Morphology and properties of low-carbon bainite

Ohtani, Hiroo; Okaguchi, Shuji; Fujishiro, Yasufumi; Ohmori, Yasuya

doi:10.1007/bf02656571

Cited by 108 publications

(51 citation statements)

References 22 publications

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“…3(a). At relatively higher temperatures just below the Bs, only carbide free BF laths formed, which were classified as B-I type upper bainite [8,9]. After being held at this temperature (just below the Bs) for an extended period of time, however, significant coalescence and thickening of BF laths occurred.…”

Section: Microstructuresmentioning

confidence: 96%

“…Bainite has a similar morphology to WF, however, it forms between Bs and Ms with its own C-curve. BF [8,9] is the carbide-free upper bainite which forms at relatively higher temperatures of the bainite regime. The aims of this study are, therefore, to clarify the fundamental difference between WF and BF and to elucidate the mechanism of WF formation in comparison with that of bainite formation in low carbon low alloy steels.…”

Section: Introductionmentioning

confidence: 99%

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Morphology and growth process of bainitic ferrite in steels

Jung

Kim

Ohmori

1998

Metals and Materials

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The morphologies and the formation mechanisms of isothermally transformed Widmanstfitten ferrite and bainite in various steels were investigated. Widmanstfitten ferrite often grew from the grain boundary ferrite allotriomorph formed by a diffusional mechanism in the temperature range of the upper C-curve, whereas, bainite grew directly from an austenite grain boundary showing its own C-curve in a TIT diagram at temperatures between Bs (bainite starting temperature) and Ms (martensite starting temperature). Both structures accompanied well-defined surface reliefs of the invariant plane strain-type, and were in the shape of a lath or a plate consisting of several parallel needle-like ferrite subunits with parallelogram cross sections. The crystallographic properties of Widmanst~itten ferrite and upper bainite were similar to those of lath martensite. Therefore, it was concluded that the difference between bainitic ferrite and Widmanst~tten ferrite existed only in the nucleation events, where both structures grew by the same mechanism.

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Section: Microstructuresmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Morphology and growth process of bainitic ferrite in steels

Jung

Kim

Ohmori

1998

Metals and Materials

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“…In the inverse pole figure maps, the boundaries between the grains that showed different orientations of 15 deg or higher were high-angle grain boundaries, which were generally considered to be effective grains. [23,24] The effective grain size of the '-S' steels were slightly larger than those of the '-D' steels because fine PF grains with approximately 3 lm were formed by the rolling processes in the dual-phase region. The effective grain size of AF in the '-S' steels was approximately 5 lm, which was larger than that of PF in the '-D' steels.…”

Section: A Microstructuresmentioning

confidence: 98%

Correlation Between Microstructures and Tensile Properties of Strain-Based API X60 Pipeline Steels

Sung

Lee

et al. 2016

Metall Mater Trans A

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The correlation between the microstructures and tensile properties of strain-based American Petroleum Institute (API) X60 pipeline steels was investigated. Eight types of strain-based API X60 pipeline steels were fabricated by varying the chemical compositions, such as C, Ni, Cr, and Mo, and the finish cooling temperatures, such as single-phase and dual-phase regions. In the 4N and 5C steels, the volume fractions of bainitic ferrite (BF) and the secondary phases increased with the increasing C and adding Cr instead of Ni. In the 5C and 6NC steels, the volume fractions of acicular ferrite (AF) and BF decreased with increasing C and adding Ni, whereas the volume fractions of polygonal ferrite (PF) and the secondary phases increased. In the 6NC and 6NM steels, the volume fraction of BF was increased by adding Mo instead of Cr, whereas the volume fractions of PF and the secondary phases decreased. In the steels rolled in the single-phase region, the volume fraction of polygonal ferrite ranged from 40 to 60 pct and the volume fraction of AF ranged from 20 to 40 pct. In the steels rolled in the dual-phase region, however, the volume fraction of PF was more than 70 pct and the volume fraction of AF was below 20 pct. The strength of the steels with a high volume fraction of AF was higher than those of the steels with a high volume fraction of PF, whereas the yield point elongation and the strain hardening exponent were opposite. The uniform elongation after the thermal aging process decreased with increasing volume fraction of PF, whereas the uniform elongation increased with increasing volume fraction of AF. The strain hardening exponent increased with increasing volume fraction of PF, but decreased with increasing volume fraction of AF and effective grain size.

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“…For low carbon, low alloy steels, classical interpretations of lower transformation products, such as by Bhadeshia [21], Bramfitt and Speer [22] and Ohtani and Ohmori [23], are somewhat inadequate as carbides and retained austenite often do not form in low carbon steels. All of the above systems heavily rely on carbides, where the dominate phase is cementite, in defining bainitic morphology.…”

Section: Phase Nomenclature For Low Carbon Steelsmentioning

confidence: 99%

Carpenter

Killmore²

2015

Metals

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Abstract:The effect of Nb on the hardenability of ultra-thin cast strip (UCS) steels produced via the unique regime of rapid solidification, large austenite grain size, and inclusion engineering of the CASTRIP © process was investigated. Continuous cooling transformation (CCT) diagrams were constructed for 0, 0.014, 0.024, 0.04, 0.06 and 0.08 wt% Nb containing UCS steels. Phase nomenclature for the identification of lower transformation product in low carbon steels was reviewed. Even a small addition of 0.014 wt% Nb showed a potent effect on hardenability, shifting the ferrite C-curve to the right and expanding the bainitic ferrite and acicular ferrite phase fields. Higher Nb additions increased hardenability further, suppressed the formation of ferrite to even lower cooling rates, progressively lowered the transformation start and finish temperatures and promoted the transformation of bainite instead of acicular ferrite. The latter was due to Nb suppressing the formation of allotriomorphic ferrite and allowing bainite to nucleate at prior austenite grain boundaries, a lower energy site than that for the intragranular nucleation of acicular ferrite at inclusions. Strength and hardness increased with increasing Nb additions, largely due to microstructural strengthening and solid solution hardening, but not from precipitation hardening. OPEN ACCESSMetals 2015, 5 1858

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Morphology and properties of low-carbon bainite

Cited by 108 publications

References 22 publications

Morphology and growth process of bainitic ferrite in steels

Morphology and growth process of bainitic ferrite in steels

Correlation Between Microstructures and Tensile Properties of Strain-Based API X60 Pipeline Steels

The Effect of Nb on the Continuous Cooling Transformation Curves of Ultra-Thin Strip CASTRIP© Steels

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