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Clodualdo Aranas - One of the best experts on this subject based on the ideXlab platform.
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Thermomechanical and thermodynamic behavior of deformed Austenite in four different steel grades
Journal of Materials Research and Technology, 2021Co-Authors: Clodualdo Aranas, Samuel F Rodrigues, Fulvio Siciliano, Jubert Pasco, E.j.p. Miranda, John J. JonasAbstract:Abstract In this work, the deformation behavior and thermodynamic aspect of four different steel grades were analyzed. This group of alloys includes a plain C-Mn, and three Nb-microalloyed steels grades. Two of the microalloyed grades are pipeline steel grades: a modified X-70 grade, and a typical X-80 steel. These materials were previously identified to produce dynamically transformed ferrite (combined with recrystallized grains) during physical simulation of hot rolling in the single Austenite Phase Field of their Phase diagrams. For C-Mn and Nb-microalloyed steels, hot deformation at a stain of 0.4 and strain rate of 1 s-1 generates 15 and 25 vol% of ferrite, respectively. In addition, the X-70 and X-80 steels yield 19 and 8 vol% of ferrite, respectively, after deformation strains of 0.4 and 0.2, and strain rate of 1 s-1. All the deformation was applied at least 53 ˚C above their respective Ae3 temperatures. The concept of transformation softening was applied to explain the occurrence of dynamic transformation during hot torsion tests. Here the driving force to dynamic transformation (DT) was taken by measuring the difference between the critical stress to DT in the Austenite Phase, and the yield stress of the ferrite that takes its place. The obstacle energy consists of the free energy between the parent and product Phases and the shear accommodation and lattice dilatation work associated with Phase transformation of Austenite to ferrite. It is shown here that, for all the selected materials, the calculated driving force is higher than the energy obstacles, which thermodynamically explains the occurrence of DT.
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in situ x ray diffraction evidence of dynamic transformation of Austenite to ferrite during hot compression test in the single Austenite Phase Field
Scripta Materialia, 2020Co-Authors: Clodualdo Aranas, Samuel F Rodrigues, Fulvio Siciliano, J J JonasAbstract:Abstract Dynamic transformation (DT) of Austenite to ferrite can take place in the single Austenite Phase Field during thermomechanical processing as shown in the literature. However, despite significant progress on this topic, limited real-time evidence of DT has been published. To address this concern, an in-situ X-ray diffraction measurement was carried out on a pipeline steel before, during and after hot compression. The appearance of ferrite peaks is evident during deformation and these peaks disappear after 9 s of isothermal holding. This work provides an in-situ evidence of both forward and backward dynamic transformation complemented with energy calculations to validate the observations.
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Effect of Number of Roughing Passes on the Dynamic Transformation of Austenite during Simulated Plate Rolling
Materials Science Forum, 2018Co-Authors: Samuel F Rodrigues, Clodualdo Aranas, Fulvio Siciliano, Gedeon Silva Reis, Brian J. Allen, John J. JonasAbstract:When Austenite is deformed within the Austenite Phase Field, it partially transforms dynamically into ferrite. Here, plate rolling simulations were carried out on an X70 steel using rough rolling passes of 0.4 strain each. The influence of the number of roughing passes on the grain size and volume fraction of induced ferrite was determined. Up to three roughing passes applied at 1100 °C followed by 5 finishing passes at 900 °C were employed. The sample microstructures were analysed by means of metallographic techniques. Both the critical strain to the onset of dynamic transformation as well as the grain size decreased with pass number during the roughing simulations. For the finishing passes, the mean flow stresses (MFS`s) applicable to each schedule decreased when a higher number of roughing passes was applied. The volume fraction of dynamically formed ferrite retained after simulated rolling increased with the roughing pass number. This is ascribed to the increased amount of ferrite retransformed into Austenite and the finer grain sizes produced during roughing. The forward transformation is considered to occur displacively while the retransformation into Austenite during holding takes place by a diffusional mechanism. This indicates that both dynamic transformation (DT) and dynamic recrystallization were taking place during straining.
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formation of widmanstatten ferrite at very high temperatures in the Austenite Phase Field
Acta Materialia, 2016Co-Authors: Rupanjit Grewal, Clodualdo Aranas, Kanwal Chadha, Davood Shahriari, M Jahazi, J J JonasAbstract:Compression tests were carried out on a 0.06wt%C-0.3wt%Mn-0.01wt%Si steel at temperatures high in the Austenite Phase Field. Eight deformation temperatures were selected in the range from 1000 to 1350 °C at 50 °C intervals. The quenched samples were examined using optical microscopy and EBSD techniques. It was observed that dynamic transformation took place and that the volume fraction of transformed ferrite first decreased with temperature (up to 1050 °C) and then increased as the delta ferrite temperature domain was approached. The EBSD results revealed the presence of Widmanstatten ferrite plates under all testing conditions, right up to 1350 °C.
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Dynamic Transformation during Plate and Strip Rolling
Materials Science Forum, 2016Co-Authors: John J. Jonas, Clodualdo Aranas, Samuel F Rodrigues, In-ho JungAbstract:Torsion simulations were carried out of both plate (long interpass times) and strip (short interpass times) rolling. Both isothermal and continuous cooling conditions were employed. The dynamic transformation of Austenite to ferrite was observed under all conditions and at all temperatures within the Austenite Phase Field. About 8 to 10 volume percent ferrite was formed in a given pass, leading to about 50 - 70 % ferrite at the end of selected simulations. During the interpass intervals, some retransformation to Austenite took place, the amount of which increased with holding time and temperature and decreased with the addition of alloying elements. It is shown that the driving force for the transformation is the softening associated with the replacement of work-hardened Austenite grains by the softer alpha Phase. The implications with respect to rolling load (i.e. mean flow stress) are also discussed.
J J Jonas - One of the best experts on this subject based on the ideXlab platform.
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in situ x ray diffraction evidence of dynamic transformation of Austenite to ferrite during hot compression test in the single Austenite Phase Field
Scripta Materialia, 2020Co-Authors: Clodualdo Aranas, Samuel F Rodrigues, Fulvio Siciliano, J J JonasAbstract:Abstract Dynamic transformation (DT) of Austenite to ferrite can take place in the single Austenite Phase Field during thermomechanical processing as shown in the literature. However, despite significant progress on this topic, limited real-time evidence of DT has been published. To address this concern, an in-situ X-ray diffraction measurement was carried out on a pipeline steel before, during and after hot compression. The appearance of ferrite peaks is evident during deformation and these peaks disappear after 9 s of isothermal holding. This work provides an in-situ evidence of both forward and backward dynamic transformation complemented with energy calculations to validate the observations.
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formation of widmanstatten ferrite at very high temperatures in the Austenite Phase Field
Acta Materialia, 2016Co-Authors: Rupanjit Grewal, Clodualdo Aranas, Kanwal Chadha, Davood Shahriari, M Jahazi, J J JonasAbstract:Compression tests were carried out on a 0.06wt%C-0.3wt%Mn-0.01wt%Si steel at temperatures high in the Austenite Phase Field. Eight deformation temperatures were selected in the range from 1000 to 1350 °C at 50 °C intervals. The quenched samples were examined using optical microscopy and EBSD techniques. It was observed that dynamic transformation took place and that the volume fraction of transformed ferrite first decreased with temperature (up to 1050 °C) and then increased as the delta ferrite temperature domain was approached. The EBSD results revealed the presence of Widmanstatten ferrite plates under all testing conditions, right up to 1350 °C.
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formation of widmanstatten ferrite in a c mn steel at temperatures high in the Austenite Phase Field
2015Co-Authors: Clodualdo Aranas, Rupanjit Grewal, Kanwal Chadha, Davood Shahriari, M Jahazi, J J JonasAbstract:Gleeble compression tests were carried out on a 0.06%C-0.3%Mn-0.01%Si steel over the temperature range 1000°C to 1350°C. Strains of 0.7 were applied at a strain rate of 1s-1. The double differentiation method was employed to determine the critical strains for the initiation of dynamic transformation (0.05 - 0.12) and dynamic recrystallization (0.10 - 0.18). The occurrence of dynamic transformation was detected at temperatures up to 1350°C. Optical and electron microscopy images indicated that Widmanstatten ferrite plates were being formed in the Austenite Phase Field and that the plates coalesced into polygonal grains during straining. These results are interpreted in terms of the flow softening model of dynamic transformation.
A Q Khan - One of the best experts on this subject based on the ideXlab platform.
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the formation of reverted Austenite in 18 ni 350 grade maraging steel
Journal of Materials Science, 1998Co-Authors: M Farooque, H Ayub, Ul A Haq, A Q KhanAbstract:Austenite reversion was studied in 18% Ni 350 grade maraging steel. The samples were heat treated from room temperature to the Austenite Phase Field and, without holding, they were cooled again to ambient temperature. The reverted Austenite which was retained after this heat treatment was examined using a scanning transmission electron microscope equipped with an energy dispersive spectroscopic system. Two morphologies of the Austenite were observed. The first forms at the martensite lath boundaries and the other nucleates inside the martensite laths in the form of Widmanstatten plates. These Widmanstatten plates mostly appear as coupled twins. The coupled twins have a distinct midrib which was found parallel to (1 1 1)γ and (1 1 0)α planes. The latter morphology of Austenite appeared only after the formation of Ni3Ti precipitates. Growth of Fe2Mo precipitates was not observed in this heat-treatment cycle. Both Nishyama–Wassermann and Kurdjumo–Sachs orientation relationships were found between the Austenite and martensite Phases. On the basis of these results, it can be suggested that intra-lath-reverted Austenite is formed on or by the local dissolution of Ni3Ti precipitates. © 1998 Kluwer Academic Publishers
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The formation of reverted Austenite in 18% Ni 350 grade maraging steel
Journal of Materials Science, 1998Co-Authors: M Farooque, H Ayub, A Ul Haq, A Q KhanAbstract:Austenite reversion was studied in 18% Ni 350 grade maraging steel. The samples were heat treated from room temperature to the Austenite Phase Field and, without holding, they were cooled again to ambient temperature. The reverted Austenite which was retained after this heat treatment was examined using a scanning transmission electron microscope equipped with an energy dispersive spectroscopic system. Two morphologies of the Austenite were observed. The first forms at the martensite lath boundaries and the other nucleates inside the martensite laths in the form of Widmanstatten plates. These Widmanstatten plates mostly appear as coupled twins. The coupled twins have a distinct midrib which was found parallel to (1 1 1)γ and (1 1 0)α planes. The latter morphology of Austenite appeared only after the formation of Ni3Ti precipitates. Growth of Fe2Mo precipitates was not observed in this heat-treatment cycle. Both Nishyama–Wassermann and Kurdjumo–Sachs orientation relationships were found between the Austenite and martensite Phases. On the basis of these results, it can be suggested that intra-lath-reverted Austenite is formed on or by the local dissolution of Ni3Ti precipitates. © 1998 Kluwer Academic Publishers
Peter Hodgson - One of the best experts on this subject based on the ideXlab platform.
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effect of molybdenum on Phase transformation and microstructural evolution of strip cast steels containing niobium
Journal of Materials Science, 2019Co-Authors: Lu Jiang, Peter Hodgson, Ross K W Marceau, Thomas Dorin, Nicole StanfordAbstract:Molybdenum (Mo) is known to have a complex effect on Phase transformations and precipitation in steels manufactured by conventional casting. The present work aims to examine the effect of Mo on Phase transformations in Nb-containing steels produced by strip casting. Advanced experimental techniques have been utilised to simulate the strip casting process, and the microstructural features of the rapid solidification are retained for further study. Two cooling conditions from the Austenite Phase Field were examined, isothermal holding and continuous cooling. It was found that at high cooling rates, the addition of Mo delayed the nucleation of bainite and lowered the bainite start temperature, but did not alter the bainite growth rate. The addition of Mo was also found to result in a slower transformation rate of polygonal ferrite under both isothermal and continuous cooling conditions. Thermodynamic simulations indicated that Mo did not affect the growth velocity of the polygonal ferrite, and quantitative metallography showed the nucleation density was significantly reduced by Mo addition. For the slowest continuous cooling rate, the addition of Mo completely inhibited pearlite formation, with bainitic ferrite forming instead. This has been suggested to be the result of the suppression of pearlite nucleation, rather than inhibition of growth.
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ferrite grain coarsening during transformation of thermomechanically processed c mn nb Austenite
Materials Science and Technology, 1992Co-Authors: R. Priestner, Peter HodgsonAbstract:AbstractThe ferrite grain size of low carbon steel is known to be refined by hot rolling in the Austenite Phase Field at temperatures too low for recrystallisation to occur. The strain thus retained in the Austenite increases ferrite nucleation density and in current models of grain refinement it is assumed that each nucleus becomes a grain in the fully transformed microstructure. In this paper it is shown that, in a heavily deformed C–Mn–Nb Austenite, ferrite grains impinged, then coarsened during the initial stages of transformation during continuous cooling. The final ferrite grain size was not established until 35% of transformation had occurred. It is suggested, firstly, that ferrite grain refinement due to controlled rolling cannot be modelled simply from observed increases in nucleation density and, secondly, that deformation of Austenite has considerably greater potential for grain refinement than is commonly observed, provided that coarsening of the ferrite during transformation can be limited.MS...
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Ferrite grain coarsening during transformation of thermomechanically processed C–Mn–Nb Austenite
Materials Science and Technology, 1992Co-Authors: R. Priestner, Peter HodgsonAbstract:AbstractThe ferrite grain size of low carbon steel is known to be refined by hot rolling in the Austenite Phase Field at temperatures too low for recrystallisation to occur. The strain thus retained in the Austenite increases ferrite nucleation density and in current models of grain refinement it is assumed that each nucleus becomes a grain in the fully transformed microstructure. In this paper it is shown that, in a heavily deformed C–Mn–Nb Austenite, ferrite grains impinged, then coarsened during the initial stages of transformation during continuous cooling. The final ferrite grain size was not established until 35% of transformation had occurred. It is suggested, firstly, that ferrite grain refinement due to controlled rolling cannot be modelled simply from observed increases in nucleation density and, secondly, that deformation of Austenite has considerably greater potential for grain refinement than is commonly observed, provided that coarsening of the ferrite during transformation can be limited.MS...
R. Priestner - One of the best experts on this subject based on the ideXlab platform.
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Microstructural Change during the Hot Working of As-Cast Austenite
Materials Science Forum, 1998Co-Authors: R. PriestnerAbstract:The direct hot rolling of the as-cast Austenite of thin slab castings requires the microstructural changes within the Austenite Phase Field that are necessary for a satisfactory product to be accommodated within a smaller degree of total reduction, within a smaller number of passes, and within a shorter time scale. Particularly in the case of microalloyed steel, the constitution of the as-cast Austenite prior to rolling differs from that of Austenite of thick slabs reheated for conventional hot rolling. Consequently, the models developed for conventional rolling employing reheated Austenite cannot be relied upon for predicting microstructural change during the rolling of as-cast Austenite. The as-cast Austenite of microalloyed steels has larger grains, is segregated, and carbonitride precipitates may be present that are not in equilibrium with their solid solution. These factors are discussed in the light of recent research. It is suggested that recrystallisation kinetics should be linearly, rather than quadratically, related to Austenite grain size, and that above a limiting carbon content the addition of Nb and Ti results in excess, eutectically precipitated, Nb-rich carbonitride due to segregation during freezing. The former leads to more rapid recrystallisation than would be predicted by the conventional models, and helps to ensure that plain C-Mn steels can be satisfactorily processed. The presence of eutectic carbonitrides means that the supersaturation of the Austenite with respect to microalloy constituents is unknown, and recrystallisation-stop temperatures cannot be modelled satisfactorily.
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Eutectic Precipitation of (TiNbV)(CN) in Cast, Microalloyed Low-C Austenite and Effects of Reheating
Materials Science Forum, 1998Co-Authors: A.k. Ibraheem, R. PriestnerAbstract:The constitution of Austenite in thin-slab cast, low-C, Mn steel microalloyed with 0.007wt%Ti, 0.04wt%Nb and 0.011wt%V was simulated in small, laboratory castings. Two carbon levels, 0.007wt% and 0.22wt%C, each at two nitrogen levels, 0.003wt% and ∼0.013wt%N, were investigated. After solidification the castings were quenched rapidly from ∼1400°C in order to investigate the eutectic carbonitrides. Samples of the castings were reheated to a range of temperatures in the Austenite Phase Field to investigate the fine precipitates that then appeared, and the re-solution of the eutectic carbonitrides. The compositions of precipitates were determined using high resolution electron microscopy with EDX and PEELS, and compared with the results of a computer model of the solution thermodynamics of (Ti x Nb v v 1-x-v )(C y N 1-y ) in Austenite. The eutectic carbonitride formed only in the higher-C steels independently of N content. However, increasing the nitrogen content of the steel increased the N:C ratio in the eutectic carbonitride. At both nitrogen levels the carbonitride was almost pure Nb(CN). After allowing for strong segregation of Nb and weak segregation of Ti to the liquid during freezing, these results agreed with the thermodynamic model, assuming the eutectic carbonitride to be in equilibrium with Austenite. The presence of the eutectic carbonitride had little effect on subsequent precipitation in reheated Austenite. The new precipitates were Nb-rich at low and intermediate temperatures, with some V at the lowest reheating temperatures. With increasing reheating temperature, first the V content and then the Nb content of these precipitates decreased, and their Ti content increased, as they also became N-rich, in approximate agreement with the computer model. At temperatures above approximately 1200°C the Ti tended to form Ti-rich Ti-Mn-oxides. The eutectic precipitates partially dissolved, but remained Nb-rich on reheating.
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The Evolution of Precipitates in Nb-Ti Microalloyed Steels during Solidification and Post-solidification Cooling
ISIJ International, 1996Co-Authors: C. Zhou, R. PriestnerAbstract:A series of Nb-Ti steels containing titanium in the range 0.005 to 0.038 wt% and nitrogen in the range 0.005 to 0.011 wt% were prepared using a base composition of 0.06 wt% carbon and 0.027 wt% niobium. Small ingots were cooled slowly in order to simulate larger castings. Cooling was interrupted at various temperatures in the Austenite Phase Field, either by quenching or by holding isothermally before quenching. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were used to investigate the morphology, distribution, composition, and particle size of carbonitrides in processed ingots. Samples of the quenched ingots were tempered for 1 hr an 600°C. Tempered hardness was used to estimate the amount of microalloy elements in solution in Austenite at the moment of quenching. Ingots containing 0.013-0.017 wt% Ti were found to be undersaturated with respect to (NbxTi1-x) (CyN1-y), and Nb-rich carbonitride were present after solidification. These were stable during cooling, and supersaturation did not occur until the ingot temperature fell below approximately 1200°C. It was found that the Nb-rich precipitates became Ti rich in the ingots quenched from 1400°C, when either the nitrogen content was increased from 0.005 to 0.011 wt% or the titanium content was 0.038 wt%. Carbonitride precipitates were not found in ingots containing less than 0.011 wt% Ti for any quench temperature down to 1000°C, although Nb-rich precipitates were present at 800°C and in mould-cooled ingots. Holding the ingots isothermally at temperatures down to 950°C for 3 hr brought the composition of precipitates and the concentration of solutes closer to equilibrium. It has concluded that, for the base composition and Ti content less than a critical value of 0.012 wt%, as-cast Austenite was more supersaturated with microalloy precipitants than expected from equilibrium considerations. Increasing the Ti content above the critical value led to interdendritic precipitation of carbonitride that precipitated during cooling and reduced the degree of supersaturation.
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ferrite grain coarsening during transformation of thermomechanically processed c mn nb Austenite
Materials Science and Technology, 1992Co-Authors: R. Priestner, Peter HodgsonAbstract:AbstractThe ferrite grain size of low carbon steel is known to be refined by hot rolling in the Austenite Phase Field at temperatures too low for recrystallisation to occur. The strain thus retained in the Austenite increases ferrite nucleation density and in current models of grain refinement it is assumed that each nucleus becomes a grain in the fully transformed microstructure. In this paper it is shown that, in a heavily deformed C–Mn–Nb Austenite, ferrite grains impinged, then coarsened during the initial stages of transformation during continuous cooling. The final ferrite grain size was not established until 35% of transformation had occurred. It is suggested, firstly, that ferrite grain refinement due to controlled rolling cannot be modelled simply from observed increases in nucleation density and, secondly, that deformation of Austenite has considerably greater potential for grain refinement than is commonly observed, provided that coarsening of the ferrite during transformation can be limited.MS...
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Ferrite grain coarsening during transformation of thermomechanically processed C–Mn–Nb Austenite
Materials Science and Technology, 1992Co-Authors: R. Priestner, Peter HodgsonAbstract:AbstractThe ferrite grain size of low carbon steel is known to be refined by hot rolling in the Austenite Phase Field at temperatures too low for recrystallisation to occur. The strain thus retained in the Austenite increases ferrite nucleation density and in current models of grain refinement it is assumed that each nucleus becomes a grain in the fully transformed microstructure. In this paper it is shown that, in a heavily deformed C–Mn–Nb Austenite, ferrite grains impinged, then coarsened during the initial stages of transformation during continuous cooling. The final ferrite grain size was not established until 35% of transformation had occurred. It is suggested, firstly, that ferrite grain refinement due to controlled rolling cannot be modelled simply from observed increases in nucleation density and, secondly, that deformation of Austenite has considerably greater potential for grain refinement than is commonly observed, provided that coarsening of the ferrite during transformation can be limited.MS...
