scholarly journals Quantitative Assessment of the Time to End Bainitic Transformation

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 925 ◽  
Author(s):  
Santajuana ◽  
Eres-Castellanos ◽  
Ruiz-Jimenez ◽  
Allain ◽  
Geandier ◽  
...  
Keyword(s):  
Low Temperature ◽  
Bainitic Ferrite ◽  
High Energy ◽  
Heat Treatments ◽  
Bainitic Transformation ◽  
Transformation Rate ◽  
General Criterion ◽  
X Ray Diffraction ◽  
X Ray ◽  
Start Temperature

Low temperature bainite consists of an intimate mixture of bainitic ferrite and retained austenite, usually obtained by isothermal treatments at temperatures close to the martensite start temperature and below the bainite start temperature. There is widespread belief regarding the extremely long heat treatments necessary to achieve such a microstructure, but still there are no unified and objective criteria to determine the end of the bainitic transformation that allow for meaningful results and its comparison. A very common way to track such a transformation is by means of a high-resolution dilatometer. The relative change in length associated with the bainitic transformation has a very characteristic sigmoidal shape, with low transformation rates at the beginning and at end of the transformation but rapid in between. The determination of the end of transformation is normally subjected to the ability and experience of the “operator” and is therefore subjective. What is more, in the case of very long heat treatments, like those needed for low temperature bainite (from hours to days), differences in the criteria used to determine the end of transformation might lead to differences that might not be assumable from an industrial point of view. This work reviews some of the most common procedures and attempts to establish a general criterion to determine the end of bainitic transformation, based on the differential change in length (transformation rate) derived from a single experiment. The proposed method has been validated by means of the complementary use of hardness measurements, X-ray diffraction and in situ high energy X-ray diffraction.

scholarly journals In-Situ High-Energy X-ray Diffraction Study of Austenite Decomposition During Rapid Cooling and Isothermal Holding in Two HSLA Steels

2021 ◽  
Vol 52 (5) ◽  
pp. 1812-1825
Author(s):  
Sen Lin ◽  
Ulrika Borggren ◽  
Andreas Stark ◽  
Annika Borgenstam ◽  
Wangzhong Mu ◽  
...  
Keyword(s):  
Isothermal Holding ◽  
Weight Percent ◽  
High Energy ◽  
Decomposition Kinetics ◽  
Bainitic Transformation ◽  
Austenite Decomposition ◽  
X Ray Diffraction ◽  
Rapid Cooling ◽  
X Ray

AbstractIn-situ high-energy X-ray diffraction experiments with high temporal resolution during rapid cooling (280 °C s−1) and isothermal heat treatments (at 450 °C, 500 °C, and 550 °C for 30 minutes) were performed to study austenite decomposition in two commercial high-strength low-alloy steels. The rapid phase transformations occurring in these types of steels are investigated for the first time in-situ, aiding a detailed analysis of the austenite decomposition kinetics. For the low hardenability steel with main composition Fe-0.08C-1.7Mn-0.403Si-0.303Cr in weight percent, austenite decomposition to polygonal ferrite and bainite occurs already during the initial cooling. However, for the high hardenability steel with main composition Fe-0.08C-1.79Mn-0.182Si-0.757Cr-0.094Mo in weight percent, the austenite decomposition kinetics is retarded, chiefly by the Mo addition, and therefore mainly bainitic transformation occurs during isothermal holding; the bainitic transformation rate at the isothermal holding is clearly enhanced by lowered temperature from 550 °C to 500 °C and 450 °C. During prolonged isothermal holding, carbide formation leads to decreased austenite carbon content and promotes continued bainitic ferrite formation. Moreover, at prolonged isothermal holding at higher temperatures some degenerate pearlite form.

scholarly journals In-Situ Characterization by High-Energy X-ray Diffraction of the Phase Transformations Leading to Transformation-Induced Plasticity-Aided Bainitic Steel

2019 ◽  
Vol 3 (4) ◽  
pp. 25
Author(s):  
Zélie Tournoud ◽  
Frédéric De Geuser ◽  
Gilles Renou ◽  
Didier Huin ◽  
Patricia Donnadieu ◽  
...  
Keyword(s):  
Carbon Content ◽  
Phase Transformations ◽  
High Energy ◽  
Heat Treatments ◽  
Treatment Temperature ◽  
Bainitic Steel ◽  
X Ray Diffraction ◽  
Transformation Induced Plasticity ◽  
X Ray

The phase transformations occurring during the heat treatments leading to transformation-induced plasticity (TRIP)-aided bainitic steel have been investigated in-situ by high-energy X-ray diffraction (HEXRD) conducted with synchrotron light at 90 keV. Direct microstructure characterization has been performed by electron microscopy using electron backscatter diffraction and orientation and phase mapping in a transmission electron microscope. HEXRD data allow the quantification of the evolution of the austenite phase fraction with the heat treatments, as well as its carbon content and the fraction of carbides, from the lattice parameter evolution. It is shown that different combinations of austenite fraction and carbon content can be reached by adjusting the heat treatment temperature.

scholarly journals The Influence of Vanadium Additions on Isothermally Formed Bainite Microstructures in Medium Carbon Steels Containing Retained Austenite

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 392 ◽  
Author(s):  
Irina Pushkareva ◽  
Babak Shalchi-Amirkhiz ◽  
Sébastien Yves Pierre Allain ◽  
Guillaume Geandier ◽  
Fateh Fazeli ◽  
...  
Keyword(s):  
Retained Austenite ◽  
Bainitic Ferrite ◽  
High Energy ◽  
Carbon Steels ◽  
Ex Situ ◽  
Transformation Rate ◽  
Medium Carbon ◽  
X Ray ◽  
Medium Carbon Steels ◽  
Carbon Mass Balance

The influence of V additions on isothermally formed bainite in medium carbon steels containing retained austenite has been investigated using in-situ high energy X-ray diffraction (HEXRD) and ex-situ electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis (EDX) techniques in the transmission electron microscope (TEM). No significant impact of V in solid solution on the bainite transformation rate, final phase fractions or on the width of bainite laths was seen for transformations in the range 375–430 °C. No strong influence on the dislocation density could be detected, although quantitative analysis was impeded by ferrite tetragonality. A reduction in the carbon content of retained austenite Cγ that is not believed to be due to competition with VC or cementite precipitation was observed. No influence of V on the carbon supersaturation in bainitic ferrite Cb could be directly measured, although carbon mass balance calculations suggest Cb slightly increases. A beneficial refinement of blocky MA and a corresponding size effect induced enhancement in austenite stability were found at the lowest transformation temperature. Overall, V additions result in a slight increase in strength levels.

In situ x-ray observation of bainitic transformation of austempered silicon alloyed steel

2009 ◽  
Vol 24 (4) ◽  
pp. 1559-1566 ◽  
Author(s):  
Xiang Chen ◽  
Esa Vuorinen
Keyword(s):  
Volume Fraction ◽  
Early Stage ◽  
Bainitic Ferrite ◽  
Bainitic Transformation ◽  
Low Carbon ◽  
X Ray Diffraction ◽  
Heterogeneous Distribution ◽  
X Ray ◽  
Austempering Temperature

The in situ x-ray diffraction observations of the bainitic transformation were conducted by using the high-temperature x-ray diffraction technique. The volume fraction and carbon content of austenite depend on the transformation temperature. The d{110} value of bainitic ferrite decreases with increasing austempering temperature, which is related to the decrease of carbon concentration in bainitic ferrite. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation at any austempering temperatures. This asymmetry diffraction peak after the formation of bainitic ferrite could be attributed to a heterogeneous distribution of carbon in different regions of austenite and show that two types of austenite with different carbon contents, low-carbon austenite (γLC) and the high-carbon austenite (γHC), exist during the transformation. The microstructure after cooling down to room temperature is presented to show the effectiveness of the x-ray diffraction analysis.

scholarly journals Carbide-Free Bainite Transformations Above and Below Martensite Start Temperature Investigated by In-Situ High-Energy X-Ray Diffraction

JOM ◽  
2021 ◽  
Author(s):  
Cécile Rampelberg ◽  
Sébastien Yves Pierre Allain ◽  
Guillaume Geandier ◽  
Julien Teixeira ◽  
Florimonde Lebel ◽  
...  
Keyword(s):  
High Energy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Start Temperature

scholarly journals Mechanochemical Reactions of Lithium Niobate Induced by High-Energy Ball-Milling

Crystals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 334 ◽  
Author(s):  
Kocsor ◽  
Péter ◽  
Corradi ◽  
Kis ◽  
Gubicza ◽  
...  
Keyword(s):  
Lithium Niobate ◽  
Ball Milling ◽  
Coulometric Titration ◽  
High Energy ◽  
Heat Treatments ◽  
X Ray Diffraction ◽  
X Ray ◽  
Reflection Measurement ◽  
Energy Ball ◽  
Mechanochemical Reactions

Lithium niobate (LiNbO3, LN) nanocrystals were prepared by ball-milling of the crucible residue of a Czochralski grown congruent single crystal, using a Spex 8000 Mixer Mill with different types of vials (stainless steel, alumina, tungsten carbide) and various milling parameters. Dynamic light scattering and powder X-ray diffraction were used to determine the achieved particle and grain sizes, respectively. Possible contamination from the vials was checked by energy-dispersive X-ray spectroscopy measurements. Milling resulted in sample darkening due to mechanochemical reduction of Nb (V) via polaron and bipolaron formation, oxygen release and Li2O segregation, while subsequent oxidizing heat-treatments recovered the white color with the evaporation of Li2O and crystallization of a LiNb3O8 phase instead. The phase transformations occurring during both the grinding and the post-grinding heat treatments were studied by Raman spectroscopy, X-ray diffraction and optical reflection measurement, while the Li2O content of the as-ground samples was quantitatively measured by coulometric titration.

Isothermal Transformation of Low Temperature Super Bainite

2010 ◽  
Vol 146-147 ◽  
pp. 1843-1848 ◽  
Author(s):  
Feng Hu ◽  
Kai Ming Wu
Keyword(s):  
Low Temperature ◽  
Carbon Content ◽  
Phase Boundary ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Isothermal Transformation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bainitic Microstructure ◽  
Incomplete Reaction

Fine-scale bainitic microstructure with excellent mechanical properties has been achieved by transforming austenite to bainite at low temperature ranging from 200oC to 300oC. Microstructural observations and hardness measurements show that transformed microstructures consist of bainitic ferrite and carbon-enriched retained austenite. The thickness of bainitic ferrite plates is less than 50 nm. The hardness reaches approximately 640 HV1. Strong austenite and/or large driving force at the low transformation temperature leads to ultra fine bainitic ferrite plates. X-ray diffraction analysis indicates that low-temperature bainite transformation is an incomplete reaction. The carbon content in carbon-enriched retained austenite is below the para-equilibrium (Ae3′) phase boundary predicted. The carbon content in bainitic ferrite is less than that T0′ phase boundary predicted.

scholarly journals Low temperature dielectric relaxation in ordinary perovskite ferroelectrics: enlightenment from high-energy x-ray diffraction

2017 ◽  
Vol 50 (20) ◽  
pp. 205305 ◽  
Author(s):  
D A Ochoa ◽  
R Levit ◽  
C M Fancher ◽  
G Esteves ◽  
J L Jones ◽  
...  
Keyword(s):  
Low Temperature ◽  
Dielectric Relaxation ◽  
High Energy ◽  
X Ray Diffraction ◽  
X Ray
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