Solidification In Mold Research Articles

Formation Mechanism and Control Strategy of Transverse Corner Cracks in Continuous Casting of 55SiCr Spring Steel

An experimental study is conducted to reveal the formation mechanism of transverse corner cracks by analyzing the metallurgical structure, crack morphology, and hot ductility. The results reveal that the corner temperature of the billet tends to be lower during mold solidification, leading to the formation of grain boundary low‐plasticity ferrite. Additionally, during the straightening process, the corner temperature of the billet falls into the serious low‐temperature brittle zone with temperature lower than 850 °C. These two factors contribute to the formation and propagation of cracks along the grain boundary ferrite under straightening forces. Therefore, after the verification of mold simulation test and industrial trial, the temperature at billet (section size 150 × 150 mm2) corner is improved by increasing the mold chamfer radius from 6 to 12 mm. This adjustment ensures that the straightening temperature at billet corner elevated from 830 to 880 °C, remaining outside the serious low‐temperature brittle zone, and the maximum depth of corner cracks decreases from 741.49 to 344.89 μm.

In Vitro Study of the Surface Roughness, Hardness, and Absorption of an Injection-Molded Denture Base Polymer, Manufactured under Insufficient Mold Solidification

The current study sought to investigate the changes in surface hardness, roughness, and moisture absorption of the Vertex ThermoSens polymer (Vertex Dental, 3D Systems, The Netherlands) following immersion in artificial saliva for various periods (7, 14, and 28 days). A total of 60 rectangular specimens with dimensions of 20 mm in length, 20 mm in width, and 3 mm in thickness were made. Due to insufficient mold solidification, these specimens were made utilizing the injection molding process. A Mitutoyo Surftest 4 roughness meter (Mitutoyo, Aurora, IL, USA) was used to measure the surface roughness of the test materials. The ThermoSens polymer hardness was assessed using the Shor method and D—HSD scale, while absorption was measured with a Sartorius analytical balance. Results indicated the highest mean hardness after 28 days (M = 77.6) (Surface 1) and the lowest for the control group (M = 59) (Surface 2). The maximum surface roughness occurred in direction 2.2 pre-immersion (Ra = 2.88 μm) and 7 days post-removal (Ra = 2.95 μm). The control group exhibited the lowest absorption (Wsp = 1.524 mg/mm3), with the highest mean values over 28 days (Wsp = 1.541 mg/mm3). The elevated flask and plaster temperature slowed polymer solidification, resulting in longer macromolecules and improved mechanical properties and surface features.

Enhanced tensile properties and intersecting nanotwins formation mechanism of Ti44Al48Nb8 alloy via electromagnetic levitation processing

Combining the electromagnetic levitation (EML) method with materials processing techniques (pressure die-casting and copper mold solidification), bulk Ti44Al48Nb8 alloy samples with different shapes were prepared, and their microstructure evolution, tensile properties and deformation behavior were systematically investigated. Assisted with a double aberration corrected transmission electron microscope (TEM) and molecular dynamics (MD) simulation, three types of intersecting nanotwins were observed and the formation mechanism of step-like and intersecting nanotwins under both tensile loading and at highly undercooled state were discussed. For the 35 g cone-shaped Ti44Al48Nb8 sample by EML, the microstructure consists of lamellar α2-Ti3Al+γ-TiAl matrix, Nb-rich and Al-rich region, showing a typical peritectic morphology. The average grain size has been significantly reduced after levitation die-casting and copper mold casting, due to the relatively high cooling rate and external stress. The rapidly solidified microstructure of a 0.6 g sample undercooled at 61 K has the similar microstructure with large samples. With the increase of bulk undercooling at 300 K, elemental segregation has been effectively inhibited and the intersecting nanotwins were formed, which shows a unique hierarchical structure. The samples processed by copper-mold casting have good tensile properties, which can be attributed to the refined microstructure, the generation of dislocation and stacking faults, and the formation of intersecting nanotwins. Based on the results of MD simulation and atomic-scale quasi-in-situ TEM observation, the analogous dissociation of dislocation dominated by pole mechanism occurs, resulting in the formation of 1/6<112> Shockley partial dislocation, 1/6<110> stair-rod dislocation and 1/3<111> Frank partial dislocation. When samples were highly undercooled, the generated internal stress can facilitate twinning at a much lower stress level, which can be beneficial for the formation of nanotwins at undercooled state.

Graphite Compactness Degree and Nodularity of High-Si Ductile Iron Produced via Permanent Mold versus Sand Mold Casting

In recent years, high-Si ductile cast irons (3–6% Si) have begun to be used more and more in the automotive and maritime industries, but also in wind energy technology and mechanical engineering. Si-alloyed ferrite has high strength, hardness and oxidation and corrosion resistance, but it has low ductility, toughness and thermal conductivity, with graphite as an important influencing factor. In this study, 4.5% Si uninoculated ductile iron solidified in thin wall castings (up to 15 mm section size) via a permanent (metal) mold versus a sand mold, was evaluated. Solidification in a metal mold led to small size, higher graphite particles (less dependent on the section size). The graphite particles’ real perimeter was 3–5% higher than the convex perimeter, while the values of these parameters were 41–43% higher in the sand mold. Increasing the casting section size led to an increased graphite perimeter, with it being much higher for sand mold. The graphite particles’ shape factors, involving the maximum and minimum size, were at a lower level for metal mold solidification, while by involving the difference between Pr and Pc, is higher for the metal mold. The shape factor, including the graphite area and maximum size, had higher values in the metal mold, sustaining a higher compactness degree of graphite particles and a higher nodularity regarding metal mold solidification (75.5% versus 67.4%). The higher was due to the graphite compactness degree level (shape factor increasing from 0.50 up to 0.80), while the lower was due to the graphite nodularity for both the metal mold (39.1% versus 88.5%) and the sand mold (32.3% versus 83.1%). The difference between the metal mold and sand mold as the average graphite nodularity increased favored the metal mold.

The Influence Of Sand Casting Mold Solidfication Pressure Variations To The Quality Of Al-Si Alloy Casting Product

The purpose of this study is to find The influence of the sand cast solidification pressure variations to the quality of an alloy Al-Si casting product. An experimental method was used in the study and the analysis of the data used descriptive analysis to explain the charts. The stages of researched process is preparation material and equipment; making the design and manufacture of a pattern; manufacture of the sand mold by 35, 40, 45, 50, and 55 kg/cm 2 pressure variation; casting process; observation of defect; measurement of the level roughness; microstructure examination; assay composition; and last test is hardness micro vickers test. The research results show that variations pressure 35 kg/cm 2 does not occur defect the needle at al. A defect of the needle that occur most frequently upon variations of the pressure of the 55 kg/cm 2 is as much as 0.62 % . Air cavities formed to variation pressure solidification 35 kg/cm 2 of 0.77 % to the least, while in variation 55 kg/cm 2 happened the number of defect air cavities the most namely 3.96 % . The mold fall defect largest namely 1.95 % happened to variation pressure 35 kg/cm 2 . Defect of sand inclusion the least of 0.06 % happened to variation pressure 55 kg/cm 2 . Defect of fins formed due to variation pressure solidification sand mold experienced the number of been fluctuating, recorded high in early then decline and to high back in highest variation. The pressure variation 35 kg/cm 2 it has value roughness flattened 3.17 and products castings the most rough happened to sand mold solidification variation pressure 55 kg/cm 2 , with on average of 5.44. the degree of hardness highest of 141.8 VHN happened to variation pressure 35 kg/cm 2 and lowest of 124.8 VHN happened to variation 55 kg/cm 2 . Concluded that the solidification of pressure variations sand mold 45 kg / cm 2 produce castings products with the most optimal average in terms of the measurement of the defective; variation pressure solidification sand mold of sand casting 35 kg / cm 2 produce a smooth surface, and the higher pressure make surface castings becomes rougher; solidification of pressure variations and coarse sand mold 35 kg / cm 2 produce micro structure with smooth grains and becomes more violent along with increasing pressure; pressure variation 35 kg / cm 2 produce a hardest surface, the higher of the pressure variation it becoming violence number progressively lower. Keywords : Pressure variations, sand casting, quality

Structure Characteristics of Silicon Alloyed Ductile Cast Iron

Experiments deal with the solidification pattern of FeSiCaMgRE-treated and un-inoculated and inoculated [Ca,Ce,S,O-FeSi] three ductile iron compositions [2.5%Si; 4%Si and 4%Si-1.6%Mo (Si:Mo = 2.5)]. Structure analysis is performed in 20mm diameter bar, resin sand mould solidification. Increasing of the Si content leads to increasing the graphite amount. Mo addition in high Si-iron limits the graphitizing effect of Si, but the graphite amount remains higher compared with conventional iron. A similar evolution is registered for graphite nodule count, while Si-Mo iron has lower nodule count compared with referred iron. For the same production conditions, graphite nodularity [according to ISO 945 evaluation] is negatively affected by Si and Si-Mo: it decreases from 95% up to 80% value, but remains at the accepted level, which means that the selected inoculant seems to be effective in these irons. For high Si-ductile irons, the nodularity evaluation must be more carefully considered, by including a minimum limit of the accepted sphericity shape factor. Increasing of the Si content leads to a prevalent ferritic matrix. Supplementary addition of Mo at the upper limit in Si-Mo affects the ferritic effect of Si, resulting an intermediary ferrite and pearlite mixture. It is found that inoculation is important for high-Si, and particularly for Si-Mo alloyed irons, requiring a high efficiency inoculation procedure.

Feeding and Cooling and Time of Thermal Treatment of a Massive Bush Made of the Complex Aluminum Bronze Cast by the Lost Foam

Abstract Small additions of Cr, Mo and W to aluminium-iron-nickel bronze are mostly located in phases κi (i=II; III; IV),and next in phase α (in the matrix) and phase γ2. They raise the temperature of the phase transformations in aluminium bronzes as well as the casts’ abrasive and adhesive wear resistance. The paper presents a selection of feeding elements and thermal treatment times which guarantees structure stability, for a cast of a massive bush working at an elevated temperature (650-750°C) made by means of the lost foam technology out of composite aluminium bronze. So far, there have been no analyses of the phenomena characteristic to the examined bronze which accompany the process of its solidification during gasification of the EPS pattern. There are also no guidelines for designing risers and steel internal chill for casts made of this bronze. The work identifies the type and location of the existing defects in the mould’s cast. It also proposes a solution to the manner of its feeding and cooling which compensates the significant volume contraction of bronze and effectively removes the formed gases from the area of mould solidification. Another important aspect of the performed research was establishing the duration time of bronze annealing at the temperature of 750°C which guarantees stabilization of the changes in the bronze microstructure - stabilization of the changes in the bronze HB hardness.

Control of substance solidification in a complex-geometry mold

The control of metal solidification in a mold of complex geometry is studied. The underlying mathematical model is based on a three-dimensional two-phase initial-boundary value problem of the Stefan type. The mathematical formulation of the optimal control problem for the solidification process is presented. This problem was solved numerically using gradient optimization methods. The gradient of the cost function was computed by applying the fast automatic differentiation technique, which yields the exact value of the cost function gradient for the chosen discrete version of the optimal control problem. The results of the study are described and analyzed. Some of the results are illustrated as plots.

Research on Solidification Heat Transfer Model of Copper Horizontal Continuous Casting

Study the horizontal continuous casting mold solidification heat transfer process is not only to optimize the structure of the mold so that it has a uniform stress field, to improve the quality of slab, to extend the mold life basis, and improve production efficiency and cost-effective method. Therefore, oxygen-free copper horizontal continuous casting process as the research object, the establishment of a level of TU1 billet continuous casting mold solidification heat transfer model for the simulation of oxygen-free copper horizontal continuous casting mold solidification and heat transfer process has laid a theoretical foundation.

Application of thermal analysis to monitor the quality of hypoeutectic cast irons during solidification in sand and metal moulds

By exploring the effects of carbon equivalent (CE = 3.4–4.2%) and inoculation (Ca, Ba, Al–FeSi alloy), the thermal analysis parameters, representative temperatures and undercooling events, during solidification of cast irons are compared with chill tendency (carbides) in cast irons. Cooling curve analyses were conducted directly in the thermal centre of samples solidified in resin sand and metal moulds to explore the utility of thermal analysis in actual casting shapes. As a reference, a Quik-cup™ system was employed with the same cooling modulus (CM = 0.75 cm). The austenite formation temperature is lower at higher CE, with higher temperatures of both the start of the eutectic reaction and end of solidification. This was more pronounced for metal mould solidification and for un-inoculated irons, respectively. The transition from white iron through mottled iron up to grey iron macrostructure is illustrated by variations of eutectic undercooling compared to the metastable equilibrium temperature, as affected by increasing carbon equivalent and applied inoculation. Inoculation affected both austenite and eutectic formation, by preventing excess eutectic undercooling during solidification, even at low carbon equivalent. The differences in solidification patterns of sand and metal mould castings are discussed, for un-inoculated and inoculated irons, at different carbon equivalent values.

The effects of casting speed on steel continuous casting process

A three dimensional simulation of molten steel flow, heat transfer and solidification in mold and “secondary cooling zone” of Continuous Casting machine was performed with consideration of standard k−e model. For this purpose, computational fluid dynamics software, FLUENT was utilized. From the simulation standpoint, the main distinction between this work and preceding ones is that, the phase change process (solidification) and flow (turbulent in mold section and laminar in secondary cooling zone) have been coupled and solved jointly instead of dividing it into “transient heat conduction” and “steady fluid flow” that can lead to more realistic simulation. Determining the appropriate boundary conditions in secondary cooling zone is very complicated because of various forms of heat transfer involved, including natural and forced convection and simultaneous radiation heat transfer. The main objective of this work is to have better understanding of heat transfer and solidification in the continuous casting process. Also, effects of casting speed on heat flux and shell thickness and role of radiation in total heat transfer is discussed.

Effects of Iron Powder Addition on the Solidification Behaviour of Hypereutectic Grey Cast Iron

The purpose of the present paper is to investigate the solidification pattern of slightly hypereutectic grey irons (CE = 4.35 - 4.45%) after an addition of a commercial iron powder, and also in a double treatment with inoculation. Chill wedges with a 0.11 - 0.43 cm cooling modulus (CM), from using resin sand and metal moulds, were used along with different thermal analysis cups (CM = 0.75 and 0.43 cm). Relative clear/mottled/total chill measurement criteria were applied. Unfavourable Mn and S contents [(%Mn) x (%S) = 0.016] and a reduced Al residual (0.0015%) led to relatively high eutectic undercooling and chill in the base iron, especially at high cooling rates (CR). With the lower CM of cups, there was more undercooling in the entire solidification range and more difference between irons. Thermal analysis and chill parameter relationships are normal, except only for iron powder treatment and resin mould solidification, where chill is higher for a relatively lower undercooling. Conventional inoculation after addition of iron powder (double treatment) showed a strong graphitizing effect, as these irons had the lowest undercooling and chill levels, in all the irons tested. It reflects the improved properties of (Mn,X)S compounds as nucleation sites for graphite [10]. This paper is the first of two papers reporting on this study.

Influence of Iron Powder Addition on the Structure Characteristics of Hypereutectic Grey Cast Iron

Slightly hypereutectic grey irons (&lt; 4.5%CE), solidified in resin and metal moulds, after an addition of iron powder, either alone or with Ca,Ba,Al-FeSi inoculation (double treatment) were characterized by structure. Iron powder had a role in limiting the carbide presence, while the supplementary inoculation led to the fewest carbides in metal mould samples. No carbides were in resin mould solidification, while graphite morphology progressed from (C + B) in the base iron up to the type (B + A) in double treated iron. Polygonal (Mn,X)S compounds acting as graphite nuclei, whose characteristics depended on the applied treatment, were found: larger size/low compactness [base iron], irregular polygonal with tendency to the highest size and complex morphology [iron powder treatment] and compact polygonal/smallest size [double treatment]. Iron powder has a negative influence on the graphite nuclei and eutectic cell characteristics, but favours austenite dendrite formation, as a reinforcement for eutectic cells. It has a limited graphitizing effect, witnessed only at high cooling rates. A double addition [iron powder + inoculant] appears to be an efficient treatment, with beneficial effects on both the austenite and graphite nucleation, affecting the final structure and chill tendency.

Study of Convective Non-Newtonian Alloy Solidification in Molds by the PSIMPLER/Finite-Volume Method

A numerical study is made of the solidification of an Al-Si alloy with 1.5-2% Si in a graphite mold, considering the pseudo-plastic behavior of the liquid alloy, based on a non-Newtonian model of the power law with n = 0.5. The fluid mechanics and heat transfer description of the transient convection-diffusion model is made using the finite-volume method. The pressure-velocity-temperature coupling is made using a new sequential algorithm called PSIMPLER which is validated by comparing it with the results from the literature for Newtonian fluid behavior solved with the SIMPLE algorithm. The stability and efficiency of the PSIMPLER method is also determined by solving natural convection and mixed convection in rectangular cavities with SIMPLE. The final results make it possible to infer that the Newtonian or non-Newtonian nature of the convection model affects the time and shape of the solidification process. It is concluded that the PSIMPLER algorithm allows the use of subrelaxation coefficient values close to one for the velocities, decreasing calculation time by more than 50%.

Development of a τ-Type Mg-Zn-Al Alloy: An Investigation of the Microstructure and Solidification Characteristics

The practical phase constituent diagram has been used to determine the composition of a low alloying τ-type Mg-Zn-Al alloy, which has a nominal element content of 7wt%Zn and 3wt%Al (ZA73), as a basis for further improvement of τ-type alloy through appropriate thermal processing and micro-alloying. The microstructure and solidification characteristics of the alloy have been experimentally examined using optical microscopy, scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry analysis. The results confirm that the as-microstructure of ZA73 alloy consists of globular equiaxed dendrite with τ phase as the only secondary phase evenly distributed in interdendritic spacing. Solidification sequence has been proposed with the help of DSC analysis and Mg-Zn-Al ternary liquidus projection phase diagram. Consistent with previous observed results for τ-type Mg-Zn-Al alloy, due to the decrease of element contents, ZA73 alloy has higher liquidus temperature (~627°C) and wider solidification range (~283°C), while at the mean time lower starting temperature of the second phase transformation (~354°C), compared to higher element containing ZA104 alloy. The phase constituent diagram has been shown to be a practical and effective tool for predicting the as-cast microstructural constituent of high zinc Mg-Zn-Al alloys under normal permanent mould solidification condition.

High-speed continuous casting of peritectic carbon steels

Productivity of an integrated steel plant is improved by high-speed casting of hypo-peritectic steels that makes the productivity of caster meet basic oxygen furnace. In high-speed casting, however, strands of the steels tending to form cracks on the shell in the mold, require off-line conditioning that limits the plant productivity and premium yield. Hypo-peritectic transformation occurring on solidification in mold results in irregular shell-surface roughness that causes non-uniform heat transfer to the mold, causing local lifting of the shell from the mold, recalescence, and surface cracks. Influential factors are summarized on the development of the surface roughness, the non-uniform heat transfer and the decline of mechanical properties of the shell upon recalesce. Effective means are presented to reduce the non-uniformity and the cracks at high casting speeds by controlling the properties of mold flux film infiltrating into the solidifying shell/mold boundary.

Abnormal transient phenomena in the continuous casting process: Part 2

This paper is the second of a series of two describing abnormal transient phenomena observed during online monitoring of a billet continuous casting machine. Special attention is paid in Part 2 to in mould solidification. A mould heat flux drift phenomenon (HFD) has been detected, but only for mould powder basicities larger than 0·8. The HFD is related to a decrease of the heat flux in the lower part of the mould and an increase in both the billet-mould friction force and mould thermocouple variability. Results of tests changing the mould powder grade during casting have provided help in explaining the HFD. The probable reason for the HFD is crystallisation of the glassy slag layer. The heat flux ratio parameter (HFR), defined as the ratio between the heat flux in the lower part of the mould and the heat flux in the upper part of the mould, has proved to be a good tool for judging the casting performance of a mould powder.

Simulation of dendritic growth in the platform region of single crystal superalloy turbine blades

A cellular automaton model of the solid-liquid interface, combined with a finite difference computation of solute diffusion has been developed to simulate single crystal solidification in molds with step changes in geometry. Simulations were carried out for columnar dendrites passing from the narrow airfoil region of a blade into the platform region, which has an increased cross-sectional area. Different shapes of isotherms moving at a constant velocity were considered in the simulations. The change in mold geometry leads to a significant increase in the undercooling in front of the dendrite tips as they spread around the mold corner. The model was applied to geometries investigated by prior authors, correctly predicting the formation of a to boundary observed experimentally.

Liquid steel flow, heat transfer and solidification in mold of continuous casters during grade transition

A computational study of the unsteady axisymmetric turbulent liquid steel flow, heat transfer and solidification in continuous casting molds during the grade transition operation is presented. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables, whereby the governing time-dependent continuity, momentum and energy equations in combination with a low-Reynolds number turbulence model are solved. A single-domain enthalpy formulation is used for simulation of the phase change phenomenon. Darcy's Law-type porous media treatment is used to account for the effect of phase change on convection. In spite of the transient nature of the incoming liquid steel velocity, increase in size of the liquid pool is not significant, whereas the increase of the volume of the mushy zone is marked and is as much as 48% relative to its initial size. Distinct temperature rise signatures on the surface of the casting were detected. The heat removal rate from the mold increases almost linearly similar to the ramping of the casting speed. Thinning of the solidified shell during tundish change is significant and must be taken into account in practice to prevent breakout.

Fluid flow, heat transfer and solidification in the mold of continuous casters during ladle change

A computational study of the transient two-dimensional turbulent fluid flow, heat transfer and solidification in continuous casting molds during the ladle change operation is presented. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables, whereby the governing time-dependent continuity, momentum and energy equations in combination with a low-Reynolds number turbulence model are solved. A single-domain enthalpy formulation is used for simulation of the phase change phenomenon. The effect of phase change on convection is accounted for using a Darcy's law-type porous media treatment. It is shown that due to the time-dependence of the inlet temperature during the ladle change, the volume occupied by the liquid phase generally expands in the radial direction during each cycle, whereas the axial extent of the liquid pool shrinks due to the greater influence of the buoyancy force. The increase in size for the liquid pool depends on the casting speed and is as much as 25% when compared to the steady-state value. The size of the mushy zone does not vary greatly over the period of ladle change. The thickness of the solidified shell shrinks during the ladle change operation to some extent. Casting surface temperatures vary over the two cycles of the ladle change operation and distinct temperature rise signatures were detected.