in construction and steel structures: In August 2020, the Ministry of Housing and Urban-Rural Development and other nine departments jointly issued the "Several Opinions on Accelerating the Development of New Building Industrialization", proposing to increase the application of hot-rolled H-shaped steel, weathering steel and fire-resistant steel; in March 2021, it was proposed to promote green building materials, prefabricated buildings and steel-structured houses to build low-carbon cities. Hot-rolled H-shaped steel is a high-performance green building material that complies with national policies and industry development directions. The product has the following advantages: good cross-sectional distribution mechanical properties; no welding required, high quality precision, high production efficiency and low consumption; small residual stress and high component bearing capacity; convenient connection structure, easy installation, short construction period; easy to standardize and low overall cost.

[0003] Hot-rolled H-beam Q235B requires a yield strength of more than 235MPa. Therefore, currently, the yield strength of the steel is usually improved by adding high manganese, high silicon, and high-cost alloy elements such as V, Nb, and Ti. Such methods have high production costs, reduce corporate benefits, and occupy more alloy resources.

[0004] Therefore, how to achieve the goal of saving resources by optimizing the alloy composition of steel sections, and at the same time ensure that product performance meets the standards by improving the production process, so as to achieve low-cost production while obtaining the required mechanical properties, is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] The purpose of the present invention is to provide a Q235B hot-rolled H-beam and a production method thereof to solve the above-mentioned problems.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The invention discloses a Q235B hot-rolled H-shaped steel and a production method thereof, which is composed of the following chemical components in mass percentage: C: 0.12-0.18%, Si: 0.12-0.25%, Mn: 0.32-0.50%, S≤0.040%, P≤0.040%, As%≤0.080%, and no expensive alloys such as V and Nb are added, and the remaining Fe element and inevitable impurity elements are not added;

[0008] The production method of Q235B hot-rolled H-beam comprises the following process steps:

[0009] a. Billet heating: The heating furnace includes preheating section, heating section 1, heating section 2 and soaking section hot charging: the temperature of the preheating section is 1100-1220℃, the temperature of heating section 1 is 1270-1310℃, the temperature of heating section 2 is 1305-1335℃, the temperature of soaking section is 1290-1320℃, the temperature of the rectangular billet is heated to 1290-1320℃, and the total time in the furnace is 120-150min;

[0010] b. Billet rolling: The rectangular billet is rolled in a single frame for 7-9 reciprocating passes, the speed of the last rough rolling pass is controlled at 4-4.5m / s, the temperature of the rough rolling wing plate is 1160-1240℃, and the intermediate billet is produced with an elongation ratio of 1:2.2-3;

[0011] c. Finishing rolling: the intermediate billet after billet rolling is continuously rolled in one direction by a universal rolling mill for 11 times; the extension ratio is 1:4-5.8, the speed of the last rolling mill of finishing rolling is controlled at 3.5-5m / s, the temperature of the wing plate of finishing rolling is 1050-1150℃, and the temperature of the wing plate of finishing rolling is controlled at 950-1020℃;

[0012] d. Cooling on cooling bed (air cooling + water mist cooling): The finished steel on the upper cooling bed is cooled in two parts. The temperature of the wing plate in the first half of air cooling is reduced from 950-1020℃ to 180-250℃, and the temperature of the wing plate in the second half of water mist cooling is reduced from 180-250℃ to less than 80℃. The water mist cooling is a combination of cooling water and compressed air. The compressed air pressure is 0.5-0.55MPa, the cooling water temperature is controlled within the range of 20℃-25℃, and the water pressure is 0.3-0.35MPa.

[0013] e. Straightening: The finished steel sections cooled on the cooling bed are passed through a ten-roll straightening machine to eliminate internal stress. The inlet temperature before straightening must be ≤80℃.

[0014] Furthermore, the rectangular billet is a rectangular billet of H-shaped steel obtained by sequentially subjecting molten iron to converter smelting, deoxidation and alloying, LF refining and continuous casting.

[0015] Furthermore, the heating time ratio of the preheating section, heating section 1, heating section 2 and soaking section hot loading is arranged as 3:4:4:3.

[0016] Furthermore, the method further includes descaling the rectangular billet before the billet rolling.

[0017] Furthermore, the method also includes finishing the straightened finished steel section.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] The present invention realizes low alloy cost by reasonably allocating alloy components, matching and designing reasonably the firing temperature and furnace time of a heating furnace, the start temperature and speed of rough rolling, the start temperature and speed of fine rolling, the final rolling temperature of fine rolling, and cooling of a cooling bed (air cooling + water mist cooling), and obtains H-shaped steel with a ferrite + pearlite structure, effectively controls the grain size in the H-shaped steel, and enables the obtained H-shaped steel to have excellent yield strength, tensile strength, elongation, and excellent comprehensive mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 This is a metallographic grain size grade diagram of the hot-rolled H-beam Q235B obtained in Example 1 of the present invention;

[0022] Figure 2 The metallographic structure banding grade diagram of the hot-rolled H-beam Q235B obtained in Example 1 of the present invention;

[0023] Figure 3 This is a metallographic grain size grade diagram of the hot-rolled H-beam Q235B obtained in Example 2 of the present invention;

[0024] Figure 4 The metallographic structure banding grade diagram of the hot-rolled H-beam Q235B obtained in Example 2 of the present invention; DETAILED DESCRIPTION

[0025] A Q235B hot-rolled H-shaped steel and a production method thereof, comprising the following chemical components in mass percentage: C: 0.12-0.18%, Si: 0.12-0.25%, Mn: 0.32-0.50%, S≤0.040%, P≤0.040%, As%≤0.080%, no addition of expensive alloys such as V and Nb, and the remainder of Fe element and inevitable impurity elements;

[0026] The production method of Q235B hot-rolled H-beam comprises the following process steps:

[0027] a. Billet heating: the heating furnace includes a preheating section, a heating section 1, a heating section 2 and a soaking section hot charging: the temperature of the preheating section is 1100-1220°C, the temperature of the heating section 1 is 1270-1310°C, the temperature of the heating section 2 is 1305-1335°C, the temperature of the soaking section is 1290-1320°C, the rectangular billet is heated to 1290-1320°C, the total furnace time is 120-150min, the rectangular billet is an H-shaped steel rectangular billet obtained by molten iron in sequence through converter smelting, deoxidation alloying, LF refining and continuous casting, and the heating time ratio of the preheating section, heating section 1, heating section 2 and soaking section hot charging is 3:4:4:3;

[0028] b. Billet rolling: The rectangular billet is rolled in a single frame for 7-9 reciprocating passes, the speed of the last rough rolling pass is controlled at 4-4.5m / s, the temperature of the rough rolling wing plate is 1160-1240℃, and the intermediate billet is produced with an elongation ratio of 1:2.2-3;

[0029] c. Finishing rolling: the intermediate billet after billet rolling is continuously rolled in one direction by a universal rolling mill for 11 times; the extension ratio is 1:4-5.8, the speed of the last rolling mill of finishing rolling is controlled at 3.5-5m / s, the temperature of the wing plate at the start of finishing rolling is 1050-1150℃, and the temperature of the wing plate at the end of finishing rolling is controlled at 950-1020℃, which can realize the recrystallization of austenite grains and further refinement of grain size. There is a 30-40s steel-waiting process from the completion of rough rolling to the start of finishing rolling, which is a process of recrystallization after crystallization refinement;

[0030] d. Cooling on cooling bed (air cooling + water mist cooling): The finished steel on the upper cooling bed is cooled in two parts. The temperature of the wing plate in the first half of air cooling is reduced from 950-1020℃ to 180-250℃, and the temperature of the wing plate in the second half of water mist cooling is reduced from 180-250℃ to less than 80℃. The water mist cooling is a combination of cooling water and compressed air. The compressed air pressure is 0.5-0.55MPa, the cooling water temperature is controlled within the range of 20℃-25℃, and the water pressure is 0.3-0.35MPa.

[0031] e. Straightening: The finished steel sections cooled on the cooling bed are passed through a ten-roll straightening machine to eliminate internal stress. The inlet temperature before straightening must be ≤80℃.

[0032] The production method of the Q235B hot-rolled H-shaped steel also includes descaling the rectangular billet before the billet rolling, and finishing the straightened finished steel.

[0033] During the billet heating process, a walking beam heating furnace is used to set the temperatures of the preheating section, heating section 1, heating section 2 and soaking section. Compared with the four-stage heating in the prior art, the heating time is shorter, the layout is reasonable, and the use of coal gas is economical, which is in line with the low-carbon environmental protection policy. The billet heating method can achieve uniform temperature inside and outside the billet and reduce oxidation and decarburization caused by long residence time in the high temperature zone.

[0034] The cooling bed is one of the indispensable auxiliary equipment in a medium-sized workshop. Its function is to transport the full-length profiles after rolling by the rolling mill and unload them onto the walking beam of the cooling bed for cooling, so that its temperature drops from 960℃ to 80-100℃. Then, the steel device under the cooling bed sends it to the straightening machine, collects it into groups and sends it to the output roller table, and then the output roller table sends it to the cold saw to cut it into fixed-length finished products.

[0035] The overall production process is: walking beam heating furnace → descaling machine → roughing mill → flying shear → finishing mill → cooling bed cooling (air cooling + water mist cooling) → straightening machine → cold saw → palletizing → packaging → finished product stand.

[0036] The invention optimizes the alloy composition matching, adopts reasonable heating furnace firing temperature and furnace time, rough rolling start temperature and speed, finishing rolling start temperature and speed, finishing rolling final rolling temperature, cooling bed cooling (air cooling + water mist cooling) in the steel rolling process, and the air cooling of the cooling bed realizes the transformation of austenite to ferrite and pearlite, realizes low alloy consumption and low production cost of the new alloy composition, meets the organizational performance requirements of hot-rolled H-shaped steel, and saves precious metal resources; also, by designing a composite alloy composition, utilizing the influence of each alloy element on the process and the quality of rolled materials, and by studying the effect of the rolling process under specific composition on the organizational performance of steel materials, a method for stable production of Q235B steel under the new composition is developed and put into practice, which reduces the cost while ensuring that the steel quality meets the requirements of the new national standard, improves the enterprise efficiency, saves alloy resources, and meets the needs of the rapid development of the national economy.

[0037] Compared with the prior art, the present invention gives full play to the advantages of multiple micro-alloy strengthening and rolling line temperature control processes. Under the condition of low alloy composition, the metallographic structure and mechanical properties required by the national standard can still be obtained, which greatly reduces the consumption of precious metals and greatly reduces the production cost. It is a green and sustainable innovative production process. In addition, the finishing rolling and final rolling temperature required by the Q235B production method is lower than that of the traditional pure hot rolling process, the degree of oxidation on the surface of the rolled material is relatively light, the iron oxide dust is greatly reduced, and the environment is improved. The surface of the finished steel has no hardened layer, the structure is ferrite + pearlite, and the structure uniformity is good. The production method is fully suitable for the stable mass production of Q235B hot-rolled H-shaped steel.

[0038] The production method of hot-rolled H-beam Q235B provided by the present invention adopts a low-temperature and short-time billet heating process (1290-1320°C, 120-150min) according to the influence of elements such as C, Si, and Mn on the solid solubility product. The heating time is short, which effectively hinders the growth of austenite grains during the heating process, ensures the fineness of the original austenite grain size during the heating process, and solves the problem of low material strength and plasticity caused by difficulty in grain refinement in the subsequent rolling process. In the production method of the hot-rolled H-shaped steel Q235B provided by the present invention, the starting rolling temperature and speed of the blanking, the starting rolling temperature and speed of the finish rolling, and the finishing rolling temperature can be controlled, so that the grain size of the H-shaped steel of the present invention can be refined and the ferrite can be uniformly nucleated. Finally, the hot-rolled H-shaped steel Q235B with a grain size of 7.5-9 or above, a band grade of 0, a ReH (MPa) yield strength of 260MPa or above, a Rm (MPa) tensile strength of 400MPa or above, an A (%) elongation after fracture (the direction of the sample is H≤40) of 34% or above, and a V-shaped Charpy impact energy of 35J or above at 20°C can be obtained. In addition, the method can also produce hot-rolled I-shaped steel Q235B and hot-rolled split T-shaped steel Q235B.

[0039] In order to further understand the present invention, a production method of hot-rolled H-beam Q235B provided by the present invention is described in detail below in conjunction with embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0040] 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 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 belong to the scope of protection of the present invention.

[0041] The composition, process parameters and performance test results of the H-beam in Examples 1-6 are shown in Table 1-3 below:

[0042] Table 1 Composition of Q235BH steel in the examples

[0043]

[0044] Table 2 Process parameters in the Q235BH steel production method in the embodiment

[0045]

[0046] Table 3 Performance test results of Q235B steel after artificial aging in the embodiment

[0047]

[0048] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A Q235B hot-rolled H-beam, characterized in that: It is composed of the following chemical components in mass percentage: C: 0.12-0.18%, Si: 0.12-0.25%, Mn: 0.32-0.50%, S≤0.040%, P≤0.040%, As%≤0.080%, and the balance of Fe element and unavoidable impurity elements; The production method of Q235B hot-rolled H-beam comprises the following process steps: a. Billet heating: The heating furnace includes preheating section, heating section 1, heating section 2 and soaking section hot charging: the temperature of the preheating section is 1100-1220℃, the temperature of heating section 1 is 1270-1310℃, the temperature of heating section 2 is 1305-1335℃, the temperature of soaking section is 1290-1320℃, the temperature of the rectangular billet is heated to 1290-1320℃, and the total time in the furnace is 120-150min; b. Billet rolling: The rectangular billet is rolled in a single frame for 7-9 reciprocating passes, the speed of the last rough rolling pass is controlled at 4-4.5m / s, the temperature of the rough rolling wing plate is 1160-1240℃, and the intermediate billet is produced with an elongation ratio of 1:2.2-3; c. Finishing rolling: the intermediate billet after the billet rolling is continuously rolled in one direction by a universal rolling mill for 11 times; the extension ratio is 1:4-5.8, the speed of the last rolling mill of the finishing rolling is controlled at 3.5-5m / s, the temperature of the wing plate of the finishing rolling is 1050-1150℃, and the temperature of the wing plate of the finishing rolling final rolling is controlled at 950-1020℃; d. Cooling on cooling bed: The finished steel on the upper cooling bed is cooled in two parts. The temperature of the wing plate in the first half is reduced from 950-1020℃ to 180-250℃ by air cooling, and the temperature of the wing plate in the second half is reduced from 180-250℃ to less than 80℃ by water mist cooling. The water mist cooling is a combination of cooling water and compressed air. The compressed air pressure is 0.5-0.55MPa, the cooling water temperature is controlled within the range of 20℃-25℃, and the water pressure is 0.3-0.35MPa. e. Straightening: After cooling on the cooling bed, the finished steel is passed through a ten-roll straightening machine to eliminate internal stress. The inlet temperature before straightening must be ≤80℃; The rectangular billet is a rectangular billet of H-shaped steel obtained by sequentially subjecting molten iron to converter smelting, deoxidation alloying, LF refining and continuous casting.

2. The Q235B hot-rolled H-beam according to claim 1, characterized in that: The heating time ratio of the preheating section, heating section 1, heating section 2 and soaking section hot loading is 3:4:4:

3.

3. The Q235B hot-rolled H-beam according to claim 1, characterized in that: The method also includes descaling the rectangular billet before the billet rolling.

4. The Q235B hot-rolled H-beam according to claim 1, characterized in that: It also includes finishing the straightened finished steel sections.

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