CN113637907B - Production method of 72-grade cord steel with coarse breaking rate lower than 1.0 per kiloton - Google Patents
Production method of 72-grade cord steel with coarse breaking rate lower than 1.0 per kiloton Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
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- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/02—Dephosphorising or desulfurising
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C21C7/072—Treatment with gases
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C21C7/076—Use of slags or fluxes as treating agents
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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Abstract
The invention discloses a method for producing 72-grade cord steel with a rough wire breakage rate lower than 1.0 time/kiloton, which mainly comprises three stages: 1) smelting and refining, 2) continuous casting and heating of square billets, and 3) rolling and controlled cooling; the method is characterized in that: in the rolling and cooling control stage, stelmor cooling control is adopted for cooling control, and the concept of fast cooling before 630 ℃ and slow cooling after 630 ℃ is adopted for controlling. The rapid cooling treatment is carried out at the temperature of above 630 ℃, so that the sufficient supercooling degree can be ensured, and the abnormality of cementite is avoided; after 630 ℃, slow cooling can prolong the growth time of pearlite, so that the space between pearlite lamellae is larger, and iron scales are thicker and more compact. The 72-grade cord steel produced by the process has good plasticity and harness property and uniformity: the tensile strength of the wire rod is more than or equal to 950MPa, the elongation is more than or equal to 8 percent, the surface shrinkage is more than or equal to 36 percent, the same circle difference of the strength is less than or equal to 60MPa, the spacing between pearlite pieces is more than or equal to 130nm, and the thickness of iron scale is more than or equal to 12 mu m. And the user batch verification proves that the rough wire breaking rate in the deep processing process is lower than 1.0 time per kiloton, and the user requirements are met.
Description
Technical Field
The technical scheme belongs to the field of steel materials, and particularly relates to a production method of 72-grade cord steel with low rough wire breakage rate (less than 1.0 time/kiloton).
Background
The cord steel wire rod is a raw material for manufacturing a tire meridian, the demand is high, the downstream deep processing process comprises a plurality of working procedures, the first working procedure is mechanical descaling, and in the dephosphorization process, the wire rod is repeatedly bent, and the surface iron scale and the matrix are stripped, so that the wire rod has the subsequent drawing condition. The wire rod is only subjected to bending action during mechanical descaling and is not subjected to a drawing deformation process, and the fracture occurring during this process is called rough stretch-breaking. Manual welding is needed after the wire rod is subjected to rough drawing, the risk of breakage of materials in the subsequent processing process is increased, unnecessary manual labor is generated, and partial material waste is caused. According to the requirements of users, the rough wire breaking rate of 72-grade cord steel should be less than 1.0 times/kiloton, but the wire breaking rate level of the actual 72-grade cord steel is about 10.0 times/kiloton, which is far higher than the requirements of users.
The types of rough snapping of the cord steel wire rod mainly include three types: foreign matter is pressed in, necked down and leveled and brittle failure. Foreign matter is pressed into the surface of the wire rod, and foreign matters such as cutting nodules on the end part of a billet, broken roll collar particles in a rolling line and the like which are not cleaned are pressed into the surface of the wire rod, so that the integrity of the wire rod is damaged; the necking is mainly due to the fluctuation of tension in rolling, and the diameter of a wire rod becomes thin until the wire rod is broken by pulling; flush brittle failure is mainly caused by scratching of the surface of the wire rod during the transportation, and a crack source is formed. According to the occurrence frequency, three types of fractures are arranged as follows: flush brittle fracture (70%), neck (20%), foreign matter pressed in (10%).
Although the cord steel wire rod is in various forms, the rough breaking of the cord steel wire rod is in a strong relation with low plasticity and non-uniformity of the wire rod, the rough breaking phenomenon of the cord steel can be greatly reduced by improving the plasticity and the passing performance of the wire rod, the labor cost is reduced, the labor efficiency is improved, and the cord steel wire rod has obvious economic cost.
CN111534753A provides a chromium alloying cord steel wire rod and a production process, the chromium alloying cord steel wire rod comprises the following chemical components by weight percent: c: 0.68-0.82%, Mn: 0.20 to 0.40%, Si: 0.15-0.30%, Cr: 0.30 to 0.40 percent of Fe, less than or equal to 0.012 percent of P, less than or equal to 0.008 percent of S, less than or equal to 0.05 percent of Ni, less than or equal to 0.05 percent of Cu, less than or equal to 0.03 percent of Mo, less than or equal to 0.003 percent of Al, less than or equal to 0.002 percent of Ti, less than or equal to 0.002 percent of [ O ], less than or equal to 0.005 percent of [ N ], and the balance of Fe and inevitable impurities. The production process comprises the following steps: smelting molten steel, and adding chromium alloy in the process of converter tapping; refining to obtain molten steel; continuously casting molten steel obtained after refining to obtain a steel billet; and heating the steel billet to obtain a chromium alloying cord steel wire rod, and performing controlled cooling on the chromium alloying cord steel wire rod. The invention adopts micro-alloying, increases the chromium content, reduces the carbon content and the manganese content to make up the performance of the wire rod and the finished steel wire, improves the carbon segregation of the wire rod, reduces the probability of forming net carbon, can simultaneously improve the plasticity and the processing performance of the wire rod and reduce the stranding and wire breaking rate of the steel wire rod cord thread processing process. The patent application emphasizes that the performance of the wire rod is improved by adopting the microalloying of the cord steel, and the concept that the excellent structure is obtained by improving the cooling control and further the rough drawing and wire breaking rate of the wire rod is obviously different from the concept of the invention.
CN111069280A discloses a method for producing a low-strength cord steel wire rod, which is characterized in that parameters such as the number of cooling water tanks, the pressure of a water cooling tank, the spinning temperature, the roller speed, the air volume of a fan and the like after finish rolling are designed, the spinning temperature is controlled to be 935-950 ℃, the roller speed at an inlet section is controlled to be 0.65-0.90 m/s, the opening and closing of the fan and a heat-insulating cover are reasonably adjusted, and the temperature of each area is controlled, so that the purpose of improving the tissue performance of the wire rod is achieved. The wire rod produced by the technical scheme has the following properties: the tensile strength of the 72-grade cord steel wire rod is 700-980 MPa; the tensile strength of the 82-grade cord steel wire rod is 900-1100 MPa; the tensile strength of the 92-grade cord steel wire rod is 1000-1230 MPa; the sorbite content of the cord steel wire rod of any level is less than or equal to 80 percent, the level of the network carbide is less than or equal to 3, and the size of the pearlite colony is 20-40 mu m. The technical scheme can improve the quality problems of the core part and the surface of the wire rod generated in the drawing process, and the wire breakage rate in the drawing and stranding processes can be reduced by more than 50%. The emphasis of the improvement in this patent application is in the pull break and strand break, which are significantly different from the rough pull (shucking) break in strength of the present invention.
CN109082597A discloses a hot-rolled wire rod for a cord with 2000mpa tensile strength and a production method thereof. The wire rod comprises the following components in percentage by weight: c: 0.59 to 0.64%, Si: 0.36-0.40%, Mn: 0.10-0.14%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, Cr: 0.10-0.25%, B: 0.0005 to 0.0015%. The production method comprises the following steps: smelting in a converter; RH vacuum treatment; continuously casting into small square billets; slowly cooling the casting blank; heating a casting blank; carrying out high-speed rolling; spinning; air-cooling and standby. By reducing the carbon content, improving the silicon content and matching process, the diameter of the wire rod can reach 3.0-3.5 mm on the premise of ensuring that the tensile strength is more than 4000MPa, so that the homogenization performance of the wire rod section structure is better, the gamma crystal grains are micronized, the aging during wire drawing processing is inhibited, and the fracture of cementite is inhibited; and the strength and the wire drawing limit of the wire are improved, the number of times of strand twisting and wire breaking is not more than 2 per ton of steel, and the secondary processing of a user can be omitted and simplified, so that the production cost is reduced and the production efficiency is improved. CN109023073A discloses a hot-rolled wire rod for a cord thread with the tensile strength of 3000mpa and a production method thereof. The wire rod comprises the following components in percentage by weight: c: 0.65 to 0.70%, Si: 0.36-0.40%, Mn: 0.10-0.14%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, Cr: 0.10-0.25%, B: 0.0005 to 0.0015%. The production method comprises the following steps: smelting in a converter; RH vacuum treatment; continuously casting into small square billets; slowly cooling the casting blank; heating a casting blank; carrying out high-speed rolling; spinning; air-cooling and standby. By reducing the carbon content, improving the silicon content and matching process, the diameter of the wire rod can reach 3.0-3.5 mm on the premise of ensuring that the tensile strength is more than 4000MPa, so that the homogenization performance of the wire rod section structure is better, the gamma crystal grains are micronized, the aging during wire drawing processing is inhibited, and the fracture of cementite is inhibited; and the strength and the wire drawing limit of the wire are improved, the number of times of strand twisting and wire breaking is not more than 2 per ton of steel, and the secondary processing of a user can be omitted and simplified, so that the production cost is reduced and the production efficiency is improved. CN109023074A discloses a hot-rolled wire rod for cord thread with 4000 MPa-level tensile strength, which comprises the following components in percentage by weight: c: 0.71-0.75%, Si: 0.36-0.40%, Mn: 0.10-0.14%, P is less than or equal to 0.01%, S is less than or equal to 0.01%, Cr: 0.10-0.25%, B: 0.0005 to 0.0015%. The production method comprises the following steps: smelting in a converter; RH vacuum treatment; continuously casting into small square billets; slowly cooling the casting blank; heating a casting blank; carrying out high-speed rolling; spinning; air-cooling and standby. By reducing the carbon content, improving the silicon content and matching process, the diameter of the wire rod can reach 3.0-3.5 mm on the premise of ensuring that the tensile strength is more than 4000MPa, so that the homogenization performance of the wire rod section structure is better, the gamma crystal grains are micronized, the aging during wire drawing processing is inhibited, and the fracture of cementite is inhibited; and the strength and the wire drawing limit of the wire are improved, the number of times of strand twisting and wire breaking is not more than 2 per ton of steel, and the secondary processing of a user can be omitted and simplified, so that the production cost is reduced and the production efficiency is improved. The above 3 patents mainly focus on different levels of strength of the components and corresponding processes, and do not relate to the rough pulling (shelling) matters of the present invention.
CN111996349A discloses a production method of a low-strength and high-elongation cord steel wire rod, which comprises the working procedures of smelting, continuous casting and continuous rolling, coping, billet heating, rolling, spinning and controlled cooling; the tensile strength of the produced cord steel wire rod is 950-1020 MPa, the interlayer spacing of pearlite plates is 0.2-0.25 mu m, the surface shrinkage is more than 40%, and the sorbitizing rate is 60-70%. The method of using a heat engine to roll and properly reducing the cooling speed after spinning is adopted to produce the low-strength and high-elongation cord steel wire rod with excellent indexes, thereby not only ensuring the subsequent drawing performance of the wire rod, but also improving the fatigue performance of the product by more than 15 percent, further prolonging the service cycle of the material and saving the material. This patent emphasizes the various structural and performance parameters of the finished wire rod and illustrates the excellent drawing and fatigue properties under these conditions, unlike the present invention.
CN109957711A discloses a cord steel wire rod and a production method thereof, wherein the wire rod comprises the following components in percentage by weight: [C]0.88 to 0.93 percent, 0.20 to 0.40 percent of [ Si ], 0.25 to 0.40 percent of [ Mn ], less than or equal to 0.010 percent of [ P ], 0.0060 to 0.012 percent of [ S ], 0.0005 to 0.0012 percent of [ Al ], 0.0004 to 0.0008 percent of [ Ti ], 0.0015 to 0.0025 percent of total oxygen and 0.15 to 0.35 percent of [ Cr ], and the balance of Fe and inevitable impurities. The production method comprises the steps of smelting, continuous casting, billet heating, rolling, spinning and cooling, the interlayer spacing of the pearlite plates of the produced cord steel wire rod is 0.14-0.17 mu m, and the wire rod has the wire breakage rate of 1-3 times per ton in the steel cord processing process. The yarn breakage rate refers to the drawing breakage and strand breakage, not the rough drawing (shucking) breakage emphasized by the present invention.
CN106480360A discloses a high-carbon steel wire rod and an oxide inclusion control method thereof. The wire rod comprises the following components in percentage by weight: 0.70-0.83% of C, 0.15-0.30% of Si, 0.45-0.55% of Mn, less than or equal to 0.013% of P, 0.0040-0.011% of S, 0.0005-0.0010% of Ca0.0003-0.0008% of Mg. The control method of the oxide inclusion of the high-carbon steel wire rod comprises the steps of converter smelting, LF furnace refining, continuous casting, continuous rolling and wire rod rolling, wherein the top slag component of the LF refining is CaO 40-55%, SiO 30-45%, MgO 5-10%, AlO 3-8%, and the oxide inclusion component in steel is CaO-SiO-AlO-MgO system; refining the molten steel for 40-60 min; the refining temperature is 1450 and 1520 ℃; in the refining process, the Ca content of ferrosilicon and ferromanganese added is 0.015-0.05 percent, and the Mg content is 0.02-0.05 percent. The oxide inclusion size of the cord steel wire rod produced by the scheme is not more than 15um, and the broken wire is not more than 0.4 times per ton in the production process of a monofilament 0.20mm cord steel wire. This patent emphasizes a method of inclusion control and its benefits on strand breakage rate, not related to rough draw (shucking).
CN108396221A discloses a high-carbon steel wire rod for low-mesh cementite precipitation for filament drawing and a production method thereof. 0.79 to 0.84 percent of C, 0.20 to 0.40 percent of Si, 0.45 to 0.55 percent of Mn0.010 percent, less than or equal to 0.010 percent of P, 0.0020 to 0.010 percent of S, 0.0005 to 0.00010 percent of Al0.0002 to 0.0006 percent of Ti0.0005 to 0.0025 percent of total oxygen, and the balance of iron and inevitable impurities. The high-carbon steel wire rod is used for producing fine steel wires with the diameter of 0.22mm, the broken wire rate of the produced steel wire cords is not more than 3 times per ton, and the use requirements of users are met.
CN105506479 discloses a wire rod for a 70-grade cord outer winding wire and a production method thereof. The steel comprises the following components in percentage by weight: c: 0.68-0.72%, Mn: 0.20-0.45%, Si: 0.20-0.40%, P is less than or equal to 0.010%, S is less than or equal to 0.010%, Mg: 0.0003% -0.0008%, Ca: 0.0002% -0.006%, total oxygen: 0.0015-0.0025%, Cu less than or equal to 0.05%, and the balance of iron and inevitable impurities. The method comprises the steps of refining LF at 1540-1590 ℃ for 60-120 minutes; the superheat degree of molten steel of the continuous casting tundish is not more than 30 ℃; the cooling speed of the rolled wire rod before phase change is 10-15 ℃/s, the phase change temperature is 650-670 ℃, and the wire rod coiling temperature is 250-400 ℃. The sorbite content of the produced wire rod is between 65 and 80 percent, and the wire breakage rate is not more than 0.4 times per ton.
CN102268596 provides a high-carbon steel wire rod for producing thin steel wires, which comprises the following chemical components in percentage by weight: c: 0.6% -0.88%, Si: 0.1-1.0%, Mn: 0.3 to 1.0 percent of the total weight of the alloy, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.020 percent of P + S, less than or equal to 0.004 percent of N, less than or equal to 0.002 percent of O, less than or equal to 0.002 percent of Al, less than or equal to 0.002 percent of Ti, less than or equal to 0.001 percent of Mg, less than or equal to 0.1 percent of other inevitable impurities and the balance of iron. The high-carbon steel wire rod has reasonable component design, excellent processing performance, low melting point of inclusions in the wire rod, elongation along the rolling direction in the hot rolling process, length-width ratio larger than 3, and capability of reducing the wire breakage rate of a steel wire processing process by 16-28%.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for producing 72-grade cord steel with low rough wire breakage rate (less than 1.0 time per kiloton) aiming at the defects of the prior art, so that the manual welding is reduced, the fracture risk of materials in the post-processing process is reduced, and the unnecessary waste of the materials is avoided.
The technical scheme adopted by the invention for solving the problems is as follows:
a production method of 72-grade cord steel with low rough wire breakage rate (less than 1.0 time/kiloton) comprises the following chemical components in percentage by weight: 0.69-0.73% of C, 0.20-0.45% of Si, 0.45-0.65% of Mn, less than or equal to 0.015% of P, less than or equal to 0.015% of S, less than or equal to 0.10% of Cu, less than or equal to 0.20% of Ni, 0.10-0.18% of Cr, less than or equal to 0.15% of (Nb + V + Ti), less than or equal to 0.007% of N, less than or equal to 0.008% of Als, and the balance of Fe and impurity elements; the production process comprises the following steps: molten iron desulphurization → converter smelting → argon blowing → LF furnace treatment → square billet continuous casting → square billet heating → high speed wire rolling → stelmor controlled cooling → coil collection. The specific process method comprises the following steps:
2) molten iron desulphurization: a magnesium powder spraying desulfurization process is adopted, and the [ S ] discharged from a station is less than or equal to 0.010 percent;
2) smelting in a converter: the tapping temperature is 1630-1700 ℃; tapping time is more than or equal to 4 min; C. mn and Si are controlled according to the lower limit of standard components;
3) argon blowing: the time of bottom argon blowing is more than or equal to 4min; argon pressure is 0.3-0.6 MPa; argon flow of 7.0-10.0 Nm 3 /min；
4) And (3) LF furnace treatment: CaO-SiO adopted in LF refining 2 -Al 2 O 3 Refining the slag system, and controlling the target value of the slag alkalinity to be 1.5-3.5; the treatment time of the LF furnace is more than or equal to 28min, and argon is blown in the whole process;
5) and (3) square billet continuous casting: the superheat degree of the tundish molten steel is less than or equal to 25 ℃; the pulling speed is 1.00-1.30 m/min; the section size of the casting blank is 200 multiplied by 200mm, and the casting blank is specified to be 6000-6080 mm;
6) heating the square billet: the temperature of a rolling soaking section is 1070-1220 ℃, and the temperature difference of the cross section is less than or equal to 30 ℃; the furnace pressure is kept at micro positive pressure, and the atmosphere in the furnace is kept at weak reducing atmosphere; the furnace time is 125-185 min;
7) high-speed wire rolling: the initial rolling temperature is 950-1050 ℃, the temperature of the steel wire entering a finishing mill is 880-920 ℃, the temperature of the steel wire entering a reducing sizing mill is 890-930 ℃, the spinning temperature is 880-940 ℃, the outlet speed of 20 frames of pre-finish rolling is 7.8m/s, and the diameter of a wire rod is 5.5 mm;
8) stelmor controlled cooling: the stelmor air cooling line is 97 meters long, and totally 14 groups of fans are provided, and the air volume of No. 1-4 fans is 210000m 3 The air volume of a No. 5-10 fan is 154000m 3 The air volume of a No. 11-14 fan is 125000m 3 H is used as the reference value. The fan power turn-on condition is as follows: 80% of fan No. 1-2, 100% of fan No. 3-4, and 80% of fan No. 5 and subsequent fans, wherein all fans are adjusted to be 50% after the surface temperature of the wire rod is reduced to 630 ℃; the heat preservation cover is fully opened;
the stelmor air-cooled roller way speed is 0.80-1.04 m/s, the roller way starting speed is 0.8m/s, the 1-10 # fan roller way speed range is 1.03, and the maximum value of the 10# fan roller way speed is 1.04 m/s; the speed range of the No. 10-14 fan roller way is 0.95, and the speed of the No. 14 fan roller way is 0.85 m/s;
9) and (3) volume collection: and after the wire rod is cooled to room temperature in air, performing coiling, bundling and packaging to obtain the 72-grade cord steel with low rough wire breakage rate (less than 1.0 time/kiloton).
Preferably, in the step 6), the furnace pressure is kept at micro-positive pressure, the pressure range is 20-40Pa, the furnace cavity can be filled with furnace gas, external cold air is prevented from flowing in, and furnace end black steel and furnace temperature are prevented from greatly fluctuating; the atmosphere in the furnace is kept in a weak reducing atmosphere, mainly hydrogen and carbon monoxide, and can be realized by an air consumption coefficient, the range of the air consumption coefficient is 1.3-1.5, and the oxidation degree of the billet steel in the heating process can be slowed down.
Preferably, in the stelmor controlled cooling step, parameters are adjusted according to the external environment temperature to achieve the slow cooling effect. The following three cases can be specifically distinguished:
1) when the temperature of the external environment is lower than 5 ℃, the spinning temperature is preferably 880-900 ℃, 80% of a fan No. 1-2, 100% of a fan No. 3-4, 80% of a fan No. 5-6 and 50% of a fan No. 7-14, so as to ensure that the temperature of the wire rod is reduced to 630 ℃ to obtain a slow cooling effect;
2) when the external environment temperature is 5-20 ℃, the spinning temperature is preferably 900-920 ℃, a 1# to 2# fan is opened by 80%, a 3# to 4# fan is opened by 100%, a 5# to 7# fan is opened by 80%, and an 8# to 14# fan is adjusted to 50% so as to ensure that the slow cooling effect is obtained after the temperature of the wire rod is reduced to 630 ℃;
3) when the external environment temperature is higher than 20 ℃, the spinning temperature is preferably selected to be 920-940 ℃, the fan 1# to 2# is opened by 80%, the fan 3# to 4# is opened by 100%, the fan 5# to 8# is opened by 80%, and the fan 9# to 14# is adjusted to be 50% so as to ensure that the slow cooling effect is obtained after the temperature of the wire rod is reduced to 630 ℃.
The microstructure of the cord steel produced by the method has excellent characteristics, and specifically comprises the following steps: the structure is beneficial to cold drawing treatment, the scale shedding performance is good, and the phenomenon of rough stretch breaking is not easy to occur in the deep processing process.
Compared with the prior art, the invention has the beneficial effects that:
in the cold control process, the idea of fast cooling before 630 ℃ and slow cooling after 630 ℃ is adopted for control. The rapid cooling treatment is carried out at the temperature of above 630 ℃ (the rapid cooling speed range is more than or equal to 12.0 ℃/s), so that enough supercooling degree can be ensured, and abnormal precipitation of cementite is avoided; after 630 ℃, slow cooling (the slow cooling speed range is less than or equal to 7.5 ℃/s) can prolong the growth time of pearlite, so that the space between pearlite lamellae is larger, and the iron scale is thicker and more compact. The wire rod can be ensured to have stronger plasticity due to the larger distance between pearlite lamellae, the stripping integrity of the iron scale in the rough drawing process can be improved due to the thick and compact iron scale, and the surface scratch of the material caused by the adhesion of the small iron scale on the rough drawing wheel is avoided.
72-grade cord steel produced by the process of the invention
Has good plasticity and harness property and uniformity: the tensile strength of the wire rod is more than or equal to 950MPa, the elongation is more than or equal to 8 percent, the surface shrinkage is more than or equal to 36 percent, the same circle difference of the strength is less than or equal to 60MPa, the spacing between pearlite pieces is more than or equal to 130nm, and the thickness of iron scale is more than or equal to 12 mu m. And the 72-grade cord steel produced by the method is verified by users in batches, the rough wire breakage rate in the deep processing process is lower than 1.0 time per kiloton, and the requirements of the users are met.
Drawings
FIG. 1 shows the scanning electron microscope morphology of the spacing between the pearlite plates of the 72-grade cord steel wire rod produced by the process of the invention, and as shown in the figure, under the magnification of 30000 times, the spacing between the pearlite plates of the wire rod can be observed to be about 161nm, which is larger than the required lower limit range (not less than 130 nm).
FIG. 2 shows the scanning electron microscope morphology of the scale of the cross section of 72 grade cord steel produced by the process of the invention, and as shown in the figure, under the magnification of 2500 times, the thickness of the scale of the wire rod can be observed to be larger than the required lower limit range (not less than 12 μm).
Detailed Description
In order to better understand the present invention, the following examples are further provided to illustrate the content of the present invention, but the present invention is not limited to the following examples.
Examples 1 to 4
The embodiment provides a production method of 72-grade cord steel with low rough wire breaking rate (less than 1.0 time/kiloton), and the production flow is as follows: molten iron desulphurization → converter smelting → argon blowing → LF furnace treatment → square billet continuous casting → square billet heating → high speed wire rolling → stelmor controlled cooling → coil collection. The specific chemical components (excluding Fe and unavoidable impurities) of the 72-grade cord steel of each example are shown in table 1.
Table 1 table of chemical compositions (unit wt%) of examples
The specific process method of each embodiment is as follows:
1) molten iron desulphurization: the magnesium powder spraying desulfurization process is adopted, and the [ S ] discharged from the station is less than or equal to 0.010 percent;
2) smelting in a converter: the tapping temperature is 1630-1700 ℃; tapping time is more than or equal to 4 min; C. mn and Si are controlled according to the lower limit of standard components;
3) argon blowing: the time of bottom argon blowing is more than or equal to 4 min; argon pressure is 0.3-0.6 MPa; argon flow is 7.0-10.0 Nm 3/min;
4) and (3) LF furnace treatment: CaO-SiO adopted in LF refining 2 -Al 2 O 3 Refining the slag system, and controlling the target value of the slag alkalinity to be 1.5-3.5; the treatment time of the LF furnace is more than or equal to 28min, and argon is blown in the whole process;
5) and (3) square billet continuous casting: the superheat degree of the tundish molten steel is less than or equal to 25 ℃; the pulling speed is 1.00-1.30 m/min; the section size of the casting blank is 200 multiplied by 200mm, and the casting blank is sized to be 6000-6080 mm;
6) heating a square billet: the temperature of a rolling soaking section is 1070-1220 ℃, and the temperature difference of the cross section is less than or equal to 30 ℃; keeping the furnace pressure at micro-positive pressure, wherein the pressure range is 20-40 Pa; the weak reducing atmosphere in the furnace is mainly hydrogen and carbon monoxide, and the air consumption coefficient range is 1.3-1.5; the furnace time is 125-185 min;
7) high-speed wire rolling: the initial rolling temperature is 950-1050 ℃, the temperature of the steel wire entering a finishing mill is 880-920 ℃, the temperature of the steel wire entering a reducing sizing mill is 890-930 ℃, the spinning temperature is 880-940 ℃, the outlet speed of 20 frames of pre-finish rolling is 7.8m/s, and the diameter of a wire rod is 5.5 mm;
8) stelmor controlled cooling: the stelmor air cooling line is 97 meters long, and totally 14 groups of fans are provided, and the air volume of No. 1-4 fans is 210000m 3 The air volume of a No. 5-10 fan is 154000m 3 The air volume of a No. 11-14 fan is 125000m 3 H is used as the reference value. The fan power turn-on condition is as follows: blower opening of No. 1-2 80%The fans 3# to 4# are opened by 100 percent, the fans 5# and the subsequent fans are opened by 80 percent, and all the fans are adjusted to be 50 percent after the surface temperature of the wire rod is reduced to 630 ℃; the heat preservation cover is fully opened;
the stelmor air-cooled roller way speed is 0.80-1.04 m/s, the roller way starting speed is 0.8m/s, the 1-10 # fan roller way speed range is 1.03, and the maximum value of the 10# fan roller way speed is 1.04 m/s; the speed range of the No. 10-14 fan roller way is 0.95, and the speed of the No. 14 fan roller way is 0.85 m/s;
9) and (3) volume collection: and after the wire rod is cooled to room temperature in air, performing coiling, bundling and packaging to obtain the 72-grade cord steel with low rough wire breakage rate (less than 1.0 time/kiloton).
In the stelmor cooling control step, parameters are adjusted according to the external environment temperature to achieve the slow cooling effect. The following three cases can be specifically distinguished:
1) when the temperature of the external environment is lower than 5 ℃, the spinning temperature is preferably 880-900 ℃, 80% of a fan No. 1-2, 100% of a fan No. 3-4, 80% of a fan No. 5-6 and 50% of a fan No. 7-14, so as to ensure that the temperature of the wire rod is reduced to 630 ℃ to obtain a slow cooling effect;
2) when the external environment temperature is 5-20 ℃, the spinning temperature is preferably 900-920 ℃, a fan 1# to 2# is opened by 80%, a fan 3# to 4# is opened by 100%, a fan 5# to 7# is opened by 80%, and a fan 8# to 14# is adjusted to 50% so as to ensure that the slow cooling effect is obtained after the temperature of the wire rod is reduced to 630 ℃;
3) when the external environment temperature is higher than 20 ℃, the spinning temperature is preferably selected to be 920-940 ℃, the fan 1# to 2# is opened by 80%, the fan 3# to 4# is opened by 100%, the fan 5# to 8# is opened by 80%, and the fan 9# to 14# is adjusted to be 50% so as to ensure that the slow cooling effect is obtained after the temperature of the wire rod is reduced to 630 ℃.
The main process parameters of each example are shown in table 2.
TABLE 2 Main Process parameters of the examples
As shown in figures 1 and 2, the pearlife sheet spacing of 72-grade cord steel wire rod produced in the example is larger than or equal to 130nm, and the iron scale thickness is larger than or equal to 12 μm. The results of the organization and performance tests for the various examples are shown in table 3.
TABLE 3 examples organization Properties and gross tensile failure
Remarking: the different diameters of the wire rods can cause the mechanical properties to change obviously, and the diameters of the 72-grade cord steel wire rods in the above embodiments of the invention are all
As can be seen from Table 3: 72 grade cord steel produced according to the process of the invention
Has good plasticity and harness property and uniformity: the tensile strength of the wire rod is more than or equal to 950MPa, the elongation is more than or equal to 8 percent, the surface shrinkage is more than or equal to 36 percent, the strength same circle difference is less than or equal to 60MPa, the spacing between pearlite pieces is more than or equal to 130nm, and the thickness of iron scale is more than or equal to 12 mu m; and through user batch verification, the rough wire breaking rate in the deep processing process is lower than 1.0 time per kiloton, and the requirements of users are met.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, many modifications and changes can be made without departing from the inventive concept of the present invention, and these modifications and changes are within the protection scope of the present invention.
Claims (6)
1. A production method of 72-grade cord steel with a rough breaking rate lower than 1.0 times per kiloton mainly comprises three stages: (1) smelting and refining, (2) continuous casting and heating of square billets, and (3) rolling and cooling control; the method is characterized in that: in the rolling and controlled cooling stage, the controlled cooling adopts a stelmor controlled cooling process of fast cooling before 630 ℃ and slow cooling after 630 ℃, the speed range of fast cooling is more than or equal to 12.0 ℃/s, and the speed range of slow cooling is less than or equal to 7.5 ℃/s;
the cord steel comprises the following chemical components in percentage by weight: 0.69-0.73% of C, 0.20-0.45% of Si, 0.45-0.65% of Mn, less than or equal to 0.015% of P, less than or equal to 0.015% of S, less than or equal to 0.10% of Cu, less than or equal to 0.20% of Ni, 0.10-0.18% of Cr, less than or equal to 0.15% of (Nb + V + Ti), less than or equal to 0.007% of N, less than or equal to 0.008% of Als, and the balance of Fe and impurity elements;
the production method comprises the following steps:
1) molten iron desulphurization: the magnesium powder spraying desulfurization process is adopted, and the [ S ] discharged from the station is less than or equal to 0.010 percent;
2) smelting in a converter: the tapping temperature is 1630-1700 ℃; tapping time is more than or equal to 4 min; C. mn and Si are controlled according to the lower limit of standard components;
3) argon blowing: the time of bottom blowing argon is more than or equal to 4 min;
4) LF refining: CaO-SiO adopted in LF refining 2 -Al 2 O 3 Refining the slag system, and controlling the target value of the slag alkalinity to be 1.5-3.5; the treatment time of the LF furnace is more than or equal to 28min, and argon is blown in the whole process;
5) and (3) square billet continuous casting: the superheat degree of the tundish molten steel is less than or equal to 25 ℃; the pulling speed is 1.00-1.30 m/min;
6) heating the square billet: the temperature of a billet soaking section is 1070 to 1220 ℃, and the temperature difference of the cross section is less than or equal to 30 ℃; the furnace pressure is kept at micro positive pressure, and the atmosphere in the furnace is kept at weak reducing atmosphere; the furnace time is 125-185 min;
7) high-speed wire rolling: the initial rolling temperature is 950-1050 ℃, the temperature of the steel plate entering a finishing mill is 880-920 ℃, the temperature of the steel plate entering a reducing sizing mill is 890-930 ℃, and the spinning temperature is 880-940 ℃;
8) stelmor controlled cooling: the stelmor air cooling line is 97 meters long, and totally 14 groups of fans are provided, and the air volume of No. 1-4 fans is 210000m 3 The air volume of a No. 5-10 fan is 154000m 3 The air volume of a No. 11-14 fan is 125000m 3 H; the fan power turn-on condition is as follows: 80% of fan No. 1-2, 100% of fan No. 3-4, and 80% of fan No. 5 and subsequent fans, wherein all fans are adjusted to be 50% after the surface temperature of the wire rod is reduced to 630 ℃; the heat preservation cover is fully opened;
the stelmor air-cooled roller way speed is 0.80-1.04 m/s, the roller way starting speed is 0.8m/s, the 1-10 # fan roller way speed range is 1.03, and the maximum value of the 10# fan roller way speed is 1.04 m/s; the speed range of the No. 10-14 fan roller way is 0.95, and the speed of the No. 14 fan roller way is 0.85 m/s;
9) and (3) volume collection: and after the wire rod is cooled to room temperature in air, performing coiling, bundling and packaging to obtain 72-grade cord steel with the rough wire breakage rate lower than 1.0 time/kiloton.
2. The method for producing 72 grade cord steel with a rough breaking ratio lower than 1.0 times/kiloton according to claim 1, wherein: in the rolling and cooling control stage, when the external environment temperature is lower than 5 ℃, the spinning temperature in the rolling step is selected to be 880-900 ℃, the blower No. 1-2, the blower No. 3-4, the blower No. 5-6 and the blower No. 7-14 of a stelmor air cooling line are respectively opened by 80%, 100% and 80% respectively;
when the external environment temperature is 5-20 ℃, the spinning temperature in the rolling step is 900-920 ℃, the blower No. 1-2 of the stelmor air cooling line is opened by 80%, the blower No. 3-4 is opened by 100%, the blower No. 5-7 is opened by 80%, and the blower No. 8-14 is adjusted to be 50%;
when the external environment temperature is higher than 20 ℃, the spinning temperature in the rolling step is selected to be 920-940 ℃, and the blowing temperature of the No. 1-2 fan of the stelmor air cooling line is 80%, the blowing temperature of the No. 3-4 fan is 100%, the blowing temperature of the No. 5-8 fan is 80%, and the blowing temperature of the No. 9-14 fan is adjusted to be 50%.
3. A method for producing 72 grade cord steel with a rough breaking ratio lower than 1.0 times per kiloton according to claim 1, characterized in that: in the step 3), the argon pressure is 0.3-0.6 MPa; argon flow of 7.0-10.0 Nm 3 /min。
4. A method for producing 72 grade cord steel with a rough breaking ratio lower than 1.0 times per kiloton according to claim 1, characterized in that: in the step 5), the section size of the casting blank is (200 +/-15) × (200 +/-15) mm, and the casting blank is 6000-6080 mm in fixed length.
5. A method for producing 72 grade cord steel with a rough breaking ratio lower than 1.0 times per kiloton according to claim 1, characterized in that: in the step 6), the furnace pressure is kept at micro-positive pressure, and the pressure range is 20-40 Pa; the furnace is in weak reducing atmosphere, and the air consumption coefficient ranges from 1.3 to 1.5.
6. A method for producing 72 grade cord steel with a rough breaking ratio lower than 1.0 times per kiloton according to claim 1, characterized in that: in the step 7), the finish rolling outlet speed is 7.8 +/-0.5 m/s, and the diameter of the wire rod is 5.5 +/-0.25 mm.
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