The mechanism of bainite transformation

Fang, Hongwei; Yang, Jing-an; Yang, Zhigang; Bai, Bing; Liu, D.-Y.; Xu, Ping

doi:10.1051/jp4:2003885

Cited by 4 publications

(3 citation statements)

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“…By different researchers, it was suggested as being similar to various common microstructures in steels, including granular bainite (GB) [37], quasipolygonal ferrite (QF) [16,38,39], Widmanstätten ferrite (WF) [40] and bainitic ferrite (BF) [2,3]. Differently, a mixture of these microstructures was regarded as AF in research [35,41].…”

Section: Discussion Acicular Ferrite Transformation Mechanismmentioning

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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Section: Discussion Acicular Ferrite Transformation Mechanismmentioning

confidence: 99%

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

2017

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“…Formation of bainite comprises both diffusional and displacive mechanism [3], [4]. Bainite transformation comprises cooperative competition of sympathetic nucleation and ledge wise growth [5].…”

Section: Introductionmentioning

confidence: 99%

Effect of Hot Deformation on Impact Toughness of High Strength Steel

Kavathekar¹,

Hiwarkar²,

Pawar³

et al. 2020

IJMMM

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High Strength steel offers good combination of strength and toughness properties. These properties of high strength steel are strongly influenced by the hot deformation and controlled cooling parameters. The hot deformation behavior of low carbon high strength steel and its effects can be entailed and detailed by the analysis of microstructural and mechanical properties. In the present study, hot deformation was carried out in the temperature range of 1060°C to 1300°C followed by natural air cooling and forced air cooling. The microstructures were characterized by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM).The mechanical behavior was investigated by hardness, tensile and Charpy V-notch impact tests. The test results indicate that, decrease in deformation temperature from 1300°C to 1060°C increases the impact strength from 13J to 31J. The microstructure evaluation shows that the toughness of the steel was enhanced by the formation of fine Bainitic sheaves and finer bainitic packets in lath-like bainitic structure at lower deformation temperature.

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“…Bainite steels, by virtue of transformation features, have a complex multiphase structure being formed as a result of superposition of shear and diffusion mechanisms of transformation [11,12]. The main factors determining properties of bainite structure steel can include: the availability of carbon atoms and other alloying elements in iron crystal lattice; boundaries of grains, packets, crystals of bainite; cementite particles; inclusions of retained austenite; dislocations and internal stress fields caused by structural elements [13][14][15][16]. A knowledge of quantitative regularities and mechanisms of work hardening of steel with bainite structure allows to control purposefully the structure-phase states of steel and its mechanical properties [11,17,18].…”

Section: Introductionmentioning

confidence: 99%

Bainite steel: structure and work hardening

Gromov¹,

Nikitina²,

Ivanov³

et al. 2016

VNMSTU

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Using the methods of transmission electron diffraction microscopy, a quantitative evolution analysis of defective and carbide subsystems of medium-carbon steel with a bainite structure under a compression strain up to 36% has been performed. A quantitative analysis of carbon redistribution has been carried out, as well as the dependence established of the concentration of carbon atoms arranged in a crystal lattice of-and-iron on structural defects in cementite particles lying in a number of bainite plates and intra-phase boundaries, and on the degree of deformation. It has been demonstrated that scalar dislocation density, material volume with deformation twins, a number of stress concentrators, the amplitude of crystal lattice curvature-torsion, the disorientation degree of fragments are increased with the growth of the degree of deformation and average longitudinal fragment sizes are decreased. The long-range stress fields have been estimated. The possible causes of the different stages of parameter changes of the carbide phase and dislocation substructure with deformation have been discussed. Strengthening mechanisms with the boundaries of the plates and fragments, scalar dislocation density, long-range stress fields, and cementite particles, the interstitial atoms have been estimated. It has been shown that the largest contribution to the amount of work hardening of the steel examined leads to substructural hardening (hardening due to long-range internal stress fields and structure fragmentation) and solid-solution hardening, due to the introduction of carbon atoms into the crystal lattice of the ferrite. It has been suggested that the cause of softening of steel with a bainite structure at high (over 15%) degrees of deformation is the activation of the process of deformation fine-scale twinning.

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The mechanism of bainite transformation

Cited by 4 publications

References 0 publications

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

Effect of Hot Deformation on Impact Toughness of High Strength Steel

Bainite steel: structure and work hardening

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