Method for manufacturing hot dip galvanized steel sheet

摘要

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. Specifically, the present invention provides a method for manufacturing a hot dip galvanized steel sheet comprising: subjecting a steel sheet to hot dip galvanizing and subsequent temper rolling; bringing the steel sheet into contact with acidic solution having pH buffering capacity; retaining the steel sheet for 1 second to 60 seconds after the contact with the acidic solution; and rinsing the steel sheet with water, to form a zinc oxide layer on a coating surface of the steel sheet, characterized in that the method further comprising:;carrying out the temper rolling by either rolling the steel sheet first with a dull roll having Ra≧2.0 μm at rolling reduction rate ≦5% and then with a bright roll having Ra≦0.1 μm at rolling reduction rate ≦3% or rolling the steel sheet first with a bright roll having Ra≦0.1 μm at rolling reduction rate ≦3% and then with a dull roll having Ra≦2.0 μm at rolling reduction rate ≦5%.

主权项

1. A method for manufacturing a hot dip galvanized steel sheet comprising: subjecting a steel sheet to hot dip galvanizing and subsequent temper rolling; bringing the steel sheet into contact with acidic solution having pH buffering capacity; retaining the steel sheet for 1 second to 60 seconds after the contact with the acidic solution; and rinsing the steel sheet with water, to form a zinc oxide layer on a coating surface of the steel sheet, wherein the method further comprising:
carrying out the temper rolling by either rolling the steel sheet first with a dull roll having Ra≧2.0 μm at rolling reduction rate ≦5% and then with a bright roll having R≦0.1 μm at rolling reduction rate ≦3% or rolling the steel sheet first with a bright roll having Ra≦0.1 μm at rolling reduction rate ≦3% and then with a dull roll having Ra≧2.0 μm at rolling reduction rate 5%.