Metal treatment – Process of modifying or maintaining internal physical... – With casting or solidifying from melt
Patent
1998-04-01
2000-02-15
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
With casting or solidifying from melt
148547, 148593, 266102, C21D 810
Patent
active
060248084
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a seamless steel pipe manufacturing technology, more particularly, the invention relates to a method and apparatus for manufacturing a seamless steel pipe having excellent strength, toughness and corrosion resistance. The said apparatus is not only fitted for performing the said manufacturing method, but also suitable to be used broadly for manufacturing various kinds of seamless steel pipes.
BACKGROUND ART
In the steel industry, which is characterized by huge facilities and a large energy consumption, a combination of steps in the manufacturing process, socalled "on-line processing", has been developed in order to simplify the process and reduce the energy consumption. In manufacturing of the steel plate (steel strip and thick plate), a thermo-mechanical treatment in the on-line process has been adopted widely. The conventional heat treatment (such as quenching, tempering, etc.) with using apparatus, which are placed separately from the plate rolling line, is considerably decreased.
On the contrary, in the field of the seamless steel pipe manufacturing, most of the pipes are still treated in a so-called "off-line process", wherein apparatus such as a heating furnace, a cooling equipment and a tempering furnace are installed on the separate line, from the pipe manufacturing line, because the requirement for reliability and quality of the pipe product is very severe. Naturally, it is difficult to reduce the energy consumption in such manufacturing process.
A considerably large space is necessary for the off-line process carried out in the conventional factory layout, since differences of processing speed between each independent step of the process require spaces such as a billetyard to keep the billet before piercing, a space for temporal storage of the pipe before heat treatment. Furthermore, the manufacturing cost increases inevitably because of the conveyance, since the materials should be conveyed from a step to another step, transportation means such as a conveyor, a crane, a truck and operation of loading and unloading, are required.
Recently, in the field of the seamless steel pipe manufacturing, there is a tendency to introduce a so-called "direct quenching process", wherein pipes are quenched immediately after hot working with utilization of the heat retained during the hot-working. By use of this process, it is able to reduce the manufacturing cost remarkably, because a heating furnace for quenching is unnecessary.
For example, as disclosed in Publication of Japanese Patent Application (referred to as PJPA here after) Nos. 56-166324, 58-120720, 58-224116, 56020423, 60-033312, 60-075523 seamless steel pipes, including the direct quenching process in which the steel pipes are forcibly cooled immediately after finish rolling are proposed, and some of these methods have been put into practical use. Unfortunately, products obtained through the direct quenching process have a disadvantage, that the toughness and corrosion resistance of those are inferior to those of the conventional products, which are quenched and tempered in the off-line process, because the products treated by the direct quenching usually have a coarser grain size in microstructure than that of the conventional products treated by quenching and tempering in the off-line process.
In the field of the steel plate manufacturing, as mentioned above, various methods of the direct (on-line) heat treatment of the plate after hot rolling are proposed. For example, PJPA Nos. 62-139815, 63-223125 and 64-055335 disclose methods of directly quenching and tempering of steel plates, which have been worked in the non-recrystallization state and then recrystallized in order to refine grain structure. Since these methods require heavy reduction rolling at a relatively low temperature area, i.e., the non-recrystallization area, it is difficult to be applied to steel pipe rolling, which is accompanied by more complex plastic deformation than that of the plate rolling. For example, steel pipe rolling
REFERENCES:
patent: 5186769 (1993-02-01), Hunt et al.
H. Biller: "Das Walzen Nahtloser Rohre-Probleme der Verfahrensauswahl", Stahl u. Eisen, vol. 106, No. 9, May 5, 1986, pp. 431-437.
K. Oberem: "Herstellung nahtloser Rohre", Stahl u. Eisen, vol. 104, No. 25/26, Dec. 17, 1984, pp. 1339-1343.
The Iron and Steel Institute of Japan vol. 71, No. 8, pp. 40-47, Jun. 1985.
Kondo Kunio
Okada Yasutaka
Tanimoto Seiji
Sumitomo Metal Industries Ltd.
Yee Deborah
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