Production method of quenched and tempered silver bright steel for hydraulic piston rod

Abstract

The invention belongs to the technical field of metallurgy, and relates to a production method of quenched and tempered silver bright steel for a hydraulic piston rod. The adopted process route comprises a converter, an LF furnace, an RH furnace, continuous casting, hot rolling, straightening, induction heating, precession type water cooling, roller hearth type continuous annealing furnace tempering, fixed-length round steel head and tail cutting, turning, roll finishing and rust-proof packaging. According to the steel produced through the method, the tensile strength is larger than or equal to 1000 Mpa, the yield strength is larger than or equal to 800 Mpa, the ductility is larger than or equal to 28%, the percentage reduction of area is larger than or equal to 60%, and AKV2 at-40 DEG C is larger than or equal to 60 J. The material can be directly blanked and processed into rod and shaft parts with the diameter of 20-38 mm, and the fatigue bench test of the material can reach 1 million times without damage; the method can be widely applied to manufacturing oil cylinder piston rod products for engineering machinery such as excavators.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy and relates to a production method of a quenched and tempered silver bright steel for a hydraulic piston rod. BACKGROUND

[0002] The hydraulic piston rod is a key moving part in a hydraulic system and must have high strength, high toughness, high fatigue life and good wear resistance. Currently widely used materials such as 45 steel, 40Cr, 42CrMo and the like medium carbon alloy structural steel, although the performance can meet the use requirements after quenching and tempering, but there are problems such as long production cycle, high energy consumption, easy deformation, high risk of cracking, serious environmental pollution and the like.

[0003] Document CN117107142A discloses a production method of a non-quenched and tempered steel for an 800Mpa grade hydraulic piston rod, adopting a process route of converter + LF furnace + RH furnace + continuous casting + hot rolling, the chemical composition of the steel is C = 0.38% ~ 0.43%, Si = 0.15% ~ 0.35%, Mn = 0.90% ~ 1.05%, P ≤ 0.025%, S ≤ 0.015%, Cr = 0.10% ~ 0.25%, V = 0.06% ~ 0.11%, Al = 0.005% ~ 0.025%, Nb = 0.02% ~ 0.04%, N = 0.010% ~ 0.020%, H ≤ 0.0002%, O ≤ 0.0020%, and the rest is Fe and inevitable impurities. The steel produced by the method is used to trial-produce an oil cylinder piston rod part, without quenching and tempering treatment of the whole section of the part, energy saving and environmental protection, the fatigue bench test reaches 600,000 times without damage; and can be widely applied to manufacturing an oil cylinder piston rod for excavators and the like engineering machinery.

[0004] Although the non-quenched and tempered steel realizes energy saving and environmental protection to a certain extent, the strength, toughness and fatigue performance are still difficult to meet the use requirements of high-end hydraulic piston rods. Especially under high load and high frequency working conditions, the fatigue life and low temperature impact toughness of the traditional non-quenched and tempered steel are still insufficient.

[0005] Therefore, it is of important industrial application value and market prospect to develop a quenched and tempered silver bright steel with high strength, high toughness, excellent fatigue performance and good machining performance. SUMMARY

[0006] To solve the above technical problems, the application provides a production method of a quenched and tempered silver bright steel for a hydraulic piston rod, which realizes comprehensive improvement of the performance of the steel material through optimized component design and precise control of the quenching and tempering process, and meets the use requirements of high-end hydraulic components.

[0007] The technical scheme adopted by the application is a production method of a quenched and tempered silver bright steel for a hydraulic piston rod, and the key process steps include:

[0008] S1: In the smelting process, control the converter tapping C≥0.08%, P≤0.012%, adopt LF+RH furnace refining process, LF furnace refining whole process argon blowing, slagging deoxidation, white slag holding time≥30min, process control Als=0.020~0.035%, temperature≥1600℃ after using vanadium-nitrogen alloy, nitriding cored wire, ladle bottom blowing nitrogen to increase nitrogen; RH vacuum degassing treatment, under the vacuum degree 0.5tor, vacuum holding time not less than 20min, on-line detection of nitrogen content, using bottom blowing nitrogen, nitriding cored wire to adjust the amount of nitrogen and argon soft blowing for 20 minutes, the outgoing molten steel H≤2ppm, O≤10ppm;

[0009] S2: In the continuous casting process, adopt whole process protection casting, tundish superheat continuous furnace≤25℃, open furnace≤35℃, billet size is 280×280mm;

[0010] S3: In the heating process, billet heating time 300~480min, heating section temperature 1200~1260℃, soaking section temperature 1220~1270℃;

[0011] S4: In the rolling process, bar and wire 850 two-roll flat alternating mill large reduction rolling, open rolling temperature≥1100℃, finish rolling adopts three-roll mill rolling, finish rolling temperature≥750℃;

[0012] S5: In the finishing process, round steel adopts two-roll straightening machine straightening, bending degree q≤2.0mm / m;

[0013] S6: In the induction heating, rotary water cooling process, adopt rotating bottom roller, round steel rotates forward, forward speed 0.01m / s, adopt 6 groups of induction coil heating, water inlet temperature 880-950℃, round steel water outlet red temperature 40-60℃;

[0014] S7: In the roller bottom type continuous annealing furnace tempering process, quenched round steel is uniformly distributed on the roller, one layer of material, uniform speed forward, natural gas heating, 560-600℃ for 4 hours, out of the furnace air cooling;

[0015] S8: Cut off the round bar head and tail and ultrasonic flaw detection blind area part;

[0016] S9: In the truck, roll light process, tempered round steel q≤2.0mm / m, truck diameter decreases by 2.2mm, diameter size tolerance is (0, -0.04)mm, roll light ensures the surface finish Ra≤3.2μm;

[0017] S10: In the rust prevention packaging process, round steel surface is sprayed with oil-based rust preventive oil, and then bundled with rubber-covered binding wire, then wrapped and packaged with waterproof plastic film, sealed with transparent adhesive tape, and finally wrapped and protected with the outermost layer of bamboo.

[0018] Furthermore, in the S4 rolling process, the reduction amount in the first pass is controlled to be 70 mm, and the reduction amount in the second pass is controlled to be 65 mm.

[0019] Furthermore, in the S6 induction heating and swirling water cooling process, the swirling water cooling uses 20 evenly distributed high-pressure water nozzles as a cooling water ring, with 4 water rings arranged at 0.2-meter intervals to cool the round steel, and the water pressure of a single water ring is 0.8-1.2 MPa.

[0020] Furthermore, in S8, the length of the round steel head and tail cut off is 100±5mm each.

[0021] Furthermore, the chemical composition of the steel by weight percentage is as follows: C: 0.42%–0.45%, Si: 0.25%–0.35%, Mn: 0.95%–1.05%, P≤0.015%, S≤0.003%, Cr: 0.20%–0.25%, V: 0.15%–0.20%, Ni≤0.25%, Al: 0.015%–0.025%, Nb: 0.02%–0.04%, N: 0.010%–0.015%, Cu≤0.20%, Mo≤0.15%, H≤0.0002%, O≤0.0020%, with the remainder being Fe and essential impurities.

[0022] Furthermore, the final steel produced has the following properties: tensile strength ≥1000Mpa, yield strength ≥850Mpa, elongation ≥28%, reduction of area ≥60%, and AKV2 ≥60J at -40℃. It can be directly cut and processed into rod and shaft parts with diameters of 20-38mm, and can withstand 1 million fatigue bench tests without damage.

[0023] This invention achieves the preparation of high-performance quenched and tempered silver bright steel through the following technical means:

[0024] 1. Scientific basis and synergistic effect of ingredient design

[0025] The properties of steel essentially depend on its chemical composition and the form in which it exists in its microstructure.

[0026] This invention achieves optimization of toughness and fatigue performance through the following element ratios:

[0027] Carbon (C): As the most basic strengthening element, the C content is controlled between 0.42% and 0.45%. This ensures strength through solid solution strengthening and carbide formation, while avoiding a decrease in toughness and weldability due to excessive carbon content. This range ensures a sufficient proportion of martensite after quenching, providing a basis for tempering.

[0028] Manganese (Mn): Mn improves the stability of austenite, enhances hardenability, and promotes the formation of fine-grained ferrite and bainite. With a content of 0.95%–1.05%, it helps achieve a uniform microstructure transformation within a larger cross-section, preventing the formation of coarse microstructure in the core.

[0029] Chromium (Cr): Cr enhances strength and hardenability through solid solution strengthening and carbide formation, while also improving corrosion resistance. Its content should be controlled between 0.20% and 0.25% to avoid temper brittleness caused by excessive Cr.

[0030] Vanadium (V) and niobium (Nb): As strong carbonitride forming elements, V and Nb precipitate fine VN and NbC particles during rolling in the austenitic region, pinning grain boundaries and inhibiting austenitic grain growth (Zener pinning effect), thus achieving grain refinement. During tempering, V further precipitates secondary carbides, resulting in precipitation strengthening (secondary hardening effect). A Nb content of 0.02%–0.04% and a V content of 0.15%–0.20% balances both grain refinement and precipitation strengthening.

[0031] Nitrogen (N): N combines with V to form VN, which precipitates during controlled rolling and tempering, enhancing the precipitation strengthening effect. Precise nitrogen control (0.010%–0.015%) ensures that the VN precipitates are small in size and uniformly distributed, improving strength without significantly impairing toughness.

[0032] Aluminum (Al): As a deoxidizer, Al forms AlN particles, which inhibit the coarsening of austenite grains during heating and further refine the microstructure.

[0033] Low sulfur and phosphorus control: S and P form MnS inclusions and grain boundary segregation, respectively, leading to decreased toughness and sensitivity to hydrogen-induced cracking. The high purity design with S≤0.003% and P≤0.015% significantly improves the low-temperature impact toughness and fatigue life of steel.

[0034] 2. Technological Principles of High-Purity Smelting

[0035] Gases and inclusions in steel are the main causes of fatigue crack initiation and toughness degradation. This invention employs an LF+RH dual refining process to achieve ultra-low gas and inclusion control.

[0036] LF refining: Argon blowing and stirring promote the collision, growth, and flotation of inclusions, and effective desulfurization and deoxidation are achieved under a reducing atmosphere of white slag. Als is controlled at 0.020% to 0.035% to ensure sufficient aluminum deoxidation and avoid Al2O3 cluster inclusions.

[0037] RH vacuum treatment: Under a high vacuum of ≤0.5tor, the molten steel is circulated and degassed, reducing the hydrogen content to ≤2ppm to avoid "white spot" defects; the oxygen content is ≤10ppm to reduce oxide inclusions. Soft blowing argon promotes the further flotation of tiny inclusions, improving the cleanliness of the molten steel.

[0038] Nitrogen control technology: Nitrogen is precisely added through bottom blowing nitrogen and nitriding of cored wire to ensure that N and V are fully combined to form VN, thus avoiding the adverse effects of free nitrogen on toughness.

[0039] 3. Organizational control mechanisms of controlled rolling and cooling and quenching and tempering treatment

[0040] (1) High-reduction rolling (controlled rolling)

[0041] Under conditions of initial rolling at ≥1100℃ and final rolling at ≥750℃, rolling with large deformation induces dynamic recrystallization of austenite, refining the original austenite grains. The fine austenite grains transform into even finer ferrite, bainite, or martensite structures after phase transformation, significantly improving toughness and strength (Hall-Petch relationship).

[0042] (2) Swirl-type water cooling (controlled cooling)

[0043] The round steel bar advances while rotating, induction heating to 880–950℃, followed by rapid cooling through multiple sets of high-pressure water rings. Rotation ensures uniform circumferential cooling, preventing structural stress and deformation caused by uneven cooling. Rapid cooling transforms austenite into fine lath martensite or lower bainite, resulting in a quenched microstructure with high strength and hardness. The reheat temperature is controlled between 40–60℃ to avoid excessive internal stress within the martensitic transformation range, reducing the risk of cracking.

[0044] (3) Medium-temperature tempering (quenching and tempering)

[0045] Holding at 560–600℃ for 4 hours decomposes the quenched martensite into tempered sorbite—a microstructure composed of fine, spherical carbides uniformly distributed within a ferrite matrix. Tempered sorbite exhibits excellent strength-toughness balance: the ferrite matrix provides toughness, while the carbides provide strength. Furthermore, V and Nb carbonitrides precipitate further during tempering (secondary precipitation strengthening), enhancing overall performance.

[0046] 4. Surface integrity assurance through precision machining and protection

[0047] Turning and rolling: Turning reduces the diameter of the skin by 2.2mm to remove the decarburized layer and defects on the surface, and rolling makes the surface roughness Ra≤3.2μm, reducing stress concentration sources and significantly improving fatigue life.

[0048] Rust-proof packaging: Spraying rust-preventive oil, wrapping with waterproof film, and covering with woven bags and bamboo strips to form a multi-layered protective system to prevent rust during storage and transportation and maintain the surface condition of the steel.

[0049] The beneficial effects of this invention are as follows: Through closed-loop control of composition, process, structure, and performance, the steel produced by this invention has high strength and good toughness, especially excellent low-temperature impact performance; the final product performance reaches: tensile strength ≥1000MPa, yield strength ≥850MPa, elongation ≥28%, reduction of area ≥60%, impact energy AKV2 at -40℃ ≥60J, fatigue life exceeding 1 million cycles, and can be directly used to process hydraulic piston rods and pin-type parts with diameters of 20-38mm. The production process is stable and suitable for mass production; it eliminates the customer's tempering and brightening processes, reducing overall costs; it is environmentally friendly and energy-saving, meeting the requirements of green manufacturing. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 Metallographic structure of steel in Example 1;

[0052] Figure 2 This is a microstructure diagram of the steel after quenching and tempering in Example 1;

[0053] Figure 3 Metallographic structure of steel in Example 2;

[0054] Figure 4 This is a microstructure diagram of the steel after quenching and tempering in Example 2;

[0055] Figure 5 Metallographic structure of steel in Example 3;

[0056] Figure 6 This is a microstructure diagram of the steel after quenching and tempering in Example 3. Detailed Implementation

[0057] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0058] This invention provides a method for producing tempered bright silver steel for hydraulic piston rods. The process route is as follows: converter + LF furnace + RH furnace + continuous casting + hot rolling + straightening + induction heating + swirl water cooling + rolling hearth continuous annealing furnace tempering + cut-off ends of standard-length round steel + rolling + polishing + rust-proof packaging.

[0059] The production process includes the following key steps:

[0060] (1) Smelting: The steel tapping from the converter is controlled with C≥0.08% and P≤0.012%; LF+RH dual refining is adopted. Argon is blown and white slag is maintained for ≥30min throughout the LF furnace. Als=0.020~0.035% throughout the process. After the temperature is ≥1600℃, vanadium-nitrogen alloy, nitrided cored wire, and bottom blowing nitrogen in the ladle are used to increase nitrogen; RH vacuum degassing treatment is carried out. The vacuum degree is below 0.5tor and the vacuum holding time is not less than 20min. The nitrogen content is detected online. The nitrogen amount is adjusted by bottom blowing nitrogen and nitrided cored wire and argon soft blowing is carried out for 20 minutes. The molten steel leaving the station has H≤2ppm and O≤10ppm.

[0061] (2) Continuous casting: Full protection casting, tundish superheat ≤25℃, furnace superheat ≤35℃, billet cross section is 280×280mm;

[0062] (3) Heating: The billet heating time is 300-480 min, the heating section is 1200-1260℃, and the soaking section is 1220-1270℃;

[0063] (4) Rolling: The 850 bar and wire rod two-roll alternating horizontal and vertical rolling mill adopts large reduction for rolling. The reduction of the first and second passes is controlled at 70mm and 65mm respectively; the initial rolling temperature is ≥1100℃; the final rolling adopts a three-roll rolling mill with a final rolling temperature ≥750℃.

[0064] (5) Finishing: The round steel is straightened using a two-roll straightener, with a curvature q≤2.0mm / m. It passes the ultrasonic flaw detection of Grade A according to GB / T 4162, and the magnetic flux leakage of 0.3*20mm is also qualified.

[0065] (6) Induction heating and rotary water cooling: A rotating bottom roller is used to propel the round steel forward at a speed of 0.01 m / s. Six sets of induction coils are used for heating, with an inlet water temperature of 880-950℃. The rotary water cooling system uses 20 evenly distributed high-pressure water nozzles as a cooling water ring, with four water rings spaced 0.2 meters apart to cool the round steel. The water pressure of a single water ring is 0.8-1.2 MPa. The outflow temperature of the round steel is 40-60℃.

[0066] (7) Tempering treatment: Roller hearth continuous annealing furnace: After quenching, the round steel is evenly distributed on the roller conveyor, one layer of material is laid, and it moves forward at a constant speed. It is heated by natural gas and held at 560-600℃ for 4 hours. It is then air-cooled after being taken out of the furnace.

[0067] (8) Cutting off the head and tail of the fixed-length round steel: Cut off the head and tail of the round bar and the ultrasonic flaw detection blind area. The length of the head and tail cut off is 100±5mm.

[0068] (9) Steel sheet and roller polishing: Tempered round steel q≤2.0mm / m, steel sheet diameter reduced by 2.2mm, diameter tolerance is (0, -0.04)mm, roller polishing ensures surface finish Ra≤3.2μm.

[0069] (10) Rust-proof packaging: The round steel surface is sprayed with oil-based rust-preventive oil and bundled with rubber-coated binding wire. Then, it is wrapped with waterproof plastic film to prevent oil leakage and sealed with transparent tape. It is then encased in a woven bag as the outermost layer. Finally, it is wrapped with bamboo strips for the outermost layer of protection. This ensures that the material will not rust within one year after production.

[0070] The chemical composition of the steel by weight percentage is as follows: C: 0.42%–0.45%, Si: 0.25%–0.35%, Mn: 0.95%–1.05%, P≤0.015%, S≤0.003%, Cr: 0.20%–0.25%, V: 0.15%–0.20%, Ni≤0.25%, Al: 0.015%–0.025%, Nb: 0.02%–0.04%, N: 0.010%–0.015%, Cu≤0.20%, Mo≤0.15%, H≤0.0002%, O≤0.0020%, with the remainder being Fe and essential impurities.

[0071] Example 1:

[0072] The chemical composition of the steel involved in this embodiment, by weight percentage, is as follows: C: 0.43%, Si: 0.30%, Mn: 1.00%, P: 0.012%, S: 0.002%, Cr: 0.22%, V: 0.18%, Al: 0.020%, Nb: 0.03%, N: 0.012%, O: 0.0015%, H: 0.0001%, with the balance being Fe.

[0073] The specific process parameters are as follows:

[0074] Smelting: LF white slag time 35min, RH vacuum 20min, soft blowing argon 20min;

[0075] Continuous casting: Tundish superheated to 22℃;

[0076] Rolling: Initial rolling temperature 1120℃, final rolling temperature 760℃;

[0077] Quenching: Induction heating to 920℃, water cooling to 50℃ for red-hot recovery;

[0078] Tempering: 580℃×4h air cooling.

[0079] The steel produced according to the above method was subjected to performance testing: Rm = 1015 MPa, Rp0.2 = 860 MPa, A = 29%, Z = 62%, AKV2 = 65 J at -40℃, and fatigue life > 1 million cycles.

[0080] The metallographic structure of rolled steel is as follows Figure 1 As shown, the microstructure of the steel after quenching and tempering is as follows: Figure 2 As shown.

[0081] Example 2:

[0082] The chemical composition of the steel involved in this embodiment, by weight percentage, is as follows: C: 0.42%, Si: 0.30%, Mn: 1.04%, P: 0.012%, S: 0.002%, Cr: 0.23%, V: 0.16%, Al: 0.020%, Nb: 0.03%, N: 0.012%, O: 0.0015%, H: 0.0001%, with the balance being Fe.

[0083] The specific process parameters are as follows:

[0084] Smelting: LF white slag time 32min, RH vacuum 25min, soft blowing argon 24min;

[0085] Continuous casting: Tundish superheated to 24℃;

[0086] Rolling: Initial rolling at 1150℃, final rolling at 770℃;

[0087] Quenching: Induction heating to 900℃, water cooling to 48℃ for reddening;

[0088] Tempering: 575℃×4h air cooling.

[0089] The steel produced according to the above method was subjected to performance testing: Rm = 1020MPa, Rp0.2 = 850MPa, A = 30%, Z = 60%, AKV2 = 68J at -40℃, and fatigue life > 1 million cycles.

[0090] The metallographic structure of rolled steel is as follows Figure 3 As shown, the microstructure of the steel after quenching and tempering is as follows: Figure 4 As shown.

[0091] Example 3:

[0092] The chemical composition of the steel involved in this embodiment, by weight percentage, is as follows: C: 0.45%, Si: 0.25%, Mn: 0.95%, P: 0.012%, S: 0.002%, Cr: 0.25%, V: 0.20%, Al: 0.020%, Nb: 0.03%, N: 0.013%, O: 0.0015%, H: 0.0001%, with the balance being Fe.

[0093] The specific process parameters are as follows:

[0094] Smelting: LF white slag time 32min, RH vacuum 20min, soft blowing argon 20min;

[0095] Continuous casting: Tundish superheated to 23℃;

[0096] Rolling: initial rolling at 1130℃, final rolling at 760℃;

[0097] Quenching: Induction heating to 890℃, water cooling to 40℃ for red-hot recovery;

[0098] Tempering: 600℃×4h air cooling.

[0099] The steel produced according to the above method was subjected to performance testing: Rm = 1010 MPa, Rp0.2 = 845 MPa, A = 29%, Z = 67%, AKV2 = 70 J at -40℃, and fatigue life > 1 million cycles.

[0100] The metallographic structure of rolled steel is as follows Figure 5 As shown, the microstructure of the steel after quenching and tempering is as follows: Figure 6 As shown.

[0101] As can be seen from the test results of Examples 1 to 3, the tempered bright silver steel for hydraulic cylinder piston rods produced by the method of the present invention has excellent test indicators, low gas content and low non-metallic inclusions, and can well meet the requirements of high strength, high toughness and fatigue life for hydraulic cylinder piston rods.

[0102] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0103] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for producing tempered bright silver steel for hydraulic piston rods, characterized in that, Key process steps include: S1: In the smelting process, the C content of the steel tapped from the converter is controlled to be ≥0.08%, and the P content is ≤0.012%. The LF+RH furnace refining process is adopted. Argon is blown throughout the LF furnace refining process for slag formation and deoxidation. The white slag holding time is ≥30 min. The process control Als is 0.020~0.035%. After the temperature is ≥1600℃, vanadium-nitrogen alloy, nitrided cored wire, and nitrogen addition through bottom blowing in the ladle are used. RH vacuum degassing treatment is carried out at a vacuum degree below 0.5tor, with a vacuum holding time of not less than 20 min. The nitrogen content is detected online. The nitrogen amount is adjusted by bottom blowing nitrogen and nitrided cored wire, and argon is softly blown for 20 minutes. The H content of the molten steel leaving the station is ≤2ppm and the O content is ≤10ppm. S2: In the continuous casting process, full-process protective casting is adopted. The superheat of the tundish in the continuous casting furnace is ≤25℃, and the furnace temperature is ≤35℃. The billet size is 280×280mm. S3: In the heating process, the billet heating time is 300-480 min, the heating section temperature is 1200-1260℃, and the soaking section temperature is 1220-1270℃. S4: In the rolling process, the bar and wire rod are rolled by a two-roll alternating horizontal and vertical rolling mill with a large reduction rolling temperature of ≥1100℃, and the final rolling is carried out by a three-roll rolling mill with a final rolling temperature of ≥750℃. S5: In the finishing process, round steel is straightened using a two-roll straightener, with a curvature q≤2.0mm / m; S6: In the induction heating and rotary water cooling process, a rotating bottom roller is used, and the round steel rotates forward at a speed of 0.01m / s. Six sets of induction coils are used for heating, with an inlet water temperature of 880-950℃ and a round steel outlet red-hot temperature of 40-60℃. S7: In the tempering process of the roller hearth continuous annealing furnace, the quenched round steel is evenly distributed on the roller conveyor, one layer of material is laid, and it moves forward at a constant speed. It is heated by natural gas, held at 560-600℃ for 4 hours, and then air-cooled after being taken out of the furnace. S8: Cut off the beginning and end of the round bar and the blind area of ​​ultrasonic flaw detection; S9: In the rolling and polishing processes, the tempered round steel q≤2.0mm / m, the rolling diameter is reduced by 2.2mm, the diameter tolerance is (0, -0.04)mm, and the polishing ensures a surface finish Ra≤3.2μm; S10: In the rust prevention packaging process, the surface of the round steel is sprayed with oil-based rust-preventive oil, bundled with rubber-coated binding wire, then wrapped with waterproof plastic film, sealed with transparent tape and the outermost layer of woven bag, and finally protected with bamboo strips.

2. The method for producing a quenched and tempered bright silver steel for a hydraulic piston rod as described in claim 1, characterized in that, In the S4 rolling process, the reduction in the first pass is controlled to be 70 mm, and the reduction in the second pass is controlled to be 65 mm.

3. The method for producing a quenched and tempered bright silver steel for a hydraulic piston rod as described in claim 2, characterized in that, In the S6 induction heating and vortex water cooling process, the vortex water cooling uses 20 evenly distributed high-pressure water nozzles as a cooling water ring, with 4 water rings arranged at 0.2-meter intervals to cool the round steel. The water pressure of a single water ring is 0.8-1.2 MPa.

4. The method for producing tempered bright silver steel for hydraulic piston rods as described in claim 3, characterized in that, In S8, the length of each end of the round steel bar cut off is 100±5mm.

5. A method for producing tempered bright silver steel for hydraulic piston rods as described in any one of claims 1-4, characterized in that, The chemical composition of the steel by weight percentage is as follows: C: 0.42%–0.45%, Si: 0.25%–0.35%, Mn: 0.95%–1.05%, P≤0.015%, S≤0.003%, Cr: 0.20%–0.25%, V: 0.15%–0.20%, Ni≤0.25%, Al: 0.015%–0.025%, Nb: 0.02%–0.04%, N: 0.010%–0.015%, Cu≤0.20%, Mo≤0.15%, H≤0.0002%, O≤0.0020%, with the remainder being Fe and essential impurities.

6. The method for producing a quenched and tempered bright silver steel for a hydraulic piston rod as described in claim 5, characterized in that, The final steel produced has the following properties: tensile strength ≥1000Mpa, yield strength ≥850Mpa, elongation ≥28%, reduction of area ≥60%, and AKV2 ≥60J at -40℃. It can be directly cut into rod and shaft parts with diameters of 20-38mm, and can withstand 1 million fatigue bench tests without damage.

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