Delamination effect on impact properties of ultrafine-grained low-carbon steel processed by warm caliber rolling

Tadanobu Inoue, Fuxing Yin, Yuuji Kimura, Kaneaki Tsuzaki, Shojiro Ochiai

Research output: Contribution to journalArticlepeer-review

142 Citations (Scopus)


Bulk ultrafine-grained (UFG) low-carbon steel bars were produced by caliber rolling, and the impact and tensile properties were investigated. Initial samples with two different microstructures, ferrite-pearlite and martensite (or bainite), were prepared and then caliber rolling was conducted at 500 °C. The microstructures in the rolled bars consisted of an elongated UFG structure with a strong α-fiber texture. The rolled bar consisting of spheroidal cementite particles that distributed uniformly in the elongated ferrite matrix of transverse grain sizes 0.8 to 1.0 μm exhibited the best strength-ductility balance and impact properties. Although the yield strength in the rolled bar increased 2.4 times by grain refinement, the upper-shelf energy did not change, and its value was maintained from 100 °C to -40 °C. In the rolled bars, cracks during an impact test branched parallel to the longitudinal direction of the test samples as temperatures decreased. Delamination caused by such crack branching appeared, remarkably, near the ductile-to-brittle transition temperature (DBTT). The effect of delamination on the impact properties was associated with crack propagation on the basis of the microstructural features in the rolled bars. In conclusion, the strength-toughness balance is improved by refining crystal grains and controlling their shape and orientation; in addition, delamination effectively enhances the low-temperature toughness.

Original languageEnglish
Pages (from-to)341-355
Number of pages15
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Issue number2
Publication statusPublished - Feb 2010
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys


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