There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

J. Appl. Cryst.の発刊に際して

https://zenodo.org/record/1258680/files/article.pdf

The influences of temperature and microstructure on the tensile properties of a CoCrFeMnNi high-entropy alloy

Dynamic and post-dynamic recrystallization under hot, cold and severe plastic deformation conditions

The goal in the heat treatment or thermomechanical processing of steel is to improve the mechanical properties. For structural steel applications the general aim is to refine the ferrite grain size as this is the only method that improves both the strength and toughness simultaneously. For conventional hot rolling and accelerated cooling processes, it is difficult to refine the grain size below 5 μm without extensive alloying. However, it has been found that inducing transformation during deformation (i.e. dynamic transformation) can lead to grain sizes of the order of 1 μm, even in very simple steel compositions. The exact mechanism(s) for this transformation process are still being debated, and this has also been complicated by recent studies where such grain sizes can be obtained by static transformation from austenite that has been heavily deformed at low temperatures prior to the transformation. This chapter reviews the various major studies related in particular to dynamic transformation and considers the contributions from the deformed austenite structure developed prior to the transformation and the potential for dynamic recrystallisation of the ferrite. A key factor is proposed to be the early three-dimensional impingement of the ferrite which also provides an insight into cases where ultrafine grains are achieved statically.

Dynamic strain-induced ferrite transformation (DSIT) in steels

Thermo-mechanical treatments were performed to exploit the recrystallisation and deformation induced ferrite transformation (DIFT) during processing and study their effect on the microstructure and strength-ductility balance of a low-carbon, low alloy CMnSiAl TRIP-aided steel containing a small amount of Mo and Nb. A particular focus of the work was to study the influence of prior transformation of retained austenite to martensite (i.e., absence of the TRIP effect) on the strength-ductility balance of the steel by comparing the tensile properties of samples quenched in water and in liquid nitrogen. It was observed that the formation of high carbon martensite as a result of the prior transformation of retained austenite does not necessarily lead to brittle failure. The work also revealed that the TRIP effect per se may not play a major role and it is the deformation of a composite microstructure comprising hard and soft phases, which allows TRIP aided steels to offer a better combination of mechanical properties (strength, ductility and strain hardening) in comparison with conventional high strength steels (HSS) like high strength interstitial free (HS-IF) steel and high strength low alloy steel (HSLA) and other first generation advanced high strength steels (AHSS) like dual phase (DP) steels. The new insight into the TRIP effect may further be exploited in the design of alloy composition and subsequent thermo-mechanical treatments.

The Mechanical Properties of Low Alloy TRIP-Aided Steel: The Role of Retained Austenite

An austenitic Ni-30%Fe model alloy was employed to investigate the texture and substructure development within the deformed matrix and dynamically recrystallized (DRX) grains during hot torsion deformation. Both the deformed matrix and DRX grains predominantly displayed the crystallographic texture components expected for simple shear deformation. The characteristics of the deformed matrix texture evolution during deformation largely resulted from the preferred consumption of high Taylor factor components by new recrystallized grains. Likewise, the comparatively weaker crystallographic texture of DRX grains became increasingly dominated by low Taylor factor components as a result of their easier nucleation and lower consumption rate during DRX. There was a significant difference in the substructure formation mechanism between the deformed matrix and DRX grains for a given texture component. The deformed matrix substructure was largely characterized by “organized”, banded subgrain arrangements with alternating misorientations, while the substructure of DRX grains was more “random” in character and displayed complex, more equiaxed subgrain/cell arrangements characterized by a local accumulation of misorientations. Substructure characteristics of individual orientation components were principally consistent with the corresponding Taylor factor values.

Texture and Substructure Development during Dynamic Recrystallization in Ni-30Fe Austenite

Effect of carbon on the hot deformation behaviour in Nb-steels

The current work has investigated the texture development in an austenitic Ni-30Fe model alloy during deformation within the dynamic recrystallization (DRX) regime and after post-deformation annealing. Both the deformed matrix and DRX texture displayed the expected FCC shear components, the latter being dominated by the low Taylor factor grains, which was presumably caused by their lower consumption rate during DRX. The deformed matrix grains were largely characterized by organized, microband structures, while the DRX grains showed more random, complex subgrains/cell arrangements. The latter substructure type proved to be significantly less stable during post-deformation annealing. The recrystallization of the deformed matrix occurred through nucleation and growth of new grains fully replacing the deformed structure, as expected for the classical static recrystallization (SRX). Unlike the DRX grains, the SRX texture was essentially random. By contrast, a novel softening mechanism was revealed during annealing of the fully DRX microstructure. The initial post-dynamic softening stage involved rapid growth of the dynamically formed nuclei and migration of the mobile boundaries in line with the well-established metadynamic recrystallization (MDRX) mechanism, which weakened the starting DRX texture. However, in parallel, the sub-boundaries within the deformed DRX grains progressively disintegrated through dislocation climb and dislocation annihilation, which ultimately led to the formation of dislocation-free grains. Consequently, the weakened DRX texture largely remained preserved throughout the annealing process.

Hossein Beladi

Papers

Dynamic strain-induced ferrite transformation (DSIT) in steels

The Mechanical Properties of Low Alloy TRIP-Aided Steel: The Role of Retained Austenite

Texture and Substructure Development during Dynamic Recrystallization in Ni-30Fe Austenite

Effect of carbon on the hot deformation behaviour in Nb-steels

Texture Evolution and Softening Processes in an Austenitic Ni-30Fe Alloy Subjected to Hot Deformation and Subsequent Annealing