Low-carbon steel hot-rolled wire rod and manufacturing method thereof

Abstract

The invention provides a low-carbon steel hot-rolled wire rod and a manufacturing method thereof, and relates to the field of steel smelting. During preparation, on one hand, smelting and rolling process parameters are controlled through the technological processes of converter smelting, RH treatment, continuous casting, cogging, blank grinding and rolling controlled cooling, and on the other hand, wire rod component design is carried out, and the wire rod component design comprises 0.012%-0.028% of C, 0.02%-0.05% of Si, 0.15%-0.25% of Mn, 0.009%-0.020% of B and the balance Fe and inevitable impurities; wherein the content of part of impurity components is limited as follows: the sum of the mass percent of Cr, Ni and Cu is less than or equal to 0.03%, Al is less than or equal to 0.010%, S is less than or equal to 0.010%, P is less than or equal to 0.010%, O is less than or equal to 0.0050%, and N is less than or equal to 0.0050%; the comprehensive performance of the wire rod is effectively improved, and the use requirement of the galvanized steel wire for weaving a net is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel smelting, and particularly relates to a low-carbon steel hot-rolled wire rod and a manufacturing method thereof. BACKGROUND

[0002] Low-carbon steel wire rods are widely used in galvanized steel wires, such as planting greenhouses, breeding farm fences, electric welding meshes, highway guardrails, factory fences, etc. Among them, the electric welding mesh is mainly prepared by drawing, galvanizing and other processes of ordinary low-carbon steel, and is applied to building walls and insulation layers as a reinforcing material. The electric welding mesh has good toughness and corrosion resistance, which can effectively prevent wall cracking and leakage, and improve the service life of the building. In the industrial field, the galvanized steel wire for high-speed guardrails is mainly prepared by low-carbon or ultra-low-carbon wire rods. These protective facilities need to withstand a large external force impact and long-term outdoor corrosion, and their strength and corrosion resistance need to be able to withstand harsh natural environments.

[0003] Some special-purpose galvanized steel wires require high-end weaving meshes, and the deformation amount in the processing process is large. Therefore, the steel wire not only needs to have high strength, but also needs to have excellent plastic toughness. The carbon content in the chemical composition of the ultra-low-carbon steel wire rod is extremely low, and it has obvious advantages in toughness and ductility. During the process of weaving the steel wire mesh, the galvanized steel wire needs to be bent and deformed multiple times in a very short time. The characteristics of the ultra-low-carbon steel can ensure that the steel wire is not easy to break during the processing process, thereby ensuring the production efficiency and product quality. In addition, the wire rod for weaving galvanized steel wire has high requirements for purity and surface quality. On the one hand, it reduces the breakage of the steel wire caused by inclusions during severe deformation. On the other hand, the surface quality determines the bonding effect between the surface and the zinc layer during the galvanizing process. Whether hot galvanizing or electroplating zinc process is used, the steel wire prepared by the ultra-low-carbon steel can obtain a uniform and strongly adhered galvanized layer, thereby significantly improving the corrosion resistance of the steel wire.

[0004] The ultra-low-carbon steel wire rods developed by the prior art, such as CH1T and DT, are used to produce hollow rivets and special-shaped bolts with large deformation after downstream drawing. These products mainly bear compression deformation and are mostly non-stress parts. For parts that need to bear stress, such as weaving, these products cannot meet the requirements. Patent CN112058912B introduces an ultra-low-carbon steel wire rod, which uses titanium micro-alloying to design the steelmaking and rolling process parameters to improve the surface hardness and tensile strength of the wire rod and steel wire, but cannot meet the requirement of good plasticity. Patent CN102021278A introduces an ultra-low-carbon steel for steel plates and a manufacturing method, which uses titanium-boron and titanium-niobium alloying to obtain a steel plate with a combination of coarse grains and fine grains through process optimization, thereby improving the performance index of the steel plate. This method is only suitable for steel types that require deep drawing performance, and cannot be applied to wire rods with large drawing and torsional deformation. SUMMARY

[0005] The present application aims to provide a low carbon steel hot-rolled wire rod and a manufacturing method thereof, by designing the chemical composition and manufacturing process of the wire rod, so that the prepared low carbon steel hot-rolled wire rod meets the use requirements of high deformation galvanized woven steel wire.

[0006] To achieve the above-mentioned purpose, the present application proposes the following technical solutions: In a first aspect, a low carbon steel hot-rolled wire rod is provided, which has a chemical composition including, in terms of mass percentage: C 0.012-0.028%, Si 0.02-0.05%, Mn 0.15-0.25%, B 0.009-0.020%, and the rest being Fe and unavoidable impurities; wherein the content of part of the impurities is limited as follows: the sum of the mass percentages of Cr, Ni and Cu is ≤0.03%, Al ≤0.010%, S ≤0.010%, P ≤0.010%, O ≤0.0050%, and N ≤0.0050%.

[0007] Further, the tensile strength of the low carbon steel hot-rolled wire rod is 290-350 MPa, the reduction of area is not less than 80%, and the elongation is not less than 35%.

[0008] Further, in the microstructure of the low carbon steel hot-rolled wire rod, the A-type and C-type inclusions are not more than 1.0 grade, the B-type and C-type inclusions are not more than 0.5 grade, the size of Al2O3 inclusions and TiN inclusions is not more than 5 μm, and the size of inclusions within 1 mm from the surface of the cross section of the wire rod is not more than 15 μm.

[0009] Further, the low carbon steel hot-rolled wire rod has a main metallographic structure of ferrite, the content of the ferrite is not less than 98.5%, and the grain size of the ferrite is 70-100 μm.

[0010] In a second aspect, a manufacturing method of a low carbon steel hot-rolled wire rod is provided, including the following steps: 1) Molten steel pretreatment: KR desulfurization is used for molten iron entering the furnace, and before treatment, the mass percentage of each chemical composition of the molten iron is Si 0.45-0.75%, Mn ≤0.25%, P% ≤0.11%, S% ≤0.045%, and Ti% ≤0.06%; after treatment, S in the molten iron is ≤0.003%, the temperature of the molten steel is not less than 1320℃, not less than 98% of the desulfurization slag is removed after desulfurization, and the resulfurization rate is not more than 1%; 2) Converter smelting: desulfurized molten iron is added into the converter, the amount is 92~95%, the rest is scrap steel; by adjusting the amount of CaO added, the converter final slag basicity is controlled to be 5~7, the mass percentage of each chemical component at the end of the converter is C 0.03~0.06%, P%≤0.010%, S%≤0.010%, the tapping temperature is not less than 1670℃; 1.6~1.8kg / t aluminum ingot and 2~3kg / t lime are sequentially added into the ladle during the tapping process, and the argon pressure of the ladle is adjusted to 0.8~0.9MPa; 0.5~1.0kg / t low-carbon steel slag surface deoxidizer is added to the surface of the molten steel at the end of the tapping, and the argon pressure of the ladle is adjusted to 0.3~0.4MPa; 3) RH vacuum treatment: after the molten steel enters the RH, the vacuum degree is adjusted to 100mbar, the molten steel is sequentially subjected to oxygen blowing decarburization, deoxidation and composition adjustment, calcium treatment and soft stirring, so that the composition of the molten steel is C 0.012~0.028%, Si 0.02~0.05%, Mn 0.15~0.25%, B 0.009~0.020%, and the molten steel is lifted to the continuous casting position when the temperature reaches 1626~1630℃; 4) Billet continuous casting: three-stage cooling weak cooling process is adopted, wherein the first stage is mold cooling, the mold water flow is controlled to be 3050~3060L / min; the second stage is two cooling sections using three-zone water mist cooling, and the end light press-down process is performed after the two cooling sections cooling; the third stage is surface quenching cooling of the billet, the water flow is controlled to be 550~600L / min, and the water pressure is controlled to be 15~18bar, the grain size in the range of 5mm from the surface of the billet is controlled to be 20~30μm; 5) Continuous rolling breakdown: 7-stand continuous rolling breakdown is adopted, the corner temperature of the billet after each pass is not less than 900℃, and the corner cooling speed of the billet on the cooling bed is not more than 8℃ / s; 6) Billet grinding: the billet is sequentially ground by rough grinding, fine grinding and shot blasting, and then detected by flaw detection; 7) controlled cooling by rolling: 26 stands of rolling are adopted, including 6 stands of rough rolling, 6 stands of medium rolling, 4 stands of pre-precision rolling, 8 passes of precision rolling and 2 passes of reducing diameter machine rolling, the control opening rolling temperature is 1000-1030℃, the temperature of the corner of the rolled piece at the first to sixth stands is not less than 850℃; after the rolling of the reducing diameter machine, two section water cooling boxes are opened, the temperature difference between the core and the surface of the wire rod is not more than 6℃ when the wire rod is discharged; the Stelmor air cooling line is used for controlled cooling, when the temperature of the wire rod lap joint point is not less than 750℃, the surface cooling speed of the wire rod is controlled to be 5-7℃ / s; when the wire rod is cooled to 650-750℃, the surface cooling speed of the wire rod is controlled to be 1-2℃ / s, then air cooling is adopted to reduce to room temperature, and the hot-rolled wire rod with a diameter of 5.0-5.5mm is obtained; the chemical components in the hot-rolled wire rod include, by mass percent: C 0.012-0.028%, Si 0.02-0.05%, Mn 0.15-0.25%, B 0.009-0.020%, and the rest is Fe and inevitable impurities; wherein, the content of part of the impurity components is limited as follows: the sum of the mass percentages of three chemical components of Cr, Ni and Cu is ≤0.03%, Al ≤0.010%, S ≤0.010%, P ≤0.010%, O ≤0.0050%, N ≤0.0050%.

[0011] Further, the specific process of the step 3) RH vacuum treatment process for oxygen blowing decarburization, deoxidization and composition adjustment, calcium treatment and soft stirring of the molten steel is as follows: Oxygen blowing decarburization: according to the incoming composition, oxygen blowing decarburization is started, the oxygen blowing amount is controlled according to E O2 =2000C%+49, the carbon content is adjusted to 0.01-0.015%, and 0.06-0.07kg / t of aluminum ingot is added to the molten steel; wherein, E O2 represents the oxygen blowing amount, and C% represents the mass percentage of chemical component C; Deoxidization and composition adjustment: the oxygen content of the molten steel is determined, and aluminum ingot is added for deoxidization treatment according to the oxygen content, the added amount of aluminum ingot is 0.1-0.2kg / t, and the aluminum content in the molten steel is controlled to be ≤0.005% at the end of deoxidization; boron iron 0.6-0.8kg / t is added according to the composition of the molten steel to adjust the composition of the molten steel to C 0.012-0.028%, Si 0.02-0.05%, Mn 0.15-0.25%, B 0.009-0.020%; Calcium treatment: after breaking the vacuum, calcium treatment is performed on the molten steel, 240-260m of calcium wire is fed into the molten steel at a feeding speed of 5-8m / s, and the argon flow rate of the bottom blowing of the ladle is controlled to be 350-420NL / min during the calcium treatment; Soft stirring: the argon flow rate of the bottom blowing of the ladle is controlled to be 50-70 NL / min, after static treatment for 8-10min, ashed rice husk is added on the surface of the molten steel for heat preservation treatment.

[0012] Further, the second stage of the step 4) adopts three-zone water mist cooling, and the specific process parameters of the terminal light press-down process after the cooling of the second stage are as follows: The water quantity of the three-zone water mist cooling is respectively 110-115 L / min, 70-80 L / min and 40-60 L / min, and the parameters of the terminal light press-down process are as follows: the press-down distribution is in the 2nd-6th roller, the press-down amount of the 2nd-3rd roller is 3-4 mm, and the press-down amount of the 4th-6th roller is 2-3 mm, and the corner temperature during the press-down of the 1st-4th roller is not less than 850℃.

[0013] Further, the specific content of the step 6) is as follows: The coarse grinding adopts a 18-mesh grinding wheel, the linear speed of the grinding wheel is 60 m / min, the moving speed of the blank during the grinding is 35 m / min, the grinding wheel pressure is controlled to be 30-50 MPa during the corner grinding, the grinding wheel pressure is controlled to be 35-60 MPa during the grinding of the four surfaces, the grinding depth, width and length ratio should be not less than 1:6:10, and the surface roughness of the blank is controlled to be 62-65 Rz; The fine grinding adopts a 35-mesh grinding wheel, the linear speed of the grinding wheel is 70 m / min, the moving speed of the blank during the grinding is 25 m / min, the grinding wheel pressure is controlled to be 20-25 MPa during the corner grinding, the grinding wheel pressure is controlled to be 25-40 MPa during the grinding of the four surfaces, and the surface roughness of the blank is not more than 20 Rz; The shot blasting adopts shot particles with a particle size of 2.5-3 mm, and the speed of the shot particles is controlled to be 5-8 m / s during the shot blasting; The flaw detection adopts magnetic particle flaw detection, the moving speed of the blank during the flaw detection is 0.20-0.25 m / s, the water solution containing 0.5-0.7 g / L fluorescent magnetic particles is sprayed to the surface of the blank, the observation is performed by using ultraviolet light with an intensity of not less than 950 μm / cm 2 , and the number of defects of each blank is required to be not more than 2.

[0014] Further, the maximum air volume of the fan during the controlled cooling process by using the Stelmor air cooling line is 280,000 m 3 / h.

[0015] In a third aspect, a galvanized steel wire for weaving is provided, which is prepared by pickling, rough drawing, fine drawing, annealing and galvanizing of the hot-rolled wire rod prepared by the above low-carbon steel hot-rolled wire rod or the above manufacturing method; The wire rod is pickled by hydrochloric acid to remove the surface oxide skin, the concentration of the hydrochloric acid is controlled to be 20-22%, and the pickling time is 8-10 min; The disc rod removing the oxide skin is rough-drawn into steel wire with a diameter of 2.9-3.2 mm, and then the steel wire is fine-drawn in a forward direction to 0.8-1.3 mm, and the strength of the steel wire is controlled to be 470-500 MPa; The steel wire after drawing is placed into a N2 protective atmosphere pit-type annealing furnace, the annealing temperature is 600-700 DEG C, and the holding time is 3-4 h; The steel wire after annealing is subjected to on-line pickling, water washing and galvanizing treatment, the zinc liquid temperature is controlled to be 470-480 DEG C, and the strength of the finally prepared steel wire is 420-430 MPa.

[0016] From the above technical solution, the technical solution of the present application has the following beneficial effects: The low-carbon steel hot-rolled rod and the manufacturing method thereof disclosed by the present application solve the problems of abnormal wire breakage in the twisting deformation process and the serious influence on product quality and production efficiency when low-carbon steel is used to prepare woven galvanized steel wire, the composition and manufacturing process of the low-carbon steel hot-rolled rod are redesigned, the inclusions, metallographic structure and mechanical properties of the prepared hot-rolled rod are controlled, the comprehensive performance of the rod is comprehensively improved, and the performance requirements for manufacturing high-end woven are met. In the hot-rolled rod, the chemical components include C 0.012-0.028%, Si 0.02-0.05%, Mn 0.15-0.25%, B 0.009-0.020% by mass percentage, and the rest is Fe and inevitable impurities; the content of part of the impurity components is limited as follows: the sum of the mass percentages of three chemical components of Cr, Ni and Cu is ≤0.03%, Al is ≤0.010%, S is ≤0.010%, P is ≤0.010%, O is ≤0.0050%, and N is ≤0.0050%, a low-carbon low-silicon component system is used, and a certain amount of boron is added to improve the comprehensive performance of the material; secondly, the process flow of converter smelting-RH treatment-large billet continuous casting-billet breaking-billet grinding-rolling and controlled cooling is used to finely control the smelting and rolling process parameters.

[0017] The hot-rolled rod prepared by the manufacturing process and the component design of the present application is subjected to pickling-rough drawing-fine drawing-annealing-galvanizing to prepare a woven galvanized steel wire with a strength of 420-430 MPa, which fully meets the strict requirements of modern industry and civil field on the quality and performance of high-end woven steel wire, and has significant economic and social benefits.

[0018] It should be understood that all combinations of the aforementioned concepts and additional concepts described in greater detail below can be seen as part of the subject matter of the present disclosure as long as such concepts are not mutually contradictory.

[0019] The foregoing and other aspects, embodiments and features of the present teachings are more fully described below, in connection with the accompanying drawings. Other aspects, embodiments and features of the present teachings will become apparent from the following description, including the descriptions of the examples, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings are not drawn to scale. In the drawings, each identical, or nearly identical, component that is illustrated in various figures is represented with a like numeral. For purposes of clarity, not every component is called out in every drawing. There is now be described, by way of example, embodiments of various aspects of the present teachings with reference to the accompanying drawings, in which: Figure 1 Flow chart of the manufacturing method of the low carbon steel hot-rolled wire rod disclosed by the present application; Figure 2 Microstructure of the low carbon steel hot-rolled wire rod made by Example 1 of the present application; Figure 3 Microstructure of the low carbon steel hot-rolled wire rod made by Example 2 of the present application. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described below in connection with the drawings of the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application. Unless otherwise defined, the technical terms or scientific terms used herein should be understood as the common meanings by those skilled in the art.

[0022] The terms "first", "second", and similar terms used herein do not necessarily connote an order of importance, but are used to distinguish one element from another, and are not used herein to denote a limitation of the number of elements. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", "including" and the like are specifically intended to be open-ended terms that are inclusive of the presence of one or more elements, components, steps, operations, elements and / or the like, but do not exclude the presence of one or more other elements, components, steps, operations, elements and / or the like.

[0023] The special-purpose ultra-low-carbon wire net plating galvanized steel wire has a large deformation in the processing process, and requires that the material has good plasticity and toughness while ensuring strength. However, the existing technology uses low-carbon steel to prepare the wire net plating galvanized steel wire, and there are problems such as abnormal wire breakage in the twisting deformation process, which seriously affects the product quality and production efficiency. Therefore, the present application aims to provide a low-carbon steel hot-rolled wire rod and a manufacturing method thereof. The composition of the hot-rolled wire rod is redesigned, and the process flow of converter-RH treatment-continuous casting-billet grinding-rolling and controlled cooling is adopted. The smelting and rolling process parameters are controlled to significantly improve the comprehensive performance of the wire rod and meet the use requirements of high-end wire net for low-carbon steel wire rod.

[0024] In combination Figure 1 The manufacturing method of the low-carbon steel hot-rolled wire rod disclosed in the present application comprises the following steps: Step S1 molten steel pretreatment: KR desulfurization is used for the molten iron entering the furnace, and the mass percentages of the chemical components of the molten iron before treatment are Si 0.45-0.75%, Mn≤0.25%, P%≤0.11%, S%≤0.045%, and Ti%≤0.06%; after treatment, S in the molten steel is ≤0.003%, the temperature of the molten steel is not lower than 1320℃, not less than 98% of the desulfurization slag after desulfurization is removed, and the resulfurization rate is not more than 1%; Step S2 converter smelting: the molten steel after desulfurization is added to the converter, and the addition amount is 92-95%, and the rest is scrap steel; by adjusting the amount of CaO added, the basicity of the converter final slag is controlled to be 5-7, and the mass percentages of the chemical components at the end of the converter are C 0.03-0.06%, P%≤0.010%, S%≤0.010%, and the tapping temperature is not lower than 1670℃; during the tapping process, 1.6-1.8 kg / t of aluminum ingot and 2-3 kg / t of lime are sequentially added to the ladle, and at the same time, the argon pressure of the ladle is adjusted to 0.8-0.9 MPa; 0.5-1.0 kg / t of low-carbon steel slag surface deoxidizer is added to the surface of the molten steel at the end of the tapping, and the argon pressure of the ladle is adjusted to 0.3-0.4 MPa; Step S3 RH vacuum treatment: after the molten steel enters the RH, the vacuum degree is adjusted to 100 mbar, and the molten steel is sequentially subjected to oxygen blowing decarburization, deoxidation and composition adjustment, calcium treatment and soft stirring, so that the composition of the molten steel is C 0.012-0.028%, Si 0.02-0.05%, Mn 0.15-0.25%, and B 0.009-0.020%, and the molten steel is lifted to the continuous casting station when the temperature of the molten steel reaches 1626-1630℃; Among them, the specific process for oxygen blowing decarburization, deoxidation and composition adjustment, calcium treatment and soft stirring of the molten steel is as follows: oxygen blowing decarburization: according to the inlet composition, oxygen blowing decarburization is started, and the E O2=2000C%+49 to regulate the oxygen blowing amount, the carbon content is adjusted to 0.01~0.015%, and 0.06~0.07kg / t of aluminum ingot is added to the molten steel; wherein, E O2 represents the oxygen blowing amount, and C% represents the mass percentage of chemical composition C; Deoxidation and composition adjustment: the molten steel is subjected to oxygen determination operation, and aluminum ingot is added for deoxidation treatment according to the oxygen content, the added amount of aluminum ingot is 0.1~0.2kg / t, and the aluminum content in the molten steel is controlled to be ≤0.005% at the end of deoxidation; boron iron 0.6~0.8kg / t is added according to the composition of the molten steel, and the composition of the molten steel is adjusted to C 0.012~0.028%, Si 0.02~0.05%, Mn 0.15~0.25%, and B 0.009~0.020%; Calcium treatment: after breaking the vacuum, the molten steel is subjected to calcium treatment, 240~260m of calcium wire is fed into the molten steel, the feeding speed is 5~8m / s, and the argon gas flow rate of the ladle bottom blowing is controlled to be 350~420NL / min during calcium treatment; Soft stirring: the argon gas flow rate of the ladle bottom blowing is controlled to be 50~70 NL / min, and after 8~10min of static treatment, ashed rice husk is added on the surface of the molten steel for heat preservation treatment.

[0025] Step S4 billet continuous casting: a three-stage cooling weak cooling process is adopted, wherein, the first stage is mold cooling, and the mold water flow rate is controlled to be 3050~3060L / min; the second stage is two-stage cooling section adopting three-zone water mist cooling, and a terminal light reduction process is performed after the two-stage cooling section cooling; wherein, the water amount of the three-zone water mist cooling is 110~115L / min, 70~80L / min, and 40~60L / min respectively, the terminal light reduction process parameters are: the reduction is distributed in the 2~6 rollers, the reduction amount of the 2~3 rollers is 3~4mm, the reduction amount of the 4~6 rollers is 2~3mm, and the corner temperature is not less than 850℃ when the 1~4 rollers are reduced; the third stage is billet surface quenching cooling, the water flow rate is controlled to be 550~600 L / min, and the water pressure is controlled to be 15~18bar, and the grain size in the range of 5mm from the surface of the billet is controlled to be 20~30μm; The three-stage cooling process effectively solves the problems of reducing porosity and shrinkage of low-carbon steel, and effectively solves the surface quality problem caused by high boron content.

[0026] Step S5 continuous rolling breakdown: 7-stand continuous rolling breakdown is adopted, and the corner temperature of the billet after each pass is not less than 900℃, and the corner cooling speed of the billet on the cooling bed is not more than 8℃ / s; Step S6 blank grinding: the blank is ground in turn by rough grinding, fine grinding and shot blasting, and after grinding, flaw detection is carried out; specifically, the rough grinding adopts a 18-mesh grinding wheel, the linear speed of the grinding wheel is 60 m / min, and the moving speed of the blank during grinding is 35 m / min; when the corner is ground, the grinding wheel pressure is controlled to be 30-50 MPa; when the four surfaces are ground, the grinding wheel pressure is controlled to be 35-60 MPa; the grinding depth, width and length ratio should not be less than 1:6:10, and the grinding control blank surface roughness is 62-65 Rz; the fine grinding adopts a 35-mesh grinding wheel, the linear speed of the grinding wheel is 70 m / min, and the moving speed of the blank during grinding is 25 m / min; when the corner is ground, the grinding wheel pressure is controlled to be 20-25 MPa; when the four surfaces are ground, the grinding wheel pressure is controlled to be 25-40 MPa; the grinding control blank surface roughness is not more than 20 Rz; the shot blasting adopts a shot with a particle size of 2.5-3 mm, and the shot speed is controlled to be 5-8 m / s during shot blasting; the flaw detection adopts magnetic powder flaw detection, the moving speed of the blank during flaw detection is 0.20-0.25 m / s, a water solution containing 0.5-0.7 g / L fluorescent magnetic powder is sprayed on the surface of the blank, and observation is carried out by using ultraviolet light with an intensity of not less than 950 μm / cm 2 , and the number of defects of each blank is required to be not more than 2; Since the ultra-low carbon steel is relatively soft, the parameters must be strictly controlled during grinding to reduce the generation of grinding burrs and grinding marks, therefore, in the present application, the blank is ground by combining rough grinding, fine grinding and shot blasting, and the grinding process is redesigned.

[0027] Step S7 rolling and controlled cooling: 26-stand rolling is adopted, including 6-stand rough rolling, 6-stand medium rolling, 4-stand pre-precision rolling, 8-pass precision rolling and 2-pass reducing diameter machine rolling, the rolling temperature is controlled to be 1000-1030℃, the corner temperature of the rolled piece at the 1st-6th stand is not less than 850℃; after the reducing diameter machine rolling, two-section water cooling boxes are opened, and the temperature difference between the core and the surface of the wire rod when the wire rod is discharged is controlled to be not more than 6℃; the wire rod is cooled by using a Stelmor air cooling line, when the temperature of the wire rod lap joint point is not less than 750℃, the surface cooling speed of the wire rod is controlled to be 5-7℃ / s, the maximum air volume of the fan during the cooling process is 280,000 m 3 / h; when the wire rod is cooled to 650-750℃, the surface cooling speed of the wire rod is controlled to be 1-2℃ / s, then air cooling is adopted, and the temperature is reduced to room temperature, thereby obtaining a hot-rolled wire rod with a diameter of 5.0-5.5 mm; The chemical components in the hot-rolled wire rod obtained through the above steps include, in terms of mass percentage: C 0.012-0.028%, Si 0.02-0.05%, Mn 0.15-0.25%, B 0.009-0.020%, and the rest is Fe and inevitable impurities; wherein, the content of part of the impurity components is limited as follows: the sum of the mass percentages of three chemical components of Cr, Ni and Cu ≤0.03%, Al ≤0.010%, S ≤0.010%, P ≤0.010%, O ≤0.0050%, and N ≤0.0050%; Among them, C is the most important component element, although the carbon content is low in low carbon steel, but it has a significant impact on the performance of steel. Carbon dissolves in iron to form a solid solution, which makes the arrangement of iron atoms more compact, thereby improving the strength and hardness of the steel. With the increase of carbon content, the strength and hardness of the steel will gradually increase. In addition, carbon can also promote the formation of fine carbide particles in steel, which hinders the movement of dislocations, thereby improving the toughness of the steel. Carbon can also combine with other elements such as B in steel to form carbides, improving the overall properties of the material. The steel wire for weaving requires the finished steel wire to have good strength, toughness and good corrosion resistance. According to the characteristics of the product, the strength and toughness of the finished steel wire, the weldability and corrosion resistance are considered, and the carbon content range is set to 0.012-0.028%.

[0028] Si can play a role in solid solution strengthening, while reducing the oxygen content in the steel; at the same time, Si can also improve the strength of ferrite in pearlite, play a role in solid solution strengthening, and thus improve the strength of the final finished steel wire. High silicon content will reduce the toughness of the steel. Therefore, in low carbon steel, the silicon content needs to be strictly controlled within a proper range to balance the strength and toughness. The Si content range of the present application is 0.02-0.05%.

[0029] Mn belongs to carbide forming elements, which can play a role in solid solution strengthening to improve the strength of the wire rod, and can also combine with harmful elements S to reduce the hot brittleness; but when the content is too high, the strength and hardness will increase greatly, which will easily reduce the plasticity and processing performance of the wire rod. The Mn content range of the present application is 0.15-0.25%.

[0030] B can improve the hardness and strength of low carbon steel, and the addition of trace boron can significantly improve the hardness and strength of the steel. Boron tends to segregate at the austenite grain boundary, reducing the grain boundary energy and hindering the nucleation of ferrite, resulting in the refinement of ferrite grains and thus improving the processability of low carbon steel. In addition, boron can also fix N in the form of BN, thereby reducing the influence of N on work hardening. The B content range of the present application is 0.009-0.020%, boron can combine with N to form BN particles dispersed in ferrite, which can improve the strength and plasticity, and also can form boron-carbon phase with a small amount of carbon to improve the strength of cementite.

[0031] The existence of Cr, Ni and Cu as residual elements increases the brittleness of the steel, and significantly reduces the toughness and impact toughness of the steel. Meanwhile, these elements promote the aging hardening of the steel, causing the performance of the steel to change during long-term use, which may affect the service life thereof. Therefore, the content of Cr+Ni+Cu is limited to ≤0.03% in the present application.

[0032] Al is a harmful element in the present application. As a deoxidizing element in ultra-low carbon steel, the content of Al needs to be strictly controlled after the removal of oxygen. Al2O3 inclusions are formed by the combination of Al and O in the steel, and the Al2O3 inclusions have large size, are easy to agglomerate, have high melting point and poor plasticity, and are one of the main reasons for the breakage of fine wires. The content of Al in the scheme should be controlled to be less than or equal to 0.010%.

[0033] S, P, O and N are harmful impurity elements, and the lower the content, the better. Therefore, the content of S in the wire rod is ≤0.010%, the content of P is ≤0.010%, the content of O is ≤0.0050%, and the content of N is ≤0.0050%.

[0034] In the microstructure, the A-type and C-type inclusions in the low-carbon steel hot-rolled wire rod are not more than 1.0 level, the B-type and C-type inclusions are not more than 0.5 level, the size of Al2O3 inclusions and TiN inclusions is not more than 5μm, the size of inclusions in the range of 1mm from the surface of the wire rod cross section is not more than 15μm, the metallographic structure is mainly ferrite, the content of the ferrite is not less than 98.5%, the ferrite grain size is 70~100μm, the hard structure level of martensite and bainite is 0, finally, the tensile strength of the prepared low-carbon steel hot-rolled wire rod is 290~350MPa, the reduction of area is not less than 80%, and the elongation is not less than 35%.

[0035] The present application also discloses a galvanized steel wire prepared from the hot-rolled wire rod, and the preparation process comprises the following steps: the hot-rolled wire rod is subjected to pickling, rough drawing, fine drawing, annealing and galvanizing; first, the wire rod is subjected to hydrochloric acid pickling to remove the surface oxide scale, the concentration of the hydrochloric acid is controlled to be 20~22%, and the pickling time is 8~10min; then, the wire rod after removing the oxide scale is subjected to rough drawing to a steel wire with a diameter of 2.9~3.2mm, and then the steel wire is subjected to fine drawing to 0.8~1.3mm in the forward direction, and the strength of the steel wire is controlled to be 470~500MPa; then, the steel wire after drawing is placed in a N2 protective atmosphere pit-type annealing furnace, the annealing temperature is 600~700℃, and the holding time is 3~4h; finally, the steel wire after annealing is subjected to on-line pickling, water washing and galvanizing treatment, the temperature of the zinc liquid is controlled to be 470~480℃, and finally the strength of the prepared steel wire is 420~430MPa.

[0036] The low-carbon steel hot-rolled wire rod and the manufacturing method thereof disclosed by the present application will be further described in detail below in combination with specific embodiments.

[0037] According to the steel pretreatment→converter smelting→RH treatment→billet continuous casting→continuous rolling breakdown→billet dressing→rolling and controlled cooling process, the low-carbon steel hot-rolled wire rod examples 1 and 2 with the chemical components in Table 1 are smelted.

[0038] Table 1 Chemical components of examples, wt.%

[0039] The implementation details of each process step are as follows: 1) Steel pretreatment The molten iron is pretreated, and the requirements before and after the pretreatment are shown in Table 2.

[0040] The implementation details of each process step are as follows: 1) Steel pretreatment The molten iron is pretreated, and the requirements before and after the pretreatment are shown in Table 2.

[0041] Table 2 Molten iron pretreatment parameters

[0042] 2) Converter smelting The desulfurized molten iron is added to the converter, and high-quality scrap steel is added; by adjusting the amount of CaO added, the converter final slag basicity, rolling basicity and converter endpoint control are shown in Table 3.

[0043] Table 3 Converter endpoint control parameters

[0044] Table 4 Alloy and slag addition and control parameters

[0045] The aluminum ingot and lime are sequentially added to the ladle during the tapping process, and at the same time, the argon pressure of the ladle is adjusted to 0.85 MPa, and the alloy and slag addition and control parameters are shown in Table 4.

[0046] 3) RH vacuum treatment Vacuum extraction: After the molten steel enters the RH, vacuum is quickly extracted, and the vacuum degree is reduced to 100 mbar; Oxygen blowing decarburization: according to the incoming composition, oxygen blowing decarburization is started, and the oxygen blowing amount E O2 (Nm 3 ) and the mass percentage of carbon C% are determined according to E O2=2000C%+49 to control the oxygen blowing amount, the carbon content is adjusted to 0.01~0.015%, and aluminum ingots are added to the molten steel, and the examples 1 and 2 are added 0.065 kg / t and 0.07 kg / t respectively.

[0047] Deoxidation and composition adjustment: the molten steel is subjected to oxygen determination operation, and aluminum ingots are added for deoxidation treatment according to the oxygen content, the aluminum ingot addition amount, the aluminum content after deoxidation, the boron iron addition amount and the molten steel composition are shown in the following table 5.

[0048] Table 5 Alloy and slag addition amount and control parameter

[0049] Calcium treatment: after breaking the space, the molten steel is subjected to calcium treatment, and the examples 1 and 2 are fed with calcium wire 252m and 245m respectively, and the feeding speed is 7m / s, and the argon flow rate of the ladle bottom blowing is controlled to be 400NL / min during calcium treatment.

[0050] Soft stirring: the argon flow rate of the ladle bottom blowing of the examples 1 and 2 is controlled to be 58 NL / min and 67 NL / min respectively, the static treatment is 8min and 10min respectively, and then the ashed rice husk is added on the surface of the molten steel for heat preservation treatment, and the molten steel is lifted to the continuous casting position when the temperature reaches 1628℃.

[0051] 4) Billet continuous casting: The continuous casting adopts a weak cooling process with three-stage cooling, and the cooling parameters are shown in the following table 6; the corner temperature is not less than 850℃ when 1~4 pairs of rollers are pressed down.

[0052] Table 6 Continuous casting cooling parameters

[0053] 5) Continuous rolling breakdown The 7-stand continuous rolling breakdown is adopted, and the billet corner temperature after each pass is not less than 900℃, and the billet corner cooling speed of the examples 1 and 2 on the upper cooling bed is 5.6 and 6.2℃ / s respectively.

[0054] 6) Billet grinding Because the ultra-low carbon steel is soft, the parameters must be strictly controlled during grinding to reduce the generation of grinding burrs and grinding marks, therefore, in the present application, the billet adopts the mode of rough grinding+fine grinding+shot blasting, and the grinding process is redesigned, and flaw detection is used to ensure the billet quality; the specific repair parameters of rough grinding, fine grinding, shot blasting and flaw detection are shown in the following tables 7, 8 and 9.

[0055] Table 7 Rough grinding parameters

[0056] Table 8 Fine grinding and shot blasting parameters

[0057] Table 9 Inspection parameters

[0058] 7) Controlled cooling The 26-stand rolling was adopted, including 6-stand rough rolling + 6-stand medium rolling + 4-stand pre-precision rolling + 8-pass precision rolling + 2-pass reducing diameter rolling, and the main parameters of rolling and controlled cooling are shown in Table 10.

[0059] Table 10 Rolling and cooling parameters

[0060] The wire rod specifications of the rolled wire rods of Examples 1 and 2 were 5.5 mm, and the mechanical properties, metallographic structure and inclusion detection were performed.

[0061] The tensile strength of the wire rod was controlled to be 290-350 MPa, the reduction of area was not less than 80%, and the elongation was not less than 35%, and the specific data of the detection of Examples 1 and 2 are shown in Table 11, and two samples were detected for each example.

[0062] Table 11 Mechanical property data of the hot-rolled wire rod prepared in Examples 1 and 2

[0063] The inclusions of the rolled wire rods of Examples 1 and 2 were detected by GB / T 10561, and the detection results are shown in Table 12.

[0064] Table 12 Inclusion detection data of the hot-rolled wire rod prepared in Examples 1 and 2

[0065] The metallographic structure of the wire rod was mainly ferrite, the ferrite content reached 99%, and the ferrite grain size was 70-100 μm; nitric acid alcohol etching was adopted, the hard structure level of martensite and bainite was 0; the metallographic structure photos of Examples 1 and 2 are shown in Figure 2 and 3 respectively, and the BN particle precipitates of element B distributed in the ferrite in the structure can significantly improve the deformation ability of the matrix.

[0066] The No. 1 hot-rolled wire rod samples prepared in the above-mentioned Embodiments 1 and 2 are used to prepare galvanized steel wires for weaving nets, which are prepared from the wire rod through pickling-coarse drawing-fine drawing-annealing-zinc plating; first, the wire rod is pickled with hydrochloric acid to remove the surface oxide scale, the concentration of the hydrochloric acid is controlled to be 22%, and the pickling time is 10 min; second, the wire rod from which the oxide scale is removed is coarsely drawn to 3.0 mm, and then the steel wire is fine drawn to 1.0 mm in the forward direction, and the strength of the steel wire is 486 MPa and 497 MPa; third, the steel wire after drawing is put into a N2-protected atmosphere pit-type annealing furnace, the annealing temperature is 650 ℃, and the holding time is 4 h. Finally, the steel wire after annealing is subjected to on-line pickling, water washing and zinc plating treatment, the temperature of the zinc liquid is controlled to be 475 ℃, and the final strength of the prepared steel wire is 421 MPa and 427 MPa.

[0067] Although the present application has been disclosed with reference to the preferred embodiments, it is not intended to limit the present application. Those skilled in the art, without departing from the spirit and scope of the present application, can make various modifications and improvements. Therefore, the scope of protection of the present application is defined by the claims.

Claims

1. A low carbon steel hot rolled wire rod, characterized in that: Its chemical composition, calculated by mass percentage, includes: C 0.012~0.028%, Si 0.02~0.05%, Mn 0.15~0.25%, B 0.009~0.020%, and the rest is Fe and unavoidable impurities; among which, the content of some impurity components is limited to: the sum of the mass percentages of the three chemical components Cr, Ni and Cu ≤0.03%, Al ≤0.010%, S ≤0.010%, P ≤0.010%, O ≤0.0050%, and N ≤0.0050%.

2. The low carbon steel hot rolled wire rod according to claim 1, characterized in that: The tensile strength of the low carbon steel hot rolled wire rod is 290-350 MPa, the cross-sectional shrinkage is not less than 80%, and the elongation is not less than 35%.

3. The low carbon steel hot rolled wire rod according to claim 1, characterized in that: In the microstructure of the low carbon steel hot rolled wire rod, the number of Class A and Class C inclusions does not exceed level 1.0, the number of Class B and Class C inclusions does not exceed level 0.5, the size of Al2O3 inclusions and TiN inclusions does not exceed 5 μm, and the size of inclusions within 1 mm from the surface in the wire rod cross section does not exceed 15 μm.

4. The low carbon steel hot rolled wire rod according to claim 1, characterized in that: The metallographic structure of the low-carbon steel hot-rolled wire rod is mainly ferrite, the ferrite content is not less than 98.5%, and the ferrite grain size is 70-100 μm.

5. A method for manufacturing a low carbon steel hot rolled wire rod, characterized in that: The steps include: 1) Molten steel pretreatment: KR desulfurization is applied to the molten iron before desulfurization. The mass percentage of each chemical composition of the molten iron before desulfurization is Si 0.45~0.75%, Mn≤0.25%, P%≤0.11%, S%≤0.045%, Ti%≤0.06%; after desulfurization, the S content of the molten iron is ≤0.003%. The temperature of the molten steel is not lower than 1320℃. After desulfurization, not less than 98% of the desulfurization slag is removed to ensure that the resulfurization rate does not exceed 1%. 2) Converter smelting: Desulfurized molten iron is added to the converter at a rate of 92-95%, with the remainder being scrap steel. The basicity of the converter slag is controlled to 5-7 by adjusting the amount of CaO added. The mass percentages of the chemical components at the converter endpoint are C 0.03-0.06%, P% ≤ 0.010%, S% ≤ 0.010%, and the tapping temperature is not less than 1670°C. During the tapping process, 1.6-1.8 kg / t of aluminum ingots and 2-3 kg / t of lime are added to the ladle, and the argon pressure in the ladle is adjusted to 0.8-0.9 MPa. At the end of tapping, 0.5-1.0 kg / t of low-carbon steel slag surface deoxidizer is added to the surface of the molten steel, and the argon pressure in the ladle is adjusted to 0.3-0.4 MPa. 3) RH vacuum treatment: After the molten steel enters the RH, the vacuum degree is adjusted to 100mbar. The molten steel is subjected to oxygen decarburization, deoxidation, composition adjustment, calcium treatment and soft stirring in sequence, so that the molten steel composition is C 0.012~0.028%, Si 0.02~0.05%, Mn 0.15~0.25%, and B 0.009~0.020%. When the molten steel temperature reaches 1626~1630℃, it is hoisted to the continuous casting station; 4) Billet continuous casting: A three-stage weak cooling process is used. In the first stage, the mold is cooled with a water flow rate controlled at 3050-3060 L / min. In the second stage, the secondary cooling section adopts three-zone water mist cooling, and a terminal soft reduction process is performed after the secondary cooling section. The third stage is the billet surface quenching cooling, with a water flow rate controlled at 550-600 L / min and a water pressure controlled at 15-18 bar. The grain size within 5 mm from the billet surface is controlled to 20-30 μm. 5) Continuous rolling: 7-stand continuous rolling is used for billet opening. The temperature of the billet corner after each billet opening is not less than 900℃, and the cooling rate of the billet corner on the upper cooling bed does not exceed 8℃ / s; 6) Blank grinding: The blank is ground in sequence by rough grinding, fine grinding and shot blasting, and then subjected to flaw detection after grinding; 7) Rolling controlled cooling: 26 stands are used for rolling, including 6 roughing rolls, 6 intermediate rolls, 4 pre-finishing rolls, 8 finishing rolls and 2 sizing mill rolls. The starting rolling temperature is controlled at 1000-1030°C, and the temperature of the corners of the rolled pieces in stands 1-6 is not lower than 850°C. After the sizing mill rolls, two water cooling boxes are opened to control the temperature difference between the core and the surface of the wire rod during the extrusion process to not exceed 6°C. A Stelmor air cooling line is used for controlled cooling. When the temperature of the wire rod lap point is not lower than 750°C, the cooling rate of the wire rod surface is controlled to be 5-7°C / s. When the wire rod is cooled to 650-750°C, the cooling rate of the wire rod surface is controlled to be 1-2°C / s, and then air cooling is used to cool the wire rod to room temperature to obtain a hot-rolled wire rod with a diameter of 5.0-5.5 mm. The chemical components of the hot-rolled wire rod include, by mass percentage, C 0.012-0.028%, Si 0.02~0.05%, Mn 0.15~0.25%, B 0.009~0.020%, and the rest are Fe and unavoidable impurities; among which, the content of some impurities is limited to: the sum of the mass percentages of the three chemical components of Cr, Ni and Cu ≤0.03%, Al≤0.010%, S≤0.010%, P≤0.010%, O≤0.0050%, N≤0.0050%.

6. The method for manufacturing a low carbon steel hot rolled wire rod according to claim 5, characterized in that: The specific process of oxygen blowing decarburization, deoxidation and composition adjustment, calcium treatment and soft stirring of the molten steel during the RH vacuum treatment in step 3) is as follows: Oxygen blowing decarburization: according to the inbound composition, start oxygen blowing decarburization, according to E O2 =2000C%+49 to regulate the oxygen blowing amount, adjust the carbon content to 0.01~0.015%, and add 0.06~0.07kg / t of aluminum ingots to the molten steel; among them, E O2 Indicates the oxygen blowing amount, C% indicates the mass percentage of chemical component C; Deoxidation and composition adjustment: oxygenate the molten steel and add aluminum ingots for deoxidation according to the oxygen content. The amount of aluminum ingots added is 0.1-0.2 kg / t. After deoxidation, the aluminum content in the molten steel is controlled to ≤0.005%. Add 0.6-0.8 kg / t of ferroboron according to the composition of the molten steel and adjust the composition of the molten steel to C 0.012-0.028%, Si 0.02-0.05%, Mn 0.15-0.25%, and B 0.009-0.020%. Calcium treatment: After breaking the air, the molten steel is calcium treated by feeding 240~260m calcium wire into the molten steel at a feeding speed of 5~8m / s. During calcium treatment, the argon flow rate of the bottom blowing of the ladle is controlled at 350~420NL / min; Soft stirring: Control the argon flow rate at the bottom of the ladle to 50~70 NL / min, and after static treatment for 8~10 minutes, add ashing rice husks to the surface of the molten steel for insulation treatment.

7. The method for manufacturing a low carbon steel hot rolled wire rod according to claim 5, characterized in that: In step 4), the second stage secondary cooling section adopts three-zone water mist cooling, and the specific process parameters for performing the terminal soft reduction process after cooling in the secondary cooling section are: The water volumes of the three-zone water mist cooling are 110~115L / min, 70~80L / min, and 40~60L / min respectively. The process parameters for the terminal light pressing are: the pressing is distributed among the 2nd to 6th pairs of rollers, the pressing amount of the 2nd to 3rd pairs of rollers is 3~4mm, the pressing amount of the 4th to 6th pairs of rollers is 2~3mm, and the corner temperature must not be lower than 850℃ when the 1st to 4th pairs of rollers are pressing.

8. The method for manufacturing low carbon steel hot rolled wire rod according to claim 5, characterized in that: The specific contents of step 6) blank grinding are as follows: The rough grinding adopts an 18-grit grinding wheel with a linear speed of 60 m / min and a blank moving speed of 35 m / min. When grinding corners, the grinding wheel pressure is controlled to be 30-50 MPa; when grinding four sides, the grinding wheel pressure is controlled to be 35-60 MPa. The grinding depth, width and length ratio should be no less than 1:6:10, and the blank surface roughness is controlled to be 62-65 Rz. The finishing process uses a 35-grit grinding wheel with a linear speed of 70 m / min. The workpiece moving speed during grinding is 25 m / min. When grinding corners, the grinding wheel pressure is controlled at 20-25 MPa. When grinding four sides, the grinding wheel pressure is controlled at 25-40 MPa. The surface roughness of the workpiece is controlled to not exceed 20 Rz. The shot blasting uses pellets with a particle size of 2.5-3 mm, and the pellet speed is controlled at 5-8 m / s during shot blasting; The flaw detection adopts magnetic particle testing. During the flaw detection, the moving speed of the blank is 0.20~0.25m / s. An aqueous solution containing 0.5~0.7g / L fluorescent magnetic powder is sprayed onto the surface of the blank with a strength of not less than 950μm / cm 2 The ultraviolet rays are used for observation and the number of defects in each billet is required to be no more than 2.

9. The method for manufacturing low carbon steel hot rolled wire rod according to claim 5, characterized in that: In step 7), the maximum air volume of the fan during the cooling process using the Stelmor air cooling line is 280,000 m 3 / h.

10. A galvanized steel wire for mesh weaving, prepared by pickling, rough drawing, fine drawing, annealing and galvanizing the low-carbon steel hot-rolled wire rod according to any one of claims 1 to 4 or the hot-rolled wire rod produced by the manufacturing method according to any one of claims 5 to 9; The wire rod is pickled with hydrochloric acid to remove surface oxide scale, the hydrochloric acid concentration is controlled to be 20-22%, and the pickling time is 8-10 minutes; The descaled wire rod is coarse-drawn to a steel wire with a diameter of 2.9-3.2 mm, and then the steel wire is finely drawn in the forward direction to a diameter of 0.8-1.3 mm. The strength of the steel wire is controlled to be 470-500 MPa. The drawn steel wire is placed in a pit annealing furnace with a N2 protective atmosphere at a temperature of 600-700°C for 3-4 hours. The annealed steel wire is subjected to online pickling, water washing and galvanizing treatments, the temperature of the zinc solution is controlled at 470-480° C., and the strength of the final steel wire is 420-430 MPa.

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