A controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars

Abstract

The invention discloses a controlled rolling and controlled cooling method for HRB400 grade hot-rolled ribbed steel bars, belonging to the technical field of controlled rolling and controlled cooling of steel bars. The method comprises the following steps: heating the steel billet in a heating furnace, rolling, and passing through water in three stages, cooling the steel billet to a temperature of 820-840° C. on an upper cooling bed, naturally cooling the steel billet, shearing the steel billet, and storing the steel billet; wherein the pressure of the water pipe is 0.9 MPa-1.1 MPa; the valve opening degree of the first water pipe is above 90%, and the nozzle pressure is 0.7-0.9 MPa; the valve opening degree of the second water pipe is 28-32%, and the nozzle pressure is 0.1-0.3 MPa; the valve opening degree of the third water pipe is 4-6%, and the nozzle pressure is 0.04-0.06 MPa; and the steel billet comprises the following chemical compositions by weight: C: 0.22-0.25%, Si: 0.22-0.60%, Mn: 1.30-1.55%, V: 0.030-0.040%, P≤0.045%, S≤0.045%, and Ceq: 0.47-0.54%. The controlled rolling and controlled cooling manufacturing method of the present invention can reduce the content of alloys such as Si, Mn, and V, while ensuring that large-size HRB400 grade hot-rolled ribbed steel bars of Φ36 mm and above meet national standards.

Description

Technical Field

[0001] The invention relates to the technical field of controlled rolling and controlled cooling of steel bars, and in particular to a controlled rolling and controlled cooling method for HRB400 grade hot-rolled ribbed steel bars. Background Art

[0002] At present, HRB400E high-strength earthquake-resistant steel bars have become the mainstream of construction steel bars due to their good processability, weldability, process performance, mechanical properties and stability and reliability.

[0003] In November 2018, relevant national ministries and commissions mandated that domestic steel companies producing construction steel comply with the new standard GB / T1499.2-2018. This new standard imposes strict limits on the morphology of the quench layer and the cross-sectional hardness difference (ΔHV ≤ 40) in the cross-section microstructure of rebar. Conventional processes for producing rebar that meets the new standard require the addition of alloying elements such as manganese and silicon, or microalloying elements such as vanadium, niobium, and titanium, through solid solution strengthening and precipitation strengthening to increase strength. However, this alloying method increases production costs by 50 to 100 yuan per ton, and excessively increasing alloying element content can also affect the weldability of the bar. For example, to ensure the performance of HRB400-grade rebar, domestic steel companies currently employ microalloying with five key elements—carbon, silicon, manganese, phosphorus, and sulfur—as well as vanadium-nitrogen alloys. However, the price of vanadium-nitrogen alloys has continued to rise in the past two years, reaching a peak of over 800,000 yuan per ton. This has significantly increased production costs and is inconsistent with the current trend of energy conservation and consumption reduction in the steel industry.

[0004] With the implementation of my country's new national standard for rebar (GB / T1499.2-2018) and market demand, newly built rebar production lines in recent years have increasingly adopted high-speed bar production processes to increase production and efficiency. This has further prompted the transformation and upgrading of traditional rebar production lines, and the search for new production processes to reduce production costs. On existing rebar production lines, how to reduce the alloy composition of rebar through new technologies and processes to achieve efficiency and reduce production costs remains an unresolved issue in the prior art. Therefore, this patent, based on existing rolling mill equipment, invents a controlled rolling and cooling method for manufacturing large-size HRB400-grade hot-rolled ribbed steel bars (Φ36mm or Φ40mm). Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention provides a controlled rolling and cooling method for manufacturing HRB400-grade hot-rolled ribbed steel bars. This method reduces the content of alloys such as Si, Mn, and V, while ensuring that large-size HRB400-grade hot-rolled ribbed steel bars (Ø36 mm and larger) meet national standards. This method is achieved through the following techniques.

[0006] A controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars comprises the following steps:

[0007] The billet is heated in a heating furnace, rolled, and passed through water in three stages before being cooled to a temperature of 820-840°C on the upper cooling bed, cooled naturally, and sheared.

[0008] The main pipe pressure of the water penetration is 0.9MPa~1.1MPa; the valve opening degree of the first section of water penetration is more than 90%, and the nozzle pressure is 0.7~0.9MPa; the valve opening degree of the second section of water penetration is 28~32%, and the nozzle pressure is 0.1~0.3MPa; the valve opening degree of the third section of water penetration is 4~6%, and the nozzle pressure is 0.04~0.06MPa;

[0009] In terms of weight percentage, the steel billet contains the following chemical composition: C: 0.22-0.25%, Si: 0.22-0.60%, Mn: 1.30-1.55%, V: 0.030-0.040%, P≤0.045%, S≤0.045%, and Ceq: 0.47-0.54%.

[0010] Furthermore, the steel billet comprises the following chemical composition in weight percentage: C: 0.22~0.25%, Si: 0.22~0.60%, Mn: 1.30~1.55%, V: 0.030~0.040%, P≤0.045%, S≤0.045%, Ceq: 0.47~0.54%.

[0011] Furthermore, when heating in a heating furnace, the temperature of the preheating section is not greater than 950°C, and the heating time is not less than 50 minutes; wherein, when the temperature of the steel billet entering the furnace is less than 300°C, the temperature of the heating section is 1190±20°C, and the temperature of the soaking section is 1180±20°C; when the temperature of the steel billet entering the furnace is ≥300°C, the temperature of the heating section is 1180±20°C, and the temperature of the soaking section is 1170±20°C.

[0012] Furthermore, when the steel bar specification is Φ36mm, the rolling adopts a flat box + vertical box + elliptical + round hole series, with a total of 12 rolling passes, including 6 rough rolling passes, and the rough rolling outlet material shape is Φ84±1mm; 2 intermediate rolling passes, and the intermediate rolling outlet material shape is Φ63±0.5mm; 4 finishing rolling passes, and the finished hole is a Φ36mm threaded hole.

[0013] Furthermore, when the steel bar specification is Φ40mm, the rolling adopts a flat box + vertical box + elliptical + round hole series, with a total of 12 rolling passes, including 6 rough rolling passes, and the rough rolling outlet material shape is Φ86±1mm; 2 intermediate rolling passes, and the intermediate rolling outlet material shape is Φ65±0.5mm; 4 finishing rolling passes, and the finished hole is a Φ40mm threaded hole.

[0014] Furthermore, during the rolling process, the finishing rolling temperature is 1000~1080℃, and the final rolling temperature is 1050~1100℃.

[0015] Furthermore, the first, second and third water penetration stages are all equipped with backwash devices, which can effectively prevent water from being carried out, thus avoiding rust on the surface of the rolled piece and cleaning the iron oxide scale on the surface of the rolled piece.

[0016] A large-size HRB400 grade hot-rolled ribbed steel bar with a diameter of Φ36 mm or Φ40 mm is produced by adopting the above-mentioned HRB400 grade hot-rolled ribbed steel bar controlled rolling and controlled cooling method.

[0017] Compared with the prior art, the present invention is beneficial in that:

[0018] The controlled rolling and cooling method for HRB400-grade hot-rolled ribbed steel bars with a diameter of 36 mm or 40 mm can reduce the content of alloys such as Si, Mn, and V by approximately 0.06wt%, 0.05wt%, and 0.01wt%, respectively. This method saves 304,000 yuan in annual production costs for 15,200 tons of steel bars. It also ensures that HRB400-grade hot-rolled ribbed steel bars with a diameter of 36 mm or larger meet national standards. DETAILED DESCRIPTION

[0019] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0020] The present invention exemplarily provides a method for controlled rolling and controlled cooling of HRB400 grade hot-rolled ribbed steel bars, comprising the following steps:

[0021] The billet is heated in a heating furnace, rolled, and passed through water in three stages before being put on a cooling bed with a temperature of 820-840°C. It is then naturally cooled, sheared, and stored.

[0022] Among them, the main pipe pressure of the water penetration is 0.9MPa~1.1MPa; the valve opening degree of the first section of water penetration is more than 90%, and the nozzle pressure is 0.7~0.9MPa; the valve opening degree of the second section of water penetration is 28~32%, and the nozzle pressure is 0.1~0.3MPa; the valve opening degree of the third section of water penetration is 4~6%, and the nozzle pressure is 0.04~0.06MPa.

[0023] In some examples of the present invention, the steel billet comprises the following chemical composition, calculated by weight percentage: C: 0.22-0.25%, Si: 0.22-0.60%, Mn: 1.30-1.55%, V: 0.030-0.040%, P≤0.045%, S≤0.045%, Ceq: 0.47-0.54%.

[0024] In some examples of the present invention, the heating is carried out in a heating furnace, and the heating time is not less than 50 minutes; wherein, when the temperature of the steel billet entering the furnace is less than 300°C, the temperature of the preheating section is not greater than 950°C, the temperature of the heating section is 1190±20°C, and the temperature of the soaking section is 1180±20°C; when the temperature of the steel billet entering the furnace is ≥300°C, the temperature of the preheating section is not greater than 950°C, the temperature of the heating section is 1180±20°C, and the temperature of the soaking section is 1170±20°C.

[0025] In some examples of the present invention, when the steel bar specification is Φ36mm, the rolling adopts a flat box + vertical box + elliptical + round hole series, with a total of 12 rolling passes, including 6 rough rolling passes, and the rough rolling outlet material shape is Φ84±1mm; 2 intermediate rolling passes, and the intermediate rolling outlet material shape is Φ63±0.5mm; 4 finishing rolling passes, and the finished hole is a Φ36mm threaded hole.

[0026] In some examples of the present invention, when the steel bar specification is Φ36 mm, the rolling parameters for 12 passes are shown in Table 1. The billet specification is 162 mm*162 mm.

[0027] Table 1 Rolling parameters of Φ36mm large-size HERB400E steel bars

[0028]

[0029] In some examples of the present invention, when the steel bar specification is Φ40mm, the rolling adopts a flat box + vertical box + elliptical + round hole series, with a total of 12 rolling passes, including 6 rough rolling passes, and the rough rolling outlet material shape is Φ86±1mm; 2 intermediate rolling passes, and the intermediate rolling outlet material shape is Φ65±0.5mm; 4 finishing rolling passes, and the finished hole is a Φ40mm threaded hole.

[0030] In some examples of the present invention, when the steel bar specification is Φ40 mm, the rolling parameters for 12 passes are shown in Table 2. The billet specification is 162 mm*162 mm.

[0031] Table 2 Rolling parameters of Φ40mm large-size HERB400E steel bars

[0032]

[0033] In some examples of the present invention, during the rolling process, the finishing rolling temperature is 1000-1080°C, and the final rolling temperature is 1050-1100°C.

[0034] The technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] 1. Composition control: The alloy element composition of HRB400E steel billet is shown in Table 3 below.

[0036] Table 3 Alloy element composition of HRB400E steel billet

[0037]

[0038] 2. The cooling process control is shown in Table 4 below.

[0039] Table 4 Controlled cooling process

[0040]

[0041] The controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars of the present invention comprises the following steps:

[0042] S1. Accept the steel billet according to the following composition: C: 0.22~0.25%, Si: 0.22~0.60%, Mn: 1.30~1.55%, V: 0.030~0.040%, P≤0.045%, S≤0.045%, Ceq: 0.47~0.54%;

[0043] S2. Place the steel billet in step S1 in a heating furnace and heat it for no less than 50 minutes; wherein, when the steel billet entering the furnace temperature is less than 300°C, the temperature of the preheating section is no more than 950°C, the temperature of the heating section is 1190±20°C, and the temperature of the soaking section is 1180±20°C; when the steel billet entering the furnace temperature is ≥300°C, the temperature of the preheating section is no more than 950°C, the temperature of the heating section is 1180±20°C, and the temperature of the soaking section is 1170±20°C;

[0044] S3, rolling the steel billet in step S2 for a total of 12 rolling passes, wherein when rolling Φ36mm, the rough rolling outlet material shape is Φ84±1mm, the intermediate rolling outlet material shape is Φ63±0.5mm, and the finished product is Φ36mm thread; when rolling Φ40mm, the rough rolling outlet material shape is Φ86±1mm, the intermediate rolling outlet material shape is Φ65±0.5mm, and the finished product is Φ40mm thread, the finishing rolling temperature is 1000°C~1080°C, and the final rolling temperature is 1050°C~1100°C;

[0045] S4. Set three sections of water penetration after the outlet of the finishing mill, and ensure that the pressure of the water penetration main pipe is between 0.9MPa and 1.1MPa; the valve opening degree of the first section is more than 90%, and the nozzle pressure is about 0.8MPa; the valve opening degree of the second section is about 30%, and the nozzle pressure is about 0.2MPa; the valve opening degree of the third section is about 5%, and the nozzle pressure is about 0.05MPa; the steel billet in step S3 passes through the first section of water penetration, the second section of water penetration and the third section of water penetration in sequence, and is naturally cooled on the cooling bed, and the temperature of the upper cooling bed is 820℃~840℃; shearing and storage.

[0046] 3. Classification of controlled rolling and controlled cooling methods:

[0047] Controlled rolling and controlled cooling method 1: The steel billet composition is controlled by the original composition in Table 1, and the controlled cooling process is the original controlled cooling process in Table 2. The remaining operating steps and process parameters are the same as those of the controlled rolling and controlled cooling method for HRB400 grade hot-rolled ribbed steel bars of the present invention.

[0048] Controlled rolling and controlled cooling method 2: The steel billet composition is controlled by the original composition in Table 1, and the controlled cooling process adopts the controlled cooling process of the present invention in Table 2. The remaining operating steps and process parameters are the same as those of the controlled rolling and controlled cooling method of HRB400 grade hot-rolled ribbed steel bars of the present invention.

[0049] Controlled rolling and controlled cooling method 3: The composition of the steel billet is controlled by the composition of the present invention in Table 1, and the controlled cooling process adopts the original controlled cooling process in Table 2. The remaining operating steps and process parameters are the same as those of the controlled rolling and controlled cooling method of HRB400 grade hot-rolled ribbed steel bars of the present invention.

[0050] Controlled rolling and controlled cooling method 4: The steel billet composition is controlled by the composition of the present invention in Table 1, and the controlled cooling process is controlled by the controlled cooling process of the present invention in Table 2. The remaining operating steps and process parameters are the same as those of the controlled rolling and controlled cooling method of HRB400 grade hot-rolled ribbed steel bars of the present invention.

[0051] The present invention specifically sets up the following eight groups of comparative experiments.

[0052] The compositions of the steel billets for the eight tests are shown in Table 5. The controlled rolling and controlled cooling processes used in the eight tests and the steel bar quality inspection results are shown in Table 6.

[0053] The national standard GB / T 1499-2018 for quality inspection requires: lower yield strength ReL ≥ 400MPa, tensile strength Rm ≥ 540MPa, elongation after fracture A / % ≥ 16, and elongation Agt / % ≥ 7.5.

[0054] Table 5 Composition of each group of steel billets (wt,%)

[0055]

[0056] Table 6 Controlled rolling and controlled cooling processes used by each group and steel bar quality inspection results

[0057]

[0058] As shown in Table 6, although the yield strength of Groups 3 and 4 is improved compared with Groups 1 and 2, the yield strength of the HRB400E steel bars with a diameter of 36 mm exceeds the internal control upper limit of 510 MPa and does not meet the national standard requirements.

[0059] Compared with Group 7 and Group 8, the yield strength of Group 5 and Group 6 is lower, and the yield strength of the rolled Ф36mm and Ф40mm large-size HRB400E steel bars exceeds the internal control lower limit of 420MPa, which does not meet the national standard requirements.

[0060] As demonstrated above, the controlled rolling and cooling method of the present invention can produce large-size HRB400E rebar (Ø36mm and Ø40mm) that meets national standards, while also reducing the content of alloys such as Si, Mn, and V, effectively lowering production costs. For example, comparing Group 4 with Group 8, the Si, Mn, and V content were reduced by approximately 0.06wt%, 0.05wt%, and 0.01wt%, respectively. This translates to a cost savings of 304,000 RMB for the annual production of 15,200 tons of rebar.

[0061] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details of the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

Claims

1. A controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars, characterized in that: The following steps are involved: The billet is heated in a heating furnace, rolled, and passed through water in three stages before being cooled to a temperature of 820-840°C on the upper cooling bed, cooled naturally, and sheared. The main pipe pressure of the water penetration is 0.9MPa~1.1MPa; the valve opening degree of the first section of water penetration is more than 90%, and the nozzle pressure is 0.7~0.9MPa; the valve opening degree of the second section of water penetration is 28~32%, and the nozzle pressure is 0.1~0.3MPa; the valve opening degree of the third section of water penetration is 4~6%, and the nozzle pressure is 0.04~0.06MPa; The specification of the HRB400 grade hot-rolled ribbed steel bar is Φ36mm or Φ40mm; the steel billet contains the following chemical composition by weight: C: 0.22~0.25%, Si: 0.22~0.60%, Mn: 1.30~1.55%, V: 0.030~0.040%, P≤0.045%, S≤0.045%, Ceq: 0.47~0.54%.

2. The controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars according to claim 1, characterized in that: The heating furnace is heated, the preheating section temperature is not greater than 950°C, and the heating time is not less than 50 minutes; wherein, when the temperature of the steel billet entering the furnace is less than 300°C, the temperature of the heating section is 1190±20°C, and the temperature of the soaking section is 1180±20°C; when the temperature of the steel billet entering the furnace is ≥300°C, the temperature of the heating section is 1180±20°C, and the temperature of the soaking section is 1170±20°C.

3. The controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars according to claim 1, characterized in that: When the steel bar specification is Φ36mm, the rolling adopts a flat box + vertical box + elliptical + round hole series, with a total of 12 rolling passes, including 6 rough rolling passes, and the rough rolling outlet material shape is Φ84±1mm; 2 intermediate rolling passes, and the intermediate rolling outlet material shape is Φ63±0.5mm; 4 finishing rolling passes, and the finished hole is a Φ36mm threaded hole.

4. The controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars according to claim 1, characterized in that: When the steel bar specification is Φ40mm, the rolling adopts a flat box + vertical box + elliptical + round hole series, with a total of 12 rolling passes, including 6 rough rolling passes, and the rough rolling outlet material shape is Φ86±1mm; 2 intermediate rolling passes, and the intermediate rolling outlet material shape is Φ65±0.5mm; 4 finishing rolling passes, and the finished hole is a Φ40mm threaded hole.

5. The controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars according to claim 3 or 4, characterized in that: During the rolling process, the finishing rolling temperature is 1000-1080°C, and the final rolling temperature is 1050-1100°C.

6. The controlled rolling and cooling method for HRB400 grade hot-rolled ribbed steel bars according to claim 1, characterized in that: The first water penetration section, the second water penetration section and the third water penetration section are all provided with a back-blowing water device.

7. A large-size HRB400 grade hot-rolled ribbed steel bar of Φ36 mm or Φ40 mm produced by the controlled rolling and controlled cooling method for HRB400 grade hot-rolled ribbed steel bars according to claim 1.

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