A wire rod for super-fine automobile control wire and a manufacturing method thereof

Abstract

The application discloses a kind of super-fine automobile control wire rod and its manufacturing method, wire rod chemical composition:[C]0.60%~0.64%, [Si]0.15%~0.20%, [Mn]0.50%~0.60%, [Cr]0.05%~0.10%, [P]≤0.015%, [S]0.0020%~0.010%, total oxygen 0.0010%~0.0025%, [Als]0.0002%~0.0010%, [Co]0.0003%~0.0010%, [Nb]0.0003%~0.0012%, [Se]0.00002%~0.0003%.Manufacturing method includes steel liquid smelting and continuous casting, casting blank heating and rolling, wire rod rolling, wire rod laying, wire rod cooling, the application is by component and process control makes wire rod in single filament diameter 0.13mm~0.14mm automobile control wire processing process ply broken filament rate index is reduced from 1.0 to 0.6, meet the quality requirement of user super-fine automobile control wire production.

Description

TECHNICAL FIELD

[0001] The application relates to a kind of ultra-fine automobile control wire rod and its manufacturing method, and belongs to the technical field of wire rod. BACKGROUND

[0002] The automobile control wire rod is used for the production of automobile brake wire, direction control wire and other products related to the safe operation of automobile, which requires the wire rod to have good drawing performance. The wire rod is easy to draw, which not only reduces the wire breakage rate, but also reduces the power consumption in the wire rod drawing process, achieving the purpose of saving energy.

[0003] A "high-carbon steel wire rod for producing fine steel wire" is disclosed in Chinese patent application No. CN202210812570.5. The chemical composition of the wire rod is as follows: a kind of ultra-high strength wire rod, steel wire, cord and manufacturing method, the chemical composition of the wire rod is as follows: [C] 0.83% ~ 0.87%, [Si] 0.13% ~ 0.24%, [Mn] 0.48% ~ 0.65%, [W] 0.0003% ~ 0.0025%, [Mo] 0.0005% ~ 0.0020%, ALs 0.0001% ~ 0.0005%, T.O 0.0008% ~ 0.0015%, the rest is Fe and unavoidable impurities. Through the design of chemical composition and production process, the U-type fatigue life of 2x0.3mm specification ultra-high strength steel wire cord made of the wire rod reaches 44000 times.

[0004] With the tightening of national energy-saving and environmental protection policies, metal product manufacturers need steel plants to provide high-quality wire rods to meet the production requirements of automobile control wire with a single wire diameter of 0.13mm ~ 0.14mm (original single wire diameter of 0.20mm), realize the upgrading of automobile control wire products, and achieve the purpose of high efficiency and energy saving and emission reduction of automobile manufacturing.

[0005] The hypoeutectoid steel wire rod with a carbon content of 0.7% is applied in the field of automobile control wire manufacturing to achieve the best combination of strength and flexibility of automobile control wire. In the production process of the wire rod, the chemical composition of the automobile control wire rod needs to be strictly controlled. In addition, the hypoeutectoid steel wire rod used for automobile control wire production has proeutectoid ferrite precipitated, coarse proeutectoid ferrite or network-shaped proeutectoid ferrite significantly reduces the drawing performance of the wire rod in the production process of automobile control wire, which is easy to cause the wire rod to break during drawing. Thick or thin pearlite lamellar structure also easily leads to wire breakage during the preparation of automobile control wire. Therefore, the chemical composition and microstructure of the hypoeutectoid steel wire rod used for automobile control wire production need to be strictly controlled. SUMMARY

[0006] The present application aims to provide a kind of super fine automobile control wire wire rod and its manufacturing method, by the design of chemical composition and production process, performance meets the production requirement of single filament diameter 0.13mm~0.14mm automobile control wire.

[0007] To solve the above problems, the technical scheme adopted by the present application is as follows:

[0008] A kind of super fine automobile control wire wire rod, chemical composition is as follows according to mass percentage:[C]0.60%~0.64%, [Si]0.15%~0.20%, [Mn]0.50%~0.60%, [Cr]0.05%~0.10%, [P]≤0.015%, [S]0.0020%~0.010%, total oxygen 0.0010%~0.0025%, [Als]0.0002%~0.0010%, [Co]0.0003%~0.0010%, [Nb]0.0003%~0.0012%, [Se]0.00002%~0.0003%, the balance is Fe and inevitable impurities.

[0009] Further, wire rod pearlite spherulite size 2~22 μm (EBSD detection result), proeutectoid ferrite thickness is not more than 4 μm, no closed or semi-closed network ferrite structure appears.

[0010] Further, the grain pearlite spherulite misorientation difference is ≤10 °, accounting for 35%~60%, and the pearlite spherulite misorientation difference is 10 °~30 °, accounting for 28%~47%.

[0011] Further, the tensile strength of the wire rod is 920~980 MPa, and the area reduction is 40%~55%.

[0012] Further, the wire rod rolling specification is 5.0~6.0mm.

[0013] A kind of super fine automobile control wire wire rod manufacturing method, including liquid steel smelting and continuous casting, billet heating and rolling, wire rod rolling, wire rod wire drawing, wire rod cooling, wherein,

[0014] Billet heating and rolling: billet heating total furnace time is 3.6~4.5h, the temperature in soaking section is controlled at 1220~1250℃, the soaking section holding time is 35~50min, after billet heating, continuous rolling is carried out, and the final rolling temperature of continuous rolling is controlled at 920~1030℃;

[0015] Rod rolling: the total heating time of the continuous rolling billet is 145-165 min, the temperature of the soaking section is 1120-1150℃, and the soaking time is 35-55 min; after the continuous rolling billet is heated, it is subjected to rough rolling, intermediate rolling, pre-precision rolling, precision rolling and double-module rolling, and then rod wire drawing is performed; the temperature of the rolled piece at the exit of the intermediate rolling is 830-880℃, the deformation rate of the rolled piece at the last stand of the intermediate rolling is 7-10 s -1 ; the temperature of the rolled piece at the exit of the pre-precision rolling is 970-990℃, the deformation rate of the rolled piece at the last stand of the pre-precision rolling is 50-70 s -1 ; the temperature of the rolled piece at the exit of the precision rolling is 920-960℃, and the deformation rate of the rolled piece at the last stand of the precision rolling is 760-800 s -1 ;

[0016] Rod wire drawing: the temperature of the rod wire drawing is controlled at 910-940℃;

[0017] Rod cooling: after the wire drawing, the rod is subjected to water bath treatment, and the cooling speed of the rod during the water bath process is controlled at 10-20℃ / s.

[0018] Further, the cross-sectional size of the continuous casting billet is (300-350) mm*(400-450) mm, and the cross-sectional size of the continuous rolling billet is (140-180) mm*(140-180) mm.

[0019] Further, the grain size of the surface position of the cross section of the continuous rolling billet is controlled at 30-60μm, the grain size of the 1 / 4 side length position is controlled at 35-70μm, and the grain size of the core is controlled at 40-70μm.

[0020] Further, after the molten steel is smelted, LF refining is adopted, the LF furnace refining time is controlled at 35-45 min, the refining temperature is controlled at 1480-1540℃, argon stirring is performed during the refining process, and the argon flow is controlled at 300-500 NL / min.

[0021] Further, during the straightening process, the surface temperature of the edge of the continuous casting billet is 885-915℃, and the temperature of the corner of the continuous casting billet is 790-830℃.

[0022] Compared with the prior art, the rod wire produced by adopting the technical scheme of the present application has the following advantages: the size of the pearlite ball is 2-22μm, the thickness of the eutectoid network ferrite is not greater than 4μm, and no closed or semi-closed network ferrite structure appears; during the twisting process of the rod wire with a single wire diameter of 0.13mm-0.14mm for automobile control wire, the twisted wire breakage rate index is reduced from 1.0 to 0.6, which meets the quality requirements of the user for ultra-fine automobile control wire production. DETAILED DESCRIPTION

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0024] The chemical composition design principles of the wire rod described in this invention are as follows (by mass percentage):

[0025] The chemical composition of the wire rod applicable to this invention is as follows: [C] 0.60%–0.64%, [Si] 0.15%–0.20%, [Mn] 0.50%–0.60%, [Cr] 0.05%–0.10%, [P] ≤0.015%, [S] 0.0020%–0.010%, total oxygen 0.0010%–0.0025%, [Als] 0.0002%–0.0010%, [Co] 0.0003%–0.0010%, [Nb] 0.0003%–0.0012%, [Se] 0.00002%–0.0003%, with the balance being Fe and unavoidable impurities.

[0026] The pearlite pellet size of the wire rod is 2–22 μm. The fine pearlite grains in the wire rod suppress the formation of microcracks during the drawing process, reducing the wire breakage rate. The proeutectoid ferrite thickness of the wire rod is no greater than 4 μm, and no closed or semi-closed network ferrite structure is observed.

[0027] The grain orientation characteristics of the wire rod are as follows: 35%–60% of the grains have a pearlite cluster orientation difference ≤10°; 28%–47% have a pearlite cluster orientation difference 10°–30° (excluding endpoint values); and the remainder are grains with a pearlite cluster orientation difference ≥30°. By controlling the orientation difference distribution of the pearlite grains in the wire rod, the generation of microcracks in the wire rod during the automotive control line production process is suppressed, thereby improving the wire rod's drawing performance.

[0028] The wire rod has a tensile strength of 920–980 MPa and a shrinkage rate of 40%–55%.

[0029] The rationale for setting the range of chemical composition of the wire rod in this invention is as follows.

[0030] Carbon: If the carbon content in the wire rod is too low, it will not meet the strength requirements of the user during wire drawing; if the carbon content is too high, it will increase the wire breakage rate during the wire production process and reduce the quality of the finished automotive control line. Therefore, the carbon content in this invention is controlled at 0.60% to 0.64%.

[0031] Silicon: Silicon is the main deoxidizing element in high-carbon steel. Low silicon content will result in insufficient deoxidation of the molten steel; excessive silicon content will lead to coarse silicate inclusions after deoxidation, thus reducing the quality of the finished product from the automotive control line. Furthermore, silicon increases the eutectoid transformation temperature of steel, causing the austenite-to-pearlite transformation to occur in the high-temperature region, increasing the interlamellar spacing of the pearlite structure, which is detrimental to quality control in automotive control lines. Therefore, the silicon content in this invention is controlled at 0.15%–0.20%.

[0032] Manganese: Manganese is also an element that improves the strength of wire rod; however, excessive manganese content leads to severe segregation in the wire rod, which is detrimental to improving its cold working performance. Manganese has the effect of lowering the eutectoid transformation temperature of steel, refining the pearlite lamellar spacing, and improving the processing performance of wire rod used for automotive control lines. Therefore, the manganese content in this invention is controlled at 0.50% to 0.60%.

[0033] Chromium: Chromium in wire rod improves hardenability, inhibits the formation of coarse ferrite and network ferrite, refines the wire rod microstructure, and improves the machinability of wire rod used for automotive control lines. Excessive chromium content in wire rod leads to excessive work hardening during processing, rapid increase in wire strength, and increased wire breakage rate during drawing. Therefore, the chromium content in this invention is controlled at 0.05%–0.10%.

[0034] Phosphorus: Phosphorus tends to form banded segregation in wire rods, which can easily cause wire breakage during drawing. Therefore, the phosphorus content in this invention is controlled at ≤0.015%.

[0035] Sulfur: High sulfur content in steel reduces the drawing performance of wire rods during automotive control line production. Since MnS inclusions have good deformability, an appropriate amount of sulfur in the steel can reduce the harmful effects of non-deformable inclusions and prevent the formation of microcracks caused by these inclusions. Therefore, the sulfur content in this invention is controlled at 0.0020%–0.010%.

[0036] Oxygen: When the oxygen content is low, the inclusions in the wire rod have poor deformation ability, which is not conducive to the processing of automotive control lines; when the oxygen content in the wire rod is high, the inclusions in the steel are large in size and numerous, which easily leads to cracking and breakage of automotive control lines during processing. Therefore, in this invention, the total oxygen content of the wire rod is controlled at 0.0010% to 0.0025%.

[0037] Acid-soluble aluminum: When the acid-soluble aluminum content is high, large Al2O3 inclusions will appear in the steel; 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 cracks are easily formed between the inclusions and the matrix during processing, leading to breakage of the automotive control lines. Therefore, the acid-soluble aluminum content in this invention is controlled at 0.0002% to 0.0010%.

[0038] Cobalt: Cobalt can inhibit grain growth in steel billets during heating, reducing the probability of coarse proeutectoid ferrite or network ferrite in wire rods, and lowering the wire breakage rate during ultra-fine automotive control line production. Cobalt improves the drawing performance of wire rods by inhibiting grain growth in steel billets and refining the pearlite structure. However, high cobalt content leads to severe work hardening during wire processing, making the wire prone to cracking and breakage. Therefore, the cobalt content in this invention is controlled at 0.0003% to 0.0010%.

[0039] Niobium: Niobium can inhibit grain growth in steel billets during heating, reducing the likelihood of coarse proeutectoid ferrite or network ferrite in wire rods. Niobium can refine the wire rod microstructure, improving its machinability. Niobium can also inhibit the propagation of internal cracks in wire rods or steel wires through the precipitation of niobium compounds. However, excessively high niobium content in steel leads to significant work hardening during deformation, reducing the wire rod's deep processing capability. Therefore, the niobium content in this invention is controlled at 0.0003%–0.0012%.

[0040] While cobalt and niobium can improve the drawing performance of wire rods, they cause severe work hardening and increased crack susceptibility in the final stage of ultra-fine wire drawing. This invention, building upon the reduction of crack susceptibility in wire rods or wires by niobium, further reduces crack susceptibility in the final drawing stage of wire rods by using selenium.

[0041] Selenium: In steel, selenium forms selenides with elements such as manganese and niobium. Selenides are finer than sulfides and have a more significant inhibitory effect on the propagation of microcracks, reducing the crack sensitivity of wire rods in the final drawing stage of ultra-fine steel wire. However, excessively high selenium content in steel reduces the drawing performance of wire rods. Therefore, the selenium content in this invention is controlled at 0.00002% to 0.0003%.

[0042] The method for manufacturing wire rod of the present invention includes the following steps:

[0043] Steelmaking and Continuous Casting: After smelting, the molten steel is refined using an LF furnace. The LF furnace refining time is controlled at 35–45 min, and the refining temperature is controlled at 1480–1540℃. Argon gas is used for stirring during the refining process, and the argon gas flow rate is controlled at 300–500 NL / min. The refined molten steel is then continuously cast, and the cross-sectional dimensions of the continuously cast billet are (300–350) mm * (400–450) mm. During the straightening process, the surface temperature of the edge of the continuously cast billet is 885–915℃, and the corner temperature is 790–830℃.

[0044] Billet heating and rolling: The total furnace time for continuous casting billet heating is 3.6–4.5 hours. The temperature in the soaking zone is controlled at 1220–1250℃, and the holding time in the soaking zone is 35–50 minutes. After heating, the continuous casting billet is continuously rolled, and the final rolling temperature is controlled at 920–1030℃. The cross-sectional dimensions of the continuously rolled billet are (140–180) mm * (140–180) mm. The grain size at the centerline surface of the cross-section of the continuously rolled billet is controlled at 30–60 μm, the grain size at 1 / 4 of the side length is controlled at 35–70 μm, and the grain size in the core is controlled at 40–70 μm.

[0045] Wire rod rolling: The total furnace time for continuously rolled steel billets is 145–165 min, with a soaking temperature of 1120–1150℃; grain size is controlled through high-temperature diffusion in the billet; the soaking time is 35–55 min. After heating, the billet undergoes roughing, intermediate rolling, pre-finishing, finishing, and double-module rolling before wire rod production. The wire rod diameter is 5.5 mm. The temperature of the rolled piece exiting the intermediate rolling mill is 830–880℃, and the deformation rate in the last stand of the intermediate rolling mill is 7–10 s. -1 The pre-finishing rolling temperature of the rolled piece is 970–990℃, and the deformation rate of the rolled piece in the last stand of the pre-finishing rolling is 50–70 s. -1 The finishing temperature of the rolled piece is 920–960℃, and the deformation rate of the rolled piece in the last stand of the finishing mill is 760–800 s. -1 ;

[0046] Wire rod spinning: The wire rod spinning temperature is controlled between 910 and 940℃. By using a higher wire rod spinning temperature, the cooling rate of the wire rod on the air-cooled roller conveyor is increased, laying the foundation for controlling the final microstructure of the wire rod.

[0047] Wire rod cooling: After wire drawing, the wire rod undergoes a water bath treatment, with the cooling rate controlled between 10 and 20°C / s. After final cooling, the wire rod is predominantly sorbitic with a sorbitization rate of 80% to 90%, which facilitates wire drawing by the user.

[0048] Examples of the present invention are described below.

[0049]

[0050]

[0051]

[0052]

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A type of wire rod for ultra-fine automotive control lines, characterized in that, The ultra-fine automotive control wire has a single filament diameter of 0.13–0.14 mm. The chemical composition of the wire rod used, by mass percentage, is as follows: [C] 0.60%–0.64%, [Si] 0.16%–0.20%, [Mn] 0.50%–0.58%, [Cr] 0.05%–0.10%, [P] ≤0.015%, [S] 0.0020%–0.010%, total oxygen 0.0010%–0.0025%, [Als] 0.0002%–0.0010%, [Co] 0.0003%–0.0010%, [Nb] 0.0003%–0.0012%, [Se] 0.00002%~0.0003%, balance being Fe and unavoidable impurities; the pearlite pellet size of the wire rod is 2~22μm, the proeutectoid ferrite thickness is no more than 4μm, and no closed or semi-closed network ferrite structure is observed.

2. The wire rod for ultra-fine automotive control lines according to claim 1, characterized in that, Pearlite clusters with an orientation difference ≤10° account for 35%–60%, while pearlite clusters with an orientation difference of 10°–30° account for 28%–47%.

3. The wire rod for ultra-fine automotive control lines according to claim 1, characterized in that, The wire rod has a tensile strength of 920–980 MPa and a shrinkage rate of 40%–55%.

4. The wire rod for ultra-fine automotive control lines according to claim 1, characterized in that, The wire rod is rolled to a diameter of 5.0–6.0 mm.

5. A method for manufacturing wire rod for ultra-fine automotive control lines according to any one of claims 1 to 4, comprising steel smelting and continuous casting, billet heating and rolling, wire rod rolling, wire rod wire drawing, and wire rod cooling, characterized in that, Billet heating and rolling: The total furnace time for billet heating is 3.6 to 4.5 hours, the temperature of the soaking zone is controlled at 1220 to 1250℃, the holding time of the soaking zone is 35 to 50 minutes, and the billet is continuously rolled after heating. The final rolling temperature of the continuous rolling is controlled at 920 to 1030℃. Wire rod rolling: The total furnace time for continuously rolled steel billets is 145–165 min, the soaking zone temperature is 1120–1150℃, and the soaking zone holding time is 35–55 min; after heating, the continuously rolled steel billets undergo roughing, intermediate rolling, pre-finishing, finishing rolling, and double-module rolling before wire rod production; the temperature of the rolled piece exiting the intermediate rolling mill is 830–880℃, and the deformation rate of the rolled piece in the last stand of the intermediate rolling mill is 7–10 s. -1 The pre-finishing rolling temperature of the rolled piece is 970–990℃, and the deformation rate of the rolled piece in the last stand of the pre-finishing rolling is 50–70 s. -1 The finishing temperature of the rolled piece is 920~960℃, and the deformation rate of the rolled piece in the last stand of the finishing mill is 760~800s. -1 ; Wire rod spinning: The wire rod spinning temperature is controlled between 910 and 940℃; Wire rod cooling: After wire drawing, the wire rod is treated with a water bath. The cooling rate during the water bath process is controlled between 10 and 20°C / s.

6. The method for manufacturing a wire rod for ultra-fine automotive control lines according to claim 5, characterized in that, The cross-sectional dimensions of the continuously cast billet are (300~350)mm*(400~450)mm, and the cross-sectional dimensions of the continuously rolled billet are (140~180)mm*(140~180)mm.

7. A method for manufacturing a wire rod for ultra-fine automotive control lines according to claim 5, characterized in that, The grain size at the centerline surface of the cross-section of the continuously rolled billet is controlled to be 30–60 μm, the grain size at the 1 / 4 edge length position is controlled to be 35–70 μm, and the grain size at the core is controlled to be 40–70 μm.

8. A method for manufacturing a wire rod for ultra-fine automotive control lines according to claim 5, characterized in that, After the molten steel is smelted, it is refined by LF furnace. The refining time in the LF furnace is controlled at 35 to 45 minutes, and the refining temperature is controlled at 1480 to 1540℃. Argon gas is used for stirring during the refining process, and the argon gas flow rate is controlled at 300 to 500 NL / min.

9. A method for manufacturing a wire rod for ultra-fine automotive control lines according to claim 5, characterized in that, During the straightening process, the surface temperature of the edge of the continuously cast billet is 885-915℃, and the temperature of the corner of the continuously cast billet is 790-830℃.

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