Austenite grain growth in medium and high-carbon steels microalloyed with niobium

Coladas, R.; Masounave, Jacques; Guérin, G.; Baïlon, J.-P.

doi:10.1179/030634577790432857

Cited by 27 publications

(41 citation statements)

References 6 publications

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“…It is well known that in plain carbon steels the PAGS increases continuously and exponentially with temperature [12]. However, in microalloyed steels is usual to observe two-step grain growth [12,13]. In the niobium microalloyed steel studied in the present work this two-step growth is found during a continuous heating.…”

Section: Resultssupporting

confidence: 55%

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Kinetics of Austenite Grain Growth during a Continuous Heating of a Niobium Microalloyed Steel

Martín

Caballero

Capdevila

et al. 2004

MSF

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Abstract. Grain growth is a thermally activated process in which the average grain size increases as temperature and time increases. The driving force for grain growth results from the decrease in the free energy associated with the reduction in total grain boundary energy. There are several known factors that influence the migration of grain boundaries such as second phase particles precipitated in the matrix and the solute elements segregated at grain boundaries. The austenite grain boundaries are revealed using the thermal etching method. Carbon extraction replicas were prepared to determine the composition and size of precipitates present in the matrix. In this work, the evolution of the average prior austenite grain size (PAGS) of a low carbon steel microalloyed with niobium is studied as a function of temperature and heating rate. Austenite grains show a twostage growth. It has been found that as heating rate increases, the grain coarsening temperature (T GC ) increases and the grain size at that temperature decreases. T GC temperature lies around 40-60ºC below the temperature for complete dissolution of carbonitrides (T DISS ).

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Section: Resultssupporting

confidence: 55%

“…2 shows the austenitic microstructure formed after heating up to three different temperatures at a rate of 5ºC/s. It is well known that in plain carbon steels the PAGS increases continuously and exponentially with temperature [12]. However, in microalloyed steels is usual to observe two-step grain growth [12,13].…”

Section: Resultsmentioning

confidence: 99%

Kinetics of Austenite Grain Growth during a Continuous Heating of a Niobium Microalloyed Steel

Martín

Caballero

Capdevila

et al. 2004

MSF

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“…Nevertheless, other investigators argue strongly in favor of the solute drag effect (e.g. Coladas et al 7) ) or of a combination of the both effects. 8,9) Thermodynamic analysis is known to be an important method for optimizing both the chemistry and process design of microalloyed steels for thermomechanical processing.…”

Section: Introductionmentioning

confidence: 95%

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

et al. 2009

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A good combination of strength and toughness in HSLA steels can be achieved by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at lower temperatures by solute drag or by precipitation pinning. In this study, the recrystallization behavior of four Nb-microalloyed model alloys which were designed to show either extensive or almost no precipitation, was compared by multi-hit torsion tests and double hit compression tests. A good consistency between the different types of tests was found and the results were verified by optical micrographs. Further, by construction of softeningtime-temperature diagrams the recrystallization behavior was linked to the precipitation state of the material which was investigated by thermodynamical equilibrium calculations and by experimental observations from TEM-EDX, Inductively Coupled Plasma Mass Spectroscopy and X-ray Diffraction. Quantitative agreement between the experimental measurements and the calculations for precipitated mass fraction and precipitate composition as a function of temperature and steel composition is demonstrated.KEY WORDS: recrystallization; microalloyed steels; precipitation; solute drag. 911© 2009 ISIJ tions with experimental data from Craven et al. 13)The objective of the present paper is to separate both retarding mechanisms, i.e. solute drag and precipitation pinning, by investigating model alloys designed to show either extensive or almost no precipitation. Moreover, the recrystallization kinetics of four Nb-microalloyed steels during hot deformation is linked to the morphology and composition of the precipitates and the amount of Nb-solutes found in these materials. The recrystallization kinetics were investigated combining different hot deformation testing techniques while information on the precipitation state of the material was obtained from thermodynamic equilibrium calculations and from a combination of experimental observation techniques. With this work, a contribution to the understanding of the fundamental mechanisms responsible for the retardation of austenite recrystallization in Nb-microalloyed steels is achieved. Experimental ProcedureFour model alloys were designed and casted as 100 kg ingots in a Pfeiffer vacuum furnace operated under argon gas atmosphere. The chemical composition of these alloys can be found in Table 1. The C-Mn-reference alloy, without additional Nb, represents a reference steel. The second alloy, a lowC-Mn-Nb alloy containing only a few ppm C, allowed to study the effect of Nb in solid solution. The third alloy (C-Mn-Nb) was designed to study the effect of NbC-precipitates on the recrystallization kinetics. To have the highest fraction of NbC precipitates possible, a stoichiometric Nb/C-ratio of 8/1 was chosen. Finally, the fourth alloy (C-Mn-Nb-N) was designed to study the influence of N on the recrystallization and precipitation behavior. The cast blocks were thermomechanically processed under conditions comparable to those during industrial steel plate rolli...

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“…Speer and Hansen [3] investigated the austenite recrystallization in Nb microalloyed steels, showing that the solute drag effects on the austenite recrystallization are very small compared to the effect of carbonitride precipitation. Nevertheless, other investigators argue strongly in favor of the solute drag effect [6] or of a combination of the both effects [7]. The objective of the present paper is to separate both retarding mechanisms, by investigating model alloys designed to show either extensive or almost no precipitation.…”

Section: Introductionmentioning

confidence: 99%

Control of the Austenite Recrystallization in Niobium Microalloyed Steels

Vervynckt

Verbeken

Thibaux

et al. 2010

MSF

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Abstract. The use of heavy gauge steel sheets for structural applications very often requires a combination of high yield strength and adequate toughness. The most cost effective way to realize a high yield strength and a high ductility in a low alloyed steel is grain refinement. In industrial practice, this refinement is realized by controlled processing. This process consists of controlling the slab reheating temperature, applying a large amount of hot deformation below the nonrecrystallization temperature (T nr ) and accelerated cooling. A better knowledge of T nr could optimize the process and the best mechanical properties could be reached against the lowest cost. T nr can be raised by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at low temperatures either by solute drag or by precipitation pinning. In this study, the recrystallization behavior of five Nb-microalloyed model alloys with various Nb contents, was evaluated by double hit compression tests. Further, the precipitation state of the materials was investigated experimentally by Inductively Couples Mass Spectroscopy and X-ray Diffraction. The construction of recrystallization-time-temperature diagrams and precipitation-timetemperature diagrams showed that both mechanisms, i.e. recrystallization and precipitation, strongly influence each other.

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Austenite grain growth in medium and high-carbon steels microalloyed with niobium

Cited by 27 publications

References 6 publications

Kinetics of Austenite Grain Growth during a Continuous Heating of a Niobium Microalloyed Steel

Kinetics of Austenite Grain Growth during a Continuous Heating of a Niobium Microalloyed Steel

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

Control of the Austenite Recrystallization in Niobium Microalloyed Steels

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