Effects of untransformed ferrite on Charpy impact toughness in 1.8-GPa-grade hot-press-forming steel sheets

Min Cheol Jo; Jaeyeong Park; Seok Su Sohn; Seongwoo Kim; Jinkeun Oh; Sunghak Lee

doi:10.1016/j.msea.2017.09.027

Effects of untransformed ferrite on Charpy impact toughness in 1.8-GPa-grade hot-press-forming steel sheets

Min Cheol Jo, Jaeyeong Park, Seok Su Sohn, Seongwoo Kim, Jinkeun Oh, Sunghak Lee

Research output: Contribution to journal › Article › peer-review

28 Citations (Scopus)

Abstract

Hot press forming (HPF) steel sheets are austenitized, press-formed, and rapidly cooled to obtain a martensitic microstructure with an ultra-high strength. When they are insufficiently austenitized, their microstructures might contain a small amount of untransformed ferrite, which can deteriorate impact toughness as well as strength, but its causes and relevant fracture mechanisms have not been clearly verified yet. In this study, thus, 1.8-GPa-grade HPF sheets were austenitized at various temperature and time, and their tensile and Charpy impact test results were analyzed in relation with untransformed ferrite and its effect on fracture mechanisms. In the HPF sheets containing the untransformed ferrite, voids were formed mostly at ferrite/martensite interfaces, and were grown and propagated linearly to form a cleavage crack, whereas deformation bands were well developed without voids or cracks in the non-ferrite-containing sheets. The highly localized strains accommodated in the soft ferrite made ferrite/martensite interfaces or ferrite itself work as fracture initiation sites, which led to the brittle fracture and consequently to the deterioration of impact energy. This result can provide an important idea for optimization of austenitization conditions demanded for ultra-high strength and excellent impact toughness in HPF applications.

Original language	English
Pages (from-to)	65-72
Number of pages	8
Journal	Materials Science and Engineering A
Volume	707
DOIs	https://doi.org/10.1016/j.msea.2017.09.027
Publication status	Published - 2017 Nov 7
Externally published	Yes

Bibliographical note

Funding Information:
This work was supported by POSCO [grant number; 2017Y046 ], and Brain Korea 21 PLUS Project for Center for Creative Industrial Materials.

Publisher Copyright:
© 2017 Elsevier B.V.

Keywords

Charpy impact energy
Hot-press-forming (HPF) steel
Strain localization
Untransformed ferrite

ASJC Scopus subject areas

General Materials Science
Condensed Matter Physics
Mechanics of Materials
Mechanical Engineering

Access to Document

10.1016/j.msea.2017.09.027

Cite this

@article{827af2972092445da4acef7fac1aee8f,

title = "Effects of untransformed ferrite on Charpy impact toughness in 1.8-GPa-grade hot-press-forming steel sheets",

abstract = "Hot press forming (HPF) steel sheets are austenitized, press-formed, and rapidly cooled to obtain a martensitic microstructure with an ultra-high strength. When they are insufficiently austenitized, their microstructures might contain a small amount of untransformed ferrite, which can deteriorate impact toughness as well as strength, but its causes and relevant fracture mechanisms have not been clearly verified yet. In this study, thus, 1.8-GPa-grade HPF sheets were austenitized at various temperature and time, and their tensile and Charpy impact test results were analyzed in relation with untransformed ferrite and its effect on fracture mechanisms. In the HPF sheets containing the untransformed ferrite, voids were formed mostly at ferrite/martensite interfaces, and were grown and propagated linearly to form a cleavage crack, whereas deformation bands were well developed without voids or cracks in the non-ferrite-containing sheets. The highly localized strains accommodated in the soft ferrite made ferrite/martensite interfaces or ferrite itself work as fracture initiation sites, which led to the brittle fracture and consequently to the deterioration of impact energy. This result can provide an important idea for optimization of austenitization conditions demanded for ultra-high strength and excellent impact toughness in HPF applications.",

keywords = "Charpy impact energy, Hot-press-forming (HPF) steel, Strain localization, Untransformed ferrite",

author = "Jo, {Min Cheol} and Jaeyeong Park and Sohn, {Seok Su} and Seongwoo Kim and Jinkeun Oh and Sunghak Lee",

note = "Funding Information: This work was supported by POSCO [grant number; 2017Y046 ], and Brain Korea 21 PLUS Project for Center for Creative Industrial Materials. Publisher Copyright: {\textcopyright} 2017 Elsevier B.V.",

year = "2017",

month = nov,

day = "7",

doi = "10.1016/j.msea.2017.09.027",

language = "English",

volume = "707",

pages = "65--72",

journal = "Materials Science and Engineering A",

issn = "0921-5093",

publisher = "Elsevier Ltd",

}

TY - JOUR

T1 - Effects of untransformed ferrite on Charpy impact toughness in 1.8-GPa-grade hot-press-forming steel sheets

AU - Jo, Min Cheol

AU - Park, Jaeyeong

AU - Sohn, Seok Su

AU - Kim, Seongwoo

AU - Oh, Jinkeun

AU - Lee, Sunghak

N1 - Funding Information: This work was supported by POSCO [grant number; 2017Y046 ], and Brain Korea 21 PLUS Project for Center for Creative Industrial Materials. Publisher Copyright: © 2017 Elsevier B.V.

PY - 2017/11/7

Y1 - 2017/11/7

N2 - Hot press forming (HPF) steel sheets are austenitized, press-formed, and rapidly cooled to obtain a martensitic microstructure with an ultra-high strength. When they are insufficiently austenitized, their microstructures might contain a small amount of untransformed ferrite, which can deteriorate impact toughness as well as strength, but its causes and relevant fracture mechanisms have not been clearly verified yet. In this study, thus, 1.8-GPa-grade HPF sheets were austenitized at various temperature and time, and their tensile and Charpy impact test results were analyzed in relation with untransformed ferrite and its effect on fracture mechanisms. In the HPF sheets containing the untransformed ferrite, voids were formed mostly at ferrite/martensite interfaces, and were grown and propagated linearly to form a cleavage crack, whereas deformation bands were well developed without voids or cracks in the non-ferrite-containing sheets. The highly localized strains accommodated in the soft ferrite made ferrite/martensite interfaces or ferrite itself work as fracture initiation sites, which led to the brittle fracture and consequently to the deterioration of impact energy. This result can provide an important idea for optimization of austenitization conditions demanded for ultra-high strength and excellent impact toughness in HPF applications.

AB - Hot press forming (HPF) steel sheets are austenitized, press-formed, and rapidly cooled to obtain a martensitic microstructure with an ultra-high strength. When they are insufficiently austenitized, their microstructures might contain a small amount of untransformed ferrite, which can deteriorate impact toughness as well as strength, but its causes and relevant fracture mechanisms have not been clearly verified yet. In this study, thus, 1.8-GPa-grade HPF sheets were austenitized at various temperature and time, and their tensile and Charpy impact test results were analyzed in relation with untransformed ferrite and its effect on fracture mechanisms. In the HPF sheets containing the untransformed ferrite, voids were formed mostly at ferrite/martensite interfaces, and were grown and propagated linearly to form a cleavage crack, whereas deformation bands were well developed without voids or cracks in the non-ferrite-containing sheets. The highly localized strains accommodated in the soft ferrite made ferrite/martensite interfaces or ferrite itself work as fracture initiation sites, which led to the brittle fracture and consequently to the deterioration of impact energy. This result can provide an important idea for optimization of austenitization conditions demanded for ultra-high strength and excellent impact toughness in HPF applications.

KW - Charpy impact energy

KW - Hot-press-forming (HPF) steel

KW - Strain localization

KW - Untransformed ferrite

UR - http://www.scopus.com/inward/record.url?scp=85029377366&partnerID=8YFLogxK

U2 - 10.1016/j.msea.2017.09.027

DO - 10.1016/j.msea.2017.09.027

M3 - Article

AN - SCOPUS:85029377366

SN - 0921-5093

VL - 707

SP - 65

EP - 72

JO - Materials Science and Engineering A

JF - Materials Science and Engineering A

ER -

Effects of untransformed ferrite on Charpy impact toughness in 1.8-GPa-grade hot-press-forming steel sheets

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

Access to Document

Other files and links

Fingerprint

Cite this