Dynamic Transformation Mechanism for Producing Ultrafine Grained Steels

Zhao, Lijia; Park, Nokeun; Tian, Yanzhong; Shibata, Akinobu; Tsuji, Nobuhiro

doi:10.1002/adem.201701016

Cited by 18 publications

(10 citation statements)

References 156 publications

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“…The transformation happening during deformation is called dynamic transformation (DT), and the occurrence of DT has been confirmed by some experimental studies under particullar conditions. 5155) Recently, Zhao et al 50,56) have found that two different mechanisms happen sequentially in certain materials and hot-deformation conditions, resulting to form UFG microstructures. Figure 15(a) schematically illustrates the mechanisms.…”

Section: Simpler Ways To Fabricate Ultrafine Grained Metals Without Smentioning

confidence: 99%

Formation Mechanism of Ultrafine Grained Microstructures: Various Possibilities for Fabricating Bulk Nanostructured Metals and Alloys

et al. 2019

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Severe plastic deformation (SPD) have had a revolutionary impact in fabricating ultrafine grained (UFG) or nanostructured metallic materials with bulky dimensions. It is, however, difficult to understand from a viewpoint of conventional metallurgy why UFG microstructures form in the as-deformed (as-SPD-processed) state without annealing process. The mechanism of UFG evolution has not yet been perfectly recognized and even some confusions have been induced. Experimental results of systematic observations on the evolution of microstructures during SPD were introduced in the present manuscript, and it was concluded from the results that the formation of UFG microstructures during SPD could be understood in terms of the grain subdivision mechanism. Consequently, the UFG microstructures formed by SPD have the deformed (strain-hardened) characteristics, which influences their mechanical properties. Besides the breakthrough in grain refinement, some features of SPD processes have become barriers for practical applications of UFG materials and scaling-up of the processes. Several new processes combining phase transformation with plastic deformation were introduced for fabricating UFG microstructures without huge plastic strains, and UFG microstructures successfully obtained by the new processes were shown. Finally, recent finding of fully recrystallized UFG microstructures in some alloys having average grain sizes of several hundred nano-meters was exhibited. The fully recrystallized UFG metals all showed both high strength and large ductility, because of the capability of strain hardening in the structures. These recent results are expected to open great possibilities of UFG or nanostructured metals as advanced structural materials. [

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Section: Simpler Ways To Fabricate Ultrafine Grained Metals Without Smentioning

confidence: 99%

Formation Mechanism of Ultrafine Grained Microstructures: Various Possibilities for Fabricating Bulk Nanostructured Metals and Alloys

et al. 2019

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“…Thermomechanical controlled processing (TMCP) and strain-induced ferrite transformation by austenite deformation are considered two primary strategies to produce ultrafine ferrite grains [1]. The present work will primarily focus on the analysis of the latter, also known as dynamic transformation of austenite to ferrite.…”

Section: Introductionmentioning

confidence: 99%

Strain-Induced Ferrite Formation During Steckel Mill Simulations with Varying Roughing Pass Schedules

Palhano

Aranas

Rodrigues

et al. 2019

Metals

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It has been previously demonstrated that austenite may undergo partial dynamic transformation (DT) during the plate rolling process. Austenite dynamically transforms into unstable ferrite during hot deformation even at very high temperatures. In this work, the plate rolling simulations, with emphasis on Steckel mill operations, through torsion testing under isothermal conditions were performed on an X70 steel. Four different roughing schedules were tested followed by five finishing passes with pass strains of 0.3 applied at 900 °C. The roughing schedules had zero, one, two and three roughing passes at a temperature of 1100 °C, strain of 0.4 and strain rate of 1 s−1. The stress–strain curves as well as the mean flow stress (MFS) behaviors indicated that both dynamic transformation (DT) and dynamic recrystallization (DRX) occurred during straining. The critical strains for the onset of DT and DRX were determined by means of the double differentiation method and the critical strain values decreased with the number of roughing and finishing strains from the first going to the last pass. It was observed that the volume fraction of the dynamically formed ferrite increased sharply during the finishing stage as the number of previous roughing passes increased, which can be attributed to higher strain accumulation. The results presented here indicate that improved models are needed to control the microstructure of the material during subsequent cooling.

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“…Meanwhile, the ductility simultaneously increases with the strength, due to the grain refinement. Now, the main strategies for the refinement of grains can be divided into two types [1,2]. One is the severe plastic deformation (SPD), another is the advanced thermomechanical process (ATP).…”

Section: Introductionmentioning

confidence: 99%

“…One is the severe plastic deformation (SPD), another is the advanced thermomechanical process (ATP). Due to the limitation of specimen size, the ATP process is more suitable to the industrial production than SPD [1,2]. In terms of grains refined by ATP process, the main methods are shown as follows: deformation-induced transformation (DIT) [3][4][5], cold rolling and annealing (CRA) [6], warm deformation (WD), amongst others.…”

Section: Introductionmentioning

confidence: 99%

Effect of Temperature Scheme on Microstructure and Mechanical Properties during Medium Carbon Steel Warm Processing

Fan

Chen

2019

Metals

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Influence of temperature scheme on the microstructure and properties variation of medium carbon steel warm deformation was studied with testing equipment of Gleeble-3500, SEM, TEM, EBSD, and φ350 reversal rolling mill. The results show that the temperature of 650 facilitates the formation of ultrafine homogeneous microstructure. The microstructure formed during temperature range of 650–700 °C is relative homogeneous and fine. The mechanical properties of warm rolling are influenced by the cooling modes. The lower cooling rate is benefit to the combination of strength and ductility.

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Dynamic Transformation Mechanism for Producing Ultrafine Grained Steels

Cited by 18 publications

References 156 publications

Formation Mechanism of Ultrafine Grained Microstructures: Various Possibilities for Fabricating Bulk Nanostructured Metals and Alloys

Formation Mechanism of Ultrafine Grained Microstructures: Various Possibilities for Fabricating Bulk Nanostructured Metals and Alloys

Strain-Induced Ferrite Formation During Steckel Mill Simulations with Varying Roughing Pass Schedules

Effect of Temperature Scheme on Microstructure and Mechanical Properties during Medium Carbon Steel Warm Processing

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