Steel material for hot forming, hot formed part, and method for manufacturing thereof

A steel material for hot forming, comprising:

• a base steel sheet;
• and
• a plating layer formed on the base steel sheet, and
• the following Relational Expression 1 is satisfied,
• Carbon
• ⁢
• segregation
• ⁢
• index
• ⁢
• before
• ⁢
• hot
• forming:
• C
• (
• peak
• ,
• before
• ⁢
• HPF
• )
• /
• C
• (
• nom
• ,
• before
• ⁢
• HPF
• )
• ≥
• 1.5
• [
• Relational
• ⁢
• Expression
• ⁢
• 1
• ]
• where C(peak, before HPF) is the highest carbon value of a carbon peak that appears first in a carbon profile as a result of GDS analysis, in a direction of the base steel sheet from a ⅓ point of a thickness of the plating layer on a surface, and C(nom, before HPF) is a nominal carbon value of steel.

A method for manufacturing a steel material for hot forming, the method comprising:

• obtaining a plated steel sheet using a steel slab, and
• performing batch annealing on the plated steel sheet in a one-step manner of the following batch annealing condition 1,
• [Batch Annealing Condition 1]
• Temperature range (T1):
• 500 to 800° C.
• Retention time (t1):
• 1 minute or more (retention time at a target temperature)
• Temperature increase velocity (H1):
• 20 to 160° C./hr (temperature increase velocity to a target temperature).

A method for manufacturing a steel material for hot forming, the method comprising:

• obtaining a plated steel sheet using a steel slab, and
• performing batch annealing on the plated steel sheet in a two-step manner of the following batch annealing condition 2],
• [Batch Annealing Condition 2]
• Temperature range of section 1 (T2-1):
• 500 to 780° C.
• Retention time of section 1 (t2-1):
• 1 minute or more (retention time at a target temperature)
• Temperature increase velocity of section 1 (H2-1):
• 20 to 160° C./hr (temperature increase velocity to a target temperature)
• Temperature range of section 2 (T2-2):
• 600 to 800° C.
• Retention time of section 2 (t2-2):
• 50 minutes or more (retention time at a target temperature)
• Temperature increase velocity of section 2 (H2-2):
• 0.25 to 160° C./hr (temperature increase velocity to a target temperature).