"In-situ" Observation of the .DELTA./.GAMMA. Phase Transformation on the Surface of Low Carbon Steel Containing Phosphorus at Various Cooling Rates

Liu, Zhongzhu; Kobayashi, Yoshinao; Yang, Jian; Nagai, Kotobu; Kuwabara, Mamoru

doi:10.2355/isijinternational.46.847

Cited by 34 publications

(34 citation statements)

References 22 publications

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“…Finally, the substantial reduction of other γ-phase, which would precipitate in the other positions during the nucleating period and pass the observed surface during the growing period under the normal conditions, also leads to the decrease of γ-phase. The transformation process mentioned above during continuous cooling agrees partially with the descriptions by Yin, 9,10) Phelan 12,13) and Liu,14) where these researchers made detailed "in-situ" observations of the δ→γ transformation at some certain cooling rates, but there still exists some differences between the previous investigations with the present work because of the particularity of duplex stainless steels.…”

Section: γ→δ Phase Transformationsupporting

confidence: 70%

“…For example, Yin 10) found that the incoherent δ/γ interphase boundaries (abbreviated as IBs hereafter) were always unstable with finger-like morphology during δ→γ transformation, which developed along δ/δ grain boundaries (abbreviated as GBs hereafter) at low supercoolings and even into the δ-ferrite matrix at higher supercoolings for the transformation. Liu 14) also showed that the phosphorus content and cooling rates had significant influences on the δ→γ transformation in low carbon steels.…”

Section: Introductionmentioning

confidence: 99%

“…8) The Confocal Scanning Laser Microscope (CLSM) has recently provided a convenient possibility of making an "insitu" observation of the phase transformation on the surface of samples at high temperatures. Since the 1990's, Yin,9,10) Kimura, 11) Phelan, 12,13) Liu, 14) Chen, 15) and other researchers [16][17][18][19][20][21][22][23] have applied the CLSM to make in situ observations of the phase transformation of steels or alloys at special heating or cooling rates. For example, Yin 10) found that the incoherent δ/γ interphase boundaries (abbreviated as IBs hereafter) were always unstable with finger-like morphology during δ→γ transformation, which developed along δ/δ grain boundaries (abbreviated as GBs hereafter) at low supercoolings and even into the δ-ferrite matrix at higher supercoolings for the transformation.…”

Section: Introductionmentioning

confidence: 99%

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In-situ Observation of δ↔γ Phase Transformations in Duplex Stainless Steel Containing Different Nitrogen Contents

Zhao

Sun

et al. 2017

ISIJ International

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The characteristics of the γ ↔δ phase transformations were observed on the surface of duplex stainless steels with different nitrogen concentrations by the Ultra High Temperature Confocal Laser Scanning Microscope (UHT-CSLM). The effects of the nitrogen content on the phase transformations are discussed based on the experimental results and thermodynamic calculations. It is found that the migration of the δ/γ IB is the main form of the phase transformation and leads to the continuous decline and final disappearance of the retained γ-phase during the γ→δ phase transformation in the high nitrogen steel (N1) and low nitrogen steel (N2). During the δ→γ phase transformation, the γ -cells prefer to precipitate along the δ/δ GBs and develop into the δ -ferrite matrix with finger-like or sword-like patterns. Then the γ-cells also nucleate in the δ -grains with a sword-like pattern and the growing speed in the longitudinal direction is much faster than that in the lateral direction. More importantly, the high nitrogen content can hinder the migration of δ/γ IBs during the γ→δ transformation and also promote the nucleation and growth of γ -phase during the δ→γ transformation by increasing both the starting and finishing temperatures of the phase transformation. Interestingly, the original δ/δ GB which is covered by the precipitation of γ -phase during the δ→γ transformation will reappear first at the same position by the moving of δ/γ IBs during the γ→δ transformation, but it is unstable and migrates fast with further heating.

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Section: γ→δ Phase Transformationsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In-situ Observation of δ↔γ Phase Transformations in Duplex Stainless Steel Containing Different Nitrogen Contents

Zhao

Sun

et al. 2017

ISIJ International

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“…The effect of phosphorus on phase transformation temperature is recently proved by an ''in-situ'' observation of the = transformation by the present authors. 20) The same LPS and HPS samples are firstly hold at 1723 K for 1200 s and then cooled to an ambient temperature with a 0.33 K/s cooling rate. The observed starting temperatures of = transformation in LPS and HPS samples are close at about 1698-1701 K. However, as the transformation continues, the transformation process in the Table 3 The equilibrium distribution coefficient and diffusion coefficient of the solute elements for mathematical calculation.…”

Section: Phosphorus Micro-segregationmentioning

confidence: 99%

Interaction between Phosphorus Micro-Segregation and Sulfide Precipitation in Rapidly Solidified Steel—Utilization of Impurity Elements in Scrap Steel

et al. 2007

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Copper is one of the main residual elements in steel, especially in recycled scrap steel. Sulfur and phosphorus are two of the main impurities in steel, and it may result in a large emission of slag and CO 2 to remove them from steel. Utilization of these elements has been an important and difficult matter for metallurgist. In the present paper, the as-cast steels containing different concentrations of copper, sulfur and phosphorus are prepared by strip casting process or laboratory rapid solidification process. The effect of phosphorus addition on sulfide precipitation is investigated and discussed with respect to the morphology, size, and composition of sulfide. Both experimental results and mathematical calculation showed that the addition of phosphorus retards the sulfide precipitation at high temperature, promotes more copper bearings and smaller sulfides precipitation at low temperature. On the other hand, sulfide precipitates are shown to reduce the micro-segregation degree of phosphorus in steel, which may be because some phosphorus dissolves in sulfide and sulfide particles provide more interfaces for phosphorus to distribute.

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“…Several studies using CSLM have been reported involving low carbon steel [11][12][13][14], stainless steel [15] and metallic glass materials [16]. Therefore, this novel equipment is applied to perform an in-situ observation of solidification process of Alloy 718.…”

Section: Introductionmentioning

confidence: 99%

Application of Confocal Scanning Laser Microscope in Studying Solidification Behavior of Alloy 718

Shan¹,

Lü²,

Xu³

et al. 2010

7th International Symposium on Superalloy 718 and Derivatives (2010)

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Alloy 718 has a very long history, it is still used extensively, which accounts for more than 50% of commercial superalloy productions in the world. The reason is that Alloy 718 exhibits good strength, excellent weldability and lastly, but most importantly, reasonable cost. Recently, confocal scanning laser microscope (CSLM) offers a convenient way for conducting a real-time and continuous in-situ observation of phase transformations at high temperatures. Several studies using CSLM have been reported for low carbon steel, stainless steel and metallic glass materials. The aim of this paper is to study the solidification behavior of Alloy 718 using confocal scanning laser microscope. In addition to the in-situ observation of solidification at different cooling rates, the analysis of microstructure evolution was conducted by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results show that the cooling rate has a great impact on the solidification behavior of Alloy 718. Variation of secondary dendrite arm spacing, morphology change in MC carbide, and Laves phase after solidification at different cooling rates are studied in details. IntroductionAlloy 718 is an age-hardenable wrought superalloy used for elevated temperature gas-turbine applications, which is famous for its excellent balance of properties and reasonable cost, accounting for more than 50% of commercial superalloy productions in the world [1]. With the development of land-based power generation and aircraft propulsion, scaling-up of components has become the necessity. In response to market demands the size of Alloy 718 ingot produced by VIM-ESR-VAR triple melting has increased markedly over the past 10 years [2][3][4][5][6][7]. However, the solutes segregation problem, mainly niobium segregation, is a big issue for producing large size Alloy 718 ingots. Particularly, some macrosegregations such as freckles and white spots formed during the solidification process may lead to failure of entire ingot. Therefore the indepth studies of solidification behavior of Alloy 718 are still needed.

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"In-situ" Observation of the .DELTA./.GAMMA. Phase Transformation on the Surface of Low Carbon Steel Containing Phosphorus at Various Cooling Rates

Cited by 34 publications

References 22 publications

<i>In-situ</i> Observation of <i>δ</i>↔<i>γ</i> Phase Transformations in Duplex Stainless Steel Containing Different Nitrogen Contents

<i>In-situ</i> Observation of <i>δ</i>↔<i>γ</i> Phase Transformations in Duplex Stainless Steel Containing Different Nitrogen Contents

Interaction between Phosphorus Micro-Segregation and Sulfide Precipitation in Rapidly Solidified Steel—Utilization of Impurity Elements in Scrap Steel

Application of Confocal Scanning Laser Microscope in Studying Solidification Behavior of Alloy 718

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"In-situ" Observation of the .DELTA./.GAMMA. Phase Transformation on the Surface of Low Carbon Steel Containing Phosphorus at Various Cooling Rates

Cited by 34 publications

References 22 publications

<i>In-situ</i> Observation of <i>δ</i>↔<i>γ</i> Phase Transformations in Duplex Stainless Steel Containing Different Nitrogen Contents

<i>In-situ</i> Observation of <i>δ</i>↔<i>γ</i> Phase Transformations in Duplex Stainless Steel Containing Different Nitrogen Contents

Interaction between Phosphorus Micro-Segregation and Sulfide Precipitation in Rapidly Solidified Steel&mdash;Utilization of Impurity Elements in Scrap Steel

Application of Confocal Scanning Laser Microscope in Studying Solidification Behavior of Alloy 718

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Interaction between Phosphorus Micro-Segregation and Sulfide Precipitation in Rapidly Solidified Steel—Utilization of Impurity Elements in Scrap Steel