scholarly journals Identification of Precipitates in Cr-Mn-N Based Steel After Thermal Exposures

2014 ◽  
Vol 22 (34) ◽  
pp. 51-57
Author(s):  
Michal Ondruška ◽  
Mária Dománková ◽  
Miroslav Jáňa ◽  
Milan Marônek
Keyword(s):  
Grain Boundaries ◽  
Isothermal Annealing ◽  
Discontinuous Precipitation ◽  
Isothermal Holding ◽  
Steel Structure ◽  
Thermal Exposure ◽  
Holding Time ◽  
Secondary Phases ◽  
Σ Phase ◽  
Annealing Twins

Abstract The paper deals with the identification of precipitates in the Cr-Mn-N steels after thermal exposure. The purpose of the study is to clarify the M2N precipitation by isothermal annealing at the temperatures of 750 and 900 °C with a holding time of 5, 10, 30 min, 1 hr. and 10 hrs. Microstructure of austenitic steel was characterised by the typical presence of annealing twins. Stepwise etching was observed at the holding time of 5 and 10 minutes, but at the holding time of 30 minutes, secondary particles were precipitated at the grain boundaries. Corrosion tests revealed that holding time significantly affected steel structure. M2N is the dominant precipitate, but the occurrence of σ-phase was occasionally observed especially at the interface of discontinuous precipitation and austenitic matrix. Slight increase of hardness at the grain boundaries was caused due to the precipitation of secondary phases during isothermal holding. The maximum hardness of 294 HV was measured on the sample isothermally annealed at 750 °C and holding for 10 hrs. The research provides theoretical basis for the heat affecting of steels, such as, for example, in welding.

Effect of Hafnium on the Microstructure and Creep Property of a Hot Corrosion Resistant Superalloy

2015 ◽  
Vol 816 ◽  
pp. 641-647 ◽  
Author(s):  
Jie Shan Hou ◽  
Jian Ting Guo ◽  
Chao Yuan ◽  
Yong An Guo ◽  
Gu Song Li ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Creep Property ◽  
Thermal Exposure ◽  
Boundary Phase ◽  
Primary Carbide ◽  
Bayesian Neural Network ◽  
Creep Life ◽  
Σ Phase

The effects of the selective addition of Hafnium (Hf) on the grain boundary, phase, carbides and creep properties of experimented nickel superalloy after standard heat treatment and long-term exposure were investigated. Predicted by the Bayesian neural network, the creep life is prolonged with Hf content of 0-0.6 mass%, which is more effective at low stresses. The decrease of creep life of Hf free alloy after long term exposure was pronounced. Comparative study showed that the mainly small, coherent, blocky and closely spaced MC(2)and M23C6carbides precipitated on the grain boundaries in the 0.4wt% Hf contained alloy, and that relatively larger, incoherent MC(1)carbides precipitated on the grain boundaries in the Hf free alloy. During long term thermal exposure, fine discrete M23C6carbides decomposed from primary carbide, inducing a layer along the grain boundary, and the coarsening of grain boundary in Hf free alloy is more pronounced. At high stresses, the Hf-free alloy exhibited a stronger tendency of rafting than the 0.4Hf alloy, while the tendency of appearance of rafting was very similar at low stresses. However, Hf can render the alloy prone to the formation of σ phase, according to D-electrons method. Thus, the Hf content needs to be controlled to a suitable level.

scholarly journals Processing of Bi–Sr–Ca–Cu–O glasses using platinum and alumina crucibles

1992 ◽  
Vol 7 (8) ◽  
pp. 2035-2039 ◽  
Author(s):  
T.G. Holesinger ◽  
D.J. Miller ◽  
S. Fleshler ◽  
L.S. Chumbley
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Grain Boundaries ◽  
Annealed Sample ◽  
Substrate Material ◽  
Superconducting Phase ◽  
Transition Temperatures ◽  
Secondary Phases ◽  
Second Phases ◽  
Potential Substrate

Reactions with alumina and platinum crucibles were studied during the preparation of Bi2Sr2Ca1Cu2Oy “2212” glasses. In particular, reactions with Al2O3 are of interest since alumina is a potential substrate material in applications of this superconductor. Glasses processed using alumina crucibles were completely homogeneous and free of secondary phases although the material contained 2.26 at. % Al in solution. After heat treatments, Al was found in the form of SrCaAlOy particles located primarily along grain boundaries of the 2212 superconducting phase. Platinum contamination was minimal (<0.02 at. %) and no Pt-containing secondary phases were found in amorphous or annealed samples. Glasses made with Pt crucibles were found to contain small amounts of CaO, Sr14−xCaxCu24O41, and 2201 as second phases. Differential thermal analysis (DTA) suggested that the crystallization processes were essentially the same for all samples although the small amount of Al seemed to slow the kinetics leading to the formation of 2212. Neither Al nor Pt was detected within the 2212 phase. The measured superconducting compositions in each annealed sample were nearly the same with identical transition temperatures of 88 K. Overall differences in stoichiometry were accommodated by changes in the number and composition of the secondary phases present.

Properties of ZrO2–Al2O3 composite as a function of isothermal holding time

2007 ◽  
Vol 25 (5-6) ◽  
pp. 374-379 ◽  
Author(s):  
J.K.M.F. Daguano ◽  
C. Santos ◽  
R.C. Souza ◽  
R.M. Balestra ◽  
K. Strecker ◽  
...  
Keyword(s):  
Isothermal Holding ◽  
Holding Time ◽  
Al2o3 Composite

Temperature-induced structural transition of ceria by bulk reduction under hydrogen atmosphere

CrystEngComm ◽  
2018 ◽  
Vol 20 (31) ◽  
pp. 4359-4363 ◽  
Author(s):  
Takeshi Matsukawa ◽  
Akinori Hoshikawa ◽  
Toru Ishigaki
Keyword(s):  
High Temperature ◽  
Structural Transition ◽  
Isothermal Holding ◽  
Hydrogen Atmosphere ◽  
Holding Time

Ceria (CeO2) was kinetically reduced in hydrogen depending on the isothermal holding time at high temperature.

scholarly journals Study on σ Phase in Fe–Al–Cr Alloys

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1092 ◽  
Author(s):  
Jintao Wang ◽  
Shouping Liu ◽  
Xiaoyu Han
Keyword(s):  
Mechanical Properties ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Thermodynamic Calculation ◽  
Second Phase ◽  
Σ Phase ◽  
Austenitic Transformation ◽  
The Matrix ◽  
The Relationship

In this paper, a method of using the second phase to control the grain growth in Fe–Al–Cr alloys was proposed, in order to obtain better mechanical properties. In Fe–Al–Cr alloys, austenitic transformation occurs by adding austenitizing elements, leading to the formation of the second phase and segregation at the grain boundaries, which hinders grain growth. FeCr(σ) phase was obtained in the Fe–Al–Cr alloys, which had grains of several microns and was coherent and coplanar with the matrix (Fe2AlCr). The nucleation of σ phase in Fe–Al–Cr alloy was controlled by the ratio of nickel to chromium. When the Ni/Cr (eq) ratio of alloys was more than 0.19, σ phase could nucleate in Fe–Al–Cr alloy. The relationship between austenitizing and nucleation of FeCr(σ) phase was given by thermodynamic calculation.

scholarly journals A New Approach to the Study of Multi-Pass Welds–Microstructure and Properties of Welded 20-mm-Thick Superduplex Stainless Steel

2019 ◽  
Vol 9 (6) ◽  
pp. 1050 ◽  
Author(s):  
Maria Valiente Bermejo ◽  
Kjell Hurtig ◽  
Daniel Eyzop ◽  
Leif Karlsson
Keyword(s):  
Stainless Steel ◽  
Arc Welding ◽  
Gas Metal Arc Welding ◽  
Secondary Phases ◽  
Σ Phase ◽  
Flux Cored Arc Welding ◽  
Welding Sequence ◽  
Superduplex Stainless Steel ◽  
Secondary Austenite ◽  
The Impact

Type 2507 superduplex stainless steel 20 mm in thickness was multi-pass-welded with Gas Metal Arc Welding (GMAW) and Flux-Cored Arc Welding (FCAW) processes. Recommended and higher arc energies and inter-pass temperatures were used. Thermal cycles were monitored using a recently developed procedure involving the successive instrumentation of the multi-pass welds, pass by pass, by addition of thermocouples in each weld pass. The repeatability of temperature measurements and survival rate of more than 90% of thermocouples confirmed the reliability of the procedure. Reheating by subsequent passes caused a progressive increase in the austenite content of the weld metal. The as-deposited GMAW passes with higher-than-recommended arc energy showed the lowest presence of nitrides. Therefore, the cooling rate—and not the time exposed at the critical temperature range—seems to be the key factor for nitride formation. The welding sequence layout also plays an important role in the distribution of secondary phases. A larger amount and concentration of secondary austenite and σ-phase was found for a larger number of subsequent passes in the immediate vicinity of a specific weld pass. The impact toughness exceeded requirements for all welds. Differences in absorbed energies were related to the amount of micro-inclusions found with the FCAW weld showing the lowest absorbed energies and highest amount of micro-inclusions. Pitting corrosion preferentially initiated in locations with secondary austenite and σ-phase. However, in the absence of these secondary phases, the HAZ containing nitrides was the weakest location where pitting initiated. The results of this work have implications on practical welding for superduplex stainless steels: the current recommendations on maximum arc energy should be revised for large thickness weldments, and the importance of the welding sequence layout on the formation of secondary phases should be considered.

Effect of isothermal process parameters on semi-solid microstructure of chip-based Al–Cu–Mn–Ti alloy prepared by SIMA method

2020 ◽  
Vol 34 (33) ◽  
pp. 2050385
Author(s):  
Ye Wang ◽  
Maoliang Hu ◽  
Hongyu Xu ◽  
Zesheng Ji ◽  
Xuefeng Wen ◽  
...  
Keyword(s):  
Process Parameters ◽  
Ostwald Ripening ◽  
Isothermal Holding ◽  
Treatment Temperature ◽  
Holding Time ◽  
Isothermal Treatment ◽  
Isothermal Process ◽  
Semi Solid ◽  
Average Size ◽  
Relationship Of

A typical Al–Cu–Mn–Ti aluminum alloy chip was adopted to prepare semi-solid billets by a Strain-Induced Melt Activation (SIMA) method, and the effects of isothermal process parameters on the semi-solid microstructure evolution of the alloy were investigated in this work. The result showed that semi-solid billets with highly spheroidal and homogeneous fine grains could be prepared from chips by the SIMA method. With the increase of isothermal temperature, the finer and near-spherical grains are obtained, the grains coarsen and became ellipse at 903 K because of the coarsening mechanisms of coalescence and Ostwald ripening. The relationship of isothermal holding time and grains size followed the LSW theory well, and more spherical microstructure can be brought by prolonging the holding time until 3000 s. Thus, the optimal isothermal treatment temperature is 893 K and holding time is 3000 s, the corresponding average size and roundness of grains are 137 [Formula: see text]m and 1.108, respectively.

scholarly journals Additive Manufacturing with Superduplex Stainless Steel Wire by CMT Process

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 272 ◽  
Author(s):  
Malin Lervåg ◽  
Camilla Sørensen ◽  
Andreas Robertstad ◽  
Bård M. Brønstad ◽  
Bård Nyhus ◽  
...  
Keyword(s):  
Additive Manufacturing ◽  
Volume Fraction ◽  
Steel Wire ◽  
Oil And Gas Industry ◽  
Secondary Phases ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Σ Phase ◽  
Wide Range ◽  
Wire Arc Additive Manufacturing

For many years, the oil and gas industry has utilized superduplex stainless steels due to their high strength and excellent corrosion resistance. Wire arc additive manufacturing (WAAM) was used with superduplex filler wire to create walls with different heat input. Due to the multiple heating and cooling cycles during layer deposition, brittle secondary phases may form such as intermetallic sigma (σ) phase. By inspecting deposited walls within wide range of heat inputs (0.40–0.87 kJ/mm), no intermetallic phases formed due to low inter-pass temperatures used, together with the high Ni content in the applied wire. Lower mechanical properties were observed with high heat inputs due to low ferrite volume fraction, precipitation of Cr nitrides and formation of secondary austenite. The walls showed good toughness values based on both Charpy V-notch and CTOD (crack tip opening displacement) testing.

scholarly journals New insights into microstructure of irradiated beryllium based on experiments and computer simulations

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
M. Klimenkov ◽  
P. Vladimirov ◽  
U. Jäntsch ◽  
V. Kuksenko ◽  
R. Rolli ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Gas Bubbles ◽  
Atomic Scale ◽  
Average Height ◽  
Secondary Phases ◽  
Atomistic Modelling ◽  
Transmission Electron ◽  
Intermetallic Precipitates ◽  
Diffusion Mechanisms ◽  
Small Bubbles

Abstract The microstructural response of beryllium after neutron irradiation at various temperatures (643–923 K) was systematically studied using analytical transmission electron microscope that together with outcomes from advanced atomistic modelling provides new insights in the mechanisms of microstructural changes in this material. The most prominent feature of microstructural modification is the formation of gas bubbles, which is revealed at all studied irradiation temperatures. Except for the lowest irradiation temperature, gas bubbles have the shape of thin hexagonal prisms with average height and diameter increasing with temperature. A high number density of small bubbles is observed within grains, while significantly larger bubbles are formed along high-angle grain boundaries (GB). Denuded zones (DZ) nearly free from bubbles are found along both high- and low-angle grain boundaries. Precipitations of secondary phases (mainly intermetallic Al-Fe-Be) were observed inside grains, along dislocation lines and at GBs. EDX analysis has revealed homogeneous segregation of chromium and iron along GBs. The observed features are discussed with respect to the available atomistic modelling results. In particular, we present a plausible reasoning for the abundant formation of gas bubbles on intermetallic precipitates, observation of various thickness of zones denuded in gas bubbles and precipitates, and their relation to the atomic scale diffusion mechanisms of solute-vacancy clusters.

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