scholarly journals Characteristics and Formation Tendency of Freckle Segregation in Electroslag Remelted Bearing Steel

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 246
Author(s):  
Wei Yan ◽  
Yang Zhang ◽  
Weiqing Chen ◽  
Jing Li
Keyword(s):  
Thermal Effects ◽  
Liquid Fraction ◽  
Compositional Analysis ◽  
Threshold Value ◽  
Bearing Steel ◽  
Freckle Formation ◽  
Simulation Calculation ◽  
Steel Ingots ◽  
Dendritic Arm Spacing ◽  
Equiaxed Grains

Undesirable macro segregation defects, freckles, restrict the commercial production of large-sized electroslag remelting (ESR) bearing steel ingots through degradation of the mechanical properties and service lifetime. In order to clarify the freckle characteristics and formation tendency as well as the formation mechanism, freckles from an industrial large-sized GCr15SiMn ESR ingot were investigated through structural and compositional analysis, along with simulation calculation. The results show that freckles consist of (Si, Mn, Cr)-enriched equiaxed grains and occur in about the 1/2 radius region at the middle-upper part of the ESR ingot, where the secondary dendritic arm spacing (SDAS) and solidification front angle are large but cooling rate is small. The absolute value of relative Rayleigh number, Ra, also reaches its maximum in the 1/2 radius region, with a liquid fraction of 0.3–0.5, corresponding to the region where freckles form. Based on the experimental and simulation results, to evaluate the freckle formation in industrial-scale GCr15SiMn ESR ingots, the threshold value of relative Ra, a freckle criterion considering the compositional and thermal effects, was determined to be about −0.023.

Freckle formation and prevention in high strength low alloy steel ingots

2020 ◽  
Vol 117 (3) ◽  
pp. 309
Author(s):  
Wei Yan ◽  
Yang Zhang ◽  
Weiqing Chen ◽  
Jing Li
Keyword(s):  
Solidification Front ◽  
Hsla Steel ◽  
Vertical Direction ◽  
High Strength ◽  
Threshold Value ◽  
Front Angle ◽  
Freckle Formation ◽  
Steel Ingots ◽  
Liquid Flows ◽  
Free Area

Freckles considerably limit the development of larger electro-slag remelting (ESR) ingots. To simulate the freckling conditions in ESR ingots, high-strength low alloy (HSLA) steel was solidified with varying solidification front angles. Note that the freckling potential is enhanced and the orientation of freckle channel tends to be in the vertical direction with increase in solidification front angle. This is because the tilted solidification front contributes the available buoyancy and transports light (Si, Mn, Cr)-enriched liquid flows upwards toward the mush zone and then accumulates in the open segregation channel. For freckle formation in experimental HSLA steel ingots, a modified Rayleigh number (Ra) that considers the anisotropy of permeability and solidification front angle was evaluated and a threshold value of Ra that separates the freckled and freckle-free area was determined to be 0.79.

Microstructure Evolution and Coarsening Mechanism of 7075 Semi-Solid Aluminum Alloy Pre-Deformed by ECAP Method

2016 ◽  
Vol 256 ◽  
pp. 294-300 ◽  
Author(s):  
Jin Long Fu ◽  
Yu Wei Wang ◽  
Kai Kun Wang ◽  
Xiao Wei Li
Keyword(s):  
Aluminum Alloy ◽  
Solid State ◽  
Ostwald Ripening ◽  
Liquid Fraction ◽  
Isothermal Holding ◽  
Angular Pressing ◽  
Average Grain Size ◽  
Semi Solid ◽  
Equiaxed Grains ◽  
Kinetics Of

To investigate the influence of refined grains on the microstructure of 7075 aluminum alloy in semi-solid state, a new strain induced melting activation (SIMA) method was put forward containing two main stages: pre-deformation with equal channel angular pressing (ECAP) method and isothermally holding in the semi-solid temperature range. The breaking up and growth mechanisms of the grains and kinetics of equiaxed grains coarsening during the semi-solid holding were investigated. The results showed that the average grain size after ECAP extrusion decreased significantly, e.g., microstructure with average globular diameter less than 5μm was achieved after four-pass ECAP extrusion. Obvious grain coarsening had been found during isothermal holding in the semi-solid state and the roundness of the grains increased with the increasing holding time. The proper microstructure of 66.8μm in diameter and 1.22 in shape factor was obtained under proper soaking condition (at 590°C for 15 min). Two coarsening mechanisms, namely, coalescence in lower liquid fraction and Ostwald ripening in higher liquid fraction contributed to the grain growth process.

The Exchange-Correlation Field Effect over the Magnetoacoustic-Gravitational Instability in Plasmas

2017 ◽  
Vol 72 (10) ◽  
pp. 915-921 ◽  
Author(s):  
A. Rasheed ◽  
M. Jamil ◽  
Young-Dae Jung ◽  
A. Sahar ◽  
M. Asif
Keyword(s):  
Thermal Effects ◽  
Analytical Study ◽  
Significant Contribution ◽  
Gravitational Instability ◽  
Threshold Value ◽  
Electron Exchange ◽  
Recoil Effect ◽  
Exchange Correlation ◽  
Correlation Potential ◽  
Jeans Instability

AbstractJeans instability with magnetosonic perturbations is discussed in quantum dusty magnetoplasmas. The quantum and smaller thermal effects are associated only with electrons. The quantum characteristics include exchange-correlation potential, recoil effect, and Fermi degenerate pressure. The multifluid model of plasmas is used for the analytical study of this problem. The significant contribution of electron exchange is noticed on the threshold value of wave vector and Jeans instability. The presence of electron exchange and correlation effects reduce the time to stabilise the phenomenon of self-gravitational collapse of massive species. The results of Jeans instability by magnetosonic perturbations at quantum scale help to disclose the details of the self-gravitating dusty magnetoplasma systems.

Dynamic characteristics of threshold value and extension field selections for vacuum-blowing cleaning system

2021 ◽  
Author(s):  
Yuan Xi ◽  
Yan Dai ◽  
Xi-long Zhang ◽  
Gaohong He
Keyword(s):  
Average Velocity ◽  
Structural Parameters ◽  
Threshold Value ◽  
Structural Parameter ◽  
Extension Field ◽  
Cleaning System ◽  
Simulation Calculation ◽  
Computational Fluid Dynamics Cfd ◽  
Computational Resources ◽  
Grid Computation

To provide theoretical guidelines for threshold value selections on performance characteristics of extension field, the flow characteristic in the vacuum-blowing cleaning system was simulated using the average velocity and pressure of the front inlet surface, and the average velocity of the outlet surface, as indices to evaluate the effect of the extension field’s structural parameters. It is found that the extension field parameters have implications for the simulation calculation, and that each parameter has a corresponding threshold. If the structural parameter is greater than the corresponding threshold, the calculation result is not affected, and the threshold values are analyzed by using computational fluid dynamics (CFD). The dimensions of the front, back, left, and right extension fields are recommended as follows: lf=lb=ll=lr=210 mm and θf =θb =θl =θr =55 degree. The flow field distribution characteristic does not have a distinct difference with or without the extension field corner. The extension field with a corner can be used if high accuracy is required. However, to reduce the amount of grid computation and shorten the calculation time, the corner extension field model is not recommended. Finally, the simulation results are verified experimentally and can be used to improve the calculation accuracy and reduce the required computational resources.

Transmission Electron Microscopy Studies of X210CrW12 and 100CR6 Thixo-Cast Steels

2012 ◽  
Vol 186 ◽  
pp. 311-314 ◽  
Author(s):  
Lukasz Rogal ◽  
Jan Dutkiewicz
Keyword(s):  
Chemical Composition ◽  
Liquid Fraction ◽  
Eutectic Mixture ◽  
Residual Austenite ◽  
Bearing Steel ◽  
Transmission Electron ◽  
Cast Steels ◽  
Contamination Effect ◽  
Cold Worked ◽  
Average Size

Two kinds of deformed carbon steel were used as a feedstock for thixoforming: X210CrW12 tool steel cold worked, of composition 2,1 %C, 10,5 %Cr, 0,7 %W, 0,4 %Si (all in weight %), and bearing steel 100Cr6: (0,9% C, 1,4% Cr, 0,4% Mn, 0,3% Si, 0,2% Cu). The microstructures of X210CrW12 steel after thixoforming process at temperature of 1230°C, performed at 30 % of liquid show presence of globular grains (average size from 30 µm 50 µm) surrounded by the eutectic mixture. Measured chemical composition of the austenite in globules was: 2,5% C, 0,4% Si, 0,7% Mn, 12% Cr, 1,3% W, 0,1%V, 87% Fe and that of the eutectic mixture: 5%C, 0,4% Si, 0,6%, Mn, 1,1%, W, 17,5% Cr, 75,4% Fe in thixocast of X210CrW12 steel. Measured carbon content is too high, most probably due to contamination effect. TEM studies of this steel after thixoforming shows that the eutectic mixture consists of ferrite α-Fe and Cr7C3 carbides. Thixoforming of 100Cr6 bearing steel was conducted at temperature of 1420°C at about 25 % of liquid fraction. Thixocast microstructure consists of globular grains consisting of martensite needles and residual austenite (20 μm to 40 μm in size and average composition 0,9%C, 1,4 %Cr, 0,5%Mn, 0,3%Si). The chemical composition of the eutectic is following: 2,4% C, 2,6% Cr, 0,2%Si, 0,6%Mn.

Numerical Studies on Channel Formation and Growth During Solidification: Effect of Process Parameters

2006 ◽  
Vol 129 (4) ◽  
pp. 548-558 ◽  
Author(s):  
Jayesh Jain ◽  
Arvind Kumar ◽  
Pradip Dutta
Keyword(s):  
Cooling Rate ◽  
Process Parameters ◽  
Thermal Gradient ◽  
Chloride Solution ◽  
Liquid Fraction ◽  
Process Conditions ◽  
Channel Formation ◽  
Initial Concentration ◽  
Numerical Studies ◽  
Freckle Formation

In the present work, solidification of a hyper-eutectic ammonium chloride solution in a bottom-cooled cavity (i.e. with stable thermal gradient) is numerically studied. A Rayleigh number based criterion is developed, which determines the conditions favorable for freckles formation. This criterion, when expressed in terms of physical properties and process parameters, yields the condition for plume formation as a function of concentration, liquid fraction, permeability, growth rate of a mushy layer, and thermophysical properties. Subsequently, numerical simulations are performed for cases with initial and boundary conditions favoring freckle formation. The effects of parameters, such as cooling rate and initial concentration, on the formation and growth of freckles are investigated. It was found that a high cooling rate produced larger and more defined channels which are retained for a longer durations. Similarly, a lower initial concentration of solute resulted in fewer but more pronounced channels. The number and size of channels are also found to be related to the mushy zone thickness. The trends predicted with regard to the variation of number of channels with time under different process conditions are in accordance with the experimental observations reported in the literature.

Parametric excitation of surface waves in a strongly inhomogeneous plasma

1991 ◽  
Vol 46 (2) ◽  
pp. 299-307 ◽  
Author(s):  
G. Brodin ◽  
J. Lundberg
Keyword(s):  
Growth Rate ◽  
Surface Wave ◽  
Surface Waves ◽  
Parametric Excitation ◽  
Transition Layer ◽  
Low Temperatures ◽  
Thermal Effects ◽  
Inhomogeneous Plasma ◽  
Resonance Region ◽  
Threshold Value

The parametric excitation of surface waves in a warm inhomogeneous plasma is investigated. It is demonstrated that the coupling between the surface wave and plasmons that can be excited in the transition layer must be taken into account. The growth rate and the threshold value for the instability process are calculated. It is also shown that thermal effects are of importance even for very low temperatures, since the plasmons can now propagate out of the resonance region.

scholarly journals Some Similarities / Differences between Steel Static and Virtual Brass Static Casting

2017 ◽  
Vol 17 (1) ◽  
pp. 109-114
Author(s):  
P. Kwapisiński ◽  
A. A. Ivanova ◽  
B. Kania ◽  
W. Wołczyński
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Thermal Gradient ◽  
Gradient Field ◽  
Innovative Method ◽  
Columnar Grains ◽  
Steel Ingots ◽  
Equiaxed Grains ◽  
Structural Zones ◽  
Mathematical Interpretation

Abstract An innovative method for determining the structural zones in the large static steel ingots has been described. It is based on the mathematical interpretation of some functions obtained due to simulation of temperature field and thermal gradient field for solidifying massive ingot. The method is associated with the extrema of an analyzed function and with its points of inflection. Particularly, the CET transformation is predicted as a time-consuming transition from the columnar- into equiaxed structure. The equations dealing with heat transfer balance for the continuous casting are presented and used for the simulation of temperature field in the solidifying virtual static brass ingot. The developed method for the prediction of structural zones formation is applied to determine these zones in the solidifying brass static ingot. Some differences / similarities between structure formation during solidification of the steel static ingot and virtual brass static ingot are studied. The developed method allows to predict the following structural zones: fine columnar grains zone, (FC), columnar grains zone, (C), equiaxed grains zone, (E). The FCCT-transformation and CET-transformation are forecast as sharp transitions of the analyzed structures. Similarities between steel static ingot morphology and that predicted for the virtual brass static ingot are described.

Sign in / Sign up

Export Citation Format

Share Document