A preparation process of low-loss hot-rolled round bar steel

Abstract

The application relates to a preparation process of low-loss hot-rolled round bar steel, and belongs to the technical field of steel preparation processes. The preparation process of the low-loss hot-rolled round bar steel comprises the following steps: high-temperature purging treatment is conducted on a steel billet to obtain pretreated steel billets; the pretreated steel billets are subjected to multi-pass hot rolling to obtain steel billet materials; the steel billet materials are subjected to annealing treatment to obtain semi-finished steel bars; and the semi-finished steel bars are subjected to multi-pass drawing treatment and secondary annealing treatment to obtain steel finished products. The steel prepared by the preparation process has balanced mechanical properties such as tensile strength and yield strength, excellent elongation after fracture, and high use reliability; the preparation process is a hot rolling, drawing and annealing preparation process, and has strong process compatibility and is convenient for large-scale production.

Description

Technical Field

[0001] This invention belongs to the technical field of steel bar preparation technology, and relates to a preparation process for low-loss hot-rolled round bar steel bars. Background Technology

[0002] Hot-rolled round bar steel bars are widely used in construction, power transmission, and machinery manufacturing due to their high manufacturing efficiency and broad applicability. With increasing industry demands for energy efficiency and mechanical properties, the market demand for low-loss, high-strength steel bars continues to grow. In existing technologies, some steel bar products employ high-area-reduction drawing processes to achieve high strength, resulting in excessively high martensite content, which increases magnetic loss and fails to meet the needs of energy-saving scenarios. Other low-loss steel bars are achieved through simplified heat treatment processes, but these suffer from poor mechanical properties and are prone to fracture. Meanwhile, some existing manufacturing processes suffer from unreasonable hot-rolling parameter control and inappropriate annealing atmosphere selection, leading to poor surface quality and insufficient microstructure uniformity, further negatively impacting the overall product performance. Summary of the Invention

[0003] The purpose of this invention is to provide a low-loss hot-rolled round bar steel bar preparation process. The steel bars prepared by this invention have balanced mechanical properties such as tensile strength and yield strength, excellent elongation after fracture, and high reliability. This preparation process is a hot rolling, drawing, and annealing process with strong process compatibility and is easy to scale up for production.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] A process for preparing low-loss hot-rolled round bar steel bars includes the following steps:

[0006] S1. The steel billet is subjected to high-temperature purging treatment to obtain a pretreated steel billet;

[0007] S2. The pretreated steel billet is hot rolled in multiple passes to obtain steel billet material;

[0008] S3. Anneal the steel billet material to obtain semi-finished steel bars;

[0009] S4. The semi-finished steel bars are subjected to multiple drawing processes and secondary annealing to obtain the finished steel bars.

[0010] As a preferred embodiment of the present invention, the steel billet in step S1 comprises, by mass percentage, 0.20-0.25% C, 0.50-0.80% Si, 1.20-1.60% Mn, 0.025-0.050% V, 0.015-0.030% Nb, 0.020-0.040% Ti, ≤0.045% P, ≤0.045% S, ≤0.30% Cr, ≤0.30% Ni, ≤0.30% Cu, with the remainder being Fe and unavoidable impurity elements.

[0011] As a preferred technical solution of the present invention, the parameters of the high-temperature purging treatment in step S1 are a purging temperature of 120-150℃ and a wind pressure of 0.6-0.8MPa. High-temperature purging can effectively remove impurities from the surface of the billet and avoid impurities from embedding into the matrix during hot rolling, thus affecting the uniformity of the microstructure. Multiple hot rolling combined with residual heat preservation can refine the austenite grains and control the grain orientation, laying a good foundation for subsequent phase transformation.

[0012] As a preferred embodiment of the present invention, the hot rolling in step S2 is a multi-pass hot rolling process. The temperature of the first hot rolling is 1050-1080℃, the speed is 0.18-0.28m / s, and the hot rolling is carried out in 6 passes. After each pass, the rolling speed is reduced to 0.8-1.0m / s and the residual heat is maintained for 3-5s. The temperature of the second hot rolling is 980-1020℃, the speed is 12-15m / s, and the hot rolling is carried out in 12 passes. After each pass, the rolling speed is reduced to 0.6-0.8m / s and the residual heat is maintained for 3-4s. The temperature of the third hot rolling is 910-950℃, the hot rolling is carried out in 8 passes, and the rolling speed is reduced to 0.4-0.6m / s and the residual heat is maintained for 3-4s.

[0013] As a preferred technical solution of the present invention, the annealing process in step S3 is a two-stage annealing. The first stage is the preheating stage: heating to 850-900℃, holding for 80-100 minutes and then rapidly water cooling. The two-stage annealing can eliminate the internal stress of hot rolling and further optimize the matrix structure.

[0014] As a preferred technical solution of the present invention, the second heat preservation stage in step S3 is as follows: the temperature is raised to 500-600°C, and the temperature is maintained for 30-40 minutes under a nitrogen protective atmosphere, and then cooled with the furnace to below 200°C before being removed from the furnace.

[0015] As a preferred technical solution of the present invention, the multi-pass drawing process of the semi-finished steel bars in step S4 is 3-4 passes of drawing process, the surface reduction rate of the first drawing process is 12-18%, the surface reduction rate of the second drawing process is 22-28%, and the surface reduction rate of the remaining drawing processes is 18-22%.

[0016] As a preferred technical solution of the present invention, the conditions for the secondary annealing process in step S4 are: heating to 500°C, preheating for 5 minutes, and holding in the furnace for 1-1.5 minutes under an argon protective atmosphere and a furnace temperature of 1150-1180°C.

[0017] The beneficial effects of this invention are:

[0018] The steel bars prepared by the process of this invention have balanced mechanical properties such as tensile strength and yield strength, excellent elongation after fracture, and high reliability in use. The preparation process is a hot rolling, drawing, and annealing process with strong process compatibility and is easy to scale up for production. Detailed Implementation

[0019] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0020] Example 1

[0021] A process for preparing low-loss hot-rolled round bar steel bars includes the following steps:

[0022] S1. A high-temperature purging device is used to remove iron filings, dust and residual protective slag adhering to the surface of the steel billet. The purging temperature is 120℃ and the air pressure is 0.6MPa to obtain a pretreated steel billet.

[0023] The steel billet mentioned in step S1, by mass percentage, includes C 0.24%, Si 0.60%, Mn 1.40%, V 0.035%, Nb 0.020%, Ti 0.030%, P≤0.045%, S≤0.045%, Cr≤0.30%, Ni≤0.30%, Cu≤0.30%, with the remainder being Fe and unavoidable impurity elements;

[0024] S2. The pretreated steel billet is hot rolled in multiple passes to obtain steel billet material;

[0025] The hot rolling in step S2 is a multi-pass hot rolling process. The first hot rolling temperature is 1050℃, the speed is 0.18m / s, and the hot rolling is carried out in 6 passes. After each pass, the rolling speed is reduced to 0.8m / s and the residual heat is maintained for 3s. The second hot rolling temperature is 980℃, the speed is 12m / s, and the hot rolling is carried out in 12 passes. After each pass, the rolling speed is reduced to 0.6m / s and the residual heat is maintained for 3s. The third hot rolling temperature is 910℃, the hot rolling is carried out in 8 passes. After each pass, the rolling speed is reduced to 0.4m / s and the residual heat is maintained for 3s.

[0026] S3. Anneal the steel billet material to obtain semi-finished steel bars;

[0027] The annealing process described in step S3 is a two-stage annealing process. The first stage is the preheating stage: heating to 850°C and holding for 80 minutes; the second stage is the holding stage: heating to 500°C and holding for 30 minutes under a nitrogen protective atmosphere, followed by furnace cooling to below 200°C before being removed from the furnace.

[0028] S4. Perform multiple drawing processes on the semi-finished steel bars and a second annealing process to obtain the finished steel bars.

[0029] The multi-pass drawing process for the semi-finished steel bars in step S4 is a 3-pass drawing process. The surface area reduction rate of the first drawing process is 12%, the surface area reduction rate of the second drawing process is 22%, and the surface area reduction rate of the third drawing process is 18%. The conditions for the secondary annealing process are heating to 500°C, preheating for 5 minutes, and holding in the furnace for 1 minute under an argon protective atmosphere and a furnace temperature of 1150°C.

[0030] Example 2

[0031] A process for preparing low-loss hot-rolled round bar steel bars includes the following steps:

[0032] S1. A high-temperature purging device is used to remove iron filings, dust and residual protective slag adhering to the surface of the steel billet. The purging temperature is 135℃ and the air pressure is 0.7MPa to obtain a pretreated steel billet.

[0033] The steel billet mentioned in step S1, by mass percentage, includes C 0.24%, Si 0.60%, Mn 1.40%, V 0.035%, Nb 0.020%, Ti 0.030%, P≤0.045%, S≤0.045%, Cr≤0.30%, Ni≤0.30%, Cu≤0.30%, with the remainder being Fe and unavoidable impurity elements;

[0034] S2. The pretreated steel billet is hot rolled in multiple passes to obtain steel billet material;

[0035] The hot rolling process described in step S2 is a multi-pass hot rolling process. The first hot rolling is performed at a temperature of 1065℃ and a speed of 0.23m / s, with 6 passes, each lasting 35s, followed by a 4s heat treatment at a roll speed of 0.9m / s. The second hot rolling is performed at a temperature of 1000℃ and a speed of 14m / s, with 12 passes, each lasting 80s, followed by a 4s heat treatment at a roll speed of 0.7m / s. The third hot rolling is performed at a temperature of 930℃, with 8 passes, each lasting 45s, followed by a 4s heat treatment at a roll speed of 0.5m / s.

[0036] S3. Anneal the steel billet material to obtain semi-finished steel bars;

[0037] The annealing process described in step S3 is a two-stage annealing process. The first stage is the preheating stage: heating to 880°C and holding for 90 minutes; the second stage is the holding stage: heating to 550°C and holding for 35 minutes under a nitrogen protective atmosphere, followed by furnace cooling to below 200°C before being removed from the furnace.

[0038] S4. Perform multiple drawing processes on the semi-finished steel bars and a second annealing process to obtain the finished steel bars.

[0039] The multi-pass drawing process for the semi-finished steel bars in step S4 is a 4-pass drawing process. The surface area reduction rate of the first drawing process is 15%, the surface area reduction rate of the second drawing process is 25%, and the surface area reduction rate of the third and fourth drawing processes is 20%. The conditions for the secondary annealing process are heating to 500°C, preheating for 5 minutes, and holding in the furnace for 1.5 minutes under an argon protective atmosphere and a furnace temperature of 1165°C.

[0040] Example 3

[0041] A process for preparing low-loss hot-rolled round bar steel bars includes the following steps:

[0042] S1. A high-temperature purging device is used to remove iron filings, dust and residual protective slag adhering to the surface of the steel billet. The purging temperature is 150℃ and the air pressure is 0.8MPa to obtain a pretreated steel billet.

[0043] The steel billet mentioned in step S1, by mass percentage, includes C 0.24%, Si 0.60%, Mn 1.40%, V 0.035%, Nb 0.020%, Ti 0.030%, P≤0.045%, S≤0.045%, Cr≤0.30%, Ni≤0.30%, Cu≤0.30%, with the remainder being Fe and unavoidable impurity elements;

[0044] S2. The pretreated steel billet is hot rolled in multiple passes to obtain steel billet material;

[0045] The hot rolling process described in step S2 is a multi-pass hot rolling process. The first hot rolling is performed at a temperature of 1080℃ and a speed of 0.28m / s, with 6 passes, each lasting 40s, followed by a 5s heat preservation at a roll speed of 1.0m / s. The second hot rolling is performed at a temperature of 1020℃ and a speed of 15m / s, with 12 passes, each lasting 90s, followed by a 4s heat preservation at a roll speed of 0.8m / s. The third hot rolling is performed at a temperature of 950℃, with 8 passes, each lasting 50s, followed by a 4s heat preservation at a roll speed of 0.6m / s.

[0046] S3. Anneal the steel billet material to obtain semi-finished steel bars;

[0047] The annealing process described in step S3 is a two-stage annealing process. The first stage is the preheating stage: heating to 900°C and holding for 100 minutes; the second stage is the holding stage: heating to 600°C and holding for 40 minutes under a nitrogen protective atmosphere, followed by furnace cooling to below 200°C before being removed from the furnace.

[0048] S4. Perform multiple drawing processes on the semi-finished steel bars and a second annealing process to obtain the finished steel bars.

[0049] The multi-pass drawing process for the semi-finished steel bars in step S4 is a 4-pass drawing process. The surface area reduction rate of the first drawing process is 18%, the surface area reduction rate of the second drawing process is 28%, and the surface area reduction rate of the remaining drawing processes is 22%. The conditions for the secondary annealing process are heating to 500°C, preheating for 5 minutes, and holding in the furnace for 1.5 minutes under an argon protective atmosphere and a furnace temperature of 1180°C.

[0050] Comparative Example 1

[0051] Compared with Example 3, Comparative Example 1 differs in step S2;

[0052] The hot rolling in step S2 is a multi-pass hot rolling process. The temperature of the first hot rolling is 1080℃, the speed is 0.28m / s, the hot rolling is 6 passes, and the time is 40s each time. The temperature of the second hot rolling is 1020℃, the speed is 15m / s, the hot rolling is 12 passes, and the time is 90s each time. The temperature of the third hot rolling is 950℃, the hot rolling is 8 passes, and the time is 50s each time.

[0053] Everything else is the same.

[0054] Comparative Example 2

[0055] Compared with Example 3, Comparative Example 2 differs in step S4;

[0056] The surface area reduction rate is 25% for the first drawing pass, 20% for the second and third drawing passes, and 15% for the fourth drawing pass.

[0057] Everything else is the same.

[0058] Comparative Example 3

[0059] Compared with Example 3, Comparative Example 3 differs in step S4;

[0060] The multi-pass drawing process for the semi-finished steel bars in step S4 is a 4-pass drawing process. The area reduction rate of the first drawing process is 15%, the area reduction rate of the second drawing process is 25%, and the area reduction rate of the third and fourth drawing processes is 20%. The conditions for the secondary annealing process are heating to 500°C, preheating for 5 minutes, holding in the furnace for 1.5 minutes at a furnace temperature of 900°C under an argon protective atmosphere.

[0061] Everything else is the same.

[0062] The mechanical properties of the samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested according to GB / T 228.1-2021, and the test results are shown in Table 1.

[0063] Table 1 Mechanical Performance Data

[0064]

[0065] As can be seen from the test results in Table 1, compared with Comparative Examples 1-3, the steel bars prepared in Examples 1-3 of the present invention have higher tensile strength, yield strength and other mechanical properties.

[0066] This invention eliminates hot-rolled internal stress and further optimizes the matrix structure through two-stage annealing. Then, a drawing process with low surface area reduction in the first two passes and high surface area reduction in the subsequent passes is adopted to promote the transformation of some austenite in the matrix into martensite. The transformed martensite undergoes plastic deformation during subsequent drawing. Combined with a secondary high-temperature annealing process, the formed martensite undergoes partial reverse transformation, ultimately achieving precise control of the martensite content and enabling the steel bar to obtain higher tensile strength, yield strength and other mechanical properties.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any indirect modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A process for preparing low-loss hot-rolled round bar steel bars, characterized in that, The preparation process includes the following steps: S1. A high-temperature purging device is used to remove iron filings, dust and residual protective slag adhering to the surface of the steel billet. The purging temperature is 120-150℃ and the air pressure is 0.6-0.8Mpa to obtain a pretreated steel billet. S2. The pretreated steel billet described in S1 undergoes a first hot rolling process, with the temperature set at 1050-1080℃, the speed at 0.18-0.28m / s, 6 passes, each lasting 30-40s, followed by a reduction in roll speed to 0.8-1.0m / s and a residual heat hold for 3-5s. This is followed by a second hot rolling process, with the temperature set at 980-1020℃, the speed at 12-15m / s, 12 passes, each lasting 70-90s, followed by a reduction in roll speed to 0.6-0.8m / s and a residual heat hold for 3-4s. Finally, a third hot rolling process is performed, with the temperature set at 910-950℃, 8 passes, each lasting 40-50s, followed by a reduction in roll speed to 0.4-0.6m / s and a residual heat hold for 3-4s, yielding the steel billet material. S3. Anneal the steel billet material to obtain semi-finished steel bars; S4. The semi-finished steel bars described in S3 are subjected to multiple drawing processes and a second annealing process to obtain finished steel bars. The multiple drawing processes consist of 3-4 drawing processes. The area reduction rate of the first drawing process is 12-18%, the area reduction rate of the second drawing process is 22-28%, and the area reduction rate of the remaining drawing processes is 18-22%.

2. The manufacturing process of low-loss hot-rolled round bar steel bars according to claim 1, characterized in that: The steel billet mentioned in step S1 contains, by mass percentage, 0.20-0.25% C, 0.50-0.80% Si, 1.20-1.60% Mn, 0.025-0.050% V, 0.015-0.030% Nb, 0.020-0.040% Ti, ≤0.045% P, ≤0.045% S, ≤0.30% Cr, ≤0.30% Ni, ≤0.30% Cu, with the remainder being Fe and unavoidable impurity elements.

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