Prediction Model for the Austenite Grain Size in the Coarse Grained Heat Affected Zone of Fe-C-Mn Steels: Considering the Effect of Initial Grain Size on Isothermal Growth Behavior

-i - AbstractIn this thesis, the influence of various dilute Nb additions (0.005-0.02 wt%) on austenite microstructure evolution along thermomechanical processing, in terms of austenite recrystallisation and grain growth, were investigated using steels with three carbon content levels.At the homogenisation temperature of 1250°C, all dilute Nb additions were dissolved in low carbon steels whereas the Nb dissolution limits for 0.4 wt% and 0.6 wt% C steels were 0.012 wt% and 0.08 wt%, respectively. Dilute Nb additions did not show significant influence on homogenised austenite grain size. The dramatic increase in C contents was more influential, which decreased the homogenised austenite grain size.The influence of dilute Nb additions and C contents on dynamic recrystallisation behaviour was studied by rough rolling at high deformation temperature with low strain rate. The dilute Nb additions were found to increase the critical strain of dynamic recrystallisation whereas C contents showed no influence on the dynamic recrystallisation behaviour.The austenite recrystallisation behaviour after finish rolling and after the holding period between finishing passes were studied by means of interrupted plane strain compression (PSC) tests and double hit PSC tests. It was found that with low Nb supersaturation, recrystallisation happened prior to Nb precipitation. Solute Nb in austenite delayed the onset of austenite recrystallisation through solute drag effect.With high Nb supersaturation, Nb precipitation occurred before the onset of recrystallisation which completely retarded austenite recrystallisation.The austenite grain growth during the holding period between finish rolling passes was studied by the evolution of prior-austenite grain size before and after the 20s holding period at the highest finish rolling temperature (1050°C). There was no Nb precipitation found and the difference in austenite grain growth behaviour was Abstract -iiattributed to the solute drag effect from both Nb and C in solution. It was found that Nb in solution suppressed austenite grain growth. However, the effectiveness of solute Nb in suppressing austenite grain growth was affected by the C content. Acknowledgement

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“…In this work an activation energy of Q =350kJmol À1 is used, which was determined by multiple regression analysis for several Nb-containing steels by Uhm et al [49]. The mobility factor M 0 is a scaling parameter which can be determined from a limited number of experimental grain growth data.…”

Section: Grain Growth Modelmentioning

confidence: 99%

In situ measurement and modelling of austenite grain growth in a Ti/Nb microalloyed steel

Maalekian

¹

,

Radis

²

,

Militzer

³

et al. 2012

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In situ measurement and modelling of austenite grain growth in a Ti/Nb microalloyed steel Maalekian, M.; Radis, R.; Militzer, M.; Moreau, A.; Poole, W. J.In situ measurement and modelling of austenite grain growth in a Ti/Nb microalloyed steel Abstract Using a novel laser ultrasonics technique in situ measurements of austenite grain growth were conducted during continuous heating (10°Cs À1 ) and subsequent isothermal holding at various temperatures in the range 950-1250°C in a microalloyed linepipe steel. Based on the experimental results, a grain growth model was developed, which includes the pinning effect of precipitates present in the steel. Analyzing the grain growth behaviour and using the advanced thermo-kinetic software MatCalc, an approach was developed to estimate the initial distribution of precipitates in the as-received material and their dissolution kinetics. The evolution of the volume fractions and mean particle sizes of NbC and TiN leads to a time-dependent pinning pressure that is coupled with the proposed grain growth model to successfully describe the observed kinetics of austenite grain growth. The predictive capabilities of the model are illustrated by its application to independent grain growth data for rapid heat treatment cycles that are typical of the weld heat affected zone.

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“…The C solute drag effect on the austenite grain boundary migration was observed in a number of studies [210][211][212]. For example, Uhm et al [210] studied the austenite isothermal grain growth behaviour with a series of plain carbon steels containing 0.08 wt% to 0.32 wt% carbon with the isothermal holding time up to 10 mins.…”

Section: Influence Of C On Austenite Grain Growth Behaviourmentioning

confidence: 99%

“…For example, Uhm et al [210] studied the austenite isothermal grain growth behaviour with a series of plain carbon steels containing 0.08 wt% to 0.32 wt% carbon with the isothermal holding time up to 10 mins. They found out that the tendency for grain growth is reduced with the increase of C content, which indicates that the C segregation on the grain boundaries exert a solute drag effect on the grain boundary migration.…”

Section: Influence Of C On Austenite Grain Growth Behaviourmentioning

confidence: 99%

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

Cui¹,

Patel²,

Palmiere³

2015

HSLA Steels 2015, Microalloying 2015 &Amp; Offshore Engineering Steels 2015

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-i - AbstractIn this thesis, the influence of various dilute Nb additions (0.005-0.02 wt%) on austenite microstructure evolution along thermomechanical processing, in terms of austenite recrystallisation and grain growth, were investigated using steels with three carbon content levels.At the homogenisation temperature of 1250°C, all dilute Nb additions were dissolved in low carbon steels whereas the Nb dissolution limits for 0.4 wt% and 0.6 wt% C steels were 0.012 wt% and 0.08 wt%, respectively. Dilute Nb additions did not show significant influence on homogenised austenite grain size. The dramatic increase in C contents was more influential, which decreased the homogenised austenite grain size.The influence of dilute Nb additions and C contents on dynamic recrystallisation behaviour was studied by rough rolling at high deformation temperature with low strain rate. The dilute Nb additions were found to increase the critical strain of dynamic recrystallisation whereas C contents showed no influence on the dynamic recrystallisation behaviour.The austenite recrystallisation behaviour after finish rolling and after the holding period between finishing passes were studied by means of interrupted plane strain compression (PSC) tests and double hit PSC tests. It was found that with low Nb supersaturation, recrystallisation happened prior to Nb precipitation. Solute Nb in austenite delayed the onset of austenite recrystallisation through solute drag effect.With high Nb supersaturation, Nb precipitation occurred before the onset of recrystallisation which completely retarded austenite recrystallisation.The austenite grain growth during the holding period between finish rolling passes was studied by the evolution of prior-austenite grain size before and after the 20s holding period at the highest finish rolling temperature (1050°C). There was no Nb precipitation found and the difference in austenite grain growth behaviour was Abstract -iiattributed to the solute drag effect from both Nb and C in solution. It was found that Nb in solution suppressed austenite grain growth. However, the effectiveness of solute Nb in suppressing austenite grain growth was affected by the C content. Acknowledgement

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Prediction Model for the Austenite Grain Size in the Coarse Grained Heat Affected Zone of Fe-C-Mn Steels: Considering the Effect of Initial Grain Size on Isothermal Growth Behavior

Cited by 99 publications

References 11 publications

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

In situ measurement and modelling of austenite grain growth in a Ti/Nb microalloyed steel

Thermomechanical Processing of Structural Steels with Dilute Niobium Additions

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