Manufacturing method for hot press formed steel member

A method for manufacturing a hot press formed steel member, the method comprising heating a steel sheet and subjecting the steel sheet to at least one time of hot press forming, the steel sheet comprising, as a chemical composition in mass percent,

• C in a content of 0.15% to 0.4%;
• Si in a content of greater than 1.0% to 1.65%;
• Al in a content of 0.5% or less, excluding 0%;
• Mn in a content of 1% to 3.5%;
• Ti in a content of 0.10% or less, excluding 0%;
• B in a content of 0.005% or less, excluding 0%;
• and
• iron,
• wherein:
• a heating temperature is equal to or higher than Ac3 transformation temperature,
• a starting temperature of the hot press forming is in a range from the heating temperature to a martensite start (Ms) temperature, and
• cooling from [(Ms temperature)−150° C.] down to 80° C. is performed so that a tempering parameter (λ) as specified by Expression (1) is in a range from 7100 to 8030:
• λ
• =
• 293
• ×
• {
• log
• (
• ∑
• n
• =
• 1
• 5000
• ⁢
• t
• n
• ′
• 3600
• )
• +
• 20
• }
• -
• 430
• ×
• [
• Si
• ]
• (
• 1
• )
• where λ represents the tempering parameter;
• [Si] represents the content, in mass percent, of Si in the steel;
• and tn′ represents a value as specified by Expression (2):
• ⁢
• t
• n
• ′
• =
• 3600
• ×
• 10
• ^
• {
• T
• n
• -
• 1
• +
• 273
• 293
• ×
• (
• log
• ⁢
• t
• n
• -
• t
• n
• -
• 1
• 3600
• +
• 20
• )
• -
• 20
• }
• (
• 2
• )
• where tn represents an n-th time, in seconds, when a total cooling time from [(Ms temperature)−150° C.] down to 80° C. is divided into 5000 equal parts;
• Tn represents a temperature (° C.) at the n-th time tn, where t0 is 0 second, and T0 is [(Ms temperature)−150° C.];
• and 10^{ } represents { }-th power of 10.