Method of producing coated or plated steel sheet

A method of producing a coated or plated steel sheet, the method comprising:

• an oxidizing process of heating a blank sheet having a chemical composition containing, in mass %, Si:
• 0.10% or more and 2.00% or less, and Mn:
• 1.00% or more and 5.00% or less, under the following conditions:
• atmosphere:
• oxygen concentration of 1000 volume ppm or more and 30,000 volume ppm or less, and
• heating temperature:
• 600° C. or more;
• a reducing process of holding the blank sheet under the following conditions:
• atmosphere:
• hydrogen concentration of 8 vol % or more and 30 vol % or less,
• holding temperature:
• 700° C. or more, and
• holding time:
• 20 s or longer;
• a soaking process of holding the blank sheet under the following conditions:
• atmosphere:
• hydrogen concentration of 0.2 vol % or more and less than 8 vol %,
• soaking temperature:
• 700° C. or more and less than 900° C., and
• soaking time:
• 20 s to 300 s;
• a rapid heating process of heating the blank sheet under the following conditions:
• atmosphere:
• hydrogen concentration of 0.2 vol % or more and 30 vol % or less,
• average heating rate from the soaking temperature:
• 10° C./s or more, and
• maximum arrival temperature:
• the soaking temperature+10° C. or more;
• a cooling process of cooling the blank sheet under the following conditions:
• atmosphere:
• hydrogen concentration of 0.2 vol % or more and 30 vol % or less,
• residence time in a temperature range from the maximum arrival temperature in the rapid heating process to the soaking temperature:
• 20 s or shorter, and
• cooling stop temperature:
• 500° C. or less;
• and
• a coating or plating treatment process of carrying out a coating or plating treatment on one or both sides of the blank sheet to obtain the coated or plated steel sheet.