Steel sheet for hot press forming, method of producing steel sheet for hot press forming, hot pressed member, and method of producing hot pressed member

A method of producing a steel sheet for hot press forming, the method comprising:

• immersing a base steel sheet in a hot-dip coating bath for 1 s or more, wherein the hot-dip coating bath comprises a chemical composition containing
• Si:
• 7 mass % to 11 mass %,
• Mg:
• 0.6 mass % to 1.9 mass %,
• one or both of Ca and Sr:
• in total, 1.0% to 10% of Mg in atomic concentration, and
• Fe:
• 0 mass % to 5 mass %,
• with the balance being Al and inevitable impurity;
• and
• cooling to the solidification point of the hot-dip coating bath at an average cooling rate of 20° C./s or less.

A hot pressed member comprising:

• steel material;
• an Al—Fe intermetallic compound layer formed on both sides of the steel material;
• and
• an oxide coating layer formed on the Al—Fe intermetallic compound layer and containing Mg and one or both selected from Ca and Sr, wherein
• diffusible hydrogen concentration in the steel material is 0.25 mass ppm or less.

A method of producing a hot pressed member, the method comprising:

• heating a steel sheet for hot press forming;
• and
• hot press forming the steel sheet for hot press forming heated in the heating, wherein
• the steel sheet for hot press forming comprises a base steel sheet and a coated layer on both sides of the base steel sheet,
• the coated layer comprises a chemical composition containing
• Si:
• 7 mass % to 11 mass %,
• Mg:
• 0.6 mass % to 1.9 mass %,
• one or both of Ca and Sr:
• in total, 1.0% to 10% of Mg in atomic concentration, and
• Fe:
• 0 mass % to 30 mass %,
• with the balance being Al and inevitable impurity, wherein
• concentration of Mg solute in Al phase in the coated layer is less than 1 mass %, and
• average thickness of the coated layer is 10 μm or more and 30 μm or less on each side of the base steel sheet, and
• in the heating,
• temperature is increased from a heating start temperature of 50° C. or less to a heating temperature that is from the Ac3 transformation temperature of the base steel sheet to 1000° C.