Complex heterogeneous precipitation in titanium–niobium microalloyed Al-killed HSLA steels—I. (Ti,Nb)(C,N) particles

Craven, A. J.; He, Ketai; Garvie, L. A. J.; Baker, T. N.

doi:10.1016/s1359-6454(00)00194-4

Cited by 157 publications

(96 citation statements)

References 12 publications

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“…Moreover, Zou and Kirkaldy 11) showed quantitative agreement between equilibrium calculations and the experimentally determined stoichiometry of (Nb, Ti)(C, N) precipitates in a non-deformed material. So far, the present authors found no direct comparison between the calculated equilibrium mole fraction of elements in a precipitate and experimental observations of the stoichiometry of precipitates during or after hot deformation, except a recent publication by Liu 12) who compared his calcula-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.…”

Section: Introductionmentioning

confidence: 67%

“…So far, researchers determined the stoichiometry of the complex (Nb, Ti)(C, N) precipitates mainly with TEM, using EDX measurements on thin foils or by indexing diffraction patterns 23) on carbon extraction replicas. More recently, Craven et al 13) described also the use of Parallel Electron Energy Loss Spectroscopy (PEELS) to determine the stoechiometry of precipitates. A PEELS spectrum from a precipitate in a microalloyed steel is compared to PEELS spectra taken from samples of commercial NbC and NbN powders.…”

Section: Stoichiometry Of the Precipitates Measured Bymentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 67%

Section: Stoichiometry Of the Precipitates Measured Bymentioning

confidence: 99%

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

et al. 2009

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“…The particle size, morphology, and chemistry observed in this work correspond to those reported for similar steel compositions and processing parameters. [16][17][18][19][20][21][22] The precipitate parameters and compositions varied with TMP schedule (Table I; Figure 5). For particles in the >20 nm size range, the average diameter was the smallest, and the number density and volume fraction were the highest for the 1248 K (975°C) deformation temperature TMP schedule, compared to other two schedules.…”

Section: A Optical Microscopymentioning

confidence: 99%

Strengthening Mechanisms in Thermomechanically Processed NbTi-Microalloyed Steel

Kostryzhev

Marenych

Killmore³

et al. 2015

Metall Mater Trans A

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The effect of deformation temperature on microstructure and mechanical properties was investigated for thermomechanically processed NbTi-microalloyed steel with ferrite-pearlite microstructure. With a decrease in the finish deformation temperature at 1348 K to 1098 K (1075 °C to 825 °C) temperature range, the ambient temperature yield stress did not vary significantly, work hardening rate decreased, ultimate tensile strength decreased, and elongation to failure increased. These variations in mechanical properties were correlated to the variations in microstructural parameters (such as ferrite grain size, solid solution concentrations, precipitate number density and dislocation density). Calculations based on the measured microstructural parameters suggested the grain refinement, solid solution strengthening, precipitation strengthening, and work hardening contributed up to 32 pct, up to 48 pct, up to 25 pct, and less than 3 pct to the yield stress, respectively. With a decrease in the finish deformation temperature, both the grain size strengthening and solid solution strengthening increased, the precipitation strengthening decreased, and the work hardening contribution did not vary significantly. The effect of deformation temperature on microstructure and mechanical properties was investigated for thermomechanically processed NbTi-microalloyed steel with ferrite-pearlite microstructure. With a decrease in the finish deformation temperature at 1348 K to 1098 K (1075°C to 825°C) temperature range, the ambient temperature yield stress did not vary significantly, work hardening rate decreased, ultimate tensile strength decreased, and elongation to failure increased. These variations in mechanical properties were correlated to the variations in microstructural parameters (such as ferrite grain size, solid solution concentrations, precipitate number density and dislocation density). Calculations based on the measured microstructural parameters suggested the grain refinement, solid solution strengthening, precipitation strengthening, and work hardening contributed up to 32 pct, up to 48 pct, up to 25 pct, and less than 3 pct to the yield stress, respectively. With a decrease in the finish deformation temperature, both the grain size strengthening and solid solution strengthening increased, the precipitation strengthening decreased, and the work hardening contribution did not vary significantly.

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“…Among Nb, V and Ti, Ti is thermodynamically the first element to precipitate during solidification. This element effectively bonds with nitrogen and produces Ti(N) at higher temperatures [5] and it can also result in formation of several complex Ti containing compounds in ferrite [8]. In order to understand the precipitation sequence and to determine the possible contribution to effective strengthening of these steels, a detailed characterization of these nanoscale compounds is essential.…”

Section: Introductionmentioning

confidence: 99%

Novel ultrafine Fe(C) precipitates strengthen transformation-induced-plasticity steel

Tirumalasetty

Fang

et al. 2012

Acta Materialia

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A transmission electron microscopy (TEM) study was conducted on nanoprecipitates formed in Ti microalloyed TRIP assisted steels, revealing the presence of Ti(N), Ti 2 CS, and a novel type of ultra-fine Fe(C) precipitates. The matrix/precipitate orientation relationships, sizes and shapes were investigated in detail. The ultrafine, disc-shaped Fe(C) precipitates have sizes of 2-5 nm and possess a hexagonal close packed (hcp) crystal structure with lattice parameters a = 5.73 ± 0.05 Å, c = 12.06 ± 0.05 Å. They are in a well-defined Pitsch Schrader (P-S) orientation relationship with the basal plane of the precipitate parallel to the [110] habit plane of the surrounding body centred cubic (BCC) ferritic matrix. Detailed analysis of precipitate distribution, orientation relationship, lattice mismatch, and inter-particle spacing suggest that these ultrafine precipitates contribute considerably to the strengthening of these steels.

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Complex heterogeneous precipitation in titanium–niobium microalloyed Al-killed HSLA steels—I. (Ti,Nb)(C,N) particles

Cited by 157 publications

References 12 publications

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

Strengthening Mechanisms in Thermomechanically Processed NbTi-Microalloyed Steel

Novel ultrafine Fe(C) precipitates strengthen transformation-induced-plasticity steel

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