METHOD FOR PREVENTING OCCURRENCE OF TEMPER COLOR IN BOX ANNEALING

摘要

PROBLEM TO BE SOLVED: To reduce the occurrence of temper color in subjecting a steel-sheet coil to box annealing for softening or stress relieving. SOLUTION: In applying box annealing to the steel-sheet coil under reducing- gas atmosphere: the steel-sheet coil is temporarily held, in the course of temperature-raise to soaking temperature, in the temperature region of 350-430 deg.C to exclude the moisture adhering to the steel-sheet surface and the moisture resultant from the reduction of iron oxides at the steel-sheet surface while applying through vaporization; and the temperature-raise to soaking temperature is restarted when the dew point of the atmosphere gas becomes <=-20 deg.C.