High-carbon steel wire rod suitable for mechanical descaling and production process of high-carbon steel wire rod

Abstract

The invention relates to a high-carbon steel wire rod suitable for mechanical descaling and a production process of the high-carbon steel wire rod. The high-carbon steel wire rod comprises the following chemical components: 0.81%-0.83% of C, 0.22%-0.30% of Si, 0.78%-0.83% of Mn, less than or equal to 0.015% of P, less than or equal to 0.012% of S, 0.27%-0.30% of Cr, less than or equal to 0.10% of V, less than or equal to 0.010% of Al, less than or equal to 0.10% of Ni, less than or equal to 0.10% of Cu, less than or equal to 0.0070% of N and the balance of Fe and impurities. The sorbite proportion in the wire rod structure is greater than or equal to 90%; the grain size grade is greater than or equal to 8.0 grade. The after-rolling controlled cooling technology is utilized to ensure that the thickness and the structure of the scale on the surface of the wire rod are suitable for mechanical descaling, and after-rolling waste heat is utilized for online aging treatment, so that the percentage reduction of area of the wire rod is increased, and the risk of brittle failure of the wire rod is reduced; and in addition, the uniformity of the same-circle performance of the wire rod is improved by adjusting technological parameters such as Jiangling, roller speed and air volume.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wire rod production, and particularly relates to a high-carbon steel wire rod suitable for mechanical descaling and a production process thereof. BACKGROUND

[0002] Prestressed steel strand is usually obtained by drawing and stranding after pickling of wire rod. Although the pickling method for treating the surface scale of the wire rod is efficient, it is easy to cause environmental pollution and has high production cost. Considering the environmental protection and cost reduction factors, the production of prestressed steel strand gradually develops towards the mechanical descaling method which is more environmentally friendly. However, the surface scale of the traditional prestressed steel strand wire rod is thin and very dense, which is particularly suitable for acid pickling removal. When the mechanical method is used to remove the surface scale of the wire rod, part of the scale will tightly adhere to the surface of the wire rod, which will cause the scale to be not removed completely, and the drawing powder cannot be effectively attached in the subsequent drawing process, thereby seriously affecting the drawing quality. In addition, due to the long aging period of high-carbon steel wire rod after rolling, brittle fracture of the wire rod often occurs when mechanical descaling is performed (a large stress needs to be applied to the wire rod). Therefore, it is necessary to develop a wire rod suitable for mechanical descaling and stable in performance, which can reduce environmental pollution and production cost while ensuring the drawing performance and effect of the wire rod.

[0003] A Chinese patent application with the publication number CN115090698A discloses a "SWRH82B wire rod rolling production process suitable for mechanical peeling", and the process flow is: billet heating→ high-pressure descaling→ rough and medium rolling→ finishing and reducing sizing→ wire drawing→ controlled cooling→ finishing and packaging. In the production process, the wire drawing temperature is controlled to be 930-950℃, the phase change pre-cooling speed is 12.1-14℃, the cover temperature is ≥560℃, and the cover air cooling is performed, so that a FeO proportion of about 70% and a thickness of ≥14μm of the scale structure suitable for mechanical peeling is finally obtained. Although the SWRH82B wire rod produced by the process can meet the requirements of mechanical peeling, the tensile strength of the wire rod fluctuates greatly, and the tensile strength fluctuation of the same circle is 40-120MPa, and the performance stability is poor.

[0004] The Chinese patent application with the publication number CN117772784A discloses a "production method of pickling-free 82B wire rod", in which the wire rod is controlled to have a wire drawing temperature of 930-950℃, and is cooled to have a wire drawing temperature of 930-750℃, 750-550℃ and 550-350℃ in sequence, and then is cooled out of the cooling chamber, so that the wire rod has an iron oxide scale thickness of ≥23μm, a tensile strength of 1130-1235MPa, and a range of 105MPa. By controlling the microstructure, thickness and phase structure of the iron oxide scale on the surface of the 82B wire rod in the hot rolling process, a 82B wire rod product with an iron oxide scale easy to peel off is produced, so that the pickling and phosphorizing processes can be omitted in the downstream drawing process, and the iron oxide scale can be completely removed by using a simple mechanical peeling process. Although the wire rod produced by the production method can meet the requirements of mechanical peeling, the contents of FeO and Fe3O4 in the structure of the iron oxide scale are not effectively controlled, which can easily lead to an excessively thick iron oxide scale, and after mechanical descaling, not only the material loss is large, but also the tensile strength of the wire rod fluctuates greatly, and the performance stability is poor. SUMMARY

[0005] The present application provides a high-carbon steel wire rod suitable for mechanical descaling and a production process thereof, which uses post-rolling controlled cooling technology to ensure that the thickness and structure of the iron oxide scale on the surface of the wire rod are suitable for mechanical descaling, uses the residual heat after rolling for "online aging" treatment to improve the wire rod reduction of area and reduce the risk of brittle fracture of the wire rod, and adjusts process parameters such as Jialing, roller speed and air volume to improve the uniformity of the performance of the wire rod.

[0006] In order to achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0007] A high-carbon steel wire rod suitable for mechanical descaling, the chemical composition of the wire rod is C: 0.81%-0.83%, Si: 0.22%-0.30%, Mn: 0.78%-0.83%, P≤0.015%, S≤0.012%, Cr: 0.27%-0.30%, V≤0.10%, Al≤0.010%, Ni≤0.10%, Cu≤0.10%, N≤0.0070%, and the balance is Fe and unavoidable impurities.

[0008] The sorbite in the wire rod structure is ≥90%, the grain size grade is >8.0 grade, and the decarburization layer thickness is ≤0.8%D, D being the diameter of the wire rod.

[0009] The tensile strength of the wire rod is 1180-1240MPa, and the reduction of area is ≥28%; the structure ratio of the iron oxide scale on the surface of the wire rod is FeO:Fe3O4=3:1, and the thickness of the iron oxide scale is 15-20μm.

[0010] A production process of high-carbon steel wire rod suitable for mechanical descaling, the production process comprising the following steps: hot metal pretreatment, converter smelting, LF refining, continuous casting, heating, rolling, wire drawing, air cooling, coil collecting and slow cooling; wherein the following processes are controlled:

[0011] 1) hot metal pretreatment: KR hot metal pretreatment is adopted, desulfurizing agent is sprayed into the hot metal ladle for desulfurization, the S content in the treated hot metal is less than or equal to 0.010%, and the slag is cleaned;

[0012] 2) converter smelting: the tapping temperature of the converter is controlled to be 1620-1640℃, argon is blown at the bottom of the ladle for stirring during tapping; the tapping composition is controlled to be, by mass percentage, C: 0.74%-0.77%, Si: 0.17%-0.22%, Mn: 0.72%-0.78%, Cr: 0.22%-0.27%, P≤0.015%, and Al≤0.006%; the adding sequence of the deoxidizer and alloy slag material is as follows: the silicon calcium barium is added after 30% of the tapping amount, the lime, silicon-manganese alloy and high-carbon chromium iron are added after 40% of the tapping amount, and the fluorite is added after 50% of the tapping amount;

[0013] 3) LF refining: the LF refining furnace is kept at a micro-positive pressure of 40-70kPa, arc heating is adopted, and the arc light is not leaked out; one or more than one of carbon powder, silicon-iron powder and silicon carbide is used as the deoxidizer, the white slag refining time is more than 15 minutes, the refining slag system comprises, by mass percentage, SiO2: 15%-23%, CaO: 45%-55%, Al2O3: 6-10%, MgO≤8%, and FeO+MnO≤0.8%; the refining slag system basicity R is controlled to be 2.0-3.0; the final slag basicity is controlled to be 2.0-3.0; the composition of the molten steel is adjusted to be, by mass percentage, C: 0.81%-0.83%, Si: 0.23%-0.28%, Mn: 0.78%-0.83%, Cr: 0.27%-0.30%, P≤0.015%, S≤0.012%, Al≤0.006%, Ti≤0.0030%, and N≤0.0050%; soft blowing is performed for 20-30 minutes, carbonized rice husk is added when the molten steel temperature reaches 1525-1535℃, and the molten steel is poured into the continuous casting machine;

[0014] 4) continuous casting: the tundish with a slag dam and the immersion type integral water gap with the argon sealing function are adopted during pouring, the water gap insertion depth is 100-120mm; the tundish is filled with argon and swept at least 3 minutes before pouring, the whole pouring process is protected by argon, the crystallizer protection slag is the protection slag special for the peritectic steel; the step starting speed is controlled to be 0.80-0.90m / min, the process speed is 1.95-2.05m / min, the crystallizer water flow is 130-140m 3 / h, the current of the end electromagnetic stirring is 250 A, the frequency is 3 Hz, the current of the end electromagnetic stirring is 320 A, the frequency is 8 Hz; the liquid level fluctuation in the crystallizer is controlled within the range of ±3 mm; the billet is discharged into the holding pit for slow cooling for more than 48 h or is hot sent to the rolling heating furnace;

[0015] 5) heating: the billet is heated by the regenerative heating furnace, the temperature of the preheating section is 800-950℃, the temperature of the heating section is 1090-1150℃, the temperature of the soaking section is 1130-1170℃, the heating time is 120-180 min, the air-fuel ratio is 0.50-0.60, and the residual oxygen content in the furnace is controlled to be less than 1.5% by volume;

[0016] 6) rolling: the open rolling temperature of the billet is 1010-1050℃, the initial rolling reduction is greater than 50 mm, the temperature entering the finishing rolling unit is 900-940℃, and the temperature entering the reducing and sizing unit is 910-940℃;

[0017] 7) wire drawing: the wire drawing temperature is 900-940℃;

[0018] 8) air cooling and slow cooling: the air cooling is carried out by the Stelmor air cooling line, each fan is equipped with a Jialing device, the cooling speed is controlled to be 0.5-20℃ / s, the roller speed is controlled in sections, the Stelmor air cooling line is equipped with a holding cover to realize slow cooling, the coiling temperature is controlled to be 550-650℃, and the thickness of the iron oxide skin on the surface of the coil is controlled to be in the range of 15-20μm.

[0019] In the molten iron pretreatment process, the desulfurizer is composed of 85%-95% lime powder and 5%-15% fluorite powder by mass percentage.

[0020] In the converter smelting process, the weight ratio of the molten iron is 85%-88%, and the weight ratio of the scrap steel is 12%-15%;

[0021] In the LF refining process, the auxiliary materials are added in the following order: the lime, fluorite and deoxidizer are added when the power is supplied for the first time; the lime and deoxidizer are supplemented according to the desulfurization condition when the power is supplied for the second time; the remaining time is divided into batches to add the silica and low-alkalinity composite slag, and the silicon carbide is used for deoxidation.

[0022] The full length of the scattered volume cooling line in the Stelmor air cooling line is 120.2m, and 9 groups of 25 centrifugal fans are arranged, wherein: the first group to the seventh group are each provided with 3 centrifugal fans, and 21 centrifugal fans are arranged along the longitudinal direction of the air cooling line; the eighth group and the ninth group are each provided with 2 centrifugal fans, and 4 centrifugal fans are arranged along the longitudinal direction of the air cooling line; the air volume of the first group and the second group of centrifugal fans is 205,000 cubic feet / h, and the air volume of the third group to the ninth group of centrifugal fans is 185,000 cubic feet / h; the air cooling line roller is divided into 14 sections, and the length of the first section and the last section is 4.6m, and the length of the second section to the thirteenth section is 9.25m; the adjustment mode of the Jialing device: the Jialing device corresponding to the first group of centrifugal fans, the second group of centrifugal fans, the third group to the ninth group of centrifugal fans, the cross-sectional area ratio of the two sides and the center air chamber is 4.0:1, 4.5:1 and 5.0:1 respectively, and the angle of the Jialing device is 33°, 30° and 27.2° respectively.

[0023] The frequency of the first group and the second group of centrifugal fans is set to 50Hz, and the frequency of the third group to the fifth group of centrifugal fans is set to 45Hz; the roller speed of the first section to the sixth section of the roller is set to 0.80m / s, 0.90m / s, 1.00m / s, 1.10m / s, 1.20m / s and 1.25m / s in turn; the roller speed of the seventh section to the fourteenth section is set to 1.30m / s.

[0024] The heat preservation cover is arranged in 22 groups along the longitudinal direction of the air cooling line, wherein the first group to the eleventh group of heat preservation covers are opened, and the twelfth group to the twenty-second group of heat preservation covers are closed; the PF line is provided with a heat preservation channel, and the coil is heat preserved at a temperature of 350-500 DEG C.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] 1) A kind of hot rolled high carbon steel wire rod for prestressed steel strand suitable for mechanical descaling, stable performance and not easy to brittle, while ensuring that the wire rod has high drawing performance, reduce environmental pollution, reduce production cost;

[0027] 2) Utilize the thickness and structure of the iron oxide skin on the surface of the wire rod after rolling controlled cooling technology to ensure that it is suitable for mechanical descaling, utilize the after-rolling residual heat to carry out "on-line aging" treatment, improve the wire rod section shrinkage, reduce the brittle risk of the wire rod;In addition, by adjusting the Jialing, roller speed, air volume and other process parameters, the uniformity of the wire rod performance (including mechanical properties, drawing performance and welding performance) in the same circle is improved;

[0028] 3) The tensile strength of the produced SWRH82B wire rod is 1180-1240MPa, the section shrinkage is greater than or equal to 28%, the proportion of sorbite is more than 90%, the grain size is more than 8.0, the decarburization layer thickness is less than or equal to 0.8D (D is the diameter of the wire rod), there is no abnormal structure such as grain boundary cementite and martensite, and the uniformity of the structure and performance is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the cooling temperature curve of the wire rod in the embodiment of the application.

[0030] Figure 2 is the micrograph one (grain size) of the wire rod finished product in the embodiment of the application.

[0031] Figure 3 is the micrograph two (structure) of the wire rod finished product in the embodiment of the application.

[0032] Figure 4 is the micrograph three (lamellar spacing of sorbite) of the wire rod finished product in the embodiment of the application.

[0033] Figure 5 is the micrograph four (thickness of iron oxide scale) of the wire rod finished product in the embodiment of the application. DETAILED DESCRIPTION

[0034] The high-carbon steel wire rod suitable for mechanical descaling provided by the application has the following chemical composition in terms of mass percentage: C: 0.81% to 0.83%, Si: 0.22% to 0.30%, Mn: 0.78% to 0.83%, P≤0.015%, S≤0.012%, Cr: 0.27% to 0.30%, V≤0.10%, Al≤0.010%, Ni≤0.10%, Cu≤0.10%, N≤0.0070%, and the balance being Fe and inevitable impurities.

[0035] The sorbite in the wire rod structure is ≥90%; the grain size grade is >8.0 grade; and the decarburized layer thickness is ≤0.8% D, D being the diameter of the wire rod.

[0036] The tensile strength of the wire rod is 1180 to 1240 MPa, and the reduction of area is ≥28%; the structure ratio of the iron oxide scale on the surface of the wire rod is FeO: Fe3O4=3:1, and the thickness of the iron oxide scale is 15 to 20 μm.

[0037] The production process of the high-carbon steel wire rod suitable for mechanical descaling provided by the application comprises the following steps: hot metal pretreatment, converter smelting, LF refining, continuous casting, heating, rolling, wire drawing, air cooling, coil collecting and slow cooling; and the following processes are controlled:

[0038] 1) hot metal pretreatment: KR hot metal pretreatment is adopted, and a desulfurizer is sprayed into the hot metal ladle for desulfurization, so that the S content in the treated hot metal is ≤0.010%, and the slag is clean;

[0039] 2) Converter smelting: the converter tapping temperature is controlled at 1620-1640℃, and the ladle bottom argon stirring is applied during tapping; the tapping composition is controlled at C: 0.74%-0.77%, Si: 0.17%-0.22%, Mn: 0.72%-0.78%, Cr: 0.22%-0.27%, P≤0.015%, and Al≤0.006% by mass percent; the adding sequence of deoxidizer and alloy slag material is as follows: the calcium-silicon-barium is added after the tapping amount reaches 30%, the lime, silicon-manganese alloy and high-carbon chromium iron are added after the tapping amount reaches 40%, and the fluorite is added after the tapping amount reaches 50%;

[0040] 3) LF refining: the LF refining furnace is kept at 40-70kPa micro-positive pressure, the submerged arc heating is adopted, and the arc light is not leaked out; one or more than one of carbon powder, silicon-iron powder and silicon carbide is used as deoxidizer, the white slag refining time is more than 15 minutes, the refining slag system includes SiO2: 15%-23%, CaO: 45%-55%, Al2O3: 6-10%, MgO≤8%, and FeO+MnO≤0.8% by mass percent, the refining slag system basicity R is controlled at 2.0-3.0, the final slag basicity is controlled at 2.0-3.0, the steel liquid composition is adjusted to C: 0.81%-0.83%, Si content 0.23%-0.28%, Mn: 0.78%-0.83%, Cr: 0.27%-0.30%, P≤0.015%, S≤0.012%, Al≤0.006%, Ti≤0.0030%, and N≤0.0050% by mass percent, the soft blowing is performed for 20-30min, the carbonized rice husk is added when the steel liquid temperature reaches 1525-1535℃, and the steel liquid is transferred to the continuous casting machine for pouring;

[0041] 4) Continuous casting: the tundish with slag dam and the immersion type integral water gap with argon sealing function are adopted during pouring process, the water gap insertion depth is 100-120mm; the tundish is purged with argon at least 3min before starting pouring, the argon protection is applied during the whole pouring process, the mold protection slag is the mold protection slag special for peritectic steel; the starting casting speed is controlled at 0.80-0.90m / min, the process casting speed is 1.95-2.05m / min, the mold water flow is 130-140m 3 / h, the first end electromagnetic stirring current is 250A and the frequency is 3Hz, the last end electromagnetic stirring current is 320A and the frequency is 8Hz; the mold liquid level fluctuation is controlled within the range of ±3mm; the billet is discharged into the holding pit for slow cooling for more than 48h or is hot sent to the rolling heating furnace;

[0042] 5) Heating: the billet is heated by the regenerative heating furnace, the preheating temperature is 800-950℃, the heating temperature is 1090-1150℃, the soaking temperature is 1130-1170℃, the heating time is 120-180min, the air-fuel ratio is 0.50-0.60, and the furnace residual oxygen content is controlled at less than 1.5% by volume ratio.

[0043] 6) Rolling: billet opening rolling temperature 1010-1050℃, initial rolling reduction ≥50mm, temperature entering finishing rolling mill 900-940℃; temperature entering reducing and sizing mill 910-940℃;

[0044] 7) Wire drawing: wire drawing temperature 900-940℃;

[0045] 8) Air cooling and slow cooling: air cooling is carried out by Stelmor air cooling line, each fan is equipped with a Jialing device, the cooling rate is controlled at 0.5-20℃ / s; the roller speed is controlled in sections; the Stelmor air cooling line is equipped with a heat preservation cover to realize slow cooling, the coiling temperature is controlled at 550-650℃; the iron oxide scale thickness on the surface of the wire rod is controlled within the range of 15-20μm.

[0046] In the molten iron pretreatment process, the desulfurizer is composed of 85%-95% lime powder and 5%-15% fluorite powder by mass percentage.

[0047] In the converter smelting process, the weight ratio of molten iron is 85%-88%, and the weight ratio of scrap steel is 12%-15%;

[0048] In the LF refining process, the auxiliary materials are added in the following order: lime, fluorite and deoxidizer are added when the power is supplied for the first time; lime and deoxidizer are supplemented according to the desulfurization condition when the power is supplied for the second time; the remaining time is divided into batches to add silica and low alkalinity composite slag, and silicon carbide is used for deoxidation.

[0049] The Stelmor air cooling line has a total length of 120.2m, and is equipped with 9 groups of 25 centrifugal fans, wherein: the 1st-7th groups are each equipped with 3 centrifugal fans, and the 21 centrifugal fans are arranged along the longitudinal direction of the air cooling line; the 8th and 9th groups are each equipped with 2 centrifugal fans, and the 4 centrifugal fans are arranged along the longitudinal direction of the air cooling line; the air volume of the 1st and 2nd centrifugal fans is 205,000 cubic feet / h, and the air volume of the 3rd-9th centrifugal fans is 185,000 cubic feet / h; the roller of the air cooling line is divided into 14 sections, and the length of the first section and the last section is 4.6m, and the length of the 2nd-13th sections is 9.25m; the adjustment mode of the Jialing device: the Jialing device corresponding to the 1st, 2nd, 3rd-9th centrifugal fans, the cross-sectional area ratio of the two sides to the center air chamber is 4.0:1, 4.5:1, 5.0:1 respectively, and the angle of the Jialing device is 33°, 30°, 27.2° respectively.

[0050] The frequency of the centrifugal fan of the first group and the second group is set to 50Hz, and the frequency of the centrifugal fan of the third group to the fifth group is set to 45Hz; the roller speed of the first section to the sixth section of the roller table is set to 0.80m / s, 0.90m / s, 1.00m / s, 1.10m / s, 1.20m / s and 1.25m / s in sequence; and the roller speed of the seventh section to the fourteenth section is set to 1.30m / s.

[0051] The heat preservation covers are arranged in 22 groups along the longitudinal direction of the air cooling line, wherein the first group to the eleventh group of heat preservation covers are opened, and the twelfth group to the twenty-second group of heat preservation covers are closed; the PF line is provided with a heat preservation channel, and the coiled wire is preserved at a temperature of 350-500℃.

[0052] In order to more directly embody the present application, the embodiments of the present application are further described in combination with examples. The following examples are merely preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any skilled person in the art can obtain the technical solutions within the technical range disclosed by the present application, including simple changes or equivalent replacements, which are within the protection scope of the present application.

[0053]

EXAMPLE

[0054] In the present embodiment, the chemical composition of the high-carbon steel wire rod is C: 0.81%, Si: 0.22%, Mn: 0.80%, Cr: 0.27%, P: 0.011%, S: 0.008%, Ni: 0.01%, Cu: 0.02%, V: 0.01%, Al: 0.004%, N: 0.042%, and the rest is Fe.

[0055] In the present embodiment, the high-carbon steel wire rod is produced by using the production process flow of “KR desulfurization pretreatment + 100t converter + LF refining + 150mm*150mm eight-flow square billet continuous casting + regenerative walking beam heating furnace heating + high-pressure water descaling + rough rolling + intermediate rolling + pre-precision rolling + precision rolling + reducing sizing + wire drawing + air cooling transportation + coil collecting + PF line heat preservation channel slow cooling”, and the specific process is as follows:

[0056] 1. Smelting:

[0057] 1) KR hot metal pretreatment: desulfurization agent (composition of 90% lime powder + 10% fluorite powder) is sprayed into the hot metal ladle for desulfurization, and the S content of the treated hot metal is ≤0.010%, and the slag is clean.

[0058] 2) Converter smelting: the proportion of molten iron is about 86%, the proportion of scrap steel is 14%, Ti, Mo, Ni scrap steel is prohibited to be added to prevent the formation of high hardness oxides and reduce the drawing performance of the material. The tapping composition is adjusted according to the lower limit of internal control to prevent carbonization and nitrogen content increase in the refining process. The tapping composition of this embodiment is C: 0.76%, Si: 0.19%, Mn: 0.73%, Cr: 0.24%, P: 0.011%; the tapping temperature is 1632℃, and the ladle is strongly stirred by argon bottom blowing during tapping. In order to ensure the residual aluminum and titanium content in the steel, low-aluminum alloy is added, and alumina slag is not allowed to be used, and the Al content in the steel is controlled below 0.006%. Ensure that the end point carbon content and temperature hit once, if secondary point blowing occurs, it must be treated by reducing the cover first.

[0059] 3) LF furnace refining: maintain a slight positive pressure (60kPa) in the LF refining furnace, use submerged arc heating, and the arc light does not leak out. The white slag refining time is 17 minutes, the refining slag system is SiO2: 18%, CaO: 52%, Al2O3: 7.2%, MgO: 6.4%, FeO+MnO: 0.43%, and the slag system basicity R is 2.1. The auxiliary material adding sequence is: add lime 200kg, fluorite 40kg, diffusion deoxidizer silicon carbide 75kg, and carbon powder 38kg at the first time of power transmission. According to the desulfurization situation, add lime 100kg, diffusion deoxidizer silicon carbide 42kg, and carbon powder 22kg at the second time of power transmission. Add silica 120kg and low basicity composite slag 200kg in batches during the remaining time, and use silicon carbide 20kg for deoxidation. The final slag basicity is 2.3. The steel composition is adjusted to C: 0.83%, Si: 0.24%, Mn: 0.81%, Cr: 0.28%, P: 0.007%, S: 0.004%, Al: 0.002%, Ti: 0.0022%, N: 0.0031%. The soft blowing time is 23min, and carbonized rice husk 70kg is added when the steel liquid temperature reaches 1530℃, and then it is transferred to the continuous casting machine for pouring.

[0060] 2, continuous casting: use six-machine six-stream arc-shaped 150mmx150mm square billet continuous casting machine for pouring, use tundish with slag wall during pouring process, the immersion type integrated water gap is sealed by sealing pad and has argon sealing capacity, the water gap insertion depth is 120mm. The tundish is purged with argon 3min before pouring, the whole pouring process is protected by argon, and the crystallizer protection slag adopts the crystallization steel special protection slag. The starting speed control is 0.90m / min, the process speed is 2.0m / min, the crystallizer water flow is 135m 3 / h, the first end electromagnetic stirring current is 250A, the frequency is 3Hz, the last end electromagnetic stirring current is 320A, the frequency is 8Hz, and the liquid level fluctuation in the crystallizer is ≤±3mm. The steel billet is directly hot sent to the rolling heating furnace.

[0061] 3, rolling:

[0062] 1) Billet heating: heating using a regenerative heating furnace, preheating section temperature 931 °C, heating section temperature 1121 °C, soaking section temperature 1157 °C, heating time 144 min, air-fuel ratio 0.58, furnace residual oxygen content 1.1%.

[0063] 2) Controlled rolling: billet size 150 mm x 150 mm, rolled product size Rolled using Morgan 6th generation mill set; billet breakdown temperature 1035 °C, initial rolling using 65 mm large reduction amount, entry to finishing mill set temperature 923 °C, entry to reducing sizing temperature 931 °C, wire rod delivery temperature 916 °C. By increasing the controlled rolling temperature and wire rod delivery temperature, the wire rod surface oxide scale thickness can be effectively increased, in this embodiment the wire rod surface oxide scale thickness is 16 μm.

[0064] 3) Controlled cooling: controlled cooling using Stelmor air cooling line, air cooling line spreader cooling line total length 120.2 meters, equipped with 9 groups of 25 centrifugal fans, the 1st to 7th groups each equipped with 3 centrifugal fans for a total of 21 centrifugal fans, arranged along the longitudinal direction of the air cooling line; the 8th to 9th groups each equipped with 2 centrifugal fans for a total of 4 centrifugal fans, arranged along the longitudinal direction of the air cooling line. The air volume of the 1st to 2nd groups of centrifugal fans is 205,000 cubic feet / h, the air volume of the 3rd to 9th groups of centrifugal fans is 185,000 cubic feet / h. Each centrifugal fan is equipped with a Jialing device, and the air cooling line is equipped with a heat preservation cover to achieve delayed cooling. The controlled cooling rate in this embodiment is 6 °C / s. To achieve delayed cooling and standard cooling, the air cooling line roller bed is divided into 14 sections, the first section is 4.6 meters long, the 2nd to 13th sections are each 9.25 meters long, and the 14th section is 4.6 meters long, each section of the roller bed is equipped with an independent motor to achieve segmented control of the roller bed speed.

[0065] ① Jialing device adjustment; the Jialing adjustment corresponding to the 1st, 2nd, and 3rd to 9th groups of centrifugal fans is that the cross-sectional area ratio of the two sides to the center air chamber is 4.0:1, 4.5:1, and 5.0:1, respectively, i.e. the Jialing device angle corresponding to the 1st, 2nd, and 3rd to 9th groups of centrifugal fans is 33°, 30°, and 27.2°, respectively. This allows the coil to have uniform temperature changes at the early cooling stage (900-650 °C), the middle phase transformation stage (550-650 °C), and the late slow cooling stage (350-500 °C), and ensures that the performance difference between the lap joint and non-lap joint positions changes as little as possible.

[0066] ②Controlled cooling parameter adjustment; the frequency of the first and second group of centrifugal fans is set to 50HZ, and the frequency of the third to fifth group of centrifugal fans is set to 45HZ. The roller speeds of the first to sixth roller tables are 0.80m / s, 0.90m / s, 1.00m / s, 1.10m / s, 1.20m / s, and 1.25m / s, respectively, and the roller speeds of the seventh to fourteenth roller tables are 1.30m / s. In order to obtain a high tensile strength of the wire rod, a fast cooling speed (900→650℃) is used in the early stage, the cooling speed is 12-15℃ / s, and a small air volume is used in the intermediate stage to offset the back temperature generated by the phase transition, so that the coil temperature is controlled at 550-650℃.

[0067] ③Slow cooling parameter adjustment; the first to eleventh group of heat preservation covers are opened, and the twelfth to twenty-second group of heat preservation covers are closed; a heat preservation passage is arranged on the PF line (water cooling + air cooling combined line). When the coil enters the slow cooling stage, the heat preservation cover is closed and the coil is preserved at 350-500℃ through the heat preservation passage of the PF line. Firstly, the internal organizational stress and thermal stress of the wire rod can be effectively reduced, the cross-sectional reduction is improved, and the risk of drawing brittle fracture is reduced; secondly, the eutectoid transformation of the iron oxide scale generated in the high temperature stage is controlled, FeO is relatively loose, and Fe3O4 generated by the eutectoid transformation has high density and hardness. By controlling the ratio of FeO:Fe3O4 along the thickness direction of the iron oxide scale to be 3:1, the structure of the iron oxide scale is loose inside and dense outside, and the iron oxide scale can be flaky and fall off when the mechanical descaling is used, and the falling rate of the iron oxide scale can reach 100%.

[0068] In this embodiment, as shown in Figure 1 , the wire rod is rapidly cooled from the fast cooling zone (650-900℃) to the sorbite phase transition temperature interval (550-650℃) under the action of the first and second group of centrifugal fans, and then enters the iron oxide eutectoid transformation interval (350-500℃) through air cooling (500-550℃) after the sorbite phase transition is completed. The temperature difference between the left, middle and right positions of the same temperature measurement point of the wire rod is in the range of 5-29℃, and the temperature change is relatively uniform. In this temperature range, the sorbite lamellar spacing of the wire rod at each position tends to be consistent, and the grain size and mechanical properties are uniform.

[0069] In this embodiment, the length of each coil of the wire rod coil is 3.1 meters, one coil of the produced coil is cut, segmented according to 300mm, sequentially marked as 01#-10#, and sequentially marked as 01#-10# for performance and organizational inspection. The test results are as follows: the tensile strength is in the range of 1182-1234MPa, the difference is 52MPa; the cross-sectional reduction rate is in the range of 26%-31%, the difference is 5%; the sorbite proportion is in the range of 85%-92% (as shown in Figure 3 , the sorbite proportion is 92%, and the remaining is ferrite), the difference is 7%; and the grain size is all 8.5 (as shown in Figure 2The decarburization layer depth is in the range of 37.55-47.63 μm, and the sorbite lamellar spacing is in the range of 0.11-0.17 μm (as shown in Figure 4 The sorbite lamellar spacing is 0.11 μm, there is no abnormal structure such as grain boundary cementite and martensite, the surface oxide scale thickness is in the range of 15-20 μm (as shown in Figure 5 The oxide scale thickness is 15.2 μm, and the thickness of Fe0 and Fe304 along the oxide scale thickness direction is 11.43 μm and 3.774 μm respectively, the thickness ratio is 3.03:1, which meets the requirement of mechanical descaling.

[0070] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A high-carbon steel wire rod suitable for mechanical descaling, characterized in that, The chemical composition of the wire rod, by mass percentage, is: C: 0.81%–0.83%, Si: 0.22%–0.30%, Mn: 0.78%–0.83%, P≤0.015%, S≤0.012%, Cr: 0.27%–0.30%, V≤0.10%, Al≤0.010%, Ni≤0.10%, Cu≤0.10%, N≤0.0070%, with the balance being Fe and unavoidable impurities.

2. The high-carbon steel wire rod suitable for mechanical descaling according to claim 1, characterized in that, The wire rod microstructure contains ≥90% sorbite; grain size grade >8.0; decarburized layer thickness ≤0.8%D, where D is the wire rod diameter.

3. The high-carbon steel wire rod suitable for mechanical descaling according to claim 1, characterized in that, The wire rod has a tensile strength of 1180-1240 MPa and a reduction of area of ​​≥28%; the iron oxide scale structure ratio on the surface of the wire rod is FeO:Fe3O4=3:1, and the iron oxide scale thickness is 15-20 μm.

4. A production process for high-carbon steel wire rod suitable for mechanical descaling as described in claim 1, 2, or 3, characterized in that, The production process includes hot metal pretreatment, converter smelting, LF refining, continuous casting, heating, rolling, wire drawing, air cooling, coiling, and slow cooling; the main controlled processes are as follows: 1) Heating: The steel billet is heated in a regenerative heating furnace. The preheating section temperature is 800-950℃, the heating section temperature is 1090-1150℃, the soaking section temperature is 1130-1170℃, the heating time is 120-180min, the air-fuel ratio is 0.50-0.60, and the residual oxygen content in the furnace is controlled below 1.5% by volume. 2) Rolling: The initial rolling temperature of the billet is 1010~1050℃, the initial rolling reduction is ≥50mm, the temperature of the billet entering the finishing mill is 900~940℃; the temperature of the billet entering the sizing mill is 910~940℃. 3) Spinning: The spinning temperature is 900-940℃; 4) Air cooling and slow cooling: The Stellmore air cooling line is used for air cooling. Each fan is equipped with a Galing device, and the cooling rate is controlled at 0.5-20℃ / s. The roller speed is controlled in segments. The Stellmore air cooling line is equipped with an insulation cover to achieve slow cooling, and the coil temperature is controlled at 550-650℃. The thickness of the iron oxide scale on the surface of the wire rod is controlled within the range of 15-20μm.

5. The production process for high-carbon steel wire rod suitable for mechanical descaling according to claim 4, characterized in that, The Stellmore air-cooled line has a total length of 120.2m and is equipped with 25 centrifugal fans in 9 groups. Groups 1 through 7 each have 3 centrifugal fans, totaling 21 fans arranged longitudinally along the air-cooled line; groups 8 and 9 each have 2 centrifugal fans, totaling 4 fans arranged longitudinally along the air-cooled line. The airflow rate of the centrifugal fans in groups 1 and 2 is 205,000 cubic meters per hour, and the airflow rate of the centrifugal fans in groups 3 through 9 is 185,000 cubic meters per hour. The air-cooled roller conveyor is divided into 14 sections. The length of the first and last sections is 4.6m, and the length of the second to thirteenth sections is 9.25m. The adjustment method of the Jialing device is as follows: the cross-sectional area ratios of the two sides to the central air chamber of the Jialing devices corresponding to the first group of centrifugal fans, the second group of centrifugal fans, and the third to ninth groups of centrifugal fans are 4.0:1, 4.5:1, and 5.0:1, respectively, and the angles of the Jialing devices are 33°, 30°, and 27.2°, respectively.

6. The production process for high-carbon steel wire rod suitable for mechanical descaling according to claim 5, characterized in that, The frequency of the centrifugal fans in groups 1 and 2 is set to 50Hz, and the frequency of the centrifugal fans in groups 3 to 5 is set to 45Hz; the roller speeds of sections 1 to 6 are set to 0.80m / s, 0.90m / s, 1.00m / s, 1.10m / s, 1.20m / s, and 1.25m / s respectively; and the roller speeds of sections 7 to 14 are set to 1.30m / s.

7. The production process for high-carbon steel wire rod suitable for mechanical descaling according to claim 4, characterized in that, The insulation cover is set in 22 groups along the air-cooling line. The insulation covers in groups 1 to 11 are open, and the insulation covers in groups 12 to 22 are closed. The PF line is set with insulation channels and is coiled to keep warm at a temperature of 350 to 500℃.

8. The production process for high-carbon steel wire rod suitable for mechanical descaling according to claim 4, characterized in that, Additionally, the following processes are controlled: 1) Hot metal pretreatment: KR hot metal pretreatment is adopted, and desulfurizing agent is injected into the hot metal ladle for desulfurization. After treatment, the S content in the hot metal is ≤0.010%, and the slag is removed. 2) Converter smelting: The converter tapping temperature is controlled at 1620-1640℃, and argon gas is blown into the ladle for stirring during the tapping process; the steel composition is controlled by mass percentage as follows: C: 0.74%-77%, Si: 0.17%-0.22%, Mn: 0.72%-0.78%, Cr: 0.22%-0.27%, P≤0.015%, Al≤0.006%; the deoxidizer and alloy slag are added in the following order: silicon-calcium-barium is added after the steel tapping amount reaches 30%; lime, silicon-manganese alloy and high-carbon ferrochrome are added after the steel tapping amount reaches 40%; fluorite is added after the steel tapping amount reaches 50%. 3) LF Refining: The LF refining furnace maintains a slight positive pressure of 40–70 kPa, employs submerged arc heating, and ensures no arc leakage; it uses one or more of the following as deoxidizers: carbon powder, ferrosilicon powder, and silicon carbide; the white slag refining time is more than 15 minutes; the refining slag system, by mass percentage, includes SiO2: 15%–23%, CaO: 45%–55%, Al2O3: 6%–10%, MgO≤8%, FeO+MnO≤0.8%; the basicity R of the refining slag system is controlled at 2.0–3.0; the basicity of the final slag is controlled at 2. 0~3.0; Adjust the steel composition by mass percentage to C: 0.81%~0.83%, Si: 0.23%~0.28%, Mn: 0.78%~0.83%, Cr: 0.27%~0.30%, P≤0.015%, S≤0.012%, Al≤0.006%, Ti≤0.0030%, N≤0.0050%; Soft blow for 20~30min, when the steel temperature reaches 1525~1535℃, add carbonized rice husks, and transfer to the continuous casting machine for pouring; 4) Continuous casting: The casting process uses a tundish with a slag-blocking wall and an immersion-type integral nozzle with argon sealing function. The nozzle insertion depth is 100-120mm. Argon gas is used to purge the tundish at least 3 minutes before casting begins, and argon gas protection is maintained throughout the casting process. A special protective slag for peritectic steel is used in the mold. The initial casting speed is controlled at 0.80-0.90 m / min, the process casting speed is 1.95-2.05 m / min, and the mold water flow rate is 130-140 m³ / min. 3 / h, the first electromagnetic stirring current is 250A and the frequency is 3Hz, the last electromagnetic stirring current is 320A and the frequency is 8Hz; the liquid level fluctuation in the crystallizer is controlled within ±3mm; the billet is slowly cooled in the heat preservation pit for more than 48 hours after it leaves the line or is hot-sent to the rolling mill heating furnace.

9. The production process for high-carbon steel wire rod suitable for mechanical descaling according to claim 8, characterized in that, In the hot metal pretreatment process, the desulfurizing agent consists of 85% to 95% lime powder and 5% to 15% fluorite powder by mass percentage; in the converter smelting process, the weight ratio of hot metal is 85% to 88%, and the weight ratio of scrap steel is 12% to 15%.

10. The production process for high-carbon steel wire rod suitable for mechanical descaling according to claim 8, characterized in that, During the LF refining process, the auxiliary materials are added in the following order: lime, fluorite and deoxidizer are added during the first power supply; lime and deoxidizer are added again during the second power supply according to the desulfurization situation; silica and low-alkalinity composite slag are added in batches during the remaining time, and silicon carbide is used for deoxidation.

Images