Classifications

• • 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
  • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron

Definitions

• the invention relates to a long product such as a wire or a bar for the manufacture by cold forming, in particular by cold striking, of processed products such as bolts, said processed products having a tensile strength greater than 1000 MPa and less than 1170 MPa and a yield strength R e0.002 , greater than 900 MPa.
• steel 38C4 is generally used (according to AFNOR standard) containing approximately 0.38% carbon and approximately 1% chromium.
• the steel is hot rolled to make a wire which is subjected to a globulation treatment to make it suitable for cold striking, it is drawn to give it the desired final diameter, then cut sections that are shaped by cold striking, the parts obtained are then hardened and returned and as the hardening treatment deforms the parts, the bolts are straightened.
• This technique has the disadvantage of comprising numerous operations, in particular two heat treatments, and of being expensive.
• 38C4 steel containing 1% chromium is expensive; in addition, it contains a high carbon content, which makes it relatively sensitive to the delayed rupture caused by hydrogen.
• the steel is hot rolled, it is optionally drawn, it is put into a crown and the crowns are subjected to a quenching and tempering treatment. Plots are sheared and shaped by cold striking; there is no need to heat treat or straighten the parts.
• This technique has the advantage of reducing the manufacturing operations, but on the one hand the steel used which is of the 38C4 type has the same drawbacks as in the previous technique and on the other hand the crown heat treatment leads to heterogeneities features along the wire; this results in dispersions of mechanical characteristics on the bolts.
• the object of the invention is to propose a long product such as a wire or a bar for cold forming, in particular by cold striking, of class 10.9, which makes it possible to eliminate the heat treatment on the parts, at the developed state, after cold forming, which has homogeneous characteristics over its entire length, which is economical and which has improved resistance to cracking by hydrogen.
• the subject of the invention is a long product such as a wire or a bar for the manufacture by cold deformation, in particular by cold stamping of produced products such as bolts, said produced produced having resistance to tensile strength greater than 1000 MPa and less than 1170 MPa and an elastic limit R e0.002 , greater than 900 MPa, made of steel in the quenched and tempered state containing by weight: the rest being iron and impurities resulting from the fusion of raw materials.
• the steel may also contain 0.12% to 0.25% nickel and 0.04% to 0.15% molybdenum.
• the chemical composition of the steel comprises: the rest being iron and impurities resulting from the fusion of raw materials.
• the wire or bar has a martensitic micrographic structure returned with possibly islands of bainite returned.
• the quenching and tempering are carried out continuously.
• the sulfur content is limited to 0.015% at most but in the steels intended to produce parts which will be machined, the sulfur content can go up to 0.025%, because this element improves the machinability of the steels.
• Phosphorus is an embrittling element and its content must remain below 0.015%.
• the steel may contain nickel and molybdenum. These elements have a favorable effect on the hardenability and it is required that their contents are between 0.12% and 0.25% for nickel and between 0.04% and 0.15% (preferably 0.08%) for the molybdenum.
• the steel is quenched with aluminum and contains low levels of this element. It also contains nitrogen introduced by the process.
• the steel which has just been defined is used in the form of a semi-finished product such as a billet which is rolled on a wire train to produce a wire with a diameter of for example between 5.5 mm and 18 mm .
• the rolled wire is then drawn to obtain the final diameter and a good surface condition; the diameter can be for example between 4.5 mm and 17.5 mm.
• the wire In the austenitization oven the wire is brought to a temperature above 900 ° C, temperature at which it remains less than 5 min. This very short time has the advantage of not enlarging the austenitic grain, which in the end makes it possible to obtain a very fine structure favorable to good resistance to fatigue, good resilience and an aptitude for shaping. cold.
• the controlled atmosphere makes it possible not to decarburize on the surface.
• the quenching is carried out with water containing polymers of the PAG or PVP type or with accelerated quenching oil.
• Water is used with additives or oil to avoid causing streaks on the wires.
• Tempering is carried out at a temperature between 450 ° C and 600 ° C.
• a wire is thus obtained, the structure of which is returned martensite possibly containing islands of returned bainite.
• This wire has a tensile strength Rm between 900 MPa and 1000 MPa, an elastic limit R e0.002 , greater than 850 MPa and a necking greater than 65%.
• the yarn thus obtained is of class 10.9; it has the advantage of not requiring heat treatment after cold stamping. As it was produced by a continuous process, it has very homogeneous characteristics over its entire length. The chromium content being low, it is inexpensive. Thanks to its low carbon content, it has good resistance to hydrogen cracking. Finally, this wire has a ductility at least as good as that of 38C4 globulated steel wires.
• the wire according to the invention exhibited limit crushing rates of between 70% and 76% while the globulized 38C4 wire had limit crushing rates between 60% and 80% although its resistance is between 530 and 540 MPa only.
• This wire can be used for any type of shaping by cold deformation and to make any type of part produced cold. It can for example be used in cold bending or in cold forging or in cold drawing.
• the heat treatment must be carried out continuously, but the austenitization oven can be replaced by an induction heating device.
• any type of continuous device can be used for quenching and for tempering.
• steel grade claimed can also be used to manufacture quenched quenched bars intended for cold deformation.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Heat Treatment Of Articles (AREA)
• Forging (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=9420633

Family Applications (1)

Country Status (4)

Cited By (5)

Citations (3)

• 1991
  • 1991-12-30 FR FR9116310A patent/FR2685708B1/fr not_active Expired - Fee Related
• 1992
  • 1992-10-26 DE DE1992614421 patent/DE69214421T2/de not_active Expired - Fee Related
  • 1992-10-26 EP EP19920402902 patent/EP0550294B1/de not_active Expired - Lifetime
  • 1992-10-26 ES ES92402902T patent/ES2092656T3/es not_active Expired - Lifetime

Patent Citations (3)

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