A production method of 70# high carbon hard wire steel rod for spring

Abstract

The application discloses a production method of 70# high-carbon hard wire steel wire rod for spring, which comprises the following steps: hot metal pretreatment, converter smelting, LF refining, continuous casting, casting blank heating, rolling, finishing, and drawing after pickling and phosphating treatment of the wire rod, wherein the total compression rate is controlled to be 80-85%, and the finished product diameter is 5.5-12.0 mm. The application aims at solving the technical problems of insufficient composition control precision, casting blank quality defects, poor surface quality, poor organization uniformity and low process efficiency in the production of the existing 70# steel wire rod.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and particularly relates to a method for producing 70# high-carbon hard wire rod for springs. It is especially suitable for the industrial production of 70# steel wire rod for springs, and the resulting product can be used to manufacture various helical springs, leaf springs, and mechanical damping components. Background Technology

[0002] High-carbon hardened wire rod for springs requires high strength, elastic limit, and good toughness matching, while also having strict requirements for surface quality, internal purity, and microstructure uniformity. Currently, the production of 70# steel wire rod mainly faces the following technical challenges:

[0003] Insufficient precision in component control: The content of harmful elements such as S and P in the existing process is too high, usually only ≤0.035%, which leads to a decrease in the plasticity and toughness of the wire rod, and cracks are easily generated during the drawing process.

[0004] Cast billet quality defects: High carbon steel is prone to defects such as center segregation, shrinkage cavities and porosity during continuous casting, which is particularly serious when producing small square billets, resulting in uneven mechanical properties of the subsequently rolled wire rod.

[0005] Surface quality issues: Continuously cast billets are prone to defects such as vibration marks and corner cracks, which can lead to surface folds and cracks after rolling, affecting the fatigue performance and service life of wire rods.

[0006] Poor uniformity of structure: The spacing between pearlite lamellars in wire rod produced by existing processes is uneven, and there is a network of cementite, which leads to unstable drawing performance and high wire breakage rate.

[0007] Low process efficiency: Some processes use two-stage firing, which is complex, energy-intensive, results in low yield, and high production costs.

[0008] The aforementioned problems make it difficult for existing 70# steel wire rods to meet the requirements of high-end springs for high strength, high toughness, and high fatigue performance, thus hindering the technological upgrading of the spring industry. Summary of the Invention

[0009] To address the technical problems existing in the production of 70# steel wire rod, such as insufficient precision in composition control, defects in cast billet quality, poor surface quality, poor microstructure uniformity, and low process efficiency, the present invention aims to provide a production method that can stably produce 70# high-carbon hard wire rod for springs with high purity, high surface quality, and uniform microstructure, and the resulting product meets the requirements of high-end spring manufacturing.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] This invention discloses a method for producing 70# high-carbon hard wire rod for springs, comprising the following steps:

[0012] Hot metal pretreatment: Hot metal is subjected to three removal processes to control S≤0.005%, P≤0.010%, and temperature 1250-1300℃;

[0013] Converter smelting: Single slag method is adopted for smelting, and the final slag basicity is controlled at 3.0-3.5; the final temperature is 1640-1660℃, and the C content is 0.60-0.65%; ferromanganese and ferrosilicon are added during the tapping process for deoxidation and alloying, and aluminum is used for final deoxidation.

[0014] LF Refining: Refining time 30-40 min, the steel composition is controlled as follows by mass percentage: C: 0.67-0.72%, Si: 0.20-0.30%, Mn: 0.60-0.70%, P≤0.015%, S≤0.010%, Als: 0.015-0.030%, the remainder being Fe and unavoidable impurities; the steel temperature is controlled at 1550-1570℃.

[0015] Continuous casting: 150×150mm square billet cross-section is used, and the continuous casting speed is 1.9-2.1m / min (preferably 2.0m / min); the crystallizer uses electromagnetic stirring with a current intensity of 200-250A and a frequency of 3-5Hz; the secondary cooling zone adopts a weak cooling regime with a specific water content of 0.8-1.0L / kg; after the billet exits the crystallizer, a light reduction technique is used with a reduction of 3-5mm.

[0016] Heating of billet: Heating temperature 1050-1080℃, holding time 90-120min, furnace atmosphere controlled as weakly reducing to prevent surface decarburization;

[0017] Rolling: A one-fire forming process is adopted, with roughing temperature of 1000-1050℃, finishing temperature of 850-880℃, and final rolling temperature of 800-830℃; controlled rolling and controlled cooling technology is adopted, with wire drawing temperature of 800-820℃, and the fan speed of the Steyrmo cooling line is controlled at 0.8-1.2m / s, followed by air cooling after cooling to 600℃;

[0018] Finishing: After pickling and phosphating, the wire rod is drawn with a total compression rate controlled at 80-85% and a finished diameter of 5.5-12.0mm.

[0019] Furthermore, after pretreatment, the molten iron has S≤0.004% and P≤0.008%.

[0020] Furthermore, the basicity of the final slag from the converter smelting is 3.0-3.2, and the final temperature is 1645-1655℃.

[0021] Furthermore, the composition of the molten steel, by mass percentage, is C: 0.68-0.71%, Si: 0.22-0.28%, Mn: 0.62-0.68%, P≤0.012%, S≤0.009%, with the remainder being Fe and impurities.

[0022] Furthermore, the electromagnetic stirring current intensity of the crystallizer is 200-250A, and the frequency is 3-5Hz.

[0023] Furthermore, the specific water content in the secondary cooling zone of continuous casting is 0.85-0.95 L / kg, and the light reduction is 3.5-4.5 mm.

[0024] Furthermore, the billet heating temperature is 1060-1070℃, and the holding time is 100-110min.

[0025] Furthermore, the final rolling temperature is 810-820℃, the wire drawing temperature is 805-815℃, and the fan speed of the Steyrmo cooling line is 0.9-1.1m / s.

[0026] Furthermore, the total compression rate during drawing is 82-84%, and the diameter of the finished steel wire is 6.0-8.0 mm.

[0027] Furthermore, the mechanical properties of the prepared 70# steel wire rod meet the following requirements: tensile strength 1200-1400MPa, yield strength ≥900MPa, elongation after fracture ≥9%, reduction of area ≥35%, pearlite lamellar spacing 100-150nm, and wire breakage rate ≤0.5%.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0029] Precise composition control: Through molten iron pretreatment and LF refining, the P and S contents are controlled at ≤0.015% and ≤0.010% respectively, which significantly improves the purity of molten steel and enhances the plasticity and toughness of wire rod.

[0030] Excellent billet quality: The use of electromagnetic stirring and light reduction technology effectively reduces center segregation and shrinkage cavities, with a billet center segregation index ≤1.1, meeting the requirements for high-end spring steel.

[0031] High surface quality: By optimizing the crystallizer parameters and the secondary cooling process, the surface oscillation mark depth of the billet is ≤0.3mm, there are no corner cracks, and the surface finish of the rolled wire rod is high.

[0032] Good uniformity of structure: The obtained wire rod has uniform pearlite lamellar spacing of 100-150nm, no network cementite, tensile strength of 1200-1400MPa, yield strength ≥900MPa, elongation after fracture ≥9%, and reduction of area ≥35%, meeting the mechanical performance requirements of high-end springs.

[0033] High process efficiency: The one-fire forming process simplifies the production process, reduces energy consumption by 15-20%, increases the yield to over 98%, and significantly reduces production costs.

[0034] Stable drawing performance: The wire breakage rate during wire drawing is reduced to below 0.5%, meeting the requirements of large-scale continuous drawing production. Detailed Implementation

[0035] Example 1

[0036] This embodiment provides a method for producing 70# high-carbon hard wire rod for springs, including the following steps:

[0037] Hot metal pretreatment: The hot metal is subjected to three removal processes, and after treatment, S=0.004%, P=0.008%, and the temperature is 1280℃.

[0038] Converter smelting: Single slag method is adopted, with a final slag basicity of 3.2; final temperature of 1650℃ and C content of 0.62%; ferromanganese and ferrosilicon are added during tapping for deoxidation and alloying, and aluminum is finally deoxidized.

[0039] LF Refining: Refining time 35 min, the composition of molten steel is controlled by mass percentage as follows: C: 0.69%, Si: 0.25%, Mn: 0.65%, P: 0.012%, S: 0.008%, Als: 0.022%, the remainder being Fe and unavoidable impurities; molten steel temperature 1560℃.

[0040] Continuous casting: 150×150mm square billet cross section, continuous casting speed 2.0m / min; crystallizer electromagnetic stirring current 220A, frequency 4Hz; secondary cooling zone water volume 0.9L / kg; billet light reduction 4mm.

[0041] Billet heating: heating temperature 1070℃, holding time 100min, furnace atmosphere is weakly reducing.

[0042] Rolling: The process of forming material in one fire is adopted. The roughing temperature is 1020℃, the finishing temperature is 860℃, and the final rolling temperature is 810℃. The wire drawing temperature is 810℃. The fan speed of the Steyrmo cooling line is 1.0m / s. After cooling to 600℃, it is air-cooled.

[0043] Finishing: After pickling and phosphating, the wire rod is drawn with a total compression rate of 82% and a finished diameter of 6.5mm.

[0044] The mechanical properties of the obtained 70# steel wire rod are as follows: tensile strength 1320MPa, yield strength 950MPa, elongation after fracture 10%, reduction of area 38%, pearlite lamellar spacing 120nm, no network cementite, and wire breakage rate 0.3%.

[0045] Example 2

[0046] This embodiment is basically the same as Embodiment 1, except that:

[0047] The composition of LF refined molten steel is: C: 0.71%, Si: 0.22%, Mn: 0.68%, P: 0.014%, S: 0.009%, Als: 0.025%, with the remainder being Fe and impurities.

[0048] The water content in the secondary cooling zone of continuous casting is 0.8 L / kg, and the light reduction is 3 mm.

[0049] The final rolling temperature is 820℃, the wire drawing temperature is 820℃, and the fan speed of the Steilmo cooling line is 1.2m / s.

[0050] The mechanical properties of the obtained 70# steel wire rod are: tensile strength 1380MPa, yield strength 980MPa, elongation after fracture 9%, reduction of area 36%, pearlite lamellar spacing 110nm, and wire breakage rate 0.4%.

[0051] Comparative Example

[0052] The production of 70# steel wire rod is carried out using existing conventional processes, as detailed below:

[0053] Hot metal pretreatment: S=0.020%, P=0.025%.

[0054] Converter smelting: final slag basicity 2.5, final C=0.58%.

[0055] LF Refined: Composition: C: 0.73%, Si: 0.35%, Mn: 0.78%, P=0.030%, S=0.025%.

[0056] Continuous casting: 150×150mm square billet, casting speed 1.6m / min, no electromagnetic stirring, no light pressing.

[0057] Heating: Temperature 1100℃, holding time 80min.

[0058] Rolling: One-time rolling, final rolling temperature 850℃, wire drawing temperature 850℃, natural air cooling.

[0059] The mechanical properties of the obtained 70# steel wire rod are as follows: tensile strength 1150MPa, yield strength 820MPa, elongation after fracture 7%, reduction of area 28%, uneven pearlite lamellar spacing with a maximum of 200nm, presence of a small amount of network cementite, and wire breakage rate of 2.8%.

[0060] Comparing Examples 1 and 2 with the comparative example, it can be seen that the 70# steel wire rod produced by the method of the present invention is significantly superior to the prior art in terms of composition control, mechanical properties, microstructure uniformity and drawing performance.

[0061] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing 70# high-carbon hard wire rod for springs, characterized in that, Includes the following steps: Hot metal pretreatment: control S≤0.005%, P≤0.010%, temperature 1250-1300℃; Converter smelting: Single slag method is adopted for smelting, and the final slag basicity is controlled at 3.0-3.5; the final temperature is 1640-1660℃, and the C content is 0.60-0.65%; ferromanganese and ferrosilicon are added during the tapping process for deoxidation and alloying, and aluminum is used for final deoxidation. LF Refining: Refining time 30-40 min, the steel composition is controlled as follows by mass percentage: C: 0.67-0.72%, Si: 0.20-0.30%, Mn: 0.60-0.70%, P≤0.015%, S≤0.010%, Als: 0.015-0.030%, the remainder being Fe and unavoidable impurities; the steel temperature is controlled at 1550-1570℃. Continuous casting: 150×150mm square billet cross section is used, and the continuous casting speed is 1.9-2.1m / min; the crystallizer adopts electromagnetic stirring, with a current intensity of 200-250A and a frequency of 3-5Hz; the secondary cooling zone adopts a weak cooling regime with a specific water content of 0.8-1.0L / kg; after the billet exits the crystallizer, a light reduction technique is used, with a reduction of 3-5mm; Heating of billet: Heating temperature 1050-1080℃, holding time 90-120min, furnace atmosphere controlled as weakly reducing to prevent surface decarburization; Rolling: A one-fire forming process is adopted, with roughing temperature of 1000-1050℃, finishing temperature of 850-880℃, and final rolling temperature of 800-830℃; controlled rolling and controlled cooling technology is adopted, with wire drawing temperature of 800-820℃, and the fan speed of the Steyrmo cooling line is controlled at 0.8-1.2m / s, followed by air cooling after cooling to 600℃; Finishing: After pickling and phosphating, the wire rod is drawn with a total compression rate controlled at 80-85% and a finished diameter of 5.5-12.0mm.

2. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, After pretreatment, the molten iron has S≤0.004% and P≤0.008%.

3. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, The basicity of the final slag from the converter smelting is 3.0-3.2, and the final temperature is 1645-1655℃.

4. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, The composition of the molten steel, by mass percentage, is C: 0.68-0.71%, Si: 0.22-0.28%, Mn: 0.62-0.68%, P≤0.012%, S≤0.009%, with the remainder being Fe and impurities.

5. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, The electromagnetic stirring current of the crystallizer is 200-250A, and the frequency is 3-5Hz.

6. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, The specific water volume in the secondary cooling zone of continuous casting is 0.85-0.95 L / kg, and the light reduction is 3.5-4.5 mm.

7. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, The billet is heated to 1060-1070℃ and held for 100-110 minutes.

8. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, The final rolling temperature is 810-820℃, the wire drawing temperature is 805-815℃, and the fan speed of the Steyrmo cooling line is 0.9-1.1m / s.

9. The method for producing 70# high-carbon hard wire rod for springs according to claim 1, characterized in that, The total compression rate during drawing is 82-84%, and the diameter of the finished steel wire is 6.0-8.0 mm.

10. The method for producing 70# high-carbon hard wire rod for springs according to any one of claims 1-9, characterized in that, The mechanical properties of the prepared 70# steel wire rod meet the following requirements: tensile strength 1200-1400MPa, yield strength ≥900MPa, elongation after fracture ≥9%, reduction of area ≥35%, pearlite lamellar spacing 100-150nm, and wire breakage rate ≤0.5%.