The present invention concerns a method of producing long-length articles from hot-rolled carbon steel, such as, wire, strip and rolled sections.
Methods of producing long-length articles from hot-rolled steel, such as high-strength wire, are well known in the prior art. For example, a hot-rolled wire rod is first subjected to heat treatment, whereupon the surface of the heat-treated rod is prepared for subsequent deformation by descaling and applying a sublubricant coat of lime, borax or copper. The rod is then subjected to cold plastic deformation, such as drawing, to obtain wire of a requisite cross-section.
Heat-treating is employed for obtaining a metal structure which would enable subsequent cold deformation, accomplished in stages, to be effected with heavy overall reductions (up to 75-90%) which are needed to provide a preassigned strength.
To prevent wire embrittlement, cold plastic deformation is alternated with additional heat-treating operations (annealing or patenting).
Depending on the designation of high-strength wire, the heat-treating operations (normalizing, patenting or quenching with subsequent tempering) as well as cold plastic deformation schedules, pass or overall reductions in particular, may vary during drawing.
In a number of cases the long-length articles -- wire -- are produced by only heat-treating the wire rod, e.g. by quenching with subsequent tempering, bainitizing, etc. However, wire made in the above manner, featuring perfect elongation and relaxation resistance, corrodes readily and has inadequate strength.
The wire produced by the use of only cold plastic deformation without preliminary heat treatment (such as patenting) possesses an adequate strength but has a very low state of plastic characteristics. Moreover, the drawing of such wire often leads to breaks because of its enhanced brittleness.
Known in the art is a method of producing long-length articles by plastic deformation of wire rods with simultaneous heating. Usually the above method is applicable to the so-called "hard-to-work" high-alloy (with chromium, titanium or tungsten) steels. However, in the case of using carbon steel as well, the metal should be always subjected to a preliminary heat-treating operation -- annealing or normalizing.
When producing reinforcement high-strength wire, low-temperature tempering is used as a final operation to increase its ductility.
Also known is a method which consists essentially in that the long-length articles -- wire -- after preliminary heat-treating (patenting) and subsequent cold deformation are subjected to axial tension and concurrent heating to a temperature within the range of 300-400.degree.C. The latter operation, during which the processes of polygonization and blocking of dislocations by admixture atoms (nitrogen, oxygen, carbon) take place, contributes to the enhancement of rheological properties (relaxation resistance) of reinforcement and spring wire (see, e.g. British Pat. Nos. 748357, 969191, 969192. The wire subjected to the above operation features high physicomechanical characteristics and rheological properties.
Similar properties are obtainable by a more efficient method, wherein immediately after the last cold plastic deformation of a heat-treated (patented) wire rod, it is subjected to a subsequent plastic deformation combined with concurrent heating to a temperature within a range of 350.degree.-500.degree.C and axial tension.
This operation of the plastic deformation of wire heated concurrently to a temperature in the 300.degree.-600.degree.C range will be referred to as warm deformation.
Thus, all the known methods of producing high-strength wire are always characterized by heat-treatment of wire rod prior to drawing. The heat-treating operation is conducted on cumbersome and low efficiency equipment in heat-treating departments, and plastic deformation (drawing) is conducted in drawing shops. This fact creates considerable time loss and a high cost of in- or intrashop transportation resulting in a reduction in labour productivity and an increase in production cost.