A production method for improving the grain size of threaded steel

Abstract

The present invention relates to a production method for improving the grain size of threaded steel, comprising the following steps: (1) heating: placing a threaded steel billet into a heating furnace for heating, the heating temperature being 1050-1100°C, and keeping the temperature for 15-20 minutes; (2) controlling rolling: the rough rolling temperature is 1000-1050°C, the rolled piece is rolled to a diameter of Φ20-30 mm, and then cooled by three sections of water-cooled rollers, the third section of the water-cooled rollers is cooled and then the temperature is returned to 900-930°C before finishing rolling, the finishing rolling temperature is controlled at 900-950°C, and the rolling is extended. The stretch ratio is 2.7 to 3.1, and the product is finished by finishing rolling to the finished product size of the rebar; (3) controlled cooling: the temperature of the rebar after leaving the finished rolling mill is 950 to 1000 ° C, and after passing through a water-cooled roller, it is cooled to 850 to 900 ° C, and then the rolled piece is naturally cooled to room temperature after being put on a cooling bed. The method of the present invention can make more than 80% of the ferrite in the steel precipitate along the original austenite grain boundary, and increase the grain size to grade 9 to 10. The main performance indicators of the rebar are ReL: 410 to 440 MPa, Rm: 580 to 630 MPa, and Agt: 12 to 18%.

Description

Technical Field

[0001] The invention relates to the technical field of threaded steel production, in particular to a production method for improving the grain size of threaded steel. Background Art

[0002] Rebar is widely used in civil engineering projects such as housing, bridges, and roads. It requires certain mechanical strength, bending deformation resistance, and process welding performance. When Ceq ≤ 0.54%, the main performance indicators of rebar are ReL ≥ 400MPa, Rm ≥ 540MPa, and Agt ≥ 9.0%, and its metallographic structure is F+P. The raw material billet for rebar production is carbon structural steel or low-alloy structural steel that has undergone a killed smelting process. To ensure the mechanical properties of the finished steel bar, the tensile strength is mainly increased by adding alloying elements.

[0003] There are two main methods for controlling the quality of rebar: one is to improve the microstructure and properties by treating the residual heat during rolling; the other is to improve the microstructure and properties by adding microalloying elements such as V and Nb to produce precipitation strengthening of carbon and nitrides and fine grain strengthening. However, the above methods have the following problems:

[0004] (1) The rolled piece has good tensile properties after water penetration, but it is easy to have abnormal structure;

[0005] (2) By adding trace amounts of V, Nb and other alloys to the molten steel, individual microalloying and composite microalloying are carried out to refine the grains and ensure tensile properties, but the material cost increases.

[0006] Therefore, it is necessary to develop a low-cost method for preparing rebar that has good tensile properties and is relatively low in cost. This requires precise control of the structure of the rebar to meet the tensile performance requirements. Summary of the Invention

[0007] The present invention aims to address the problems of rebars with good tensile properties being prone to abnormal microstructures and the high cost of microalloyed rebar. By proposing a production method for improving the grain size of rebar, the present invention controls the rolling temperature and cooling rate of the rebar to achieve a specific distribution of pearlite and ferrite, thereby improving product performance and reducing production costs.

[0008] A production method for improving the grain size of threaded steel according to the present invention comprises the following steps:

[0009] (1) Heating: Place the rebar billet in a heating furnace for heating at a temperature of 1050-1100°C for 15-20 minutes;

[0010] (2) Controlled rolling: The rough rolling temperature is 1000-1050℃. After the rolled piece is rolled to a diameter of Φ20-30mm, it is cooled by three water-cooled rollers: the cooling rate of the first water-cooled roller is 150-200℃ / s, cooling to 790-840℃, passing through the warming roller, returning to 860-890℃, passing through the second water-cooled roller, cooling to 800-830℃, passing through the warming roller, returning to 850-880℃, passing through the third water-cooled roller, cooling to 800-8400℃, passing through the warming roller, returning to 900-930℃ before finishing rolling, controlling the finishing temperature at 900-950℃, the elongation ratio at 2.7-3.1, and finishing rolling to the finished size of rebar;

[0011] (3) Controlled cooling: The temperature of the rebar after leaving the finished rolling mill is 950-1000℃. It passes through a water-cooled roller with a cooling rate of 100-250℃ / s. After cooling to 850-950℃, the rolled piece is placed on a cooling bed and naturally cooled to room temperature.

[0012] The threaded steel in the present invention contains the following chemical components in percentage by mass: C: 0.22-0.25%, Si: 0.30-0.45%, Mn: 0.80-1.10%, S: 0.020-0.045%, and the balance is Fe and unavoidable impurity elements.

[0013] The threaded steel billet in the present invention is a 150-165*150-165mm square billet.

[0014] The hot-rolled microstructure of the threaded steel prepared in the present invention is ferrite and pearlite.

[0015] The present invention utilizes air cooling equipment to control the cooling speed of the rolled piece, and controls the cooling speed of each rolled piece by adjusting the rotation speed of the air cooling motor and the conveying speed of the cooling bed.

[0016] In the threaded steel product prepared by the present invention, more than 80% of the ferrite is precipitated along the original austenite grain boundaries, thereby increasing the grain size to level 9 to 10. The main performance indicators of the threaded steel are ReL: 430 to 470 MPa, Rm: 570 to 640 MPa, and Agt: 12 to 18%.

[0017] The process principle of the inventive method is as follows:

[0018] The rolled piece undergoes multiple stages of water cooling and temperature recovery to make the temperature inside and outside the rolled piece uniform. When entering the finishing mill, the group temperature is controlled at 900-950℃. Through controlled rolling, fine and uniform ferrite + pearlite grains are obtained, and the grain size reaches above level 9.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention can accurately control the proportion and distribution of the structure, so that more than 80% of the ferrite in the steel is precipitated along the original austenite grain boundaries, thereby increasing the grain size and effectively improving the mechanical properties of the threaded steel;

[0021] (2) The process circuit provided by the present invention is simple, highly operable, and easy to control;

[0022] (3) The present invention has low production cost and saves energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is a metallographic structure diagram of the threaded steel obtained in Example 1 of the present invention;

[0024] Figure 2 1 is a metallographic structure diagram of the threaded steel obtained in Example 2 of the present invention;

[0025] Figure 3 3 is the metallographic structure diagram of the threaded steel obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0026] To better explain the technical solution of the present invention, the technical solution of the present invention is further described below with reference to specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any form. Any changes or equivalent substitutions that do not deviate from the concept of the present invention are included in the scope of protection of the present invention.

[0027] Table 1 below is a list of the mass percentages of the chemical components contained in the threaded steel of various embodiments of the present invention;

[0028] Table 2 below is a list of the values ​​of the production process parameters of threaded steel in various embodiments of the present invention;

[0029] Table 3 below is a list of mechanical property test results of various embodiments of the present invention.

[0030] A production method for improving the grain size of threaded steel according to the present invention comprises the following steps:

[0031] (1) Heating: Place the rebar billet in a heating furnace for heating at a temperature of 1050-1100°C for 15-20 minutes;

[0032] (2) Controlled rolling: The rough rolling temperature is 1000-1050℃. After the rolled piece is rolled to a diameter of Φ20-30mm, it is cooled by three water-cooled rollers: the cooling rate of the first water-cooled roller is 150-200℃ / s, cooling to 790-840℃, passing through the warming roller, returning to 860-890℃, passing through the second water-cooled roller, cooling to 800-830℃, passing through the warming roller, returning to 850-880℃, passing through the third water-cooled roller, cooling to 800-8400℃, passing through the warming roller, returning to 900-930℃ before finishing rolling, controlling the finishing temperature at 900-950℃, the elongation ratio at 2.7-3.1, and finishing rolling to the finished size of rebar;

[0033] (3) The temperature of the rebar after leaving the finished rolling mill is 950-1000℃. It passes through a water-cooled roller with a cooling rate of 100-250℃ / s. After cooling to 850-950℃, the rolled piece is placed on a cooling bed and naturally cooled to room temperature.

[0034] The threaded steel in the present invention contains the following chemical components in percentage by mass: C: 0.22-0.25%, Si: 0.30-0.45%, Mn: 0.80-1.10%, S: 0.020-0.045%, and the balance is Fe and unavoidable impurity elements.

[0035] The threaded steel billet in the present invention is a 150-165*150-165mm square billet.

[0036] Table 1 List of mass percentages of chemical components contained in the threaded steel of various embodiments of the present invention

[0037]

[0038] Table 2 List of values ​​of production process parameters of threaded steel in various embodiments of the present invention

[0039]

[0040] Table 3 Mechanical properties test results of various embodiments of the present invention

[0041]

[0042] It can be seen from Table 3 above that the grain size of the threaded steel produced by the method of the present invention is in the range of 9 to 10.

[0043] Attachment Figures 1 to 3The metallographic structures of the rebar produced in Examples 1-3 are shown. As can be seen from the figures, the rebar steel produced in Examples 1-3 of the present invention has distinct ferrite and pearlite microstructures, uniformly distributed across the field of view, and an average grain size of 6-10 μm. This demonstrates that the present method can effectively reduce the alloying element content of rebar while maintaining the same performance.

Claims

1. A production method for improving the grain size of threaded steel, characterized in that The steps include: (1) Heating: Place the rebar billet in a heating furnace for heating at a temperature of 1050-1100°C for 15-20 minutes; (2) Controlled rolling: The rough rolling temperature is 1000-1050℃. After the rolled piece is rolled to a diameter of Φ20-30mm, it is cooled by three water-cooled rollers: the cooling rate of the first water-cooled roller is 150-200℃ / s, and it is cooled to 790-840℃. After passing through the warming roller, it is warmed to 860-890℃. After passing through the second water-cooled roller, it is cooled to 800-830℃. After passing through the warming roller, it is warmed to 850-880℃. After passing through the third water-cooled roller, it is cooled to 800-840℃. After passing through the warming roller, it is warmed to 900-930℃ and then starts finishing rolling. The finishing temperature is controlled at 900-950℃, the elongation ratio is 2.7-3.1, and the finished steel is finished to the size of the rebar. (3) Controlled cooling: The temperature of the rebar after leaving the finished rolling mill is 950-1000℃. After passing through the water-cooled roller, it is cooled to 850-950℃. After being put on the cooling bed, it is naturally cooled to room temperature. The threaded steel comprises the following chemical components in mass percentage: C: 0.22-0.25%, Si: 0.30-0.45%, Mn: 0.80-1.10%, S: 0.020-0.045%, and the balance is Fe and unavoidable impurity elements; the hot-rolled microstructure of the threaded steel is ferrite and pearlite; more than 80% of the ferrite in the finished threaded steel product is precipitated along the original austenite grain boundaries, increasing the grain size to grade 9-10, and the average grain size is 6-10 μm.

2. The method for improving the grain size of threaded steel according to claim 1, wherein: The threaded steel billet is a 150-165*150-165 mm square billet.

3. The method for improving the grain size of threaded steel according to claim 1, wherein: The main performance indicators of the threaded steel are ReL: 410-440 MPa, Rm: 580-630 MPa, and Agt: 14.8-18.2%.

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