Understanding of the Bainite Transformation in a Nano-Structured Bainitic Steel

2011 ◽  
Vol 172-174 ◽  
pp. 123-128 ◽  
Author(s):  
Peter D. Hodgson ◽  
Ilana Timokhina ◽  
Xiang Yuan Xiong ◽  
Yoshitaka Adachi ◽  
Hossein Beladi
Keyword(s):  
Retained Austenite ◽  
Three Dimensional ◽  
Bainitic Ferrite ◽  
Atom Probe ◽  
Crystallographic Analysis ◽  
Heat Treated ◽  
Bainitic Microstructure ◽  
Wide Range ◽  
Equilibrium Level ◽  
Parent Austenite

A 0.79C-1.5Si-1.98Mn-0.98Cr-0.24Mo-1.06Al-1.58Co (wt%) steel was isothermally heat treated at 200°C for 10 days to form a nano-scale bainitic microstructure consisting of nanobainitic ferrite laths with high dislocation density and retained austenite films. The crystallographic analysis using TEM and EBSD revealed that the bainitic ferrite laths are close to the Nishiyama-Wassermann orientation relationship with the parent austenite. There was only one type of packet identified in a given transformed austenite grain. Each packet consisted of two different blocks having variants with the same habit plane, but different crystallographic orientations. The presence of fine C-rich clusters and Fe-C carbides with a wide range of compositions in bainitic ferrite was revealed by Three-dimensional Atom Probe Tomography (APT). The high carbon content of bainitic ferrite compared to the para-equilibrium level of carbon in ferrite, absence of segregation of carbon to the austenite/bainitic ferrite interface and absence of partitioning of substitutional elements between the retained austenite and bainitic ferrite were also found using APT.

CHARACTERIZATION OF NANO-STRUCTURED BAINITIC STEEL

2012 ◽  
Vol 05 ◽  
pp. 1-8 ◽  
Author(s):  
HOSSEIN BELADI ◽  
ILANA B. TIMOKHINA ◽  
PETER D. HODGSON ◽  
YOSHITAKA ADACHI
Keyword(s):  
Treatment Time ◽  
Bainitic Ferrite ◽  
Atom Probe ◽  
Crystallographic Analysis ◽  
Bainitic Steel ◽  
Heat Treated ◽  
Dislocation Densities ◽  
Equilibrium Level ◽  
Parent Austenite

A 0.79 C -1.5 Si -1.98 Mn -0.98 Cr -0.24 Mo -1.06 Al -1.58 Co ( wt %) steel was isothermally heat treated at 200°C for 10 days to produce a nano-structured bainitic steel. The microstructure consisted of nanobainitic ferrite laths with a high dislocation density and retained austenite films having extensive twins. The crystallographic analysis using TEM and EBSD revealed that the bainitic ferrite laths are close to the Nishiyama-Wassermann orientation relationship with their parent austenite. There was only one type of packet identified in a given transformed austenite grain. Each packet consisted of two different blocks having variants with the same habit plane, but different crystallographic orientations. Atom Probe Tomography (APT) revealed that the carbon content of nanobainitic ferrite laths was much higher than expected from the para-equilibrium level. This was explained due to the long heat treatment time, which led to the formation of fine Fe - C clusters on areas with high dislocation densities in bainitic ferrite laths.

Specifications for Hard Condensed Matter Specimens for Three-Dimensional High-Resolution Tomographies

2013 ◽  
Vol 19 (3) ◽  
pp. 726-739 ◽  
Author(s):  
P. Bleuet ◽  
G. Audoit ◽  
J.-P. Barnes ◽  
J. Bertheau ◽  
Y. Dabin ◽  
...  
Keyword(s):  
Sample Preparation ◽  
Heterogeneous Media ◽  
Effective Properties ◽  
Condensed Matter ◽  
Three Dimensional ◽  
Atom Probe ◽  
Preparation Technique ◽  
Ion Milling ◽  
Wide Range ◽  
Mechanical Machining

AbstractTomography is a standard and invaluable technique that covers a large range of length scales. It gives access to the inner morphology of specimens and to the three-dimensional (3D) distribution of physical quantities such as elemental composition, crystalline phases, oxidation state, or strain. These data are necessary to determine the effective properties of investigated heterogeneous media. However, each tomographic technique relies on severe sampling conditions and physical principles that require the sample to be adequately shaped. For that purpose, a wide range of sample preparation techniques is used, including mechanical machining, polishing, sawing, ion milling, or chemical techniques. Here, we focus on the basics of tomography that justify such advanced sample preparation, before reviewing and illustrating the main techniques. Performances and limits are highlighted, and we identify the best preparation technique for a particular tomographic scale and application. The targeted tomography techniques include hard X-ray micro- and nanotomography, electron nanotomography, and atom probe tomography. The article mainly focuses on hard condensed matter, including porous materials, alloys, and microelectronics applications, but also includes, to a lesser extent, biological considerations.

scholarly journals Hydrogen diffusion and the percolation of austenite in nanostructured bainitic steel

2014 ◽  
Vol 470 (2168) ◽  
pp. 20140108 ◽  
Author(s):  
L. C. D. Fielding ◽  
E. J. Song ◽  
D. K. Han ◽  
H. K. D. H. Bhadeshia ◽  
D.-W. Suh
Keyword(s):  
Hydrogen Diffusion ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Bainitic Ferrite ◽  
Effective Diffusivity ◽  
Steel Sample ◽  
Thin Plates ◽  
Heat Treated ◽  
Diffusion Of Hydrogen

The diffusion of hydrogen in austenite is slower than in ferrite. Experiments have been conducted to study the behaviour of hydrogen in a nanostructured steel sample consisting of a mixture of thin plates of bainitic ferrite and intervening films of retained austenite, with the latter phase present in a quantity larger than the percolation threshold, i.e. it has three-dimensional connectivity. The structure was then heat treated to control the fraction of austenite, and hence to study the role of hydrogen when the austenite decomposes below the value required to sustain percolation. The experiments have involved both thermal desorption analysis and permeation, and when combined with theoretical analysis, indicate a significant influence of percolating austenite in hindering the passage of hydrogen into the steel during hydrogen charging, and its permeation through the composite nanostructure. The effect is not as large as might be expected from a simple comparison of independent data on the diffusivities of hydrogen in the two lattices, because the effective diffusivity in ferrite is found to be much smaller than in the defect-free ferrite, owing to trapping effects. The morphology of the austenite is demonstrated to play a role by comparing with a sample containing a larger volume fraction of austenite but present as isolated grains which are ineffective to the permeation of hydrogen.

Atomic Scale Investigation of Solutes and Precipitates in High Strength Steels

2013 ◽  
Vol 762 ◽  
pp. 14-21 ◽  
Author(s):  
Peter Hodgson ◽  
Subrata Mukherjee ◽  
Hossein Beladi ◽  
Xiang Yuan Xiong ◽  
Ilana B. Timokhina
Keyword(s):  
Retained Austenite ◽  
Thermomechanical Processing ◽  
Bainitic Ferrite ◽  
High Strength Steels ◽  
High Strength ◽  
Atom Probe ◽  
Atomic Scale ◽  
Isothermal Hold ◽  
Local Defects ◽  
Lower Carbon

Two steels, ferritic, high strength with interphase precipitation and nanobainitic, were used to show the advances in and application of atom probe. The coexistence of the nanoscale, interphase Nb-Mo-C clusters and stoichiometric MC nanoparticles was found in the high strength steel after thermomechanical processing. Moreover, the segregation of carbon at different heterogeneous sites such as grain boundary that reduces the solute element available for fine precipitation was observed. The APT study of the solutes redistribution between the retained austenite and bainitic ferrite in the nanobainitic steel revealed: (i) the presence of two types of the retained austenite with higher and lower carbon content and (ii) segregation of carbon at the local defects such as dislocations in the bainitic ferrite during the isothermal hold.

Slow Bainite: an Opportunity to Determine the Carbon Content of the Bainitic Ferrite during Growth

2011 ◽  
Vol 172-174 ◽  
pp. 111-116 ◽  
Author(s):  
Francisca García Caballero ◽  
Michael K. Miller ◽  
Carlos García-Mateo
Keyword(s):  
Solid Solution ◽  
Carbon Content ◽  
Atom Probe Tomography ◽  
Early Stage ◽  
Bainitic Ferrite ◽  
Atom Probe ◽  
Transformation Kinetics ◽  
Bainite Transformation ◽  
Parent Austenite ◽  
Kinetics Of

The amount of carbon in solid solution in bainitic ferrite at the early stage of transformation has been directly determined by atom probe tomography at 200 °C, taking advantage of the extremely slow transformation kinetics of a novel nanocrystalline steel. Results demonstrated that the original bainitic ferrite retains much of the carbon content of the parent austenite providing strong evidence that bainite transformation is essentially displacive in nature.

Distribution of Dislocations in Nanostructured Bainite

2011 ◽  
Vol 172-174 ◽  
pp. 117-122 ◽  
Author(s):  
J. Cornide ◽  
Goro Miyamoto ◽  
Francisca García Caballero ◽  
Tadashi Furuhara ◽  
Michael K. Miller ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Atom Probe Tomography ◽  
Bainitic Ferrite ◽  
Transformation Strain ◽  
Atom Probe ◽  
Ferrite Plate ◽  
Transmission Electron ◽  
Bainitic Microstructure ◽  
Distribution Of Dislocations ◽  
Very Low Temperature

The dislocation density in ferrite and austenite of a bainitic microstructure obtained by transformation at very low temperature (300 °C) has been determined using transmission electron microscopy. Observations revealed that bainitic ferrite plates consist of two distinctive regions with different substructures. A central region in the ferrite plate is observed with dislocations that may result from lattice-invariant deformation at the earlier stage of bainite growth. As plastic deformation occurs in the surrounding austenite to accommodate the transformation strain as growth progresses, the Ferrite/Austenite interface has also a very distinctive dislocation profile. In addition, atom-probe tomography suggested that dislocation tangles observed in the vicinity of the ferrite/austenite interface might trap higher amount of carbon than single dislocations inside the bainitic ferrite plate.

scholarly journals Experimental Investigation of Engineering Materials under Repetitive Impact with Slurry Conditions

2020 ◽  
Vol 69 (1) ◽  
Author(s):  
F. Brownlie ◽  
T. Hodgkiess ◽  
A. M. Galloway ◽  
A. Pearson
Keyword(s):  
Three Dimensional ◽  
Test Rig ◽  
Cast Irons ◽  
Ductile Materials ◽  
Heat Treated ◽  
Wide Range ◽  
Post Test ◽  
Engineering Materials ◽  
Repetitive Impact ◽  
Dimensional Surface

AbstractIn some industrial situations, components are subject to repetitive impact in the presence of a slurry. A novel repetitive impact-with-slurry test rig was developed to evaluate the behaviour of a wide range of engineering materials in such conditions. The test materials could be categorised into five main groups – heat treated steels, stainless steels, chromium cast irons, hardfacing coatings and superalloys. Three-dimensional surface topography was used to quantify the depths and volumes of the produced wear scars. Post-test metallurgical examination was also conducted to further evaluate the wear processes. The wear mechanisms could be split into two main groups of materials; ductile materials were observed to plastically deform and hard/brittle materials demonstrated cracking/spalling mechanisms. Hardened martensitic-type materials exhibited the greatest resistance to repetitive impact wear.

scholarly journals Bainitic reaction and microstructure evolution in two normalized and tempered steels designed for service at elevated temperatures

2017 ◽  
Vol 17 (4) ◽  
pp. 22-36
Author(s):  
Z. Ławrynowicz
Keyword(s):  
Heat Treatment ◽  
Retained Austenite ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Integral Intensity ◽  
Bainitic Ferrite ◽  
Residual Austenite ◽  
Thin Foils ◽  
Bainitic Microstructure ◽  
Conventional Heat Treatment

Abstract In the present work conventional heat treatment like normalizing (bainitic microstructure) and tempering of the alloys has been performed. The materials used in this study were two steels, one the laboratory prepared experimental low alloy Cr-Mo steel in comparison to typical commercial 10CrMo9-10 steel. The determined carbon concentrations of the residual austenite at the different temperatures of bainite transformation supports the hypothesis that the growth of bainitic ferrite occurs without any diffusion with carbon being partitioned subsequently into the residual austenite. It was found that bainitic reaction has stopped when average carbon concentration of the untransformed austenite is close to the T0 line and supports formation of bainitic ferrite by a shear mechanism, since diffusionless transformation is not possible beyond the T0 curve. Normalized samples were air cooled down to room temperature before tempering at various temperatures in the range of 500-750°C. Samples have been austenitized at 980°C for 0.5 hour air cooled and tempered at 500, 550, 600, 650, 700 and 750°C for 1 hour. After heat treatment, the assessment in the microstructure and phase precipitation was made using the samples prepared for metallographic and transmission electron microscope (TEM) on thin foils analysis. Quantitative X-ray analysis was used to determine the retained austenite content after heat treatment like normalizing and tempering and the total volume fraction of the retained austenite was measured from the integral intensity of the (111)γ and (011)α peaks. The changes observed in the microstructure of the steel tempered at the higher temperature, i.e. 750°C were more advanced than those observed at the temperature of 500°C. Performed microstructural investigations have shown that the degradation of the microstructure of the examined steel was mostly connected with the processes of recovery and polygonization of the matrix, disappearance of lath bainitic microstructure, the growth of the size of M23C6 carbides, and precipitation of the secondary M2C precipitates. The magnitude of these changes depended on the temperature of tempering.

Application of Advanced Experimental Techniques for the Microstructural Characterization of Nanobainitic Steels

2011 ◽  
Vol 172-174 ◽  
pp. 1249-1254 ◽  
Author(s):  
Ilana Timokhina ◽  
Hossein Beladi ◽  
Xiang Yuan Xiong ◽  
Yoshitaka Adachi ◽  
Peter D. Hodgson
Keyword(s):  
Dislocation Density ◽  
Carbon Content ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Accurate Determination ◽  
Bainitic Ferrite ◽  
Microstructural Characterization ◽  
Atom Probe ◽  
Isothermal Heat Treatment ◽  
Local Composition

A 0.79C-1.5Si-1.98Mn-0.98Cr-0.24Mo-1.06Al-1.58Co (wt%) steel was isothermally heat treated at 350°C bainitic transformation temperature for 1 day to form fully bainitic structure with nano-layers of bainitic ferrite and retained austenite, while a 0.26C-1.96Si-2Mn-0.31Mo (wt%) steel was subjected to a successive isothermal heat treatment at 700°C for 300 min followed by 350°C for 120 min to form a hybrid microstructure consisting of ductile ferrite and fine scale bainite. The dislocation density and morphology of bainitic ferrite, and retained austenite characteristics such as size, and volume fraction were studied using Transmission Electron Microscopy. It was found that bainitic ferrite has high dislocation density for both steels. The retained austenite characteristics and bainite morphology were affected by composition of steels. Atom Probe Tomography (APT) has the high spatial resolution required for accurate determination of the carbon content of the bainitic ferrite and retained austenite, the solute distribution between these phases and calculation of the local composition of fine clusters and particles that allows to provide detailed insight into the bainite transformation of the steels. The carbon content of bainitic ferrite in both steels was found to be higher compared to the para-equilibrium level of carbon in ferrite. APT also revealed the presence of fine C-rich clusters and Fe-C carbides in bainitic ferrite of both steels.

scholarly journals Effect of Ausforming on the Macro- and Micro-texture of Bainitic Microstructures

2021 ◽  
Author(s):  
Adriana Eres-Castellanos ◽  
Lucia Morales-Rivas ◽  
Jose Antonio Jimenez ◽  
Francisca G. Caballero ◽  
Carlos Garcia-Mateo
Keyword(s):  
Deformation Temperature ◽  
Prior Austenite ◽  
Thermomechanical Processing ◽  
Bainitic Ferrite ◽  
Fiber Texture ◽  
Variant Selection ◽  
Electron Backscattered Diffraction ◽  
Transformation Texture ◽  
Heat Treated ◽  
Bainitic Microstructure

Abstract The reason why variant selection phenomena occur in ausforming treatments is still not known. For that reason, in this work, the effect of compressive deformation on the macro and micro-texture of a bainitic microstructure was analyzed in a medium-carbon high-silicon steel subjected to ausforming treatments, where deformation was applied at 520 °C, 400 °C and 300 °C. The as-received material presented a very weak $$\left\langle {3\, 3\, 1} \right\rangle$$ 3 3 1 fiber texture along the rod axis, due to prior thermomechanical processing. For the samples isothermally heat-treated, it was detected that the bainitic ferrite inherited a $$\left\langle {1\, 0\, 0} \right\rangle$$ 1 0 0 fiber texture from the $$\left\langle {1\, 1\, 0} \right\rangle$$ 1 1 0 fiber texture present in the prior austenite. The intensity of this transformation texture was more pronounced as the deformation temperature decreased. Also, variant selection was examined at different scales by combining Electron-Backscattered Diffraction and X-ray Diffraction. The quantification of the fraction of crystallographic variants under certain conventions for every condition revealed variant selection in samples subjected to ausforming treatments, where these phenomena were stronger as the deformation temperature was lower. Finally, some of the theories proposed so far to explain these variant selection phenomena were tested, showing that variants were not selected based on their Bain group and that their selection can be better described in terms of their belonging to packets, if these are defined according to a global reference frame. This suggests that the phenomena might have to do with the effect of deformation mechanisms on the prior austenite.

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