Carbon Content Distribution Research Articles

Microstructure Evolution of Cold‐Rolled Dual Phase Steel Simulated by Cellular Automata

The microstructure evolution simulation of the whole process, i.e., the cooling after hot rolling, cold rolling, recrystallization, austenitizing, slow cooling, and quenching, for dual phase steel is conducted based on the cellular automata model. The state values of fraction, morphology, grain size, and carbon concentration distribution etc. of austenite, ferrite, and pearlite were obtained. The calculated kinetics curves and microstructure morphology with different chemical composition and heating or cooling rates agree well with the experiment. The growth of new phase is controlled by both interface mobility and carbon diffusivity due to the carbon diffusion in austenite and the driving force for phase interface migration are interacted with each other.

Modeling of the Austenitization of Ultra-high Strength Steel with Cellular Automation Method

A model for simulating the austenitization of ultra-high strength steel during hot stamping is developed using a cellular automata approach. The microstructure state before quenching can be predicted, including grain size, volume fraction of austenite, and distribution of carbon concentration. In this model, a real initial microstructure is used as an input to simulate austenitization, and the intrinsic chemical difference is utilized to describe the ferrite and pearlite phases. The kinetics of austenitization is simulated by simultaneously considering continuous nucleation, grain growth, and grain coarsening. The UHSS is reduced to a Fe-Mn-C ternary system to calculate the driving force during extent growth in ferrite. The simulation results show that the transformation of ferrite to austenite can be divided into three stages in the condition of a heating rate of 10 K (−263 °C)/s. The transformation rate is determined by two factors, carbon concentration and temperature. The carbon concentration plays a major role at the early stages, as well as the temperature is the main factor at the later stages. The A c3 calculated is about 1073 K (800 °C) close to the measured value [1067.1 K (794.1 °C)]. Austenite grain coarsening was calculated by a curvature-driven model. The simulated morphology of the microstructure agrees well with the experimental result. Most of the dihedrals of the grain boundaries at the triple junctions are close to 120 deg. Finally, tensile tests were implied, as dwelling time increased from 3 to 10 minutes, the austenite grain size increased from 6.95 to 9.44 μm while the tensile strength decreased from 276.4 to 258.3 MPa.

Micromodeling of the Diffusion‐Controlled Equiaxed Peritectic Solidification

Principles of the statistical solidification theory are used for the mathematical formulation of the micro‐diffusion field modeling during the equiaxed grain growth controlled by diffusion. It is proposed to use the Averaged Voronoi Polyhedron concept for the representation of the domain of elementary diffusion field. This approach is applied for the peritectic transformation modeling with the assumption of a partial mixing of the intercrystalline liquid phase. The results of the evolution of the volume fractions of the liquid, austenite, and ferrite phases during primary solidification and the peritectic transformation simulation are presented as well as carbon concentration distribution along the grain radius in the ferrite and liquid phase at the instant of initiation of the peritectic solidification and in the austenite at the moment of peritectic solidification termination.

Modeling of distortions after carburization and quenching processes of large gears

A new finite element model is developed to predict the deformations, stresses, phase compositions and carbon concentration gradients that arise as a consequence of the physical processes involved in a carburization and quenching process of a large steel gear. Firstly, the diffusion of carbon at elevated temperatures in the austenitic range is studied in a diffusion model. Secondly, the calculated carbon concentration distribution is used as an input for a model that couples the thermal, metallographic and mechanical effects during the quenching process and calculates the evolution of the temperature, phase composition and deformation history at any point in the gear. Two effects typical for oil quenching of large gears are incorporated in the model. The first is the influence of the gear's own weight while hanging on chains before, during and after entering the quench bath. The second is the three-dimensional effect that it takes time between the moment the gear enters the oil quenching bath and the moment when the gear is fully immersed. The non-uniform temperature distribution over the gear's axis causes a non-homogeneous plastic deformation. A diffusion-thermo-metallo-mechanical model that takes these effects into account is compared with a model that does not. The results show that these effects should be incorporated.

Microstructure and Mechanical Properties of New Type Bainitic Carburized Steel for Gear

This paper presents the microstructure, mechanical properties and carburized behavior of new type bainitic carburized steel. The results show that after new carburized steel is normalized at 920°C and tempered at 300°C, its microstructure consists of bainitic ferrite and residual austenite, and belongs to the carbide-free bainite or atypical bainite. Large or small cross-section size new carburized steel bar all have reached the performance requirements of Cr-Ni carbonized steel. The microstructure of new carburized steel surface consists of high carbon martensite and residual austenite after carburized and air-cooled, It retains austenite fraction of the new carburized steel and 18Cr2Ni4WA steel are about 18% and 38%, respectively. Carbon concentration gradient of new carburized steel changes smoothly and have ideal carbon concentration distribution. Effective carburizing surface depth of new carburized steel is about 0.6mm and is smaller than 18Cr2Ni4WA steel. The gear entities made of new carburized steel meet the technical requirements of heavy duty carburized gear.

Modeling of Carburization and Thermal Stress Analysis for Ethylene Cracking Furnace Tube

The ethylene cracking furnace tube is one of the most important components of an ethylene cracking furnace. Carburization of furnace tube is one of the most important causes which lead the tube to fail. In this paper, the model that describes diffusion of carbon and the precipitation of carbides was established based on Fick’ law and equilibrium constant method. The finite difference method was adopted to simulate the distribution of carbon concentration. By applying the model, the distribution of carbon concentration along thickness in HP-Nb tubes was predicted for the different service times. According to the temperature distribution of furnace tube, obtained by the analysis of heat transfer, the thermal stresses of the furnace tube with various carburization extents were analyzed by using the finite element code ABAQUS for the actual heating process of an ethylene cracking furnace. The analysis results show that the maximum circumferential thermal stress exists near the inner wall of the carburized tube, which usually causes cracking of the carburized tube along the longitudinal direction.

Solute transport and composition profile during direct metal deposition with coaxial powder injection

Direct metal deposition (DMD) with coaxial powder injection allows fabrication of three-dimensional geometry with rapidly solidified microstructure. During DMD, addition of powder leads to the interaction between laser and powder, and also the redistribution of solute. The concentration distribution of the alloying element is very important for mechanical properties of the deposited clad material. The evolution of concentration distribution of carbon and chromium in the molten pool is simulated using a self-consistent three-dimensional model, based on the solution of the equations of mass, momentum, energy conservation and solute transport in the molten pool. The experimental and calculated molten pool geometry is compared for model validation purposes.

Using artificial neural network models to produce soil organic carbon content distribution maps across landscapes

Soil organic carbon (SOC) content is an important soil quality indicator that plays an important role in regulating physical, chemical and biological properties of soil. Field assessment of SOC is time consuming and expensive. It is difficult to obtain high-resolution SOC distribution maps that are needed for landscape analysis of large areas. An artificial neural network (ANN) model was developed to predict SOC based on parameters derived from digital elevation model (DEM) together with soil properties extracted from widely available coarse resolution soil maps (1:1 000 000 scale). Field estimated SOC content data extracted from high-resolution soil maps (1:10 000 scale) in Black Brook Watershed in northwestern New Brunswick, Canada, were used to calibrate and validate the model. We found that vertical slope position (VSP) was the most important variable that determines distributions of SOC across the landscape. Other variables such as slope steepness, and potential solar radiation (PSR) also had significant influence on SOC distributions. The prediction of the selected two-input-node SOC model (VSP and coarse resolution soil map recorded SOC as inputs) had a correlation coefficient of 0.92 with measured values, and model predicted SOC values had 47.9% of the total points within ±0.5% of the measured values and 70.6% within ±1% of the measured values. The prediction od the selected four-input-node model (VSP, slope steepness, PSR and coarse resolution SOC values as inputs) had a correlation coefficient of 0.98 with measured values and model predicted SOC values had 75% of the total points within ±0.5% of the measured values and 87% within ±1% of the measured values. The prediction of the five-input-nodes model with soil drainage as additional input had a correlation coefficient of 0.99 with measured values, and model predicted SOC values had 87% of the total points within ±0.5% of the measured values and 98% of the total points within ±1% of the measured values. The calibrated SOC prediction model was used to produce a high-resolution SOC map for the Black Brook Watershed and the resulting SOC distribution map is considered to be realistic. Results indicated that DEM-derived hydrological parameters together with widely available coarse resolution soil map data could be used to produce high-resolution SOC maps with the ANN method.Key words: Soil organic carbon, artificial neural network model, high-resolution soil maps, digital elevation model, vertical slope position

The carbon distribution in multicrystalline silicon ingots grown using the directional solidification process

In this study, we performed a numerical simulation of the growth of multicrystalline silicon ingots using the DSS method and compared the results with the experiments. The thermal flow field and the carbon concentration distribution during the growth process were analyzed under the same operating conditions. The carbon concentration distribution in the grown ingots was measured and the results compared with that of the simulation predictions. The simulation results are in good agreement with the experimental ones. The simulation shows that in a directional solidification furnace carbon impurities accumulate easily in the melt near the central region of the melt/crystal interface due to convection. This is the main reason for the non-uniformity of the carbon concentration in ingots grown in the DSS furnace. In order to improve the uniformity of carbon distribution in the melt, a higher convexity of crystalline front interface in the central region needs to be maintained during the growth process to reduce the strength of melt convection around the crystalline front interface.

Flow, Solidification, and Solute Transport in a Continuous Casting Mold with Electromagnetic Brake

AbstractA three‐dimensional mathematical model is developed to study coupled turbulent flow, heat, solute transport, and solidification in a slab continuous caster with electromagnetic brake. Based on the analogy analysis, all the governing equations can be expressed as a general differential equation and be solved by a general numerical method. Numerical results show that a small corner‐vortex appears near the free surface due to the interaction between the moving solidified shell and the upward flow. Influenced by the fluid flow, the temperature and solute distribution can also be divided into the upper and lower recirculation zones but the distribution of carbon concentration is opposite to that of temperature. The three‐dimensional magnetic field can effectively damp the local flow and affect heat and solute transfer in the mold.

Numerical prediction on the erosion in the hearth of a blast furnace during tapping process

The erosion caused by mass transfer in hearth is the most important factor for determining blast furnace campaign life. To support a helpful insight information of mass transfer for the hearth of the No. 2 blast furnace at CSC (China Steel Corporation), a numerical model including the mass transfer of carbon in thermal convective flow from a blast furnace hearth has been developed during the steady tapping process (based on a uninterrupted tapping process assumption). The three dimensional Navier–Stokes equation combined with the transport equations of energy and species with conjugate heat transfer and physical dissolution source is solved by the finite control volume scheme subjected to the segregated iterate under propriety boundary conditions. The results showed the concentration distribution of carbon expressed in terms of mass flux for analyzing the erosion of carbon brick in the blast furnace hearth with the different conditions including the status of dead-man, production of liquid iron, carbon concentration at the inlet, and porosity distribution in coke zone during tapping process at steady state. The result is useful to mitigate the erosion caused by mass transfer, and prolong the life span of the blast furnace.

Measurement of Carbon Content in Steel by LIBS Which Transmits a Laser Beam in Optical Fiber

Utilizing new laser transmission technology, we have developed a laser induced breakdown spectrometer (LIBS) that allows to obtain uniform energy profile by transmitting high-energy laser emitted from GP-YAG through optical fiber, implemented measurement of carbon content in steel and demonstrated its capability of accurate and fast measurement. The spectrometer made it possible to measure both carbon content distribution in the depth direction and average carbon content in steel at the same time by setting the diameter of the laser light with energy of 90 mJ to 0.9 mm on samples after transmitting it by the optical fiber. In addition, we were able to find carbon content in steel in a coefficient of correlation over 0.99 by using 50 shots average data after 3.6 μm from surface.

A study on carbon concentration distribution and microstructure of P/M materials prepared by carbusintering

Carbusintering (CBS) process was used to produce powder metallurgy (P/M) parts (Fe–2Ni–1.5Cu– xC). Influence of sintering parameters such as temperature on diffusion coefficient of carbon was investigated. The specimen with the porosity of 6–13% got the carbon content of the surface ranged from 1.23 to 1.32 wt.%. After heat treatment, the hardness and impact energy were enhanced to 48 HRC (484 HV) and 13 J, respectively. The change in carbon concentration along the case depth was determined quantitatively by means of chemical analysis. The carbon concentration profile was satisfactorily modeled by classical solution derived from Fick’s second law. An undesired acicular structure was observed in the specimen with low green compact density due to the high carbon content. CBS process can provide outstanding performance in surface hardening of P/M materials. The use of CBS process was able to make process simple by taking sintering and carburizing as one step. The higher carbon content of the surface in P/M parts can be easily achieved compared to conventional carburizing.

Directional Solidification of Multicrystalline Silicon Using the Accelerated Crucible Rotation Technique

Employing the accelerated crucible rotation technique, we grew multicrystalline silicon by the directional solidification process. The distribution of carbon concentration determined by Fourier transform infrared spectroscopy demonstrated that application of accelerated crucible rotation homogenized the carbon concentration in the grown ingot. Attempts were made to explain the effect of crucible rotation on homogenization of carbon concentration in terms of segregation phenomena. Moreover, growth striations induced by the crucible rotation were observed in the axial direction of the ingot.

Estimation of growth rate in unidirectionally solidified multicrystalline silicon by the growth-induced striation method

Multicrystalline silicon was grown by unidirectional solidification method using the accelerated crucible rotation technique. The application of the accelerated crucible rotation technique in unidirectional solidification method induced growth striations across the axial direction of the grown crystal. This striation pattern was observed from carbon concentration distribution, obtained by using Fourier transform infrared spectroscopy. The generated striation pattern was found to be weak and discontinuous. Some striations were absent, probably due to back melting, caused during each crucible rotation. From the growth striations and applied time period in crucible rotation, the growth rate was estimated by using Fourier transformation analysis.

Numerical Simulation on Carburizing and Quenching of Gear Ring

The carburizing process of the gear ring was simulated by taking into account the practical carburizing and quenching techniques of the gear ring and by solving the diffusion equation. The carbon content distribution in the carburized layer was obtained. Based on the results, the quenching process of the gear ring was then simulated using the metallic thermodynamics and FEM; it was found that the carburization remarkably affects the quenching process. Microstructures and stress distributions of the gear ring in the quenching process were simulated, and the results are confirmed by experiments.

Modeling of reaustenitization of hypoeutectoid steels with cellular automaton method

A model for simulating reaustenitization of hypoeutectoid Fe–C steel has been developed using a cellular automaton approach (CA). The prior microstructure state for quenching can be predicted through grain size, fraction of austenite, and distribution of carbon concentration. The kinetics of austenitization are simulated by simultaneously considering continuous nucleation, grain growth and grain coarsening. In the current CA model, carbon distribution in ferrite ( α), austenite ( γ) and α/ γ interface is calculated without identifying the state of each cell. The competition between the nucleation and early stage grain growth in the pearlite is revealed, and the simultaneous phase transformation from ferrite to austenite and the austenitic grain coarsening in the austenitic region are also shown. A simple approach is proposed to eliminate the artificial anisotropy problem in representing microstructure evolution in CA method. The simulated results are in good agreement with the available experimental data.

유한요소법을 이용한 SNCM 합금강의 침탄열처리 공정 해석

Heat treatment is a controlled heating and cooling process to improve the physical and/or mechanical properties of metal products without changing their shapes. Today finite element method is widely used to simulate lots of manufacturing processes including heat treatment and surface hardening processes, which aims to reduce the number of time- and cost-consuming experimental tryouts. In this study we tried, using this method, to simulate the full carburizing process that consists of carburizing, diffusing and quenching, and to predict the distribution of carbon contents, phase fraction and hardness, thermal deformation and other mechanical characteristics as the results. In the finite element analysis deformation, heat transfer, phase transformation and diffusion effects are taken into consideration. The carburizing process of a lock gear, a part of the car seat recliner, that is manufactured by the fine blanking process is adopted as the analysis model. The numerical results are discussed and partly compared with experimental data. And a combination of process parameters that is expected to give the highest surface hardness is proposed on the basis of this discussion.

Prediction and digital mapping of soil carbon storage in the Lower Namoi Valley

Estimation and mapping carbon storage in the soil is currently an important topic; thus, the knowledge of the distribution of carbon content with depth is essential. This paper examines the use of a negative exponential profile depth function to describe the soil carbon data at different depths, and its integral to represent the carbon storage. A novel method is then proposed for mapping the soil carbon storage in the Lower Namoi Valley, NSW. This involves deriving pedotransfer functions to predict soil organic carbon and bulk density, fitting the exponential depth function to the carbon profile data, deriving a neural network model to predict parameters of the exponential function from environmental data, and mapping the organic carbon storage. The exponential depth function is shown to fit the soil carbon data adequately, and the parameters also reflect the influence of soil order. The parameters of the exponential depth function were predicted from land use, radiometric K, and terrain attributes. Using the estimated parameters we map the carbon storage of the area from surface to a depth of 1 m. The organic carbon storage map shows the high influence of land use on the predicted storage. Values of 15–22 kg/m2 were predicted for the forested area and 2–6 kg/m2 in the cultivated area in the plains.

Phase field modelling of the interfacial condition at the moving interphase during the γ → α transformation in C–Mn steels

The phase field model is used to simulate the γ → α transformation in an Nb microalloyed C–Mn steel during cooling from different austenitisation temperatures. The model provides qualitative information on the developing microstructure, as well as quantitative information on both the ferrite fraction formed and the carbon concentration distribution in the remaining austenite. The initial austenitic microstructure (grain morphology and dimensions) and the nucleation conditions (nucleus density and nucleation undercooling) are set as input data of the model; they are derived by metallographic and dilatometric tests. The interface mobility is used as a fitting parameter to optimise the agreement between the experimental ferrite fraction curve, obtained by dilatometry, and the simulated ferrite fraction. A strong decrease of the γ/α interface mobility is found when the austenitisation temperature decreases from 1373 to 1173 K. A good agreement is obtained between the simulated microstructure and the actual microstructure observed after cooling.