Spring steel material, single leaf spring and manufacturing method thereof

Abstract

The invention discloses a spring steel material, a single-piece steel leaf spring and a manufacturing method thereof. The spring steel material comprises, by weight percentage, C: 0.48%-0.56%, Si: 1.00%-1.20%, Mn: 0.70%-1.00%, Cr: 0.80%-1.00%, V: 0.15%-0.25%, Mo: 0.05%-0.07%, Nb: 0.02%-0.04%, Cu: 0.00%-0.50%, P: ≤0.025%, S: ≤0.025%, Ti: 0.020%-0.025%, Als: 0.010%-0.040%, N: 0.0020%-0.0080%, and the rest is Fe and inevitable impurities. The material can ensure that a 45mm thick single-piece steel leaf spring leaf is completely hardened. The main process flow of the present invention using spring steel material to manufacture a single-piece steel leaf spring leaf is as follows: cutting → drilling blind holes → rolling → quenching → tempering → shot peening → painting → assembling. The manufactured single-piece steel leaf spring leaf has a tensile strength Rm of 1700-1850 MPa and a yield strength Rp0.2 of 1550-1650 MPa; an elongation after fracture A≥9%, a cross-sectional shrinkage Z≥30%, and a fatigue life (loading stress 800±500 MPa)≥200,000 times.

Description

Technical Field

[0001] The invention belongs to the field of automobile materials, and in particular relates to a spring steel material, a single-piece leaf spring and a manufacturing method thereof. Background Art

[0002] The single leaf spring is a simple beam that bears concentrated loads. Theoretically, compared with other leaf springs and multi-leaf springs, it has the advantages of lighter weight and no friction between leaves. As commercial vehicle design technology develops towards lightweight, single leaf springs will inevitably become the development trend of leaf springs. At the same time, the application of single leaf springs also puts higher requirements on spring steel materials and manufacturing processes.

[0003] At present, the spring steel material used in single leaf springs is mainly 52CrMoV4, which contains alloy elements such as V and Mo. It has fine grains, good toughness and hardenability in the state of use, and can be used to manufacture single leaf springs with a thickness of less than 40mm. However, for single leaf springs with a thickness of 38mm to 45mm, the hardenability of 52CrMoV4 material cannot fully meet the needs.

[0004] In addition, since the design full-load static stress of a single-leaf steel leaf spring is 30% to 40% higher than that of a conventional steel leaf spring, the spring steel material is required to have higher strength and toughness. Generally, the tensile strength Rm is required to be ≥ 1750MPa, the yield strength Rp0.2 is required to be ≥ 1550MPa, the elongation after fracture A is required to be ≥ 9%, and the cross-sectional shrinkage rate Z is required to be ≥ 30%. The tensile strength Rm of the 52CrMoV4 material is 1450 to 1600MPa, and the yield strength Rp0.2 is 1300 to 1450MPa, which cannot meet the design full-load static stress requirements of a single-leaf steel leaf spring. Summary of the invention

[0005] Aiming at the problem that 52CrMoV4 material cannot meet the hardenability and mechanical property requirements of a single-piece steel leaf spring with a thickness of 38mm to 45mm, the present invention provides a high hardenability and high strength and toughness spring steel material, which can ensure that a 45mm thick single-piece steel leaf spring is completely hardened, has high strength and toughness, and is economical, and can ensure the performance of a large-section single-piece steel leaf spring.

[0006] The technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides a spring steel material, which comprises, by weight percentage, C: 0.48% to 0.56%, Si: 1.00% to 1.20%, Mn: 0.70% to 1.00%, Cr: 0.80% to 1.00%, V: 0.15% to 0.25%, Mo: 0.05% to 0.07%, Nb: 0.02% to 0.04%, Cu: 0.00% to 0.50%, P: ≤0.025%, S: ≤0.025%, Ti: 0.020% to 0.025%, Als: 0.010% to 0.040%, N: 0.0020% to 0.0080%, and the remainder is Fe and unavoidable impurities.

[0008] In some specific embodiments provided by the present invention, the above-mentioned spring steel material is used to manufacture a single-piece steel leaf spring leaf with a thickness of ≤45 mm.

[0009] In some specific embodiments provided by the present invention, the above-mentioned spring steel material is used to manufacture a single-piece steel leaf spring leaf with a thickness of 38 mm to 45 mm.

[0010] In some specific embodiments provided by the present invention, the above-mentioned spring steel material is used to manufacture a single-piece steel leaf spring leaf with a thickness of 40 mm to 45 mm.

[0011] In a second aspect, the present invention provides a method for manufacturing a single-piece steel leaf spring leaf, which adopts the above spring steel material, and the main process flow is as follows: cutting → drilling blind holes → rolling → quenching → tempering → shot peening → painting → assembly.

[0012] In some embodiments provided by the present invention, the rolling heating temperature is 900-1000°C, the temperature of the reed after rolling is 700-800°C, and the reed is slowly cooled in the heat preservation cover to a temperature of ≤200°C before being quenched out of the cover.

[0013] In some embodiments provided by the present invention, the quenching includes: heating the reed to 820-880° C. and then quenching in oil.

[0014] In some embodiments provided by the present invention, during the quenching process, the reed is swung along with the quenching fixture, the swung frequency is 20 to 25 times per minute, and the swung time is 120 to 150 seconds.

[0015] In some embodiments provided by the present invention, the quenched reed is tempered to 400-450°C.

[0016] In a third aspect, the present invention provides a single-piece leaf spring leaf produced by the above-mentioned manufacturing method of the single-piece leaf spring leaf leaf.

[0017] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0018] 1. The spring steel material provided by the present invention has high hardenability and high toughness, which can ensure that a single-piece steel leaf spring leaf with a thickness of 45 mm or less can be fully hardened, thereby ensuring the heat treatment quality of the single-piece steel leaf spring leaf.

[0019] 2. The present invention improves the strength of a single-piece steel leaf spring leaf. The tensile strength Rm of the manufactured single-piece steel leaf spring leaf is 1700-1850 MPa, and the yield strength Rp0.2 is 1550-1650 MPa; the elongation after fracture A≥9%, and the cross-sectional shrinkage Z≥30%.

[0020] 3. The present invention significantly improves the fatigue performance of the single-piece steel leaf spring leaf, and the fatigue life (loading stress 800±500MPa) of the manufactured single-piece steel leaf spring leaf is ≥200,000 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide an understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solution of the present invention and do not constitute a limitation to the technical solution of the present invention.

[0022] Figure 1 The effect of Si on the tempering stability in the spring steel material provided by the present invention is demonstrated. DETAILED DESCRIPTION

[0023] In order to make the purpose and advantages of the technical solution of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the data in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] Aiming at the problem that 52CrMoV4 material cannot meet the hardenability and mechanical property requirements of a single-piece steel leaf spring with a thickness of 38 mm to 45 mm, the spring steel material provided by the present invention comprises, by weight percentage, C: 0.48% to 0.56%, Si: 1.00% to 1.20%, Mn: 0.70% to 1.00%, Cr: 0.80% to 1.00%, V: 0.15% to 0.25%, Mo: 0.05% to 0.07%, Nb: 0.02% to 0.04%, Cu: 0.00% to 0.50%, P: ≤0.025%, S: ≤0.025%, Ti: 0.020% to 0.025%, Als: 0.010% to 0.040%, N: 0.0020% to 0.0080%, and the rest is Fe and unavoidable impurities. This spring steel material can ensure that the single-piece steel leaf spring leaf with a thickness of 45mm and below is fully hardened.

[0025] The elements in the spring steel material provided by the present invention and their effects on the performance of the single-piece steel leaf spring spring are shown in Table 1:

[0026] Table 1

[0027]

[0028]

[0029] The principle of the present invention for improving the hardenability of spring steel material by controlling the element content is as follows: the present invention controls the contents of Mn, Cr and Mo, which have a significant influence on the hardenability, to ensure that a single-piece steel plate spring leaf with a thickness of 45 mm or less can be completely hardened. Specifically, the Mn content is controlled to be 0.70% to 1.00%, the Cr content is 0.80% to 1.00%, and the Mo content is 0.05% to 0.07%, thereby improving the hardenability of the material (J30≥56HRC).

[0030] The principle of improving the mechanical properties and tempering stability of spring steel materials by controlling the element content is as follows: Si≤0.40% in 52CrMoV4 material, and the tempering stability, yield strength and tensile strength of spring steel materials are improved by increasing the Si content to 1.00%-1.20%.

[0031] In addition, since the single-piece steel leaf spring reed is required to have high strength and high toughness, and the strength and toughness of metal materials are a pair of contradictory properties, generally the higher the strength, the higher the toughness. The present invention ensures that the toughness remains unchanged or improved while the strength of the spring steel material is improved through grain refinement. In order to refine the grains and improve the toughness of the spring steel material, the present invention micro-alloys the spring steel material, controls the content of the following elements: V: 0.15-0.25%, Mo: 0.05-0.07%, Nb: 0.02-0.04%, Ti: 0.020%-0.025%, Als: 0.010%-0.040%, and controls N: 0.0020%-0.0080%. The obtained single-piece steel leaf spring reed has a finer grain size (≥10 grades), which ensures the toughness of the single-piece steel leaf spring reed.

[0032] For special areas such as coastal areas and saline-alkali lands, Cu can be appropriately added to ensure that the single-piece steel leaf spring has a certain corrosion resistance. Specifically, the Cu element content is controlled to be: 0.00% to 0.50%.

[0033] The manufacturing method of the single-piece steel leaf spring provided by the present invention adopts the above spring steel material, and the process flow is as follows: blanking→blind hole drilling→rolling→quenching→tempering→shot peening→painting→assembly.

[0034] Specifically, the requirements for each step in the process are:

[0035] Drilling blind holes:

[0036] The center hole is used for positioning, therefore, the present invention has no special requirements for the hole diameter, but requires that the center hole is a blind hole, and its depth is about 1 / 2 of the thickness of the single-piece steel leaf spring leaf, so as to reduce stress concentration and ensure that the single-piece steel leaf spring leaf has a sufficiently long fatigue life.

[0037] Rolling:

[0038] Rolling process: The heating temperature is 900-1000°C, and the designed cross section is rolled through 3-5 times, and the temperature after rolling is about 700-800°C. Since the spring steel material provided by the present invention has high hardenability, a slow cooling process is required after rolling to eliminate the internal thermal stress of rolling to avoid cracks in the single-piece steel leaf spring leaf. After rolling, the single-piece steel leaf spring leaf is placed in a heat-insulating cover. The placement time is determined according to factors such as the number of products and weather to ensure that the temperature of the single-piece steel leaf spring leaf out of the cover is ≤200°C.

[0039] Quenching:

[0040] The quenching heating temperature is 820-880℃, the holding time is 45-90min, and the quenching fixture is used to clamp the single-piece steel leaf spring leaf when taking it out. In order to ensure that the single-piece steel leaf spring leaf can be quenched and the material has a finer grain size, the time from the quenching furnace to the oil tank should be shortened as much as possible to reduce the intermediate heat loss and ensure that the temperature of the single-piece steel leaf spring leaf is not lower than 780℃ (generally 780℃-850℃) when entering the oil.

[0041] During quenching, the single leaf spring leaf is swung with the quenching fixture to fully cool the single leaf spring leaf before being taken out of the oil tank. The quenching time is determined according to the product specifications and quantity. Generally, the single leaf spring leaf is swung with the quenching fixture for 120 to 150 seconds, and the swung frequency is 20 to 25 times / minute to ensure that the single leaf spring leaf has a faster cooling speed during quenching.

[0042] Tempering:

[0043] In order to ensure that the single-leaf steel leaf spring has good comprehensive mechanical properties, the tempering temperature is controlled at 400-450°C and the holding time is 60-120 minutes.

[0044] Based on the above requirements, the present invention provides a method for manufacturing a single-piece steel leaf spring leaf:

[0045] In some embodiments, the rolling heating temperature is 900-1000°C, the temperature of the single leaf spring leaf after rolling is 700-800°C, and the single leaf spring leaf is slowly cooled in the insulation cover to a temperature of ≤200°C before being quenched out of the cover.

[0046] In some embodiments, the quenching includes: heating the single-piece steel leaf spring to 820-880° C. and then quenching in oil.

[0047] In some embodiments, during the quenching process, the single-piece steel leaf spring leaf is swung along with the quenching fixture, with a swung frequency of 20 to 25 times per minute and a swung time of 120 to 150 seconds.

[0048] In some embodiments, the quenched single-piece steel leaf spring leaf is tempered to 400-450° C., and then water-cooled to below 100° C. after tempering.

[0049] The technical solution of the present invention will be described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto. Unless otherwise specified, conventional operations and process parameters are used for steps not mentioned in the following embodiments.

[0050] Example 1

[0051] This embodiment provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring leaf. The single-piece front leaf spring leaf has a specification of 90×40 mm and uses a spring steel material with a chemical composition as shown in Table 2. The process flow is as follows: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly, wherein:

[0052] Rolling steps: The heating temperature is 950°C, and the design cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is about 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring about 100°C and then quenched out of the cover.

[0053] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0054] Tempering step: temper the quenched single-piece steel leaf spring to 430°C, keep warm for 90 minutes, and water cool after tempering.

[0055] Table 2 Chemical composition of spring steel material used in Example 1 (wt%)

[0056]

[0057] The microstructure of the single-piece steel leaf spring produced in this embodiment is shown in Table 3, and the mechanical properties are shown in Table 4. The bench test was carried out according to GB / T19844 "Steel Leaf Spring", and the results are shown in Table 5.

[0058] Table 3 Microstructure of the single-piece steel leaf spring leaf manufactured in Example 1

[0059] Decarburization depth Metallographic structure Grain size This embodiment is measured 0.16mm Level 1 Level 10

[0060] Table 4 Mechanical properties of the single-piece steel leaf spring leaf manufactured in Example 1

[0061]

[0062] Table 5 Bench test of the single-piece steel leaf spring produced in Example 1

[0063]

[0064] The above results show that the single-piece leaf spring produced by the spring steel material provided in this embodiment meets the design requirements (fatigue life ≥ 200,000 times).

[0065] Example 2

[0066] The present invention provides a method for manufacturing a single-piece front leaf spring for a heavy-duty vehicle developed in coastal areas. The single-piece front leaf spring has a specification of 90×38 mm and adopts a spring steel material with a chemical composition as shown in Table 6. The process flow is as follows: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly, wherein:

[0067] Rolling steps: The heating temperature is 950°C, and the design cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is about 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring about 100°C and then quenched out of the cover.

[0068] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 830°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0069] Tempering step: temper the quenched single-piece steel leaf spring to 440°C, keep it at this temperature for 90 minutes, and water cool it after tempering.

[0070] Table 6 Chemical composition of spring steel material used in Example 2 (wt%)

[0071]

[0072] The microstructure of the single-piece leaf spring spring manufactured in this embodiment is shown in Table 7, the mechanical properties are shown in Table 8, the salt spray test results are shown in Table 9, and the bench test is carried out according to GB / T19844 "Leaf Spring", and the results are shown in Table 10.

[0073] Table 7 Microstructure of the single-piece steel leaf spring leaf manufactured in Example 2

[0074] Decarburization depth Metallographic structure Grain size This embodiment is measured 0.13mm Level 1 Level 10

[0075] Table 8 Mechanical properties of the single-piece steel leaf spring leaf manufactured in Example 2

[0076]

[0077] Table 9 Salt spray resistance time of the single-piece steel leaf spring spring manufactured in Example 2

[0078] Example 2 Conventional leaf spring 1 308h 248h 2 311h 257h 3 306h 251h average 308h 252h

[0079] EQY-2-2016 requires that the salt spray test of leaf springs should be ≥240h.

[0080] Table 10 Bench test of the single-piece steel leaf spring leaf manufactured in Example 2

[0081]

[0082] The above results show that the single-piece leaf spring produced by the spring steel material provided in this embodiment meets the design requirements (fatigue life ≥ 200,000 times), and the salt spray resistance time of the leaf spring is 20% higher than that of the conventional leaf spring.

[0083] Example 3

[0084] This embodiment provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring leaf. The single-piece front leaf spring leaf has a specification of 75×45 mm and uses a spring steel material with a chemical composition as shown in Table 11. The process flow is as follows: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly, wherein:

[0085] Rolling steps: The heating temperature is 980°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is about 760°C. It is slowly cooled in the insulation cover to the temperature of the spring about 100°C and then quenched out of the cover.

[0086] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 840°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 800°C when entering the oil.

[0087] Tempering step: temper the quenched single-piece steel leaf spring to 430°C, keep warm for 90 minutes, and water cool after tempering.

[0088] Table 11 Chemical composition of spring steel material used in Example 3 (wt%)

[0089]

[0090] The microstructure of the single-piece steel leaf spring produced in this embodiment is shown in Table 12, and the mechanical properties are shown in Table 13. The bench test was carried out according to GB / T19844 "Steel Leaf Spring", and the results are shown in Table 14.

[0091] Table 12 Microstructure of the single-piece steel leaf spring leaf manufactured in Example 3

[0092] Decarburization depth Metallographic structure Grain size The present invention is measured 0.23mm Level 1 Level 10

[0093] Table 13 Mechanical properties of the single-piece steel leaf spring spring manufactured in Example 1

[0094]

[0095] Table 14 Bench test of single-piece steel leaf spring leaf manufactured in Example 1

[0096]

[0097] The above results show that the single-piece leaf spring produced by the spring steel material provided in this embodiment meets the design requirements (fatigue life ≥ 200,000 times).

[0098] Example 4

[0099] This embodiment provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring leaf, the single-piece front leaf spring leaf has a specification of 90×40 mm, and the process flow is as follows: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly, wherein:

[0100] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0101] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0102] Tempering step: temper the quenched single-piece steel leaf spring to 450°C, keep warm for 90 minutes, and water cool after tempering.

[0103] The chemical composition of the single-piece steel leaf spring material manufactured in this embodiment is shown in Table 15, the hardness and grain size of the spring leaf are shown in Table 16, and the mechanical properties are shown in Table 17.

[0104] Table 15 Chemical composition (wt%) of spring steel materials used in Comparative Examples 1 to 5 and Example 4

[0105] V Nb Ti Als N Comparative Example 1 0.20 — — — — Comparative Example 2 — 0.024 — — — Comparative Example 3 0.20 0.024 — — — Comparative Example 4 0.20 0.024 0.023 — — Comparative Example 5 0.20 0.024 — 0.022 0.0046 Example 4 0.20 0.024 0.023 0.022 0.0046

[0106] - means not added.

[0107] Table 16 Hardness and grain size of the single-piece steel leaf spring leaves manufactured in Comparative Examples 1 to 5 and Example 4

[0108]

[0109] Table 17 Mechanical properties of the single-piece steel leaf spring leaves manufactured in Comparative Examples 1 to 5 and Example 4

[0110]

[0111] Comparative Example 1

[0112] This comparative example provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring spring leaf, the single-piece front leaf spring spring leaf having a specification of 90×40 mm, and the only difference from Example 4 is that a spring steel material with a chemical composition as shown in Table 15 is used, and the process flow and parameters are the same as those of Example 4, including: blanking→blind hole drilling→rolling→quenching→tempering→shot peening→painting→assembly, wherein:

[0113] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0114] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0115] Tempering step: temper the quenched single-piece steel leaf spring to 450°C, keep warm for 90 minutes, and water cool after tempering.

[0116] The hardness and grain size of the single-piece steel leaf spring produced in this comparative example are shown in Table 16, and the mechanical properties are shown in Table 17.

[0117] Comparative Example 2

[0118] This comparative example provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring spring leaf, the single-piece front leaf spring spring leaf has a specification of 90×40 mm, and the only difference from Example 4 is that a spring steel material with a chemical composition as shown in Table 15 is used, and the process flow and parameters are the same as those of Example 4, and the process flow is as follows: blanking→blind hole drilling→rolling→quenching→tempering→shot peening→painting→assembly, wherein:

[0119] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0120] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0121] Tempering step: temper the quenched single-piece steel leaf spring to 450°C, keep warm for 90 minutes, and water cool after tempering.

[0122] The hardness and grain size of the single-piece steel leaf spring produced in this comparative example are shown in Table 16, and the mechanical properties are shown in Table 17.

[0123] Comparative Example 3

[0124] The present invention provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring leaf, wherein the single-piece front leaf spring leaf has a specification of 90×40 mm, and the only difference from Example 4 is that a spring steel material with a chemical composition as shown in Table 15 is used, and the process flow and parameters are the same as those of Example 4, and the process flow is as follows: blanking→blind hole drilling→rolling→quenching→tempering→shot peening→painting→assembly, wherein:

[0125] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0126] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0127] Tempering step: temper the quenched single-piece steel leaf spring to 450°C, keep warm for 90 minutes, and water cool after tempering.

[0128] The hardness and grain size of the single-piece steel leaf spring produced in this comparative example are shown in Table 16, and the mechanical properties are shown in Table 17.

[0129] Comparative Example 4

[0130] This comparative example provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring spring leaf, the single-piece front leaf spring spring leaf has a specification of 90×40 mm, and the only difference from Example 4 is that a spring steel material with a chemical composition as shown in Table 15 is used, and the process flow and parameters are the same as those of Example 4, and the process flow is as follows: blanking→blind hole drilling→rolling→quenching→tempering→shot peening→painting→assembly, wherein:

[0131] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0132] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0133] Tempering step: temper the quenched single-piece steel leaf spring to 450°C, keep warm for 90 minutes, and water cool after tempering.

[0134] The hardness and grain size of the single-piece steel leaf spring produced in this comparative example are shown in Table 16, and the mechanical properties are shown in Table 17.

[0135] Comparative Example 5

[0136] This comparative example provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring spring leaf, the single-piece front leaf spring spring leaf has a specification of 90×40 mm, and the only difference from Example 4 is that a spring steel material with a chemical composition as shown in Table 15 is used, and the process flow and parameters are the same as those of Example 4, and the process flow is as follows: blanking→blind hole drilling→rolling→quenching→tempering→shot peening→painting→assembly, wherein:

[0137] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0138] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept at this temperature for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. The temperature of the single-piece steel leaf spring leaf is 780°C when entering the oil.

[0139] Tempering step: temper the quenched single-piece steel leaf spring to 450°C, keep warm for 90 minutes, and water cool after tempering.

[0140] The hardness and grain size of the single-piece steel leaf spring produced in this comparative example are shown in Table 16, and the mechanical properties are shown in Table 17.

[0141] Comparative Example 6

[0142] This comparative example provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring spring leaf, the single-piece front leaf spring spring leaf has a specification of 90×40 mm, and is different from Example 4 in that the Si content in the spring steel material is 0.75% and the tempering temperature, and the process flow and parameters are basically the same as those of Example 3, including: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly, wherein:

[0143] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0144] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept warm for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. When entering the oil, the temperature of the single-piece steel leaf spring leaf is 780°C. After quenching to below 100°C, the single-piece steel leaf spring leaf is taken out.

[0145] Tempering step: temper the quenched single-piece steel leaf spring to 400, 450, 500, 550 or 600°C, with a holding time of 90 minutes, and water-cool to below 100°C after tempering.

[0146] Comparative Example 7

[0147] This comparative example provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring spring leaf, the single-piece front leaf spring spring leaf has a specification of 90×40 mm, and is different from Example 4 in that the Si content in the spring steel material is 0.25% and the tempering temperature, and the process flow and parameters are the same as those of Example 4, including: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly, wherein:

[0148] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0149] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept warm for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. When entering the oil, the temperature of the single-piece steel leaf spring leaf is 780°C. After quenching to below 100°C, the single-piece steel leaf spring leaf is taken out.

[0150] Tempering step: temper the quenched single-piece steel leaf spring to 400, 450, 500, 550 or 600°C, with a holding time of 90 minutes, and water-cool to below 100°C after tempering.

[0151] Comparative Example 8

[0152] This comparative example provides a method for manufacturing a heavy-duty vehicle single-piece front leaf spring leaf, the single-piece front leaf spring leaf has a specification of 90×40 mm, and the process flow and parameters are the same as those of Example 4, except that the Si content in the spring steel material is 1.1% and the tempering temperature, including: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly, wherein:

[0153] Rolling steps: the heating temperature is 950°C, and the designed cross section is rolled through 5 rollings. After rolling, the temperature of the single-piece steel leaf spring is 750°C. It is slowly cooled in the heat preservation cover to the temperature of the spring 100°C and then taken out of the cover for quenching.

[0154] Quenching steps: the rolled single-piece steel leaf spring leaf is heated to 820°C and kept warm for 90 minutes; it is clamped with a quenching fixture, and the single-piece steel leaf spring leaf is swung with the quenching fixture for 150 seconds at a frequency of 25 times / minute, and then immersed in quenching oil. When entering the oil, the temperature of the single-piece steel leaf spring leaf is 780°C. After quenching to below 100°C, the single-piece steel leaf spring leaf is taken out.

[0155] Tempering step: temper the quenched single-piece steel leaf spring to 400, 450, 500, 550 or 600°C, with a holding time of 90 minutes, and water-cool to below 100°C after tempering.

[0156] The change of the hardness of the single-piece steel leaf spring produced in Comparative Examples 6 to 8 with the tempering temperature is as follows: Figure 1 As shown, it can be seen that under the same Si content, the higher the tempering temperature, the lower the hardness of the single-piece steel leaf spring spring; under the same tempering temperature, the higher the Si content, the higher the hardness of the single-piece steel leaf spring spring.

[0157] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features invented herein.

Claims

1. A method for manufacturing a single-piece steel leaf spring leaf, which is used to make a spring steel material, It is characterized in that The spring steel material comprises, by weight percentage, C: 0.48% to 0.56%, Si: 1.00% to 1.20%, Mn: 0.70% to 1.00%, Cr: 0.80% to 1.00%, V: 0.15% to 0.25%, Mo: 0.05% to 0.07%, Nb: 0.02% to 0.04%, Cu: 0.00% to 0.50%, P: ≤0.025%, S: ≤0.025%, Ti: 0.020% to 0.025%, Als: 0.010% to 0.040%, N: 0.0020% to 0.0080%, and the rest is Fe and unavoidable impurities; Used to manufacture single-piece steel leaf spring leaves with a thickness of ≤45mm; The manufacturing method has the following main process flow: blanking → blind hole drilling → rolling → quenching → tempering → shot peening → painting → assembly; The rolling heating temperature is 900-1000℃, and the reed is slowly cooled in the heat preservation cover until the temperature of the reed is ≤200℃ before quenching. The quenching comprises: heating the reed to 820-880°C and then quenching in oil; During the quenching process, the reed is swung along with the quenching fixture, with a swaying frequency of 20 to 25 times per minute and a swaying time of 120 to 150 seconds; The tempering comprises: tempering the quenched reed to 400-450°C.

2. The method for manufacturing a single-piece leaf spring according to claim 1, Features: Used to manufacture single-piece steel leaf spring leaves with a thickness of 38mm to 45mm.

3. The method for manufacturing a single-piece leaf spring according to claim 1, Features: Used to manufacture single-piece steel leaf spring leaves with a thickness of 40mm to 45mm.

4. A single-piece leaf spring spring, It is characterized in that The single-piece steel leaf spring is prepared by the manufacturing method of any one of claims 1 to 3.

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