EP3831970B1 - Acier à ressort présentant une durée de vie en fatigue supérieure, et son procédé de fabrication - Google Patents

Acier à ressort présentant une durée de vie en fatigue supérieure, et son procédé de fabrication Download PDF

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EP3831970B1
EP3831970B1 EP19841872.5A EP19841872A EP3831970B1 EP 3831970 B1 EP3831970 B1 EP 3831970B1 EP 19841872 A EP19841872 A EP 19841872A EP 3831970 B1 EP3831970 B1 EP 3831970B1
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Prior art keywords
steel
controlled
fatigue life
spring steel
temperature
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German (de)
English (en)
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EP3831970A4 (fr
EP3831970A1 (fr
Inventor
Zan YAO
Feng Jin
Genjie WAN
Yanfeng QI
Zhenping Wu
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C1/00—Manufacture of metal sheets, metal wire, metal rods, metal tubes by drawing
    • B21C1/003—Drawing materials of special alloys so far as the composition of the alloy requires or permits special drawing methods or sequences
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/20—Controlling or regulating processes or operations for removing cast stock
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/072—Treatment with gases
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/58—Oils
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
    • C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • C21D9/5735—Details
    • C21D9/5737—Rolls; Drums; Roll arrangements
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/562—Details
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese

Definitions

  • the present invention relates to a spring steel and a method for manufacturing the same, in particular to a spring steel having a superior fatigue life and a method for manufacturing the same, wherein the steel may be used to manufacture automotive springs having a machining strength of at least 2020 MPa, an area reduction rate ⁇ 40%, a fine structure, a high steel purity, as well as a low cost and a superior fatigue life.
  • springs are widely used in various aspects of social production and people's lives, such as transportation, machinery manufacturing, automobile industry, military industry and daily life.
  • the spring is used within its elastic range and should return to its original state after unloading. It is desired to have plastic deformation as small as possible.
  • steel wire should have high elastic limit, yield strength and tensile strength. The higher the yield ratio, the closer the elastic limit is to the tensile strength, and thus the higher the strength utilization rate, resulting in a spring having higher elastic force.
  • the spring relies on elastic deformation to absorb impact energy.
  • the spring steel wire does not have to have high plasticity, but it must at least have plasticity that can endure spring forming and sufficient toughness that can endure impact energy.
  • the spring usually works for a long time under alternating stress, so they must have high fatigue limit, and good creep and relaxation resistance.
  • the conventional Cr-V family, Cr-Mn family, and Si-Mn family spring steel materials cannot meet the requirements of the high-strength spring production.
  • the commonly used Si-Cr family spring steel with higher strength and better yield ratio has already reached the limits of the strength and fatigue life.
  • CN 101 787 493 B discloses a high-strength spring steel alloy comprising: 0.56%-0.64%C, 0.80%-1.10%Si, 0.80%-1.20%Mn, P ⁇ 0.035%, S ⁇ 0.03%, 0.80%-1.20%Cr , 0.60%-1.00% Mo, 0.20%-0.30% V, 0.05%-0.12% Nb, 0.01%-0.060% N, 0.02%-0.07% RE, and a balance of Fe.
  • Mn, Cr, Mo alloying elements are added to the above designed material in relatively high amounts, wherein Mo is mainly used to improve the tempering stability, long-lasting creep resistance and heat resistance of the steel.
  • CN 100 455 691 C discloses a spring steel alloy comprising 0.4-0.6% C, 1.7-2.5% Si, 0.1-0.4 Mn, 0.5-2.0% Cr, 0-0.006% N, and 0.021-0.07% Al.
  • a design route featuring a high-carbon, high-silicon and low-manganese alloy is adopted.
  • a main consideration is to control the amount, size and shape of the residual austenite to enhance the hydrogen embrittlement resistance of the steel. High requirements are imposed on the quenching and tempering process for the material.
  • the high content of alloying AL increases the difficulty in controlling the inclusions in smelting, and the hard and brittle alumina can easily lead to reduction of the fatigue life of the spring.
  • CN 1 279 204C discloses a spring steel alloy having a compositional design as follows: 0.30-0.50% C, 0.80-2.0% Si, 0.50-1.0% Mn, 0.40-1.0% Cr, 0.01-0.5% W, 0.08-0.30% V, 0.005-0.25% of rare earth elements, and optional 0.001-0.10% of B.
  • a design featuring low carbon is mainly adopted for this alloy.
  • the content of the Si element is increased to enhance the strength.
  • the W element is used to improve the hardenability of the steel, improve deformation resistance and prevent decarburization.
  • CN 1 039 725C discloses a low-decarburized, high-toughness spring steel for automobile suspension springs.
  • the steel comprises 0.5-0.7% C, 1.0-3.5% Si, 0.3-1.5% Mn, 0.3-1.0% Cr, 0.05-0.5% V and/orNb, less than 0.02% of P, less than 0.02% of S, 0.5-5.0% Ni and other unavoidable impurities, the remainder being Fe.
  • a relatively large amount of the Ni element is added, and thus the alloy cost is high.
  • EP 2 096 184 A1 teaches a spring steel wire wherein the contents of C, Si, Mn, Cr, Ti, B, and other elements are specified; the contents (mass%) of B, Ti, and N satisfy the expression (1) below; the amount of solid solute B is in the range of 0.0005% to 0.0040%; the remainder in the spring steel wire is composed of Fe and unavoidable impurities; and the solid solute B concentrates at the grain boundaries of pearlite nodules, 0.03 ⁇ B / Ti / 3.43 - N ⁇ 5.0.
  • EP 2 543 747 A1 teaches a seamless steel pipe for a high-strength hollow spring, which comprises 0.20 to 0.70 mass% of C, 0.5 to 3.0 mass% of Si, 0.1 to 3.0 mass% of Mn, 0.030 mass% or less (including 0%) of P, 0.030 mass% or less (including 0%) of S, 0.02 mass% or less (including 0%) of N, and the remainder made up by Fe and unavoidable impurities, and which is characterized in that carbide has an equivalent circle diameter of 1.00 ⁇ m or less.
  • the existing technical solutions involving alloying mainly increase material strength by adjustment of the C, Si and Mn elements. If the Si content is too low, the elastic limit of the material will be reduced, and the elasticity attenuation resistance will become poor. If the Si content is too high, the plasticity of the material will be deteriorated; at the same time, the difficulty in controlling decarburization will be increased, affecting the fatigue life of the spring. The addition of alloying elements in excessively high amounts will lead to higher material costs and affect the precipitation size at the same time, resulting in degraded fatigue performance of the material. The designed strength of the material is still low, and the fatigue life of the spring is not considered much.
  • One object of the present invention is to provide a spring steel having a superior fatigue life and a method for manufacturing the same.
  • the spring steel has a machining strength ⁇ 2020 MPa, good plastic toughness, an area reduction rate ⁇ 40%, and a fatigue life ⁇ 800000 cycles. It can meet the application requirements of high-stress springs in the industries such as automobiles and machinery.
  • the spring steel of the present invention is defined in claim 1 and the method of manufacturing the same is defined in claim 4.Further improvements are subject to the dependent claims.
  • the microstructure of the spring steel according to the present invention is a tempered troostite + sorbite structure.
  • the original austenite grain size is ⁇ 80 ⁇ m; the size of alloying nitride and carbide precipitates is 5-60 nm; and the maximum width of a monoparticle inclusion is ⁇ 30 ⁇ m.
  • C is an essential component for ensuring the room temperature strength and hardenability of the spring steel, and it is also an element for the spring steel to achieve a high elastic limit and good elasticity attenuation resistance.
  • the C content is less than 0.52%, the strength of the alloy spring steel cannot be guaranteed to achieve 2020 MPa or higher, and it is also undesirable for precipitation of carbides/nitrides of microalloying elements.
  • the C content is too high, the carbide size will be too large in the tempering process, and the plasticity of the material deteriorates, which is undesirable for maintaining good plastic toughness under high strength, and thus affects the fatigue life of the material.
  • the content of the C element must be less than 0.62%.
  • Si is a non-carbide forming element. It is mainly solid-dissolved in the ferrite phase to play a strengthening role. Increasing the alloying silicon content is desirable for improving the elastic limit and elasticity attenuation resistance of the material, thereby optimizing the spring performances. However, if the Si content is too high, the plasticity of the material will be deteriorated, which is undesirable for spring forming, and affects the life of the finished spring. At the same time, the high content of Si will increase the tendency of decarburization during the production and heat treatment of the material, resulting in increased processing cost. Upon comprehensive consideration, the Si content in the present material is controlled in the range of 1.2-1.45%.
  • Mn is an additive element commonly used in steel. It can effectively improve hardenability and strength while having little influence on the plasticity of the steel. To ensure the strength and hardenability of the alloy, the Mn content cannot be less than 0.25%. When the Mn content is too high, it will cause serious segregation, and at the same time, it will cause grain growth. Hence, Mn in the steel needs to be controlled, and the allowable range is 0.25-0.75%.
  • Cr has the effect of improving the hardenability of the spring steel, and allows for precipitation of alloy cementite in the tempering process to increase the strength of the material.
  • the Cr element also has the effect of refining the structure. Therefore, in order to utilize the effect of Cr on solid solution strengthening and precipitation strengthening while improving the material structure, the Cr content should be controlled within 0.30-0.80% in the design of the present material.
  • V and Nb elements are commonly added to steel as microalloying elements. These two types of elements have a strong tendency to form nitrides and carbides, thereby increasing the precipitation and nucleation rate of carbides/nitrides during tempering, and refining the structure.
  • the carbides/nitrides of V and Nb are precipitated during the wire rod rolling process, which is desirable for reducing the austenite grain size in the material, and improving the strength and plasticity of the material. Nano-sized precipitates are beneficial to the improvement of the material strength, plasticity and fatigue life. When the contents of V and Nb in the alloy are too high, the size of the precipitates will increase.
  • (2Nb+V)/(20N+C) in the steel is in the range of 0.15-0.37.
  • the original austenite grain size in the material is ⁇ 80 ⁇ m after quenching and tempering treatment, and the size of the precipitates in the steel is controlled in the range of 5-60 nm.
  • Al mainly has a deoxygenation effect in the steel.
  • alumina formed by deoxygenation with Al is a hard and brittle phase which has a significant influence on the fatigue life of the spring.
  • Large brittle inclusions are one of the main factors that cause abnormal spring fracture.
  • the Al content is controlled to be ⁇ 0.0045% in the steel, and the oxygen content is controlled in the range of 0.0005-0.0040%.
  • the width of a monoparticle inclusion in the steel needs to be controlled at ⁇ 30 ⁇ m.
  • the contents of the harmful P and S elements in the steel are controlled at 0.015% or less and 0.015% or less respectively to increase the purity of the steel.
  • the beneficial effects of the present invention include:
  • the strength of the spring steel produced using the steel composition and manufacturing method according to the present invention can reach 2020 MPa or higher.
  • the cost of this alloy is low.
  • the material strengthened by the nano-sized precipitates has good plastic toughness and good spring formability at the same time, and cracking during the processing is prevented.
  • the finished spring has a high fatigue life, which can meet the requirements of automotive lightweight as well as high strength and long service life in the machinery industry. This is desirable for promoting the technical level of the industry, and brings about favorable economic benefits.
  • Examples A1-10# according to the present invention and three Comparative Steel Grades B1-3# are shown in Table 1 below, and the specific manufacturing methods are as follows: Examples A1-5# according to the present invention, and Comparative Steel Grades B1 and B2 alloys were smelted with the use of an electric furnace, and Example A6-10# and Comparative Steel Grade B3 alloys were smelted with the use of a converter. Then, secondary refining was performed, wherein Examples A1-3#, A6-8#, and Comparative Steel Grade B1 alloys were treated with an LF furnace plus VD refining, while Examples A4-5#, A9-10#, Comparative Steel Grade B2, and B3 alloys were treated with LF plus RH.
  • A1-6#, and B1 were vacuum degassed for 30 minutes, and A7-10#, B2, and B3 were vacuum degassed for 35 minutes.
  • the final O content was controlled at 0.0005-0.0040%, the N content was 0.001-0.009%, and the H content was less than 2 ppm.
  • A1-4# and B1 were cast into 300 mm round billets, A5-6# were cast into 450 mm round billets, A7-9# and B2 were cast into 320*420 mm square billets, and A10# and B3 were cast into 500mm square billets.
  • a tundish covering agent and a casting mold with good sealing performance were used to protect the slag in the casting process.
  • the blooming temperature for the A1-5# and B1 continuously cast billets was 1050 °C, and the end face size of the rolled small square blanks was 115 mm.
  • the heating temperature for A6-7# and B2 square billets was 1270 °C, and the size of the rolled blanks was 125 mm.
  • the heating temperature for A8-10# and B3 square billets was 1100 °C, and the size of the rolled blanks was 170 mm.
  • the furnace temperature of the heating furnace for A1-4# and B1 was controlled at 920 °C, and the holding time was 1.0 h.
  • the temperature of the heating furnace for A5-10#, B2 and B3 was controlled at 1150 °C, and the holding time was 3.0 h.
  • the rolling speed was controlled to be 15-115 m/s.
  • the online temperature control scheme for the A1-6# and B1 alloys, the inlet temperature of the finishing rolling unit was 880-950 °C, the inlet temperature of the reducing and sizing unit was 840-950 °C, and the silking temperature was 800-890 °C; for the A7-10#, B2 and B3 alloys, the inlet temperature of the finishing rolling unit was 950-1050 °C, the inlet temperature of the reducing and sizing unit was 940-970 °C, and the silking temperature was 870-950 °C.
  • the dimensions of the A1-5#, B1 and B2 alloy rolled wire rods were ⁇ 5-15mm respectively, and the rolling specifications of the A6-10# and B3 alloy wire rods were ⁇ 16-28mm.
  • the Stelmor cooling process was: the air volume was 40% for fans F1-F4, 10% for fans F5-F7, 5% for fans F8-F12, and 40% for fans F13-F14.
  • the Stelmor cooling process was: the air volume was 50% for fans F1-F4, 20% for fans F5-F7, 15% for fans F8-F12, and 35% for fans F13-F14.
  • the structure of the wire rods after the Stelmor cooling was sorbite plus a very small amount of ferrite.
  • the wire rods were drawn prior to heat treatment.
  • the quenching and tempering treatment temperatures for the drawn steel wires were divided into three groups, wherein the heating temperature was 850 °C and the tempering temperature was 550 °C for A1-2# and B1; the heating temperature was 980 °C and the tempering temperature was 470 °C for A3-7# and B2; and the heating temperature was 1100 °C and the tempering temperature was 370 °C for A8-10# and B3.
  • the mechanical properties of the high-strength springs of Examples A1-A10 and the Comparative Steel Grades B1-B3 are shown in Table 2 below. As can be seen from the table, the strength of the alloys all reach 2020 MPa or higher, higher than that of the samples of Comparative Examples B1-B3. At the same time, the area reduction rate of the materials can still reach 40% or higher. A good combination of plasticity and toughness is obtained.
  • the high-strength springs according to the present invention and the comparative alloys were made into the same type of helical springs, and the fatigue life of the helical springs was measured using a spring fatigue testing machine according to GBT16947-2009 "Helical Spring Fatigue Testing Standard". The results are shown in Table 3.

Claims (5)

  1. Acier à ressort ayant une durée de vie en fatigue supérieure, dans lequel sa composition chimique sur la base du pourcentage en masse est :
    C : 0,52-0,62 % ;
    Si : 1,20-1,45 % ;
    Mn : 0,25-0,75 % ;
    Cr : 0,30-0,80 % ;
    V : 0,01-0,15 % ;
    Nb : 0,001-0,05 % ;
    N : 0,001-0,009 % ;
    O : 0,0005-0,0040 % ;
    P : ≤0,015 % ;
    S : ≤0,015 % ;
    Al : ≤0,0045 % ;
    un reste de Fe et d'impuretés inévitables, dans lequel la relation suivante est satisfaite : 0,02≤(2Nb+V)/(20N+C)≤0,40 ;
    l'acier à ressort présente une résistance à la traction ≥ 2020 MPa, un taux de réduction de surface ≥ 40 %, et une durée de vie en fatigue
    ≥ 800 000 cycles selon GBT16947-2009 "norme de test à la fatigue de ressort hélicoïdal" ;
    l'acier à ressort présente une microstructure qui est une structure de troostite + sorbite revenue, une taille d'origine de grain d'austénite
    ≤ 80 µm, une taille de précipités de nitrure et carbure d'alliage dans l'intervalle de 5-60 nm, et une largeur maximale d'inclusions de monoparticules ≤ 30 µm.
  2. Acier à ressort ayant une durée de vue en fatigue supérieure selon la revendication 1, dans lequel 0,045 ≤ 2 Nb + V / 20 N + C ≤ 0,37 .
    Figure imgb0005
  3. Acier à ressort ayant une durée de vie en fatigue selon la revendication 2, dans lequel 0,15 ≤ 2 Nb + V / 20 N + C ≤ 0,37 .
    Figure imgb0006
  4. Procédé pour la fabrication de l'acier à ressort ayant une durée de vie en fatigue supérieure selon la revendication 1 ou 2 ou 3, comprenant : fusion, coulée continue, laminage grossier, laminage de fil à vitesse élevée, refroidissement contrôlé Stelmor, tréfilage de fil machine, et traitement de trempe et revenu, dans lequel
    un four électrique ou un convertisseur est utilisé pour la fusion ; après la fusion, un raffinage secondaire est réalisé avec l'utilisation d'un four LF plus traitement de dégazage VD ou RH ; pendant le raffinage LF, les composition et basicité d'un laitier synthétique sont ajustées pour contrôler les teneurs en les éléments P et S dans l'acier pour être inférieures à 0,015 % et 0,015 % ; une agitation en présence d'argon est réalisée pour permettre une réaction complète entre un laitier de raffinage et des inclusions dans l'acier fondu pour réaliser une dénaturation et élimination des inclusions ; la durée de dégazage sous vide VD ou RH est supérieure à 30 minutes pour contrôler une teneur en O finale à 0,0005-0,0040 %, une teneur en N finale à 0,0010-0,0090 %, et une teneur en H inférieure à 2 ppm ; une durée de neutralisation de la poche de coulée est supérieure à 15 min à la fin du raffinage pour faciliter la flottaison d'inclusions de grandes particules, de sorte que la taille des inclusions dans l'acier fondu est inférieure à 30 µm ;
    le laminage grossier adopte un procédé de production de chauffage double, dans lequel une billette de coulée est transformée en bloom en une ébauche carrée ou ronde de 115-170 mm à une température de 1 050-1 270°C, et une réduction de laminage totale est supérieure à 40 % ;
    dans le laminage de fil à vitesse élevée, le chauffage d'un four de chauffage est contrôlé à 920-1 150°C, et la durée de maintien est de 1,0-3,0 h ; une vitesse de laminage est contrôlée à 15-115 m/s dans le procédé de laminage de fil machine à vitesse élevée ; un schéma de contrôle de température en ligne est le suivant : une température d'entrée d'une unité de laminage de finition est de 880-1 050°C, une température d'entrée d'une unité de réduction-équilibrage est de 840-970°C, et une température de silking est de 800-950°C ;
    dans le refroidissement contrôlé Stelmor, les volumes d'air de 14 soufflantes sur une ligne Stelmor sont ajustés dans les intervalles suivants : les soufflantes F1-F7 présentent un volume d'air de 10-100 %, les soufflantes F8-F12 présentent un volume d'air de 0-50 %, et les soufflantes F13-F14 présentent un volume d'air de 0-50 % ;
    lorsque le fil machine est tréfilé, une vitesse de tréfilage n'est pas supérieure à 3,5 m/min ;
    dans le traitement de trempe et revenu, une température de chauffage avant le traitement de trempe et revenu du fil en acier tréfilé est contrôlée dans l'intervalle de 850-1 100°C ; de l'huile ou de l'eau est utilisée comme milieu de trempe ; une température du milieu de trempe est contrôlée à 15-40°C ; et une température de revenu est contrôlée à 370-550°C, de sorte qu'une taille des précipités de nitrure et carbure dans un fil d'acier fini est contrôlée dans l'intervalle de 5-60 nm.
  5. Procédé pour la fabrication de l'acier à ressort ayant une durée de vie en fatigue supérieure selon la revendication 4, dans lequel une machine de coulée continue est utilisée pour couler une billette ronde ou carrée ayant une dimension de 320-500 mm ; pendant le procédé de coulée continue, une vitesse de tréfilage est contrôlée dans l'intervalle de 0,5-0,8 m/min, et une réduction légère de queue est contrôlée pour être supérieure à 10 mm, afin de contrôler une ségrégation du carbone dans un noyau de la billette pour atteindre une cible inférieure à 1,08.
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