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Author

Min Chul Jo

Other affiliations: Samsung
Bio: Min Chul Jo is an academic researcher from Pohang University of Science and Technology. The author has contributed to research in topics: Austenite & Twip. The author has an hindex of 10, co-authored 19 publications receiving 281 citations. Previous affiliations of Min Chul Jo include Samsung.

Papers
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TL;DR: In this paper, the authors show favorable effects of the Mn-segregated band, by carefully controlling the composition, size, and shape of austenite in Mn-rich and Mn-lean bands in medium-Mn duplex steels.

111 citations

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TL;DR: It is demonstrated how the non-recrystallized austenite can be a metamorphosis in 1.5-GPa-grade steel sheet design by actively utilizing non- Recrystallization region and TRansformation-Induced Plasticity (TRIP) mechanism in a cold-rolled and annealed Fe-Mn-Al-C-based steel.
Abstract: Needs for steel designs of ultra-high strength and excellent ductility have been an important issue in worldwide automotive industries to achieve energy conservation, improvement of safety, and crashworthiness qualities. Because of various drawbacks in existing 1.5-GPa-grade steels, new development of formable cold-rolled ultra-high-strength steels is essentially needed. Here we show a plausible method to achieve ultra-high strengths of 1.0~1.5 GPa together with excellent ductility above 50% by actively utilizing non-recrystallization region and TRansformation-Induced Plasticity (TRIP) mechanism in a cold-rolled and annealed Fe-Mn-Al-C-based steel. We adopt a duplex microstructure composed of austenite and ultra-fine ferrite in order to overcome low-yield-strength characteristics of austenite. Persistent elongation up to 50% as well as ultra-high yield strength over 1.4 GPa are attributed to well-balanced mechanical stability of non-crystallized austenite with critical strain for TRIP. Our results demonstrate how the non-recrystallized austenite can be a metamorphosis in 1.5-GPa-grade steel sheet design.

49 citations

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TL;DR: In this paper, microstructural evolutions of small Zn infiltrations or cracks as well as formation behavior of various intermetallic phases were investigated by detailed micro structural evolutions.

48 citations

Journal ArticleDOI
TL;DR: In this article, an austenitic high-Mn TRIP steel was suggested to achieve a good strength-ductility balance, and 1.2µwt.% Cu was added as an element for increasing stacking fault energy (SFE) as well as an Austenite stabilizer to exploit a transition from TRIP to TWIP.

44 citations

Journal ArticleDOI
TL;DR: In this article, a hybrid Al-matrix composite reinforced with both SiC and B4C ceramic particulates was fabricated to increase the volume fraction of ceramics by a liquid pressing process.
Abstract: In this study, a hybrid Al-matrix composite reinforced with both SiC and B4C ceramic particulates (SiCp or B4Cp, respectively) was fabricated to increase the volume fraction of ceramics by a liquid pressing process, and its dynamic and ballistic properties were compared with those of monolithic Al-matrix composites reinforced with SiCp or B4Cp. The hybrid composite demonstrated a very high dynamic compressive strength (over 1.5 GPa), along with a good total strain of 11.7%, which readily reached an undiscovered strength area (far over 1.2 GPa) of typical composites. This was basically attributed to the highest ceramic fraction (60 vol%), together with strongly-bonded ceramic/Al interfaces and synergetic hybrid effects of SiCps and B4Cps. After the ballistic test, the hybrid composite was radially cracked with a small hole-mark and a few fallen-off debris, which indicated the higher ballistic properties than those of the SiCp- or B4Cp-reinforced composite because of outstanding dynamic compressive strength and strain.

41 citations


Cited by
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Journal ArticleDOI
TL;DR: A three-level heterogeneous grain structure with grain sizes spanning the nanometer to micrometer range, imparting a high yield strength well in excess of 1 GPa leads to a sustainable strain hardening rate, a record-wide hysteresis loop in load−unload−reload stress−strain curve and hence high back stresses.
Abstract: Ductility, i.e., uniform strain achievable in uniaxial tension, diminishes for materials with very high yield strength. Even for the CrCoNi medium-entropy alloy (MEA), which has a simple face-centered cubic (FCC) structure that would bode well for high ductility, the fine grains processed to achieve gigapascal strength exhaust the strain hardening ability such that, after yielding, the uniform tensile strain is as low as ∼2%. Here we purposely deploy, in this MEA, a three-level heterogeneous grain structure (HGS) with grain sizes spanning the nanometer to micrometer range, imparting a high yield strength well in excess of 1 GPa. This heterogeneity results from this alloy's low stacking fault energy, which facilitates corner twins in recrystallization and stores deformation twins and stacking faults during tensile straining. After yielding, the elastoplastic transition through load transfer and strain partitioning among grains of different sizes leads to an upturn of the strain hardening rate, and, upon further tensile straining at room temperature, corner twins evolve into nanograins. This dynamically reinforced HGS leads to a sustainable strain hardening rate, a record-wide hysteresis loop in load-unload-reload stress-strain curve and hence high back stresses, and, consequently, a uniform tensile strain of 22%. As such, this HGS achieves, in a single-phase FCC alloy, a strength-ductility combination that would normally require heterogeneous microstructures such as in dual-phase steels.

316 citations

Journal ArticleDOI
TL;DR: This review explores the multiple levels of heterogeneities in multi-principal-element alloys that contribute to lattice friction and back stress hardening, as a general strategy towards strength–ductility synergy beyond current benchmark ranges.
Abstract: Conventional alloys are usually based on a single host metal. Recent high-entropy alloys (HEAs), in contrast, employ multiple principal elements. The strength of HEAs is considerably higher than traditional solid solutions, as the many constituents lead to a rugged energy landscape that increases the resistance to dislocation motion, which can also be retarded by other heterogeneities. The wide variety of nanostructured heterogeneities in HEAs, including those generated on the fly during tensile straining, also offer elevated strain-hardening capability that promotes uniform tensile ductility. Citing recent examples, this review explores the multiple levels of heterogeneities in multi-principal-element alloys that contribute to lattice friction and back stress hardening, as a general strategy towards strength-ductility synergy beyond current benchmark ranges.

255 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed the strategy of tailoring strain delocalization to evade long-standing strength-ductility trade-off dilemma, where the achieving of strengthductility synergy depends on the delocalizing of localized strains.

197 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new steel family called TWIP, which combines twinning and martensite transformation during straining to achieve high-strength steel families, some of them being already used in body in white (Dual Phase (DP) and TRIP steels).

113 citations

Journal ArticleDOI
TL;DR: In this article, a review of Fe-Mn-al-C steels is presented to elucidate the complex relations between the chemical composition of the steel, the test temperature, the external loads and the processing parameters.
Abstract: During the last years, the scientific and industrial community has focused on the astonishing properties of Fe-Mn-Al-C steels. These high advanced steels allow high-density reductions about ~15% lighter than conventional steels, high corrosion resistance, high strength (ultimate tensile strength (UTS) ~1 Gpa) and at the same time ductilities above 60%. The increase of the tensile or yield strength and the ductility at the same time is almost a special feature of this kind of new steels, which makes them so interesting for many applications such as in the automotive, armor and mining industry. The control of these properties depends on a complex relationship between the chemical composition of the steel, the test temperature, the external loads and the processing parameters of the steel. This review has been conceived to tried to elucidate these complex relations and gather the most important aspects of Fe-Mn-Al-C steels developed so far.

109 citations