Abstract: An object of the present invention is to make it possible, without necessitating an alkali pretreatment, to form a zinc oxide layer having excellent sliding properties on a hot dip galvanized steel sheet not subjected to alloying after galvanizing and thus having a relatively low degree of surface activity. Another object of the present invention is to make it possible to manufacture a hot dip galvanized steel sheet having higher area ratio of Zn oxide layer formed on a coating surface and larger thickness of the Zn oxide layer.

Abstract: The present invention has an object to provide a manufacturing method of a long large-diameter composite cemented carbide roll and a hot rolling method of steel using the same. The roll manufacturing method covers a composite cemented carbide roll formed by engaging with, and fixing to, a steel arbor, a sleeve comprising an outer layer made of a cemented carbide formed by integrating a plurality of previously sintered cylindrical formed members and an inner layer made of a steel material formed on the inner surface of the outer layer. The sleeve has a sectional area ratio So/Si of the sectional area So of the outer layer and the sectional area Si of the inner layer in a cross-section perpendicular to the rotation axis within a range of from 0.3 to 20. The sleeve has a length within a range of from 520 to 6,000 mm. When hot-rolling steel, the cemented carbide rolls of the invention are used as work rolls of at least one stand for a roughing mill and/or a finishing mill.