Metal treatment – Stock – Ferrous
Patent
1998-07-14
2000-08-22
Yee, Deborah
Metal treatment
Stock
Ferrous
148333, 148334, 148530, 148532, 148534, 148537, 148599, 148598, 148595, 428598, 428595, 428606, C21D 806, C22C 3818, C22C 3812
Patent
active
061066370
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns ready-to-use metal wires and methods for obtaining said wires. These ready-to-use wires are utilized, for example, to reinforce plastic or rubber articles, and in particular pipes, belts, plys and pneumatic tires.
The term "ready-to-use wire" as employed in this application means, in a manner known in the field, that this wire can be used for the proposed application without subjecting it to a heat treatment that could modify its metallurgical structure, and without subjecting it to deformation of its metal substance, for example, to a drawing process that can modify its diameter.
Patent application WO-A-92/14811 describes a method for obtaining ready-to-use wire comprising a steel substrate whose structure involves more than 90% cold-hammered annealed martensite, the steel having a carbon content of not less than 0.05% and not more than 0.6%, this substrate being coated with a metal alloy other than steel, for instance a brass alloy. The method for obtaining this wire includes a hardening treatment on a cold-hammered wire, involving heating the wire above transformation point AC3 to give it a homogeneous austenitic structure and then quick-cooling it at the rate of at least 150.degree. C./second, below the end point of the martensitic transformation. After this hardening treatment, at least two metals are deposited on the wire, and the wire is heated to stimulate by diffusion the formation of an alloy of these two metals, generally brass. The wire is then cooled and cold-hammered. The method described in this document includes the following specific advantages: perlitic steel; ready-to-use wire thus obtained; breaks; holds down production costs.
However, the method described in this document has the following drawbacks: coating does not always correspond precisely to the temperature necessary to obtain sufficient strength prior to drawing. of the temperature variation introduced following the inevitable dispersion of the heating systems. necessary to cool it at high speed in order to obtain a structure that is totally or almost totally martensitic. If the cooling speed is too slow, phases other than martensite can appear, such as bainite, for example. This high hardening speed is a major manufacturing constraint.
It is generally known that, in the methods for fabricating martensitic steel pieces, the addition of an alloy element such as vanadium or chromium makes it possible to improve the hardenability and strength following the precipitation of carbonitrides and/or vanadium or chromium carbides during annealing. However, the usual treatment times are several tens of minutes, even several hours, so as to permit precipitation.
SUMMARY OF THE INVENTION
It has been determined, quite unexpectedly, that the precipitation in the form of carbonitrides and/or carbides of an alloy element such as vanadium, molybdenum or chromium could take place rapidly in wires with a diameter under 3 mm, and that this precipitation during annealing made it possible to avoid the above cited drawbacks a) and b), and the presence of these alloys during hardening made it possible to avoid drawback c) cited above, by permitting gentler hardening.
Consequently, the invention covers a ready-to-use metal wire with the following characteristics: 0.2% by weight and not more than 0.6% by weight; the steel also contains at least one alloy element chosen from the group consisting of vanadium, molybdenum and chromium, the steel containing not less than 0.08% and not more than 0.5% by weight of the alloy element or of all the alloy elements combined; annealed martensite;
This ready-to-use wire is preferably coated with a metal alloy other than steel, deposited on a microalloy steel substrate with the abovementioned characteristics.
The method according to the invention to produce this ready-to-use wire is characterized by the following points: less than 0.2% by weight and not more than 0.6% by weight; the steel also contains at least one alloy element chosen from the group comprised of va
REFERENCES:
patent: 5167727 (1992-12-01), Kim et al.
patent: 5261974 (1993-11-01), Hyodo et al.
patent: 5503688 (1996-04-01), Arnaud et al.
Arnaud Jean-Claude
Depraetere Eric
Francois Marc
Serre Raoul
Michelin & Cie
Yee Deborah
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