scholarly journals Influence of strain reversal on dynamic transformation in microalloyed steels deformed above the Ae3 temperature

2017 ◽  
Vol 52 (20) ◽  
pp. 12427-12444 ◽  
Author(s):  
L. Sun ◽  
K. Muszka ◽  
B. P. Wynne ◽  
E. J. Palmiere
2012 ◽  
Vol 715-716 ◽  
pp. 655-660 ◽  
Author(s):  
K. Muszka ◽  
Lin Sun ◽  
Bradley P. Wynne ◽  
Eric J. Palmiere ◽  
W.M. Rainforth

Recent observations show that the strain reversal affects significantly and in a complex way both the static recrystallisation (SRX) and strain-induced precipitation (PPT) kinetics in Nb-microalloyed steel. It is already known that the recrystallisation stagnation is a consequence of the competition between the driving pressure for recrystallisation and the pinning pressure caused by the strain-induced precipitation of Nb (C,N) precipitates. Both of these parameters depend in turn on the local dislocation density. Thus, it is expected that a variation of the local dislocation density due to reversal of the strain will affect at the same time the local driving and the pinning pressures, which will cause the difference in the hardening levels. In the present paper, the influence of strain path change on microstructure evolution and mechanical behaviour in Nb-microalloyed steel (API X-70 grade) was studied. The deformation schedules were designed in order to investigate an effect of strain reversal on both static recrystallisation and strain-induced precipitation process kinetics. Flow curves recorded during deformation of X-70 steel showed clear influence of applied strain path on both static recrystallisation kinetics and strain-induced precipitation process.


2013 ◽  
Vol 58 (3) ◽  
pp. 745-750 ◽  
Author(s):  
D. Dziedzic ◽  
K. Muszka ◽  
J. Majta

Abstract Austenite morphology is one of the main factors determining austenite-ferrite transformation kinetic and effectively affects the final microstructure and properties. The basic criteria for proper assessment of the austenite transformation products, theirs refinement, is the relation between the nucleation to growth rates. The main factor accelerating both, the nucleation rate of austenite during heating, and ferrite during cooling is the presence of accumulated deformation energy. The primary aim of this work is to increase our knowledge of the effects of deformation - its accumulated energy on the austenite structure and properties. Two specific steel grades were selected for the present investigation, i.e. microalloyed and IF steel, essentially different in equilibrium transformation temperatures. Obtained austenitic microstructures were analyzed, first of all as a start point for the austenite-to-ferrite transformation. Specific case of this transformation was considered i.e. Strain Induced Dynamic Transformation SIDT. The characteristic feature of the SIDT is the strong dependence of theirs kinetic on the austenite morphology, especially grain size. Thermomechanical processing, that utilize the SIDT, is one of the most effective ways to produce ultrafine-grained steel. One of the main benefits of the austenite refinement, just before the γ→α transformation, is its significant effect on the microstructure evolution during subsequent thermomechanical processing. Experimental results clearly show how direct and positive influence the austenite grain refinement has on the composition and refinement of transformation products. Presented study was focused on Strain Induced Dynamic Reverse Transformation. It is proved that this kind of transformation is very efficient way to intensify thermomechanical processing of microalloyed steels. Dynamic transformation kinetics were analyzed based upon flow curves recorded during the SIDT process. The main effect of presented research is analyze of influence of prior microstructure on dynamically formed austenite morphology


2013 ◽  
Vol 753 ◽  
pp. 542-545 ◽  
Author(s):  
Dominik Dziedzic ◽  
Krzysztof Muszka ◽  
Janusz Majta ◽  
Eric J. Palmiere

The Strain-Induced Dynamic Transformation (SIDT) is an efficient way to overcome the limitation of grain refinement during the conventional thermomechanical controlled processing (TMCP) of steels. The present study deals with the effects of austenite morphology on the SIDT in microalloyed and IF steels. The discussion of the processing route in terms of chemical composition, deformation schedules, heating and cooling conditions is carried out by the means of torsion tests with deformation in metastable conditions. As it was expected, the microstructure of microalloyed steel was clearly controlled by the microalloying elements what, in turn, directly affectedthe SIDT products. Examination of water-quenched microstructures, just after deformation, revealed the morphology of "strain-induced ferrite". The kinetics of SIDT were observed and analyzed using the strain-stress curves. It is shown that presence of strain-induced precipitations in microalloyed steels accelerates kinetic of SIDT - by reducing the amount of Nb in solution. The changes in ferrite refinement of the experimental steels were explained from the view of the austenite morphology and processing parameters.


Author(s):  
Joseph Ben Prestel

Beginning around 1860, authors in the Egyptian capital portrayed Cairo’s changing cityscape and the recent emergence of local newspapers in terms of their impact on rationality (‘aql). In their descriptions, these contemporaries depicted rationality as an education of the heart that especially enabled men from the middle class to control their bodies and passions. The chapter shows that Cairo’s transformation was, however, not always associated with rising rationality by drawing on a different set of sources. Police and court records from the 1860s and 1870s demonstrate that contemporaries also described processes of urban change as a danger to the “honor” of lower-class women. Like the debates in Berlin, emotional practices in Cairo thus served as a way to address the social formation of the Egyptian capital during a time of dynamic transformation.


Author(s):  
Joseph Ben Prestel

Between 1860 and 1910, Berlin and Cairo went through a period of dynamic transformation. During this period, a growing number of contemporaries in both places made corresponding arguments about how urban change affected city dwellers’ emotions. In newspaper articles, scientific treatises, and pamphlets, shifting practices, such as nighttime leisure, were depicted as affecting feelings like love and disgust. Looking at the ways in which different urban dwellers, from psychologists to revelers, framed recent changes in terms of emotions, this book reveals the striking parallels between the histories of Berlin and Cairo. In both cities, various authors associated changes in the city with such phenomena as a loss of control over feelings or the need for a reform of emotions. The parallels in these arguments belie the assumed dissimilarity between European and Middle Eastern cities during the nineteenth century. Drawing on similar debates about emotions in Berlin and Cairo, the book provides a new argument about the regional compartmentalization of urban history. It highlights how the circulation of scientific knowledge, the expansion of empires, and global capital flows led to similarities in the pasts of these two cities. By combining urban history and the history of emotions, this book proposes an innovative perspective on the emergence of different, yet comparable cities at the end of the nineteenth century.


Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 26
Author(s):  
Krzysztof Muszka ◽  
Mateusz Sitko ◽  
Paulina Lisiecka-Graca ◽  
Thomas Simm ◽  
Eric Palmiere ◽  
...  

The experimental and numerical study of the effects of the recrystallization behavior of austenite model alloys during hot plate rolling on reverse rolling is the main goal of the paper. The computer models that are currently applied for simulation of reverse rolling are not strain-path-sensitive, thus leading to overestimation of the processing parameters outside the accepted process window (e.g., deformation in the partial austenite recrystallization region). Therefore, in this work, a particular focus is put on the investigation of strain path effects that occur during hot rolling and their influence on the microstructure evolution and mechanical properties of microalloyed austenite. Both experimental and numerical techniques are employed in this study, taking advantage of the integrated computational material engineering concept. The combined isotropic–kinematic hardening model is used for the macroscale predictions to take into account softening effects due to strain reversal. The macroscale model is additionally enriched with the full-field microstructure evolution model within the cellular automata framework. Examples of obtained results, highlighting the role of the strain reversal on the microstructural response, are presented within the paper. The combination of the physical simulation of austenitic model alloys and computer modeling provided new insights into optimization of the processing routes of advanced high-strength steels (AHSS).


2018 ◽  
Vol 941 ◽  
pp. 633-638
Author(s):  
John Joseph Jonas ◽  
Clodualdo Aranas Jr. ◽  
Samuel F. Rodrigues

Under loading above the Ae3 temperature, austenite transforms displacively into Widmanstätten ferrite. Here the driving force for transformation is the net softening during the phase change while the obstacle consists of the free energy difference between austenite and ferrite as well as the work of shear accommodation and dilatation during the transformation. Once the driving force is higher than the obstacle, phase transformation occurs. This phenomenon was explored here by means of the optical and electron microscopy of a C-Mn steel deformed above their transformation temperatures. Strain-temperature-transformation (STT) curves are presented that accurately quantify the amount of dynamically formed ferrite; the kinetics of retransformation are also specified in the form of appropriate TTRT diagrams. This technique can be used to improve the models for transformation on accelerated cooling in strip and plate rolling.


2004 ◽  
Vol 467-470 ◽  
pp. 223-228
Author(s):  
K.M. Banks

Various microstructure models for Nb-bearing steels were tested under industrial strip rolling conditions to establish a relationship between grain size and toughness in Ti-Nb-V microalloyed steels. For similar Nb contents, microstructure models for Nb steels were found to adequately describe recrystallisation kinetics in more complex Ti-Nb-V steels. For thick-walled linepipe (11.6mm), a minimum of 0.04%Nb is required to achieve adequate toughness. Retained strain was the dominant processing parameter factor affecting ferrite grain size. The predicted minimum amount of retained strain after the last pass required for sufficient grain refinement concurred with laboratory simulation results. For the rolling schedules investigated, metadynamic recrystallisation was predicted to occur during roughing, whilst static recrystallisation was predominant during finishing.


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