Manufacturing method of surface low-decarburization 70 steel wire rod

Abstract

The invention discloses a manufacturing method of a surface low-decarburization 70 steel wire rod. The 70 steel comprises the following smelting components in percentage by weight: 0.68-0.72% of C; 0.17% to 0.30% of Si; 0.60% to 0.70% of Mn; less than or equal to 0.020% of P; s: less than or equal to 0.010%; al: less than or equal to 0.004%; o: < = 40 PPM; n: < = 50 PPM; 0.10% or less of Ni; less than or equal to 0.10% of Cr; and 0.10% or less of Cu. The thickness of the surface decarburized layer of the 70 steel wire rod is smaller than or equal to 0.03 mm, no obvious decarburization phenomenon exists, and the requirement for no decarburization of the surface of the drawn steel wire is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-speed wire rod production, and particularly relates to a manufacturing method for 70 steel wire rods with low surface decarburization. Background Art

[0002] As a commonly used carbon steel for wire ropes, 70 steel is widely used in the manufacture of various types of wire ropes due to its high strength and good toughness. The wide application of this steel makes 70 steel occupy an important position in the wire rod market. According to the national standard "GB / T 4354-2008 Hot-rolled wire rods of high-quality carbon steel", for wire rods with a carbon content above 60, the decarburized layer depth ≤ 2.5D% or ≤ 2.0D%, and the decarburized layer depth of Φ5.5mm wire rods rolled by the normal production process is controlled within 1.0D%, which can meet the normal use requirements of customers. However, when downstream customers develop wire ropes for fishing, elevators, and automobiles, when the surface decarburization of the wire rod is serious, Widmanstatten structure or coarse ferrite is formed at the decarburized surface of the steel after wire annealing, and it extends inward along the grain boundaries, affecting subsequent drawing and use. As Figure 1 shown, where (a) is the surface decarburization state of the wire rod in the early stage, (b) is the surface decarburization state of the wire after drawing (attempting to reach 2.6mm); (c) is the decarburized morphology of the wire before heat treatment, and (d) is the decarburized morphology of the wire after heat treatment. In view of this, the decarburized layer of 70 steel produced by the existing process can no longer meet the use requirements. This requirement far exceeds the industry standard and is extremely difficult to control. To meet the processing requirements of customers' high-end products and enhance the market competitiveness of products, a manufacturing method for 70 steel wire rods with no surface decarburization is urgently needed.

[0003] According to the prior art, the published patent No. CN102284478B proposes a rolling method that can reduce the decarburization of high-carbon steel wire rods. This method includes continuous casting billet heating, rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and cooling in the Stelmor method. Rolling is carried out under low-temperature conditions. By adopting the forward-shifted stand rolling method, the final rolling speed is greater than 30m / s, thereby shortening the heating time, reducing the residence time of the steel billet in the high-temperature area, accelerating the rolling rhythm, reducing fuel consumption, improving the metal yield, increasing production efficiency, and reducing the harm of surface decarburization of high-carbon steel wire rods. Its advantage is that the heating time is shortened by the forward-shifted stand method, reducing the surface decarburization of the wire rod. However, the heating temperature of its steel billet is controlled at 910-950°C, and the furnace temperature is too low, which places a large load on conventional rolling mills and does not have universal applicability.

[0004] Publication No. CN103305675B proposes a method for controlling the decarburized layer on the surface of hot-rolled wire rods for steel cord. This method includes closing some burners at the adjacent position of the preheating section and the heating section during the step of heating the steel billet, and controlling the temperature of the preheating section at 700 - 760 °C with a preheating time of 56 - 66 minutes; the temperature of the first half of the heating section is 890 - 930 °C, the heating temperature of the second half of the heating section is 930 - 970 °C, and the heating time of the heating section is 56 - 66 minutes; the soaking section temperature is 970 - 1010 °C with a soaking time of 44 - 52 minutes; the rolling start temperature is 950 - 980 °C, and the spinning temperature is 860 - 890 °C, and the Stelmor controlled cooling line is used for cooling. Its advantage is that the temperature control is relatively low during the steel billet heating process, but the heating time of each heating section is relatively long, resulting in low production efficiency.

[0005] Publication No. CN104451084A proposes a method for manufacturing high-quality spring steel with a low decarburized layer. The specific steps are as follows: the first step is electric arc furnace smelting - ladle refining - continuous casting; the second step is rolling the 160 * 160 mm continuous casting bloom with a 1350 rolling mill - finishing; the third step is rolling wire rods or bars. The heating process of the heating furnace is that the soaking temperature is 900 - 1000 °C, the heating and holding time is ≥ 2 hours, the billet discharging temperature is 900 - 950 °C, and the temperature difference between the positive and negative sides is ≤ 40 °C. The controlled cooling process is that after rolling into wire rods or bars, it is cooled slowly online or the bars are stacked and cooled, all heat preservation covers are closed, the cooling rate is 40 - 80 °C / h, and the decarburized layer of the finished steel is less than 0.8D%. Its advantage is that it can effectively reduce the decarburized layer on the surface of the steel, but this method requires ingot blooming production, and the production line is limited.

[0006] Publication No. CN112899466A proposes a heating furnace control method for preventing decarburization of spring steel. The steel type of the spring round steel used is 60Si2MnA, and a three-section walking beam heating furnace and mixed gas are used as fuel for heating. To prevent decarburization, a heating and cooling rate system for different shutdown time periods is designed to avoid long-term high-temperature heating of the steel billet in the heating section; to reduce the time in the furnace, according to the rolling rhythm of each specification, a billet charging rule is formulated to match it, and the total time of the steel billet in the furnace is controlled within 90 - 110 min; according to the requirements of the time in the furnace and the rolling start temperature, a reasonable heating and warming curve is formulated to avoid long-term high-temperature heating; according to the decarburization-prone property of this material, the in-furnace atmosphere parameters are adjusted and formulated to match it. Its advantage is that decarburization control is achieved through detailed operations such as the heating and cooling rate system, billet charging rule, and heating and warming curve, but the decarburization control effect is not clear.

[0007] Therefore, in view of multiple factors affecting decarburization, the present invention optimizes process parameters such as the heating furnace temperature, furnace gas atmosphere, time in the furnace, and steel charging method through experiments to reduce the thickness of the decarburized layer on the surface of the wire rod. Summary of the Invention

[0008] The object of the present invention is to provide a manufacturing method for 70 steel wire rods with low surface decarburization. Through reasonable composition, smelting control, and the coordination of heating and rolling processes, 70 steel wire rods with low surface decarburization are produced.

[0009] The present invention is realized through the following technical solutions: A 70 steel wire rod with low surface decarburization, characterized in that it comprises the following components in mass percentages: C: 0.68 - 0.72%; Si: 0.17 - 0.30%; Mn: 0.60 - 0.70%; P: ≤0.020%; S: ≤0.010%; Al: ≤0.004%; O: ≤40 PPM; N: ≤50 PPM; Ni: ≤0.10%; Cr: ≤0.10%; Cu: ≤0.10%; the balance being Fe and unavoidable impurities.

[0010] The present invention also discloses the manufacturing method of the above-mentioned wire rod: including the steps of hot metal pretreatment, converter smelting, LF treatment, continuous casting, heating, rolling, cooling, finished product finishing, and slow cooling; characterized in that: In the smelting step: bottom blowing nitrogen / argon gas is switched during the later stage of converter blowing. Adding sinter ore, pellet ore at the end of blowing or purging nitrogen for temperature adjustment after blowing is prohibited. The control targets for the blowing end point are: C: ≥0.08%, P: ≤0.015%, tapping temperature: 1600°C - 1650°C. The addition sequence of deoxidizers and alloys is: calcium silicate barium - low-aluminum ferrosilicon - high-carbon ferromanganese, and a low-nitrogen carburizer is used to supplement carbon; appropriate amounts of deoxidizers are added for reblowing or overoxidized heats, and a carburizer is used for pre-deoxidation when starting to tap; the alloy addition amount is fine-tuned according to the hot metal composition, blowing control conditions, etc.; argon is blown throughout the tapping process; slag is blocked during tapping, and the ladle slag volume is strictly controlled, and long-term large argon stirring is avoided in the later stage of tapping. The target composition after the furnace is: C: 0.58 - 0.68%, Si: 0.15 - 0.25%, Mn: 0.50 - 0.65%, P: ≤0.015%, S: ≤0.018%, the temperature after the furnace: ≥1520°C. The molten steel enters the LF furnace station and keeps argon stirring, adding lime and fluorite in batches to make slag, and keeping the white slag time not less than 15 min. The composition is fine-tuned to the control range, and aluminum-containing materials are prohibited. The soft blowing time is ≥10 min, and 40 - 60 Kg of covering agent is added after soft blowing.

[0011] The continuous casting steps are as follows: control the superheat of the tundish at 28 ± 5°C, produce continuous casting billets with a cross-section of 168mm * 168mm, the drawing speed is 2.0 - 2.2m / min, maintain a constant drawing speed during casting, the water flow rate in the mold is 120 - 140 m³ / h, the parameters of the mold electromagnetic stirring are: current 250A, frequency 3Hz, the parameters of the final electromagnetic stirring are: current 320A, frequency 6Hz, maintain the tundish liquid level height: ≥850mm, the tundish slag thickness: ≤150mm, the thickness of the liquid slag layer: 5 - 8mm, the submerged nozzle insertion depth: 80 - 100mm, the tundish type: stopper ladle. It is necessary to confirm that there are no defects such as out-of-square and bulging in the steel billet that affect rolling.

[0012] The rolling steps are as follows: charge the steel into the reheating furnace in an empty step, control the soaking section temperature of the billet entering the furnace: 1060 - 1100°C, the air-fuel ratio: 0.7 ± 0.03 in the heating section, 0.6 - 0.65 in the soaking section, use descaling, the descaling water pressure: 13 - 15MPa. The temperature entering the first finishing mill: 860 - 920°C, the temperature entering the second finishing mill: 860 - 900°C, the spinning temperature: 860 - 890°C, the rolling speed: 100m / s.

[0013] The cooling steps are as follows: the starting speed of the air-cooling roller table: 0.9m / s, for the fans, fans 1 - 2 are turned on at 85%, fans 3 - 4 are turned on at 80%, fans 5 - 6 are turned on at 60%, and the heat preservation covers are fully opened.

[0014] The finished product finishing steps are as follows: cut off the white line at the head, the parts with unqualified dimensions and harmful defects, and there shall be no defects such as cracks, folds, ears, scabs, laminations and inclusions, etc. Gaskets are added to the head and tail of the wire rod and bagged for protection.

[0015] The slow cooling steps are as follows: after the wire coil is taken off the production line, it is put into the warehouse and centrally stacked for slow cooling.

[0016] Furthermore: the structure is sorbite + pearlite, and the chemical composition of the finished wire rod meets the requirements of the GB / T4354 - 2008 standard.

[0017] The advantages of the present invention are as follows: for the low decarburized 70 steel wire rod of the present invention, the surface decarburization problem of the wire rod is effectively solved by optimizing the reheating furnace process. There is no obvious decarburization phenomenon on the surface of the wire rod, and there are sporadic ferrite traces on the surface of individual samples, with a depth within 0.03mm. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the surface decarburization of the wire rod in the prior art; Figure 2 It is a schematic diagram of no decarburization on the surface of the wire rod in Example 70; Figure 3 It is the metallographic diagram of the structure of the wire rod in Example 70. Detailed Embodiments

[0019] The present invention discloses a surface low-decarburized 70 steel wire rod, which comprises the following components in mass percentage: C: 0.68 - 0.72%; Si: 0.17 - 0.30%; Mn: 0.60 - 0.70%; P: ≤0.020%; S: ≤0.010%; Al: ≤0.004%; O: ≤40 PPM; N: ≤50 PPM; Ni: ≤0.10%; Cr: ≤0.10%; Cu: ≤0.10%; the balance is Fe and unavoidable impurities.

[0020] The present invention also discloses a manufacturing method of the above-mentioned wire rod steel, which includes an iron melt pretreatment step, a converter smelting step, an LF treatment step, a continuous casting step, a heating step, a rolling step, a cooling step, a finished product finishing step, and a slow cooling step; wherein: The smelting step: During the later stage of converter blowing, the bottom blowing is switched from nitrogen to argon. It is prohibited to add sinter ore or pellet ore at the end of blowing or to purge nitrogen for temperature adjustment after blowing. The control targets for the blowing end point are: C: ≥0.08%, P: ≤0.015%, tapping temperature: 1600°C - 1650°C. Argon is blown throughout the tapping process, and the charging pipe is aligned with the steel flow to prevent alloy caking. Alloy is added when about 1 / 4 of the steel has been tapped and finished when 3 / 4 of the steel has been tapped. The tapping time is not less than 3 minutes. The addition sequence of deoxidizer and alloy is: calcium silicate barium - low-aluminum ferrosilicon - high-carbon ferromanganese, and a low-nitrogen carburizer is used; for reblowing or overoxidized heats, appropriate amounts of deoxidizer are added, and a carburizer can be used for pre-deoxidation; the alloy addition amount can be slightly adjusted according to the iron melt composition, blowing control conditions, etc.; argon is blown throughout the tapping process; slag is blocked during tapping, and the slag volume in the ladle is strictly controlled. Long-term large-argon stirring is avoided in the later stage of tapping. The post-furnace targets are: C: 0.58 - 0.68%, Si: 0.15 - 0.25%, Mn: 0.50 - 0.65%, P: ≤0.015%, S: ≤0.018%, post-furnace temperature: ≥1520°C. The molten steel enters the LF furnace station and keeps argon stirring. Lime and fluorite are added in batches to make slag, and the white slag time is not less than 15 minutes. A low-nitrogen carburizer is used, and it is prohibited to add aluminum-containing deoxidizer. It is prohibited to add alloy and carburizer during tapping or static blowing. The soft blowing time is ≥10 minutes, and 40 - 60 Kg of covering agent is added after soft blowing.

[0021] The continuous casting steps: Carry out full-process protected casting, use high-carbon steel protective slag, maintain a black slag state, and strictly prohibit the slag surface from turning red. Control the superheat of the tundish at 28 ± 5°C. The continuous casting billet is produced with a cross-section of 168mm * 168mm, the drawing speed is 2.0 - 2.2m / min, maintain a constant drawing speed during casting, and the drawing speed fluctuation does not exceed 0.1m / min. The water flow rate of the mold is 120 - 140 m³ / h. The parameters of the mold electromagnetic stirring: current 250A, frequency 3Hz. The parameters of the final electromagnetic stirring: current 320A, frequency 6Hz. Maintain the tundish liquid level height: ≥850mm, the tundish slag thickness: ≤150mm, the liquid slag layer thickness: 5 - 8mm, the submerged nozzle insertion depth: 80 - 100mm. Select a stopper ladle for the tundish type. The billet must be ensured to have no defects such as square deviation and bulging that affect rolling.

[0022] The rolling steps: Use a walking beam type reheating furnace for billet heating, the gas is a mixed gas of blast furnace gas + converter gas. The temperature of the preheating section of the reheating furnace is 800 - 900°C, the temperature of the heating section is 1000 - 1030°C, the temperature of the soaking section is 1060 - 1100°C, the air-fuel ratio is 0.60 - 0.65, and hot charging and empty-step steel charging are adopted; Turn on the descaling water, and the descaling pressure is 13 - 15MPa; The rolling process includes rough rolling, medium rolling, pre-finishing rolling, finishing rolling (6 + 4 distribution), and wire laying. The temperature entering the finishing rolling is 860 - 920°C, the temperature between finishing rolling stands is 860 - 900°C, the wire laying temperature is 860 - 890°C, the rolling speed is 100m / s. There are 2 groups of water tanks distributed before, between, and after the finishing rolling respectively, and control the temperature during the rolling process to the target range.

[0023] The cooling steps: Use a Stelmor air-cooling line to cool the wire rod. The roller speeds of each section of the air-cooling line are 900 / 950 / 1000 / 1100 / 1170 / 1240 / 1000 / 1010 / 1020 / 1060 / 1200 / 1250mm / s respectively. For the fans: Fans 1 - 2 operate at 85%, fans 3 - 4 operate at 80%, fans 5 - 6 operate at 60%, and all the heat preservation covers are opened.

[0024] The finished product finishing steps: Cut off the white line at the head, parts with unqualified dimensions and harmful defects, and there shall be no defects such as cracks, folds, ears, scabs, laminations, and inclusions. Add gaskets to the head and tail of the wire rod and cover with bags for protection.

[0025] The slow cooling steps: After the coil is taken off the line, it is put into the heat preservation storage, centrally stacked for slow cooling, and the heat preservation cloth is covered after stacking is completed.

[0026] The following further illustrates this solution through examples.

[0027] Examples: Select three components and carry out trial production of low-decarbonization 70 wire rod according to the following process. Specifically as follows: 1. Converter smelting: When smelting 70 steel in a converter, the hot metal charged meets the blowing requirements, as shown in Table 1.

[0028] Table 1 Hot metal composition and charging amount

[0029] During the blowing process, lime, magnesite lumps, dolomite lumps, etc. are added for slag making, dephosphorization, and desulfurization. At 9 minutes of blowing, the bottom blowing of nitrogen and argon is switched. The carbon content at the end of blowing is 0.082 - 0.098%, the phosphorus at the end is 0.012 - 0.014%, and the tapping temperature is 1616 - 1622°C. During the tapping process, 70 kg of calcium-silicon-barium is added to each ladle for deoxidation, alloys are added to increase silicon and manganese, and a low-nitrogen carburizer is used to supplement carbon. The alloy consumption and composition are shown in Table 2.

[0030] Table 2 Converter tapping alloy amount and post-furnace composition

[0031] 2. LF refining treatment: After the molten steel enters the LF furnace station, argon stirring is maintained throughout the process. Lime and fluorite are added in batches for slag making. The amount of active lime per ladle is 0.6 - 0.7 t, and the amount of fluorite balls is 0.2 - 0.3 t. Calcium carbide is used for deoxidation to make a reducing white slag, and the white slag time is maintained for not less than 15 minutes. Silicon-manganese, ferrosilicon, and low-nitrogen carburizer are added for composition adjustment based on the post-converter composition. After the composition and temperature meet the requirements of the steel grade control, it is taken out of the treatment position. The soft argon blowing time is 10 - 13 minutes, and 50 - 60 Kg of covering agent is added after soft blowing.

[0032] 3. Bloom continuous casting: For the bloom, the long nozzle of the tundish and the tundish are protected by argon blowing, and a covering agent is added to the tundish. During the casting process, a high-carbon steel protective slag is used, and the slag surface is maintained in a black slag state. The superheat of the molten steel in the tundish is 26 - 29°C. The constant drawing speed of 2.1 m / min is used for casting with a stopper ladle, the water flow rate of the mold is 129 - 132 m³ / h, and the electromagnetic stirring parameters of the mold are set: current 250 A, frequency 3 Hz, and the electromagnetic stirring parameters at the end: current 320 A, frequency 6 Hz. The casting process runs normally. The tundish liquid level height is measured at 880 mm, the tundish slag thickness is 93 mm, the liquid slag layer thickness of the mold is 6 mm, and the submerged nozzle insertion depth is 88 mm.

[0033] When 60 tons of molten steel is cast in the tundish, a sample is taken in the tundish to test the chemical composition, as shown in Table 3.

[0034] Table 3 Chemical composition of 70 steel (%)

[0035] The bloom section is 168 mm * 168 mm, without obvious square-off, bulging, scratching and other defects. The bloom is directly sent to the high-speed wire rod mill for charging by hot delivery.

[0036] 4. Rolling and cooling; The billets are hot-delivered, and the reheating furnace is charged with steel in an empty-step manner, with one empty step for each charged billet. The heating process is shown in Table 4.

[0037] Table 4 Heating process of 70 steel

[0038] After the billets are discharged from the furnace, high-pressure water descaling is used to remove the surface scale, and the descaling water pressure is 15 MPa. The billets pass through 6 roughing stands, 6 intermediate rolling stands, 6 pre-finishing stands and 10 finishing stands respectively, and the finishing stands are distributed as "6 + 4". The rolling process is shown in Table 5.

[0039] Table 5 Rolling process of 70 steel

[0040] After the wire rods are spun, they enter the air-cooling roller table for cooling. The speeds of the 1st - 12th sections of the roller table are 900 / 950 / 1000 / 1100 / 1170 / 1240 / 1000 / 1010 / 1020 / 1060 / 1200 / 1250 mm / s respectively. For the fans: the 1st - 2nd fans are turned on at 85%, the 3rd - 4th fans are turned on at 80%, the 5th - 6th fans are turned on at 60%, and the heat preservation covers are fully opened.

[0041] After the wire rods are coiled, they are subjected to finishing. The white line at the head, non-conforming dimensions and harmful defect parts are cut off. After adding gaskets at the head and tail of the coil, they are packed and covered with packaging bags for protection. After the coils are taken off the production line, they are stored in the warehouse and stacked centrally for slow cooling.

[0042] 5. Dimensional accuracy: The dimensions of 70 wire rods from different coils are randomly inspected, as shown in Table 6.

[0043] Table 6 Dimensional accuracy of 70 steel wire rods

[0044] 6. Physical properties: The mechanical properties and metallographic structure of the wire rods are inspected, as shown in Table 7. There is no decarburization phenomenon on the surface of the wire rods, and the structure is sorbite + pearlite, see Attachment Figure 2 ( Figure 2 Both A and B are the surface shapes at different angles), Figure 3 .

[0045] Table 7 Physical properties of 70 steel wire rods

[0046] 7. Usage effect of wire rods: According to the usage feedback, all 70 wire rod customers in each embodiment have used it. There is no obvious decarburization phenomenon on the surface of the wire rods rolled by the new process, which meets the requirements of no decarburization on the surface of the steel wire after the customer's drawing and the processing requirements of subsequent processes, and the usage effect is good.

Claims

1. A method for manufacturing a surface low decarburization 70 steel wire rod, characterized in that: The composition comprises the following components in mass percentage: C: 0.68-0.72%; Si: 0.17-0.30%; Mn: 0.60-0.70%; P：≤0.020%； S: ≤0.010%; Al: ≤0.004%; O: ≤40PPM; N: ≤50PPM; Ni: ≤0.10%; Cr: ≤0.10%; Cu: ≤0.10%; the rest are Fe and unavoidable impurities.

2. A method for manufacturing a surface low decarburization 70 steel wire rod as claimed in claim 1, comprising a molten iron pretreatment step, a converter smelting step, a LF treatment step, a continuous casting step, a heating step, a rolling step, a cooling step, a finished product finishing step, and a slow cooling step; characterized in that: The smelting steps are as follows: switching to bottom nitrogen and argon gas in the late stage of converter blowing; blowing endpoint control target: C: ≥0.08%, P: ≤0.015%, tapping temperature: 1600°C-1650°C; the order of adding deoxidizers and alloys: silicon calcium barium-low aluminum silicon iron-high carbon manganese iron, using low nitrogen carburizer; blowing argon throughout the tapping process; slag blocking tapping, strictly controlling the amount of slag under the ladle, and avoiding long-term large argon stirring in the late stage of tapping; target composition after the furnace: C: 0.58-0.68%, Si: 0.15-0.25%, Mn: 0.50-0.65%, P: ≤0.015%, S: ≤0.018%, and temperature after the furnace: ≥1520°C; molten steel enters the LF furnace station and keeps argon blowing and stirring, lime and fluorite are added in batches to make slag, and the white slag time is kept not less than 15min; soft blowing time is ≥10min, and 40-60Kg of covering agent is added after soft blowing; The continuous casting step: controlling the superheat of the tundish to 28±5°C, the continuous casting billet is produced with a cross section of 168mm*168mm, the pulling speed is 2.0-2.2m / min, the pulling speed is kept constant during the casting process, the water flow rate of the crystallizer is 120-140 m³ / h, the electromagnetic stirring parameters of the crystallizer are: current 250A, frequency 3Hz, the electromagnetic stirring parameters at the end are: current 320A, frequency 6Hz, the liquid level height of the tundish is maintained: ≥850mm, the slag thickness of the tundish is: ≤150mm, the thickness of the liquid slag layer is: 5-8mm, the water nozzle insertion depth is: 80-100mm, and the tundish type is selected as a stopper rod bag; the billet must ensure that there are no defects such as de-squareness and bulging that affect rolling; The rolling steps include: controlling the temperature of the soaking section of the billet into the furnace to be 1060-1100°C, the air-fuel ratio to be 0.7±0.03 in the heating section and 0.6-0.65 in the soaking section, dephosphorization is used, and the dephosphorization water pressure is 13-15MPa; the first finishing temperature is 860-920°C, the second finishing temperature is 860-900°C, the spinning temperature is 860-890°C, and the rolling speed is ≥100m / s; The cooling step: the initial speed of the air-cooled roller is 0.9 m / s, the fans are: 1-2# fans are turned on 85%, 3-4# fans are turned on 80%, 5-6# fans are turned on 60%, and the heat preservation cover is fully opened; The slow cooling step includes: the wire coils are put into storage after being taken off the production line, and are centrally stacked for slow cooling.

3. The method for manufacturing the surface low decarburization 70 steel wire rod according to claim 2, characterized in that: The prepared 70 steel wire rod has a structure of troostite + pearlite.

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