Wire rod for steel wire cord and preparation method of wire rod

Abstract

The invention discloses a steel wire rod for a steel wire cord and a preparation method of the steel wire rod. The steel wire rod comprises the following components in percentage by mass: 0.82%-0.85% of C, 0.20%-0.30% of Si, 0.40%-0.50% of Mn, less than or equal to 0.012% of P, 0.0040%-0.010% of S, 0.0010%-0.0025% of total oxygen, 0.0005%-0.0015% of Als, 0.0001%-0.0010% of Nb, 0.0004%-0.0010% of Co, 0.0002%-0.0010% of Mg and the balance of iron and inevitable impurities. By designing an optimal chemical component system and matching with a production process matched with the optimal chemical component system, the steel wire cord prepared from the steel wire rod has high lay length uniformity, the lay length standard deviation is not larger than 0.7 mm, and the performance requirement of the mechanical manufacturing field for the steel wire cord is met.

Description

Technical Field

[0001] The present invention relates to the technical field of materials and metallurgy, and more specifically, to a wire rod for a steel cord and a preparation method thereof. Background Art

[0002] High carbon steel wire rods are widely used in the production of steel cords, bead wires, automotive control wires, hose wires and other products. Wire rods are processed by drawing and plying during use, so users have strict requirements on the processing performance of wire rods. The uniformity of the twist length after plying is an important indicator for evaluating the quality of steel cords. If the uniformity of the twist length of the steel cord does not meet the use requirements, it is easy to cause fatigue fracture of the steel cord during service.

[0003] The Chinese invention patent with publication number CN102268596B discloses a high carbon steel wire rod for producing fine steel wire, the chemical composition weight percentage of the wire rod is: [C]: 0.6% to 0.88%, [Si]: 0.1% to 1.0%, [Mn]: 0.3% to 1.0%, [P] ≤ 0.015%, [S] ≤ 0.010%, [N] ≤ 0.004%, [O] ≤ 0.002%, [Al] ≤ 0.002%, [Ti] ≤ 0.002%, [Mg] ≤ 0.001%, other unavoidable impurities are not higher than 0.1%, and the rest is iron. However, the high carbon steel wire rod prepared by it. The patent application focuses on optimizing the production process of cord steel wire rod, increasing output, and reducing production costs, and has not been specially designed from the perspective of improving the uniformity of the lay length of the steel cord.

[0004] With the increasing requirements for equipment service performance in the manufacturing field, in order to meet the user's requirements for the processing performance of wire rods for steel cords, especially the requirements for the uniformity of the twist pitch of steel wires made from wire rods, it is urgent to develop a precision wire rod for steel cords so that the steel cords prepared by wire rods have higher twist pitch uniformity and meet the performance requirements of steel cords in the mechanical manufacturing field. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a wire rod for steel cord and a preparation method thereof, so that the steel cord prepared by the wire rod has a higher twist uniformity and meets the performance requirements of the steel cord in the field of mechanical manufacturing.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A wire rod for steel cord comprises the following components in mass percentage: C: 0.82%-0.85%, Si: 0.20%-0.30%, Mn: 0.40%-0.50%, P≤0.012%, S: 0.0040%-0.010%, total oxygen: 0.0010%-0.0025%, Als: 0.0005%-0.0015%, Nb: 0.0001%-0.0010%, Co: 0.0004%-0.0010%, Mg: 0.0002%-0.0010%, and the balance is iron and inevitable impurities.

[0008] The present invention also discloses a method for preparing the wire rod for steel cord as described above, comprising the following steps: converter smelting, LF refining, continuous casting, continuous casting billet heating and continuous rolling, wire rod rolling, and wire rod cooling;

[0009] In the converter smelting, scrap steel and molten iron are used as furnace materials, and the scrap steel ratio is 3% to 10%;

[0010] In the continuous casting, the molten steel subjected to the LF refining treatment is continuously cast to obtain a continuously cast ingot;

[0011] During the continuous casting billet heating and continuous rolling, the continuous casting billet off the line in the continuous casting process is sent into a heating furnace for heating, and the heated continuous casting billet is continuously rolled, and the final rolling temperature is 950° C. to 1000° C.;

[0012] In the wire rod rolling, the steel billet after continuous rolling is heated in a heating furnace, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire laying in sequence;

[0013] During the cooling of the wire rod, the wire rod is cooled on an air-cooled roller after spinning to obtain the wire rod for the steel cord.

[0014] Implementing the embodiments of the present invention will have the following beneficial effects:

[0015] The present invention designs an optimal chemical composition system and matches it with production processes such as smelting, continuous casting billet heating and continuous rolling, rolling, cooling, etc., so that the steel cord prepared by wire rod has higher lay uniformity and the standard deviation of lay is not more than 0.7mm, which meets the performance requirements of steel cord in the field of mechanical manufacturing. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0017] 1. Chemical composition and mechanical properties

[0018] The invention discloses a wire rod for a steel cord, comprising the following components in mass percentage: C: 0.82%-0.85%, Si: 0.20%-0.30%, Mn: 0.40%-0.50%, P≤0.012%, S: 0.0040%-0.010%, total oxygen: 0.0010%-0.0025%, Als: 0.0005%-0.0015%, Nb: 0.0001%-0.0010%, Co: 0.0004%-0.0010%, Mg: 0.0002%-0.0010%, and the balance is iron and inevitable impurities.

[0019] Specifically, the mechanism of action of each alloy component in the wire rod of the present invention is as follows:

[0020] Carbon is the main element that controls the strength of the wire rod. If the carbon content of the wire rod is too low, it cannot meet the strength requirements of the user for the steel cord. If the content is too high, the strength of the steel wire will exceed the user's requirements; at the same time, a higher carbon content will increase the wire breakage rate during the drawing process of the wire rod, and the user's scrap rate will increase. Therefore, the carbon content in the present invention is controlled at 0.82% to 0.85%.

[0021] Silicon is the main deoxidizing element in high carbon steel. If the silicon content is low, the steel liquid will be insufficiently deoxidized; if the silicon content in the steel is too high, coarse silicate inclusions will appear in the steel, which will easily cause cracks between the inclusions and the matrix in the wire rod during the processing of the cord steel wire, resulting in cracking or breaking of the steel wire. Silicon increases the eutectoid transformation temperature of the steel, causes the pearlite to transform in the high temperature zone, and makes the pearlite structure of the wire rod coarse, which is not conducive to the complex deformation of the cord steel wire. Therefore, the silicon content in the present invention is controlled at 0.20% to 0.30%.

[0022] Manganese is an element that improves the strength of the wire, so that the steel wire meets the user's tensile strength requirements; manganese has the effect of reducing the eutectoid transformation temperature of steel, refining the pearlite structure of the wire rod, and improving the coordinated deformation ability of the wire rod at different parts during the cord wire processing process. Therefore, the manganese content in the present invention is controlled at 0.40% to 0.50%.

[0023] Phosphorus is easy to form band segregation in the wire rod, which reduces the coordinated deformation ability of different parts of the wire rod during the processing of the cord steel wire and causes cracking and breaking of the steel wire. Therefore, the phosphorus content in the present invention is controlled to be no higher than 0.012%.

[0024] A high sulfur content in the steel reduces the cold working performance of the wire rod and is prone to cause delamination and cracking of the wire rod during the processing of the cord steel wire. Since MnS inclusions have good deformation ability, an appropriate amount of sulfur in the steel can reduce the harm of non-deformable inclusions in the steel, prevent the generation of micro cracks caused by inclusions, and improve the uniform deformation ability of the steel wire. Therefore, the sulfur content in the present invention is controlled at 0.0040% to 0.010%.

[0025] When the oxygen content is low, the inclusions in the wire rod have a high melting point and poor deformation ability, and cracks are easy to appear between the inclusions and the matrix, which is not conducive to the processing of the cord steel wire; when the oxygen content is high, the inclusions in the steel are large in size, which is easy to cause micro cracks in the process of wire rod processing cord steel wire, causing the steel wire to crack. Therefore, the total oxygen content of the wire rod in the present invention is controlled at 0.0010% to 0.0025%.

[0026] When the acid-soluble aluminum content in the wire rod is too low, the melting point of the inclusions in the steel is high, and the deformation ability of the inclusions decreases, which is not conducive to the processing of the cord steel wire. 2 O 3 The increase of the content will easily lead to cracking of the cord steel wire during processing. Therefore, the content of the acid-soluble aluminum in the present invention is controlled to be 0.0005% to 0.0015%.

[0027] The niobium element uses undissolved compounds to hinder the coarsening of the grains of the steel billet during the heating process of the steel billet, ensuring that the wire rod structure meets the requirements of the cord wire processing. However, a higher niobium content causes the wire rod to be severely hardened during the steel wire processing process, and the coordinated deformation ability of different parts of the wire rod decreases, which easily leads to cracking and breaking of the steel wire. Therefore, the niobium content of the present invention is controlled at 0.0001% to 0.0010%.

[0028] Cobalt is dissolved in steel to improve its strength. However, the cobalt content in steel should not be too high to prevent the higher wire rod strength from reducing the drawing performance of the wire rod. Cobalt increases the precipitation temperature of proeutectoid ferrite, increases the transformation temperature of austenite to pearlite, inhibits the appearance of Widmanstätten structure in the wire rod, reduces the content of troostite in the wire rod, and improves the uniform deformation performance of the wire rod. Therefore, the cobalt content in the present invention is controlled at 0.0004% to 0.0010%.

[0029] The magnesium element controls the oxygen content in the steel and also controls the type of inclusions in the steel. A higher magnesium content causes magnesium-aluminum spinel inclusions to appear in the steel, which reduces the processing performance of the wire rod. An appropriate amount of magnesium content in the steel improves the deformation performance of the inclusions, expands the area with higher deformation of the inclusions, and is conducive to improving the coordinated deformation ability of the wire rod. Therefore, the magnesium content of the present invention is controlled at 0.0002% to 0.0010%.

[0030] In a specific embodiment, the tensile strength of the wire rod is 1050 MPa to 1150 MPa; and the standard deviation of the lay length is no more than 0.7 mm.

[0031] In a specific embodiment, the pearlite lamellae spacing at the surface of the wire rod of the present invention is 0.12μm to 0.16μm, the pearlite lamellae spacing at 1 / 4 diameter from the surface is 0.15μm to 0.22μm, and the pearlite lamellae spacing at the core is 0.18μm to 0.26μm.

[0032] 2. Production technology

[0033] The present invention also discloses a method for preparing a wire rod for steel cord as in any embodiment, comprising the following steps: converter smelting, LF refining, continuous casting, continuous casting billet heating and continuous rolling, wire rod rolling, and wire rod cooling.

[0034] Further, the method specifically includes the following steps:

[0035] S1. In converter smelting, scrap steel and molten iron are used as furnace charge, and the scrap steel ratio is 3% to 10%; slag stopper is used after the converter.

[0036] In S2 and LF refining, the molten steel discharged from the converter is sent to the LF furnace for refining. The refining temperature of the LF furnace is 1460°C to 1550°C, and the refining time is 30min to 50min. Argon stirring is performed during the refining process of the molten steel, and the argon flow rate is 200NL / min to 500NL / min.

[0037] S3. During continuous casting, the molten steel subjected to LF refining treatment is continuously cast to obtain a continuously cast ingot.

[0038] In a specific embodiment, during continuous casting, the cross-sectional size of the continuous casting billet is (250-300) mm × (350-400) mm; the surface temperature of the edge of the continuous casting billet during the straightening process is 900°C-935°C, and the temperature of the corner of the continuous casting billet is 785°C-830°C; the size of the molten steel inclusions at the LF entry position is not greater than 65 μm, and the size of the molten steel inclusions at the tundish position is not greater than 40 μm.

[0039] S4. During the continuous casting billet heating and continuous rolling, the continuous casting billet off the line in the continuous casting process is sent to a heating furnace for heating, and the heated continuous casting billet is continuously rolled, and the final rolling temperature of the continuous rolling is 950°C to 1000°C.

[0040] In a specific embodiment, the total furnace heating time of the continuous casting slab is 3.5h-4.2h; the soaking section temperature is 1200°C-1240°C, and the holding time is 40min-50min; and the original austenite grain size of the continuous rolling slab is 35μm-80μm.

[0041] S5. During the wire rod rolling, the steel billet after continuous rolling is heated in a heating furnace, and then sequentially subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire drawing.

[0042] In a specific embodiment, during the wire rod rolling, the wire rod is produced by a square billet, the total furnace time of the billet is 140min to 160min, the temperature of the heating section is 1000°C to 1160°C, the temperature of the soaking section is 1100°C to 1150°C, and the insulation time of the billet soaking section is 30min to 50min. By high-temperature diffusion of the billet, the segregation of elements such as carbon and manganese is reduced, and the grain size of the billet is controlled; the billet is heated to 880°C to 900°C, and the pearlite content in the core of the billet is 10% to 1 5%; the billet is heated to 980℃~1000℃, and the austenite content of the core structure of the billet is 95%~100%; after the billet is heated, it is subjected to high-pressure water descaling, rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling, and then the wire rod spinning operation is carried out; the billet high-pressure water descaling pressure is ≥14MPa; the wire rod pre-finishing rolling temperature is 985℃~1005℃; the finishing rolling temperature is 900℃~930℃; the double module temperature is 900℃~940℃; the wire rod spinning temperature is 900℃~920℃. The higher wire rod spinning temperature increases the cooling speed of the wire rod on the air-cooled roller, laying the foundation for controlling the final structure of the wire rod. The wire rod rolling specification is 5.0mm~6.5mm.

[0043] S6, during the cooling of the wire rod, the wire rod is cooled on an air-cooled roller after spinning to obtain a wire rod for steel cord.

[0044] In a specific embodiment, during the cooling of the wire rod, the wire rod is cooled on an air-cooled roller after spinning, and the cooling speed of the wire rod surface is controlled to be 15°C / s to 25°C / s.

[0045] The following are specific embodiments

[0046] Examples 1-6

[0047] The chemical composition, preparation process and performance parameters of the wire rods of Examples 1-6 of the present invention are shown in Table 1.

[0048] Table 1 Chemical composition, preparation process and performance parameters of wire rods of Examples 1-6

[0049]

[0050]

[0051] According to the above results, the present invention has carried out a large number of systematic experimental studies from the aspects of alloy element screening and proportioning, converter smelting, LF refining, continuous casting, continuous casting billet heating and continuous rolling, wire rod rolling, wire rod cooling process design optimization, etc., and finally determined the component system and its manufacturing process that can meet the purpose of the present invention, so that the steel cord prepared by wire rod has higher twist uniformity, and the standard deviation of twist is not more than 0.7mm, which meets the performance requirements of steel cord in the field of mechanical manufacturing.

[0052] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A wire rod for steel cord, It is characterized in that The following components are included in mass percentage: C: 0.82%~0.85%, Si: 0.20%~0.30%, Mn: 0.40%~0.50%, P≤0.012%, S: 0.0040%~0.010%, total oxygen: 0.0010%~0.0025%, Als: 0.0005%~0.0015%, Nb: 0.0001%~0.0010%, Co: 0.0004%~0.0010%, Mg: 0.0002%~0.0010%, and the balance is iron and unavoidable impurities.

2. The wire rod for steel cord according to claim 1, It is characterized in that The tensile strength of the wire rod is 1050MPa-1150MPa; the standard deviation of the lay length is ≤0.7mm.

3. The wire rod for steel cord according to claim 1, It is characterized in that The pearlite lamellae spacing at the surface of the wire rod is 0.12μm~0.16μm, the pearlite lamellae spacing at 1 / 4 diameter from the surface is 0.15μm~0.22μm, and the pearlite lamellae spacing at the center is 0.18μm~0.26μm.

4. A method for preparing a wire rod for a steel cord according to any one of claims 1 to 3, It is characterized in that The following steps are involved: Converter smelting, LF refining, continuous casting, continuous casting billet heating and rolling, wire rod rolling, wire rod cooling; In the converter smelting, scrap steel and molten iron are used as furnace materials, and the scrap steel ratio is 3% to 10%; In the continuous casting, the molten steel subjected to the LF refining treatment is continuously cast to obtain a continuously cast ingot; During the continuous casting billet heating and continuous rolling, the continuous casting billet off the line in the continuous casting process is sent into a heating furnace for heating, and the heated continuous casting billet is continuously rolled, and the final rolling temperature is 950° C. to 1000° C.; In the wire rod rolling, the steel billet after continuous rolling is heated in a heating furnace, and then subjected to rough rolling, intermediate rolling, pre-finishing rolling, finishing rolling, and wire laying in sequence; During the cooling of the wire rod, the wire rod is cooled on an air-cooled roller after spinning to obtain the wire rod for the steel cord.

5. The preparation method according to claim 4, It is characterized in that In the LF refining, the molten steel discharged from the converter is put into the LF furnace for refining treatment. The refining temperature of the LF furnace is 1460°C to 1550°C, and the refining time is 30min to 50min. Argon stirring is performed during the molten steel refining process, and the argon flow rate is 200NL / min to 500NL / min.

6. The preparation method according to claim 4, It is characterized in that In the continuous casting, the surface temperature of the edge of the continuous casting billet during the straightening process is 900°C to 935°C, and the temperature of the corner of the continuous casting billet is 785°C to 830°C; the size of the molten steel inclusions at the LF inlet position is ≤65μm, and the size of the molten steel inclusions at the tundish position is ≤40μm.

7. The preparation method according to claim 4, It is characterized in that During the continuous casting billet heating and continuous rolling, the total heating time of the continuous casting billet in the furnace is 3.5h-4.2h; the temperature of the soaking section is 1200°C-1240°C, and the holding time is 40min-50min; the original austenite grain size of the continuous rolling billet is 35μm-80μm.

8. The preparation method according to claim 4, It is characterized in that In the wire rod rolling, the total furnace time of the steel billet is 140min-160min, the temperature of the heating section is 1000℃-1160℃, the temperature of the soaking section is 1100℃-1150℃, the insulation time of the steel billet soaking section is 30min-50min, the steel billet is heated to 880℃-900℃, and the pearlite content in the core of the steel billet is 10%-15%; the steel billet is heated to 980℃-1000℃, and the core of the steel billet is 10%-15%. The austenite content of the local structure is 95% to 100%; after the billet is heated, it undergoes high-pressure water descaling, rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling before the wire rod spinning operation is carried out; the high-pressure water descaling pressure of the billet is ≥14MPa; the pre-finishing rolling temperature of the wire rod is 985℃~1005℃; the finishing rolling temperature is 900℃~930℃; the double module temperature is 900℃~940℃; the wire rod spinning temperature is 900℃~920℃.

9. The preparation method according to claim 4, It is characterized in that During the wire rod cooling, the wire rod is cooled on an air-cooled roller after spinning, and the cooling speed of the wire rod surface is controlled to be 15°C / s to 25°C / s.

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