Incomplete Recrystallization and Subsequent Microstructural Evolution during Intercritical Annealing in Cold-rolled Low Carbon Steels

Ogawa, Takeshi; Maruyama, Naoki; Sugiura, Norío; Yoshinaga, Naoki

doi:10.2355/isijinternational.50.469

Cited by 54 publications

(50 citation statements)

References 17 publications

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“…It was shown in a previous study, 52) that the recrystallization behavior of this material is quite unlike the one of a conventional cold-rolled dual-phase steel. 53) This is a result of the low dislocation density in the warm deformed ferrite which retards recrystallization. It was concluded from detailed microstructure and texture evaluations that grain growth prevails over recrystallization.…”

Section: Grain Size Stabilitymentioning

confidence: 99%

Microstructure Control during Fabrication of Ultrafine Grained Dual-phase Steel: Characterization and Effect of Intercritical Annealing Parameters

2012

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An ultrafine grained (UFG) ferrite/cementite steel was subjected to intercritical annealing in order to obtain an UFG ferrite/martensite dual-phase (DP) steel. The intercritical annealing parameters, namely, holding temperature and time, heating rate, and cooling rate were varied independently by applying dilatometer experiments. Microstructure characterization was performed using scanning electron microscopy (SEM) and high-resolution electron backscatter diffraction (EBSD). An EBSD data post-processing routine is proposed that allows precise distinction between the ferrite and the martensite phase. The sensitivity of the microstructure to the different annealing conditions is identified. As in conventional DP steels, the martensite fraction and the ferrite grain size increase with intercritical annealing time and temperature. Furthermore, the variations of the microstructure are explained in terms of the changes in phase transformation kinetics due to grain refinement and the manganese enrichment in cementite during warm deformation.

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Section: Grain Size Stabilitymentioning

confidence: 99%

Microstructure Control during Fabrication of Ultrafine Grained Dual-phase Steel: Characterization and Effect of Intercritical Annealing Parameters

2012

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“…The sample heated at 10°C/s showed a partially recrystallized matrix, whereas the number of recrystallized grains was very low in the sample heated at 200°C/s. A previous study 18) showed that the hardness curve shifted markedly to higher temperatures if the sample is fully recrystallized using a preheat treatment before any continuous heating occurs. However, the same study 18) also showed that the hardness curve of a recrystallized sample shifts toward higher temperatures with increasing heating rate, because an increasing heating rate shortens the time for any formation of austenite.…”

Section: Microstructural Observations and Microhardness Measurementsmentioning

confidence: 99%

“…A previous study 18) showed that the hardness curve shifted markedly to higher temperatures if the sample is fully recrystallized using a preheat treatment before any continuous heating occurs. However, the same study 18) also showed that the hardness curve of a recrystallized sample shifts toward higher temperatures with increasing heating rate, because an increasing heating rate shortens the time for any formation of austenite. In the case of recrystallized samples, the shift in the hardness curve toward higher temperatures was around 25°C on increasing the heating rate from 10°C/s to 200°C/s.…”

Section: Microstructural Observations and Microhardness Measurementsmentioning

confidence: 99%

Microstructural Evolution of Carbon Steels in Hot Stamping Processes

2012

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Hot stamping is a very promising method for producing ultrahigh-strength automotive components. The heating and cooling conditions in the conventional hot stamping process are quite limited. To improve the productivity of the process and/or the mechanical properties of the product, optimizing the heating and cooling conditions is an important and urgent research subject.In this study, the influence of the heating rate, heating temperature, and cooling conditions on the microstructure and mechanical properties of 0.22%C-2.5%Mn steel was investigated. Samples were heated at two different heating rates (10°C/s and 200°C/s) to various temperatures and then either cooled in air or quenched using water sprays. The sample heated at 200°C/s to 800°C and then immediately quenched in water exhibited a very fine martensite microstructure having a grain size with an average diameter of 4 μm and a hardness value around 550 Hv. The sample heated above Ac3 and subsequently cooled in air exhibited a full martensite microstructure and a hardness of 450 Hv. A model that predicted the precipitation of cementite during cooling was developed to clarify the cause of the difference in hardness of the martensite in the samples that were quenched in water and cooled in air. The calculations showed that the hardness of samples cooled in air was lower mainly because of the decrease in the solid solution hardening of C owing to the precipitation of cementite below the Ms temperature. Drawing on the results obtained, hot stamping technology is discussed and favorable operational conditions proposed.

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“…The role of the carbide particles, Crcarbides in particular, should be taken into account too. During intercritical annealing, a complex interaction between recrystallization, grain growth, and phase transformation occurs 9,10 . The degree of such interplay depends, first of all, on the chemical composition of the steel (e.g., microalloying additions) and processing parameters 8,11,12 .…”

Section: Introductionmentioning

confidence: 99%

Effect of Cr Additions on Ferrite Recrystallization and Austenite Formation in Dual-Phase Steels Heat Treated in the Intercritical Temperature Range

et al. 2016

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An experimental investigation was conducted using laboratory-processed low carbon Mn-Mo-Nb-Ti-B dual phase steel with additions of 0.2Cr or 0.6%Cr. This study investigates the effect of Cr additions on ferrite recrystallization and austenite formation during continuous annealing in the intercritical temperature range. It was found that moderate additions of Cr (0.2%) accelerates the ferrite recrystallization (nucleation and growth) resulting in coarse ferrite grains. An increase in Cr content up to 0.6% also accelerates the ferrite recrystallization which in addition to the presence of Cr-rich carbides facilitates the austenitization predominantly through the nucleation process resulted in finer austenite grains. Thereby, the higher Cr content increases the volume of homogenized and refined martensite in the final quenched structure.

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Incomplete Recrystallization and Subsequent Microstructural Evolution during Intercritical Annealing in Cold-rolled Low Carbon Steels

Abstract: Fig. 11. Schematics of the microstructural evolution during intercritical annealing.

Cited by 54 publications

References 17 publications

Microstructure Control during Fabrication of Ultrafine Grained Dual-phase Steel: Characterization and Effect of Intercritical Annealing Parameters

Microstructure Control during Fabrication of Ultrafine Grained Dual-phase Steel: Characterization and Effect of Intercritical Annealing Parameters

Microstructural Evolution of Carbon Steels in Hot Stamping Processes

Effect of Cr Additions on Ferrite Recrystallization and Austenite Formation in Dual-Phase Steels Heat Treated in the Intercritical Temperature Range

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