Apparatus and process for on-line heat treatment of high-speed wire rod based on energy recycling

Abstract

A high-speed wire online heat treatment device and process based on energy recycling, relating to the technical fields of metal wire manufacturing and material heat treatment, and waste heat power gen

Description

TECHNICAL FIELD The present disclosure relates to an apparatus and process for on-line heat treatment of a high-speed wire rod based on energy recycling, and belongs to the technical fields of metal wire manufacturing, material heat treatments, and steel production waste heat-based power generation. BACKGROUND Currently, the conventional high-speed wire rods are cooled by a stelmor line after spinning to control the structural transformation inside and outside China. With the continuous development of China's economy, the fast-changing development in the automobile and transportation fields, and the gradual increase of light-weighting requirements, advanced requirements have been put forward for the strength and toughness of high-speed wire rods. The microstructure, mechanical properties, and same-circle performance uniformity of a high-speed wire rod on a stelmor cooling line are often controlled by adjusting parameters such as a length of an air-cooling line, an air volume of a fan, a speed of a roller table, and an insulation cover. Due to an insufficient cooling capacity of the stelmor cooling line, hypereutectoid steel and hypoeutectoid wire rods will be respectively in secondary network carbide and tertiary cementite precipitation temperature ranges for a long time on an air-cooling roller table. In addition, due to the insufficient cooling capacity of the stelmor cooling line, the same-circle performance uniformity is poor, and it is difficult to allow the production of high-speed wire rods with high strength and toughness requirements such as steels for bridge cables at a grade of 1,960 MPa or more and super-strong steel strands at a grade of 2,200 MPa or more. Specifically, the existing cooling methods for high-speed wire rods include the following (there are various square / round billet sizes, and 220 mm x 220 mm is taken as an example for illustration): 1. Off-line salt bath in a steel mill: steel billet —> rolling —> spinning —> cooling (air-cooling) by a stelmor cooling line —> coiling —> single / multi-wire pay-off —> straightening —> descaling —> heating —> salt bath —> cleaning —> coiling. 2. Off-line salt bath in a wire drawing mill (downstream of a steel mill): (1) steel billet —> rolling —> spinning —> cooling by a stelmor cooling line —> coiling; and (2) after arriving at the wire drawing mill: single / multi-wire pay-off —> descaling / pickling —> heating —> salt bath —> cleaning —> wire drawing —> take-up. 3. On-line salt bath in a wire drawing mill: (1) steel billet —> rolling —> spinning (such as a wire rod with a diameter of 15 mm) —> cooling (air-cooling) by a stelmor cooling line —> coiling 09 07 25 —> single / multi-wire pay-off —> descaling —> heating —> salt bath —> cleaning —> coiling; and (2) after arriving at the wire drawing mill: single / multi-wire pay-off —> straightening —> descaling / pickling —> heating —> salt bath —> cleaning —> wire drawing —> take-up. Chinese Patent 202210328695.0 discloses a wire rod for a 2,200 MPa-grade steel wire and a manufacturing method thereof. However, this patent adopts high-speed wire rod rolling, stelmor cooling, and a salt bath. In the manufacturing method of this patent, a wire rod is air-cooled and then treated in a salt bath, namely, off-line salt bath production, which also makes procedures cumbersome and complicated. The Xingcheng Special Steel Works Co., Ltd. and the ANSTEEL in China adopt an on-line water-bath treatment, which makes up for the deficiencies of an air-cooling line to some extent. However, an air film is rapidly formed on a surface of a wire rod when entering water on-line to hinder the convection with water, such that a cooling rate of the wire rod is extremely unstable, a process is extremely difficult to control, it is still impossible to control the isothermal sorbite phase transformation of the wire rod, and properties of a material fluctuate greatly. When an off-line lead bath is adopted, a wire rod needs to be reheated, and it leads to a cumbersome process, high energy consumption and carbon emissions, and a high cost for the treatment of residual lead on a surface of a wire rod and a waste lead liquid. In addition, when an off-line lead bath is adopted, a lead smoke, a lead dust, and a volatile vapor generated during production are toxic and will cause harm to the human body and the environment. Therefore, it has been stipulated in the document No. 40 "Guidance Catalogue for Industrial Structure Adjustment (2005)" issued by the National Development and Reform Commission in 2005 that the off-line lead bath should be eliminated. Molten salts have physical properties such as high specific heat capacity, high heat exchange capacity, and excellent stability, and have become a prominent cooling / heat exchange medium instead of air-cooling and water-cooling. Internationally, DLP of the Nippon Steel Corporation and the Qingdao Iron and Steel Holding Group Co., Ltd., the Baosteel Group, the Shagang Group, and the Henan Jiyuan Iron &Steel (Group) Co., Ltd. in China all adopt a molten salt as a cooling medium for an on-line or off-line salt-bath treatment. When an off-line salt bath is adopted, an air-cooled wire rod needs to undergo procedures such as re-unpacking, descaling, pay-off, reheating, and take-up, resulting in a low production efficiency, a low yield rate, and a high cost. In terms of energy utilization, during an iron and steel manufacturing process, only 30% to 50% of energy is effectively utilized, and a large amount of remaining energy exists in a form of waste heat, which has a great recovery potential. A waste heat recovery technique has been used in procedures such as ironmaking, steelmaking, and sintering. However, a technique for recovering waste heat of a cooling bed for a bar material is still immature, and there is no technique for recovering waste heat produced after rolling of a wire rod. 09 07 25 There is no mature technique for recovering waste heat produced after wire rolling inside and outside China. Conventionally, a heat source of an air-cooling line after rolling is unstable, and a wire rod is cooled by a fan, which causes difficult wind energy collection, heat dispersion, a low temperature, a large waste heat fluctuation, a difficult heat-water balance, and an extremely-low utilization rate of heat energy recovered at a low temperature, thereby limiting the development of waste heat recovery after rolling. For example, the Avesta mill in Sweden adopts an energy recovery system for heat energy of a steel slab on a steel slab cooling bed, and circulating water supplied by a boiler is heated by heat radiation of a steel slab to about 85°C through a lining pipe of the steel slab cooling bed. Such a heat recovery system can merely allow a low-temperature steam and has an extremely-low energy utilization rate. In the prior art, the molten-salt energy-storage technique is mainly used in solar thermal power stations, but is not used in the iron and steel field. In addition, in the prior art, a wire rod or a drawn wire material produced after a salt-bath treatment faces the problem that a residual salt on a surface cannot be totally removed. Because a molten salt has moisture absorption and corrosion characteristics, a residual salt at a lap joint can aggravate the corrosion, and the wire breakage will be exacerbated during a downstream wire-making process, that is, the residual salt on the surface will aggravate the corrosion. The current known method for removing a salt on a surface is air blowing + high-pressure water spraying. A molten salt will be solidified after being sprayed with water, which increases the difficulty of salt removal through spraying. In addition, there is a lap joint in a wire rod, and the air blowing + high-pressure water spray method cannot completely remove a residual salt at the lap joint. Currently, when a wire rod is incubated in an off-line salt bath in a steel mill and then subjected to surface salt removal, the wire rod or a steel wire will be straightened to facilitate the removal of a residual salt on a straightened steel wire, but a surface of the wire rod or the steel wire is easily scratched. In the prior art, after a wire rod is incubated in an off-line salt bath, only air blowing is adopted to allow surface salt removal, and because the air blowing cannot completely remove a salt, the wire rod will be heavily corroded half a year later. In the prior art, when the air blowing + high-pressure water spraying method is adopted for surface salt removal, a light red rust is produced on a surface due to water stains, which cannot be blown away and will aggravate the corrosion. Moreover, a residual salt at a lap joint makes the corrosion intensified. At present, there is a lack of an eco-friendly and low-carbon integrated apparatus with a high production efficiency, a stable liquid level, high temperature uniformity, efficient surface salt removal, a high heat exchange efficiency, waste heat recovery after rolling, energy recycling, and 09 07 25 molten-salt energy storage / peak-regulating power generation, which can not only effectively improve the microstructure, mechanical properties, and same-circle performance uniformity of a high-speed wire rod through an on-line heat treatment, but also allow the waste heat recovery for energy recycling and energy storage / peak-regulating power generation. In view of the current problems that a stelmor line has an insufficient cooling capacity, a cooling rate of a water bath treatment fluctuates greatly, an off-line lead bath is not eco-friendly, and an off-line salt bath has a low production efficiency, a low yield rate, and a high cost and leads to incomplete surface salt removal, the present disclosure proposes an apparatus and process for on-line heat treatment of a high-speed wire rod based on energy recycling. In the present disclosure, the precipitation of a secondary network carbide of a hypereutectoid steel and a tertiary cementite of a hypoeutectoid steel is inhibited through on-line rapid quenching-isothermal transformation-controlled cooling-cleaning of a wire rod to allow a sorbite / bainite treatment of the wire rod, which not only makes a high-speed wire rod have a high on-line production efficiency, a prominent surface quality, a high strength, excellent plasticity, excellent toughness, and prominent same-circle mechanical property uniformity, but also allows the waste heat recovery after rolling for molten-salt energy storage / peak-regulating power generation, thereby allowing the purposes of low-carbon environmental protection and energy recycling. SUMMARY A problem to be solved by the present disclosure is to provide an apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling, including an on-line heat treatment device, a waste heat recovery system, and a molten-salt energy storage / peak-regulating power generation system that are coupled. In the above apparatus, a wire rod produced after spinning enters the on-line heat treatment device to undergo on-line rapid quenching-isothermal transformation-controlled cooling-cleaning, which can effectively inhibit the precipitation of a secondary network carbide of a hypereutectoid steel and a tertiary cementite of a hypoeutectoid steel and allow the control of a sorbite / bainite treatment, structural uniformity, and a surface quality of the wire rod; a heated molten salt for a salt bath is allowed to pass through the waste heat recovery system to allow the recovery of a waste heat after rolling; and heat recovered by the waste heat recovery system is stored and released by the molten-salt energy storage / peak-regulating power generation system to allow molten-salt energy storage / peak-regulating power generation. The present disclosure also provides a process for on-line heat treatment of a high-speed wire rod based on energy recycling, which has advantages such as a low cost, low-carbon environmental protection, and energy recycling. The process can not only make a high-speed wire rod have a high on-line production efficiency, a prominent surface quality, a high strength, 09 07 25 excellent plasticity, excellent toughness, and prominent same-circle mechanical property uniformity, but also allow the waste heat recovery after rolling for molten-salt energy storage / peak-regulating power generation, thereby allowing the purposes of low-carbon environmental protection and energy recycling. The present disclosure also provides a wire rod manufactured by the process for on-line heat treatment of a high-speed wire rod based on energy recycling. The present disclosure also provides a use of the wire rod in a bainite cold-heading steel, a spring steel, a tool steel, a bearing steel, a bridge cable, a steel strand, a bead cord, a cutting wire, or a diamond wire. To solve the above technical problem, the present disclosure adopts the following technical solutions: An apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling, characterized by comprising an on-line heat treatment device, a waste heat recovery system, and a molten-salt energy storage / peak-regulating power generation system, wherein the on-line heat treatment device comprises a fast-cooling tank (1), an isothermal tank (3), a controlled air-cooling unit, a cleaning system, and an oven-drying unit (14) through which a wire rod passes sequentially from the fast-cooling tank (1) through to the oven-drying until (14); (i.e. sequentially from left to right as shown in Figure 1 and Figure 7); the fast-cooling tank (1) and the isothermal tank (3) both contain a molten salt; a first lower tank body (2) configured to circulate the molten salt with the fast-cooling tank (1) is provided below the fast-cooling tank (1); a second lower tank body (4) configured to circulate the molten salt with the isothermal tank (3) is provided below the isothermal tank (3); the waste heat recovery system comprises a salt-salt heat exchanger (15) configured to perform a heat exchange between the molten salt in the first lower tank body (2) and molten salt from a low-temperature storage tank (22) and between the molten salt in the second lower tank body (4) and molten salt from the low- temperature storage tank (22); the molten salt, from the low-temperature storage tank (22), after the heat exchange in the salt-salt heat exchanger (15) flows to the molten-salt energy storage / peak-regulating power generation system; the cleaning system is connected to a salt / water separation system (24); the cleaning system comprises a first cleaning device (8) having a plurality of nozzles, a third annular air blade (9), a stepped water tank (10), a fourth annular air blade (11), a second cleaning device (12) having a plurality of nozzles, and a fifth annular air blade (13) that are arranged sequentially; the controlled air-cooling unit comprises a first annular air blade (6) and a second annular air blade (7) that are arranged between the isothermal tank (3) and the cleaning system; and wherein the wire rod passes sequentially from the first cleaning device (8) to the fifth annular blade (13) 09 07 25 a roller table is provided inside the stepped water tank (10), and the roller table is provided with 2 to 7 falling sections, wherein there is an overlap distance of 100 mm to 1,500 mm between a horizontal projection of a tail of a previous one of the falling sections and a horizontal projection of a head of a next one of the falling sections, each of the falling sections forms a step, and each of the falling sections comprises 3 to 20 rollers arranged sequentially and extending upwards in an inclined manner and has a falling height of 100 mm to 500 mm, an inclination angle of 10° to 60°, and a roller spacing of 50 mm to 400 mm; an ultrasonic vibration unit is provided inside the stepped water tank (10); the molten-salt energy storage / peak-regulating power generation system comprises an intermediate storage tank (16) configured to store the molten salt heated in the salt-salt heat exchanger (15); the intermediate storage tank (16) is connected to a high-temperature storage tank (18); the molten salt in the high-temperature storage tank (18) is configured to supply heat for a power generation unit, and the molten salt after supplying the heat is stored in the low-temperature storage tank (22); and the molten salt in the low-temperature storage tank (22) is returned to a shell side of the salt-salt heat exchanger (15) and the intermediate storage tank (16). Further, a flue gas collection system is provided above the fast-cooling tank, the isothermal tank, the controlled air-cooling unit, and the cleaning system. Further, a temperature of the molten salt in the fast-cooling tank is 250°C to 600°C, and a cooling rate of the fast-cooling tank is at least 30°C / s; and a temperature of the molten salt in the isothermal tank is 400°C to 585°C. A process using the apparatus for on-line heat treatment of the high-speed wire rod based on energy recycling includes the following steps: SOI. salt-bath-based fast cooling: rapidly quenching a first wire rod with a temperature of 800°C to l,050°C, in a 250°C to 600°C molten salt in the fast-cooling tank for 4 s to 40 s to obtain a second wire rod; S02. salt-bath-based isothermal transformation: subjecting the second wire rod to isothermal transformation for 30 s to 400 s in a 400°C to 585°C molten salt in the isothermal tank to obtain a third wire rod; S03. controlled cooling: purging the third wire rod out of the isothermal tank with 200°C to 550°C hot air in the first annular air blade for 5 s to 20 s to obtain a fourth wire rod, and purging the fourth wire rod with compressed air in the second annular air blade for 5 s to 30 s to obtain a fifth wire rod; S04. cleaning: allowing the fifth wire rod obtained after the controlled cooling to enter the cleaning system, and subjecting the fifth wire rod to residual surface salt removal with the first cleaning device having a plurality of nozzles, the third annular air blade, the stepped water tank, 09 07 25 the fourth annular air blade, the second cleaning device having a plurality of nozzles, and the fifth annular air blade sequentially to obtain a sixth wire rod; S05. oven-drying: oven-drying the sixth wire rod obtained after the cleaning in the oven-drying unit, and coiling to obtain a finished product; S06. heat release of the molten salt for salt baths through a tube side of the salt-salt heat exchanger: allowing the molten salt heated to 430°C to 610°C in the fast-cooling tank and the isothermal tank to first overflow into the first lower tank body and the second lower tank body respectively and then enter the salt-salt heat exchanger through a pipeline, such that the molten salt undergoes the heat release through the tube side of the salt-salt heat exchanger and then is circulated into the first lower tank body and the second lower tank body respectively; S07. heat absorption of the waste heat recovery system: allowing a cooling salt at 230°C to 350°C to enter the shell side of the salt-salt heat exchanger from the low-temperature storage tank of the molten-salt energy storage / peak-regulating power generation system and absorb heat of the molten salt at a high temperature in the tube side of the salt-salt heat exchanger until a temperature of the cooling salt arises to 400°C to 585°C, and returning the cooling salt at 400°C to 585°C to the molten-salt energy storage / peak-regulating power generation system, such that a heat recovery is completed; and S08. molten-salt energy storage / peak-regulating power generation: heat storage during a valley period: allowing the cooling salt at 400°C to 585°C from the shell side of the salt-salt heat exchanger to enter the intermediate storage tank of the molten-salt energy storage / peak-regulating power generation system, then enter a molten-salt furnace and be heated to 550°C to 600°C to become a molten salt at 550°C to 600°C, and then enter the high-temperature storage tank for the heat storage; and heat release during a peak period: using a heat of the molten salt at 550°C to 600°C in the high-temperature storage tank to produce a high-temperature steam, allowing the high-temperature steam to enter the power generation unit for power generation, and allowing the molten salt dropped to 230°C to 350°C to enter the low-temperature storage tank for circulation, such that the peak-regulating power generation is achieved, where the molten salt is a cooling medium / heating medium including two or more selected from a group consisting of potassium nitrate, sodium nitrate, lithium nitrate, calcium nitrate, silver nitrate, potassium nitrite, and sodium nitrite, and a moisture content in the molten salt for the salt baths does not exceed 1 wt.%. A wire rod manufactured by the process of the present disclosure is also disclosed. A use of the wire rod of the present disclosure in a bainite cold-heading steel, a spring steel, a tool steel, a bearing steel, a bridge cable, a steel strand, a bead cord, a cutting wire, or a diamond wire is alsodisclosed. The raw material wire rods of the present disclosure are 92Si, 97Si, Y10B21, and 55SiCrA, and compositions of 92Si, 97Si, Y10B21, and 55SiCrA are shown in Table 1. In Table 1, the remaining components all are Fe. Table 1 Compositions of wire rods Brand Component system / % c Si Mn Cr V B 92Si 0.92-0.95 0.20-0.40 0.70-0.90 0.20-0.30 0.02-0.03 - 97Si 0.97-1.00 0.70-0.80 0.70-0.90 0.20-0.30 0.02-0.03 - Y10B21 0.18-0.23 <0.10 0.70-0.90 0.10-0.30 - 0.0010-0.0030 55SiCrA 0.50-0.60 1.35-1.50 0.60-0.80 0.60-0.80 - - Structures of the wire rods of the present disclosure after a salt-bath treatment (with sorbite structures as examples) are shown in Table 2 below. Table 2 Structures after a salt-bath treatment Brand Sorbitizing rate Interlamellar spacing Network carbide 92Si >95% <100nm <2.0 grade 97Si >96% <100nm <2.0 grade 09 07 25 Mechanical properties of the wire rods of the present disclosure after a salt-bath treatment (with sorbite structures as examples) are shown in Table 3 below. Table 3 Mechanical properties of the wire rods after a salt-bat i treatment Brand Tensile strength Section shrinkage rate Same-circle mechanical fluctuation range 92Si >1480MPa >32% <50MPa 97Si >1550MPa >30% <50MPa The present disclosure has the following technical effects or advantages: The present disclosure discloses an apparatus and process for on-line heat treatment of a high-speed wire rod based on energy recycling, which are provided to allow the on-line heat treatment of a wire rod on a high-speed wire rod rolling production line, the recovery of a waste heat after rolling, and the peak-regulating power generation through molten-salt energy storage, thereby allowing the energy recycling. The on-line salt-bath process of the present disclosure is as follows: continuous casting billet (220 mm x 220 mm square billet) —> rolling —> spinning (a wire rod with a diameter of 15 mm) —> salt-bath treatment —> cleaning —> coiling, which has a high production efficiency and a short flow, can omit various procedures such as pay-off, shot blasting-based phosphorus removal, reheating, and take-up, and can truly allow the eco-friendly, low-carbon, and efficient production. The apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling in the present disclosure can allow a sorbite / bainite treatment of a wire rod, improve a proportion of a sorbite / bainite structure, and weaken or eliminate a risk of abnormal structures. Therefore, 09 07 25 the apparatus can be used to produce wire rods for bainite cold-heading steels, spring steels, tool steels, bearing steels, bridge cables, steel strands, bead cords, cutting wires, and diamond wires. In the apparatus, a waste heat after rolling is recovered through heat concentration of the fast-cooling tank and the isothermal tank and an efficient salt-salt heat exchange and enters the molten-salt energy storage / peak-regulating power generation system, where the recovered waste heat is stored during a valley period and released for peak-regulating power generation during a peak period, which can not only make a high-speed wire rod have a high on-line production efficiency, a prominent surface quality, a high strength, excellent plasticity, excellent toughness, and prominent same-circle mechanical property uniformity, but also allow the waste heat recovery after rolling for molten-salt energy storage / peak-regulating power generation, thereby allowing the purposes of low-carbon environmental protection and energy recycling. The present disclosure adopts air blade + rinsing + stepped water tank + ultrasonic oscillation washing to clean a wire rod, which can ensure that a lap joint of the wire rod can also be fully cleaned. The present disclosure is suitable for a direct salt-bath treatment of a wire rod obtained after spinning, a waste heat recovery after rolling, and molten-salt energy storage / peak-regulating power generation. The apparatus of the present disclosure has a reasonable overall structural design. Parameters such as circulation, a flow rate, a liquid level, a temperature, and a flow field of a molten salt in the continuous on-line heat treatment device can be controlled to effectively ensure the liquid level stability, temperature uniformity, and accuracy of a cooling medium / heating medium in the salt-bath fast-cooling tank and the salt-bath isothermal tank. The controlled air-cooling unit can effectively ensure a controlled cooling capacity for a wire rod. The cleaning system can effectively ensure a surface quality of a wire rod. The heat concentration of the salt-bath fast-cooling tank and the salt-bath isothermal tank can effectively ensure the waste heat recovery, where a molten salt is used to store and release a heat, thereby effectively ensuring the waste heat recovery for energy storage / peak-regulating power generation. The salt-bath fast-cooling of the present disclosure can effectively control the precipitation of a secondary network carbide of a hypereutectoid steel and a tertiary cementite of a hypoeutectoid steel, and effectively control the transformation of hypereutectoid and hypoeutectoid wire rods from an austenite to a sorbite / bainite. The salt-bath isothermal transformation can effectively control the transformation of untransformed austenites of hypereutectoid and hypoeutectoid steels into sorbites / bainites. The controlled air-cooling unit can effectively control the structural uniformity of hypereutectoid and hypoeutectoid steels after phase transformation. Finally, a wire rod is cleaned to remove a residual molten salt on a surface and oven-dried, such that the surface quality and structure property uniformity of the wire rod can be effectively controlled. The existing conventional air-cooled wire rod has a structure (with a sorbite structure as an example) as follows: an interlamellar spacing: about 120 pm, a sorbitizing rate: 80% to 90%, and same-circle performance uniformity: about 80 MPa. A wire rod obtained after the heat treatment in the present disclosure has a microstructure as follows: an interlamellar spacing: about 80 pm, a sorbitizing rate: higher than or equal to 95%, and same-circle performance uniformity: about 30 MPa. The existing conventional air-cooled wire rod (with a sorbite structure as an example) has mechanical properties as follows: a tensile strength: 1,400 MPa, a section shrinkage rate: 30%, and a grade of wires manufactured downstream: 1,960 MPa or less. A wire rod obtained after the heat treatment in the present disclosure has mechanical properties as follows: a tensile strength: 1,512 MPa, a section shrinkage rate: 35%, and a grade of wires manufactured downstream: 2,200 MPa or more. 09 07 25 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic structural diagram of the apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling in the present disclosure; FIG. 2 is an image illustrating a tempered troostite + tempered martensite + residual austenite structure obtained in Example 1 of the present disclosure; FIG. 3 is an image illustrating a bainite structure obtained in Example 2 of the present disclosure; FIG. 4 is an image illustrating a bainite structure obtained in Example 3 of the present disclosure; FIG. 5 is an image illustrating a sorbite structure obtained in Example 4 of the present disclosure; FIG. 6 shows the process for on-line heat treatment of a high-speed wire rod based on energy recycling in the present disclosure; and FIG. 7 is a schematic structural diagram of the apparatus in Example 2 of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS The present disclosure is further described in detail below with reference to the accompanying drawings and specific examples. The following examples are only intended to illustrate the present disclosure, rather than to limit the scope of the present disclosure. Example 1 As shown in FIG. 1 and FIG. 7, an apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling is provided, including an on-line heat treatment device, a waste heat recovery system, and a molten-salt energy storage / peak-regulating power generation system. 09 07 25 The on-line heat treatment device includes a fast-cooling tank 1, an isothermal tank 3, a controlled air-cooling unit, a cleaning system, and an oven-drying unit 14 through which a wire rod passes sequentially from left to right as shown in Figure 1 and Figure 7. The fast-cooling tank 1 and the isothermal tank 3 both contain a molten salt. A first lower tank body 2 configured to circulate a molten salt with the fast-cooling tank 1 is provided below the fast-cooling tank 1; a second lower tank body 4 configured to circulate a molten salt with the isothermal tank 3 is provided below the isothermal tank 3. The waste heat recovery system includes a salt-salt heat exchanger 15 configured to perform a heat exchange between a molten salt in each of the first lower tank body 2 and the second lower tank body 4, and molten salt from a low-temperature storage tank (22). A molten salt undergoing a heat exchange in the salt-salt heat exchanger 15 flows to the molten-salt energy storage / peak-regulating power generation system. A flue gas collection system 5 is provided above the fast-cooling tank 1, the isothermal tank 3, the controlled air-cooling unit, and the cleaning system. A salt / water separation system 24 is connected to the cleaning system; the cleaning system includes a first cleaning device 8 having a plurality of nozzles , a third annular air blade 9, a stepped water tank 10, a fourth annular air blade 11, a second cleaning device 12 carrying a plurality of nozzles,, and a fifth annular air blade 13 that are arranged sequentially from left to right as shown in Figure 1 and Figure 7; the controlled air-cooling unit includes a first annular air blade 6 and a second annular air blade 7 that are arranged between the isothermal tank 3 and the cleaning system. The molten-salt energy storage / peak-regulating power generation system includes an intermediate storage tank 16 configured to store a molten salt heated in the salt-salt heat exchanger 15; the intermediate storage tank 16 is connected to a high-temperature storage tank 18; a molten salt in the high-temperature storage tank 18 is configured to supply heat for a power generation unit, and a molten salt after supplying a heat is stored in a low-temperature storage tank 22; and the molten salt in the low-temperature storage tank 22 is returned to a shell side of the salt-salt heat exchanger 15 and the intermediate storage tank 16. A cooling rate of the fast-cooling tank 1 is 30°C / s. A roller table is provided inside the stepped water tank 10, and the roller table is provided with 2 falling sections, where there is an overlap distance of 100 mm between a horizontal projection of a tail of a previous falling section and a horizontal projection of a head of a next falling section, each falling section forms a step, and each falling section includes 3 rollers arranged sequentially from left to right (as shown in Figure 1 and Figure 7 of the drawings) and extending upwards in an inclined manner and has a falling height of 100 mm, an inclination angle of 60°, and a roller spacing of 50 mm; and an ultrasonic vibration unit is provided inside the 09 07 25 stepped water tank 10. A process for on-line heat treatment of a high-speed wire rod based on energy recycling is provided, including the following steps: e. Heating a molten salt in the fast-cooling tank by a wire rod obtained after spinning: A first wire rod with a temperature of 800°C obtained after spinning was rapidly quenched in a 250°C molten salt in the fast-cooling tank 1 for 4 s to obtain a second wire rod, such that a temperature of the molten salt arose by 180°C. f. Heating a molten salt in the isothermal tank by the second wire rod: The second wire rod was subjected to isothermal transformation for 30 s in a 400°C molten salt in the isothermal tank 3 to obtain a third wire rod, such that a temperature of the molten salt in the isothermal tank arose by210°C. g. Controlled cooling: The third wire rod out of the isothermal tank 3 was purged with 200°C hot air in the first annular air blade 6 for 5 s and then purged with compressed air in the second annular air blade 7 for 5 s to obtain a fourth wire rod. h. Cleaning: The fourth wire rod obtained after the controlled cooling was allowed to enter the cleaning system, and subjected to residual surface salt removal with the first cleaning device 8, the third annular air blade 9, the stepped water tank 10, the fourth annular air blade 11, the second cleaning device 12, and the fifth annular air blade 13 sequentially to obtain a fifth wire rod. i. Oven-drying: The fifth wire rod obtained after the cleaning was oven-dried in the oven-drying unit 14 and then coiled to obtain a finished product. j. Heat release of molten salts for salt baths through a tube side of the salt-salt heat exchanger 15: Molten salts respectively heated to 430°C and 610°C in the fast-cooling tank 1 and the isothermal tank 3 were allowed to first overflow into the first lower tank body 2 and the second lower tank body 4 respectively and then enter the salt-salt heat exchanger 15 through a pipeline, such that the molten salts underwent a heat release through the tube side of the salt-salt heat exchanger 15 and then were circulated into the first lower tank body 2 and the second lower tank body 4 respectively. k. Heat absorption of the waste heat recovery system: A 230°C cooling salt was allowed to enter the shell side of the salt-salt heat exchanger 15 from the low-temperature storage tank 22 of the molten-salt energy storage / peak-regulating power generation system and absorb heat of a high-temperature molten salt in the tube side of the salt-salt heat exchanger 15 until a temperature of the cooling salt arose to 400°C, and a 400°C cooling salt was returned to the molten-salt energy storage / peak-regulating power generation system, such that a heat recovery was completed. 1. Molten-salt energy storage / peak-regulating power generation: Heat storage during a valley period: The 400°C cooling salt from the shell side of the salt-salt heat exchanger 15 was allowed to enter the intermediate storage tank 16 of the molten-salt energy storage / peak-regulating power 09 07 25 generation system, then enter a molten-salt furnace 17 and be heated to 550°C, and then enter the high-temperature storage tank 18 for the heat storage. Heat release during a peak period: Heat of a 550°C molten salt in the high-temperature storage tank 18 was used to produce a high-temperature steam, the high-temperature steam was allowed to enter the power generation unit for power generation, and when a temperature of the molten salt dropped to 230°C, a resulting 230°C molten salt was allowed to enter the low-temperature storage tank 22 for circulation, such that the peak-regulating power generation was achieved. The process in this example was a quenching-tempering process. A temperature of the molten salt in the fast-cooling tank 1 was 250°C, and a temperature of the molten salt in the isothermal tank 3 was 400°C. The process in this example was designed to have an annual treatment quantity of 350,000 tons / year, a tapping quantity of about 120 t / h, and an annual operation time of about 2,640 h. When cooled, a wire rod was subjected to an isothermal heat treatment in the salt-bath section to produce a high-strength steel while producing heat of 2.59 x 107 kJ / h. According to a recovery rate of 70%, it was preliminarily predicted that heat of 1.81 x 107 kJ / h could be recovered and used in the coupled molten-salt heat-storage system for power generation. The molten salt was a cooling medium / heating medium including two or more selected from the group consisting of potassium nitrate, sodium nitrate, lithium nitrate, calcium nitrate, silver nitrate, potassium nitrite, and sodium nitrite, and a moisture content in the molten salt was 1 wt.%. As shown in FIG. 2 and FIG. 6, the process in this example is a quenching-tempering process, and a tempered troostite + tempered martensite + residual austenite structure is obtained in this example. An image of the tempered troostite + tempered martensite + residual austenite structure is shown in FIG. 2. In this example, the raw material is 55SiCrA, and the wire rod product has a same-circle performance uniformity of about 50 MPa, a tensile strength of 1,989 MPa, and a section shrinkage rate of 47%. A use of the wire rod of this example in a spring steel, a tool steel, a bearing steel, a bridge cable, a steel strand, a bead cord, a cutting wire, or a diamond wire is also provided. Example 2 As shown in FIG. 7, an apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling is provided, including: a fast-cooling tank 1, a first lower tank body 2, an isothermal tank 3, a second lower tank body 4, a flue gas collection system 5, a first annular air blade 6, a second annular air blade 7, a first cleaning device 8, a third annular air blade 9, a stepped water tank 10, a fourth annular air blade 11, a second cleaning device 12, a fifth annular air blade 13, an oven-drying unit 14, a salt-salt heat exchanger 15, an intermediate storage tank 16, 09 07 25 a molten-salt furnace 17, a high-temperature storage tank 18, a superheater 19, an evaporator 20, a preheater 21, a low-temperature storage tank 22, a steam drum 23, and a salt / water separation system 24. The apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling in this example includes an on-line heat treatment device, a waste heat recovery system, and a molten-salt energy storage / peak-regulating power generation system. The on-line heat treatment device includes a fast-cooling tank 1, an isothermal tank 3, a first annular air blade 6, a second annular air blade 7, a first cleaning device 8, a third annular air blade 9, a stepped water tank 10, a fourth annular air blade 11, a second cleaning device 12, a fifth annular air blade 13, and an oven-drying unit 14 through which a wire rod passes sequentially from left to right as shown in Figure 7. The fast-cooling tank 1 and the isothermal tank 3 both contain a molten salt. A first lower tank body 2 configured to circulate a molten salt with the fast-cooling tank 1 is provided below the fast-cooling tank 1; a second lower tank body 4 configured to circulate a molten salt with the isothermal tank 3 is provided below the isothermal tank 3. The waste heat recovery system includes a salt-salt heat exchanger 15 configured to perform a heat exchange between a molten salt in each of the first lower tank body 2 and the second lower tank body 4, and molten salt from a low-temperature storage tank (22); and the salt-salt heat exchanger 15 includes a tube side configured to allow a heat release of a molten salt for a salt bath and a shell side configured to hold a cooling salt, where heated molten salts in the first lower tank body 2 and the second lower tank body 4 are allowed to undergo a heat release in the tube side of the salt-salt heat exchanger 15, a cooling salt in the shell side of the salt-salt heat exchanger 15 absorbs heat of a high-temperature molten salt in the tube side of the salt-salt heat exchanger 15, and a heated cooling salt is returned to the molten-salt energy storage / peak-regulating power generation system, such that a heat recovery is completed. A flue gas collection system 5 is provided above the fast-cooling tank 1 and the isothermal tank 3. A salt / water separation system 24 is provided below the stepped water tank 10 and is connected to the stepped water tank 10. The molten-salt energy storage / peak-regulating power generation system includes an intermediate storage tank 16 configured to store a molten salt heated in the shell side of the salt-salt heat exchanger 15; the intermediate storage tank 16 is connected to a molten-salt furnace 17; a molten salt in the intermediate storage tank 16 is first heated by the molten-salt furnace 17, then enters the high-temperature storage tank 18, and then passes through a superheater 19 and an evaporator 20, such that water undergoes heat absorption to become a high-temperature steam and then enters a steam drum 23 for direct power generation; the steam drum 23 is arranged between 09 07 25 the superheater 19 and the evaporator 20; and a molten salt after supplying heat is stored in a low-temperature storage tank 22 through a preheater 21, and the molten salt in the low-temperature storage tank 22 is returned to a shell side of the salt-salt heat exchanger 15 and the intermediate storage tank 16. A temperature of the molten salt in the fast-cooling tank 1 is 400°C, and a cooling rate of the fast-cooling tank 1 is 50°C / s; and a temperature of the molten salt in the isothermal tank 3 is 585°C. As shown in FIG. 7, a roller table is provided inside the stepped water tank 10, and the roller table is provided with 7 falling sections to form steps, where there is an overlap distance of 1,500 mm between a horizontal projection of a tail of a previous falling section and a horizontal projection of a head of a next falling section, each falling section forms a step, and each falling section includes 20 rollers arranged sequentially from left to right as shown in Figure 7 and extending upwards in an inclined manner and has a falling height of 500 mm, an inclination angle of 30°, and a roller spacing of 400 mm; and an ultrasonic vibration unit is provided inside the stepped water tank 10. Preferably, a salt-bath fast-cooling roller table, a salt-bath isothermal roller table, a controlled air-cooling roller table, and a cleaning roller table all are made of a 316L stainless steel, with a roller body length of 1,540 mm, a roller diameter of 120 mm, and a roller spacing of 253 mm. Preferably, speeds of the salt-bath fast-cooling roller table, the salt-bath isothermal roller table, the controlled air-cooling roller table, and the cleaning roller table all are variable, and can be 0.01 m / s. Preferably, components of the fast-cooling tank 1, the first lower tank body 2, the isothermal tank 3, and the second lower tank body 4 that are in contact with a molten salt all are made of a 316L or 347H material, and have a thickness of 5 mm. Preferably, a first molten-salt pump is provided in the salt-bath fast-cooling tank to regulate parameters such as circulation, a flow rate, a liquid level, a temperature, and a flow field of a molten salt in the fast-cooling tank 1 and the first lower tank body 2. Preferably, a second molten-salt pump is provided in the salt-bath isothermal tank to regulate parameters such as circulation, a flow rate, a liquid level, a temperature, and a flow field of a molten salt in the isothermal tank 3 and the second lower tank body 4. Preferably, an amount of a molten salt for a salt bath is 1001. Preferably, the controlled air-cooling unit can allow the control of slow cooling of a wire rod out of a salt tank with a cooling rate of 3°C / s. Preferably, the cleaning system can allow the removal of a residual salt on a wire rod, and a resulting salt solution is recycled. Preferably, the flue gas collection system 5 can allow the condensation and recycling of a salt 09 07 25 mist, and salt-containing water is allowed to enter the cleaning system for recycling. Preferably, the salt / water separation system 24 utilizes high-temperature waste heat to allow the crystallization and precipitation of a salt and makes a resulting water vapor discharged into the cleaning system for recycling. Preferably, a heat exchange area of the salt-salt heat exchanger 15 is 100 m2. Preferably, pipelines at junctions of the salt-salt heat exchanger 15 with the first lower tank body 2 and the second lower tank body 4 each are provided with a filter mesh, which can mechanically filter an iron oxide scale out, thereby allowing the concentrated collection of the iron oxide scale. Preferably, the molten-salt energy storage / peak-regulating power generation system can utilize a coal gas for heating and energy storage, which can improve a regulation capacity of peak-regulating power generation of the molten-salt energy storage / peak-regulating power generation system. Preferably, an amount of a molten salt used for the molten-salt energy storage / peak-regulating power generation system is 5001. Preferably, components of the high-temperature storage tank 18 and the intermediate storage tank 16 that are in contact with a molten salt all are made of a 347H material, and have a thickness of 5 mm. A process for on-line heat treatment of a high-speed wire rod based on energy recycling is provided, including the following steps: e. Heating a molten salt in the fast-cooling tank by a wire rod obtained after spinning: A first wire rod with a temperature of l,050°C obtained after spinning was rapidly quenched in a 400°C molten salt in the fast-cooling tank 1 for 40 s to obtain a second wire rod, such that a temperature of the molten salt arose by 200°C. f. Heating a molten salt in the isothermal tank by the second wire rod: The second wire rod was subjected to isothermal transformation for 400 s in a 585°C molten salt in the isothermal tank 3 to obtain a third wire rod, such that a temperature of the molten salt in the isothermal tank arose by 10°C. g. Controlled cooling: The third wire rod out of the isothermal tank 3 was purged with 550°C hot air in the first annular air blade 6 for 20 s and then purged with compressed air in the second annular air blade 7 for 30 s to obtain a fourth wire rod. h. Cleaning: The fourth wire rod obtained after the controlled cooling was allowed to enter the cleaning system, and subjected to residual surface salt removal with the first cleaning device 8, the third annular air blade 9, the stepped water tank 10, the fourth annular air blade 11, the second cleaning device 12, and the fifth annular air blade 13 sequentially to obtain a fifth wire rod. i. Oven-drying: The fifth wire rod obtained after the cleaning was oven-dried in the 09 07 25 oven-drying unit 14 and then coiled to obtain a finished product. j. Heat release of molten salts for salt baths through a tube side of the salt-salt heat exchanger 15: Molten salts respectively heated to 600°C and 595°C in the fast-cooling tank 1 and the isothermal tank 3 were allowed to first overflow into the first lower tank body 2 and the second lower tank body 4 respectively and then enter the salt-salt heat exchanger 15 through a pipeline, such that the molten salts underwent a heat release through the tube side of the salt-salt heat exchanger 15 and then were circulated into the first lower tank body 2 and the second lower tank body 4 respectively. k. Heat absorption of the waste heat recovery system: A 350°C cooling salt was allowed to enter the shell side of the salt-salt heat exchanger 15 from the low-temperature storage tank 22 of the molten-salt energy storage / peak-regulating power generation system and absorb heat of a high-temperature molten salt in the tube side of the salt-salt heat exchanger 15 until a temperature of the cooling salt arose to 585°C, and a 585°C cooling salt was returned to the molten-salt energy storage / peak-regulating power generation system, such that a heat recovery was completed. 1. Molten-salt energy storage / peak-regulating power generation: Heat storage during a valley period: The 585°C cooling salt from the shell side of the salt-salt heat exchanger 15 was allowed to enter the intermediate storage tank 16 of the molten-salt energy storage / peak-regulating power generation system, then enter a molten-salt furnace 17 and be heated to 600°C, and then enter the high-temperature storage tank 18 for the heat storage. Heat release during a peak period: Heat of a 600°C molten salt in the high-temperature storage tank 18 was used to produce a high-temperature steam, the high-temperature steam was allowed to enter the power generation unit for power generation, and when a temperature of the molten salt dropped to 350°C, a resulting 350°C molten salt was allowed to enter the low-temperature storage tank 22 for circulation, such that the peak-regulating power generation was achieved. The molten salt was a cooling medium / heating medium including two or more selected from the group consisting of potassium nitrate, sodium nitrate, lithium nitrate, calcium nitrate, silver nitrate, potassium nitrite, and sodium nitrite, and a moisture content in the molten salt was 0.5 wt.%. In this example, the process is a bainite process, and a bainite structure is obtained. An image of the bainite structure is shown in FIG. 3. In this example, the raw material is Y10B21, a first temperature of the fast-cooling tank 1 is 400°C, and a second temperature of the isothermal tank 3 is 585°C. A use of the wire rod of this example in a bainite cold-heading steel is also provided. Example 3 An apparatus of this example is different from the apparatus in Example 2 merely in that: A roller table is provided inside the stepped water tank 10, and the roller table is provided 09 07 25 with 5 falling sections, where there is an overlap distance of 500 mm between a horizontal projection of a tail of a previous falling section and a horizontal projection of a head of a next falling section, each falling section forms a step, and each falling section includes 10 rollers arranged sequentially from left to right as shown in Figure 7; and extending upwards in an inclined manner and has a falling height of 300 mm, an inclination angle of 10°, and a roller spacing of 60 mm. A temperature of the molten salt in the fast-cooling tank 1 is 405°C, and a temperature of the molten salt in the isothermal tank 3 is 400°C. Speeds of the salt-bath fast-cooling roller table, the salt-bath isothermal roller table, the controlled air-cooling roller table, and the cleaning roller table all are variable, and can be 1 m / s. Components of the fast-cooling tank 1, the first lower tank body 2, the isothermal tank 3, and the second lower tank body 4 that are in contact with a molten salt all are made of a 316L or 347H material, and have a thickness of 20 mm. An amount of a molten salt for a salt bath is 500 t. The controlled air-cooling unit can allow the control of slow cooling of a wire rod out of a salt tank with a cooling rate of 15°C / s. A heat exchange area of the salt-salt heat exchanger 15 is 500 m2. An amount of a molten salt used for the molten-salt energy storage / peak-regulating power generation system is 3,000 t. Components of the high-temperature storage tank 18 and the intermediate storage tank 16 that are in contact with a molten salt all are made of a 347H material, and have a thickness of 20 mm. A process for on-line heat treatment of a high-speed wire rod based on energy recycling is provided, including the following steps: e. Heating a molten salt in the fast-cooling tank by a wire rod obtained after spinning: A first wire rod with a temperature of l,000°C obtained after spinning was rapidly quenched in a 405°C molten salt in the fast-cooling tank 1 for 10 s to obtain a second wire rod, such that a temperature of the molten salt arose by 150°C. f. Heating a molten salt in the isothermal tank by the second wire rod: The second wire rod was subjected to isothermal transformation for 100 s in a 400°C molten salt in the isothermal tank 3 to obtain a third wire rod, such that a temperature of the molten salt in the isothermal tank arose by 100°C. g. Controlled cooling: The third wire rod out of the isothermal tank 3 was purged with 300°C hot air in the first annular air blade 6 for 10 s and then purged with compressed air in the second annular air blade 7 for 10 s to obtain a fourth wire rod. h. Cleaning: The fourth wire rod obtained after the controlled cooling was allowed to enter 09 07 25 the cleaning system, and subjected to residual surface salt removal with the first cleaning device 8, the third annular air blade 9, the stepped water tank 10, the fourth annular air blade 11, the second cleaning device 12, and the fifth annular air blade 13 sequentially to obtain a fifth wire rod. i. Oven-drying: The fifth wire rod obtained after the cleaning was oven-dried in the oven-drying unit 14 and then coiled to obtain a finished product. j. Heat release of molten salts for salt baths through a tube side of the salt-salt heat exchanger 15: Molten salts respectively heated to 555°C and 500°C in the fast-cooling tank 1 and the isothermal tank 3 were allowed to first overflow into the first lower tank body 2 and the second lower tank body 4 respectively and then enter the salt-salt heat exchanger 15 through a pipeline, such that the molten salts underwent a heat release through the tube side of the salt-salt heat exchanger 15 and then were circulated into the first lower tank body 2 and the second lower tank body 4 respectively. k. Heat absorption of the waste heat recovery system: A 300°C cooling salt was allowed to enter the shell side of the salt-salt heat exchanger 15 from the low-temperature storage tank 22 of the molten-salt energy storage / peak-regulating power generation system and absorb heat of a high-temperature molten salt in the tube side of the salt-salt heat exchanger 15 until a temperature of the cooling salt arose to 500°C, and a 500°C cooling salt was returned to the molten-salt energy storage / peak-regulating power generation system, such that a heat recovery was completed. 1. Molten-salt energy storage / peak-regulating power generation: Heat storage during a valley period: The 500°C cooling salt from the shell side of the salt-salt heat exchanger 15 was allowed to enter the intermediate storage tank 16 of the molten-salt energy storage / peak-regulating power generation system, then enter a molten-salt furnace 17 and be heated to 580°C, and then enter the high-temperature storage tank 18 for the heat storage. Heat release during a peak period: Heat of a 580°C molten salt in the high-temperature storage tank 18 was used to produce a high-temperature steam, the high-temperature steam was allowed to enter the power generation unit for power generation, and when a temperature of the molten salt dropped to 300°C, a resulting 300°C molten salt was allowed to enter the low-temperature storage tank 22 for circulation, such that the peak-regulating power generation was achieved. The molten salt was a cooling medium / heating medium including two or more selected from the group consisting of potassium nitrate, sodium nitrate, lithium nitrate, calcium nitrate, silver nitrate, potassium nitrite, and sodium nitrite, and a moisture content in the molten salt was 0.3 wt.%. In this example, the process is a bainite process, and a bainite structure is obtained. An image of the bainite structure is shown in FIG. 4. In this example, the raw material is Y10B21, a first temperature of the fast-cooling tank 1 is 405°C, and a second temperature of the isothermal tank 3 09 07 25 is 400°C. A use of the wire rod of this example in a bainite cold-heading steel is also provided. Example 4 This example is different from Example 3 merely in that: A process for on-line heat treatment of a high-speed wire rod based on energy recycling is provided, including the following steps: e. Heating a molten salt in the fast-cooling tank by a wire rod obtained after spinning: A first wire rod with a temperature of 900°C obtained after spinning was rapidly quenched in a 600°C molten salt in the fast-cooling tank 1 for 15 s to obtain a second wire rod, such that a temperature of the molten salt arose by 10°C. f. Heating a molten salt in the isothermal tank by the second wire rod: The second wire rod was subjected to isothermal transformation for 50 s in a 545°C molten salt in the isothermal tank 3 to obtain a third wire rod, such that a temperature of the molten salt in the isothermal tank arose by 10°C. g. Controlled cooling: The third wire rod out of the isothermal tank 3 was purged with 400°C hot air in the first annular air blade 6 for 15 s and then purged with compressed air in the second annular air blade 7 for 20 s to obtain a fourth wire rod. h. Cleaning: The fourth wire rod obtained after the controlled cooling was allowed to enter the cleaning system, and subjected to residual surface salt removal with the first cleaning devices, the third annular air blade 9, the stepped water tank 10, the fourth annular air blade 11, the second cleaning device 12, and the fifth annular air blade 13 sequentially to obtain a fifth wire rod. i. Oven-drying: The fifth wire rod obtained after the cleaning was oven-dried in the oven-drying unit 14 and then coiled to obtain a finished product. j. Heat release of molten salts for salt baths through a tube side of the salt-salt heat exchanger 15: Molten salts respectively heated to 610°C and 555°C in the fast-cooling tank 1 and the isothermal tank 3 were allowed to first overflow into the first lower tank body 2 and the second lower tank body 4 respectively and then enter the salt-salt heat exchanger 15 through a pipeline, such that the molten salts underwent a heat release through the tube side of the salt-salt heat exchanger 15 and then were circulated into the first lower tank body 2 and the second lower tank body 4 respectively. k. Heat absorption of the waste heat recovery system: A 300°C cooling salt was allowed to enter the shell side of the salt-salt heat exchanger 15 from the low-temperature storage tank 22 of the molten-salt energy storage / peak-regulating power generation system and absorb heat of a high-temperature molten salt in the tube side of the salt-salt heat exchanger 15 until a temperature of the cooling salt arose to 585°C, and a 585°C cooling salt was returned to the molten-salt energy storage / peak-regulating power generation system, such that a heat recovery was completed. 1. Molten-salt energy storage / peak-regulating power generation: Heat storage during a valley 09 07 25 period: The 585°C cooling salt from the shell side of the salt-salt heat exchanger 15 was allowed to enter the intermediate storage tank 16 of the molten-salt energy storage / peak-regulating power generation system, then enter a molten-salt furnace 17 and be heated to 600°C, and then enter the high-temperature storage tank 18 for the heat storage. Heat release during a peak period: Heat of a 600°C molten salt in the high-temperature storage tank 18 was used to produce a high-temperature steam, the high-temperature steam was allowed to enter the power generation unit for power generation, and when a temperature of the molten salt dropped to 300°C, a resulting 300°C molten salt was allowed to enter the low-temperature storage tank 22 for circulation, such that the peak-regulating power generation was achieved. The molten salt was a cooling medium / heating medium including two or more selected from the group consisting of potassium nitrate, sodium nitrate, lithium nitrate, calcium nitrate, silver nitrate, potassium nitrite, and sodium nitrite, and a moisture content in the molten salt was 0.6 wt.%. In this example, the process is a sorbite process, and a sorbite structure is obtained. An image of the sorbite structure is shown in FIG. 5, and the sorbite structure has a sorbitizing rate of 95%, an interlamellar spacing of 75 nm, a network carbide grade of 1.0, a same-circle performance uniformity of about 30 MPa, a tensile strength of 1,512 MPa, a section shrinkage rate of 35%, and a grade of 2,200 MPa or more for wires manufactured downstream. In this example, the raw material is 92Si, a first temperature of the fast-cooling tank 1 is 600°C, and a second temperature of the isothermal tank 3 is 545°C. A use of the wire rod of this example in a spring steel, a tool steel, a bearing steel, a bridge cable, a steel strand, a bead cord, a cutting wire, or a diamond wire is also provided. Example 5 This example is different from Example 4 merely in that: the raw material is 97Si, and a product has a sorbitizing rate of 96%, an interlamellar spacing of 79 nm, a network carbide grade of 1.0, a same-circle performance uniformity of about 30 MPa, a tensile strength of 1,585 MPa, a section shrinkage rate of 31%, and a grade of 2,300 MPa or more for wires manufactured downstream. The following table 4 shows structures of the wire rods obtained after a salt-bath treatment in Examples 1 to 5 of the present disclosure. Table 4 Structures of the wire rods obtained after a salt-bath treatment in Examples 1 to 5 Structure Example 1 Tempered troostite + tempered martensite + residual austenite Example 2 Bainite Example 3 Bainite Example 4 Sorbitizing rate: 95%, interlamellar spacing: 75 nm, and network carbide grade: 1.0 Example 5 Sorbitizing rate: 96%, interlamellar spacing: 79 nm, and network carbide grade: 1.0 The following table 5 shows mechanical properties of the wire rods obtained after a salt-bath treatment in Examples 1 to 5 of the present disclosure. Table 5 Mechanical properties of the wire rods obtained after a salt-bath treatment in Examples 1 to 5 Tensile strength Section shrinkage rate Same-circle mechanical fluctuation range Example 1 1989MPa 47% 50MPa Example 2 802MPa 71% 40MPa Example 3 863MPa 62% 40MPa Example 4 1512MPa 35% 30MPa Example 5 1585MPa 31% 30MPa 09 07 25 A test method of the same-circle mechanical fluctuation range was as follows: 2 wire rods 5 m away from an end of a coil were taken; and with a position of a lap area as a base point, each wire rod was divided into 8 segments equally, and 1 tensile sample was taken from each segment. A strength difference obtained after a tensile test of tensile samples was a same-circle difference of a wire rod. The tensile test was conducted according to "GB-T 228.1-2021 Metal Materials -Tensile Test Part 1: Room-Temperature Test Method". A tensile strength and a section shrinkage rate both were obtained through the above tensile test. In the wire rods obtained after salt-bath treatments in Examples 1 to 5 of the present disclosure, a lap joint also undergoes efficient surface salt removal, and a surface does not undergo corrosion. Example 6 This example is different from Example 1 merely in that: the existing water tank was adopted, and there was no falling section. A residual salt at a lap joint of a wire rod obtained in this example is not completely removed, and the wire rod will undergo aggravated corrosion half a year later. It should be understood that, in order to simplify the present disclosure and help understand one or more aspects of the present disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together into a single embodiment, figure, or description thereof. However, the method of the present disclosure should not be interpreted as reflecting the intention that the claimed present 09 07 25 disclosure has features more than the features expressly stated in each claim. More precisely, as reflected in the claims, each aspect of the present disclosure has features less than all features of the embodiments disclosed above. Therefore, the claims following specific embodiments are hereby expressly incorporated into the specific embodiments, where each claim itself serves as a separate embodiment of the present disclosure. Although the present disclosure is described according to the limited number of examples, those skilled in the art appreciate that other examples may be conceived from the above description within the defined scope of the present disclosure. In addition, it should be noted that the language used in this specification is selected primarily for readability and teaching, but not for explaining or defining the subject of the present disclosure. Thus, without departing from the scope and spirit of the appended claims, many modifications and changes are apparent to those of ordinary skill in the art. Within the scope of the present disclosure, the disclosure of the present disclosure is illustrative rather than restrictive. The scope of the present disclosure is defined by the appended claims. The above are merely preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the protection scope of the present disclosure as defined in the appended Claims.

Claims

09 07 251. An apparatus for on-line heat treatment of a high-speed wire rod based on energy recycling, characterized by comprising an on-line heat treatment device, a waste heat recovery system, and a molten-salt energy storage / peak-regulating power generation system,wherein the on-line heat treatment device comprises a fast-cooling tank (1), an isothermal tank (3), a controlled air-cooling unit, a cleaning system, and an oven-drying unit (14) through which a wire rod passes sequentially from the fast-cooling tank (1) through to the oven-drying until (14);the fast-cooling tank (1) and the isothermal tank (3) both contain a molten salt;a first lower tank body (2) configured to circulate the molten salt with the fast-cooling tank (1) is provided below the fast-cooling tank (1); a second lower tank body (4) configured to circulate the molten salt with the isothermal tank (3) is provided below the isothermal tank (3);the waste heat recovery system comprises a salt-salt heat exchanger (15) configured to perform a heat exchange between the molten salt in the first lower tank body (2) and molten salt from a low-temperature storage tank (22) and between the molten salt in the second lower tank body (4) and molten salt from the low- temperature storage tank (22);the molten salt, from the low-temperature storage tank (22), after the heat exchange in the salt-salt heat exchanger (15) flows to the molten-salt energy storage / peak-regulating power generation system;the cleaning system is connected to a salt / water separation system (24); the cleaning system comprises a first cleaning device (8) having a plurality of nozzles, a third annular air blade (9), a stepped water tank (10), a fourth annular air blade (11), a second cleaning device (12) having a plurality of nozzles, and a fifth annular air blade (13) that are arranged sequentially; the controlled air-cooling unit comprises a first annular air blade (6) and a second annular air blade (7) that are arranged between the isothermal tank (3) and the cleaning system; and wherein the wire rod passes sequentially from the first cleaning device (8) to the fifth annular blade (13)a roller table is provided inside the stepped water tank (10), and the roller table is provided with 2 to 7 falling sections, wherein there is an overlap distance of 100 mm to 1,500 mm between a horizontal projection of a tail of a previous one of the falling sections and a horizontal projection of a head of a next one of the falling sections, each of the falling sections forms a step, and each of the falling sections comprises 3 to 20 rollers arranged sequentially and extending upwards in an inclined manner and has a falling height of 100 mm to 500 mm, an inclination angle of 10° to 60°, and a roller spacing of 50 mm to 400 mm; an ultrasonic vibration unit is provided inside the stepped water tank (10);the molten-salt energy storage / peak-regulating power generation system comprises an intermediate storage tank (16) configured to store the molten salt heated in the salt-salt heat09 07 25exchanger (15); the intermediate storage tank (16) is connected to a high-temperature storage tank (18); the molten salt in the high-temperature storage tank (18) is configured to supply heat for a power generation unit, and the molten salt after supplying the heat is stored in the low-temperature storage tank (22); and the molten salt in the low-temperature storage tank (22) is returned to a shell side of the salt-salt heat exchanger (15) and the intermediate storage tank (16).

2. The apparatus according to claim 1, characterized in that a flue gas collection system (5) is provided above the fast-cooling tank (1), the isothermal tank (3), the controlled air-cooling unit, and the cleaning system.

3. The apparatus according to claim 1, characterized in that a temperature of the molten salt in the fast-cooling tank (1) is 250°C to 600°C, and a temperature of the molten salt in the isothermal tank (3) is 400°C to 585°C.

4. A process using the apparatus for on-line heat treatment of the high-speed wire rod based on energy recycling according to any one of claims 1 to 3, characterized by comprising the following steps:SOI. salt-bath-based fast cooling: rapidly quenching a first wire rod with a temperature of 800°C to l,050°C, in a 250°C to 600°C molten salt in the fast-cooling tank (1) for 4 s to 40 s to obtain a second wire rod;S02. salt-bath-based isothermal transformation: subjecting the second wire rod to isothermal transformation for 30 s to 400 s in a 400°C to 585°C molten salt in the isothermal tank (3) to obtain a third wire rod;S03. controlled cooling: purging the third wire rod out of the isothermal tank (3) with 200°C to 550°C hot air in the first annular air blade (6) for 5 s to 20 s to obtain a fourth wire rod, and purging the fourth wire rod with compressed air in the second annular air blade (7) for 5 s to 30 s to obtain a fifth wire rod;S04. cleaning: allowing the fifth wire rod obtained after the controlled cooling to enter the cleaning system, and subjecting the fifth wire rod to residual surface salt removal with the first cleaning device (8) having a plurality of nozzles, the third annular air blade (9), the stepped water tank (10), the fourth annular air blade (11), the second cleaning device (12) having a plurality of nozzles, and the fifth annular air blade (13) sequentially to obtain a sixth wire rod;S05. oven-drying: oven-drying the sixth wire rod obtained after the cleaning in the oven-drying unit (14), and coiling to obtain a finished product;S06. heat release of the molten salt for salt baths through a tube side of the salt-salt heat exchanger (15): allowing the molten salt heated to 430°C to 610°C in the fast-cooling tank (1) and the isothermal tank (3) to first overflow into the first lower tank body (2) and the second lower tank body (4) respectively and then enter the salt-salt heat exchanger (15) through a pipeline, such that the molten salt undergoes the heat release through the tube side of the salt-salt heat exchanger09 07 25(15) and then is circulated into the first lower tank body (2) and the second lower tank body (4) respectively;S07. heat absorption of the waste heat recovery system: allowing a cooling salt at 230°C to 350°C to enter the shell side of the salt-salt heat exchanger (15) from the low-temperature storage tank (22) of the molten-salt energy storage / peak-regulating power generation system and absorb heat of the molten salt at a high temperature in the tube side of the salt-salt heat exchanger (15) until a temperature of the cooling salt arises to 400°C to 585°C, and returning the cooling salt at 400°C to 585°C to the molten-salt energy storage / peak-regulating power generation system, such that a heat recovery is completed; andS08. molten-salt energy storage / peak-regulating power generation:heat storage during a valley period: allowing the cooling salt at 400°C to 585°C from the shell side of the salt-salt heat exchanger (15) to enter the intermediate storage tank (16) of the molten-salt energy storage / peak-regulating power generation system, then enter a molten-salt furnace (17) and be heated to 550°C to 600°C to become a molten salt at 550°C to 600°C, and then enter the high-temperature storage tank (18) for the heat storage; andheat release during a peak period: using heat of the molten salt at 550°C to 600°C in the high-temperature storage tank (18) to produce a high-temperature steam, allowing the high-temperature steam to enter the power generation unit for power generation, and allowing the molten salt dropped to 230°C to 350°C to enter the low-temperature storage tank (22) for circulation, such that the peak-regulating power generation is achieved,wherein the molten salt is a cooling medium / heating medium comprising two or more selected from a group consisting of potassium nitrate, sodium nitrate, lithium nitrate, calcium nitrate, silver nitrate, potassium nitrite, and sodium nitrite, and a moisture content in the molten salt for the salt baths does not exceed 1 wt.%.

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