Online spheroidizing annealing process and system for hot-rolled wire rod

Abstract

The invention discloses an online spheroidizing annealing process and system for a hot-rolled wire rod, and belongs to the technical field of wire heat treatment in the metallurgical industry. The process combines controlled rolling, controlled cooling and on-line spheroidizing annealing, and specifically comprises the following steps: after a steel billet is heated, rolling is completed in an austenite and ferrite two-phase region, and the steel billet is immediately cooled to 20-30 DEG C higher than the Ar3 temperature through water; the whole coil of the hot-rolled wire rod enters a tunnel type annealing furnace by utilizing waste heat of the hot-rolled wire rod, heat preservation is conducted for 0.4-0.6 h at the temperature 60-80 DEG C below the A1 temperature, the form and number of separated cementite in austenite are controlled, and nucleation points are formed; the temperature is increased to 20-50 DEG C below the temperature A1, heat preservation is conducted for 8-12 h, and cementite is gathered and grows up through spheroidization; and finally, slowly cooling to below 550 DEG C at the speed of 10-20 DEG C / h, and discharging. The rolling waste heat is fully utilized, the long heating process of traditional annealing is omitted, energy consumption is remarkably reduced, the annealing time is shortened, and the production efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of wire rod application technology in the metallurgical industry. It is a process and system for online spheroidizing annealing that makes full use of the residual heat of hot-rolled wire rod. Background Technology

[0002] Traditional spheroidizing annealing involves heating wire rod at room temperature to below the A1 temperature for an extended period and then isothermally and slowly cooling it. This causes the lamellar pearlite to break into granules, which then act as nucleation sites for cementite to aggregate and grow into spherical shapes. Equiaxed spherical carbides are then uniformly distributed on the ferrite matrix. This process is the next step after hot rolling and is considered offline spheroidizing annealing, typically lasting 24–36 hours. The main purpose of annealing hot-rolled wire rod is to alter the internal structure of the material through heat treatment, thereby improving its mechanical properties, processing performance, and service performance to meet the needs of various applications.

[0003] Similar to offline spheroidizing annealing, online spheroidizing annealing also aims to obtain uniformly distributed spherical cementite, improve the material's plasticity, reduce its hardness, and meet the requirements of cold forming. The difference lies in that online spheroidizing annealing can combine controlled rolling and controlled cooling technologies to fully utilize the residual heat of the material after hot rolling, shorten or eliminate the pre-annealing heating process, reduce energy consumption, and improve annealing efficiency.

[0004] Chinese patent CN202110553269.2, "An Online Heat Treatment Process for Wire Rods," discloses a method for online heat treatment using the residual heat of rolled steel, which has some innovativeness. However, it does not clearly define the purpose and principle of the heat treatment, nor does it specify the final microstructure; the temperature range is wide, with furnace temperatures of 500–900℃ and furnace entry temperatures of 300–700℃; the holding time is as short as 0.5–4 hours, and it can only achieve general effects such as softening and stress relief. Summary of the Invention

[0005] This invention provides an online spheroidizing annealing process and system that utilizes the residual heat of wire rod, aiming to reduce energy consumption and improve the spheroidizing efficiency of hot-rolled wire rod.

[0006] The technical solution adopted in this invention is as follows: An online spheroidizing annealing process for hot-rolled wire rod comprises two parts: hot rolling and online spheroidizing annealing. Hot rolling employs controlled rolling and controlled cooling. After rolling in the austenite and ferrite two-phase region, the wire rod is immediately water-cooled to 20-30°C above the Ar3 temperature. After being coiled or rolled, the entire coil is fed into a tunnel annealing furnace for spheroidizing annealing. The spheroidizing annealing process involves: utilizing the residual heat of the hot-rolled wire rod, first holding it at 60-80°C below the A1 temperature for 0.4-0.6 hours to control the quantity and morphology of cementite precipitation in the austenite, using this as a nucleation point; then raising the temperature to 20-50°C below the A1 temperature and holding it for 8-12 hours, followed by slow cooling in the furnace to below 550°C before being removed from the furnace. This allows the cementite to aggregate and grow into spherical shapes, forming equiaxed spherical carbides uniformly distributed on the ferrite matrix.

[0007] Furthermore, the hot rolling process rolls the steel billet into wire rods with a diameter of 5 to 16 mm. After being coiled by a wire spinneret, the wire rods are transported to the hot coiling station by a Steyrmore cooling transport machine, and then transferred to the tunnel annealing furnace by a roller bed and vertical core frame conveying system.

[0008] Furthermore, the hot rolling process rolls the steel billet into large coils with a diameter of 16-50 mm. After being coiled into coils by a coiling machine, the coils are transferred to a tunnel annealing furnace via a roller bed and a vertical core frame conveying system.

[0009] Furthermore, the tunnel annealing furnace is arranged in a parallel configuration, with lifting furnace doors equipped with clamping devices installed at its inlet and outlet ends. Several radiant tubes are installed inside the furnace, and the heating medium is coal gas produced by the steel plant. Methanol cracking gas is also supplied to the furnace through a dedicated pipeline as a protective atmosphere. Several thermocouples and carbon potential detection probes are also installed inside the furnace.

[0010] Furthermore, the annealed wire rod is output from the discharge end of the tunnel annealing furnace, conveyed to the unloading position by the roller bed and vertical core frame conveying system, and then transported to the C-hook by the unloading trolley for subsequent cooling, finishing, weighing and packaging processes.

[0011] An online spheroidizing annealing system for hot-rolled wire rod includes a high-speed wire rod reducing mill or a large coil KOCKS reducing mill, a high-speed wire rod spinning machine or a large coil coiling machine, a Steyrmo cooling conveyor, a hot coil collection station, a tunnel annealing furnace, roller beds, and a vertical core-coiling frame conveying system; the roller beds and vertical core-coiling frame conveying system sequentially connect the hot coil collection station and the tunnel annealing furnace and collect and transport the coils.

[0012] Furthermore, the system also includes a preheating furnace for preheating the vertical core frame of the roller bed and vertical core frame conveying system, using steel plant-produced gas as the heating medium to preheat the vertical core frame to above 300°C.

[0013] This invention is an online spheroidizing annealing process for hot-rolled wire rod, comprising two parts: hot rolling and spheroidizing annealing. Hot rolling employs controlled rolling and controlled cooling. After rolling in the two-phase region, the wire rod is immediately water-cooled to 20-30°C above the Ar3 temperature. After being coiled or rolled, the entire coil is fed into a tunnel annealing furnace for spheroidizing annealing. This method is suitable for new production lines or upgrades of existing production lines.

[0014] The innovations and beneficial effects of this invention are as follows: Compared with offline spheroidizing annealing, online spheroidizing annealing of wire rods significantly shortens or even eliminates the heating stage in the annealing furnace. The deformation energy storage and high-density dislocations provided by two-phase rolling and post-rolling water cooling create favorable conditions for the precipitation and spheroidization of cementite in supercooled austenite. By holding the wire rod at 60–80°C below the A1 temperature for 0.4–0.6 hours, the quantity and morphology of cementite precipitation in austenite are controlled. Using this as a nucleation point, the wire rod is then heated to 20–50°C below the A1 temperature and held for 8–12 hours. After this, it is slowly cooled in the furnace to below 550°C before being removed from the furnace. This allows the cementite to aggregate and grow into spherical shapes, forming equiaxed spherical carbides uniformly distributed on the ferrite matrix. The method of this invention can achieve energy saving, consumption reduction, and improved production efficiency. Attached Figure Description

[0015] Figure 1 This is a process layout diagram for the present invention.

[0016] Figure 2 This is a 500X metallographic image of Embodiment 1 of the present invention.

[0017] Figure 3 This is a 500X metallographic image of Embodiment 2 of the present invention.

[0018] Figure 4 This is a 500X metallographic image of the comparative example of the present invention.

[0019] In the diagram: 1-High-speed wire rod reducing sizing mill, 2-Kocks reducing sizing mill for large coils, 3-High-speed wire rod spinning machine, 4-Large coil coiling machine, 5-Stelmore cooling conveyor, 6-Hot coiling station, 7-Preheating furnace, 8-Tunnel annealing furnace, 9-Roller bed and vertical coil frame conveying system, 10-Cold coiling station, 11-Unloading trolley. Detailed Implementation

[0020] The present invention will be further described below through specific embodiments.

[0021] like Figure 1As shown, an online spheroidizing annealing system for hot-rolled wire rod includes a high-speed wire rod reducing sizing mill 1, a large coil KOCKS reducing sizing mill 2, a high-speed wire rod coiler 3, a large coil coiling machine 4, a Stellmore cooling conveyor 5, a hot coil collection station 6, a hot furnace 7, a tunnel annealing furnace 8, a roller bed and vertical coil frame conveying system 9, a cold coil collection station 10, and an unloading trolley 11. Both the high-speed wire rod reducing sizing mill 1 and the large coil KOCKS reducing sizing mill 2 have low-temperature rolling capabilities. The roller bed and vertical coil frame conveying system 9 sequentially connects the preheating furnace 7, the hot coil collection station 6, the tunnel annealing furnace 8, the cold coil collection station 10, and the unloading trolley 11, and collects and transports the coils via the roller bed and vertical coil frame conveying system 9. Hot coiling station 6 has a traverse function, enabling it to operate in both online and offline modes. When online, the wire rod is coiled at hot coiling station 6; when offline, the wire rod is transported to cold coiling station 10 via a Stellmore cooling conveyor for coiling. When tunnel annealing furnace 8 is full and has not yet reached its output requirements, other products that do not require online annealing can be produced through cold coiling station 10, ensuring the overall production line's operating rate.

[0022] After being heated, the steel billet is rolled into wire rod with a diameter of 5-16 mm by a high-speed wire rod reducing and sizing mill 1. The wire rod is then coiled by a high-speed wire rod coiler 3 and rapidly transported to the hot coiling station 6 by a Stellmore cooling transport machine 5. The roller bed and vertical core frame conveying system 9 transports the wire rod piece by piece to the tunnel annealing furnace 8 for spheroidizing annealing treatment.

[0023] After heating, the steel billet can also be rolled into large coils with a diameter of 16-50mm by the KOCKS reducing and sizing mill 2. The coils are then rolled into coils by the large coil coiling machine 4 and transferred piece by piece to the tunnel annealing furnace 8 for spheroidizing annealing treatment through the roller bed and vertical core frame conveying system 9.

[0024] The tunnel-type annealing furnace 8 is equipped with lifting furnace doors with clamping devices at both the inlet and outlet ends. Several radiant tubes are installed inside the furnace, and the heating medium is steel mill-produced coal gas. A protective atmosphere, such as methanol cracking gas, is supplied to the furnace through a dedicated pipeline. Several thermocouples and carbon potential detection probes are installed inside the furnace. Annealed wire rods are output piece by piece from the outlet end of the tunnel-type annealing furnace 8, conveyed to the unwinding position via a roller bed and vertical coiling frame conveyor system 9, and then transported by an unwinding trolley 11 onto a C-shaped hook for subsequent cooling, finishing, weighing, and packaging processes.

[0025] Multiple parallel tunnel-type annealing furnaces 8 can meet the requirements of mass production, while also meeting the production requirements of small batches, multiple varieties, and different annealing processes. The preheating furnace 7 is used to preheat the vertical core frame of the roller bed and vertical core frame conveying system 9. Using the steel plant's own gas as the heating medium, the vertical core frame is preheated to above 300°C to avoid low-temperature phase transformation at the contact point between the hot-rolled high-temperature wire rod and the room-temperature vertical core frame, as well as the risk of thermal stress deformation and cracking caused by the rapid temperature rise of the vertical core frame after entering the furnace.

[0026] To verify the feasibility of the invention, we placed the programmable box-type resistance furnace next to the high-speed wire spinning machine 3 and the large coil winding machine 4, respectively. We raised the furnace temperature to the set temperature in advance, and after the wire was spun or wound, we quickly cut a section of wire and placed it in the furnace for annealing.

[0027] The box-type resistance furnace has a rated power of 10KW and a rated temperature of 1000℃. The furnace chamber uses five-sided heating with a bottom support iron and no heating wires. To prevent excessive temperature drop when the furnace door is opened, an 80mm thick steel plate is placed in the furnace chamber as a heat storage body, and refractory bricks are placed on the steel plate. The sample is placed on the refractory bricks, which corresponds to the center of the furnace chamber. The furnace temperature uniformity is tested to be within ±5℃.

[0028] The implementation method of the online spheroidizing annealing process for hot-rolled wire rod using the above system is as follows:

[0029] Example 1: Online spheroidizing annealing process for hot-rolled wire rod Online spheroidizing annealing process for hot-rolled wire rod. 150 cubic meter ML35CrMo continuous casting billets are heated for 90–150 minutes, exiting the furnace at 1000–1030℃. After multiple controlled rolling passes through roughing, intermediate rolling, and finishing rolling, the billets enter the high-speed wire rod reducing and sizing mill at 780–820℃. The wire drawing temperature is reduced to 780℃ in a water tank after reducing and sizing. The wire rod diameter is 12mm. During the test, samples were taken immediately after wire drawing and placed in a box-type resistance furnace next to the mill within 20 seconds. The samples were first held at 680℃ for 0.5 hours, then heated to 720℃ at a rate of 80℃ / h, held for 8 hours, and then cooled to 550℃ at a rate of ≤20℃ / h before exiting the furnace. The total furnace time was approximately 18 hours.

[0030] After spheroidizing annealing, the metallographic structure of the wire rod sample consisted of uniformly distributed spheroidized matter and ferrite. According to JB / T 5074-2007, the spheroidized structure was rated as grade 6. Figure 2 As shown in Table 1, the hardness and mechanical properties tested conform to the requirements of Table 4 of GB / T5953.1-2009.

[0031] Example 2: Online spheroidizing annealing process for hot-rolled wire rod After being heated for 90–150 minutes, the 150 cubic meter ML42CrMo continuously cast billet exited the furnace at a temperature of 1020–1050℃. Following multiple controlled rolling passes (roughing, intermediate rolling, and finishing rolling), the billet entered the KOCKS reducing and sizing mill at a temperature of 780–820℃. After water cooling, the coiling temperature dropped to 780℃, resulting in a wire rod diameter of 21 mm. During the test, the fly shear fragments before coiling were placed into a box-type resistance furnace next to the machine within 30 seconds. The sample was first held at 675℃ for 0.6 hours, then heated to 710℃ at a rate of 80℃ / h, held for 12 hours, and then cooled to 550℃ at a rate of ≤20℃ / h before exiting the furnace. The total furnace time was approximately 21 hours.

[0032] After spheroidizing annealing, the metallographic structure of the wire rod sample consisted of spheroidized matter + punctate spheroidized matter + ferrite. According to JB / T5074-2007, the spheroidized structure was rated as grade 5. Figure 3 As shown in Table 1, the hardness and mechanical properties tested conform to the requirements of Table 4 of GB / T5953.1-2009.

[0033] Comparative Example: High-Temperature Rolling and High-Temperature Coiling Processes A 150 cubic meter ML35CrMo continuously cast billet, after being heated for 90–150 minutes, exits the furnace at a temperature of 1000–1050℃. After multiple controlled rolling passes through roughing, intermediate rolling, and finishing rolling, it enters the reducing and sizing mill at a temperature of 880–900℃, with a wire drawing temperature of 900℃ and a wire diameter of 12mm. During the test, samples were taken immediately after wire drawing and placed in a box-type resistance furnace next to the mill within 20 seconds. The samples were first held at 680℃ for 0.5 hours, then heated to 720℃ at a rate of 80℃ / h, held for 8 hours, and then cooled to 550℃ at a rate of ≤20℃ / h before exiting the furnace. The total furnace time was approximately 18 hours.

[0034] After spheroidizing annealing, the metallographic structure of the wire rod samples consisted of spheroidized matter and pearlite + ferrite. According to JB / T 5074-2007, the spheroidized structure was evaluated as grade 3. Figure 4 As shown in Table 1, the hardness and mechanical properties tested conform to the requirements of Table 4 of GB / T5953.1-2009. Table 1. Test results of the examples and comparative examples .

[0035] Compared to Examples 1 and 2, the comparative example used high-temperature rolling and high-temperature wire drawing processes, resulting in relatively coarse austenite grains. Although the hardness and mechanical properties after online spheroidizing annealing met the requirements of Table 4 in GB / T5953.1-2009, the spheroidization level was low, making it difficult to meet the requirements for high-level cold heading. Generally, cold heading steel wire requires a spheroidization level of 4-6. This invention combines two-phase zone controlled rolling, post-rolling controlled cooling, and online spheroidizing annealing processes, significantly improving annealing efficiency while ensuring the spheroidization rate.

[0036] Field tests verified the feasibility of online spheroidizing annealing. A reasonable process layout and the realization of equipment functions are fundamental conditions for ensuring online spheroidizing annealing. This invention, based on the basic principles of offline spheroidizing annealing, combines controlled rolling and cooling with online spheroidizing annealing processes and equipment to achieve energy conservation, consumption reduction, and improved production efficiency, aligning with national low-carbon economic policies and enterprise development requirements.

Claims

1. An online spheroidizing annealing process for hot-rolled wire rod, comprising two parts: hot rolling and online spheroidizing annealing, wherein the hot rolling adopts controlled rolling and controlled cooling methods, characterized in that: After the wire rod is rolled in the austenite and ferrite two-phase region, it is immediately water-cooled to 20-30°C above the Ar3 temperature. After being coiled or rolled, the whole coil is put into a tunnel annealing furnace for spheroidizing annealing. The spheroidizing annealing process is as follows: using the residual heat of the hot-rolled wire rod, it is first held at 60-80°C below the A1 temperature for 0.4-0.6 hours to control the quantity and morphology of cementite precipitation in austenite, and this is used as the nucleation point; then the temperature is raised to 20-50°C below the A1 temperature and held for 8-12 hours, and then slowly cooled in the furnace to below 550°C before being taken out of the furnace, so that the cementite agglomerates and grows into spherical shapes to form equiaxed spherical carbides that are evenly distributed on the ferrite matrix.

2. The online spheroidizing annealing process for hot-rolled wire rod according to claim 1, characterized in that: The hot rolling process involves rolling steel billets into wire rods with a diameter of 5 to 16 mm. After being coiled by a wire spinneret, the wire rods are transported to the hot coiling station by a Steyrmore cooling transport machine, and then transferred to the tunnel annealing furnace by a roller bed and vertical core frame conveying system.

3. The online spheroidizing annealing process for hot-rolled wire rod according to claim 1, characterized in that: The hot rolling process involves rolling steel billets into large coils with a diameter of 16 to 50 mm. After being coiled into coils by a coiling machine, the coils are transferred to a tunnel annealing furnace via a roller bed and a vertical core-rolling frame conveying system.

4. The online spheroidizing annealing process for hot-rolled wire rod according to claim 1, 2, or 3, characterized in that: The tunnel-type annealing furnace is arranged in a parallel manner, with lifting furnace doors equipped with clamping devices installed at its inlet and outlet ends. Several radiant tubes are installed inside the furnace, and the heating medium is coal gas produced by the steel plant. Methanol cracking gas is also supplied to the furnace through a dedicated pipeline as a protective atmosphere. Several thermocouples and carbon potential detection probes are also installed inside the furnace.

5. The online spheroidizing annealing process for hot-rolled wire rod according to claim 1, 2 or 3, characterized in that: After annealing, the wire rod is output from the discharge end of the tunnel annealing furnace, conveyed to the unloading position by the roller bed and vertical core frame conveying system, and then transported to the C-hook by the unloading trolley for subsequent cooling, finishing, weighing and packaging processes.

6. An online spheroidizing annealing system for hot-rolled wire rod, characterized in that: It includes a high-speed wire rod reducing sizing mill or a large coil KOCKS reducing sizing mill, a high-speed wire rod spinning machine or a large coil coiling machine, a Stellmore cooling conveyor, a hot coil collection station, a tunnel annealing furnace, roller beds, and a vertical core-coiling frame conveying system; the roller beds and vertical core-coiling frame conveying system connect the hot coil collection station and the tunnel annealing furnace in sequence and collect and transport the coils.

7. The online spheroidizing annealing system for hot-rolled wire rod according to claim 6, characterized in that: It also includes a preheating furnace for preheating the vertical core frame of the roller bed and vertical core frame conveying system, using steel plant-produced gas as the heating medium to preheat the vertical core frame to above 300°C.

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