To manufacture a hot dip galvanized steel sheet in which the occurrence of blisters in a coating film can be efficiently prevented with certainly over the whole steel sheet.
In the method of manufacturing a hot dip galvanized steel sheet for undercoat painting, in which a hot rolled steel sheet is pickled and then annealed and plated by means of a continuos hot dip galvanizing line temper rolling is applied at ≥0.1% elongation percentage after plating and then heat treatment is carried out at 200-400°C for ≥3 sec. Owing to the above temper rolling at ≥0.1% elongation percentage, fine cracks are introduced into a galvanizing film. Moreover, owing to the above heat treatment at 200-400°C for ≥3 sec after the temper rolling, hydrogen occluded in the steel sheet in the reduction annealing stage in the continuous hot dip galvanizing line is released out of the steel sheet, and as a result, the occurrence of blisters in a coating film in a painting stage can be prevented.
INAGAKI JUNICHI
SAGIYAMA MASARU
YAMASHITA TAKASHI
SHIMADA SOICHI
Next Patent: CRYSTALLINE ORIENTED HARD COATED MEMBER