Measurement and evaluation of the anisothermal softening of austenite after hot deformation

Streißelberger, A.; Kašpar, Radko; Pawelski, Oskar

doi:10.1007/bf02656713

Cited by 20 publications

(8 citation statements)

References 11 publications

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“…To carry out this characterization, metallographic studies can be used [10,11], but metallography is a time-consuming and not always successful technique. 5 Calculation methods such as the "anisothermal (non-isothermal) fractional softening" [12,13] give an approximation of recrystallized fraction, but this technique includes the contribution of recovery to softening, which can be very high under certain deformation conditions and/or material characteristics [14]. Besides, it is sometimes necessary to know other empirical constitutive parameters or to make preliminary tests to approximate the yield stress of a fully recrystallized material [13,15].…”

Section: Introductionmentioning

confidence: 99%

“…5 Calculation methods such as the "anisothermal (non-isothermal) fractional softening" [12,13] give an approximation of recrystallized fraction, but this technique includes the contribution of recovery to softening, which can be very high under certain deformation conditions and/or material characteristics [14]. Besides, it is sometimes necessary to know other empirical constitutive parameters or to make preliminary tests to approximate the yield stress of a fully recrystallized material [13,15]. On the other hand, mathematical models have also been developed and simulations have been carried out in order to evaluate the austenite recrystallization or softening kinetics and the resulting grain size during hot rolling of steels, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Assessment of austenite static recrystallization and grain size evolution during multipass hot rolling of a niobium-microalloyed steel

Gómez¹,

Rancel²,

Medina³

2009

Met. Mater. Int.

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Double-deformation isothermal tests and multipass continuous-cooling hot torsion tests were used to study the evolution of austenite microstructure under isothermal and nonisothermal hot deformation of a Nb microalloyed steel. Thanks to these tests and with the assistance of microstructural characterization, it has been verified that norecrystallization temperature (T nr ) approximately corresponds to the temperature where recrystallization starts to be incomplete during rolling. An accurate method to estimate the recrystallized fraction during hot rolling from stress-strain data and with no need of metallographic studies is proposed. The results of this method have been successfully compared to metallographic measurements, the values of non-isothermal fractional 3 softening and the accumulated stress measured in the plots of mean flow stress (MFS) versus the inverse of temperature. A remarkable austenite grain refinement occurs in the first hot rolling passes after reheating. If the effect of grain size on recrystallization and precipitation is taken into account, the correlation of isothermal and continuous cooling tests is better understood.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Assessment of austenite static recrystallization and grain size evolution during multipass hot rolling of a niobium-microalloyed steel

Gómez¹,

Rancel²,

Medina³

2009

Met. Mater. Int.

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“…However, above 900 °C, good hot ductility of austenitic steel arises because the GB migration for DRX inhibits crack formation and the new recrystallized grains have a lower flow stress than the deformed matrix until they once again fill with dislocation substructure. In multistage processing, austenite usually recrystallizes statically (SRX) between passes and the GB migration inhibits the cracking [26,[34][35][36][37]. With two phases having good workability between 900 and 1200 °C, duplex stainless steel might be expected to exhibit similar properties.…”

Section: Introductionmentioning

confidence: 99%

Hot Workability of 2304 and 2205 Duplex Stainless Steels

Evangelìsta¹,

McQueen²,

Niewczas³

et al. 2004

Canadian Metallurgical Quarterly

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The duplex stainless steels 2304 and 2205 were subjected to torsion testing over the range of temperatures from 1000 to 1200 °C and strain rates from 0.1 to 5 s -1 to characterize their hot working behaviour. The flow curves exhibit a peak followed by a decline towards a steady state that is attained at high temperatures and low strain rates. The peak stresses are fitted to a sinh-Arrhenius constitutive equation with activation energies of 536 and 406 kJ/mol, respectively. The optical microstructure shows elongated austenite regions in a ferrite matrix that increase in volume fraction with a rising temperature. The austenite phase becomes more elongated as the fracture strain rises indicating that both phases codeform in the temperature regime studied.During hot deformation, the ferrite effectively undergoes dynamic recovery, thus its substructure consists of well polygonized subgrains. In contrast, dynamic restoration processes are much suppressed in the austenite phase. The austenite substructure contains dense irregular dislocation networks and the dynamic recrystallization is observed only at very high temperatures. The hot ductility of the steels is limited by the cracking at the ferrite/austenite interphase boundaries; however, it improves as the temperature rises and the strain rate declines reaching maximum true strains of about 1.2 and 3, respectively. Present results indicate that the hot workability of 2304 and 2205 duplex stainless steels can be improved modestly by multistage testing. This is attributed to the static restoration processes (static recovery of ferrite and static recrystallization of austenite) which reduce internal stress concentrations but can not inhibit interphase boundaries from nucleating the cracks.Résumé -On a soumis les aciers inoxydables duplex 2304 et 2205 à des essais de torsion dans la gamme de températures de 1000 à 1200 °C et à des vitesses de déformation de 0.1 à 5 s -1 afin de caractériser leur comportement de travail à chaud. Les courbes d'écoulement exhibent un pic suivi par un déclin vers une asymptote qui est atteinte à températures élevées et à basses vitesses de déformation. On ajuste les pics de contrainte à une équation constitutive de sinh-d'Arrhénius avec des énergies d'activation de 536 et 406 kJ/mol, respectivement. La microstructure optique montre des régions allongées d'austénite, dans une matrice de ferrite, dont la fraction volumique augmente avec une élévation de la température. La phase d'austénite s'allonge à mesure que l'effort de rupture s'élève, indiquant que les deux phases se co-déforment dans le régime de température étudié.Lors de la déformation à chaud, la ferrite subit effectivement une récupération dynamique, donc sa sous-structure consiste en sous-grains polygonaux bien formés. Par contraste, les procédés de restauration dynamique sont plutôt supprimés dans la phase d'austénite. La sous-structure de l'austénite contient des réseaux denses et irréguliers de dislocations et la recristallisation dynamique est observée seulement à des températu...

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“…under non-isothermal conditions [15,16]. The "anisothermal fractional softening" method [17,18] gives an approximation of the recrystallized fraction, but this technique includes the contribution of recovery to softening, which can be very high under certain deformation conditions and/or material characteristics [19].…”

Section: Introductionmentioning

confidence: 99%

“…Besides, it is sometimes necessary to know other empirical constitutive parameters or to make preliminary tests to approximate the yield stress of a fully recrystallized material [18,20].…”

Section: Introductionmentioning

confidence: 99%

Evolution of austenite static recrystallization and grain size during hot rolling of a V-microalloyed steel

Gómez

Rancel

Fernández

et al. 2009

Materials Science and Engineering: A

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Measurement and evaluation of the anisothermal softening of austenite after hot deformation

Cited by 20 publications

References 11 publications

Assessment of austenite static recrystallization and grain size evolution during multipass hot rolling of a niobium-microalloyed steel

Assessment of austenite static recrystallization and grain size evolution during multipass hot rolling of a niobium-microalloyed steel

Hot Workability of 2304 and 2205 Duplex Stainless Steels

Evolution of austenite static recrystallization and grain size during hot rolling of a V-microalloyed steel

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