JP7479567B2 - Method for controlling segregation and network carbide in 86-grade high-strength cord steel wire rod - Google Patents

Description

The present invention belongs to the technical field of cord steel production, and specifically relates to a method for controlling segregation and network carbides in 86-class high-strength cord steel wire rod.

In recent years, with the rapid development of China's automobile and machinery manufacturing industries, the demand for cord steel is increasing and the quality requirements for products are becoming higher. As automobiles develop in the direction of lightweight and eco-friendly, improving the strength and fatigue strength of cord steel wire can reduce the amount of cord steel wire used in tires with the same overall strength, reducing tire weight, reducing tire rolling resistance, saving energy consumption and lowering tire production costs. At present, high-strength cord steel grade 86 belongs to high-profit, high-added-value products, and has a large market size and good prospects.

Due to the requirements of its operating conditions and safety performance, cord steel has strict requirements for its chemical composition, inclusions, mechanical properties, metal structure, etc. High Al ₂ O ₃ content, non-deformable hard inclusions, and wire core segregation (network carbide) are two major problems that cause deep drawing and curl breakage in customers. Grade 86 cord has a high C content (the component weight percentages of grade 86 cord steel wire with the brand name LX86A are C: 0.85-0.90%, Si: 0.15-0.35%, Mn: 0.40-0.60%, P: ≦0.015%, S: ≦0.015%, Cr: ≦0.10%), so continuous casting segregation is heavy, and the wire is prone to form network cementite, which separates the matrix structure and causes cup-cone-shaped breakage in the cord drawing process, resulting in low production efficiency and poor cord quality.

Most domestic steel enterprises of 86 grade cord adopt the process of large billet (light reduction) + high temperature diffusion + blooming finishing + double heating and forming, and combine it with Stelmor air cooling to control the quality of wire rod reticulated carbide and decarburization. In the midst of the global economic downturn, the automobile industry is becoming more competitive, and how to reduce production and manufacturing costs and obtain higher profit margins is the goal pursued by the entire supply chain enterprises. The use of the double heating and forming process has the disadvantages of a long process, high cost, and lack of competitiveness. For example, a Chinese patent document (application number 201910798924.3) discloses a production method of high-strength cord steel billet using a double heating and forming process. That is, the large billet is rolled into a small billet, cooled, and then the small billet is heated again to roll it into 5.5 wire rod, but it has the disadvantages of a long process path and high cost.

Instead of the conventional process of "KR → BOF → LF → CC → surface sampling inspection → heating → blooming → skinning → heating → rolling control → controlled cooling", the present invention adopts the process of "KR → BOF → LF → CC → surface treatment → heating → rolling control → cooling control". By rationally designing the steelmaking and rolling processes, a method for controlling segregation and reticulate carbide in 86-grade high-strength cord steel wire rod is provided, which improves the segregation and reticulate carbide in 86-grade high-strength cord steel wire rod without secondary heating and forming, without the need for skinning, and without the support of the light reduction technology of the continuous casting machine, and reduces the customer's wire breakage caused by said problems when drawing.

To achieve the above objective, the technical means adopted in the present invention are as follows:

The method for controlling segregation and reticulated carbides in 86-grade high-strength cord steel wire rod includes a KR hot metal pre-desulfurization process, a BOF converter smelting process, an LF furnace refining process, a continuous casting CC process, a slab surface treatment process, a slab heating process, a rolling control process, and a cooling control process, and the component weight percentages of the 86-grade high-strength cord steel wire rod are C: 0.85-0.90%, Si: 0.15-0.35%, Mn: 0.40-0.60%, P: ≦0.015%, S: ≦0.010%, Cr: ≦0.010%, Al: ≦0.005%, and the remainder are Fe and unavoidable impurity elements.

In the KR hot metal pre-desulfurization process, S element is a harmful element that easily segregates, so the hot metal is pre-treated to reduce the concentration of S element in the solidification center of the slab and reduce segregation in the slab. Therefore, in the KR process, 3 to 6 kg/ton of desulfurization agent such as lime is added to the hot metal ladle and strong mechanical stirring is performed to remove the S content in the hot metal so that the S content of the hot metal in the converter is guaranteed to be ≦0.003%, and then the desulfurization slag is removed.

In the BOF converter smelting process, P is also a harmful element that is prone to segregation, and it is necessary to control the P content in the finished product to be ≦0.010%, the S content ≦0.008%, and the P + S content ≦0.016%. The specific control method is to use code-specific clean steel scrap (the main components are Fe, C, Si, Mn and other unavoidable trace elements, the total amount of which accounts for 10% to 30% of the total metal charge) in the BOF smelting to ensure that the P, S and other harmful elements in the finished product are at low levels. In addition, the converter BOF smelting adopts a "double slag" process, that is, when the silicon-manganese oxidation period of about 5±1 min is completed by blowing in the converter, the gun is turned off to ensure that the P content of the tapped steel is ≦0.010%, and the de-P slag is removed to prevent P return in the later stage of blowing in the converter, and the gun is turned on again to make slag. In the BOF converter smelting process, the converter adopts a "double stop" tapping process, that is, a combination of a slag stopper cone and a slide plate is used in the tapping process, and slag outflow detection technology is equipped to control the amount of slag outflow in the tapping process to be ≦50 kg, thereby preventing the diffusion of harmful elements such as P, S, and Ti from the slag to molten steel in the refining process. The "double stop" tapping process reduces the P and S content in the steel, and therefore reduces the segregation of the slab.

In the LF furnace refining process, the refining process adopts silicon carbide deoxidation, the refining slag adopts CaO- _SiO2 binary slag system, and the alkalinity of the final refining slag is controlled to 0.7-1.0. In the later stage of refining, large argon gas stirring is avoided (bottom blowing of argon gas is controlled so as to just blow the slag surface apart), and slag entrapment is prevented. The composition and temperature of the molten steel are adjusted to ensure that the temperature of the bull ladle is higher than the liquidus temperature of the molten steel, 35-45°C. After refining is completed, the argon gas soft blow time is ≧15min.

In the continuous casting CC process, the slab is prepared by a 10-machine 10-flow arc-shaped continuous casting machine, and the cross section of the slab is ≦160* ^160mm2 to ensure the secondary cooling strength. The arc radius of the casting machine is 10m, and the end electromagnetic stirring is 7.2m away from the meniscus. The length of the end electromagnetic stirring device is 700mm, and the inner diameter is φ380mm. The key points for controlling the segregation of the slab by continuous casting are low superheat, strong crystallizer electromagnetic stirring and end electromagnetic stirring, appropriate drawing speed, strong secondary cooling and thermal soft reduction technology, and ensuring the segregation average value of the slab center carbon ≦1.07. Specifically, in order to improve the ratio of the equiaxed crystals of the slab, continuous casting adopts low superheat casting, and the superheat of the molten steel is controlled at 10-25°C. Strong electromagnetic stirring strength can promote uniformity of molten steel temperature, cut off the growth of columnar crystals, promote nucleation, improve the ratio of equiaxed crystals, and avoid the "bridging" of solidification end columnar crystals, so the crystallizer electromagnetic stirring current is 250-350A, frequency is 2-4Hz, and the end electromagnetic stirring current is 300-400A, frequency is 5-10Hz. In order to ensure the appropriate combination of drawing speed and end electromagnetic stirring position and achieve the optimal end stirring effect, the drawing speed is controlled to 1.60-1.75m/min, with the target being 1.70m/min. In order to suppress the fractional crystallization of elements in the slab solidification process, the secondary cooling total water strong cooling is adopted, and the secondary cooling specific water amount is controlled to 1.6-1.8L/kg. In addition, the slab is cast at the electromagnetic stirring point at the discharge end and intensive water cooling is performed, which shrinks the casting flow housing and achieves the effect of "thermal soft reduction", improving the segregation of the slab.

In addition, the cooling water flow rate of different secondary cooling stages is set to change according to the temperature change of the secondary cooling process of the slab as follows: Footrest roller stage (length about 0.3 m) 9.0-11.0 m3/h, secondary cooling stage 1 (length about 2.0 m) 11.0-13.0 m3/h, secondary cooling stage 2 (length about 2.3 m) 8.0-10.0 m3/h, secondary cooling stage 3 (length about 1.4 m) 2.5-4.5 m3/h. In addition, due to the air-cooled temperature return of the slab at the terminal electromagnetic stirring point, a total water cooling area (secondary cooling stage 4) with a length of 1.5 m and a water flow rate of 1.5-3.5 m3/h is added to the subsequent air-cooling stage, which effectively reduces the temperature return of the slab before entering the leveler, reduces the probability of cracking of the hot-transported slab, and provides the effect of "thermal soft reduction", which can reduce the central segregation of the slab. At the same time, it can improve the structure of the iron oxide skin and increase the yield of metal materials.

In the slab surface treatment process, the resulting slab is cooled to below 100°C using a windshield stack, and the iron oxide skin on the slab surface is removed using a shot blasting machine, after which a layer of high-temperature decarburization prevention paint is applied to the slab surface. In order to ensure the decarburization prevention effect and prevent the increase in the amount of carbon on the wire surface, the paint mixing ratio (powder to liquid mass ratio) is controlled to 3:2, and the coating thickness is controlled to 0.2-1.0 mm. After the paint has dried, the steel slab enters the heating process.

In the slab heating process, the slab coated with high-temperature decarburization prevention paint is heated by a high-temperature diffusion process and advanced at a constant speed in the heating furnace. The time of the preheating stage of the heating furnace is controlled to 30 to 55 min. The first heating stage temperature is 950-1000°C, the time is 40 to 65 min., the second heating stage temperature is 1200-1230°C, the time is 65 to 105 min. The soaking stage temperature is 1220-1250°C, the time is 50 to 85 min., and the initial rolling temperature is 1180-1220°C. This slab heating process promotes the diffusion of C, P, S, Mn, etc. between dendrites, reduces microsegregation of elements, and is advantageous for seaming of shrinkage holes in the center of the slab.

To control the decarburization of the rolled material, it is heated in a reducing atmosphere in the heating furnace and the air-fuel ratio is controlled to 0.4 to 0.5. The heating furnace withdrawal interval is 117-190 s/piece, and the total steel piece heating time is 190-300 min.

In the rolling control process, the laying temperature is controlled to 960-980°C in accordance with the high-temperature laying process, suppressing the precipitation of core network cementite while optimizing the thickness of the iron oxide skin to 10-15 μm, making it easy to remove the iron oxide skin by mechanically peeling the wire rod, and the specifications of the rolled wire rod are φ5.5 mm.

In the cooling control process, the wire rod is dispersed on the Stelmor roller table after passing through the laying head, and the air cooling strength of the fan is adjusted to achieve a temperature drop rate of 30-35°C/s during air cooling 0-8s and a temperature drop rate of 15-30°C/s during air cooling 9-17s, and the phase transition process is approximated to isothermal transformation. In addition, the rolling fans are centrifugal fans with an air volume of 200,000 m3/h, and eight fans are turned on during production. The air volume of the first to third fans along the wire rod traveling direction is controlled to 90%, and the air volume of the fourth to sixth fans is controlled to 80%, so that the temperature of the wire rod quickly passes through the secondary cementite precipitation temperature zone, and then the wire rod undergoes phase transition at the seventh and eighth fan positions. The air volume of the seventh and eighth fans is adjusted to 70%, and the process of controlling the phase transition is approximated to isothermal transformation so that sufficient transformation of the wire rod structure is guaranteed (phase transition temperature rise < 30°C).

The present invention provides the following technical advantages over conventional techniques:

The φ5.5 mm wire produced by the method of the present invention has a sorbite ratio of ≥90%, slight segregation in the center of the wire, and no reticulated cementite in the core, meeting the user's needs for drawing.

Small billet continuous casting + wire rolling improves wire segregation and network carbide, resulting in significant cycle and cost reductions.

The method of the present invention has a simple process, is free of reticulated cementite, has a high sorbite conversion rate, has a shallow decarburized layer, can achieve energy saving, is eco-friendly and environmentally friendly, and can enhance the competitiveness of companies and create better profit margins.

1 is a photograph of the metal structure of a wire rod produced in Example 1 of the present invention. FIG. 2 is a schematic diagram of a secondary cooling system of a casting machine in an embodiment of the present invention, in which the unit of the staff is mm. FIG. 2 is a schematic plan view of a heating furnace according to an embodiment of the present invention, in which the unit of the staff is mm.

The present invention will now be described in further detail with reference to the following examples.
(Examples 1 to 4)

The method for controlling segregation and reticulated carbides in 86-grade high-strength cord steel wire rod includes the KR pre-desulfurization process → BOF converter smelting process → LF furnace refining process → continuous casting CC process → slab surface treatment process → slab heating process → rolling control process → cooling control process.

The composition of the smelted product is controlled as follows: C: 0.85-0.90%, Si: 0.15-0.35%, Mn: 0.40-0.60%, P: ≦0.010%, S: ≦0.010%, Cr: ≦0.010%, Al: ≦0.005%, and the remainder is Fe and unavoidable impurity elements.

The hot metal is pretreated with KR hot metal to a S content of ≦0.003%, and clean scrap steel (mainly Fe, C, Si, Mn and other unavoidable trace elements, total amount of which accounts for 10%-30% of the total metal charge) is used. In addition, the converter BOF smelting adopts a "double slag" process, that is, when the silicon-manganese oxidation period of 4-51 min is completed by blowing in the converter, the gun is removed to remove the de-P slag, and the gun is turned on again to make slag, so as to ensure that the P content of the tapped steel is ≦0.008%. The converter tapping adopts a "double stop" tapping process, and is equipped with slag outflow detection technology to control the amount of slag outflow to ≦50 kg. The weight percentages of the main chemical components of the steel pieces in Examples 1-4 are shown in Table 1.

In the LF furnace refining process, the refining process adopts silicon carbide deoxidation, the refining slag adopts CaO- _SiO2 binary slag system, and the alkalinity of the final refining slag in Example 1-4 is controlled to 0.7-1.0. In the later stage of refining, large argon gas stirring is avoided (the bottom blowing of argon gas is controlled so as to just blow the slag surface apart), and slag entrapment is prevented. The composition and temperature of the molten steel are adjusted so that the temperature of the heating bull ladle in Example 1-4 is higher than the liquidus temperature of the molten steel, 38°C, 38°C, 41°C, and 36°C. Refining is completed, and the argon gas soft blow time is ≧15min. In the continuous casting CC process, a small billet of 160* ^160mm2 is prepared by a 10-machine 10-flow arc-shaped continuous casting machine. The continuous casting adopts low superheat casting, the superheat of the molten steel is controlled to 10-25°C, the crystallizer electromagnetic stirring current is 250-350A, the frequency is 2-4Hz, the end electromagnetic stirring current is 300-400A, the frequency is 5-10Hz, the drawing speed is controlled according to the target of 1.70m/min, the secondary cooling total water intensive cooling is adopted, and the secondary cooling specific water amount is controlled to 1.6-1.8L/kg. In addition, the slab is cast at the electromagnetic stirring point at the discharge end, and intensive water cooling is performed so that the water flow rate is controlled to 3.0m ³ /h, which shrinks the casting flow housing, and the effect of "thermal soft reduction" is achieved, and the segregation of the slab is improved. The cross section of the slab is 160mm*160mm ² , and the main continuous casting process parameters are shown in Table 2.

The cast pieces produced by the above process are controlled so that the average carbon segregation value (obtained by sampling using the five-point drill sampling method) is ≦1.07.

The slab is cooled to below 100°C by a windshield stack, and the iron oxide skin on the surface of the slab is removed using a shot blast machine. Then, a layer of high-temperature decarburization prevention paint (ZK-003 type high-temperature decarburization prevention paint for steel slabs manufactured by Beijing Zhongke Xingye Environmental Engineering Co., Ltd. is applied to the surface of the slab. After the paint has dried, it is sent to the rolling factory for heating. The slab coated with the high-temperature decarburization prevention paint is heated by a high-temperature diffusion process and advanced at a uniform speed in the heating furnace. The time of the preheating stage of the heating furnace (shown in Figure 3) is controlled to 30-55 min, the first heating stage temperature is 950-1000°C, the time is 40-65 min, the second heating stage temperature is 1200-1230°C, the time is 65-105 min, the soaking stage temperature is 1220-1250°C, the time is 50-85 min, and the initial rolling temperature is 1180-1220°C. The steel pieces are heated in a reducing atmosphere in the heating furnace, the air-fuel ratio is controlled to 0.4-0.5, the heating furnace extraction interval is 117-190 s/piece, and the total steel piece heating time is 190-300 min.

The high-temperature laying process controls the laying temperature to 960-980°C, suppressing the precipitation of core network cementite, while optimizing the thickness of the iron oxide skin to 10-15 μm (the thickness of the iron oxide can be controlled by controlling the laying temperature and air cooling process), making it easier to remove the iron oxide skin by mechanically peeling off the wire.

After passing through the laying head, the wire is spread on the Stelmor roller table, and the air cooling strength of the fan is adjusted to achieve a temperature drop rate of 30-35℃/s during air cooling of 0-8s and a temperature drop rate of 15-30℃/s during air cooling of 9-17s. The phase transition process is close to isothermal transformation. The specific implementation method is as follows: The rolling fan is a centrifugal fan with an air volume of 200,000m3/h. During production, eight fans are turned on, and the air volume of the first to third fans along the wire's traveling direction is controlled to 90%, and the air volume of the fourth to sixth fans is controlled to 80%, so that the wire temperature quickly passes through the secondary cementite precipitation temperature zone, and the air volume of the seventh and eighth fans is adjusted to 70%, so that the phase transition is guaranteed at an isothermal temperature and the phase transition temperature rise is controlled to within 30℃ to ensure sufficient transformation of the wire structure.

The wire produced by the above process passed the tests for segregation, reticulated carbide, and decarburization, and the details are shown in Table 3.

The above is merely a specific preferred embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any equivalent replacement or modification made by any person skilled in the art based on the technical means and concept of the present invention within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention.

The present invention is not limited to the specific embodiments described above, and a person skilled in the art may implement the present invention in many other specific embodiments based on the contents disclosed in the present invention, or simple changes or modifications made based on the design structure or concept of the present invention are all within the scope of protection of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other as long as they do not conflict with each other.

Claims (6)

A method for controlling segregation and reticulated carbide in a 86-grade high-strength cord steel wire rod, comprising the steps of:
The process includes a KR hot metal pre-desulfurization process, a BOF converter smelting process, an LF furnace refining process, a continuous casting CC process, a slab surface treatment process, a slab heating process, a rolling control process, and a cooling control process, which are carried out in sequence.
The weight percentages of the components of the 86-grade high-strength cord steel wire rod are C: 0.85-0.90%, Si: 0.15-0.35%, Mn: 0.40-0.60%, P: ≦0.015%, S: ≦0.010%, Cr: ≦0.010%, Al: ≦0.005%, and the remainder being Fe and unavoidable impurity elements;
In the BOF converter smelting process, the P mass content in the finished product is controlled to be ≦0.010%, the S mass content ≦0.008%, and the total mass content of P and S is controlled to be ≦0.016%,
In the LF furnace refining process, the refining process adopts silicon carbide deoxidation, the refining slag adopts CaO- _SiO2 binary slag system, the alkalinity of the final refining slag is controlled to 0.7-1.0, argon gas is blown from the bottom of the boiler in the later stage of refining, and the composition and temperature of the molten steel are adjusted to ensure that the temperature of the boiler is higher than the liquidus temperature of the molten steel, which is 35-45°C, and when refining is completed, the argon gas soft blowing time is ≧15min;
In the continuous casting CC process, a slab with a cross section of ≦160* ^160mm2 is prepared. Continuous casting adopts low superheat casting, and the superheat of the molten steel is controlled to be 10-25°C. The crystallizer electromagnetic stirring current is 250-350A, the frequency is 2-4Hz, the end electromagnetic stirring current is 300-400A, the frequency is 5-10Hz, and the drawing speed is controlled to be 1.60-1.75m/min. Secondary cooling total water intensive cooling is adopted, and the secondary cooling specific water amount is controlled to be 1.6-1.8L/kg. The slab is cast at the outlet end electromagnetic stirring point and water cooling is performed.
In the slab surface treatment process, the slab is cooled to below 100°C by a windshield stack, and the iron oxide skin on the slab surface is removed by a shot blasting machine. Then, a layer of high-temperature decarburization prevention paint is applied to the surface of the slab. The powder and liquid mass ratio in the paint is 3:2, and the thickness of the paint film is controlled to be 0.2-1.0 mm. After the paint is dried, the slab enters the steel slab heating process.
In the slab heating process, the slab coated with high-temperature decarburization prevention paint is heated by a high-temperature diffusion process and moved forward at a uniform speed in a heating furnace; the time of the preheating stage of the heating furnace is controlled to 30-55 min; the first heating stage temperature is 950-1000°C, the time is 40-65 min; the second heating stage temperature is 1200-1230°C, the time is 65-105 min; the soaking stage temperature is 1220-1250°C, the time is 50-85 min; the initial rolling temperature is 1180-1220°C; the slab is heated in a reducing atmosphere in the heating furnace; the air-fuel ratio is controlled to 0.4-0.5; the heating furnace withdrawal interval is 117-190 s/piece; and the total slab heating time is 190-300 min;
In the rolling control process, the laying temperature is controlled to 960-980°C to suppress the precipitation of core network cementite, while optimizing the thickness of the iron oxide skin to 10-15μm, and the specification of the rolled wire rod is φ5.5mm;
In the cooling control process, the wire is spread on the Stelmor roller table after passing through the laying head, and the fan is adjusted to perform wind cooling at a temperature drop rate of 30-35°C/s from 0 to 8 s, and then wind cooling at a temperature drop rate of 15-30°C/s from 9 to 17 s, thereby controlling the relative temperature rise before and after to be less than 30°C .
2. A method for controlling segregation and reticulated carbide in a 86 class high strength cord steel wire rod. In the KR hot metal pre-desulfurization process, 3-6 kg/ton of desulfurizing agent such as lime is added to the hot metal ladle and strong mechanical stirring is performed to remove the S content in the hot metal so that the S content of the hot metal in the converter is guaranteed to be ≦0.003%, and then the desulfurization slag is removed.
2. The method for controlling segregation and reticulated carbide in a 86-grade high-strength cord steel wire rod according to claim 1. The method for controlling the content of P and S in the BOF converter smelting process is to use special clean scrap steel for the code, which accounts for 10%-30% of the total metal charge of the BOF converter, and when the silicon-manganese oxidation period of 5±1 min is completed by blowing in the converter, the gun is removed to remove the de-P slag, the gun is turned on again to make slag, and a combination of slag stopper cone and slag stopper slide plate is used in the tapping process, and slag outflow detection technology is installed to control the amount of slag outflow in the tapping process to be ≦50 kg.
2. The method for controlling segregation and reticulated carbide in a 86-grade high-strength cord steel wire rod according to claim 1. In the continuous casting CC process, the cast piece is prepared by a 10-machine 10-flow arc-shaped continuous casting machine, the arc radius of the casting machine is 10 m, the end electromagnetic stirrer is 7.2 m away from the meniscus, the length of the end electromagnetic stirrer is 700 mm, and the inner diameter is φ380 mm.
2. The method for controlling segregation and reticulated carbide in a 86-grade high-strength cord steel wire rod according to claim 1. The secondary cooling and total moisture cooling in the continuous casting CC process is carried out in the secondary cooling equipment.
The secondary cooling equipment includes a footrest roller, a first secondary cooling stage, a second secondary cooling stage, a third secondary cooling stage, and a fourth secondary cooling stage, which are arranged in this order from the upstream side to the downstream side, and the cooling water flow rate of the footrest roller stage is controlled to 9.0 to 11.0 m ³ /h, the cooling water flow rate of the first secondary cooling stage is controlled to 11.0 to 13.0 m ³ /h, the cooling water flow rate of the second secondary cooling stage is controlled to 8.0 to 10.0 m ³ /h, the cooling water flow rate of the third secondary cooling stage is controlled to 2.5 to 4.5 m ³ /h, and the cooling water flow rate of the fourth secondary cooling stage is controlled to 1.5 to 3.5 m ³ /h .
2. The method for controlling segregation and reticulated carbide in a 86-grade high-strength cord steel wire rod according to claim 1. In the cooling control process, the fan is a centrifugal fan with an air volume of 200,000 ^m3 /h, during production, 8 fans are turned on, the air volume of the 1st to 3rd fans along the wire rod moving direction is controlled to 90%, the air volume of the 4th to 6th fans is controlled to 80%, and then the wire rod is phase-transitioned at the position of the 7th and 8th fans, and the air volume of the 7th and 8th fans is adjusted to 70%;
2. The method for controlling segregation and reticulated carbide in a 86-grade high-strength cord steel wire rod according to claim 1.

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