Non-quenched and tempered steel for piston rod of automobile shock absorber and preparation method of non-quenched and tempered steel

Abstract

The preparation method comprises the steps of converter smelting, LF refining, RH vacuum degassing, argon soft blowing, continuous casting, rolling and the like, the effects of various elements of C, Mn, Cr, V and N in the steel are fully utilized, microalloying component design is carried out, the technological parameters of all the steps are accurately controlled, and the production efficiency of the piston rod of the non-quenched and tempered automobile shock absorber is improved. Rolling and cooling are controlled in the rolling process, the toughness of the steel is obviously improved, and the performance is stable and reaches the quenched and tempered steel performance. And the high-quality steel with high cleanliness, good structure uniformity and fine and uniform crystal grains is obtained, and the performance requirements of piston rod materials of shock absorbers of new energy automobiles are met. The preparation process does not need a tempering process, so that the production cost and energy consumption are reduced, and carbon is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a non-quenched and tempered steel for a piston rod of an automobile shock absorber and a preparation method thereof. Background Art

[0002] The shock absorber is an important part of the automobile suspension system, which can absorb the vibration between the car wheels and the car body, and improve the comfort and safety of the car during driving. The piston rod inside the shock absorber is an important part of the shock absorber. During its service, it is subjected to alternating axial and lateral forces. Bending fatigue fracture is a common failure form of the shock absorber piston rod. Therefore, the automobile shock absorber piston rod has strict requirements on the raw steel. First of all, the steel material is required to have good surface quality, high mechanical properties and good machining properties, and avoid surface defects such as pits, pits, and cracks; at the same time, the steelmaking process should reduce the number of non-metallic inclusions and improve the fatigue strength of the material; in addition, the number of surface pores should be reduced to prevent the surface from being exposed after grinding, which will cause waste in the future. Therefore, the steel for the automobile shock absorber piston rod is required to have the characteristics of high strength, high toughness, and high reliability. Usually, the passenger car shock absorber piston rod is made of ≤Φ30mm quenched and tempered steel. In the prior art, the processing process of such steel includes annealing treatment steps before cold drawing and subsequent processing and tempering treatment steps. Its production cycle is long and energy consumption is high, which does not conform to the development trend of green and low-carbon technology. Summary of the invention

[0003] Aiming at the technical problems of long production cycle and high energy consumption in the processing process of passenger car shock absorber piston rod steel in the prior art, the present invention proposes a method for producing high-quality non-quenched and tempered automobile shock absorber piston rod steel by using V, Nb, N composite micro-alloying components and through controlled rolling and controlled cold rolling processes.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A non-quenched and tempered steel for a piston rod of an automobile shock absorber, wherein the chemical composition thereof is as follows by weight percentage: 0.42%≤C≤0.48%, 0.15%≤Si≤0.35%, 0.60%≤Mn≤0.90%, P≤0.030%, S≤0.035%, Ni≤0.20%, Cr≤0.25%, 0.020%≤Al≤0.040%, Cu≤0.20%, V≤0.15%, Mo≤0.15%, O≤20ppm, H≤2ppm, and the balance is Fe and unavoidable impurities.

[0006] Preferably, its chemical composition by weight percentage is: C 0.45%, Si 0.28%, Mn 0.86%, Cr 0.22%, Al 0.027%, V 0.10%, N 0.0120%, P 0.014%, S 0.015%, and the balance is Fe and inevitable impurities.

[0007] Preferably, after cold drawing, the yield strength is ≥640Mpa, the tensile strength is ≥850Mpa, the cross-sectional shrinkage is ≥30%, the -20°C impact absorption energy KV2 is ≥27J, and the hardness is ≥23HRC.

[0008] The non-quenched and tempered steel for automobile shock absorber piston rod involved in the present invention belongs to micro-alloyed ferrite + pearlite type non-quenched and tempered steel, and the design principles of each component are as follows:

[0009] 1) C is the element that contributes most to the strength of steel. Carbon dissolves in steel to form interstitial solid solution, which plays a role in solid solution strengthening. In addition, when it forms carbides with strong carbide-forming elements such as V, Nb, and Ti, it plays a precipitation strengthening role. Carbon has a great influence on the strength, hardness, plasticity, toughness, decarburization tendency and microstructure of steel, and its influence often exceeds that of other alloying elements. According to the material that needs to reach a hardness ≥ HRC23 without heat treatment, the C content is required to be 0.42%-0.48%.

[0010] 2) Si is an important reducing agent and deoxidizer in the steelmaking process. In addition, Si can be dissolved in ferrite and austenite to increase the hardness and strength of steel. However, silicon content can easily cause cold work hardening during cold processing and affect the drawing performance, so the Si content should not exceed 0.35%.

[0011] 3) Mn can refine the pearlite structure and significantly improve the strength of pearlite steel, so it can improve the strength of steel, and can infinitely dissolve with Fe, improve the strength of steel through solid solution strengthening, and have a relatively small effect on plasticity. However, when the manganese content exceeds 1.5%, the toughness will decrease significantly, so the Mn content in steel should not be too high. Therefore, the Mn content in pearlite + ferrite steel should be controlled below 0.90%.

[0012] 4) The most prominent advantage of the Cr element is that it can increase the activation energy of carbon diffusion in steel, reduce the decarburization tendency and grain coarsening tendency of steel, and easily form strong carbides with C, which can significantly improve the strength and hardness of steel. Therefore, appropriate Cr elements are generally added to Japanese high-carbon steel to improve strength.

[0013] 5) Mo can maintain sufficient strength and creep resistance at high temperatures (long-term stress at high temperatures causes deformation, referred to as creep). In steel, it can improve hardenability and heat strength and prevent temper brittleness. Mo can be dissolved in ferrite, austenite and carbide, and has a solid solution strengthening effect on ferrite. It can also improve the stability of carbides and play a beneficial role in the ductility and toughness of steel.

[0014] 6) S is a commonly used alloying element in non-quenched and tempered steel and free-cutting steel. In steel, S and Mn form non-metallic inclusions of MnS, which destroy the continuity of the material matrix structure and reduce the cutting resistance during cutting. In addition, sulfides have good plastic deformation and act as a lubricant during cutting, which will reduce tool wear. Therefore, adding an appropriate amount of S to high-strength non-quenched and tempered steel can effectively improve the cutting performance.

[0015] 7) V is a strong carbonitride-forming element, and has a strong affinity with C and N elements. When they generate fine dispersed VC and VN, they can produce a strong precipitation strengthening effect, refine the grains, and improve the hardness and strength of steel, especially the yield strength ratio. Vanadium mainly exists in the form of carbonitrides in steel. Its main function is to refine the organization and grains of steel, and can improve the strength and toughness of steel. However, the price of V is relatively high. In order to save costs, the content in steel should be controlled below 0.15%.

[0016] 8) N is similar to C and is also an interstitial atom. It can be combined with chromium, aluminum, vanadium, titanium, niobium and other elements to form extremely stable nitrides, becoming a hardening and strengthening element for steel. In nitrogen-containing non-quenched and tempered steel, precipitation strengthening can occur during the rolling and cooling process due to the precipitation of ultra-microscopic nitrides. While increasing strength and hardness, excessive nitrogen will reduce the toughness of steel and increase notch sensitivity, so a reasonable nitrogen content control range should be maintained.

[0017] 9) Al is generally used in steel as a deoxidizing and nitrogen fixing agent in steelmaking, and it can also refine grains. Al has a great affinity for nitrogen, easily generates AlN, and refines grains. Al plays a leading role in nitrogen fixation, followed by Ti, then V, and then Nb. The Al combined with N in steel is acid-soluble Al. According to the ideal chemical ratio of the two elements in AlN, and considering the consumption reaction of other elements to Al, if the ratio of the acid-soluble Al content to the N content in the steel satisfies ≥3:1, AlN can be generated, VN can be prevented from being generated, and more V elements can be dissolved in austenite. Then the effect of V element on improving the hardenability of steel will be brought into play, so the Al content is controlled at 0.020%-0.040%.

[0018] The present invention also provides a method for preparing a non-quenched and tempered steel for a piston rod of an automobile shock absorber, comprising the following steps:

[0019] (1) Converter smelting: converter high carbon drawing operation, the final composition of steel tapping is controlled to be C ≥ 0.10%, P ≤ 0.020%, S ≤ 0.050%; converter tapping temperature ≥ 1600°C;

[0020] (2) Refining outside the furnace: LF furnace is used for molten steel refining and RH vacuum degassing;

[0021] (3) Continuous casting: The continuous casting billet size is 240 mm × 300 mm. It is cast using a five-machine five-stream arc continuous casting unit. The continuous casting superheat is 20-30 °C, the casting speed is 0.70-0.80 m / min, and the crystallizer electromagnetic stirring is used to improve the uniformity of alloy element precipitation during the solidification process of the billet. The remaining steel + slag in the ladle is ≥ 3.5 tons. The continuous casting billet is placed in a holding pit for insulation, and the insulation time is ≥ 48 hours.

[0022] (4) Heating: Based on the black box test of the heating test of the 240x300 billet, the temperature change curve of the billet core surface is accurately determined, and the heating parameters are accurately formulated. Specifically, step-by-step heating is adopted, with the temperature of the first heating stage at 1000-1100°C, the temperature of the second heating stage at 1210-1230°C, and the temperature of the soaking stage at 1200-1220°C; the total heating time is 2.5-3.5h, and the total time of the second heating stage and the soaking stage is ≥1.5h. High-temperature heating ensures that the alloy elements are fully melted and completely austenitized, laying the foundation for subsequent solid solution strengthening. At the same time, the material decarburization layer is strictly controlled to be ≤0.8D% (D is the diameter of the round steel) to reduce the subsequent surface processing.

[0023] (5) Rolling: Use high-pressure water for descaling and continuous rolling mill for rolling. The starting temperature of rough rolling is ≥1100℃. Water cooling is performed during rolling. The final rolling temperature is 840-880℃. Two-phase rolling is used to refine the grains. The upper cooling bed temperature is 680-720℃. The cooling bed cover is used for slow cooling to obtain a uniform ferrite + pearlite structure with a cross-sectional hardness difference of <3HBW.

[0024] Preferably, in step (1), molten iron and scrap steel are used as materials, and the furnace loading amount is 110±5 tons; the converter slag is mainly lime and light-burned dolomite, which are added in batches according to the slag conditions, 300-800 kg each time.

[0025] Preferably, step (2) specifically comprises:

[0026] (2.1) LF smelting: The refining process adopts the bottom blowing mode with argon blowing throughout the whole process, and adopts the slag washing process; the alloy adopts silicon manganese alloy, ferrosilicon, aluminum ingot or aluminum iron, high carbon ferrochrome, and carburizer, and ferrovanadium and titanium wire are added to the refining furnace; the refining furnace uses aluminum particles and silicon carbide for deoxidation, and white slag operation; LF uses a wire feeder to feed aluminum wire in the early stage to make the aluminum content reach 0.035-0.040% in order to meet the burn-off in the later process, and the final product Al must meet 0.025-0.035%, and the refining cycle is ≥40 minutes;

[0027] (2.2) RH vacuum degassing: RH is driven by nitrogen, with high vacuum for the first 20 minutes and low vacuum for the last 10 minutes. After the RH vacuum treatment, samples are taken for nitrogen content testing; the chemical composition is controlled to be C: 0.45%-0.47%, Mn: 0.80%-0.85%, Cr: 0.20%-0.25%, V: 0.10%-0.12%, N: 90-150ppm; the order of adding deoxidizer and alloy is: aluminum ingot or aluminum iron→pre-melted slag→alloy→lime; after the RH is completed, nitrogen samples are taken for analysis and nitrogen-manganese wire is fed into the steel according to the N content in the steel by a wire feeder, so that the N content meets the requirement of 0.01-0.02%; in addition, S wire is fed into the steel according to the S content in the steel by a wire feeder, so that the S content reaches 0.015-0.035%;

[0028] (2.3) Argon soft blowing: After all the ingredients meet the standards, weak argon stirring operation is performed, and the argon flow rate is controlled to make the slag surface creep slightly and the molten steel is not exposed. The soft blowing time is ≥20min.

[0029] Preferably, the electromagnetic stirring in step (3) is specifically as follows: frequency A: 105, frequency B: 55, amplitude A: 2.0, amplitude B: 1.0, and slope: 20.

[0030] Preferably, in the pouring process in step (3), the liquid level is kept stable and slag rolling is prevented, the head billet is cut ≥3m, the tail billet is cut ≥4m, and the head and tail billets are cut to ensure that the residual shrinkage holes in the billet are completely removed.

[0031] Compared with the prior art, the advantages and positive effects of the present invention are:

[0032] The preparation method of the non-quenched and tempered steel for automobile shock absorber piston rod of the present invention is to design the microalloying composition, make full use of the effects of various elements of C, Mn, Cr, V, and N in steel, and adopt the steps of converter smelting, LF refining, RH vacuum degassing, argon soft blowing, continuous casting and rolling, accurately control the process parameters of each step, control rolling and cooling during the rolling process, significantly improve the strength and toughness of the steel, and stably achieve the performance of quenched and tempered steel. High-quality steel with high cleanliness, good uniformity of organization, fine and uniform grains is obtained, the tensile strength of the steel is Rm≥850Mpa, the yield strength is Rel≥640Mpa, the cross-sectional shrinkage is Z≥30%, the impact energy KV2 at -20℃ is ≥27J, and the hardness is ≥23HRC, which meets the performance requirements of the piston rod material of the shock absorber of new energy vehicles. The preparation process does not require quenching and tempering process, reduces production costs and energy consumption, and effectively reduces carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 100X microstructure diagram of sample 1 prepared in the embodiment of the present invention;

[0034] Figure 2 500X microstructure diagram of sample 2 prepared in the embodiment of the present invention; DETAILED DESCRIPTION

[0035] In order to better understand the present invention, a detailed description is given below in conjunction with the accompanying drawings and embodiments.

[0036] Embodiment: A method for preparing non-quenched and tempered steel for automobile shock absorber piston rod, comprising the steps of converter smelting, refining outside the furnace, continuous casting, heating and rolling, specifically:

[0037] 1. Converter smelting

[0038] The furnace is equipped with hot metal and scrap steel, with a loading capacity of 110 tons, including 95 tons of hot metal and 15 tons of scrap steel. The converter slag is lime and lightly burned dolomite, which are added in 5 batches, 500 kg each time. The final composition of the converter steel is C 0.12%, P 0.010%; the converter steel tapping temperature is 1620℃, the steel tapping volume is 109 tons, and the steel tapping time is 4 minutes. The ladle slag ratio is 500 kg of lime and 450 kg of pre-melted slag; the order of adding deoxidizer and alloy is: aluminum ingot or steel core aluminum → composite deoxidizer, pre-melted slag powder → alloy → lime.

[0039] 2. Refining outside the furnace

[0040] 2.1 LF refining

[0041] The temperature of the molten steel entering the LF station is 1590℃. The argon flow rate before power on is 750NL / min. After stirring for 2-3min, the argon flow rate is reduced to 300NL / min and power on to increase the temperature. According to the slag condition, 100kg of lime is added; Al particles and SiC powder are used for diffusion deoxidation, 30kg of Al particles, 80kg of SiC powder, and the molten steel sample is taken for inspection. The alloy composition is adjusted according to the inspection results, and the slag basicity is adjusted to 4-6 at the same time. The white slag is kept for 40 minutes. The chemical composition test results are C 0.45%, Si 0.28%, Mn0.86%, Cr0.22%, V0.10%. In the early stage of LF, a wire feeder is used to feed aluminum wire, and the aluminum content is adjusted to 0.037%.

[0042] 2.2 RH vacuum degassing

[0043] LF was heated to 1610℃, and the ladle was hoisted into the RH station for vacuum degassing. Nitrogen circulation was used, and the nitrogen flow rate was 80L / min at high vacuum; the high vacuum holding time was 22 minutes; and the high vacuum degree was 27Pa. After the RH was completed, a nitrogen sample was taken for analysis. According to the N content of 75ppm in the steel, 350m of nitrogen-manganese wire was fed by a wire feeder to make the N content reach 0.012%; then the S wire was fed by a wire feeder to make the S content reach 0.015%.

[0044] 2.3 Argon soft blowing

[0045] After all the ingredients meet the standards, weak argon stirring operation is performed, and the argon flow rate is controlled to make the slag surface creep slightly and the molten steel is not exposed. The soft blowing time is 25 minutes.

[0046] 4. Continuous casting

[0047] The size of the continuous casting square billet is 240mm×300mm. It is cast by a five-machine five-stream arc continuous casting unit. The continuous casting overheat is 22~28℃, the casting speed is controlled at 0.75m / min, the temperature entering the straightening machine is 1065℃, and the continuous casting billet is kept warm in the insulation pit for 48h.

[0048] 5. Heating

[0049] A walking beam heating furnace was used, with the first heating stage at 1065°C, the second heating stage at 1225°C, and the soaking stage at 1210°C. The total heating time was 4 hours, and the high temperature diffusion (second heating stage and soaking stage) time was 1.5 hours;

[0050] 6. Rolling

[0051] The continuous casting billet with a size of 240mm×300mm is rolled into specifications Steel;

[0052] The controlled rolling and controlled cooling process is adopted for rolling, specifically, high-pressure water is used for dephosphorization, continuous rolling unit rolling, rough rolling starting temperature is 1105℃; two water tanks are filled with water, the final rolling temperature is 870℃, the upper cooling bed is 709℃, the lower cooling bed is 382℃, and the cooling bed time is 760s.

[0053] The chemical composition and weight percentage of the non-quenched and tempered steel for automobile shock absorber piston rod prepared by the above preparation method are: C 0.45%, Si 0.28%, Mn 0.86%, Cr 0.22%, Al0.027%, V 0.10%, N 0.0106%, P0.014%, S 0.015%, Cu 0.0145%, Mo 0.002%, O 10ppm, H 1.5ppm, and the rest is Fe.

[0054] The non-quenched and tempered automobile shock absorber piston rod steel prepared by the above preparation method was prepared into test pieces for performance testing. The test pieces were numbered: T1 and T2. The test items included: macrostructure, gas content, non-metallic inclusions, mechanical properties and microstructure. The specific test methods and test results are as follows:

[0055] (1) Low-magnification tissue

[0056] The macrostructure test method is: take different steels produced normally and test their general looseness, central looseness and ingot segregation. The specific test data are shown in Table 1:

[0057] Table 1 Macrostructure test results

[0058]

[0059] The following test ratings can be obtained from Table 1: general looseness, central looseness, and frame segregation are all level 0.5, indicating that the internal quality of the steel is good and the segregation is light.

[0060] (2) Gas content detection

[0061] The gas content test method is: take different steels produced normally and test the oxygen, nitrogen and hydrogen content. The specific test data are shown in Table 2:

[0062] Table 2 Gas content detection results

[0063]

[0064] It can be seen from Table 2 that the oxygen content of the non-quenched and tempered steel for automobile shock absorber piston rod prepared in this embodiment is 10.2ppm and 8.8ppm, and the hydrogen content is 1.2ppm and 1.0ppm. The low oxygen content indicates that the oxide inclusions in the steel are reduced, and the low hydrogen content reduces the "hydrogen embrittlement" tendency of the steel, greatly improving the fatigue life of the piston rod, and the technical advantage is obvious.

[0065] (3) Non-metallic inclusion detection

[0066] The non-metallic inclusion test method is: take different normally produced steels and test the non-metallic inclusions A, B, C, D and DS in the steel. The specific test data are shown in Table 3:

[0067] Table 3 Non-metallic inclusion detection results

[0068]

[0069] It can be seen from Table 3 that the inclusions of types B, C and D are all ≤0.5. Because sulfur is added to this variety to improve the processing function, the sulfide type A inclusions are ≤2.0, and there are no large-particle DS inclusions. By strictly controlling the purity of this variety, the defects such as pinholes on the surface of the piston rod after subsequent polishing can be effectively prevented, and it is also beneficial to improve the fatigue life of the piston rod.

[0070] (4) Mechanical properties testing

[0071] Different normally produced steels were taken respectively, and their mechanical properties after cold drawing were tested. The results are shown in Table 4. Through testing, it can be seen that the non-quenched and tempered automobile shock absorber piston rod steel obtained in this embodiment meets the requirements of tensile strength Rm≥850MPa, yield strength Rel≥640Mpa, cross-sectional shrinkage rate Z≥30%, -20℃ impact energy KV2≥27J, and hardness≥23HRC.

[0072] Table 4 Mechanical properties after cold drawing

[0073]

[0074] (5) Microstructure inspection

[0075] The microstructure analysis of specimens T1 and T2 showed the following results: Figure 1 , Figure 2 As shown in the figure, it can be seen that the structure is ferrite + pearlite, the structure is fine and uniform, and the spacing between pearlite lamellae is small.

[0076] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A non-quenched and tempered steel for automobile shock absorber piston rod, characterized in that: Its chemical composition by weight percentage is: 0.42%≤C≤0.48%, 0.15%≤Si≤0.35%, 0.60%≤Mn≤0.90%, P≤0.030%, S≤0.035%, Ni≤0.20%, Cr≤0.25%, 0.020%≤Al≤0.040%, Cu≤0.20%, V≤0.15%, Mo≤0.15%, O≤20ppm, H≤2ppm, and the balance is Fe and unavoidable impurities.

2. The non-quenched and tempered steel for automobile shock absorber piston rod according to claim 1, characterized in that: Its chemical composition by weight percentage is: C 0.45%, Si 0.28%, Mn 0.86%, Cr 0.22%, Al 0.027%, V 0.10%, N 0.012%, P 0.014%, S 0.015%, and the balance is Fe and inevitable impurities.

3. The non-quenched and tempered steel for automobile shock absorber piston rod according to claim 1, characterized in that: After cold drawing, the yield strength is ≥640Mpa, the tensile strength is ≥850Mpa, the cross-sectional shrinkage is ≥30%, the impact absorption energy at -20℃ KV2 is ≥27J, and the hardness is ≥23HRC.

4. A method for preparing non-quenched and tempered steel for automobile shock absorber piston rod, characterized in that: The following steps are involved: (1) Converter smelting: converter high carbon drawing operation, the final composition of steel tapping is controlled to be C ≥ 0.10%, P ≤ 0.020%, S ≤ 0.050%; converter tapping temperature ≥ 1600°C; (2) Refining outside the furnace: LF furnace is used for molten steel refining and RH vacuum degassing; (3) Continuous casting: The continuous casting billet size is 240 mm × 300 mm. It is cast using a five-machine five-stream arc continuous casting unit. The continuous casting superheat is 20-30 °C, the casting speed is 0.70-0.80 m / min, and the crystallizer electromagnetic stirring is used to improve the uniformity of alloy element precipitation during the solidification process of the billet. The remaining steel + slag in the ladle is ≥ 3.5 tons. The continuous casting billet is placed in a holding pit for insulation, and the insulation time is ≥ 48 hours. (4) Heating: Step heating is adopted, the temperature of the first heating stage is 1000-1100°C, the temperature of the second heating stage is 1210-1230°C, and the temperature of the soaking stage is 1200-1220°C; the total heating time is 2.5-3.5h, and the total time of the second heating stage and the soaking stage is ≥1.5h; (5) Rolling: Use high-pressure water for descaling and continuous rolling mill for rolling. The starting temperature of rough rolling is ≥1100℃. Water cooling is performed during rolling. The final rolling temperature is 840-880℃. Two-phase rolling is used to refine the grains. The upper cooling bed temperature is 680-720℃. The cooling bed cover is used for slow cooling to obtain a uniform ferrite + pearlite structure with a cross-sectional hardness difference of <3HBW.

5. The non-quenched and tempered steel for automobile shock absorber piston rod according to claim 4, characterized in that: In step (1), molten iron and scrap steel are used as materials, and the furnace loading amount is 110±5 tons; the converter slag is mainly lime and light-burned dolomite, which are added in batches according to the slag conditions, 300-800 kg each time.

6. The non-quenched and tempered steel for automobile shock absorber piston rod according to claim 4, characterized in that: Step (2) specifically includes: (2.1) LF smelting: The refining process adopts the bottom blowing mode with argon blowing throughout the whole process, and adopts the slag washing process; the alloy adopts silicon manganese alloy, ferrosilicon, aluminum ingot or aluminum iron, high carbon ferrochrome, and carburizer, and ferrovanadium and titanium wire are added to the refining furnace; the refining furnace uses aluminum particles and silicon carbide for deoxidation, and white slag operation; LF uses a wire feeder to feed aluminum wire in the early stage to make the aluminum content reach 0.035-0.040%, and the refining cycle is ≥40 minutes; (2.2) RH vacuum degassing: RH is driven by nitrogen, with high vacuum for the first 20 minutes and low vacuum for the last 10 minutes. After the RH vacuum treatment, samples are taken for nitrogen content testing; the chemical composition is controlled to be C 0.45%-0.47%, Mn 0.80%-0.85%, Cr 0.20%-0.25%, V 0.10%-0.12%, and N 90-150ppm; the order of adding deoxidizer and alloy is: aluminum ingot or aluminum iron→pre-melted slag→alloy→lime; after the RH is completed, nitrogen samples are taken for analysis and nitrogen-manganese wire is fed into the steel according to the N content in the steel by a wire feeder, so that the N content meets the requirement of 0.01-0.02%; in addition, S wire is fed into the steel according to the S content in the steel by a wire feeder, so that the S content reaches 0.015-0.035%; (2.3) Argon soft blowing: After all the ingredients meet the standards, weak argon stirring operation is performed, and the argon flow rate is controlled to make the slag surface creep slightly and the molten steel is not exposed. The soft blowing time is ≥20min.

7. The non-quenched and tempered steel for automobile shock absorber piston rod according to claim 4, characterized in that: The specific electromagnetic stirring in step (3) is frequency A: 105, frequency B: 55, amplitude A: 2.0, amplitude B: 1.0, and slope:

20.

8. The non-quenched and tempered steel for automobile shock absorber piston rod according to claim 4, characterized in that: During the pouring process in step (3), the liquid level is ensured to be stable and slag rolling is prevented. The head billet is cut ≥3m and the tail billet is cut ≥4m.

Images