Metal treatment – Stock – Ferrous
Patent
1991-10-09
1992-10-20
Yee, Deborah
Metal treatment
Stock
Ferrous
148598, C21D 800
Patent
active
051566923
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for manufacturing steel wires for use in wire drawing, and particularly steel wires which are subsequently subjected to final wire drawing to form steel filaments which are used in the manufacture of steel cord wires.
BACKGROUND ART
Steel cord wires and bead wires which have generally been used in tires and similar products are twisted strands made by twisting a bundle of filaments of a high carbon steel, each steel filament having a diameter of around 0.2 mm. Steel filaments which are presently used for this purpose have a tensile strength on the order of 320 kgf/mm.sup.2.
The conventional process for manufacturing such steel filaments comprises the following steps: ##STR1##
In the final lead patenting (LP) step, a 1.2.phi. steel wire is heated to about 900.degree. C. and then dipped in a molten lead bath at around 600.degree. C. to adjust the tensile strength (TS) of the wire to 125 kgf/mm.sup.2. The resulting lead-patented steel wire is used as a starting material for the final drawing, and it is pickled and plated before it is finally drawn into a filament having a tensile strength of about 320 kgf/mm.sup.2. In the above-described process, the wire drawing reduction ratio (.epsilon.) attained under these conditions is around 3.2. A higher reduction ratio is desired in order to improve the strength of the wire, but it cannot be attained due to a decrease in ductility.
In co-pending Japanese Patent Application No. 63-169480 (1988), the present inventors proposed that wire drawability can be increased by performing the final lead patenting under such conditions that the resulting wire has a relatively low tensile strength (TS) of around 115 kgf/mm.sup.2. However, the wire drawing reduction ratio (.epsilon.) attainable in this method is at most .epsilon.=4.5, and the tensile strength of the resulting filaments is on the order of 380 kgf/mm.sup.2.
In the process described in Japanese Unexamined Patent Application Kokai No. 64-15322(1989), a thermo-mechanical treatment is applied in place of the final lead patenting treatment so as to refine the resulting pearlite blocks to an average size of about 6-77 .mu.m and improve the wire drawability of the wire. This process gives steel filaments having a tensile strength on the order of 400 kgf/mm.sup.2. However, after the thermo-mechanical treatment, the wire is subjected to recrystallization by heating again at a temperature in the austenitic range followed by slow cooling. Therefore, the refinement of the pearlite blocks cannot be achieved in a stable manner, and the process involves an increased number of steps, thereby requiring a prolonged processing period and leading to increased manufacturing costs. Moreover, the reduction of area of the steel filaments obtained after the final wire drawing is on the order of 30% which is rather low since the working has been applied in a high reduction ratio region. Therefore, the resulting filaments lack stability and are susceptible to breakage during twisting into cord wires.
Japanese Examined Patent Publication No. 57-19168(1982) which corresponds to Japanese Unexamined Patent Application Kokai No. 53-30917(1978) discloses a similar strengthening or toughening method of a carbon steel by a thermo-mechanical treatment. The steel material obtained in this method is a steel rod having a diameter of from 4.0 mm to 13.0 mm and it is used in the as-treated state without further wire drawing. The thermo-mechanical treatment employed in this method is performed by applying working with a reduction of area in the range of 10% to 40% to a metastable austenitic structure at a relatively low temperature (which is below 450.degree. C. and above the Ms point) followed by isothermal heat treatment to form a structure comprising fine ferrite and cementite phases. In this case, the refinement attained by the thermo mechanical treatment is a reduction of interlaminar distance, i.e., lamellar distance, of the pearlite structure. This publication does not refer to a reduction
REFERENCES:
patent: 4046600 (1977-09-01), Yamakoshi et al.
patent: 4604145 (1986-08-01), Kanabara et al.
patent: 4983227 (1991-01-01), Reinich et al.
Sumitomo Metal Industries Ltd.
Yee Deborah
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