Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
  • C23C2/06—Zinc or cadmium or alloys based thereon
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
  • F16F1/00—Springs
  • F16F1/02—Springs made of steel or other material having low internal friction; Wound, torsion, leaf, cup, ring or the like springs, the material of the spring not being relevant
  • F16F1/024—Covers or coatings therefor

Definitions

• the present invention relates to a spring wire of a hard drawn pearlitic steel.
• Chromium-silicon springs are conveniently made from oil-hardened steel wires. Such steel wires are heated above the austenitizing temperature to a temperature ranging from 850 to 950 °C, and subsequently quenched in an oil bath so that a martensitic structure is obtained. The oil-hardened martensitic steel wires are finally subjected to a tempering treatment, e.g. in a lead bath at a temperature ranging from 350 to 550 °C. The duration and temperature of this tempering treatment determine the ultimate hardness and the final tensile strength of the steel wires.
• springs are manufactured as follows : the steel wires are coiled, stress-relieved at about 400 to 450 °C, subjected to a shot-peening treatment in order to create compressive stresses at the surface and the coiled shot-peened springs are again stress-relieved at about 250 °C.
• Coating oil-hardened steel wires with zinc has disadvantages.
• a patenting treatment instead of oil-hardening (i.e. austenitizing in the range of 850 to 950 °C and transforming from austenite to pearlite/ferrite at about 550 to 620 °C, e.g. in a lead bath or in a fluidized bed installation) followed by galvanizing and hard drawing may lead to pearlitic steel wires with acceptable mechanical properties, but this technique, although well known in other related fields, has not been applied to spring wires because of the relatively poor coilability of galvanized spring wires.
• a spring wire in a hard drawn pearlitic state covered with a zinc alloy coating has a carbon content between 0.45 and 0.75 % (preferably between 0.55 and 0.75 %, e.g. 0.55 %, 0.65 %, or 0.70 %), a silicon content between 1.00 and 1.60 %, and a chromium content between 0.50 and 1.50 % (preferably between 1.00 and 1.50 %).
• the steel wire may optionally have a vanadium content ranging from 0.0 to 0.35 %.
• the zinc alloy coating has an aluminium content between 2 and 12 %, preferably, the metallic fraction of the zinc alloy coating has an aluminium content between 4 and 6.5 %.
• the zinc alloy coating further has a wetting agent in an amount less than 0.1 % of the zinc alloy.
• a hard drawn pearlitic structure refers to a steel wire that is cold drawn by means of e.g. drawing dies and which has a structure of pearlite and/or ferrite. The higher the carbon content, the higher the content of pearlite in comparison with ferrite.
• the chromium and silicon contents are chosen in order to obtain a spring wire with a sufficient heat-resistance. Below the mentioned ranges of chromium and silicon, heat-resistance becomes insufficient, above the mentioned ranges of chromium and silicon, the final hard drawing operation may become difficult due to a decrease in ductility and due to the fact that the time necessary for the transformation from austenite to pearlite during patenting may become unduly large.
• the manganese content ranges from 0.30 to 1.20 %, preferably from
• the phosphorous and sulfur contents are preferably kept as small as possible, e.g. each below 0.035 %, e.g. each below 0.025 % or e.g. the sum of phoshorous and sulfur below 0.025 %.
• Other elements such as copper are also preferably kept to the level of unavoidable impurities. All mentioned percentages are percentages by weight of the overall steel composition.
• the aluminium content ranges from 2 to 12 %, e.g. in the metallic fraction of the zinc alloy coating, the aluminium content ranges from 4 to 6.5 %, and is preferably about the eutectic value of 5 %.
• a wetting agent is present in an amount sufficient to have wetting of the substrate steel by the alloy. Amounts smaller than 0.1 % are usually sufficient.
• the wetting agent can be cerium in an amount ranging from 0.01 % to 0.05 % and/or lanthanum in an amount ranging from 0.01 % and 0.06 %. All mentioned percentages are here percentages by weight of the zinc alloy coating.
• the inventors have discovered that, in great contrast with a convenient galvanizing operation, the operation with zinc aluminium alloy leads to improved coilability. Indeed, in a convenient galvanizing operation, uncontrolled growth of the iron-zinc reaction layer due to the presence of silicon limits coilability, while the reaction layer in the zinc aluminium coating shows improved adhesion and deformability and therefore enhances the coilability of the wire.
• the aluminium present in the zinc-aluminium alloy probably forms very quickly a thin reaction with the iron of the substrate steel and with the zinc during the coating operation and prohibits any further initiation or growth of other reaction layers.
• the chromium silicon steel coated with the zinc aluminium alloy only has a thin aluminium iron reaction layer of a rather uniform thickness around the steel. No other substantial layer of brittle zinc iron reaction layer is present.
• This aluminium iron reaction layer provides a good adherence between the zinc-aluminium coating, on the one hand, and the substrate steel, on the other hand, so that the zinc- aluminium strongly sticks to the steel wire during coiling.
• the aluminium zinc coating has a good deformability and a low friction coefficient so that hard drawn spring wires coated with the aluminium zinc coating exhibit an improved coilability.
• a spring wire according to the present invention is made as follows.
• a wire rod with following steel composition is chosen :
• the wire rod is hard drawn to an intermediate diameter of about
• the thus coated wire is hard drawn to a final diameter of 1.40 mm. At this final diameter the spring wire still has a zinc aluminium coating in a thickness ranging from 50 to 100 g/m 2 . Following mechanical properties have been determined on this spring wire as drawn :
• An invention spring wire i.e. a chromium-silicon spring wire with an aluminium-zinc coating has been compared with a stainless steel wire and with a galvanized steel wire.
• n a 8
• n t 10
• the speed of coiling has been set to 80 springs per minute and the standard deviation ⁇ on the free wire length has been used as the parameter for coilability.
• the table hereunder summarizes these results.
• an invention spring wire shows the same level of coilability as a non- coated stainless steel wire and an improved level of coilability in comparison with a galvanized steel wire. In addition thereto, no flaking occurred with an invention spring wire.
• the manufactured invention spring wire combines the advantages of heat-resistant spring steel wires with the advantages of metal-coated spring steel wires.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Springs (AREA)
• Wire Processing (AREA)

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• 1997
  • 1997-04-11 WO PCT/EP1997/001879 patent/WO1997042352A1/en active Search and Examination
  • 1997-04-11 EP EP97920689A patent/EP0958395A1/de not_active Withdrawn

Non-Patent Citations (1)

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