Controlled rolling and controlled 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, and belongs to the technical field of controlled rolling and controlled cooling of steel bars. The method comprises the following steps that a steel billet is heated by a heating furnace, rolled and subjected to three-section water penetration, the temperature of the steel billet is lowered to 820-840 DEG C when the temperature of the steel billet reaches 820-840 DEG C, and natural cooling, shearing and warehousing are conducted; wherein the pressure of a main pipe for water passing is 0.9 MPa to 1.1 MPa; the opening degree of a valve for water penetration in the first section is more than 90%, and the pressure of a nozzle is 0.7-0.9 MPa; the opening degree of a second-section water passing valve is 28-32%, and the pressure of a nozzle is 0.1-0.3 MPa; the opening degree of a third-section water passing valve is 4-6%, and the pressure of a nozzle is 0.04-0.06 MPa; the steel billet comprises the following chemical components in percentage by weight: 0.22 to 0.25 percent of C, 0.22 to 0.60 percent of Si, 1.30 to 1.55 percent of Mn, 0.030 to 0.040 percent of V, less than or equal to 0.045 percent of P, less than or equal to 0.045 percent of S and 0.47 to 0.54 percent of Ceq. By means of the controlled rolling and controlled cooling manufacturing method, the content of alloy such as Si, Mn and V can be reduced, and meanwhile it is guaranteed that the large-specification HRB400-grade hot-rolled ribbed steel bars with the diameter phi being 36 mm or above meet the national standard requirement.

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 state ministries and commissions stipulated that domestic steel enterprises will implement the new standard GB / T1499.2~2018 for the production of construction steel. The introduction of the new national standard has strict restrictions on the morphology of the quenching layer and the cross-section hardness difference (ΔHV≤40) in the metallographic structure of the steel section. If the rebar that meets the requirements of the new national standard is produced by conventional processes, it is necessary to increase the strength by adding Mn, Si alloy elements or V, Nb, Ti microalloy elements solid solution strengthening and precipitation strengthening methods. The alloying method will increase the production cost by 50 to 100 yuan / ton, and excessive increase in the content of alloy elements will also affect the welding performance of the bar. For example, in order to ensure the qualified performance of HRB400 grade rebar, the current practice of domestic steel enterprises is to control the performance by adding five elements such as C, Si, Mn, P, S and adding vanadium nitrogen alloy microalloying. However, the price of vanadium nitrogen alloy has continued to rise in the past two years. The highest price of vanadium nitrogen alloy has exceeded 800,000 yuan / t, resulting in a significant increase in production costs, which is not in line with the current trend of energy conservation and consumption reduction in the steel industry.

[0004] With the implementation of the new national standard (GB / T1499.2~2018) for rebar in my country and the market demand, the newly built rebar production lines in recent years mostly use high-speed bar production technology to increase production and efficiency, which further prompts the traditional rebar production lines to be transformed and upgraded, and find new production processes to reduce production costs. On the existing rebar production line, how to reduce the alloy composition of rebar through new technologies and new processes to achieve the goal of creating efficiency and reducing production costs is an unsolved problem in the prior art. Therefore, this patent invents a controlled rolling and controlled cooling manufacturing method for large-size HRB400 hot-rolled ribbed steel bars of Φ36mm or Φ40mm based on the existing rolling mill equipment. Summary of the invention

[0005] In view of the shortcomings of the above existing technologies, the present invention provides a controlled rolling and controlled cooling manufacturing method for HRB400 grade hot-rolled ribbed steel bars. 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 HRB400 grade hot-rolled ribbed steel bars with large specifications of Φ36mm and above meet the national standard requirements. It is specifically achieved through the following technologies.

[0006] A controlled rolling and controlled cooling method for HRB400 grade hot-rolled ribbed steel bars, comprising 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℃ on the upper cooling bed, cooled naturally, and sheared;

[0008] 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;

[0009] Measured in weight percentage, the steel billet comprises the following chemical components: 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 components 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 the 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 water penetration, the second water penetration and the third water penetration are all provided with a back-blowing device, which can effectively prevent water from being carried out, avoid rust on the surface of the rolled piece, and play the role of 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 prepared 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 controlled cooling method of the HRB400 hot-rolled ribbed steel bars with a diameter of Φ36 mm or Φ40 mm of the present invention can reduce the content of alloys such as Si, Mn, and V. The amount of Si, Mn, and V is reduced by about 0.06wt%, 0.05wt%, and 0.01wt%, respectively. When 15,200 tons of steel bars are produced annually, the cost of 304,000 yuan can be saved. At the same time, it is ensured that the HRB400 hot-rolled ribbed steel bars with a diameter of Φ36 mm or above meet the national standard requirements. 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 embodiments, but they should not be construed as limiting the protection scope 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. The temperature of the upper cooling bed is 820~840℃, and then it is 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 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 furnace is used for heating, 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 12-pass rolling parameters are shown in the following 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 12-pass rolling parameters 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 solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[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 controlled cooling method of HRB400 grade hot-rolled ribbed steel bars of the present invention comprises the following steps:

[0042] S1. Accept the steel billet according to the billet 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, placing the steel billet in step S1 in a heating furnace for heating, 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;

[0044] S3, rolling the steel billet in step S2 for a total of 12 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 1000~1080℃, and the final rolling temperature is 1050℃~1100℃;

[0045] S4. Three sections of water penetration are set after the outlet of the finishing mill, and the pressure of the water penetration main pipe is ensured to be between 0.9MPa and 1.1MPa; the first section valve opening degree is more than 90%, and the nozzle pressure is about 0.8MPa; the second section valve opening degree is about 30%, and the nozzle pressure is about 0.2MPa; the third section valve opening degree is about 5%, and the nozzle pressure is about 0.05MPa; the steel billet in step S3 passes through the first section water penetration, the second section water penetration and the third section water penetration in turn, and the upper cooling bed is naturally cooled, 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 composition of the steel billet is controlled by the original composition in Table 1, and the controlled cooling process is controlled by the original controlled cooling process in Table 2. The remaining operating steps and process parameters are the same as the controlled rolling and controlled cooling method of HRB400 grade hot-rolled ribbed steel bars of the present invention.

[0048] Controlled rolling and controlled cooling method 2: The composition of the steel billet 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 the controlled rolling and controlled cooling method of the HRB400 grade hot-rolled ribbed steel bar 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 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 composition of the steel billet 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 the controlled rolling and controlled cooling method of the HRB400 grade hot-rolled ribbed steel bar of the present invention.

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

[0052] The composition of the steel billets for the eight tests is shown in Table 5. The controlled rolling and controlled cooling processes and steel bar quality inspection results used in the eight tests 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 in each group and steel bar quality inspection results

[0057]

[0058] It can be seen from Table 6 that, compared with Group 1 and Group 2, the yield strength of Group 3 and Group 4 has increased, but the yield strength of the Ф36mm large-size HRB400E steel bars exceeds the internal control upper limit of 510MPa 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] From the above description, the controlled rolling and controlled cooling method of the present invention can produce HRB400E steel bars with large specifications of 36 mm and 40 mm that meet the national standard requirements, while reducing the content of alloys such as Si, Mn, and V, effectively reducing production costs. For example, in comparison between Group 4 and Group 8, the amount of Si, Mn, and V was reduced by approximately 0.06wt%, 0.05wt%, and 0.01wt%, respectively, and when 15,200 tons of steel bars are produced that year, 304,000 yuan in costs can be saved.

[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 in the above embodiments. Within the scope of the claims and technical concept of the present invention, the technical solution of the present invention can be modified and changed in many simple ways, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A method for controlled rolling and controlled cooling of 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℃ on the upper cooling bed, cooled naturally, and sheared; 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; The specification of the HRB400 grade hot-rolled ribbed steel bar is Φ36mm or Φ40mm; the steel billet contains the following chemical components in terms of 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%.

2. The controlled rolling and controlled cooling method for HRB400 grade hot-rolled ribbed steel bars according to claim 1, characterized in that: When heating in the heating furnace, the temperature of the preheating section is not greater than 950°C, and the heating time is not less than 50 minutes; 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 controlled 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 product hole is a Φ36mm threaded hole.

4. The controlled rolling and controlled 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 product hole is a Φ40mm threaded hole.

5. The controlled rolling and controlled 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 controlled 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 back-blowing water devices.

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

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