Swing back in kinetics nearM
              
                s
               in hypereutectoid steels

Oka, Mariko; Okamoto, Hisaki

doi:10.1007/bf02649258

Cited by 64 publications

(53 citation statements)

References 3 publications

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“…Assuming that bainitic ferrite has a plate shape and all the plate dimensions vary with temperature as described in Eq. [3], the volume of bainitic subunits can be described as [26] V…”

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%

“…4. Oka and Okamoto [3] report the formation of isothermal martensite in treatments above and below the M s temperature in hypereutectoid steels. Isothermal martensite was observed in the form of thin plates and/or leaf-like units.…”

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

111

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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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“…Assuming that bainitic ferrite has a plate shape and all the plate dimensions vary with temperature as described in Eq. [3], the volume of bainitic subunits can be described as [26] V…”

Section: Isothermal Transformation Kineticsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

111

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“…A numerical model was proposed by Azuma et al 33) The model was reported to cope with cementite formation both in ferrite and in austenite competing with the formation of bainite. 34) In order to accelerate bainite transformation, Oka 35) and Kawata et al 36) proposed an effect of undercooling below martensite start temperature (Ms) on the kinetics of bainite transformation during austempering at elevated temperatures. A partial transformation of austenite to martensite increases the nucleation site density of bainite and accelerates the reaction rate.…”

Section: Development Of High Strength Steels With Largementioning

confidence: 99%

Sheet Steel Technology for the Last 100 Years: Progress in Sheet Steels in Hand with the Automotive Industry

Takahashi

2015

ISIJ Int.

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Development in sheet steels has progressed in strong relation with automotive industry in Japan. To meet the requirements from automotive industry, various types of sheet steels including high and ultrahigh strength steel sheets have been developed. Progresses in three types of steel series will be discussed by checking the historical facts and technologies and their contributions. Introductions of interstitial free (IF) steel and continuous annealing system are the important events in mild steel developments for panels. Extensive work on finding the optimum mixtures of hard and soft phases to improve elongation of steels contributed to improve the crashworthiness of autobodies. Continuous annealing system also played an important role in producing these advanced high strength steels. Precipitation is used in a particular way which is to scavenge solute carbon and nitrogen and to prevent coarse cementite particle precipitation. It is also worth to point out that the collaborative activities particularly strong in Japan between steel manufacturers and auto companies have affected the progress in advanced sheet steels.

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“…: +48-52-341-91-08; fax +48-52-341-47-73; e-mail address: wozniak@ukw.edu.pl the main AE source. When the austempering temperature approaches the M S temperature, the transformation rate rapidly increases [11,12]. M S represents the temperature at which the formation of martensite will start.…”

Section: Introductionmentioning

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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Swing back in kinetics nearM s in hypereutectoid steels

Cited by 64 publications

References 3 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

Sheet Steel Technology for the Last 100 Years: Progress in Sheet Steels in Hand with the Automotive Industry

Application of acoustic emission to monitor bainitic and martensitic transformation

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