Production method of single-piece type guide arm for air suspension

Abstract

The invention discloses a production method of a single-piece type guide arm for an air suspension. According to the method, the content of Si is greatly increased, the element B is added, meanwhile, the action and the mutual relation among the elements are considered, Ti, Al, B and N are added at different times, Nb, V, Ti and N are adopted for composite microalloying, precious alloy Mo does not need to be added, the material cost is remarkably reduced, four-step salt bath treatment is creatively adopted, the hardness range of the cross section of the guide arm detected through a 9-point method is smaller than or equal to 2.0 HRC, and the hardness range of the cross section of the guide arm is larger than or equal to 2.0 HRC. And the fatigue life of the rack is more than 800,000 times, far higher than the industry requirement of not less than 400,000 times, and reaches the international leading level.

Description

Technical Field

[0001] This invention belongs to the field of automotive materials technology, specifically relating to a method for producing a single-piece guide arm for air suspension. Background Technology

[0002] GB7258-2017, "Technical Conditions for Safe Operation of Motor Vehicles," stipulates that the rear axle of all dangerous goods transport semi-trailers with a total mass ≥ 12,000 kg, as well as three-axle flatbed and stake semi-trailers, must be equipped with air suspension. This requirement has been mandatory since January 1, 2020. Currently, air suspension is mainly divided into two types: one is a single-airbag air suspension composed of a guide arm and a single airbag, and the other is a dual-airbag air suspension composed of a balance beam and two airbags.

[0003] In recent years, with the increasingly fierce competition in the commercial vehicle market, the application of single-airbag air suspension, which is simple in structure, low in cost, and offers good comfort, has become more and more common. At the same time, in order to achieve the goal of weight reduction, the application of single-piece guide arms has been increasing year by year. Generally speaking, the main load-bearing component of a single-airbag air suspension is the guide arm. In addition, since it is used to transport special substances such as hazardous chemicals, OEMs generally have very high requirements for the guide arm, and it is not allowed to be damaged throughout the entire life cycle of the vehicle.

[0004] Guide arms are typically made from spring flat steel, which is rolled, bent, and heat-treated (quenched and tempered) to obtain the final guide arm product. To meet the load requirements of commercial vehicles, the raw material spring flat steel is very large, with a thickness of over 45mm, and the thickest reaching 65mm. The width is also relatively large, generally between 70-100mm. Ensuring that the metallographic structure and mechanical properties of the entire cross-section are very uniform (the hardness difference of the guide arm cross-section is controlled within 2HRC) is extremely difficult, hence its high price.

[0005] To promote the progress of suspension manufacturers and accelerate the development of the commercial vehicle industry, it is essential to innovate in both material composition design and production processes, and to develop a low-cost, high-strength, and highly uniform single-piece guide arm production method. Summary of the Invention

[0006] To achieve the requirements of low cost, high strength, and high uniformity in single-piece guide arms, this invention innovates in both material composition design and manufacturing process, providing a method for producing single-piece guide arms for air suspension. First, this invention significantly increases the Si content in ordinary alloys and adds appropriate amounts of B, employing Nb, V, Ti, and N composite microalloying. This improves the material's hardenability while maintaining low cost. Furthermore, the absence of Mo significantly reduces banded segregation. Second, salt bath treatment replaces ordinary oil quenching heat treatment, resulting in a substantial improvement in the uniformity of the metallographic structure, with the hardness difference across the cross-section controlled within 2 HRC.

[0007] This invention is achieved through the following technical solution: a single-piece guide arm for air suspension (structural schematic diagram shown below). Figure 1 As shown), its composition and weight percentage are as follows: C: 0.46-0.52%, Si: 1.20-1.80%, Mn: 0.80-1.10%, P≤0.015%, S≤0.010%, Cr: 0.90-1.20%, V: 0.05-0.10%, Nb: 0.025-0.045%, Al: 0.020-0.035%, Ti: 0.020-0.040%, B: 0.0020-0.0040%, O: 0.0005-0.0015%, N: 0.0070-0.0120%, H≤0.0002%, with the balance being Fe and unavoidable impurities, and the alloy composition such that the Jo value calculated by formula (1) is not less than 124.

[0008] (1) This invention discloses a method for producing the above-mentioned single-piece guide arm for air suspension, characterized by the following steps: converter blowing, LF furnace refining, RH vacuum treatment, continuous casting of large square billets, heating in a heating furnace, continuous rolling, cutting to length, spring flat steel, blanking, variable cross-section rolling, salt bath treatment, high-intensity shot peening, and electrophoresis to obtain the finished product.

[0009] Furthermore, ferrotitanium is added during the converter blowing process when 1 / 3 of the steel is tapped from the converter; aluminum-based alloy raw materials are added 15-20 minutes after the start of LF refining; the boron content is adjusted by adding ferroboron 5-10 minutes before RH vacuum treatment; nitrogen is used as the circulating gas during RH vacuum treatment, with a total circulation time of 15-20 minutes. In the early stage (≤10 minutes), the vacuum degree is controlled at <67 Pa, and in the later stage (>10 minutes), the vacuum degree is controlled at 4-6 kPa.

[0010] Furthermore, the salt bath treatment is divided into four steps, specifically: 1) Heat in a heating furnace at a temperature of 900-930℃ for 1.5-2.0 hours; 2) Perform salt bath cooling at a temperature of 380-430℃ for 0.5-1.0 hours; 3) After the salt bath, clean the guide arm 2-3 times to ensure that the temperature of the guide arm is 260-320℃ after cleaning. 4) Temper in a tempering furnace at a temperature of 240-300℃ for 0.8-1.2 hours.

[0011] Furthermore, during salt bath treatment, the cooling medium is a molten nitrate composed of two or more of sodium nitrate, potassium nitrate, sodium nitrite, and potassium nitrite, with appropriate amounts of clean water added according to the cooling rate.

[0012] Furthermore, during high-intensity shot peening, the shot peening intensity is 0.30 mmA-0.40 mmA, and the shot peening time is 6 min-10 min.

[0013] The technical effects of this invention are as follows: (1) The present invention has made a completely new chemical composition design, which greatly increases the content of Si and adds some B to improve the hardenability of steel. It also adds four elements: Nb, V, Ti and N to give full play to the role of microalloying. The present invention does not add precious alloy Mo, which reduces the cost of steel and reduces banded segregation. (2) According to the role and interrelationship of each element, Ti, Al, B and N are added at appropriate times in this invention; (3) The present invention divides the salt bath treatment into 4 steps, making full use of the high residual temperature after the salt bath treatment for cooling and tempering, which significantly reduces energy costs and improves production efficiency. (4) The guide arm produced by this invention has low cost, high strength (1400-1500MPa), good toughness (impact energy at room temperature is above 50J), uniform structure, extreme hardness difference of cross section ≤2HRC, and fatigue life reaches the international leading level. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a single-piece guide arm; Figure 2 This is a schematic diagram of the cross-sectional hardness test for a single-piece guide arm. Detailed Implementation

[0015] The present invention will be further described in detail below through specific embodiments. In the following embodiments, many details are described in order to enable the present application to be better understood. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other materials or methods.

[0016] The composition of the single-piece guide arm for air suspension is as follows: C: 0.46-0.52%, Si: 1.20-1.80%, Mn: 0.80-1.10%, P≤0.015%, S≤0.010%, Cr: 0.90-1.20%, V: 0.05-0.10%, Nb: 0.025-0.045%, Al: 0.020-0.035%, Ti: 0.020-0.040%, B: 0.0020-0.0040%, O: 0.0005-0.0015%, N: 0.0070-0.0120%, H≤0.0002%, with the balance being Fe and unavoidable impurities, and the alloy composition ensures that the Jo value calculated by formula (1) is not less than 124.

[0017] (1) The manufacturing methods for single-piece guide arms used in air suspension are as follows: 1) Converter blowing The molten iron is converted into molten steel through a top and bottom blowing converter. The C content at the end of the converter is ≥0.10%, and the tapping temperature is ≥1600℃. The ferrotitanium is added when the converter tapping is 1 / 3 of the way through the converter blowing process. 2) LF furnace refining LF furnace refining ensures that white slag or yellowish-white slag is produced within 15 minutes of refining. Alloy raw materials with aluminum content are added 15-20 minutes after the start of LF refining. 3) RH vacuum treatment The B content was adjusted by adding ferric boron 5-10 minutes before RH vacuum treatment; nitrogen was used as the circulating gas during RH vacuum treatment, with a total circulation time of 15-20 minutes. The vacuum degree was controlled at <67 Pa in the early stage (≤10 minutes) and at 4-6 kPa in the later stage (>10 minutes). 4) Continuously cast large square billets Special protective slag is used, the superheating temperature of continuous casting is 20-35℃, the casting speed is 0.60-0.80m / min, and the cross-section of the continuous casting billet is 240mm×240mm; 5) Heating in the heating furnace The heating furnace uses high-temperature heating, with the temperature of heating section 1 and section 2 being 1200-1240℃, and the total heating time being 3-5 hours; 6) Continuous rolling; 7) Cutting to length; 8) Spring flat steel The flat steel is passed through 21 rolling mills, including roughing, intermediate, and finishing mills, and then through 4 sizing mills to ensure that the dimensions of the flat steel meet the Group 1 accuracy requirements of GB / T 33164.1. It is then slowly cooled on a cooling bed, and then cut into flat steel of appropriate length by a grinding wheel saw. Finally, it is inspected, packaged, and stored to form spring flat steel.

[0018] 9) Blanking; 10) Variable cross-section rolling The spring flat steel is cut to the required length using a band saw, and then induction heating is used at a temperature of 950-1000℃ for 40-50 seconds. After that, it is rolled in 2-5 passes to achieve the dimensional accuracy required by the customer.

[0019] 11) Salt bath treatment Salt bath treatment consists of 4 steps. Step 1: Heat in a heating furnace at a temperature of 900-930℃ for 1.5-2.0 hours. Step two: Perform salt bath cooling at a temperature of 380-430℃ for 0.5-1.0 hours; Step 3: After the salt bath, clean the guide arm 2-3 times to ensure that the temperature of the guide arm is 260-320℃ after cleaning. Step 4: Temper in a tempering furnace at a temperature of 240-300℃ for 0.8-1.2 hours.

[0020] When performing salt bath treatment, the cooling medium is a molten nitrate composed of two or more of sodium nitrate, potassium nitrate, sodium nitrite, and potassium nitrite, and appropriate amounts of clean water are added according to the cooling rate; 12) High-power shot peening The shot peening intensity is 0.30 mmA-0.40 mmA, and the shot peening time is 6 min-10 min.

[0021] 13) Electrophoresis; 14) Finished product Each guide arm undergoes magnetic particle testing, followed by painting on a dedicated electrophoresis line, then press-fitting of bushings, and finally packaging to become the finished guide arm.

[0022] The following is an illustration through specific examples: (1) The process parameters for converter blowing and LF furnace refining in Examples 1-3 are shown in Table 1 below: Table 1. Process parameters for converter blowing and LF furnace refining in Examples 1-3.

[0023] (2) The process parameters for RH vacuum treatment in Examples 1-3 are shown in Table 2 below: Table 2. Process parameters for RH vacuum treatment in Examples 1-3

[0024] (3) The parameters and media used in the salt bath treatment of Examples 1-3 are shown in Tables 3 and 4 below: Table 3. Parameters of salt bath treatment in Examples 1-3

[0025] Table 4 shows the media used in the salt bath treatments of Examples 1-3.

[0026] (4) The parameters of the high-power shot peening in Examples 1-3 are shown in Table 5 below: Table 5 Parameters of high-intensity shot peening in Examples 1-3

[0027] (5) The chemical composition and Jo value of the single-piece guide arm for the air suspension in Examples 1-3 are shown in Table 6 below: Table 6 Chemical composition and Jo value of the single-piece guide arm used in the air suspension of Examples 1-3

[0028] (6) In Examples 1-3, after variable cross-section rolling, the thickest part of the guide arm has a dimension of 56mm × 100mm. Figure 2 The 9-point method shown below is used to test the hardness of the cross-section at the position of the maximum size of the guide arm. The average hardness, range, and fatigue life of the test bench are shown in Table 7.

[0029] Table 7. Average and range of product hardness and bench fatigue life

[0030] As can be seen from Table 7, the hardness of the single-piece guide arm cross section is very uniform. The hardness of the cross section was tested using the 9-point method, and the range of all samples was ≤2.0HRC. The fatigue life of the test bench is over 800,000 cycles, which is far higher than the industry requirement of no less than 400,000 cycles, and reaches the quality level of internationally renowned guide arm manufacturers.

Claims

1. A method for manufacturing a single-piece guide arm for air suspension, characterized in that, Its composition and weight percentage are as follows: C: 0.46-0.52%, Si: 1.20-1.80%, Mn: 0.80-1.10%, P≤0.015%, S≤0.010%, Cr: 0.90-1.20%, V: 0.05-0.10%, Nb: 0.025-0.045%, Al: 0.020-0.035%, Ti: 0.020-0.040%, B: 0.0020-0.0040%, O: 0.0005-0.0015%, N: 0.0070-0.0120%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

2. The production method as described in claim 1, characterized in that, The alloy composition ensures that the Jo value calculated by formula (1) is not less than 124; 。 3. The production method as described in claim 1 or 2, characterized in that, Includes the following steps: The process involves converter blowing, LF furnace refining, RH vacuum treatment, continuous casting of large square billets, heating in a heating furnace, continuous rolling, cutting to length, spring flat steel, blanking, variable cross-section rolling, salt bath treatment, high-intensity shot peening, and electrophoresis to obtain the finished product.

4. The production method as described in claim 3, characterized in that, Ferrotitanium is added during the converter blowing process when 1 / 3 of the steel has been tapped from the converter.

5. The production method as described in claim 3, characterized in that, The aluminum-based alloy raw materials are added 15-20 minutes after the start of LF refining.

6. The production method as described in claim 3, characterized in that, The B content was adjusted by adding ferric boron 5-10 minutes before RH vacuum treatment.

7. The production method as described in claim 3, characterized in that, Nitrogen is used as the circulating gas during the RH vacuum treatment, with a total circulation time of 15-20 minutes. In the early stage (≤10 minutes), the vacuum degree is controlled at <67 Pa; in the later stage (>10 minutes), the vacuum degree is controlled at 4-6 kPa.

8. The production method according to claim 3, characterized in that, The salt bath treatment consists of four steps, specifically: 1) Heat in a heating furnace at a temperature of 900-930℃ for 1.5-2.0 hours; 2) Perform salt bath cooling at a temperature of 380-430℃ for 0.5-1.0 hours; 3) After the salt bath, clean the guide arm 2-3 times to ensure that the temperature of the guide arm is 260-320℃ after cleaning. 4) Temper in a tempering furnace at a temperature of 240-300℃ for 0.8-1.2 hours.

9. The production method as described in claim 8, characterized in that, The cooling medium for the salt bath treatment is a molten nitrate composed of two or more of sodium nitrate, potassium nitrate, sodium nitrite, and potassium nitrite, with appropriate amounts of clean water added according to the cooling rate.

10. The production method as described in claim 3, characterized in that, During the high-intensity shot peening, the shot peening intensity is 0.30 mmA-0.40 mmA, and the shot peening time is 6 min-10 min.

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