TY - JOUR

T1 - Impact Toughness of Ultrafine-Grained Interstitial-Free Steel

AU - Saray, Onur

AU - Purcek, Agencaga

AU - Karaman, Ibrahim

AU - Maier, Hans J.

N1 - Funding information: This study was supported mainly by the Scientific and Technological Research Council of Turkey (TUBITAK) under Grant 107M618. This study was also partly supported by the Scientific Research Projects of Karadeniz Technical University, under Grant 2008.112.003.6. O. Saray would like to acknowledge support from The Council of Higher Education of Turkey for the Doctoral Research Scholarship. I. Karaman would like to acknowledge the support from the U.S. National Science Foundation (NSF), Division of CMMI, Materials and Surface Engineering program, Grant 0900187, and the NSF-International Materials Institutes Program, Division of Materials Research, Grant 0844082. The authors would like to thank Eregli Iron and Steel (ERDEMIR), Inc., Zonguldak, Turkey, for their support in kindly supplying the initial materials.

PY - 2012/6/8

Y1 - 2012/6/8

N2 - Impact toughness of an ultrafine-grained (UFG) interstitial-free (IF) steel produced by equalchannel angular extrusion/pressing (ECAE/P) at room temperature was investigated using Charpy impact tests. The UFG IF steel shows an improved combination of strength and impact toughness compared with the corresponding coarse-grained (CG) one. The CG IF steel samples underwent a transition in fracture toughness values with decreasing temperature because of a sudden change in fracture mode from microvoid coalescence (ductile) to cleavage (brittle) fracture. Grain refinement down to the submicron (≈320 nm) levels increased the impact energies in the upper shelf and lower shelf regions, and it considerably decreased the ductile-tobrittle transition temperature (DBTT) from 233 K (-40 °C) for the CG steel to approximately 183 K (-90 °C) for the UFG steel. Also, the sudden drop in DBTT with a small transition range for the CG sample changed to a more gradual decrease in energy for the UFG sample. The improvement in toughness after UFG formation was attributed to the combined effects of grain refinement and delamination and/or separation in the heavily deformed microstructure. Although an obvious change from the ductile fracture by dimples to the brittle fracture by cleavage was recognized at 233 K (-40 °C) for the CG steel, no fully brittle fracture occurred even at 103 K (-170 °C) in the UFG steel.

AB - Impact toughness of an ultrafine-grained (UFG) interstitial-free (IF) steel produced by equalchannel angular extrusion/pressing (ECAE/P) at room temperature was investigated using Charpy impact tests. The UFG IF steel shows an improved combination of strength and impact toughness compared with the corresponding coarse-grained (CG) one. The CG IF steel samples underwent a transition in fracture toughness values with decreasing temperature because of a sudden change in fracture mode from microvoid coalescence (ductile) to cleavage (brittle) fracture. Grain refinement down to the submicron (≈320 nm) levels increased the impact energies in the upper shelf and lower shelf regions, and it considerably decreased the ductile-tobrittle transition temperature (DBTT) from 233 K (-40 °C) for the CG steel to approximately 183 K (-90 °C) for the UFG steel. Also, the sudden drop in DBTT with a small transition range for the CG sample changed to a more gradual decrease in energy for the UFG sample. The improvement in toughness after UFG formation was attributed to the combined effects of grain refinement and delamination and/or separation in the heavily deformed microstructure. Although an obvious change from the ductile fracture by dimples to the brittle fracture by cleavage was recognized at 233 K (-40 °C) for the CG steel, no fully brittle fracture occurred even at 103 K (-170 °C) in the UFG steel.

UR - http://www.scopus.com/inward/record.url?scp=84872044364&partnerID=8YFLogxK

U2 - 10.1007/s11661-012-1238-x

DO - 10.1007/s11661-012-1238-x

M3 - Article

AN - SCOPUS:84872044364

VL - 43

SP - 4320

EP - 4330

JO - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

JF - Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

SN - 1073-5623

ER -