Observation of an Isothermal Transformation during Quenching and Partitioning Processing

Kim, Dong H.; Speer, John G.; Kim, Han Soo; Cooman, Bruno C. De

doi:10.1007/s11661-009-9891-4

Cited by 61 publications

(40 citation statements)

References 19 publications

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“…[2] for all isothermal treatments using the experimental data for df B /dt and considering that the volume of the bainitic subunits changes with the applied temperature as described in Eq. [4]. This latter equation can be used for the steel studied and the isothermal treatments performed since the composition is within the above-mentioned ranges and temperatures are higher than 528 K. The evolution of the nucleation rate in different treatments above and below M s , obtained from the fraction curves of Figure 11 and Equations [2] and [4], is observed in Figure 13.…”

Section: Isothermal Transformation Kineticsmentioning

confidence: 98%

“…[4]. This latter equation can be used for the steel studied and the isothermal treatments performed since the composition is within the above-mentioned ranges and temperatures are higher than 528 K. The evolution of the nucleation rate in different treatments above and below M s , obtained from the fraction curves of Figure 11 and Equations [2] and [4], is observed in Figure 13. In treatments above and just at M s , for instance at 603 K and 593 K (330°C and 320°C) (Figure 13(a)), the nucleation rate increases rapidly until reaching a maximum at bainitic ferrite fractions between 0.20 and 0.30 vol.…”

Section: Isothermal Transformation Kineticsmentioning

confidence: 98%

“…Consequently, a faster transformation implies a smaller size of the bainitic subunits, which is in accordance with Eq. [4] used for the nucleation rate calculations. If this reflection is applied to the isothermal treatments below M s , in conjunction with the increment of the density of potential nucleation sites introduced by the prior athermal martensite, the nucleation rate in those treatments will be much faster, as observed in Figure 13(b).…”

Section: Isothermal Transformation Kineticsmentioning

confidence: 99%

“…This prior athermal martensite has an accelerating effect on the overall isothermal transformation close to the M s temperature, which is generally known as the ''swingback'' phenomenon. [1][2][3][4] But, how can athermal martensite contribute to this acceleration? It is well known that martensite preferentially nucleates at prior-austenite grain boundaries, i.e., at austenite-austenite (c-c) interfaces.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

Navarro-López

Sietsma

Santofimia

2015

Metall Mater Trans A

109

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A. NAVARRO-LÓ PEZ, J. SIETSMA, and M.J. SANTOFIMIA Thermomechanical processing of Advanced Multiphase High Strength Steels often includes isothermal treatments around the martensite start temperature (M s ). It has been reported that the presence of martensite formed prior to these isothermal treatments accelerates the kinetics of the subsequent transformation. This kinetic effect is commonly attributed to the creation of potential nucleation sites at martensite-austenite interfaces. The aim of this study is to determine qualitatively and quantitatively the effect of a small volume fraction of martensite on the nucleation kinetics of the subsequent transformation. For this purpose, dilatometry experiments were performed at different temperatures above and below the M s temperature for athermal martensite in a low-carbon high-silicon steel. Microstructural analysis led to the identification of the isothermal decomposition product formed above and below M s as bainitic ferrite. The analysis of the transformation processes demonstrated that the initial stage of formation of bainitic ferrite at heat treatments below M s is at least two orders of magnitude faster than above M s due to the presence of martensite.

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Section: Isothermal Transformation Kineticsmentioning

confidence: 98%

Section: Isothermal Transformation Kineticsmentioning

confidence: 98%

Section: Isothermal Transformation Kineticsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

Navarro-López

Sietsma

Santofimia

2015

Metall Mater Trans A

109

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“…The studies suggest that each type of transformation product, as well as isothermal martensite [20,21], has a separate C-curve. There is an extensive evidence about the 'Swing Back' phenomenon [11,13,30]. It is a distinct austenite decomposition acceleration just near the M S below the nose of the bainitic transformation.…”

Section: Swing Back Phenomenon In the Remaining Austenite Transformationmentioning

confidence: 99%

Application of acoustic emission to monitor bainitic and martensitic transformation

Woźniak¹,

Rożniatowski²,

Ranachowski³

2011

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The paper concerns acoustic emission (AE) measurements during isothermal martensitic and bainitic heat treatments in 100CrMnSi6-4 bearing steel. A distribution of the total RMS voltage in arbitrary unit (AU) during austempering together with the MS temperature results was determined. MS represents the temperature at which martensite starts being formed. This temperature was determined with the use of the dilatometric method. The Short Time Fourier Transform algorithm was used for displaying the signal values on spectrogram graphs. AE signals were attributed to a midrib. Midrib is a thin-plate isothermal martensite formed before lower bainite nucleation. The evolution of midribs in remaining austenite was investigated with AE measurements at the temperature near MS. Macroscopic effects of elongation changes and their division into various intensity stages related to a martensite transformation were analyzed. A comparison of the AE curves and dilatometric results suggests that the AE method determines a relatively initial stage of the martensite transformation, during which additional processes of austempering and carbon partitioning occur. Lower bainite containing the midrib was found to evolve in two stages. K e y w o r d s : bearing steels, phase transformation kinetics, acoustic methods, isothermal heat treatments, midrib, bainite

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Microstructural Evolution and Dynamic Partitioning Behavior in Quenched and Partitioned Steels

Chen

et al. 2017

steel research int.

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Direct quenching and dynamic partitioning (DQ&P) process is a promising approach and there continues to be lack of understanding concerning cooling condition in the hot strip rolling line. Here, the authors have simulated DQ&P process in low carbon Si-Mn steel using a thermal simulator. The effect of quenching temperature, relaxation process, and cooling rate on microstructure and hardness is studied. The results suggest that retained austenite is less sensitive to quenching temperature and the volume fraction of retained austenite including film-like and blocky shape is %7-11%. The relaxation process leads to ferrite transformation and recovery of defects, resulting in increase in retained austenite, and reduced hardness. It is interesting that the quenching temperature and hardness do not show an inverse relation. It is important that the isothermal transformation at high quenching temperature below M s promotes retained austenite. Moreover, the low coiling cooling rate less than 0.1 C s À1 from quenching temperature to room temperature is adequate for carbon partitioning. In the view of thermodynamics and kinetics, an appropriate processing window of coiling temperature between 200 and 320 C plus low cooling rate less than 0.1 C s À1 is proposed for hot rolled DQ&P steels.

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Observation of an Isothermal Transformation during Quenching and Partitioning Processing

Cited by 61 publications

References 19 publications

Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

Effect of Prior Athermal Martensite on the Isothermal Transformation Kinetics Below M s in a Low-C High-Si Steel

Application of acoustic emission to monitor bainitic and martensitic transformation

Microstructural Evolution and Dynamic Partitioning Behavior in Quenched and Partitioned Steels

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