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

Patent metadata

Field	Value
Publication number	US-2025137086-A1
Application number	US-202218694191-A
Country	US
Kind code	A1
Filing date	Nov 14, 2022
Priority date	Dec 22, 2021
Publication date	May 1, 2025
Grant date	—

Abstract

The present invention relates to: a steel material for hot forming, used for a vehicle, etc.; a hot formed part; and a method for manufacturing thereof.

First claim

1 .- 20 . (canceled)

21 . 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.

22 . The steel material for hot forming of claim 21 , wherein the base steel sheet comprises by wt %, C: 0.04 to 0.45%, Si: 1.5% or less (excluding 0%), Mn: 0.2 to 2.5%, P: 0.05%, S: 0.02% or less, Al: 0.01 to 0.1%, Cr: 0.01 to 5.0%, N: 0.02% or less, residual Fe, and inevitable impurities.

23 . The steel material for hot forming of claim 22 , wherein the base steel sheet comprises at least one of Mo: 0.5% or less, Ni: 0.5% or less, Nb: 0.1% or less, Ti: 0.1% or less, and B: 0.01% or less.

24 . The steel material for hot forming of claim 21 , wherein a microstructure of the base steel sheet comprises, by an area fraction, 50 to 90% of ferrite, and comprises at least one of 30% or less of pearlite, 20% or less of bainite, and 20% or less of martensite.

25 . The steel material for hot forming of claim 21 , wherein a whiteness of the steel material for hot forming is 60 or more.

26 . 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 (T 1 ): 500 to 800° C. Retention time (t 1 ): 1 minute or more (retention time at a target temperature) Temperature increase velocity (H 1 ): 20 to 160° C./hr (temperature increase velocity to a target temperature).

27 . 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 (T 2 - 1 ): 500 to 780° C. Retention time of section 1 (t 2 - 1 ): 1 minute or more (retention time at a target temperature) Temperature increase velocity of section 1 (H 2 - 1 ): 20 to 160° C./hr (temperature increase velocity to a target temperature) Temperature range of section 2 (T 2 - 2 ): 600 to 800° C. Retention time of section 2 (t 2 - 2 ): 50 minutes or more (retention time at a target temperature) Temperature increase velocity of section 2 (H 2 - 2 ): 0.25 to 160° C./hr (temperature increase velocity to a target temperature).

28 . The method for manufacturing a steel material for hot forming of claim 26 , wherein the steel slab comprises by wt %, C: 0.04 to 0.45%, Si: 1.5% or less (excluding 0%), Mn: 0.2 to 2.5%, P: 0.05% or less, S: 0.02% or less, Al: 0.01 to 0.1%, Cr: 0.01 to 5.0%, N: 0.02% or less, residual Fe, and inevitable impurities.

29 . The method for manufacturing a steel material for hot forming of claim 27 , wherein the steel slab comprises by wt %, C: 0.04 to 0.45%, Si: 1.5% or less (excluding 0%), Mn: 0.2 to 2.5%, P: 0.05% or less, S: 0.02% or less, Al: 0.01 to 0.1%, Cr: 0.01 to 5.0%, N: 0.02% or less, residual Fe, and inevitable impurities.

30 . The method for manufacturing a steel material for hot forming of claim 28 , wherein the steel slab further comprises at least one of Mo: 0.5% or less, Ni: 0.5% or less, Nb: 0.1% or less, Ti: 0.1% or less, and B: 0.01% or less.

31 . The method for manufacturing a steel material for hot forming of claim 29 , wherein the steel slab further comprises at least one of Mo: 0.5% or less, Ni: 0.5% or less, Nb: 0.1% or less, Ti: 0.1% or less, and B: 0.01% or less.

32 . The method for manufacturing a steel material for hot forming of claim 26 , wherein purge gas in a furnace during the batch annealing is one of hydrogen (H 2 ), nitrogen (N 2 ), and a mixture thereof, and a purge amount is 0.1 to 100 m 3 /hr.

33 . The method for manufacturing a steel material for hot forming of claim 27 , wherein purge gas in a furnace during the batch annealing is one of hydrogen (H 2 ), nitrogen (N 2 ), and a mixture thereof, and a purge amount is 0.1 to 100 m 3 /hr.

34 . The method for manufacturing a steel material for hot forming of claim 26 , wherein a circulation fan may operate during the batch annealing, and an amount of operation of the circulation fan is 10 rpm or more.

35 . The method for manufacturing a steel material for hot forming of claim 27 , wherein a circulation fan may operate during the batch annealing, and an amount of operation of the circulation fan is 10 rpm or more.

36 . The method for manufacturing a steel material for hot forming of claim 26 , wherein the obtaining a plated steel sheet comprises:
heating the steel slab at 1050 to 1300° C.; obtaining a hot-rolled steel sheet by finish hot rolling the heated steel slab at 800 to 950° C.; winding the hot-rolled steel sheet at 500 to 700° C.; cooling the wound hot-rolled steel sheet from a winding temperature to

Assignees

• Posco Co Ltd

Inventors

• Lee Sea-Woong
• Oh Jin-Keun
• Kim Seong-Woo
• Kim Sang-Heon
• Chun Hyo-Sik
• Lee Ru-Ri

Classifications

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C22C21/02

  with silicon as the next major constituent · CPC title

• C21D1/26

  Methods of annealing · CPC title

• C21D2211/002

  Bainite · CPC title

• C21D2211/009

  Pearlite · CPC title