Metal treatment – Stock – Ferrous
Patent
1996-10-29
1998-04-14
Yee, Deborah
Metal treatment
Stock
Ferrous
420 15, C22C 3706, C22C 3836
Patent
active
057387346
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a roll shell material which has excellent wear resistance, crack resistance and a small friction coefficient and is free from segregation even if centrifugally cast and also exhibits satisfactory resistance against cobble cracks and surface deterioration resistance.
BACKGROUND OF THE INVENTION
Hitherto, high chrome cast iron, nickel alloyed grain cast iron, adamite and so forth have been employed as the material for rolls in a rolling mill. Subsequently, a high-speed steel roll material and rolls comprising the same have been developed in order to improve the wear resistance.
For example, a roll shell material has been disclosed in Japanese Unexamined Patent Publication (JP-A) No. 4-365836, which contains C: 1.5 to 3.5%, Si: 1.5 % or less, Mn: 1.2% or less, Cr: 5.5 to 12.0%, Mo: 2.0 to 8.0%, V: 3.0 % to 10.0% and Nb: 0.6 to 7.0%, which satisfies the following formulas (1) and (2): roll shell material being free from segregation of composition and structure of the outer shell of the roll even if the roll is centrifugally cast and exhibiting wear resistance and crack resistance.
Japanese Unexamined Patent Publication (JP-A) No. 6-256888 discloses a high-speed cast steel material containing graphite and further composed of C: 1.8 to 3.6%, Si: 1.0 to 3.5%, Mn: 0.1 to 2.0%, Cr: 2.0 to 10.0%, Mo: 0.1 to 10.0 %, W: 0.1 to 10%, one or both of V and Nb: 1.5 to 10 % and the remainder which is substantially composed of Fe. This high-speed east steel material has a small friction coefficient and is capable of preventing propagation of cracks therein.
Japanese Unexamined Patent Publication (JP-A) No. 6-335712 discloses a wear and scoring resisting roll for a hot rolling mill which is composed of C: 2.0 to 4.0%, Si: 0.5 to 4.0%, Mn: 0.1 to 1.5%, Ni: 2.0 to 6.0%, Cr: 1.0 to 7.0%, V: 2.0 to 8.0%, and further contains one or more of Mo: 0.3 to 4.0%, W: 0.3 to 4.0%, Co: 1.0 to 10.0%, Nb: 1.0 to 10.0%, Ti: 0.01 to 2.0%, B: 0.02 to 0.2% and Cu: 0.02 to 1.0%.
A hot rolled product is manufactured by heating, in a heating furnace, a slab manufactured by continuous casting or blooming and having a thickness of 130 to 300 mm or by receiving the hot slab as it is, followed by hot-rolling the slab in a toughening rolling mill and a finishing rolling mill to form the slab into a strip having a thickness of 1.0 to 25.4 mm, followed by winding the strip into a coil by a winding machine (a coiler) and cooling the coil, and followed by subjecting it to processes by a variety of refining lines.
The finishing rolling mill is usually in the form of a continuous rolling mill having five to seven 4-high rolling mills arranged in series. Although 6-stand mills have been employed in the 30's of the Showa era, the majority of mills has employed seven stands in the 40's of the Showa era to improve the productivity and to be adaptable to a trend of enlarging the size of the coil. The finish rolling process sometimes encounters a so-called accident in drawing such that two plates are stacked for some reason between the stands and the stacked plates are unintentionally rolled. In particular, the probability of an accident of the foregoing type is increased in the backward stands. In a 7-stand finish rolling mill, an accident of the foregoing type takes place at the fifth and following stands. If the cobble accident happens, the temperature of the surface of the roll is locally raised owning to heat generated attributable to the friction caused from the abnormal rolling operation and that attributable to the rolling operation. When the roll is cooled with water, thermal impact sometimes generates cracks on the surface of the roll. The cobble cracks occur as described above. In general, if cobble accident happens, the roll is changed to investigate whether a crack of the roll has occurred due to the accident. If a crack is detected, the roll is ground until the crack is removed, thus resulting in an increase in the cost of the roll. If the existence of a crack is overlooked and the roll is ag
REFERENCES:
patent: 3929471 (1975-12-01), Akahori et al.
patent: 5225007 (1993-07-01), Hattori et al.
patent: 5316596 (1994-05-01), Kataoka
Ichino Kenji
Koseki Tomoya
Sawa Yoshitaka
Kawasaki Steel Corporation
Yee Deborah
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