Showing papers in "Acta Metallurgica Sinica (english Letters) in 2008"

Review on Research and Development of Magnesium Alloys

Abstract: The current research and development of magnesium alloys is summarized. Several aspects of magnesium alloys are described: cast Mg alloy, wrought Mg alloy, and novel processing. The subjects are discussed individually and recommendations for further study are listed in the final section.

Improvement of Mechanical Properties of Martensitic Stainless Steel by Plasma Nitriding at Low Temperature

Abstract: A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350°C by means of DC-pulsed plasma in 25%N2+75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350°C nitrided surface is dominated by ɛ-Fe3N and αN, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350° C because plasma nitriding produces residual compressive stress inside the modified layer.

Fem simulation of residual stresses induced by laser shock with overlapping laser spots

Abstract: The finite element method is presented to attain the numerical simulation of the residual stresses field in the material treated by laser shock processing. The distribution of residual stresses generated by a single laser shock with square and round laser spot is predicted and validated by experimental results. With the Finite Element Method (FEM) model, effects of different overlapping rates and impact sequences on the distribution of residual stresses are simulated. The results indicate that: (1) Overlapping laser shock can increase the compressive residual stresses. However, it is not effective on the growth of plastically affected depth; (2) Overlapping rate should be optimized and selected carefully for the large area treatment. Appropriate overlapping rate is beneficial to obtain a homogeneous residual stress field; (3) The impact sequence has a great effect on the residual stress field. It can greatly attenuate the phenomenon of the “residual stress hole” to obtain a homogeneous residual stress field.

Effect of Mo and Mo2C on the microstructure and properties of the cermets based on Ti(C,N)

Abstract: Effect of Mo and Mo2C on the microstructure and properties of Ti(C,N)-based cermets was investigated in this article. The results have indicated that the weight percentage of Mo from 5 to 10 can reduce Ti(C,N) grain diameter and thickness of the rim, and Ti(C,N) grain can be wetted by Ni-Cu-Mo liquid so as to get small contiguity of Ti(C,N) grain. In that way, the transverse rupture strength of Ti(C,N)-based cermets has reached 1800–1900 MPa; the fracture toughness has been due to 16–18 MPa·m1/2. But 15 wt pct Mo was not more effective on Ti(C,N)-based cermets, because the thickness of the rim becomes larger. In the circumstance of Mo2C, 5 wt pct Mo2C was good for microstructure and properties of Ti(C,N)-based cermets, but 11 wt pct Mo2C has resulted in larger contiguity of Ti(C,N) grain and big Ti(C,N) grain diameter so as to reduce transverse rupture strength and fracture toughness. So that, the effect of Mo on Ti(C,N)-based cermets is better than Mo2C.

Study on the hot deformation behaviors of Al-Zn-Mg-Cu-Cr aluminum alloy

Abstract: The hot deformation behaviors and microstructures of Al-Zn-Mg-Cu-Cr aluminum alloy have been studied using thermal simulation test, optical microscopy and transmission electron microscopy. As a result, the true stress versus true strain curves and the microstructures under various deformation conditions are obtained. The microstructures gradually incline to dynamic-recrystallization with the deformation temperature rising and the recrystallization grains refine with the decrease of deformation temperature or with raising the strain rates. The quantitative relationship between the Zener-Hollomon parameter (Z) and average recrystallization grain size in the subsequent heat treatment is set up.

Effect Of Zr Addition To Ti-Killed Steel On Inclusion Formation And Microstructural Evolution In Welding Induced Coarse-Grained Heat Affected Zone

Abstract: Effects of Zirconium on the chemical component and size distribution of Ti-bearing inclusions, favored the grain refinement of the welding induced, coarse-grained heat affected zone (CGHAZ) with enhanced impact toughness in Ti-killed steels, which were examined based on experimental observations and thermodynamic calculations. It indicated that the chemical constituents of inclusions gradually varied from the Ti-O oxide to the Ti-O+Zr-O compound oxide and a single phase of the ZrO2 oxide, as the Zr content increased from zero to 0.0100%. A trace of Zr (0.0030%–0.0080%, depending on the oxygen content in liquid steel) provided a large amount of nucleating core for Ti oxide because of the larger specific density of ZrO2 oxide, and produced a small size distribution of the inclusions favorable for acicular ferrite transformation with a high nucleation rate in the CGHAZ, and a high volume fraction of acicular ferrite was obtained in the CGHAZ, with enhanced impact toughness. Otherwise, a high content of Zr (∼0.0100%) produced a single phase ZrO2, which was impotent to nucleate acicular ferrite, and a microstructure composed of ferrite side plate and grain boundary ferrite developed in the CGHAZ. The experimental results were confirmed by thermodynamic calculations.

Simulation of vibration stress relief after welding based on FEM

Abstract: A finite element model is developed for the simulation of vibration stress relief (VSR) after welding. For the nonresonant vibration, the reduction in stress strongly depends on the amplitude of vibration. For the resonant vibration, the vibration frequency is the key for stress relief. The vibration frequency should be close to the structure natural frequency for the desired vibration mode. Only small vibration amplitude is required, which will be amplified during vibration. Vibration time does not have a major impact on vibration stress relief. When the amplitude of vibration stress relief is large, the treatment will be more effective.

Oxidation behavior of Kovar alloy in controlled atmosphere

Abstract: Controlled oxidation experiments were performed on Kovar alloy by changing oxidation atmosphere, temperature, and exposure time to produce films with different oxide type and thickness. The results indicated that single Fe3O4 and single FeO were respectively obtained when Kovar alloy was oxidized in N2-2.31%H2O-0.95%H2 at 500°C and in N2 −2.31%H2O-0.5%H2 at 1000°C, and all kinetic curves followed linear relation; mixed oxides of FeO and Fe3O4 formed when Kovar was oxidized in N2-2.31%H2 0 at 1000°C, and parabolic kinetics were obeyed. Analysis of metal-lographic cross section of oxides indicated that oxygen diffusion inward through the oxide scale is responsible for intergranular oxide, which had formed beneath the oxide scales when the oxide products were mixed oxides of FeO and Fe3O4, and which did not occur when the oxide was single FeO or Fe3O4. The oxidation model was also established.

Reciprocating extrusion of in situ Mg2Si reinforced Mg-Al based composite

Abstract: Mg 2 Si reinforced Mg-Al based composite with high amount of silicon was prepared by permanent mould casting, and then extruded by reciprocating extrusion (RE) after the composite was processed by homogenization heat treatment. The effect of RE processing on the morphology and size of Mg 2 Si and the mechanical properties of the composite were investigated, to develop new ways to refine the Mg 2 Si phase and improve its shape. The result showed that RE was very useful in refining the Mg 2 Si phase. The more the RE processing passes, the better the refining effect would be. Moreover, the uniform distribution of Mg 2 Si phases would be more in the composite. After the composite was processed by RE for 12 passes, most Mg 2 Si phases were equiaxed, with granular diameter below 20 μm, and distributed uniformly in the matrix of the composite. The mechanical properties of the composite could be increased prominently by RE processing, and were much higher than that in the as-cast state. As the temperature rises, the tensile strength is reduced. For the composite RE processed for 12 passes, the tensile strength, yield strength, and elongation are 325.9 MPa, 211.4 MPa, and 3.3% at room temperature, whereas, 288.2 MPa, 207.7 MPa, and 7.8%, respectively, at 150°C. In comparison with the properties at room temperature, the tensile strength and yield strength are high and only decrease by 11.6% and 1.8% at 150°C. The Mg 2 Si reinforced Mg-Al based composite possesses good heat resistance at 150°C. The excellent resistance to effect of heat is attributed to the high melting temperature and good thermal stability of fine Mg 2 Si phases, which are distributed uniformly in the composite, and effectively hinder the grain boundary gliding and dislocation movement.

Corrosion behavior of a zirconium-titanium based phosphonic acid conversion coating on AA6061 aluminium alloy

Abstract: The conversion coating was formed by dipping AA6061 in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid (ATMP) solution at room temperature. The formation process and the anti-corrosion performance of the conversion coating were investigated using electrochemical test and salt spray test (SST), respectively. The electrochemical test shows that the Zr/Ti and ATMP coating improves the corrosion resistance of AA6061 as good as the chromate (VI) coating. But the results of SST show that the corrosion resistance of Zr/Ti and ATMP coating is not as good as the chromate (VI) coating. The corrosion area is less than 2% after 72 h.

Deformation Behavior Of Aa6063 Aluminium Alloy After Removing Friction Effect Under Hot Working Conditions

Abstract: The hot deformation behavior of AA6063 aluminium alloy has been investigated by means of compression tests at temperatures between 400 and 520° C, and strain rates ranging from 2.5 to 10 s−1. Owing to the barreling, the theoretical model on the basis of Hilt s general method is used to calculate the flow stress of a cylindrical specimen under uniaxial simple compression so as to consider the friction effect at the die-specimen interface. A method of evaluating the friction coefficient by combining compression tests with the finite element method is presented. The real flow behavior of AA6063 aluminium alloy can be described with sinh-Arrhenius equation. The hot deformation activation energy Q derived from the corrected stress and strain data is 232.350 kJ/mol.

RELATIONSHIP BETWEEN INFRARED RADIATION AND CRYSTAL STRUCTURE IN Fe-Mn-Co-Cu-O SPINELS

Abstract: Ni3+ and Cr3+ doped Fe-Mn-Co-Cu-O spinels have been prepared by solid phase sintering. The valence states and distribution of transition ions in the spinel crystals are inferred by the consideration of thermodynamic principle and crystalline field theory. The microstructure and performance of those are studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and IRE-2 infrared radiant instrument. Ni3+ and Cr3+ occupy the vacancies or substitute the other ions in the spinel structures and form diverse spinel structures, which exhibit infrared integral emissivities of 0.93 in the whole band, and 0.94 in the band within 14-25 μm too. The content of Fe2O3 and MnO2 in the spinel crystals changes, maybe it induces infrared radiativity of spinels differently.

Corrosion resistance of hot dip galvanized steel pretreated with bis-functional silanes modified with nanoalumina

Abstract: The corrosion behavior of hot dip galvanized steel pretreated with bis-[triethoxy-silylpropyl] tetrasulfide (BTESPT) modified with alumina particles was studied. The corrosion resistance of the passiving films was evaluated by Tafel polarization curve and electrochemical impedance spectroscopy. The films formed on the galvanized steel substrate were characterized by Fourier transform infrared spectroscopy and energy dispersive X-ray spectrometry. The surface morphology of the treated hot dip galvanized steel samples was observed by Field Emission Scanning Electron Microscope. The results show that the pretreatments on the basis of silane films modified with nanoalumina particles have reduced both anodic and cathodic current densities, and increased total impedance in the measured frequency, consequently, improving corrosion protection for hot dip galvanized steel during immersion in NaCl solutions compared to chromate films and silane films.

Prediction of the Mixing Enthalpies of Binary Liquid Alloys By Molecular Interaction Volume Model

Abstract: The mixing enthalpies of 23 binary liquid alloys are calculated by molecular interaction volume model (MIVM), which is a two-parameter model with the partial molar infinite dilute mixing enthalpies. The predicted values are in agreement with the experimental data and then indicate that the model is reliable and convenient.

Effect Of Silicon Addition On Recrystallization And Phase Transformation Behavior Of High-Strength Hot-Rolled Trip Steel

Abstract: Because Si is a noncarbide forming element, a multiphase microstructure consisting of ferrite, bainite, and retained austenite, at room temperature, can be formed by controlling the thermomechanical process strictly. The cooling schedules must be restricted by the formation of pearlite and cementite. In the present article, a new integrated mathematical model for prediction of microstructure evolution during controlled rolling and controlled cooling is developed for a typical kind of low carbon Si-Mn TRIP steel, which consists of temperature simulation, recrystallization, and transformation models. The influence of Si contents has been thoroughly investigated. The calculated results indicate that Si retards recrystallization, restrains austenite grain growth as well as accelerates polygonal ferrite transformation.

MODELING OF DYNAMIC RECRYSTALLIZATION OF Ti6Al4V ALLOY USING A CELLULAR AUTOMATON APPROACH

Abstract: A cellular automaton (CA) model is established to simulate dynamic recrystallization (DRX) in the β single-phase field of Ti6Al4V alloy, and the kinetics during DRX processing has been analyzed. The model employed considers the influences of dynamic recovery, nucleation rate, strain rate and dislocation density on DRX, and practical deformation parameters, such as temperature, strain and strain rate on DRX have been considered in the simulation. The simulated DRX grain size and DRX grain shape agree well with the experimental results, which shows the availability and feasibility of the cellular automaton method for the simulation of DRX. The result of kinetics analysis of DRX reveals that the Avrami exponent is variable ranging from 2.4 to 2.9, which increases with the increase of strain rate.

Effect of deep cold treatment on two case hardening steels

Abstract: Although cold treatments have been used to reduce the retained austenite in the cases of carburised steel for many years, there is little data on deep cold temperatures below −70° C or treatment times longer than an hour or two. This study set out to determine the effects of such deep cold treatments at temperatures −150°C for 24 h. The study investigated the effects of deep cold on the microstructure, hardness profile, residual stress and internal oxidation on two typical carburising steels, 16MnCr5 and 21NiCrMo2. The study found that for both 16MnCr5 and 21NiCrMo2 carburised to a case depth of approximately 0.8 mm, the longer and colder the deep cold treatment, the more the austenite retained in the case was converted to martensite and the harder it became. After low temperature tempering, the hardness difference was smaller, but still significant. In both steels, the case appeared more refined and homogeneous after deep cold treatment. Deep cold treatment had a negligible effect on the core properties of either steel.

Microstructure of binary Mg-Al eutectic alloy wires produced by the Ohno continuous casting process

Abstract: Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting (OCC) process and the mi-crostructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The micro structure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic αa-Mg and β-Mg17Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the “bridging effect” caused by incidental elements in the alloy.

Alloying Effect of Ni And Cr on the Wettability of Copper On W Substrate

Abstract: By the sessile drop technique, the wettability of Cu/W systems with the additions of Ni and Cr has been studied under vacuum atmosphere. Effects of Ni and Cr contents and wetting temperatures on the wettability and the wetting mechanisms of copper on W substrate have been investigated in detail. The results show that the wetting angles of Cu on the W substrate are decreased with an increase in the content of Ni or Cr, and also decrease with raising the wetting temperatures. SEM, EPMA, and X-ray diffraction have been used to analyze the interfacial characteristics of the CuNi/W and CuCr/W systems. The results reveal that there is a transition layer about 2–3μm in the interface of Cu-4.0 wt pct Ni/W, in which the intermetallic phase Ni4W is precipitated. As to CuCr/W system, no reaction occurs at the interface. The two factors are that the contents of Cr and Ni and the infiltration temperature must be chosen appropriately in order to control the interfacial dissolution and reaction when the Cu-W alloys are prepared by the infiltration method.

Mechanical properties of longitudinal submerged arc welded steel pipes used for gas pipeline of offshore oil

Abstract: Since the development of offshore oil and gas, increased submarine oil and gas pipelines were installed. All the early steel pipes of submarine pipelines depended on importing because of the strict requirements of comprehensive properties, such as, anti-corrosion, resistance to pressure and so on. To research and develop domestic steel pipes used for the submarine pipeline, the Longitudinal-seam Submerged Arc Welded (LSAW) pipes were made of steel plates cut from leveled hot rolled coils by both the JCOE and UOE (the forming process in which the plate like the letter “J”, “C”, “O” or “U” shape, then expansion) forming processes. Furthermore, the mechanical properties of the pipe base metal and weld metal were tested, and the results were in accordance with the corresponding pipe specification API SPEC 5L or DNV-OS-F101, which showed that domestic LSAW pipes could be used for submarine oil and gas pipelines.

Microstructure of Mg-6.4Zn-1.1Y alloy fabricated by rapid solidification and reciprocating extrusion

Abstract: In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1Y magnesium alloy with a thickness of 50-60 μm were obtained by a melt spinning single-roller device, and the flakes were then processed into rods by reciprocating extrusion and direct extrusion. The micro structure of the alloy was analyzed by optical microscope and SEM, and the constitueni phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-1.1Y alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in α-Mg solute solution, and impede the formation of Mg3 Y2 Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3 YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the α-Mg solid solution and icosahedral Mg3 YZn6 quasicrystal. Dense rods can be made from the flakes by two-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3 YZn6 compounds are precipitated and distributed uniformly, whereas the rods possess fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: α-magnesium solid solution as matrix and fine icosahedral Mg3 YZn6 quasicrystal which disperses uniformly in the matrix.

Numerical simulation of molten pool and control strategy of kiss point in a twin-roll strip casting process

Abstract: Coupled turbulent flow, temperature fields of the twin-roll casting strip process were simulated by three-dimensional finite element method. Based on the heat balance calculation and using inverse methods between the simulations and real experiments, the relational models among casting speed, location, and coefficient of heat transfer between molten metal and rolls in different regions are given. In the simulation, the calculated surface temperatures are in good agreement with the measured values. An on-line model of kiss point is derived by simulations and the geometry of molten pool, corresponding control strategy is also proposed.

Effect of Si content on ordering degree and electromagnetic characteristics in FeSiAl alloys

Abstract: FeSiAl alloys ribbons synthesized by melt-quench were annealed in vacuum at 873 K for 60 min. The flaky powders were prepared by milling the annealed ribbons for 70 h. After milling, the powders were heat treated at 573 K for 90 min. The ordering degree of the powders lattice structure was analyzed by X-ray diffraction (XRD). The measurement of specific saturation magnetization was carried out by vibrating samples magnetometer (VSM). Complex permittivity and complex permeability in the frequency band of 0.5–18 GHz were measured with the vector network analyzer. The ordering degree of the superlattice structure increased from 0.27 to 0.49. Complex permittivity and complex permeability decreased with increasing Si content. After ordering, the specific saturation magnetization decreased from 134.2 to 85.0 A·m 2 ·kg −1 . For use in anti-EMI material, the total contents of Si and Al in FeSiAl alloys should be controlled at a low level.

Microwave permeability spectra of sputtered Fe-Co-B soft magnetic thin films

Abstract: Permeability characteristics of sputtered soft magnetic Fe4oCo4oB2o thin films are investigated in the range of 0.5 to 5 GHz by a shortened microstrip transmission line perturbation method. Excellent microwave permeability is achieved at 0.4 Pa argon pressure: f r is 3.32 GHz, the real and imaginary part of permeability at 0.5 GHz are 104 and 61, respectively. In addition, the thickness effect on permeability is also studied. The minimum damping can be achieved at the thinnest film. Different sources contributed to in-plane anisotropy are discussed briefly. The deviation between the peak frequency of the imaginary part and the zero-crossing frequency of the real part of permeability is also presented.

Amino-Tris-(Methylenephosphonic Acid) Layers Adsorption on Aa6061 Aluminum Alloy

Abstract: The amino-tri-(methylenephosphonic acid) layers were adsorbed on the surface of AA6061 aluminum alloy for improving the lacquer adhesion and corrosion inhibition as a substitute for chromate coatings. The surface structure and characteristic of the amino-tri-(methylenephosphonic acid) layers on AA6061 aluminum alloy were investigated by means of XPS and ATR-FTIR analysis. The analyzed results showed that the amino-tri-(methylenephosphonic acid) adsorption layers adsorb on the surface of aluminium alloy via acid-base interaction in a bi-dentate conformation. After the amino-tri-(methylenephosphonic acid) layers were coated with epoxy resin, the layers showed good adhesive strength and favorable corrosion resistance in contrast to chromate coatings.

MICROSTRUCTURES AND PROPERTIES OF RECIPROCATINGLY EXTRUDED Mg-6.4Zn-1.1Y ALLOYS

Abstract: An icosahedral Mg 3 YZn 6 quasicrystalline phase can be produced in Mg-Zn-Y system alloys when a proper amount of Zn and Y is contained, and it is feasible to prepare the quasicrystal phase-reinforced low-density magnesium alloy. In this article, phase constituents and the effect of reciprocating extrusion on microstructures and properties of the as-cast Mg-6.4Zn-1.1Y alloy are analyzed. The microstructure of the as-cast Mg-6.4Zn-1.1Y alloy consists of the α-Mg solid solution, icosahedral Mg3Y 2 Zn3 quasicrystal, and Mg 3 YiZn 2 and MgZn 2 compounds. After the alloy was reciprocatingly extruded for four passes, grains were refined, Mg3 Yi Znz and MgZn 2 phases dissolved into the matrix, whereas, Mg3 YZn6 precipitated and distributed uniformly. The alloy possesses the best performance at this state; the tensile strength, yield strength, and elongation are 323.4 MPa, 258.2 MPa, and 19.7%, respectively. In comparison with that of the as-cast alloy, the tensile strength, yield strength, and elongation of the reciprocatingly extruded alloy increase by 258.3%, 397.5%, and 18 times, respectively. It is concluded that reciprocating extrusion can substantially improve the properties of the as-cast Mg-6.4Zn-1.1 Y alloy, particularly for elongation. The high performance of the Mg-6.4Zn-1.1Y alloy after reciprocating extrusion can be attributed to dispersion strengthening and grain-refined microstructures.

ISOTHERMAL SECTION OF Mg-Zn-La SYSTEM IN Mg RICH CORNER AT 350 - C

Abstract: Alloys of Mg-Zn-La system in Mg rich corner at 350°C have been prepared in this study. Scanning electron microscopy (SEM), electron probe microanalysis with energy dispersive X-ray spectroscopy (EPMA-EDS), and X-ray diffraction (XRD) have been used to identify the phase equilibrium and the composition of each phase in the alloys. As a result, the isothermal section of Mg-Zn-La system in Mg rich corner at 350°C has been determined. The result shows that, in addition to some binary phases, there exists a linear ternary compound called T-phase in Mg-Zn-La system at 350°C, in which the La content is about 8 at. pct ±0.4 at. pct and the Zn content is 8 at. pct–48 at. pct. The T-phase has a C-centered orthorhombic crystal structure, and the lattice parameters are a=0.965–1.020 nm, b=1.121–1.142 nm, c=0.950–0.977 nm.

Corrosion inhibition of x70 steel in saline solution saturated with co2 by thiourea

Abstract: Corrosion monitoring techniques were performed on X70 steel in saline solution saturated with CO2 with and without thiourea additives within the concentration range 5–25 mg/L. It was found that when the concentration of the inhibitors were increased, the inhibitor efficiencies (IE) of thiourea varied with solution temperature and immersion time. The results indicated that thiourea had the highest inhibition efficiency. The potentiondynamic polarization studies revealed that thiourea are mixed-type inhibitor that mainly restrains the anodic process.

On the Monte Carlo simulation of normal grain growth

Abstract: The microstructures and their kinetics of normal grain growth are simulated using different Monte Carlo (MC) algorithms. Compared with the relative figures and the theoretical normal grain growth exponents of n=0.5, the effects of some factors of MC algorithm, i.e. the lattice types, the methods of selecting lattice sites, and the neighbors selection for energy calculations, on the simulation results of grain growth are studied. Two methods of regression were compared, and the three-parameter nonlinear regression is much more suitable for fitting the grain growth kinetics. A better model with appropriate factors included triangular lattice, the attempted site randomly selected, and the first and second nearest neighbors for energy calculations is obtained.

Research Of The Feeding Speed Adopting Cored-Wire Method To Spheroidize Ductile Iron Melt

Abstract: For settling the question of feeding speed in applying the cored-wire method to spheroidize ductile iron melt, ANSYS software was applied to simulate the heat transfer and mass transfer, and the melt time of the steel strip in the iron melt was determined by linking the heat transfer and mass transfer, and then the feeding speed was calculated. Conclusions have been drawn that the iron layer was formed on the surface of the cored-wire during the wire-feeding process. The thickness is 0.073 mm when the temperature of the iron melt is 1500°C, the time from formation to remelting of the iron layer is 0.063 s. When the temperature of the iron melt is below 1500°C, the time taken for the steel strip to melt is rapidly shortened. When the temperature of the iron melt is above 1500°C, the variation amplitude of the steel strip melt change with time is gradually diminished. The melt time of the steel strip is rapidly increased with the increase of the steel strip thickness. When the temperature of the iron melt is 1500°C and the carbon content is 4%, the melt time of a steel strip, which has a thickness of 0.5 mm, is thrice that of a steel strip whose thickness is 0.3 mm. The calculation results of the feeding speed are basically in agreement with the applied feeding speed in the factory.