Corrosion-resistant spring steel and method of production and use thereof

Abstract

The application provides a kind of corrosion-resistant spring steel and its preparation method and application, it relates to alloy steel technical field, the corrosion-resistant spring steel, according to mass percentage, its chemical composition includes: C:0.58-0.68%, Si:1.65-2.1%, Mn:0.85-1.1%, Cr:1.0-1.6%, Ni:0.45-0.95%, Cu:0.35-0.65%, Nb:0.022-0.048%, Ti:0.012-0.028%, RE:0.008-0.015%, Mo:0.12-0.25%, V:0.06-0.14%, B:0.001-0.004%, P≤0.012%, S≤0.010%, the balance is Fe and inevitable impurities.The application adjusts the chemical composition of spring steel, solves the defects such as insufficient strength of spring steel, poor corrosion resistance, greater temper brittleness, inclusion pitting and the like in the prior art from the composition of spring steel, so that the tensile yield strength and the corrosion resistance to chloride ions of spring steel are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of alloy steel technology, specifically to a corrosion-resistant spring steel, its preparation method, and its application. Background Technology

[0002] The single / few-leaf variable cross-section leaf springs of the suspension of heavy-duty trucks and new energy heavy-duty trucks need to be used for a long time on the snow melting and salt spreading roads in northern winters and the high humidity and chloride ion-containing atmospheric corrosion environment in coastal areas. At the same time, they also need to meet the design requirements of lightweight and high-stress leaf springs for the whole vehicle.

[0003] However, traditional 60Si2Mn and 50CrVA spring steels have low upper limits of strength, with yield strength generally below 1400MPa, making them unsuitable for lightweight, high-stress single-leaf springs; they also have poor resistance to chloride ion corrosion, making them prone to pitting corrosion and stress corrosion cracking, resulting in short fatigue life of the leaf springs and high after-sales failure rates in vehicles.

[0004] Existing technologies have improved traditional spring steel materials, but existing corrosion-resistant spring steels have a single alloy composition, relying solely on Cu and Ni binary corrosion protection or V / Nb reinforcement, which cannot simultaneously achieve long-term corrosion protection and ultra-high strength. Moreover, they have defects such as coarse grains, insufficient hardenability in thick specifications, hydrogen-induced delayed fracture, and tempering softening. Some existing corrosion-resistant spring steels improve corrosion performance by increasing phosphorus (P) content, but P significantly exacerbates tempering brittleness and reduces low-temperature impact toughness, posing a safety hazard of leaf spring breakage under heavy-load and bumpy conditions. Conventional spring steels have lax control over S, P, and hydrogen and oxygen gas impurities, and non-metallic inclusions and micropores can easily become sources of corrosion initiation, significantly shortening the service life of leaf springs.

[0005] In addition, the existing heat treatment only uses a two-step process of quenching and tempering, which cannot eliminate the residual stress from rolling. The stress concentration points are easily corroded by chloride ions, forming corrosion pits and accelerating spring failure. Summary of the Invention

[0006] In view of the deficiencies in the existing technology, the technical problem solved by the present invention is to provide a corrosion-resistant spring steel, its preparation method and application, which can simultaneously achieve high tensile yield strength and excellent resistance to chloride ion corrosion of spring steel.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a corrosion-resistant spring steel, the chemical composition of which, by weight percentage, comprises: C: 0.58-0.68%, Si: 1.65-2.1%, Mn: 0.85-1.1%, Cr: 1.0-1.6%, Ni: 0.45-0.95%, Cu: 0.35-0.65%, Nb: 0.022-0.048%, Ti: 0.012-0.028%, RE: 0.008-0.015%, Mo: 0.12-0.25%, V: 0.06-0.14%, B: 0.001-0.004%, P≤0.012%, S≤0.010%, balance being Fe and unavoidable impurities.

[0008] Preferably, the chemical composition of the corrosion-resistant spring steel, by mass percentage, includes: C: 0.68%, Si: 2.1%, Mn: 1.1%, Cr: 1.6%, Ni: 0.95%, Cu: 0.65%, Nb: 0.048%, Ti: 0.028%, RE: 0.015%, Mo: 0.25%, V: 0.14%, B: 0.004%, P: 0.011%, S: 0.009%, with the balance being Fe and unavoidable impurities.

[0009] Secondly, the present invention also provides a method for preparing corrosion-resistant spring steel as described in the first aspect, comprising, in sequence: smelting, continuous casting, segmented rolling, three-step composite heat treatment, and shot peening.

[0010] Preferably, the specific steps of the smelting process include, in sequence: desulfurization of molten iron, converter smelting, LF refining, and RH vacuum treatment.

[0011] Preferably, the molten iron desulfurization adopts a magnesium powder injection desulfurization process to control the sulfur content of the molten iron leaving the station to be ≤0.003%; The steps of the converter smelting include: adopting a converter top-bottom composite blowing process, with a final slag basicity of 2.7-3.1, ≤1 time of supplementary blowing, a tapping temperature of 1650-1690℃, and adding ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron in stages during tapping. The LF refining process has a total duration of ≥32 min, with bottom-blown argon stirring throughout, slag basicity of 2.5-2.9, and total oxygen ≤7 ppm. The RH vacuum treatment has the following characteristics: vacuum degree ≤ 75 Pa, and vacuum duration ≥ 22 min.

[0012] Preferably, the continuous casting process includes: using an immersion nozzle for casting, using alkaline protective slag in the tundish, a superheat of molten steel in the tundish of 21-27℃, a casting speed of 0.75-0.95m / min, using weak cooling for secondary cooling, and isothermal homogenization of the billet after obtaining it: entering the furnace at 1090-1130℃ and holding for 120-140min.

[0013] Preferably, the segmented rolling step includes: sequentially performing initial rolling, rough rolling, finish rolling and final rolling on the billet obtained from continuous casting; wherein the initial rolling temperature is 920-960℃, the rough rolling temperature is 870-900℃, and the final rolling temperature is 820-870℃.

[0014] Preferably, the three-step composite heat treatment includes: for the workpiece after segmented rolling, first holding it at 640-670℃ for 75-95 minutes; after the first cooling, holding it at 915-945℃ for 55-65 minutes; after the second cooling, holding it at 410-450℃ for 115-135 minutes, and then performing a third cooling.

[0015] Preferably, the shot peening step includes: sequentially subjecting the heat-treated workpiece to high-pressure gas shot peening and ultrasonic shot peening.

[0016] Thirdly, the present invention also provides an application of the corrosion-resistant spring steel as described in the first aspect in lightweight single-leaf or multi-leaf variable cross-section leaf springs for heavy-duty commercial vehicles.

[0017] Compared with the prior art, the advantages of the present invention are as follows: (1) This invention adjusts the chemical composition of spring steel by using a medium-to-high content of C combined with a high content of Cr, and constructs a multi-layer corrosion-resistant passivation system with Ni, Cu and Mo. At the same time, V, Nb, Ti, rare earth RE and trace amounts of B are added to achieve internal grain refinement, precipitation strengthening and high hardening penetration of thick plates in spring steel. By strictly controlling P≤0.012%, the high phosphorus content is avoided to prevent the spring steel from becoming brittle. S≤0.010% is controlled to reduce corrosion inclusions. This invention solves the defects of insufficient strength, poor corrosion resistance, large temper brittleness and pitting corrosion of spring steel in the prior art from the composition of spring steel, and greatly improves the tensile yield strength and chloride ion corrosion resistance of spring steel.

[0018] (2) The present invention also improves the spring preparation process by adopting a three-step composite heat treatment process to eliminate rolling residual stress and suppress stress corrosion, thereby further improving the tensile yield strength and chloride ion corrosion resistance of spring steel. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0020] Figure 1 Corrosion morphology images of spring steel in embodiments and comparative examples of the present invention; Wherein, (a) is a corrosion morphology diagram of the spring steel of Comparative Example 1 of the present invention; (b) is a corrosion morphology diagram of the corrosion-resistant spring steel of Example 2 of the present invention. Figure 2 The compositional line scan results of the corrosion product regions in the embodiments and comparative examples of the present invention; Wherein, (a) is the composition line scan result of the corrosion product region of the spring steel in Comparative Example 1 of the present invention; (b) is the composition line scan result of the corrosion product region of the corrosion-resistant spring steel in Example 2 of the present invention; Figure 3 The EIS performance test diagrams are of the corrosion-resistant spring steel of Example 2 and the spring steel of Comparative Example 1. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a corrosion-resistant spring steel, its preparation method, and its application. By adjusting the chemical composition of the spring steel, a multi-layer corrosion-resistant passivation system is constructed using a medium-to-high content of C combined with a high content of Cr, along with Ni, Cu, and Mo. Simultaneously, V, Nb, Ti, rare earth elements RE, and trace amounts of B are added to achieve internal grain refinement, precipitation strengthening, and high hardenability in thick plates. By strictly controlling P ≤ 0.012%, the high phosphorus content is avoided to prevent the spring steel from becoming brittle, and S ≤ 0.010% is controlled to reduce corrosion inclusions. This solves the technical problems of poor corrosion resistance and low strength of spring steel in the prior art.

[0023] To achieve the above-mentioned technical effects, the overall concept of this invention is as follows: In a first aspect, embodiments of the present invention provide a corrosion-resistant spring steel, the chemical composition of which, by mass percentage, comprises: C: 0.58-0.68%, Si: 1.65-2.1%, Mn: 0.85-1.1%, Cr: 1.0-1.6%, Ni: 0.45-0.95%, Cu: 0.35-0.65%, Nb: 0.022-0.048%, Ti: 0.012-0.028%, RE: 0.008-0.015%, Mo: 0.12-0.25%, V: 0.06-0.14%, B: 0.001-0.004%, P≤0.012%, S≤0.010%, balance being Fe and unavoidable impurities.

[0024] This invention, through extensive experimental research, has discovered that controlling the carbon (C) content at 0.58-0.68% can improve the strength of spring steel; increasing the chromium (Cr) content to 1.0-1.6% and combining it with molybdenum (Mo) at 0.12-0.25% can significantly improve the corrosion potential of spring steel; simultaneously, adjusting the copper (Cu) content to 0.35%-0.65% and the nickel (Ni) content to 0.45%-0.95% allows the Cu and Ni elements to synergistically form a denser passivation rust layer on the surface of the spring steel; adjusting the titanium (Ti) content to 0.012%-0.028% and the rare earth element (RE) content to 0.008%-0.015% can purify the steel and eliminate the source of inclusion corrosion. This invention, through a triple mechanism of improving the corrosion potential of spring steel, promoting the formation of a denser passivation rust layer on the surface of spring steel, and eliminating inclusion corrosion at its source, synergistically inhibits chloride ion pitting corrosion.

[0025] The present invention also found that adjusting the content of V to 0.06-0.14% and the content of Nb to 0.022%-0.048% can promote the precipitation strengthening of nano carbides in spring steel; adjusting the content of Ti to 0.012%-0.028% can promote grain refinement. Therefore, V, Nb and Ti form a ternary grain strengthening system, and the synergistic effect of the three elements can improve the strength, fatigue life and tempering stability of spring steel.

[0026] The present invention also found that trace amounts of element B (content of 0.001-0.004%) can improve the purification of grain boundaries, enhance the hardenability of thick plates, inhibit the penetration of hydrogen atoms along the grain, and strengthen the resistance to hydrogen embrittlement. Moreover, controlling the content at 0.001-0.004% can avoid boron embrittlement.

[0027] This invention also discovers that by strictly controlling the phosphorus content to ≤0.012%, the high-phosphorus anti-corrosion technology in existing technologies can be abandoned, thus eliminating temper brittleness and low-temperature brittleness defects. Controlling sulfur content to ≤0.010% reduces corrosion inclusions.

[0028] Therefore, this invention addresses the shortcomings of existing spring steel by adjusting its chemical composition. It employs a medium-to-high C content combined with a high Cr content, along with Ni, Cu, and Mo to construct a multi-layered corrosion-resistant passivation system. Simultaneously, it incorporates V, Nb, Ti, rare earth elements (RE), and trace amounts of B to achieve grain refinement, precipitation strengthening, and high hardenability in thick plates. By strictly controlling P ≤ 0.012% to avoid excessive brittleness due to high phosphorus content, and controlling S ≤ 0.010% to reduce corrosion inclusions, this invention solves the problems of insufficient strength, poor corrosion resistance, significant temper brittleness, and pitting corrosion in existing spring steel by improving its composition. This significantly enhances the tensile yield strength and chloride ion corrosion resistance of spring steel.

[0029] Preferably, its chemical composition, by mass percentage, includes: C: 0.68%, Si: 2.1%, Mn: 1.1%, Cr: 1.6%, Ni: 0.95%, Cu: 0.65%, Nb: 0.048%, Ti: 0.028%, RE: 0.015%, Mo: 0.25%, V: 0.14%, B: 0.004%, P: 0.011%, S: 0.009%, with the balance being Fe and unavoidable impurities.

[0030] The applicant's extensive experimental research has shown that the spring steel composed of the above-mentioned components exhibits excellent tensile strength, yield strength, and resistance to salt spray corrosion.

[0031] Secondly, embodiments of the present invention also provide a method for preparing corrosion-resistant spring steel as described above, comprising, in sequence: smelting, continuous casting, segmented rolling, three-step composite heat treatment, and shot peening.

[0032] This invention employs a three-step composite heat treatment process, which, compared to the two-step heat treatment in existing technologies, eliminates rolling stress in advance and inhibits stress corrosion at its source. Furthermore, the manufacturing process of this invention can be directly implemented on existing converter-continuous casting-hot-rolled leaf spring production lines without the need for additional large-scale metallurgical equipment; the addition of trace amounts of rare earth elements results in a wide process window, minimal fluctuations in batch performance, and stable and controllable yield.

[0033] Preferably, the specific steps of the smelting process include, in sequence: hot metal desulfurization, converter smelting, LF refining, and RH vacuum treatment. This invention, through hot metal desulfurization, LF refining, and RH vacuum treatment, can significantly reduce harmful gases such as H2 and O2.

[0034] Preferably, the hot metal desulfurization adopts a magnesium powder spraying desulfurization process to control the sulfur content of the hot metal leaving the station to ≤0.003%, thoroughly remove the desulfurization slag, and avoid sulfur reversion during smelting.

[0035] Preferably, the converter smelting steps include: adopting a converter top-bottom composite blowing process, with a scrap steel ratio of 10%-14%, a final slag basicity of 2.7-3.1, ≤1 reblowing time, a tapping temperature of 1650-1690℃, and adding ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron in stages during tapping to achieve uniform alloying.

[0036] This invention enhances molten pool stirring through top-bottom combined blowing in a converter, improving dephosphorization and reducing the final carbon-oxygen product; it stabilizes the smelting heat regime by using a stable scrap steel ratio of 10%-14%; the final slag basicity of 2.7-3.1 achieves efficient dephosphorization and ensures slag fluidity; the number of supplementary blowing cycles is ≤1 to prevent steel over-oxidation and improve metal yield and steel cleanliness; the tapping temperature is 1650-1690℃ to compensate for the temperature drop during transport, adapt to subsequent refining processes, and avoid overheating of the molten steel.

[0037] Preferably, the LF refining process has a total duration of ≥32 min, with bottom-blown argon stirring throughout, a slag basicity of 2.5-2.9, and total oxygen ≤7 ppm, which promotes the transformation of long strip-shaped MnS in steel into fine, spherical / ellipsoidal rare earth sulfides / rare earth oxysulfides (RE2O2S, RES, etc.).

[0038] Preferably, the RH vacuum treatment has a vacuum degree ≤75Pa and a holding time for degassing ≥22min. The RH vacuum treatment described above can deeply remove hydrogen and nitrogen, reducing the hydrogen content of the molten steel to approximately 0.4–1.0 ppm, thereby lowering the risk of hydrogen embrittlement.

[0039] Preferably, the continuous casting process includes: using an immersion nozzle for casting, using alkaline protective slag in the tundish, a superheat of molten steel in the tundish of 21-27℃, a casting speed of 0.75-0.95m / min, and using weak cooling for secondary cooling to reduce element segregation. Then, the billet is subjected to isothermal homogenization: entering the furnace at 1090-1130℃ and holding for 120-140min to eliminate macroscopic segregation of C, Cr, Ni, and Mo elements.

[0040] Preferably, the segmented rolling process includes: sequentially performing initial rolling, rough rolling, finish rolling, and final rolling on the billet obtained from continuous casting; the initial rolling temperature is 920-960℃, the rough rolling temperature is 870-900℃, the finish rolling enters the two-phase region, the finish rolling temperature is 820-900℃, and the final rolling temperature is 820-870℃. This invention first rolls under high temperature and high pressure to fully refine the austenite grains and homogenize the microstructure, providing a preliminary microstructure guarantee for the deformation and quality improvement in the two-phase region of the finish rolling; in the finish rolling stage, it enters the austenite + ferrite two-phase region, and deformation is carried out under the condition of two-phase coexistence. The pinning effect at the two-phase interface inhibits austenite grain growth, while providing a large number of nucleation sites for ferrite, continuously refining the austenite grains. This invention employs segmented temperature-controlled rolling, refining austenite grains through multiple passes of high pressure.

[0041] Preferably, the finishing rolling includes a front finishing rolling section and a middle and rear finishing rolling section. The temperature of the front finishing rolling section is 870-900℃, at which temperature the microstructure is γ single-phase austenite. The temperature of the middle and rear finishing rolling section is 820-870℃, and the rolling enters the austenite + ferrite two-phase interval.

[0042] This invention can eliminate elemental segregation and refine the original grains by isothermal homogenization of the cast billet and segmented rolling, thus solving defects such as hydrogen-induced delayed fracture, coarse grains, and cast billet segregation.

[0043] Preferably, the three-step composite heat treatment includes: Step 1: Holding the segmented rolled workpiece at 640-670℃ for 75-95 minutes; Step 2: Holding at 915-945℃ for 55-65 minutes after the first cooling; Step 3: Holding at 410-450℃ for 115-135 minutes after the second cooling; and then performing a third cooling. The first cooling is air cooling, the second cooling is oil cooling, and the third cooling is water cooling.

[0044] The purpose of the first heat treatment step in this invention is to release residual rolling stress and reduce stress corrosion sources; the purpose of the second heat treatment step is to achieve complete austenitization and uniform alloy solution; and the purpose of the third heat treatment step is to obtain a high-toughness tempered troostite structure. This invention employs a three-step composite heat treatment to release residual rolling stress in advance, avoid stress concentration corrosion sources, and overcome the shortcomings of traditional two-step heat treatment, which is prone to stress corrosion cracking.

[0045] Preferably, the shot peening step includes: sequentially subjecting the heat-treated workpiece to high-pressure gas shot peening and ultrasonic shot peening. Specifically, the shot peening step of the present invention includes: using stainless steel shot with a diameter of 0.2-0.4 mm, high-pressure shot peening for 10-15 min at a pressure of 0.5-0.7 MPa to ensure a surface coverage of not less than 95%; then using ultrasonic equipment with a frequency of 20-30 kHz and an amplitude of 30-50 μm for shot peening for 3-5 min to form a residual compressive stress layer of 50-80 μm thick on the workpiece surface. The present invention first achieves full coverage through high-pressure shot peening, eliminating surface micro-defects and establishing a basic compressive stress field; the subsequent ultrasonic shot peening promotes surface grain refinement, increases the peak value of residual compressive stress, optimizes the stress gradient, inhibits fatigue crack initiation and propagation, and improves fatigue resistance and hydrogen-induced fracture resistance.

[0046] In a specific embodiment, the method for preparing the corrosion-resistant spring steel of the present invention includes the following steps: S1. Hot metal desulfurization: KR magnesium spraying deep desulfurization, the sulfur content of the hot metal leaving the station is ≤0.003%, the desulfurization slag is completely removed, and sulfur reversion during smelting is avoided; S2. Converter smelting: scrap steel ratio 10%-14%, final slag basicity 2.7-3.1, replenishment blowing ≤ 1 time, tapping temperature 1650-1690℃; ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, ferroboron are added in stages during tapping to achieve uniform alloying. S3 and LF refining: total time ≥32min, bottom blowing and weak argon stirring throughout, slag basicity 2.5-2.9, total oxygen ≤7ppm, rare earth modified sulfide inclusions; S4, RH vacuum treatment: vacuum degree ≤75Pa, pressure holding and degassing time ≥22min, deep removal of hydrogen and nitrogen, reducing the risk of hydrogen embrittlement; S5, Continuous casting: Alkaline tundish protective slag, submerged entry nozzle casting, molten steel superheat 21-27℃, casting speed 0.75-0.95m / min, weak cooling with secondary cooling water to reduce element segregation; S6. Isothermal homogenization of billet: The furnace temperature is 1090-1130℃, and the holding time is 120-140min to eliminate macroscopic segregation of C, Cr, Ni and Mo; S7. Segmented rolling: The initial rolling temperature is 920-960℃, and the roughing exit temperature is 870-900℃; the finishing rolling enters the two-phase region, and the finishing rolling temperature is 820-900℃, and the final rolling temperature is 820-870℃. Multiple passes of large reduction refine the austenite grains. S8. Insulation and slow cooling: After rolling, the flat steel is covered with an insulation cover and slowly cooled to below 200℃ before air cooling to eliminate micro-cracks on the rolling surface. S9. Three-step composite heat treatment: Step 1, pre-stress relief tempering: hold at 640-670℃ for 75-95min, air cool to release residual rolling stress and reduce stress corrosion sources; Step 2, quenching: hold at 915-945℃ for 55-65min, oil cool to achieve complete austenitization and uniform alloy solution treatment; Step 3, medium-temperature tempering: hold at 410-450℃ for 115-135min, rapid water cooling after removal from the furnace to obtain a high-toughness tempered troostite structure. S10. Shot peening: The heat-treated workpiece is subjected to high-pressure gas shot peening and ultrasonic shot peening in sequence. Stainless steel shot with a diameter of 0.2-0.4mm is used. High-pressure shot peening is performed for 10-15 minutes under a pressure of 0.5-0.7MPa to ensure that the surface coverage is not less than 95%. Then, ultrasonic shot peening is performed for 3-5 minutes with a frequency of 20-30kHz and an amplitude of 30-50μm to form a residual compressive stress layer with a thickness of 50-80μm on the surface of the workpiece.

[0047] Thirdly, embodiments of the present invention also provide an application of the corrosion-resistant spring steel as described above in lightweight single-leaf or multi-leaf variable cross-section leaf springs for heavy-duty commercial vehicles.

[0048] Tests show that the corrosion-resistant spring steel of this invention can achieve a tensile strength ≥1850MPa, a yield strength ≥1620MPa, and a neutral salt spray corrosion rate ≤0.92g / (m²) after 720h. h) The bench fatigue cycle count is greater than 220,000 cycles, and the austenite grain size reaches level 8 or above. This achieves the technical effect of simultaneously meeting the dual stringent conditions of high yield strength ≥1620MPa and long-term chloride ion corrosion service. Therefore, the corrosion-resistant spring steel of this invention can be used in lightweight single / few-leaf variable cross-section leaf springs for heavy-duty commercial vehicles.

[0049] The following specific embodiments illustrate a corrosion-resistant spring steel and its preparation method according to the present invention. The raw materials used in the embodiments of the present invention are all commercially available products, which can be purchased through conventional commercial channels unless otherwise specified.

[0050] Example 1 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.58%, Si: 1.65%, Mn: 0.85%, Cr: 1.00%, Ni: 0.45%, Cu: 0.35%, Nb: 0.022%, Ti: 0.012%, RE: 0.008%, Mo: 0.12%, V: 0.06%, B: 0.001%; ​​P: 0.010%, S: 0.008%, balance Fe and unavoidable impurities.

[0051] The above-mentioned corrosion-resistant spring steel is prepared by the following method: S1. Hot metal desulfurization: KR magnesium spraying deep desulfurization, the sulfur content of the hot metal leaving the station is ≤0.003%, the desulfurization slag is completely removed, and sulfur reversion during smelting is avoided; S2. Converter smelting: scrap steel ratio 10%, final slag basicity 2.7, one additional blowing cycle, tapping temperature 1650-1670℃; ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron are added in stages during tapping to achieve uniform alloying. S3 and LF refining: The total time is 34 minutes, with weak argon stirring throughout the process, slag basicity of 2.5, and total oxygen ≤7ppm; S4, RH vacuum treatment: vacuum degree is 70Pa, pressure holding and degassing for 23min; S5, Continuous casting: alkaline tundish protective slag, submerged entry nozzle, molten steel superheat 24℃, casting speed 0.85m / min, weak cooling with secondary cooling water; S6. Isothermal heating of the billet: The furnace temperature is 1110℃, and the holding time is 130min. S7. Segmented rolling: The initial rolling temperature is 940℃, the roughing rolling exit temperature is 880℃; the finishing rolling enters the two-phase region, the temperature of the front section of the finishing rolling is 880℃, the temperature of the middle and rear sections of the finishing rolling is 860℃, and the final rolling temperature is 840℃. S8. Insulation and slow cooling: After rolling, the flat steel is covered with an insulation cover and slowly cooled to below 200℃ before being air-cooled; S9. Three-step composite heat treatment: Step 1, pre-stress relief tempering: hold at 650℃ for 85 minutes, air cool; Step 2, quenching: hold at 930℃ for 60 minutes, oil cool; Step 3, medium-temperature tempering: hold at 430℃ for 120 minutes, rapid water cooling after removal from the furnace. S10. Shot peening: The heat-treated workpiece is subjected to high-pressure gas shot peening and ultrasonic shot peening in sequence. 0.3 mm diameter stainless steel shot is used for high-pressure shot peening for 15 min at a pressure of 0.6 MPa to ensure a surface coverage of not less than 95%. Then, ultrasonic shot peening is performed for 4 min with a frequency of 25 kHz and an amplitude of 40 μm to form a 60 μm thick residual compressive stress layer on the workpiece surface.

[0052] Example 2 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.63%, Si: 1.85%, Mn: 0.98%, Cr: 1.30%, Ni: 0.70%, Cu: 0.50%, Nb: 0.035%, Ti: 0.020%, RE: 0.011%, Mo: 0.18%, V: 0.10%, B: 0.0025%; P: 0.009%, S: 0.007%, balance Fe and unavoidable impurities.

[0053] The above-mentioned corrosion-resistant spring steel is prepared by the following method: S1. Hot metal desulfurization: KR magnesium spraying deep desulfurization, the sulfur content of the hot metal leaving the station is ≤0.003%, the desulfurization slag is completely removed, and sulfur reversion during smelting is avoided; S2. Converter smelting: scrap steel ratio 10%, final slag basicity 2.7, one additional blowing cycle, tapping temperature 1650-1670℃; ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron are added in stages during tapping to achieve uniform alloying. S3 and LF refining: The total time is 34 minutes, with weak argon stirring throughout the process, slag basicity of 2.5, and total oxygen ≤7ppm; S4, RH vacuum treatment: vacuum degree is 70Pa, pressure holding and degassing for 23min; S5, Continuous casting: alkaline tundish protective slag, submerged entry nozzle, molten steel superheat 24℃, casting speed 0.85m / min, weak cooling with secondary cooling water; S6. Isothermal heating of the billet: The furnace temperature is 1110℃, and the holding time is 130min. S7. Segmented rolling: The initial rolling temperature is 940℃, the roughing rolling exit temperature is 880℃; the finishing rolling enters the two-phase region, the temperature of the front section of the finishing rolling is 880℃, the temperature of the middle and rear sections of the finishing rolling is 860℃, and the final rolling temperature is 840℃. S8. Insulation and slow cooling: After rolling, the flat steel is covered with an insulation cover and slowly cooled to below 200℃ before being air-cooled; S9. Three-step composite heat treatment: Step 1, pre-stress relief tempering: hold at 650℃ for 85 minutes, air cool; Step 2, quenching: hold at 930℃ for 60 minutes, oil cool; Step 3, medium-temperature tempering: hold at 430℃ for 120 minutes, rapid water cooling after removal from the furnace. S10. Shot peening: The heat-treated workpiece is subjected to high-pressure gas shot peening and ultrasonic shot peening in sequence. 0.3 mm diameter stainless steel shot is used for high-pressure shot peening for 15 min at a pressure of 0.6 MPa to ensure a surface coverage of not less than 95%. Then, ultrasonic shot peening is performed for 4 min with a frequency of 25 kHz and an amplitude of 40 μm to form a 60 μm thick residual compressive stress layer on the workpiece surface.

[0054] Example 3 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.68%, Si: 2.1%, Mn: 1.1%, Cr: 1.6%, Ni: 0.95%, Cu: 0.65%, Nb: 0.048%, Ti: 0.028%, RE: 0.015%, Mo: 0.25%, V: 0.14%, B: 0.004%, P: 0.011%, S: 0.009%, balance Fe and unavoidable impurities.

[0055] The above-mentioned corrosion-resistant spring steel is prepared by the following method: S1. Hot metal desulfurization: KR magnesium spraying deep desulfurization, the sulfur content of the hot metal leaving the station is ≤0.003%, the desulfurization slag is completely removed, and sulfur reversion during smelting is avoided; S2. Converter smelting: scrap steel ratio 14%, final slag basicity 3.1, one additional blowing cycle, tapping temperature 1650-1690℃; ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron are added in stages during tapping to achieve uniform alloying. S3 and LF refining: The total time is 34 minutes, with weak argon stirring throughout the process, slag basicity of 2.9, and total oxygen ≤7ppm; S4, RH vacuum treatment: vacuum degree is 70Pa, pressure holding and degassing for 23min; S5, Continuous casting: alkaline tundish protective slag, submerged entry nozzle, molten steel superheat 24℃, casting speed 0.85m / min, weak cooling with secondary cooling water; S6. Isothermal heating of the billet: The furnace temperature is 1110℃, and the holding time is 130min. S7. Segmented rolling: The initial rolling temperature is 940℃, the roughing rolling exit temperature is 870-900℃; the finishing rolling enters the two-phase region, the temperature of the front section of the finishing rolling is 880℃, the temperature of the middle and rear sections of the finishing rolling is 860℃, and the final rolling temperature is 840℃. S8. Insulation and slow cooling: After rolling, the flat steel is covered with an insulation cover and slowly cooled to below 200℃ before air cooling to eliminate micro-cracks on the rolling surface. S9. Three-step composite heat treatment: Step 1, pre-stress relief tempering: hold at 650℃ for 85 minutes, air cool; Step 2, quenching: hold at 930℃ for 60 minutes, oil cool; Step 3, medium-temperature tempering: hold at 430℃ for 120 minutes, rapid water cooling after removal from the furnace. S10. Shot peening: The heat-treated workpiece is subjected to high-pressure gas shot peening and ultrasonic shot peening in sequence. 0.4 mm diameter stainless steel shot is used for high-pressure shot peening for 15 min at a pressure of 0.5 MPa to ensure a surface coverage of not less than 95%. Then, ultrasonic shot peening is performed for 5 min at a frequency of 30 kHz and an amplitude of 50 μm to form a 50 μm thick residual compressive stress layer on the workpiece surface.

[0056] Example 4 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.63%, Si: 1.85%, Mn: 0.98%, Cr: 1.30%, Ni: 0.70%, Cu: 0.50%, Nb: 0.035%, Ti: 0.020%, RE: 0.011%, Mo: 0.18%, V: 0.10%, B: 0.0025%; P: 0.009%, S: 0.007%, balance Fe and unavoidable impurities.

[0057] The above-mentioned corrosion-resistant spring steel is prepared by the following method: S1. Hot metal desulfurization: KR magnesium spraying deep desulfurization, the sulfur content of the hot metal leaving the station is ≤0.003%, the desulfurization slag is completely removed, and sulfur reversion during smelting is avoided; S2. Converter smelting: scrap steel ratio 10%, final slag basicity 2.7, one additional blowing cycle, tapping temperature 1650-1670℃; ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron are added in stages during tapping to achieve uniform alloying. S3 and LF refining: The total time is 34 minutes, with weak argon stirring throughout the process, slag basicity of 2.5, and total oxygen ≤7ppm; S4, RH vacuum treatment: vacuum degree is 70Pa, pressure holding and degassing for 23min; S5, Continuous casting: alkaline tundish protective slag, submerged entry nozzle, molten steel superheat 24℃, casting speed 0.85m / min, weak cooling with secondary cooling water; S6. Isothermal heating of the billet: The furnace temperature is 1110℃, and the holding time is 130min. S7. Segmented rolling: The initial rolling temperature is 940℃, the roughing rolling exit temperature is 880℃; the finishing rolling enters the two-phase region, the temperature of the front section of the finishing rolling is 880℃, the temperature of the middle and rear sections of the finishing rolling is 860℃, and the final rolling temperature is 840℃. S8. Insulation and slow cooling: After rolling, the flat steel is covered with an insulation cover and slowly cooled to below 200℃ before being air-cooled; S9. Two-step heat treatment: Hold at 930℃ for 60 minutes, then oil cool; Hold at 430℃ for 120 minutes, then quickly water cool after removal from the furnace. S10. Shot peening: The heat-treated workpiece is subjected to high-pressure gas shot peening and ultrasonic shot peening in sequence. 0.3 mm diameter stainless steel shot is used for high-pressure shot peening for 15 min at a pressure of 0.6 MPa to ensure a surface coverage of not less than 95%. Then, ultrasonic shot peening is performed for 4 min with a frequency of 25 kHz and an amplitude of 40 μm to form a 60 μm thick residual compressive stress layer on the workpiece surface.

[0058] Example 5 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.58%, Si: 1.65%, Mn: 0.85%, Cr: 1.00%, Ni: 0.45%, Cu: 0.35%, Nb: 0.022%, Ti: 0.012%, RE: 0.008%, Mo: 0.12%, V: 0.06%, B: 0.001%; ​​P: 0.010%, S: 0.008%, balance Fe and unavoidable impurities.

[0059] The above-mentioned corrosion-resistant spring steel is prepared by the following method: S1. Hot metal desulfurization: KR magnesium spraying deep desulfurization, the sulfur content of the hot metal leaving the station is ≤0.003%, the desulfurization slag is completely removed, and sulfur reversion during smelting is avoided; S2. Converter smelting: scrap steel ratio 10%, final slag basicity 2.7, one additional blowing cycle, tapping temperature 1650-1670℃; ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron are added in stages during tapping to achieve uniform alloying. S3 and LF refining: The total time is 34 minutes, with weak argon stirring throughout the process, slag basicity of 2.5, and total oxygen ≤7ppm; S4, RH vacuum treatment: vacuum degree is 70Pa, pressure holding and degassing for 23min; S5, Continuous casting: alkaline tundish protective slag, submerged entry nozzle, molten steel superheat 24℃, casting speed 0.85m / min, weak cooling with secondary cooling water; S6. Isothermal heating of the billet: The furnace temperature is 1110℃, and the holding time is 130min. S7. Segmented rolling: The initial rolling temperature is 940℃, the roughing rolling exit temperature is 880℃; the finishing rolling enters the two-phase region, the temperature of the front section of the finishing rolling is 880℃, the temperature of the middle and rear sections of the finishing rolling is 860℃, and the final rolling temperature is 840℃. S8. Insulation and slow cooling: After rolling, the flat steel is covered with an insulation cover and slowly cooled to below 200℃ before being air-cooled; S9. Three-step composite heat treatment: Step 1, pre-stress relief tempering: hold at 650℃ for 85 minutes, air cool; Step 2, quenching: hold at 930℃ for 60 minutes, oil cool; Step 3, medium-temperature tempering: hold at 430℃ for 120 minutes, rapid water cooling after removal from the furnace. S10. Shot peening: The heat-treated workpieces are subjected to high-pressure gas shot peening using stainless steel shot with a diameter of 0.3 mm. The shot peening is carried out at a pressure of 0.6 MPa for 20 minutes.

[0060] Comparative Example 1 The chemical composition of commercially available 60Si2Mn spring steel, by weight percentage, is as follows: C: 0.60%, Si: 1.70%, Mn: 0.85%, Cr: 0.04%, free of Ni, Cu, Mo, V, Nb, Ti, RE, and B alloying elements; impurities P: 0.01%, S: 0.010%, balance Fe and impurities.

[0061] In its preparation method, only S9 differs from Example 1: Step S9 of Comparative Example 1 is: two-step heat treatment: quenching at 900℃ for 60 minutes followed by oil cooling, and tempering at 420℃ for 120 minutes followed by water cooling.

[0062] Comparative Example 2 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.40%, Si: 1.85%, Mn: 0.98%, Cr: 0.9%, Ni: 0.70%, Cu: 0.20%, Nb: 0.035%, Ti: 0.020%, RE: 0.011%, V: 0.10%, B: 0.0025%; P: 0.009%, S: 0.007%, balance Fe and unavoidable impurities.

[0063] The preparation method is the same as in Example 1.

[0064] Comparative Example 3 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.63%, Si: 1.85%, Mn: 0.98%, Cr: 1.30%, Ni: 0.70%, Cu: 0.50%, Nb: 0.035%, Ti: 0.03%, RE: 0.04%, Mo: 0.18%, V: 0.10%, B: 0.005%; P: 0.009%, S: 0.007%, balance Fe and unavoidable impurities.

[0065] The preparation method is the same as in Example 1.

[0066] Comparative Example 4 A corrosion-resistant spring steel, with the following chemical composition by weight percentage: C: 0.63%, Si: 1.85%, Mn: 0.98%, Cr: 1.30%, Ni: 0.70%, Cu: 0.50%, Nb: 0.035%, Ti: 0.020%, RE: 0.011%, Mo: 0.18%, B: 0.0025%; P: 0.009%, S: 0.007%, balance Fe and unavoidable impurities.

[0067] The preparation method is the same as in Example 1.

[0068] The compositions of the corrosion-resistant spring steel described in Examples 1-5 of this invention and the spring steel of Comparative Examples 1-4 are shown in Table 1: Table 1. Chemical composition (%) of corrosion-resistant spring steel in the embodiments and comparative examples of the present invention.

[0069] Performance testing The finished products obtained from each embodiment and comparative example were uniformly processed into 22mm thick variable cross-section leaf spring flat steel, and tensile test specimens, salt spray test specimens, metallographic test specimens, and bench fatigue test specimens were prepared respectively. The performance was tested using the following methods: (1) Room temperature mechanical properties test: tensile strength and yield strength are tested according to the test methods in GB / T 229.

[0070] (2) 720h neutral salt spray corrosion test and corrosion structure detection: The neutral salt spray test method in GB / T 2423.17 was used for detection.

[0071] (3) Metallographic observation of austenite grain size: Metallographic observation of austenite grain size was carried out and graded according to GB / T 6394.

[0072] (4) Leaf spring bench fatigue cycle test: The leaf spring bench fatigue cycle test shall be carried out in accordance with GB / T 19844.

[0073] (5) Electrochemical impedance EIS test: The electrochemical impedance EIS test of spring steel was carried out in accordance with GB / T 39482.1.

[0074] The test results for the above items are shown in Table 2 and Figure 1-3 As shown: Table 2 Performance test results of corrosion-resistant spring steel in the embodiments and comparative examples of the present invention

[0075] As can be seen from the data in Table 2, this invention, through optimization of the chemical composition and preparation process of spring steel, can achieve a tensile strength ≥1850MPa, a yield strength ≥1620MPa, and a neutral salt spray corrosion rate ≤0.92g / (m²) over 720 hours. 2 h), the bench fatigue cycle count is greater than 220,000 times, and the austenite grain size reaches level 8 or above. It can simultaneously meet the dual harsh conditions of high yield strength ≥1620MPa and long-term chloride ion corrosion service.

[0076] The morphology of the products from Example 2 and Comparative Example 1 after corrosion testing was inspected, such as... Figure 1 As shown, Figure 1 (b) is the corrosion-resistant spring steel of Embodiment 2 of the present invention. Figure 1 In section (a), spring steel is shown in Comparative Example 1 of the present invention. Figure 1 It can be seen that, compared with the 60Si2Mn spring steel of Comparative Example 1, the corrosion pits on the surface of the corrosion-resistant spring steel of Example 2 are significantly reduced, and a distinct protective layer is formed on the surface. Figure 2 for Figure 1 Compositional line scanning results of the corrosion product region (compositional lines are) Figure 1 (Middle Red Line) Figure 2 (a) shows the composition line scan results of the corrosion product region of the spring steel in Comparative Example 1 of the present invention; Figure 2 Image (b) shows the compositional line scan results of the corrosion product region of the corrosion-resistant spring steel in Example 2 of the present invention. Figure 2 It can be seen that a clear protective layer is formed between the corrosion layer and the substrate of the corrosion-resistant spring steel in Embodiment 2 of the present invention.

[0077] The present invention conducted EIS performance tests on the products of Example 2 and Comparative Example 1, and the test results are as follows: Figure 3 As shown ( Figure 3 In this context, DFS represents the corrosion-resistant spring steel obtained in Example 2, and 60Si2Mn represents the 60Si2Mn spring steel obtained in Comparative Example 1. Figure 3 It can be seen that, compared with the 60Si2Mn spring steel of Comparative Example 1, the cathodic and anodic chemical reactions of the corrosion-resistant spring steel of Example 2 were significantly suppressed.

[0078] Therefore, it can be seen that the present invention greatly improves the corrosion resistance of spring steel by optimizing the chemical composition of spring steel.

[0079] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0080] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A corrosion-resistant spring steel, characterized in that, Its chemical composition, by mass percentage, includes: C: 0.58-0.68%, Si: 1.65-2.1%, Mn: 0.85-1.1%, Cr: 1.0-1.6%, Ni: 0.45-0.95%, Cu: 0.35-0.65%, Nb: 0.022-0.048%, Ti: 0.012-0.028%, RE: 0.008-0.015%, Mo: 0.12-0.25%, V: 0.06-0.14%, B: 0.001-0.004%, P≤0.012%, S≤0.010%, balance being Fe and unavoidable impurities.

2. The corrosion-resistant spring steel as described in claim 1, characterized in that, Its chemical composition by mass percentage Comprising: C: 0.68%, Si: 2.1%, Mn: 1.1%, Cr: 1.6%, Ni: 0.95%, Cu: 0.65%, Nb: 0.048%, Ti: 0.028%, RE: 0.015%, Mo: 0.25%, V: 0.14%, B: 0.004%, P: 0.011%, S: 0.009%, with the balance being Fe and unavoidable impurities.

3. A method for preparing corrosion-resistant spring steel as described in claim 1 or 2, characterized in that, In order, they include: Smelting, continuous casting, segmented rolling, three-step composite heat treatment, shot peening.

4. The method for preparing corrosion-resistant spring steel as described in claim 3, characterized in that, The specific steps of the smelting process include, in sequence: desulfurization of molten iron, converter smelting, LF refining, and RH vacuum treatment.

5. The method for preparing corrosion-resistant spring steel as described in claim 4, characterized in that, The desulfurization of the molten iron adopts a magnesium powder injection desulfurization process to control the sulfur content of the molten iron leaving the station to be ≤0.003%; The steps of the converter smelting include: adopting a converter top-bottom composite blowing process, with a final slag basicity of 2.7-3.1, ≤1 time of supplementary blowing, a tapping temperature of 1650-1690℃, and adding ferrochrome, nickel plate, ferromolybdenum, ferrovanadium, ferroniobium, ferrotitanium, copper alloy, rare earth, and ferroboron in stages during tapping. The LF refining process has a total duration of ≥32 min, with bottom-blown argon stirring throughout, slag basicity of 2.5-2.9, and total oxygen ≤7 ppm. The RH vacuum treatment has the following characteristics: vacuum degree ≤ 75 Pa, and vacuum duration ≥ 22 min.

6. The method for preparing corrosion-resistant spring steel as described in claim 3, characterized in that, The continuous casting process includes: using an immersion nozzle for casting, using alkaline protective slag in the tundish, a superheat of molten steel in the tundish of 21-27℃, a casting speed of 0.75-0.95m / min, and using weak cooling for secondary cooling. After obtaining the billet, the billet is subjected to isothermal homogenization: entering the furnace at 1090-1130℃ and holding for 120-140min.

7. The method for preparing corrosion-resistant spring steel as described in claim 3, characterized in that, The segmented rolling process includes: sequentially performing initial rolling, rough rolling, finish rolling, and final rolling on the billet obtained from continuous casting; the initial rolling temperature is 920-960℃, the rough rolling temperature is 870-900℃, the finish rolling temperature is 820-900℃, and the final rolling temperature is 820-870℃.

8. The method for preparing corrosion-resistant spring steel as described in claim 3, characterized in that, The three-step composite heat treatment process includes: for the workpiece after segmented rolling, first holding it at 640-670℃ for 75-95 minutes; after the first cooling, holding it at 915-945℃ for 55-65 minutes; after the second cooling, holding it at 410-450℃ for 115-135 minutes, and then performing a third cooling.

9. The method for preparing corrosion-resistant spring steel as described in claim 3, characterized in that, The shot peening process includes: sequentially subjecting the heat-treated workpiece to high-pressure gas shot peening and ultrasonic shot peening.

10. The application of the corrosion-resistant spring steel as described in claim 1 or 2 in lightweight single-leaf or multi-leaf variable cross-section leaf springs for heavy-duty commercial vehicles.

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