scholarly journals Evolution of primary austenite during coarsening and impact on eutectic microstructure in Fe–C–Si alloys

Materialia ◽  
2019 ◽  
Vol 7 ◽  
pp. 100391 ◽  
Author(s):  
Juan Carlos Hernando ◽  
Jessica Elfsberg ◽  
Arne K. Dahle ◽  
Attila Diószegi
Keyword(s):  
Eutectic Microstructure ◽  
Primary Austenite

Research on the Microstructure and Microhardness of 9Cr18 Semi-Solid Billet

2015 ◽  
Vol 817 ◽  
pp. 278-282 ◽  
Author(s):  
Yong Jin Wang ◽  
Ren Bo Song ◽  
Ya Ping Li ◽  
Ruo Ling Bi
Keyword(s):  
Energy Dispersive Spectrometer ◽  
Eutectic Structure ◽  
X Ray Diffraction ◽  
Graded Materials ◽  
Primary Austenite ◽  
Secondary Austenite ◽  
Austenite Grains ◽  
Semi Solid ◽  
Sloping Plate ◽  
Eutectic Area

Formed in the semi-solid state, materials can obtain unconventional microstructures and properties compared with traditional method. In this paper, semi-solid billet of 9Cr18 steel was obtained through a wavelike sloping plate. Microstructure analysis of the semi-solid billet was conducted through scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). X-ray diffraction (XRD) test and microhardness test were also used to analyze the properties. The results showed that the structure of 9Cr18 semi-solid billet contained globular primary austenite and secondary austenite-Cr7C3 eutectic. Globular primary austenite grains were first formed during partial solidification in the sloping plate, and then the rest liquid metal formed secondary austenite and Cr7C3 eutectic structure surrounding the primary grains. Cr atoms had a concentration in the rest liquid side, which along with C atoms contributed to the formation of the Cr7C3 carbide. Hardness in the primary solid grain area and the eutectic area was about 330 HV and 650 HV, respectively. These specific properties were important for subsequent thixoforming of the functional graded materials.

Crystallographic features of the Al3Nb, Nb2Al and Nb(Ni1−XAlX)2 phases in a directionally solidified ternary eutectic microstructure

2019 ◽  
Vol 147 ◽  
pp. 303-310 ◽  
Author(s):  
Eder S.N. Lopes ◽  
Mariana R. Dal Bó ◽  
Victor C. Opini ◽  
Mariana G. de Mello ◽  
Carlos T. Rios ◽  
...  
Keyword(s):  
Ternary Eutectic ◽  
Eutectic Microstructure ◽  
Directionally Solidified

scholarly journals Effect of Microstructural Bands on the Localized Corrosion of Laser Surface-melted 316L Stainless Steel

CORROSION ◽  
10.5006/3779 ◽  
2021 ◽  
Author(s):  
Yoon Hwa ◽  
Christopher Kumai ◽  
Nancy Yang ◽  
Joshua Yee ◽  
Thomas Devine
Keyword(s):  
Stainless Steel ◽  
316L Stainless Steel ◽  
Microscopic Investigation ◽  
Outer Edge ◽  
Chromium Concentration ◽  
Laser Surface ◽  
Localized Corrosion ◽  
Pitting Potential ◽  
Primary Austenite ◽  
Potentiodynamic Anodic Polarization

The localized corrosion of laser surface melted (LSM) 316L stainless steel is investigated by a combination of potentiodynamic anodic polarization in 0.1M HCl and microscopic investigation of the initiation and propagation of localized corrosion. The pitting potential of LSM 316L is significantly lower than the pitting potential of wrought 316L. The LSM microstructure is highly banded as a consequence of the high laser power density and high linear energy density. The bands are composed of zones of changing modes of solidification, cycling between very narrow regions of primary austenite solidification and very wide regions of primary ferrite solidification. Pits initiate in the outer edge of each band where the mode of solidification is primary austenite plane front solidification and primary austenite cellular solidification. The primary austenite regions have low chromium concentration (and possibly low molybdenum concentration), which explains their susceptibility to pitting corrosion. The ferrite is enriched in chromium, which explains the absence of pitting in the primary ferrite regions. The presence of the low chromium regions of primary austenite solidification explains the lower pitting resistance of LSM 316L relative to wrought 316L. The influence of banding on localized corrosion is applicable to other rapidly solidified processes such as additive manufacturing.

Anisotropic Microstructure and Hydrogen Permeability of Nb-Ti-Ni Duplex Phase Alloy Prepared by Hot Forging-Rolling Technique

2006 ◽  
Vol 980 ◽  
Author(s):  
Sho Tokui ◽  
Kazuhiro Ishikawa ◽  
Kiyoshi Aoki
Keyword(s):  
Solid Solution ◽  
Hydrogen Embrittlement ◽  
Hydrogen Permeability ◽  
Rolling Direction ◽  
Hot Forging ◽  
The Other ◽  
Rolling Reduction ◽  
Eutectic Microstructure ◽  
Ni Alloys ◽  
Other Hand

AbstractIt has been demonstrated that the as-cast Nb40Ti30Ni30 duplex phase alloy, which consists of the primary (Nb, Ti) solid solution and the fine lamellar type eutectic {TiNi+(Nb, Ti)} phase, shows higher hydrogen permeability ¶ than that of pure Pd without the hydrogen embrittlement at 673K. In this alloy, the eutectic phase contributes to the suppression of the hydrogen embrittlement, while the primary one does mainly to the hydrogen permeation. It is important to note that even if the eutectic microstructure disappears and is replaced by the small spherical (Nb, Ti) phase embedded in the TiNi matrix by rolling and subsequent annealing, its high hydrogen permeability and large resistance to the hydrogen embrittlement are sustained. Furthermore, the present authors have observed that the primary (Nb, Ti) phase is largely elongated along the rolling direction. Consequently, it is expected that rolled and annealed Nb-Ti-Ni alloys show the large anisotropy of the microstructure and the hydrogen permeability. In the present work, the microstructure and hydrogen permeability ¶nof the Nb40Ti30Ni30 alloy after rolling and annealing treatments are examined in order to develop highly hydrogen permeable alloys utilizing the anisotropic microstructure.The primary (Nb, Ti) phase and the very fine eutectic {TiNi+(Nb, Ti)} phase are observed in the as-cast Nb40Ti30Ni30 alloy by scanning electron microscopy (SEM). The X-ray diffractometry (XRD) indicates that this alloy consists of the B2-TiNi intermetallic compounds and the bcc- (Nb, Ti) solid solution. The primary (Nb, Ti) phase is largely elongated along the rolling direction by forging and subsequent rolling at 1173 K. On the other hand, the eutectic microstructure becomes unclear with increasing the rolling reduction. The composite alloys in which the (Nb, Ti) phase is elongated along to the rolling direction are obtained by 69 % rolling reduction. ¶n of this sample is four times higher than that of as-cast one. On the other hand, ¶ for the sample vertical to the rolling direction is reduced to about one third of that of as-cast one. Thus, the hydrogen permeability of the Nb40Ti30Ni30 alloy varies about ten times or more depending on the direction of the primary¡]Nb, Ti¡^ phase. We conclude that it is possible to produce highly hydrogen permeable Nb-Ti-Ni alloys using the anisotropy of the microstructure prepared by hot forging and rolling.

scholarly journals On the Primary Solidification of Compacted Graphite Iron: Microstructure Evolution during Isothermal Coarsening

2018 ◽  
Vol 925 ◽  
pp. 90-97 ◽  
Author(s):  
Juan Carlos Hernando ◽  
Attila Diószegi
Keyword(s):  
Cast Iron ◽  
Morphological Evolution ◽  
Solidification Process ◽  
Primary Phase ◽  
Eutectic Solidification ◽  
Spheroidal Graphite ◽  
Cube Root ◽  
Compacted Graphite ◽  
Primary Austenite ◽  
Graphite Cast Iron

It is widely accepted that in most commercial hypoeutectic alloys, both static mechanical properties and feeding characteristics during solidification, are extremely linked to the coarseness of the primary phase. It is therefore of critical importance to provide tools to control and predict the coarsening process of the dendritic phase present in hypoeutectic melts. The characterization of the primary phase, a product of the primary solidification, has traditionally been neglected when compared to the eutectic solidification characterization in cast iron investigations. This work presents the morphological evolution of the primary austenite present in a hypoeutectic compacted graphite cast iron (CGI) under isothermal conditions. To that purpose, a base spheroidal graphite cast iron (SGI) material with high Mg content is re-melted in a controlled atmosphere and reversed into a CGI melt by controlling the Mg fading. An experimental isothermal profile is applied to the solidification process of the experimental alloy to promote an isothermal coarsening process of the primary austenite dendrite network during solid and liquid coexistence. Through interrupted solidification experiments, the primary austenite is preserved and observed at room temperature. By application of stereological relations, the primary phase and its isothermal coarsening process are characterized as a function of the coarsening time applied. The microstructural evolution observed in the primary austenite in CGI and the measured morphological parameters show a similar trend to that observed for lamellar graphite cast iron (LGI) in previous investigations. The modulus of the primary austenite, Mγ, and the nearest distance between the centre of gravity of neighbouring austenite particles, Dγ, followed a linear relation with the cube root of coarsening time.

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