Effect of the Grain Size and Deformation Substructure of Austenite on the Crystal Geometry of Bainite and Martensite in Low-Carbon Steels

Zolotarevskii, N. Yu.; Zisman, A. A.; Panpurin, S. N.; Titovets, Yu. F.; Golosienko, S. A.; Хлусова, Е. И.

doi:10.1007/s11041-014-9668-2

Cited by 16 publications

(10 citation statements)

References 11 publications

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“…This is consistent with other previous research results, [12,17,18] although in that research, the changes of grain refinement were observed from optical micrographs. However, the result of this research differs from previous studies, [14][15][16] which indicate that a coarser transformed microstructure forms after austenite deformation. There may be two different reasons for this.…”

Section: Controversial Effect Of Austenite Deformation On Effectivcontrasting

confidence: 99%

“…In the previous investigations, [12,17,18] AF microstructure is the main phase constituent after relatively slow continuous cooling, 30 [12] and 10 K/ s, [17,18] or isothermal holding at high temperatures, 773 K to 873 K (500°C to 600°C), [12] while in others, [14][15][16] with relatively high cooling rates, 50 K/ s, [14] and low transformation temperatures, 623 K [15] and 673 K (350°C and 400°C), [16] BF still dominates the transformed microstructure after austenite deformation.…”

Section: Controversial Effect Of Austenite Deformation On Effectivmentioning

confidence: 90%

“…[8][9][10][11][12][13] As for the grain refinement of low-temperature transformation products, although the effect of austenite deformation has been studied by many researchers, the results are still controversial. In a prior investigation, [14] it was shown that the effective grain size of bainite increases from 3.2 to 3.8 lm when austenite was deformed by 30 pct. Similarly, the block size of bainite was found to increase after austenite deformation, [15] and the quantity of packets in each austenite grain also decreased after austenite deformation.…”

Section: Introductionmentioning

confidence: 94%

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Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

Zhao

Palmiere

2017

Metall and Mat Trans A

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Although there has been much research regarding the effect of austenite deformation on accelerated cooled microstructures in microalloyed steels, there is still a lack of accurate data on boundary densities and effective grain sizes. Previous results observed from optical micrographs are not accurate enough, because, for displacive transformation products, a substantial part of the boundaries have disorientation angles below 15 deg. Therefore, in this research, a niobium microalloyed steel was used and electron backscattering diffraction mappings were performed on all of the transformed microstructures to obtain accurate results on boundary densities and grain refinement. It was found that with strain rising from 0 to 0.5, a transition from bainitic ferrite to acicular ferrite occurs and the effective grain size reduces from 5.7 to 3.1 lm. When further increasing strain from 0.5 to 0.7, dynamic recrystallization was triggered and postdynamic softening occurred during the accelerated cooling, leading to an inhomogeneous and coarse transformed microstructure. In the entire strain range, the density changes of boundaries with different disorientation angles are distinct, due to different boundary formation mechanisms. Finally, the controversial influence of austenite deformation on effective grain size of low-temperature transformation products was argued to be related to the differences in transformation conditions and final microstructures.

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Section: Controversial Effect Of Austenite Deformation On Effectivcontrasting

confidence: 99%

Section: Controversial Effect Of Austenite Deformation On Effectivmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 94%

See 1 more Smart Citation

Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

Zhao

Palmiere

2017

Metall and Mat Trans A

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“…For example, increasing austenite deformation [4,9,12,13] has been shown to increase the AF fraction, while 'AF-like' microstructures are produced when continuously cooled without austenite deformation [14][15][16][17]. These observations are contradicted from research [18][19][20] which indicates that even after significant amounts of austenite deformation, the transformation product still consists of parallel BF laths and the typical AF microstructure is absent.…”

Section: Introductionmentioning

confidence: 99%

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

2017

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For the class of steels collectively known as high strength low alloy (HSLA), an acicular ferrite (AF) microstructure produces an excellent combination of strength and toughness. The conditions for the occurrence of the AF transformation are, however, still unclear, especially the effects of austenite deformation and continuous cooling. In this research, a commercial HSLA steel was used and subjected to deformation via plane strain compression with strains ranging from 0 to 0.5 and continuous cooling at rates between 5 and 50°C s -1 . Based on the results obtained from optical microscopy, scanning electron microscopy and electron backscattering diffraction mapping, the introduction of intragranular nucleation sites and the suppression of bainitic ferrite (BF) laths lengthening were identified as the two key requirements for the occurrence of AF transformation. Austenite deformation is critical to meet these two conditions as it introduces a high density of dislocations that act as intragranular nucleation sites and deformation substructures, which suppress the lengthening of BF laths through the mechanism of mechanical stabilisation of austenite. However, the suppression effect of austenite deformation is only observed under relatively slow cooling rates or high transformation temperatures, i.e., conditions where the driving force for advancing the transformation interface is not sufficient to overcome the austenite deformation substructures.

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“…There have been many investigations concerning the effect of processing parameters on the effective grain sizes of steel microstructures [6][7][8][9][10][11]. However, some of the results are still controversial, especially for the influence of austenite deformation below the austenite nil-recrystallisation temperature (Tnr).…”

Section: Introductionmentioning

confidence: 99%

Influence of cooling rate on the grain-refining effect of austenite deformation in a HSLA steel

Zhao

Palmiere

2019

Materials Characterization

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Effective grain size is a direct indicator of the high angle grain boundary (HAGB) density of microstructures. A small effective grain size suggests a high density of HAGBs, which provide effective barriers to cleavage fracture. There have been many investigations concerning the effect of processing parameters on the effective grain sizes of steel microstructures. However, contradicting results were found for the influence of austenite deformation. In this research, to understand the influence of austenite deformation on effective grain size refinement, a low carbon Nb microalloyed steel was subjected to different austenite deformation conditions and was continuously cooled at a wide range of cooling rates (0.5~50˚C/s). Characteristics of transformed microstructures from recrystallised and deformed austenite were 2 analysed through optical microscopy observation and EBSD mapping. In the whole cooling rate range adopted in this research, effective grain sizes were found to be refined by austenite deformation. However, with the rise of cooling rate higher than 10˚C/s. With the rise of the cooling rate higher than 10˚C/s, effective grain sizes are reduced for recrystallised austenite, while increasingly large effective grain sizes were found for deformed austenite. According to these experimental results, the influence of austenite deformation on effective grain size in a wider cooling rate range was proposed to be cooling rate dependent, and possible explanations for the contradicting results in the literature were discussed based on that.

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Effect of the Grain Size and Deformation Substructure of Austenite on the Crystal Geometry of Bainite and Martensite in Low-Carbon Steels

Cited by 16 publications

References 11 publications

Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

Influence of cooling rate on the grain-refining effect of austenite deformation in a HSLA steel

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