EP3831970B1 - Spring steel having superior fatigue life, and manufacturing method for same - Google Patents
Spring steel having superior fatigue life, and manufacturing method for same Download PDFInfo
- Publication number
- 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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- EP
- European Patent Office
- Prior art keywords
- steel
- controlled
- fatigue life
- spring steel
- temperature
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- 229910000639 Spring steel Inorganic materials 0.000 title claims description 30
- 238000004519 manufacturing process Methods 0.000 title claims description 17
- 229910000831 Steel Inorganic materials 0.000 claims description 45
- 239000010959 steel Substances 0.000 claims description 45
- 238000005096 rolling process Methods 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 14
- 238000005496 tempering Methods 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 11
- 229910052799 carbon Inorganic materials 0.000 claims description 9
- 239000002244 precipitate Substances 0.000 claims description 9
- 238000007670 refining Methods 0.000 claims description 9
- 238000005275 alloying Methods 0.000 claims description 8
- 238000010791 quenching Methods 0.000 claims description 8
- 230000000171 quenching effect Effects 0.000 claims description 8
- 150000004767 nitrides Chemical class 0.000 claims description 7
- 238000003723 Smelting Methods 0.000 claims description 6
- 229910001566 austenite Inorganic materials 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 239000002893 slag Substances 0.000 claims description 4
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical group OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 claims description 3
- 238000009661 fatigue test Methods 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 238000004513 sizing Methods 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 2
- 238000005204 segregation Methods 0.000 claims description 2
- 238000009749 continuous casting Methods 0.000 claims 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims 2
- 229910052786 argon Inorganic materials 0.000 claims 1
- 238000007872 degassing Methods 0.000 claims 1
- 238000004925 denaturation Methods 0.000 claims 1
- 230000036425 denaturation Effects 0.000 claims 1
- 239000002245 particle Substances 0.000 claims 1
- 238000003756 stirring Methods 0.000 claims 1
- 238000009849 vacuum degassing Methods 0.000 claims 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims 1
- 239000000463 material Substances 0.000 description 30
- 229910045601 alloy Inorganic materials 0.000 description 22
- 239000000956 alloy Substances 0.000 description 22
- 239000011572 manganese Substances 0.000 description 15
- 230000000052 comparative effect Effects 0.000 description 11
- 229910052710 silicon Inorganic materials 0.000 description 8
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 6
- 229910052804 chromium Inorganic materials 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 229910052748 manganese Inorganic materials 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 229910052720 vanadium Inorganic materials 0.000 description 6
- 238000013461 design Methods 0.000 description 5
- 238000005261 decarburization Methods 0.000 description 4
- QDOXWKRWXJOMAK-UHFFFAOYSA-N dichromium trioxide Chemical compound O=[Cr]O[Cr]=O QDOXWKRWXJOMAK-UHFFFAOYSA-N 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 229910052758 niobium Inorganic materials 0.000 description 4
- 229910019582 Cr V Inorganic materials 0.000 description 3
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 3
- 229910052681 coesite Inorganic materials 0.000 description 3
- 229910052593 corundum Inorganic materials 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- BFRGSJVXBIWTCF-UHFFFAOYSA-N niobium monoxide Inorganic materials [Nb]=O BFRGSJVXBIWTCF-UHFFFAOYSA-N 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 235000012239 silicon dioxide Nutrition 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- 229910001845 yogo sapphire Inorganic materials 0.000 description 3
- 229910000851 Alloy steel Inorganic materials 0.000 description 2
- 229910006639 Si—Mn Inorganic materials 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000006392 deoxygenation reaction Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 239000002105 nanoparticle Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- 229910000859 α-Fe Inorganic materials 0.000 description 2
- 229910019830 Cr2 O3 Inorganic materials 0.000 description 1
- 229910019819 Cr—Si Inorganic materials 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910000914 Mn alloy Inorganic materials 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 229910008458 Si—Cr Inorganic materials 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000005489 elastic deformation Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 230000005923 long-lasting effect Effects 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- VASIZKWUTCETSD-UHFFFAOYSA-N manganese(II) oxide Inorganic materials [Mn]=O VASIZKWUTCETSD-UHFFFAOYSA-N 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
Classifications
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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
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- 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
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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
- 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
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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
- 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
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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
- C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
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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
- C21D9/54—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
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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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
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
- C21D9/562—Details
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- 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.
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Description
- 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.
- As an important shock absorption and functional component, 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. Hence, 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. Hence, 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.
- Along with the progress of the technologies in the automobile and machinery industries, higher requirements are imposed on the strength and fatigue life of spring parts. Development of materials with high strength, good plasticity, and high fatigue resistance for manufacturing springs has become the focus of advanced steel companies in various countries.
- At present, 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. On the other hand, 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.
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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. At the same time, 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. At the same time, the W element is used to improve the hardenability of the steel, improve deformation resistance and prevent decarburization. However, it is difficult to control smelting and heat treatment in the presence of W and the rare earth elements. -
CN 1 039 725C discloses a low-decarburized, high-toughness spring steel for automobile suspension springs. In this kind of steel, the content of the Si element is increased without reducing the C content. 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. In order to solve the decarburization problem and improve the toughness of the material, a relatively large amount of the Ni element is added, and thus the alloy cost is high. -
JP 2001 181 788 A -
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 µm 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.
- The lightweight development of automobiles and the technological progress in the machinery industry have prompted the continuous improvement of the strength of spring materials. At present, the commonly used Cr-V family, Cr-Mn family, Si-Mn family, and Cr-Si family spring steels have reached the limits of the materials.
- 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.
- To achieve the above object, 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 µm; the size of alloying nitride and carbide precipitates is 5-60 nm; and the maximum width of a monoparticle inclusion is ≤ 30 µm.
- In the compositional design of the spring steel according to the present invention:
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. When 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. However, when 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. Hence, 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.
- The 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. At the same time, with the mutual influence of these two elements taken into account, after several runs of testing, it's verified that desirable effects can be resulted when the V content is controlled at 0.01-0.15%, and the Nb content is 0.001-0.05%. An increased N content will increase the brittleness of the material. At the same time, with the effect of N on the precipitation of alloying elements taken into consideration, it is necessary to control the N content in the steel in the range of 0.001-0.009%. At the same time, in order to fulfil the purpose of refining precipitates, (2Nb+V)/(20N+C) in the steel is controlled in the range of 0.02-0.40, preferably in the range of 0.045-0.37. In some embodiments, (2Nb+V)/(20N+C) in the steel is in the range of 0.15-0.37. In order to achieve high strength, good plasticity and long fatigue life of the finished spring, the original austenite grain size in the material is ≤ 80 µm 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. However, 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. In order to have an effective control over the alumina inclusions in the steel, 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%. In order to prolong the fatigue life of the spring under high strength, the width of a monoparticle inclusion in the steel needs to be controlled at ≤ 30 µm.
- In order to ensure the toughness of the material and prevent defects such as hot brittleness and cold brittleness in the production process, 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. With the refinement of the structure and the control over the composition and size of the inclusions, 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. - The chemical compositions of 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. The structure and basicity of a synthetic slag were optimized. 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. - After smelting, 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. In the high-speed wire rod rolling process, 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 Φ5-15mm respectively, and the rolling specifications of the A6-10# and B3 alloy wire rods were Φ16-28mm. After the rolling of A1-5# and B1 alloy wire rods, 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. After the rolling of A6-10#, B2 and B3 alloy wire rods, 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. Under the same conditions, the fatigue life of the high-strength spring steel according to the present invention is superior to that of the comparative steel.
Table 1: Chemical compositions (wt%) of Examples A1-10# according to the present invention and Comparative Steel Grades B1-3# Steel No. C Si Mn Cr V Nb Al N O P S A1 0.60 1.40 0.75 0.80 0.15 0.03 0.0030 0.001 0.004 0.015 0.008 A2 0.62 1.45 0.75 0.75 0.15 0.03 0.0027 0.001 0.003 0.010 0.008 A3 0.55 1.30 0.75 0.70 0.15 0.03 0.0030 0.001 0.0015 0.010 0.008 A4 0.58 1.35 0.60 0.60 0.10 0.03 0.0045 0.001 0.0015 0.010 0.008 A5 0.54 1.35 0.55 0.70 0.05 0.05 0.0045 0.001 0.0015 0.010 0.008 A6 0.56 1.35 0.30 0.67 0.02 0.05 0.0010 0.009 0.0015 0.008 0.008 A7 0.55 1.35 0.25 0.70 0.02 0.008 0.0010 0.009 0.0005 0.008 0.008 A8 0.52 1.35 0.60 0.65 0.02 0.05 0.0010 0.009 0.001 0.008 0.015 A9 0.53 1.20 0.60 0.30 0.01 0.05 0.0020 0.005 0.001 0.008 0.004 A10 0.52 1.45 0.60 0.60 0.05 0.001 0.0020 0.005 0.001 0.008 0.004 B1 0.55 1.50 0.70 0.75 0 0 0.0020 0.005 0.001 0.008 0.004 B2 0.65 1.35 0.70 1.05 0.2 0 0.0045 0.001 0.004 0.017 0.001 B3 0.5 1.6 0.55 0.8 0.15 0.08 0.003 0.001 0.006 0.015 0.015 Table 2: Alloy steel structure according to the present invention Steel No. Original austenite grain size (µm) Nitride-carbide precipitate size (nm) Maximum width of monoparticle inclusions (µm) A1 75 10-60 28 A2 60 5-55 30 A3 55 30-55 15 A4 54 5-45 19 A5 67 10-55 25 A6 80 7-45 18 A7 60 10-56 30 A8 34 23-60 10 A9 56 12-55 25 A10 77 12-60 30 B1 90 -- 45 B2 50 15-100 50 B3 45 25-145 25 Table 3: Properties of alloy steel examples according to the present invention and comparative steel grades Steel No. Tensile strength MPa Area reduction rate % Fatigue life Number of cycles A1 2080 46 85×104 A2 2110 42 90×104 A3 2050 43 105×104 A4 2090 40 99×104 A5 2110 44 90×104 A6 2075 41 98×104 A7 2095 42 100×104 A8 2130 44 110×104 A9 2097 40 95×104 A10 2089 45 97×104 B1 1905 45 70×104 B2 2080 37 57×104 B3 2055 35 60×104
Claims (5)
- A spring steel having a superior fatigue life, wherein its chemical composition based on weight percentage is: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%;a balance of Fe and unavoidable impurities, wherein the following relationship is satisfied: 0.02≤(2Nb+V)/(20N+C)≤0.40;the spring steel has a tensile strength ≥ 2020 MPa, an area reduction rate ≥ 40 %, and a fatigue life ≥ 800000 cycles according to GBT16947-2009 "Helical Spring Fatigue Testing Standard";the spring steel has a microstructure that is a tempered troostite + sorbite structure, an original austenite grain size ≤ 80 µm, a size of alloying nitride and carbide precipitates in the range of 5-60 nm, and a maximum width of monoparticle inclusions ≤ 30 µm
- A method for manufacturing the spring steel having a superior fatigue life according to claim 1 or 2 or 3, comprising: smelting, continuous casting,rough rolling, high-speed wire rolling, Stelmor controlled cooling, wire rod drawing, and quenching and tempering treatment, whereinan electric furnace or a converter is used for the smelting; after the smelting, secondary refining is performed with the use of an LF furnace plus VD or RH degassing treatment; during the LF refining, the composition and basicity of a synthetic slag are adjusted to control the contents of the P and S elements in the steel to be lower than 0.015% and 0.015%; stirring in the presence of argon is performed to allow for full reaction between a refining slag and inclusions in the molten steel to realize denaturation and removal of the inclusions; VD or RH vacuum degassing time is more than 30 minutes to control a final O content at 0.0005-0.0040%, a final N content at 0.0010-0.0090%, and a H content of less than 2 ppm; killing time of the ladle is more than 15 min at the end of the refining to facilitate floating of large particle inclusions, so that the size of inclusions in molten steel is smaller than 30 µm;the rough rolling adopts a twice-heating production process, wherein a cast billet is bloomed into a 115-170 mm square or round blank at a temperature of 1050-1270 °C, and a total rolling reduction is higher than 40 %;in the high-speed wire rolling, heating of a heating furnace is controlled at 920-1150 °C, and holding time is 1.0-3.0 h; a rolling speed is controlled at 15-115 m/s in the high-speed wire rod rolling process; an online temperature control scheme is as follows: an inlet temperature of a finishing rolling unit is 880-1050 °C, an inlet temperature of a reducing-sizing unit is 840-970 °C, and a silking temperature is 800-950 °C;in the Stelmor controlled cooling, air volumes of 14 fans on a Stelmor line are adjusted in the following ranges: fans F1-F7 have an air volume of 10-100 %, fans F8-F12 have an air volume of 0-50 %, and fans F13-F14 have an air volume of 0-50 %;when the wire rod is drawn, a drawing speed is not higher than 3.5 m/min;in the quenching and tempering treatment, a heating temperature prior to the quenching and tempering treatment of the drawn steel wire is controlled in the range of 850-1100 °C; oil or water is used as a quenching medium; a temperature of the quenching medium is controlled at 15-40 °C; and a tempering temperature is controlled at 370-550 °C, so that a size of nitride and carbide precipitates in a finished steel wire is controlled in the range of 5-60 nm.
- The method for manufacturing the spring steel having a superior fatigue life according to claim 4, wherein a continuous casting machine is used to cast a round or square billet having a size of 320-500 mm; during the continuous casting process, a drawing speed is controlled in the range of 0.5-0.8 m/min, and a tail end soft reduction is controlled to be greater than 10 mm, so as to control carbon segregation in a core of the billet to achieve a target of lower than 1.08.
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CN201810842312.5A CN110760748B (en) | 2018-07-27 | 2018-07-27 | Spring steel with excellent fatigue life and manufacturing method thereof |
PCT/CN2019/096726 WO2020020066A1 (en) | 2018-07-27 | 2019-07-19 | Spring steel having superior fatigue life, and manufacturing method for same |
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-
2018
- 2018-07-27 CN CN201810842312.5A patent/CN110760748B/en active Active
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- 2019-07-19 WO PCT/CN2019/096726 patent/WO2020020066A1/en unknown
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- 2019-07-19 EP EP19841872.5A patent/EP3831970B1/en active Active
- 2019-07-19 US US17/261,457 patent/US20210164078A1/en not_active Abandoned
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