This invention relates to the hot rolling of elongated product, such as steel bars. More specifically, the invention concerns means and methods of in-line heat treating and finishing of the product.
Various systems are known for heat treatment of hot rolled products, such as bars. However, when the billets or blooms are produced in a caster such processes and facilities normally utilize off-line heat treating of the cast and hot rolled stock. It is known to perform certain limited heat treatments on the cast product before rolling. For example, U.S. Pat. No. 5,634,512 describes in-line thermal surface treatment of continuously cast blooms using cooling sprays to produce a bloom surface temperature of about 400-900xc2x0 C. after tempering caused by the hot core of the bloom. U.S. Pat. No. 4,786,338 discloses a system wherein product from a finishing mill is followed by a cooling line made up of a quenching zone and a temperature recovery zone before being passed to cooling beds for obtaining low temperature toughness. Japanese Published Patent Application No. Hei 63-149316 describes a method of producing steel bars and wire rods through continuous hot rolling for obtaining a directly spheriodized structure in which spheriodizing annealing is facilitated or possibly even eliminated.
Such prior art has the drawback of being limited in the capability of producing a wide variety of metallurgical structures in the rolled stock. Off-line heat-treatments to produce various microstructures normally require treatment times of 10-15 hours.
The apparatus of this invention is disposed in an intermediate position between a hot-rolling mill and a cold-finishing area for cleaning the rolled stock, cutting it to final form, bundling and packaging it for in-line production of a final product. The apparatus includes, in-line, and downstream of a hot rolling mill train, a thermocontrolled rolling device including a controlling temperature device and a sizing mill, shears, a quenching box, optionally an induction heater, a layers preparation system where layers of cut stock, such as bars, are consolidated prior to transfer to an annealing furnace, and thereafter to a cooling bed.
By selection of particular ones of these apparatus elements for use in particular cases of heat treatment, and by selection of the conditions of heat treatment, a great variety of product structures can be achieved, for example, a spheroidized steel product, a shearability or workability annealed product, a recrystallation annealed product, a solution annealed product, a quenched product (martensitic or bainitic quenching), or a quenched and tempered (quenched and stress-relieved) product.
With practice of the in-line heat treatments of this invention, prior art off-line treatment times of 10-15 hours can be reduced to about 1 to 2 hours.
For a better understanding of the invention, its operating advantages and the specific objectives obtained by its use, reference should be made to the accompanying drawings and description which relate to preferred embodiments thereof.