Low-cost long-fatigue-life spring flat steel for air suspension guide arm

Abstract

The invention provides low-cost and long-fatigue-life spring flat steel for an air suspension guide arm. The low-cost and long-fatigue-life spring flat steel comprises the following main components in percentage by mass: 0.50 to 0.55 percent of C, 0.17 to 0.40 percent of Si, 0.80 to 1.10 percent of Mn, 0.90 to 1.20 percent of Cr, less than or equal to 0.020 percent of P, less than or equal to 0.015 percent of S, 0.03 to 0.10 percent of Mo, 0.005 to 0.30 percent of Ni, 0.005 to 0.30 percent of Cu, 0.12 to 0.25 percent of V, 0.010 to 0.040 percent of Al, less than or equal to 0.0015 percent of O, 0.0050 to 0.0120 percent of N and the balance of Fe and inevitable impurity elements. Through component optimization and process control, the production cost is remarkably reduced, and the production benefit is improved. The spring flat steel provided by the invention has excellent hardenability and fracture resistance, and has high strength and high toughness after heat treatment, and the fatigue life of the spring flat steel produced from the components is more than two times of that of a similar product after the spring flat steel is processed into a guide arm.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of special steel smelting, and particularly relates to a low-cost high-fatigue-life spring flat steel for air suspension guide arm. BACKGROUND

[0002] With the implementation of the national mandatory standard GB7258-2017 Technical Conditions for Motor Vehicle Running Safety, special operation vehicles, hazardous chemical substance transport vehicles and other semitrailers need to be equipped with air suspensions. The guide arm is an important supporting component in the air suspension and plays a role in load bearing and steering. At present, the spring flat steel for air suspension guide arm is generally produced by using the German brand 52CrMoV4 material, but the 52CrMoV4 flat steel has problems of high hot-rolled hardness and easy bending, thereby resulting in high processing and production cost. The 52CrMoV4 material is prone to quenching cracks in the heat treatment process due to its high Mo component design, and the quenching cracks have a deep depth and a long length and cannot be repaired, thereby causing high guide arm scrap rate and high production cost. SUMMARY

[0003] The present application aims at the technical problems of high hot-rolled hardness, easy bending and high processing and production cost of the existing spring flat steel for air suspension guide arm, and provides a low-cost high-fatigue-life spring flat steel for air suspension guide arm, which has a 1% increase in yield rate compared with the German brand 52CrMoV4 flat steel, a cross-section hardness difference controlled within 3HRC, a quenching crack ratio in heat treatment reduced to within 0.01%, and a fatigue life increased by 2 times.

[0004] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A low-cost high-fatigue-life spring flat steel for air suspension guide arm, which mainly comprises the following components in percentage by mass: C 0.50-0.55%, Si 0.17-0.40%, Mn 0.80-1.10%, Cr 0.90-1.20%, P≤0.020%, S≤0.015%, Mo 0.03%-0.10%, Ni 0.005%-0.30%, Cu 0.005%-0.30%, V 0.12%-0.25%, Al 0.010%-0.040%, O≤0.0015%, N 0.0050%-0.0120%, and the balance is Fe and inevitable impurity elements.

[0005] As preferred, the steel grade DI value is 150-200. The calculation formula of DI value is: DI=25.4*(0.171+0.001*C+0.265*C*C)*(1+3.333*Mn)*(1+0.7*Si)*(0.321+1.45*Ni-0.612*Ni*Ni+0.125*Ni*Ni*Ni)*(1+2.16*Cr)*(1+3*Mo)*(1+0.365*Cu)*(1+1.73*V)*(1+2.5*Zr) As preferred, the rolling compression ratio is greater than or equal to 10, and the grain size is greater than or equal to 8 levels.

[0006] As preferred, it is prepared by the steps of KR hot metal pretreatment-converter smelting-LF refining-RH vacuum degassing-continuous casting-continuous casting blank slow cooling-continuous casting blank peeling-artificial grinding cleaning-heating rolling-control cooling-sawing-packing and cold storage; The heating rolling step includes heating the continuous casting blank to 1040-1080 DEG C, and keeping for greater than or equal to 160 minutes, so that the alloy elements in the steel are fully solid-solution homogenized, and the strengthening and toughening effect is played. After keeping, two high-pressure water descaling treatments are carried out, and then rolling is carried out, the opening rolling temperature is 900-950 DEG C, the final rolling temperature is 800±30 DEG C, and the target size is rolled.

[0007] As preferred, large reduction is adopted in the rough rolling process, so that deformation penetrates into the heart of the rolled piece, the reduction of the first five rough rolling passes is greater than or equal to 70%, and the total compression ratio of the rolled blank is greater than or equal to 10, so as to ensure the fine-grained, high-strength and tough mechanical properties of the rolled material.

[0008] As preferred, after the continuous casting blank is produced, it is slow-cooled in the pit, the pit temperature is greater than or equal to 700 DEG C, and the pit temperature is less than or equal to 200 DEG C, then the continuous casting blank is peeled, the peeling depth is greater than or equal to 2 mm, so as to remove the decarburized layer and the oxidation layer on the surface of the continuous casting blank, and the burrs are removed by artificial grinding.

[0009] Compared with the prior art, the application has the advantages and positive effects that: 1. The application significantly reduces production cost and improves production efficiency through component optimization and process control. Specifically, the content of high-price alloy element Mo is greatly reduced (from the high Mo design of 52CrMoV4 to 0.03%-0.10%), directly reducing the raw material procurement cost; compared with the German standard 52CrMoV4 flat steel, the yield rate is increased by 1%; at the same time, the proportion of quenching cracks generated by heat treatment is reduced to less than 0.01% (the crack proportion of the same material in the comparative example is 0.3%), which almost eliminates the scrap of the guide arm due to quenching cracks, greatly reduces the production loss and rework cost. The hot-rolled state performance is improved, the problem of high hardness and easy bending of traditional materials is solved, the equipment loss and process complexity in the subsequent processing process are reduced, and the processing and production cost is further reduced.

[0010] 2. By precisely designing the composition and controlling the DI value (150~200), the full-section hardenability of the 35-65mm thick flat steel is guaranteed. After heat treatment, the cross-sectional hardness difference can be controlled within 3HRC, meeting the load-bearing and support requirements of the single-piece thick-walled structure of the guide arm. The product's yield strength can reach over 1400MPa, and the tensile strength exceeds 1500MPa, while maintaining good plasticity (elongation after fracture ≥10%, reduction of area ≥40%) and toughness (room temperature impact energy KU2 ≥35J), which can match the load-bearing, steering, and other mechanical performance requirements of the air suspension guide arm.

[0011] 3. Through component optimization and process control, this invention increases the fatigue life of the product by 2 times compared to German standard 52CrMoV4 flat steel, significantly improving the long-term reliability of the air suspension. Attached Figure Description

[0012] Figure 1 The graphs show the hardenability variation of the steels prepared in Examples 1-3 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0013] To better understand the present invention, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0014] Based on the design of the air suspension guide arm chassis system, the guide arm is a single-piece structure, unlike the multi-piece structure of current leaf spring suspension systems. To ensure load-bearing capacity, the guide arm is generally thicker than the leaf spring, which requires the guide arm to have good hardenability to ensure that the entire cross-section obtains a good microstructure during heat treatment. The single-piece structure of the guide arm requires it to have a long service life. During use, the guide arm is mainly subjected to alternating stress, and the surface is the location of the greatest stress. Therefore, surface quality is a key indicator affecting the fatigue life of the guide arm.

[0015] Based on the requirements for strength, toughness, hardenability, and fatigue life of flat steel for air suspension guide arms, and considering low cost and low scrap rate in the production process, this invention develops a low-cost, high-fatigue-life spring flat steel for air suspension guide arms through rational design of the steel's chemical composition and special management of the production process. The aim is to provide a low-cost, high-strength, and long-life spring flat steel for air suspension guide arms with a thickness of 35-65mm and a width of 70-120mm, while meeting the low-cost manufacturing requirements of continuous casting and rolling. This product achieves a higher fatigue life while meeting the mechanical property requirements of 52CrMoV4. Example 1

[0016] A low-cost high-fatigue-life spring flat steel for air suspension guide arm, whose main components in percentage by mass are: C 0.52%, Si 0.31%, Mn 1.00%, Cr 1.15%, P 0.012%, S 0.005%, Mo 0.04%, Ni 0.016%, Cu 0.02%, V 0.17%, Al 0.023%, O 0.0009%, N 0.0087%, and the balance of Fe and inevitable impurities, has a DI value of 166.5.

[0017] The production process of the spring flat steel for air suspension guide arm is as follows: hot metal + scrap steel - BOF furnace primary refining - LF furnace refining - RH furnace vacuum degassing - CCM rectangular billet continuous casting - slow cooling - continuous casting billet peeling - manual grinding cleaning - heating rolling - controlled cooling - sawing - packaging and cold storage - finished product inspection - packaging Specifically, the hot metal refining and continuous casting steps are as follows: first smelting by converter, then LF refining, strengthening deoxidation during LF refining, and maintaining the deoxidized refining slag for not less than 15 minutes and having good fluidity. After the refining is completed, the ladle is transferred to the RH furnace for high vacuum degassing treatment, and the pressure is maintained at not less than 1.33 mbar for 20 minutes or more. The soft blowing of the ladle is not less than 30 minutes to ensure the floating of inclusions. The superheat degree of the molten steel during continuous casting is controlled at 15-35 ℃. The whole process is protected casting to prevent the generation of inclusions by contacting with air, and appropriate drawing speed and secondary cooling intensity are provided, and at the same time, light pressing down, M-EMS and F-EMS double measures are adopted for continuous casting, which effectively improves and reduces the composition segregation of the continuous casting billet. The continuous casting billet is slow-cooled in the pit at above 700 ℃, and cooled to below 200 ℃ for cold storage. The continuous casting billet is cooled to below 100 ℃ for peeling, and the surface burrs are removed manually after peeling.

[0018] The continuous casting billet heating rolling step is as follows: the continuous casting billet is heated to 1040-1080 ℃ in a high-focal mixed coal gas heating furnace for 170 min, and the total furnace time is 240-300 min. After descaling by high-pressure water, the billet is directly rolled in the 18-stand continuous rolling mill at a rough rolling temperature of 900-950 ℃ and a finish rolling temperature of 770-830 ℃. The flat steel is rolled to a size of 56 mm*100 mm. The rolling deformation process is reasonably designed, and a large reduction is adopted in rough rolling, and the reduction of the first five rough rolling passes should be ≥70%, and the total compression ratio of the rolled billet to the material is 13.

[0019] After rolling, the rolled material is slowly cooled under the temperature control cover of the cooling bed, and the rolled material is taken out of the cover when the temperature is ≤200 ℃. Then, the rolled material is sawn and cut, and then packaged and collected. Example 2

[0020] A low-cost high-fatigue-life spring flat steel for air suspension guide arm, whose main components in percentage by mass are: C 0.53%, Si 0.34%, Mn 0.98%, Cr 1.17%, P 0.013%, S 0.004%, Mo 0.06%, Ni 0.017%, Cu 0.02%, V 0.16%, Al 0.022%, O 0.0005%, N 0.0081%, and the balance of Fe and inevitable impurity elements, and its DI value is 178.7.

[0021] The production process of the above low-cost high-fatigue-life spring flat steel for air suspension guide arm is the same as that in Example 1. Example 3

[0022] A low-cost high-fatigue-life spring flat steel for air suspension guide arm, whose main components in percentage by mass are: C 0.51%, Si 0.27%, Mn 1.05%, Cr 1.12%, P 0.010%, S 0.004%, Mo 0.04%, Ni 0.017%, Cu 0.019%, V 0.20%, Al 0.018%, O 0.0008%, N 0.0072%, and the balance of Fe and inevitable impurity elements, and its DI value is 171.3.

[0023] The production process of the above low-cost high-fatigue-life spring flat steel for air suspension guide arm is the same as that in Example 1.

[0024] Comparative Example 1 The main components in percentage by mass of the 51CrV4 type spring flat steel currently used in the market are: C 0.50%, Si 0.24%, Mn 0.96%, Cr 1.03%, P 0.012%, S 0.003%, Mo 0.002%, Ni 0.016%, Cu 0.015%, V 0.12%, Al 0.030%, O 0.0015%, N 0.0051%, and the balance of Fe and inevitable impurity elements, and its DI value is 137.8, and its production process is the same as that in Example 1.

[0025] Comparative Example 2 The main components of the German standard 52CrMoV4 flat steel currently used in the market are as follows in terms of mass percentage: C 0.52%, Si 0.27%, Mn 0.93%, Cr 1.08%, P 0.013%, S 0.004%, Mo 0.16%, Ni 0.013%, Cu 0.016%, V 0.12%, Al 0.023%, O 0.0007%, N 0.0032%, and the balance is Fe and unavoidable impurity elements, and the DI value is 182.3. The production process is the same as that in Example 1.

[0026] The spring flat steels prepared in Examples 1-3 and Comparative Examples 1-2 are prepared into impact and tensile samples according to the GB / T2975-2018 standard, the room temperature tensile properties are determined according to the GB / T 228.1-2021 standard, and the room temperature impact properties are determined according to the GB / T 229-2020 standard, and the test results are shown in Table 1. As can be seen from Table 1, the yield strength of the spring flat steel prepared in Examples 1-3 can reach more than 1400 MPa, the tensile strength is more than 1500 MPa, and at the same time, good plasticity (elongation at break ≥10%, reduction of area ≥40%) and toughness (room temperature impact energy KU2≥35 J) are maintained, which completely match the mechanical performance requirements of air suspension guide arm for bearing and steering.

[0027] Table 1 Mechanical properties of spring flat steels prepared in Examples 1-3 and Comparative Examples 1-2

[0028] The spring flat steels prepared in Examples 1-3 and Comparative Examples 1-2 are sampled, prepared and determined for end quenching according to the GB / T225-2006 standard, and the results are shown in Table 2, and the quenching property change curve of the steel prepared in Examples 1-3 and Comparative Examples 1-2 is shown in Figure 1 Table 2 and Figure 1 It can be seen that the overall quenching property of the spring flat steel prepared in Examples 1-3 is improved compared with Comparative Example 1.

[0029] Table 2 End quenching properties of spring flat steels prepared in Examples 1-3 and Comparative Examples 1-2

[0030] The spring flat steels prepared in Examples 1-3 and Comparative Example 2 are detected and counted for yield rate, quenching crack ratio and fatigue life, and the results are shown in Table 3. As can be seen from the table, the yield rate of the spring flat steel prepared in the present application is improved by 1% compared with the German standard 52CrMoV4 flat steel, there is no quenching crack, and the fatigue life is obviously better than that of the 52CrMoV4 flat steel.

[0031] Table 3 Spring flat steel yield, quenching crack ratio and fatigue life of Examples 1-3 and Comparative Example 2

[0032] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can use the disclosed technology to make changes or modifications to equivalent embodiments, or apply them to other fields. However, any simple modification, equivalent change and modification of the above embodiments made in accordance with the technical essence of the present application, without departing from the technical solution of the present application, still falls within the protection scope of the present application.

Claims

1. A low-cost, high-fatigue-life air suspension guide arm spring flat steel, characterized in that, Its main components, by mass percentage, are: C 0.50-0.55%, Si 0.17-0.40%, Mn 0.80-1.10%, Cr 0.90-1.20%, P≤0.020%, S≤0.015%, Mo 0.03%-0.10%, Ni 0.005%-0.30%, Cu 0.005%-0.30%, V 0.12%-0.25%, Al 0.010%-0.040%, O≤0.0015%, N 0.0050%-0.0120%, with the balance being Fe and unavoidable impurity elements.

2. The low-cost, high-fatigue-life air suspension guide arm spring flat steel according to claim 1, characterized in that: The DI value of the steel grade is 150 to 200.

3. The low-cost, high-fatigue-life air suspension guide arm spring flat steel according to claim 1, characterized in that: Its rolling compression ratio is ≥10, and its grain size is ≥8.

4. The low-cost, high-fatigue-life air suspension guide arm spring flat steel according to claim 1, characterized in that: It is prepared through the following steps: KR molten iron pretreatment, converter smelting, LF refining, RH vacuum degassing, continuous casting, slow cooling, continuous casting billet peeling, manual grinding and cleaning, heated rolling, controlled cooling, sawing, and packing and stacking for cooling. The heating and rolling process includes heating the continuously cast billet to 1040-1080℃, holding it at that temperature for ≥160 minutes, performing two high-pressure water descaling treatments after holding, and then rolling it at an initial rolling temperature of 900-950℃ and a final rolling temperature of 800±30℃ to the target size.

5. The low-cost, high-fatigue-life air suspension guide arm spring flat steel according to claim 4, characterized in that: During the rolling process, a large reduction is adopted in the roughing rolling, with the reduction in the first five roughing rolling passes being ≥70%, and the total compression ratio from the rolled billet to the finished product being ≥10.

6. The low-cost, high-fatigue-life air suspension guide arm spring flat steel according to claim 4, characterized in that: After the continuous casting billet is produced, it is placed in the pit for slow cooling. The temperature in the pit is ≥700℃ and the temperature when it comes out of the pit is ≤200℃. After that, the continuous casting billet is peeled, and the peeling depth is ≥2mm.

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