A method of manufacturing a high surface quality steel wire for chain pins

Abstract

This invention relates to a method for manufacturing high-surface-quality steel wire for chain pins, comprising the following steps: steel smelting → continuous casting → heating of continuously cast billets → billet preparation → flaw detection and grinding of intermediate billets → wire rod heating → high-pressure water descaling → annealing → pickling and phosphating → wire drawing → finished product. The method employs a two-stage forming process, with a high compression ratio in billet rolling, wire rod rolling, and wire drawing, which reduces the impact of defects in the raw material on the finished product. During billet rolling, flame cleaning is used to remove surface defects from the billet. Before wire rod rolling, the intermediate billet undergoes surface flaw detection and full grinding to ensure a defect-free surface. Eddy current testing and high-reduction-ratio wire drawing ensure the depth of surface defects in the steel wire, and the high-reduction-ratio drawing results in higher wire hardness, improving the cutting performance for pin processing. Finally, the steel wire used in pin production can control the single-sided grinding residue to within 0.03mm, significantly improving material yield and surface defect compliance. Simultaneously, the high wire hardness provides excellent cutting performance for pin processing.

Description

Technical Field

[0001] This invention belongs to the field of wire rod technology, and specifically relates to a method for manufacturing high surface quality steel wire. Background Technology

[0002] With the continuous improvement of science and technology and process tooling, most automotive engine timing belts have been replaced by timing chains. Compared with traditional belts, timing chains not only have higher safety and reliability, but also require no maintenance for their entire lifespan, lasting as long as the engine, thus greatly reducing maintenance costs. The timing chain pin is a major component; if there are defects on its surface, it will lead to a significant reduction in the fatigue performance of the timing chain during service, and may even result in premature failure.

[0003] To ensure that the pin shaft surface is free of defects, grinding is required during the pin shaft processing. For existing steel wire products, a large grinding allowance is required, resulting in a low material yield and still not guaranteeing that the surface will be free of defects after grinding.

[0004] The production process of steel wire is long and complex. Each process is prone to surface defects, which can lead to excessive defects in the finished steel wire. Common surface defects include slag inclusions introduced by defects on the surface of the billet, folds and scratches caused by the rolling process, and bumps and squeezing damage during packaging and transportation. If these defects are not removed in the subsequent processing and grinding process and remain on the pin surface, they will cause premature failure of the entire chain.

[0005] In particular, surface defects in billets, such as slag inclusions and pits, if not cleaned properly, will be rolled into the interior of the steel and cannot be detected by surface inspection in subsequent rolling, wire drawing and other processes. After the pin shaft is ground later, these defects may be exposed on the surface again.

[0006] For current billet defects, the common practice, as disclosed in patent document CN112893794A, is to treat the billet by full grinding. However, even with full grinding, it cannot be guaranteed that the defects can be completely removed.

[0007] Currently, defects in rolling and damage from bumps and crushes during transport are mainly identified through visual inspection and sampling at the beginning and end of the process. This method can only prevent the generation of surface defects in batches. Summary of the Invention

[0008] The purpose of this invention is to provide a method for manufacturing steel wire for timing chain pins that achieves high surface quality through full-process surface quality control.

[0009] The technical solution adopted by this invention to solve the above problems is as follows: a method for manufacturing high surface quality chain pin steel wire, comprising the following steps: steel smelting (converter smelting → refining → vacuum degassing) → continuous casting → continuous casting billet heating → billet opening → intermediate billet flaw detection and grinding → wire rod heating → high-pressure water descaling → annealing → pickling and phosphating saponification → wire drawing → finished product. Specific process details are as follows:

[0010] (1) Steel smelting: Steel smelting is designed according to the elemental composition of steel wire;

[0011] (2) Continuous casting: The continuous casting process is used to pour molten steel into billets;

[0012] (3) Billet rolling: After the billet is heated in the furnace, it is rolled in two stages: rough rolling and finish rolling. After the billet exits the furnace, it is first descaled with high-pressure water at a pressure ≥20 MPa. After rough rolling, the billet is flame-cleaned to remove defects on the surface of the billet, including cracks, inclusions, and peeling, with a cleaning depth ≥1.0 mm. After flame cleaning, it is then finish-rolled to a cross-sectional area of ​​150 mm². 2 ~200mm 2 Intermediate billets are slowly cooled after being cut to prevent cracking.

[0013] (4) Infrared flaw detection and grinding: Infrared flaw detection is used to grind the defects found. After grinding, magnetic particle testing is used for re-detection. The surface defect depth of the intermediate billet is ≤0.3mm. After flaw detection, the surface is ground with a grinding depth ≥0.5mm.

[0014] (5) Heating and descaling: The intermediate billet after the above treatment is heated in a heating furnace at a temperature of ≤1100℃. After the billet is taken out of the furnace, it is descaled by high pressure water at a pressure of ≥15 MPa. When it is packaged after being taken off the production line, the surface is protected to prevent bumps and damage.

[0015] (6) Annealing and pickling phosphating: The intermediate billet is rolled into wire rod, and the wire rod is annealed and pickled phosphating coating is applied in multiple passes of wire drawing;

[0016] (7) Wire drawing: Wire drawing is carried out on a wire drawing equipment equipped with eddy current testing. First, one pass of wire drawing is performed to ensure that the surface straightness and dimensional tolerance meet the requirements of the testing. Then, eddy current testing is performed. If defects are found during testing, the machine is stopped and the wire is ground to ensure that the surface defect depth is ≤0.05mm. After testing, multiple passes of wire drawing are performed to reduce the surface area by ≥64%. After cold deformation, the surface defect depth of the steel wire, including dents and scratches, is ≤0.03mm.

[0017] Preferably, the chemical composition (wt%) of the steel wire is: C: 0.35–0.43%, Si: 0.20–0.45%, Mn: 0.50–0.70%, P: ≤0.025%, S: ≤0.010%, Cr: 1.00–1.80%, Mo: 0.15–0.40%, Al: 0.70–1.30%, with the remainder being Fe and unavoidable impurities. This is a high-Al, low-Si steel wire design.

[0018] Preferably, high-quality molten iron, scrap steel, and raw and auxiliary materials are used as materials for steelmaking to reduce the content of harmful elements in the molten steel. The molten steel is smelted in a converter for primary smelting, and the converter slags to remove C, P, and Si, and the tapping is controlled to prevent slag from falling. LF+RH refining is used. LF refining prevents Si from rising beyond the design range when smelting molten steel with high Al content, and RH vacuum degassing treatment reduces the hydrogen content in the molten steel to below 1.0 ppm.

[0019] Preferably, during continuous casting, the tundish is induction heated, the superheat of the casting does not exceed 30°C, the liquid level fluctuation in the crystallizer is ≤1.5mm, the billet segregation is improved by light pressing and electromagnetic stirring, the entire continuous casting process is protected from air to prevent secondary oxidation, and special protective slag for high-alumina steel is used.

[0020] Preferably, continuous casting yields a large square billet of 390mm*510mm, leaving room for rolling deformation during intermediate billet rolling.

[0021] Preferably, during the roughing rolling stage, the cleaning depth of the flame cleaning after roughing rolling is ≥1.5mm.

[0022] Preferably, the infrared flaw detection accuracy of the intermediate billet is 0.3 mm, so as to improve the comprehensiveness and accuracy of flaw detection as much as possible.

[0023] Preferably, the flaw detection accuracy of eddy current testing during the wire drawing stage is set to 0.05 mm, and the wire drawing speed is ≤2 m / s, so as to improve the comprehensiveness and accuracy of flaw detection.

[0024] Compared with the prior art, the advantages of the present invention are as follows:

[0025] (1) The two-fired rolling process has a large compression ratio in the billet rolling, wire rolling and wire drawing processes, which can reduce the impact of defects in the masterbatch on the finished product.

[0026] (2) Special raw and auxiliary materials and refractory materials are used in steelmaking continuous casting to ensure high internal and surface quality.

[0027] (3) When rolling the billet, flame cleaning is used to remove surface defects of the billet.

[0028] (4) Before the wire rod is rolled, the surface of the intermediate billet is inspected and fully ground to ensure that the surface of the intermediate billet is free of defects.

[0029] (5) Online eddy current testing and high surface area reduction wire drawing are used to ensure the depth of surface defects of steel wire. After high surface area reduction wire drawing, the steel wire hardness is higher, and the cutting performance of pin shaft processing is improved.

[0030] The steel wire produced using the above method can have its single-sided grinding residue controlled to within 0.03mm, significantly improving material yield and production efficiency, and greatly increasing the surface defect qualification rate of the finished pins. Simultaneously, the steel wire produced after large reduction in surface area has a tensile strength of 850-1250MPa and an HV10 hardness of 265-389, exhibiting high hardness and excellent cutting performance in pin processing. Implementation

[0031] The present invention will be further described in detail below with reference to the embodiments. The embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention. Example

[0032] The high surface quality timing chain pin steel wire involved in this embodiment has a specification of φ2.95mm and contains the following components and their mass percentages: C: 0.36%, Si: 0.25%, Mn: 0.63%, P: 0.012%, S: 0.001%, Cr: 1.24%, Mo: 0.21%, Al: 1.05%, with the balance being Fe and unavoidable impurity elements.

[0033] Its production process is as follows:

[0034] The smelting raw materials are prepared according to the chemical composition described above and proceeded in the following order: BOF converter smelting → LF refining → RH vacuum degassing → continuous casting → continuous casting billet heating → billet opening → intermediate billet flaw detection and grinding → wire rod heating → high pressure water descaling → annealing → pickling and phosphating saponification → wire drawing → finished product.

[0035] The specific processes for the above-mentioned billet rolling, intermediate billet flaw detection and grinding, and wire drawing stages are as follows:

[0036] After being heated in a reheating furnace, the continuously cast billet is rolled. After exiting the furnace, the billet undergoes high-pressure water descaling at a pressure ≥20 MPa. After rough rolling, the billet is flame-cleaned to remove surface defects such as cracks, inclusions, and scale, with a cleaning depth ≥1.5 mm. After flame cleaning, it is then finish-rolled to 150 mm. 2 Intermediate billets are slowly cooled after being cut to prevent cracking.

[0037] The intermediate billet is subjected to online fully automatic infrared flaw detection (flaw detection accuracy 0.3mm). After the defects are found are repaired and ground, magnetic particle testing is carried out to ensure that the surface defect depth of the intermediate billet is ≤0.3mm. After the flaw detection is completed, the surface is subjected to fully automatic online repair grinding with a grinding depth of 1.5mm to ensure the surface quality of the intermediate billet.

[0038] After annealing and acid pickling with phosphating and saponification coating, the wire rod undergoes multiple drawing passes on a wire drawing machine equipped with eddy current testing. The first drawing pass reduces the wire rod from φ6mm to φ5.2mm. Then, eddy current testing is performed with a testing accuracy of 0.05mm and a drawing speed of ≤2m / s. Defects found during testing are stopped and ground to ensure that the surface defect depth is ≤0.05mm. After testing, multiple drawing passes are performed to reduce the wire rod to φ2.95mm, resulting in a surface area reduction rate of 67.82%. After this high surface area reduction drawing process, the tensile strength is 950MPa and the HV10 hardness is 295.

[0039] No defects were found on the surface of the steel wire after it was ground to 0.03mm on one side, and the cutting performance was excellent. Example

[0040] The high surface quality timing chain pin steel wire involved in this embodiment has a specification of φ3.05mm and contains the following components and their mass percentages: C: 0.40%, Si: 0.25%, Mn: 0.53%, P: 0.013%, S: 0.002%, Cr: 1.48%, Mo: 0.33%, Al: 1.12%, with the balance being Fe and unavoidable impurity elements.

[0041] Its production process is as follows:

[0042] The smelting raw materials are prepared according to the chemical composition described above and proceeded in the following order: BOF converter smelting → LF refining → RH vacuum degassing → continuous casting → continuous casting billet heating → billet opening → intermediate billet flaw detection and grinding → wire rod heating → high pressure water descaling → annealing → pickling and phosphating saponification → wire drawing → finished product.

[0043] The specific processes for the above-mentioned billet rolling, intermediate billet flaw detection and grinding, and wire drawing stages are as follows:

[0044] After being heated in a reheating furnace, the continuously cast billet is rolled. After exiting the furnace, it undergoes high-pressure water descaling at a pressure ≥20 MPa. Following rough rolling, the billet is flame-cleaned to remove surface defects such as cracks, inclusions, and scale, with a cleaning depth ≥1.5 mm. After flame cleaning, it is then finish-rolled to a thickness of 200 mm. 2 After the intermediate billet is cut, it is slowly cooled off the production line to prevent cracking. The intermediate billet is subjected to online fully automatic infrared flaw detection (flaw detection accuracy 0.3mm). After the defects are found are repaired and ground, magnetic particle testing is performed to ensure that the surface defect depth of the intermediate billet is ≤0.3mm. After flaw detection, the surface is subjected to fully automatic online repair grinding to a grinding depth of 1.0mm to ensure the surface quality of the intermediate billet.

[0045] After annealing and phosphating coating, the wire rod undergoes multiple drawing passes on a wire drawing machine equipped with eddy current testing. The first drawing pass reduces the wire rod from φ5.5mm to φ5.2mm. Then, eddy current testing is performed with a testing accuracy of 0.05mm and a drawing speed of ≤2m / s. Defects found during testing are stopped and ground to ensure that the surface defect depth is ≤0.05mm. After testing, multiple drawing passes are performed to reduce the wire rod to φ3.05mm, resulting in a surface area reduction rate of 65.6%. After this large surface area reduction drawing process, the tensile strength is 970MPa and the HV10 hardness is 302.

[0046] No defects were found on the surface of the steel wire after it was ground to 0.03mm on one side, and the cutting performance was excellent.

Claims

1. A method for manufacturing high surface quality steel wire for chain pins, characterized in that: include (1) Steel smelting: Steel smelting is designed according to the elemental composition of steel wire; (2) Continuous casting: The continuous casting process is used to pour molten steel into billets; (3) Billet rolling: After the billet is heated in the furnace, it is rolled in two stages: rough rolling and finish rolling. After the billet exits the furnace, it is first descaled by high-pressure water with a pressure ≥20 MPa. After rough rolling, the billet is flame-cleaned to remove defects on the surface of the billet, including cracks, inclusions, and peeling, with a cleaning depth ≥1.0 mm. After flame cleaning, it is then finished rolled to 150 mm. 2 ~200mm 2 Intermediate billets are removed from the production line and allowed to cool slowly after the billet is finished. (4) Infrared flaw detection and grinding: Infrared flaw detection is used to grind the defects found. After grinding, magnetic particle testing is used for re-detection. The surface defect depth of the intermediate billet is ≤0.3mm. After flaw detection, the surface is ground with a grinding depth ≥0.5mm. (5) Heating and descaling: The intermediate billet after the above treatment is heated in a heating furnace at a temperature of ≤1100℃. After the billet is taken out of the furnace, it is descaled by high pressure water at a pressure of ≥15 MPa. Surface protection is applied when it is packaged after being taken off the production line. (6) Annealing and pickling phosphating: The intermediate billet is rolled into wire rod, and the wire rod is annealed and pickled phosphating coating is applied in multiple passes of wire drawing; (7) Wire drawing: Wire drawing is carried out on a wire drawing equipment equipped with eddy current testing. First, one pass of wire drawing is performed to ensure that the surface straightness and dimensional tolerance meet the requirements of the testing. Then, eddy current testing is performed. If defects are found during testing, the machine is stopped and the wire is ground to ensure that the surface defect depth is ≤0.05mm. After testing, multiple passes of wire drawing are performed to reduce the surface area by ≥64%. After cold deformation, the surface defect depth of the steel wire, including dents and scratches, is ≤0.03mm.

2. The method according to claim 1, characterized in that: The chemical composition (wt%) of the steel wire is as follows: C: 0.35–0.43%, Si: 0.20–0.45%, Mn: 0.50–0.70%, P: ≤0.025%, S: ≤0.010%, Cr: 1.00–1.80%, Mo: 0.15–0.40%, Al: 0.70–1.30%, with the remainder being Fe and unavoidable impurities.

3. The method according to claim 1, characterized in that: Steelmaking employs a converter for primary refining, where slag is formed to remove carbon, phosphorus, and silicon, and tapping is controlled to prevent slag from flowing into the steel. LF+RH refining is used, where LF refining prevents the Si content from rising beyond the design range when smelting high-Al steel, and RH vacuum degassing treatment reduces the hydrogen content in the steel to below 1.0 ppm.

4. The method according to claim 1, characterized in that: During continuous casting, induction heating is used in the tundish, the superheat of the casting does not exceed 30°C, the liquid level fluctuation in the crystallizer is ≤1.5mm, and the segregation of the billet is improved by light pressure and electromagnetic stirring. The entire continuous casting process is protected and the casting process is isolated from air.

5. The method according to claim 1, characterized in that: Continuous casting yields a large square billet of 390mm*510mm.

6. The method according to claim 1, characterized in that: During the roughing rolling stage, the cleaning depth of the flame cleaning after roughing rolling is ≥1.5mm.

7. The method according to claim 1, characterized in that: The infrared flaw detection accuracy of the intermediate billet is 0.3mm.

8. The method according to claim 1, characterized in that: During the wire drawing stage, the eddy current testing accuracy is set to 0.05mm, and the wire drawing speed is ≤2m / s.