Metal treatment – Stock – Ferrous
Patent
1992-02-05
1993-05-25
Yee, Deborah
Metal treatment
Stock
Ferrous
148598, C21D 806, C22C 3800
Patent
active
052136329
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process enabling a high-strength strain-hardened steel wire to be obtained which is usable in particular for making reinforcing strands and cables of elastomeric articles such as pneumatic tires; it also relates to the reinforcing elements (strands and cables) produced from wires obtained by such a process.
The strands and cables for the reinforcing of pneumatic tires are usually composed of steel wires comprising, in addition to iron:
These wires, whose diameter is between approximately 0.10 and 0.50 mm, more generally between 0.15 and 0.40 mm, are manufactured from a wire called "rod wire" of standard diameter of 5.5 mm, by wire drawing in several steps with intermediate thermal treatment or patenting. The conventional process comprises the following steps:
application of a first series of wire-drawing passes in order to bring the wire to a diameter in the vicinity of 3 mm (level of cross-section reduction of approximately 70%);
patenting, for example lead patenting in order to give the wire a drawability capacity again;
application of a second series of passes (level of cross-section reduction of approximately 85 to 94%);
brassing patenting;
application of a third series of wire-drawing passes in order to attain the final diameter desired (level of final cross-section reduction of 90 to 96%, even 97%).
In certain circumstances, for ordinary steel grades and depending on the final diameter desired, the three first steps may be replaced by a single wire-drawing step to a diameter of approximately 1.35 to 1.80 mm.
It should be noted that, generally, the more the diameter is reduced the greater may be the applied level of cross-section reduction.
Conventional wires of ordinary or standard quality are distinguished from second-generation wires called high-strength wires. These two types of wire are both obtained from steel chosen from within the abovementioned composition, by causing the carbon content and, optionally, the final level of cross-section reduction to be varied.
The ordinary quality wires which have, for example, a typical fracture strength of 2850 MPa are obtained from a steel having 0.72% (+0.02) carbon with application of a level of final cross-section reduction of 95 to 96.5%.
The high-strength wires are obtained from a steel having 0.82% (.+-.0.02) carbon with application of a final level of reduction of between 96 and 97%, the latter value being in practice only attained very occasionally. They have a fracture strength which can reach 3200 to 3450 MPa. However, the latter steel grade comes dangerously close to the metal of a physical limit called "eutectoid point" beyond which brittle phases of proeutectoid cementite appear, rendering the wire drawing and especially the stranding virtually impossible because of the high number of breaks. This limit, which depends on the diameter, increases as the diameter decreases and is difficult to determine insofar as a certain quantity of wire may pass the axial deformation test in the course of the wire drawing, but not the deformation stresses imposed during the assembling operations.
The manufacture of high-strength wires therefore requires being surrounded by precautions, which increases the cost, as much to the steelmaker, for the supplying of a rod wire free of segregations (brittle phases), as to the cable manufacturer during the patenting, wire-drawing, stranding and cabling operations.
Within the range of hard and medium steels (carbon content>0.4%) and, more particularly, within the composition mentioned, usually used for pneumatic tire reinforcing wires: C content of 0.68 to 0.84% (even 0.6 to 0.9%), the high strengths are always obtained with high carbon contents, although research has been carried out in parallel in order to improve the strain-hardening capacity, which also moves in the direction of high strength.
Thus, Japanese Patent No. 60.152,659 relates to a steel wire usable as reinforcing for pneumatic tires, the said steel having the following composition:
The low P and S contents are presente
REFERENCES:
patent: 3617230 (1971-11-01), Richards et al.
patent: 4889567 (1989-12-01), Fujiwara et al.
Peeters Luc
Pelletier Jean B.
Sodetal Sarl
Yee Deborah
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