Effect of Prior Austenite Grain Size on the Morphology of Nano-Bainitic Steels

Singh, Kritika; Kumar, Avanish; Singh, Aparna

doi:10.1007/s11661-018-4492-8

Cited by 36 publications

(15 citation statements)

References 23 publications

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“…Prior austenite grain size impacts the mechanical properties of nanobainite (NB) (Ref 31) by direct influence on the kinetics of transformation (Ref 32) and hence the resulting microstructure ( Ref 30,33). Revealed prior austenite grains after austenitization in tested temperature exhibited stable growth, and no abnormal grains were found (Fig.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of the Possibility to Obtain Nanostructured Bainite in High-Carbon and High-Silicon 9XC Bearing Steel

Baran

Królicka

2020

J. of Materi Eng and Perform

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The main aim of this research is the evaluation of the possibility of obtaining a nanostructured bainite after isothermal heat treatment of 9XC (according to GOST standard) bearing steel. It was found that the annealing at low temperature (250°C) allows to obtain the microstructure of nanobainite consisting of nanometric-scale bainitic ferrite laths and austenite with a dominant film-like morphology. In the case of higher isothermal treatment temperature (300°C), a microstructure was slightly coarser and the proportion of austenite with blocky morphology increased. The identification of a highly refined microstructure was performed using TEM and SAED methods. Besides, isothermal annealing temperature significantly affects hardness. The hardness difference between annealing at 250°C (630.0 ± 4.4 HV1) and 300°C (517.3 ± 1.1 HV1) was over 100 HV. Such a substantial decrease in hardness was caused by the fraction and morphology of the occurred phases. Due to the high silicon content in the tested steel (1.54%), the carbide precipitation was delayed, but locally the cementite precipitates were confirmed. Based on the research, it was found that the commercial 9XC steel is appropriate for nanostructurization in the low ranges of bainitic transformation. Designing of further heat treatment should be focused on the lowest possible temperature of isothermal annealing (even below 250°C).

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Section: Resultsmentioning

confidence: 99%

Evaluation of the Possibility to Obtain Nanostructured Bainite in High-Carbon and High-Silicon 9XC Bearing Steel

Baran

Królicka

2020

J. of Materi Eng and Perform

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“…A Fe-0.8C-2Si-1Mn-1Cr (in wt. %) alloy has been selected based on its low transformation temperatures to bainite as reported in the literature [29][30][31][32][33][34][35][36][37][38]. The C content has been fixed near 0.8 wt.…”

Section: Materials and Casting Proceduresmentioning

confidence: 99%

“…The PAGS plays an important role in defining the type, size and distribution of the low-temperature phases formed during cooling/austempering/quenching and the resultant mechanical properties (e.g., strength, ductility, fracture toughness, etc.) of steels in the final product [26][27][28][34][35][36]. Moreover, several investigations carried out on fracture surfaces have unveiled that cracks may propagate along the prior austenite grain boundaries (PAGBs) when brittle fracture takes place [47][48][49][50].…”

Section: Austenitization Of As-cast Microstructures Prior Austenitic Grain Size (Pags)mentioning

confidence: 99%

“…Solute (interdendritic) rich zones, with higher Si, Mn, and Cr concentration, would possess a smaller ΔT (less thermal energy to grow), promote solute drag effect and contain a greater amount of submicrometer size cementite undissolved precipitates, that would pin the grain boundaries, factors contributing to having a smaller austenite grain size. As both the composition and austenite grain size may influence the bainitic and martensitic transformations [26][27][28][34][35][36][63][64][65], it should be expected that the microsegregation and the inhomogeneous grain size distribution will affect these transformations. Microstructures have been etched with Vilella reagent.…”

Section: Austenitization Of As-cast Microstructures Prior Austenitic Grain Size (Pags)mentioning

confidence: 99%

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Effect of the Microsegregation on Martensitic and Bainitic Reactions in a High Carbon-High Silicon Cast Steel

Basso

Toda‐Caraballo

Eres-Castellanos

et al. 2020

Metals

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Casting processes show some weaknesses. A particular problem is presented when the workpiece needs to be subjected to heat treatments to achieve a desired microstructure. This problem arises from the microsegregation phenomena typically present in cast parts. The effect of the microsegregation on the martensitic and bainitic transformations has been investigated in a high carbon-high silicon cast steel, with the approximate composition Fe-0.8C-2Si-1Mn-1Cr (in wt. %), which was poured into 25 mm keel block-shaped sand molds. The microsegregation maps of Cr, Si, and Mn characterized by electron probe microanalysis (EPMA) show that interdendritic regions are enriched while dendrites are impoverished in these elements, implying that their partition coefficients are lower that the unity (k < 1). As-quenched martensitic and austempered bainitic microstructures (at 230 °C) were obtained and analyzed after applying an austenitization heat treatment at 920 °C (holding for 60 min). The thermal etching method used to reveal the prior austenite grain size showed a bimodal grain size distribution, with larger grains in the dendritic regions (≈22.4 µm) than in the interdendritic ones (≈6.4 µm). This is likely due to both the microsegregation and the presence of small undissolved cementite precipitates. Electron Backscatter Diffraction (EBSD) analysis carried out on the martensitic microstructure do not unveil any differences in misorientation distribution frequency and block size between the dendritic and interdendritic zones related to the microsegregation and bimodality of the austenite grain size. On the contrary, the bainitic transformation starts earlier (incubation time of 80 min), proceeds faster and bainitic ferrite plates are longer in the dendritic zones, were prior austenite grains are larger and impoverish in solute. The presence of these microsegregation pattern leads to the non-uniform development of the bainitic reaction in cast parts, modifying its kinetics and the resulting microstructures, which would probably have a major impact on the mechanical properties.

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“…Parallel furrow-like structures were observed. The grooves were the α-Fe lattice phases, which were deeply eroded by the nitric acid solution, while the embossments were the remaining γ-Fe lattice phases [27]. Three-dimensional roughness analysis showed that the strips has a height of more than 200 nm.…”

Section: Resultsmentioning

confidence: 99%

Characterization of a Nanocrystalline Structure Formed by Crystal Lattice Transformation in a Bulk Steel Material

Cui

Liu

Zhang

et al. 2018

Metals

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The formation of nanocrystalline structures in bulk metal materials is of great significance for both investigating the structural features of nanocrystalline materials and enhancing the value of bulk metal materials in engineering applications. Herein, we report a nanocrystalline structure formed by lattice transformation in a three-dimensional bulk metal material. We characterized its phase composition, three-dimensional features, and boundary structure. This nanocrystalline structure had microscale length and height and nanoscale width, which gave it a "nanoplate" structure in three-dimensional space. We observed edge dislocations in the interior of the nanocrystalline structure. A unique transitional boundary that contributed to maintaining its nanoscale size was found at the border between the parent phase and the nanocrystalline structure.

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Effect of Prior Austenite Grain Size on the Morphology of Nano-Bainitic Steels

Cited by 36 publications

References 23 publications

Evaluation of the Possibility to Obtain Nanostructured Bainite in High-Carbon and High-Silicon 9XC Bearing Steel

Evaluation of the Possibility to Obtain Nanostructured Bainite in High-Carbon and High-Silicon 9XC Bearing Steel

Effect of the Microsegregation on Martensitic and Bainitic Reactions in a High Carbon-High Silicon Cast Steel

Characterization of a Nanocrystalline Structure Formed by Crystal Lattice Transformation in a Bulk Steel Material

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