Metal treatment – Stock – Ferrous
Patent
1993-05-07
1994-05-31
Yee, Deborah
Metal treatment
Stock
Ferrous
148324, 420 15, 420 12, 428683, C22C 3836
Patent
active
053165969
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a roll shell material and a centrifugal cast composite roll which has excellent wear resistance and crack resistance.
BACKGROUND ART
Recently, the most widely used rolls for hot rolling mills, have been composite type rolls composed of an outer shell and a core material. The conventional method of producing these rolls is centrifugally casting technique, where the shell metal is first poured into the rotating mold then the core metal is added to the mold after shell solidification. Usually, wear resistant cast iron such as nickel-chromium alloyed grain iron (Ni-G) or high chromium iron (Hi-Cr) precipitating cementaite type carbide is used for the shell material, and gray iron or ductile iron is used for the core material.
For a demand for more severe rolling condition and for improvement of productivity in rolling, a roll having higher wear resistance and crack resistance has been required.
In view of such circumstance. Japanese Unexamined Patent Publication (Kokai) No. 60-124407 and Japanese Unexamined Patent Publication(Kokai) No. 61-177355 propose application of high Vanadium (V) iron for the shell material of the centrifugal cast roll.
PROBLEM TO BE SOLVED BY THE INVENTION
However, when the high Vanadium (V) iron is applied to the shell of the roll in the centrifugal casting method, V carbide having small specific gravity can segregate by centrifugal force to make the internal characteristics of the roll shell layer not uniform in the thickness direction. This tendency is more significant in greater rolls having greater thickness of the shell to cause a problem that such roll is not applicable for a practical roll.
Japanese Unexamined Patent Publication No. 58-87249 and Japanese Unexamined Patent Publication No. 1-96355 propose roll materials, in which highly alloyed steel or iron equivalent to a high speed steel is applied. However, Japanese Unexamined Patent Publication No. 58-87249 is directed to a shrink fitting or assembling roll to encounter a problem of slip between the sleeve and the arbor during rolling. On the other hand, Japanese Unexamined Patent Publication No. 1-96355 is only applicable for special manufacturing process, such as continuous casting for cladding method or so forth other than centrifugally casting process to encounter problems in its productivity and cost advantage.
In effect, upon production of the roll, although improvement of wear resistance can be achieved by applying a high carbon high V steel for the shell material, it may encounter a problem of not uniform properties in the shell due to occurrence of segregation of carbide by centrifugal force when the centrifugal casting method, which is commonly used for its high productivity and cost advantage, is employed.
It is an object of the present invention to provide a roll shell material and a centrifugal cast composite roll which has excellent wear resistance and crack resistance without any segregation even when productive and cost advantageous centrifugal casting method is employed by optimizing chemical compositions of the shell material and controlling composition of proeutectic carbide.
DISCLOSURE OF THE INVENTION
A roll shell material as defined in claim 1 is composed of C: 1.5.about.3.5%, Si: 1.5% or less, Mn: 1.2% or less, Cr: 5.5.about.12.0%, Mo: 2.0.about.8.0%, V: 3.0.about.10.0%, Nb: 0.6.about.7.0%, and satisfies the following formulae (1) and (2):
A roll shell material as defined in claim 2 is composed of C: 1.5.about.3.5%, Si: 1.5% or less, Mn: 1.2% or less, Cr: 5.5.about.12.0%, Mo: 2.0.about.8.0%, V: 3.0.about.10.0%, Nb: 0.6.about.7.0%, and further composed of one or both of Ni: 5.5% or less and Co: 10.0% or less, and satisfies the following formulae (1) and (2):
A roll shell material as defined in claim 3 is composed of C: 1.5.about.3.5%, Si: 1.5% or less, Mn: 1.2% or less, Cr: 5.5.about.12.0%, Mo: 2.0.about.8.0%, V: 3.0.about.10.0%, Nb: 0.6.about.7.0%, and further composed of one or two or more of Cu: 2.0% or less, W: 1.0% or less, Ti: 2.0%
REFERENCES:
patent: 5225007 (1993-07-01), Hattori et al.
Kawasaki Steel Corporation
Yee Deborah
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