bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer Coefficient Measurements (HTC) at the Metal-Mould Interface in Permanent Mould Casting
Authors: Rossi F. , Lázár Judit , Ignat S. , Quesada J.
Published: January 2010

Formerly based on empirical knowledge, casting is now inseparable from a scientific approach. Numerical simulation is commonly used to predict and understand the behaviour of alloys and moulds. Even if models used in software are accurate, one of the main difficulties in obtaining good results is the lack of databases. Among the needed data, the knowledge of interfacial thermal properties is one of the most significant in permanent moulding. Indeed, the cooling and solidification of the alloy are controlled by the interfacial behaviour with the mould and impact directly on the microstructure and on the formation of defects (shrinkage…). In die casting thermal conductivity at the interface is controlled by the use of different kinds and thicknesses of coatings. The fact that coatings are used in thin layers and the existence of bonding resistance increase the lack of accuracy of the data. So it appears necessary to be able to determine quickly and easily the HTC for different materials, thicknesses and process parameters. In industrial conditions it is difficult to control and reproduce the coatings. It is also important to be able to measure the HTC directly in the workshop.

Many results concerning these problems are available in the literature, but very few able to quickly lead to reliable results. The experimental device which is proposed in the present study allows the determination of the HTC. The design of the software was done to allow the full automation of measurements and calculations in the experiment. Analytical calculation of the HTC is not sufficient to give relevant results due to the phase transformations, so an indirect numerical solution based on Beck’s method has been introduced with the development of a finite difference thermal solver. The three dimensional solver was designed to take into account the heat loss (radiation and convection) and the nonlinearity of thermal equations. Calculations performed from the results of experimental casting temperatures show good match and stability.
Calculation of Energies of Coherent Interfaces and Application to the Nucleation, Growth and Coarsening of Precipitates
Authors: Sonderegger Bernhard , Holzer Ivan , Kozeschnik Ernst
Published: January 2010

Interfacial energies are essential in modelling nucleation, growth and coarsening processes in solid materials; especially nucleation rates respond very sensitively to small changes of this quantity. Thus, the prediction of interfacial energies has attracted the interest of many researchers since many years. In this work, a simple concept for the calculation of energies of coherent interfaces in multicomponent systems is presented. The model advances the classical nearest-neighbor-broken-bond concept for arbitrary interface orientations and interface curvature. The obtained result is simple enough to be expressed in a single, closed equation. Consequently, it can be easily implemented in the framework of classical nucleation theory, or in complex simulation tools for precipitate evolution based on Kampmann-Wagner type models. In this paper, the theoretical background of the model is discussed, and the results are compared to experimental data. Furthermore, a size correction function for small precipitates is presented and applied to the prediction of nucleation rates. Despite the simplicity of the model, the predictions of the model are found to be in satisfactory agreement with experimental evidence.
Coupling Continuum and Discrete Models of Materials with Microstructure: A Multiscale Algorithm
Authors: Sansalone Vittorio , Trovalusci Patrizia
Published: January 2010

The importance of a multiscale modeling to describe the behavior of materials with microstructure is commonly recognized. In general, at the different scales the material may be described by means of different models. In this paper we focus on a specific class of materials for which it is possible to identify (at the least) two relevant scales: a macroscopic scale, where continuum mechanics applies; and a microscale, where a discrete model is adopted. The conceptual framework and the theoretical model were discussed in previous work. This approach is well suited to study multifield and multiphysics problems. We present here the multiscale algorithm and the computer code that we developed to implement this strategy. The solution of the problem is searched for at the macroscale using nonlinear FEM. During the construction of the FE solution, the material behavior needs to be described at Gauss points. This step is performed numerically, formulating an equivalent problem at the microscale where the inner structure of the material is described through a lattice-like model. The two scales are conceptually independent and bridged together by means of a suitable localization-homogenization procedure. We show how different macroscopic models (e.g. Cauchy vs. Cosserat continuum) can be easily recovered starting from the same discrete system but using different bridges. The interest of this approach is shown discussing its application to few examples of engineering interest (composite materials, masonry structures, bone tissue).
X-Ray Computed Tomography Based Modelling of Polymeric Foams
Authors: Wismans J.G.F. , van Dommelen J.A.W. , Govaert L.E. , Meijer H.E.H.
Published: January 2010

A hybrid numerical-experimental approach is used to characterize the macroscopic mechanical behaviour of polymer foams. The method is based on characterization of foams with X-ray Computed Tomography and conversion of the data to Finite Element (FE) models. Results of FE analyses revealed that plasticity has a large influence on the mechanical response of these structures.
Study on Evolution of Partial Texture of Different Grains during Grain Growth in IF Steels
Authors: Tong W.P. , Chen W.Y. , Wagner Francis , Zuo L. , He J.C.
Published: January 2010

An IF steel sample was cold rolled to a reduction of 80% and subsequently submitted to annealing treatment at 650°C, 710°C and 770°C for various durations, respectively. The grain size and evolution of partial texture of small, medium and large grains were investigated during grain growth. It was found that the growth rate and partial texture characteristic were absolutely distinct at different annealing temperature, both were temperature dependent. At same annealing temperature, partial texture for various annealing time was similar, but its intensity increases with an increment of duration. And the relation between partial texture of different grains assembly and its mean grain size can be expressed by an empirical formula from experiment data.
Texture and Strain Experiments at OPAL
Authors: Garbe Ulf , Kirstein Oliver , Studer Andrew , Luzin Vladimir , Liss Klaus Dieter
Published: January 2010

In response to the development of new materials and the application of materials and components in new technologies the direct measurement, calculation and evaluation of textures and residual stresses has gained worldwide significance in recent years. Non-destructive analysis for phase specific residual stresses and textures is only possible by means of diffraction methods. The determination of global texture and the local variation of texture for example by inhomogeneous deformation are very important due to the coherence between the texture and the physical and mechanical properties of materials.
Texture and Substructure Development during Dynamic Recrystallization in Ni-30Fe Austenite
Authors: Beladi Hossein , Cizek Pavel , Hodgson Peter
Published: January 2010

An austenitic Ni-30%Fe model alloy was employed to investigate the texture and substructure development within the deformed matrix and dynamically recrystallized (DRX) grains during hot torsion deformation. Both the deformed matrix and DRX grains predominantly displayed the crystallographic texture components expected for simple shear deformation. The characteristics of the deformed matrix texture evolution during deformation largely resulted from the preferred consumption of high Taylor factor components by new recrystallized grains. Likewise, the comparatively weaker crystallographic texture of DRX grains became increasingly dominated by low Taylor factor components as a result of their easier nucleation and lower consumption rate during DRX. There was a significant difference in the substructure formation mechanism between the deformed matrix and DRX grains for a given texture component. The deformed matrix substructure was largely characterized by “organized”, banded subgrain arrangements with alternating misorientations, while the substructure of DRX grains was more “random” in character and displayed complex, more equiaxed subgrain/cell arrangements characterized by a local accumulation of misorientations. Substructure characteristics of individual orientation components were principally consistent with the corresponding Taylor factor values.
Relations of Initial Microstructure with Grain Boundary Character Distributions in a Cold Rolled and Annealed Lead Alloy
Authors: Wang Wei Guo , Zhou Bang Xin , Guo Hong
Published: January 2010

Five samples of Pb-Ca-Sn-Al alloy with different initial microstructures were processed in the same way including cold rolling with thickness reduction of 30% at the temperature of liquid nitrogen and then annealing at 270oC (0.9Tm) for 1 to 10 minutes. Electron back-scatter diffraction (EBSD) analyses indicated the initial microstructure which is at the end of primary recrystallization with a averaged grain size around 10 microns, a fair quantity of annealing twins and a random orientation can definitely result in a final grain boundary character distribution (GBCD) mainly composed of special boundaries (SBs) of which its fraction is higher than 75%, and the averaged SB cluster size exceeds 200 microns, implying the GBCD is optimized in satisfaction. However, the initial microstructures of partial recrystallization or full recrystallization but with coarser grain size are not good at producing high fraction SBs, whereas the initial microstructure of deformation with very strong textures is harmful to the formation of SBs in the processing of rolling followed by annealing. High resolution EBSD measurements revealed that the interactions between mobile incoherent ∑3 boundaries which were probably introduced by the continuous recrystallization from the distorted coherent ∑3 ones could be the formation mechanisms of the GBCD containing high fraction SBs.
Grain Boundary Character of 9Cr Feritic/Martensitic Heat Resistant Steels Strengthened by Nano-Sized MX Precipitates
Authors: Yin Feng Shi
Published: January 2010

In this work, two heats of 9Cr ferritic/martensitic heat resistant steels with different carbon and nitrogen contents were prepared. The steels were designed to have much lower carbon content than conventional 9-12Cr heat resistant steels for obtaining dense nano-sized MX precipitates. Microstructure of the two steels in different heat treatment states was analyzed by electron backscatter diffraction (EBSD) method. The results show that grain boundary character is greatly affected by carbon and nitrogen contents. Martensite in the steel with 0.02wt.% carbon and ultra low nitrogen is easier to recrystallize than that in the steel with ultra low carbon and 0.03wt.% nitrogen during tempering treatment. The effect of grain boundary character on stress rupture properties is also discussed.
Effects of Thermal Annealing on Electrical, Optical and Structural Properties of Ga-Doped ZnO Films
Authors: Chang P.C. , Lee K.H. , Tu A.N. , Chang S.J. , Lee K.L.
Published: January 2010

Ga doped ZnO (GZO) films were prepared by radio frequency (rf) magnetron sputtering on glass or silicon substrates. Electrical, optical, and structural properties of these films were analyzed in order to investigate their dependence on thermal annealing temperature. GZO films with a minimum resistivity of 5.2×10-3 Ω-cm annealed at 400°C and a transparency above 80% in visible region were observed. The temperature-dependent conductivity affected the carrier transport and was related to the localization of carriers. The results of transmission spectra were consistent with the results of atomic force microscopy (AFM) scan. X-ray diffraction analysis and electron spectroscopy for chemical analysis were also used to investigate the properties of GZO films.
Optical-Electrical Properties and Corrosion Behavior of Tantalum-Doped Indium Tin Oxide Films Deposited by Magnetron Sputtering
Authors: Dong Xian Ping , Zhang Bo , Wu Jian Sheng
Published: January 2010

Tantalum-doped indium tin oxide films were deposited on glass substrate by co-sputtering with two-targets. Tantalum-doping strengthened the orientation of the (400) plane and resulted in better crystalline structure, larger grain size and lower surface roughness. Due to the better crystallizability of the tantalum-doping films, carrier concentration and the mobility were increased. Tantalum-doping revealed better optical–electrical properties. The environmental effects on electrical properties stability and long-term reliability of tantalum-doped films in NaCl, Na2SO4 and HCl solutions at 25°C were also investigated, which simulated corrosion behavior in marine, industrial and acidic environments. The relative resistance change (△R/R) for tantalum-doped films revealed that the films had the best electrical properties stability and long-term reliability in these aggressive environments. The pre-formation of a protective oxide layer on the surface of the films had an enhancing effect on the corrosion properties.
Growth Stresses and Phase Development in Nanostructured Oxide Scales Formed on Iron Aluminides
Authors: Brito Pedro , Pinto Haroldo , Rothkirch André , Pyzalla Anke
Published: January 2010

The evolution of phase composition and growth stresses in oxide scales growing on the polycrystalline Fe-15at.%Al alloy at 700°C in air was studied by in-situ synchrotron X-ray diffraction and X-ray photoelectron spectroscopy. The oxidation kinetics was determined by thermogravimetry. The results showed that, under these conditions, metastable -Al2O3 appears only during the first minutes of oxidation and the main oxides formed since the early oxidation are -Al2O3 and -Fe2O3. High volume fractions of -Fe2O3 caused accelerated oxidation rates in the first hours. -Al2O3 and -Fe2O3 grow epitaxially, evolving compressive and tensile growth stresses, respectively.
Thin Film Depositions of CdTe Semiconductors on Amorphous and Single Crystal Substrates and Comparisons of their Properties
Authors: Sato Yuichi , Kodate Tatsushi , Arai Manabu
Published: January 2010

Thin films of CdTe semiconductors were prepared on sapphire single crystal and quartz glass substrates by a vacuum evaporation method. Crystallinity and photoluminescence properties of the obtained CdTe thin films on the substrates were semi-quantitatively compared concerning the difference of the substrate materials. Dependences of the properties on the substrate temperature in the preparations and indium doping to the thin films were also investigated.
Tailoring Exchange Coupling between Magnetic Nano-Grains of High Density Magnetic Recording Media
Authors: Qin Gao Wu , Zuo Liang
Published: January 2010

Intergranular exchange coupling between magnetic nano-grains is one of important parameters to develop magnetic recording media towards the areal density of 1000 Gbits/in2. In this presentation, various processings, involving oxide co-sputtering for perpendicular media, spontaneous phase separation for longitudinal media, and grain boundary (GB) diffusion derived from underlayer or overlayer to induce tunable exchange coupling, have been reviewed to tailor the exchange coupling, including their main principles, present achievements and engineering challenges. Much attention is paid to the physical origin of magnetically induced phase separation of Co-Cr-based alloy, which governs media noise and coercivity, and its applications to the longitudinal media. A proposal of GB diffusion is also highlighted in detail to show a feasibility to tailor the exchange coupling, including calculation results and experimental evidences.
Influence of Molybdenum and Copper on the Corrosion Resistance of High Strength Austenitic Steels
Authors: Berns Hans , Riedner Sascha , Hussong Birger
Published: January 2010

Joint alloying of 0.85 to 1.1 mass% C + N raises the strength and cold work hardening of steels with 18 to 19 mass% Cr and Mn each and allows to produce them at atmospheric pressure. A yield strength of 600 MPa is combined with a true fracture stress of almost 2500 MPa and ≈ 70 % elongation. However, there is a risk of carbide/nitride precipitation during quenching of thicker cross sections after solution annealing. The addition of Mo and Cu affects the corrosion resistance as well as the precipitation. Submersion test and current density/potential tests in several aqueous solutions characterize the corrosion behaviour. Tests on intercrystalline corrosion are used to detect the precipitation as a function of quenching rate. It is shown that the C/N ratio is of key importance in improving the properties.
Phase Transformation in Duplex Stainless Steels after Isothermal Treatments, Continuous Cooling and Cold Working
Authors: Calliari Irene , Ramous Emilio , Bassani Paola
Published: January 2010

This paper concerns the phase transformation induced by heat treatment and cold rolling in four duplex stainless steel. In 2205 and 2507 , during the isothermal heat treatments, chi-phase precipitates as small particles at the ferrite/austenite boundaries, followed by sigma precipitation. At the lowest temperature the formation kinetic of chi-phase is favoured, with the increasing of time and temperature a progressive transformation of chi to sigma occurs and the kinetic of sigma is favoured. During continuous cooling, the chi -phase appears at low cooling rates.
In low Ni grades the grain boundaries precipitation of chromium nitrides were detected , but no sigma and chi. In 2101 the austenite transforms to martensite both after cold rolling and quenching
Effects of Deformation Mode on Resistivity Curve Used for Estimating Martensite Induced in Stainless Steel
Authors: Date Hidefumi
Published: January 2010

The martensite induced in three types of austenitic stainless steel, which indicate the different stability of the austenitic phase (γ), were estimated by the resistivity measured during the tensile deformation or compressive deformation at the temperatures 77, 187 and 293 K. The resistivity curves were strongly dependent on the deformation mode. The volume fraction of the martensite (α’) was also affected by the deformation mode. The ε phase, which is the precursor of the martensite and is induced from the commencement of the deformation, decreased the resistivity. However, lots of defects generated by the deformation-induced martensite increased the resistivity. The experimental facts and the results shown by the modified parallelepiped model suggested a complicated transformation process depending on each deformation mode. The results shown by the model also suggested a linear relation between the resistivity and the martensite volume at the region of the martensite formation. The fact denoted that the resistivity is mostly not controlled by the austenite, ε phase and martensite, but by the defects induced due to the deformation-induced martensite.
Energy of Interatomic Bonds in Austenitic Steels
Authors: Shanina B.D. , Gavriljuk Valentin
Published: January 2010

Using the full-potential-full-electron-linearized-augmented-plane-wave (FLAPW) method, we carried out ab initio calculations of the electronic structure for austenitic steels of different compositions. The total set allows to find a system of equations for obtaining the value and sign of the interatomic bond energy between Fe-Fe, Fe-Mn, Fe-Cr, Fe-Ni; Ni-Ni; Cr-Cr, Mn-Mn and Mn-Cr. It is obtained that both Cr-Cr and Cr-Fe bonds are attractive, however the Cr-Cr bonds are stronger. The interaction between interstitial carbon (nitrogen) and metallic atoms is calculated. The interstitial atoms change the metal-metal interaction between the nearest neighbors.
Further Corrosion Behaviors of Low Carbon Bainitic Steel in the Environment Containing Cl- after the Rust Layer Damaged
Authors: Yang S.W. , Cui L. , He Y. , He Xin Lai
Published: January 2010

Electrochemical measurement, metallographic observation and x-ray diffraction analysis were employed to investigate the further corrosion behaviors of low carbon bainitic steel in the environment containing Cl-, after its original rust layers had been damaged on different ways. It was found the damnification of rust layers on the low carbon bainitic steel (LCBS) and steels utilized as contrasts, i.e. low carbon ferrite steel (LCS) and a commercial weathering steel 09CUPCrNi (09Cu), could be rapidly self-repaired in the further corrosion process. When damnification degree and further corrosion time were same, the resistance of rust layers and the repair degree of damnification of the low carbon bainitic steel were higher than those of contrasts. The repair ratio of inside damnification is always higher than that of crossed damnification, due to faster formation of rust layer at damaged site, in which NaCl aqueous solution is reserved after dropping. Alloy elements such as Cu and Cr obviously enhance protection of rust layer newly formed at damaged sites. These results indicate that the alloy element content in weathering steel is not enough to improve obviously corrosion resistance of steel matrix, while it is sufficient to enhance protection of rust layer.
Designing Local Properties of Constructional Elements by Local Use of Ageing Effects in Multiphase Steels
Authors: Asadi Mehdi , Palkowski Heinz
Published: January 2010

The investigations deal with processes leading to local effects of strengthening in multiphase steels, being characterized by good formability, continuous yielding, high strength and a strong bake hardening and ageing effect. Dual phase and complex phase steels are under investigation to examine the effect of thermo-mechanical processing parameters on local ageing ability and its use for designed properties. For this purpose local heat treatment by laser are studied, as well as stability of local ageing on the adjusted strength. A remarkable increase of the hardness in the heat treated zone was observed. Stability of the local strengthening effect could be confirmed. Partial heat treatment of multiphase steels by laser can open a new field of application for the local use of the strengthening effect to influence only relevant areas, thus giving potential for energy saving.
Hot Forging of Ultra High-Strength TRIP-Aided Steel
Authors: Sugimoto Kohichi , Sato Shohei , Arai Goro
Published: January 2010

Ultra high-strength TRIP-aided steel consisting of bainitic ferrite matrix and interlath retained austenite films (TBF steel) possesses high toughness and fatigue strength, as well as high resistance against hydrogen embrittlement. In this study, to improve further these mechanical properties, the effects of hot forging and subsequent isothermal transformation holding process (FIT process) on microstructure, retained austenite characteristics, tensile properties and toughness of the TBF steel with chemical composition of 0.4%C, 1.5%Si, 1.5%Mn, 0.5%Cr, 0.2%Mo, 0.05%Nb and 0.5%Al (mass%) were investigated. The FIT process brought on an excellent combination of tensile strength of 1350-1550 MPa and Charpy impact absorbed value of 100-110 J/cm2 in the developed TBF steel, exceeding so much that of SCM440 steel. The excellent combination was mainly caused by (i) refined mixed structure of bainitic ferrite and retained austenite and (ii) the increased mechanical stability of retained austenite due to the FIT process.
In Situ High Temperature X-Ray Studies on Bainitic Transformation of Austempered Silicon Alloyed Steels
Authors: Vuorinen Esa , Chen Xiang
Published: January 2010

The in-situ X-ray diffraction observations of the bainitic transformation of silicon alloyed steels were performed using the high temperature X-ray diffraction technique. The experimental results have shown that the volume fraction and carbon content of austenite remains a constant value which indicate that the transformation is almost finished after the early stages of austempering transformation. Asymmetry diffraction peaks are obtained for samples at the early stage of transformation due to a heterogeneous distribution of carbon in different regions of austenite and thus exists two types of austenite: low-carbon austenite (γLC) and the high-carbon austenite (γHC). The experimental results supports that the bainite growth is by a non-diffusive mechanism when austempering temperature is in the lower bainite transformation temperature.
Influence of Heat Treatment on the Microstructure of a High Chromium Steel Used for the Manufacture of Rolling Rolls
Authors: Pariente Ines Fernández , Artimez J.Manuel , Belzunce F.Javier , Rodríguez Cristina
Published: January 2010

The aim of this work was the study of the heat treatment optimisation of high chrome steels used for the manufacture of rolling rolls in order to obtain a final product with a high hardness and wear resistance and taking into account the very large dimensions typical of these products. The effect of modifying the maintenance temperature and time during the different phases of the heat treatment on the microstructure and hardness of this product was evaluated. The necessity of adjusting the temperature and maintenance time of the quenching heat treatment in order to obtain a martensitic/bainitic matrix with a low austenite content followed by two tempering treatments was demonstrated as the best way to obtain the optimal properties of the product for this particular application.
Technologies of Nanomodification of Low-Carbon Low Alloyed Steels
Authors: Malyshevsky V.A. , Khlusova E.I. , Orlov V.V.
Published: January 2010

Metallurgical industry can be considered as a field most accommodated for perception of nano-technologies, which in the near future will be able to provide large scale production and high level of investments return. Specially noted should physical and mechanical properties of nano-structured steels and alloys (strength, plasticity, toughness and so on) which will cardinally excel characteristics of respective materials developed using conventional technologies.
Investigations have shown that basic principles of selection of a structure up to nano-level for low-carbon low-alloy steels can be put forward, that is: 1) morphological similarity of structural components, pre-domination of globular type structures due to reduction in carbon components and rational alloying; 2) formation of fine-dispersed carbide phase of globular morphology; 3) exclusion of lengthy interphase boundaries; 4) formation of fragmented structure with boundaries close to wide-angle ones, which inherited structure of fine-grained deformed austenite.
Mechanical Properties and Forming Behavior of a Type 9%Cr Steel Containing 2%W
Authors: Peñalba Felix , Gómez Xabier , Allende R. , Carsí Manuel , Ruano Oscar
Published: January 2010

The possibilities to improve the properties of steels for tubes exposed at high temperatures are explored. The mechanical properties and forming behavior of an experimental casting of type 9Cr-ferritic steels, P92, containing 2%W, are studied. The hardenability was determined by means of continuous cooling diagrams associated with hardness measurements and microstructure observations. Tensile tests from room temperature to 650°C were carried out to determine the variation of the strength and ductility in this temperature range. In addition, Charpy impact tests were conducted to characterize the toughness of the steel and the ductile-brittle transition temperature. Finally, hot torsion tests at various temperatures and strain rates were carried out and the generalized stresses and strains to rupture for each test are determined. With these data forming stability maps were generated to characterize the best forming conditions.
Homogenization Strategy and Material Characterization of High-Manganese TRIP and TWIP Steels
Authors: Wietbrock Burkhard , Bambach M. , Seuren S. , Hirt G.
Published: January 2010

In this work a hot forming strategy, consisting of forging and hot rolling, to homogenize casted blocks of high-manganese steels with 0.3 % carbon and 22 % manganese is introduced. The resulting distribution of carbon and manganese is evaluated by microprobe scans. The micro-segregation of manganese could be reduced from 7 weight percent to 2.
To create the obtained hot forming strategy hot compression tests have been carried out. The deformation behavior has been characterized for two steels with 22 % manganese and between 0.3 and 0.7 % carbon content in the temperature range between 700 and 1200°C and strain rates between 0.1 and 10 s-1.
Microstructural Evaluation of API 5L X80 Pipeline Steels Submitted to Different Cooling Rates
Authors: Bott Ivani de Souza , Vieira A.A.H. , de Souza L. Felipe G. , Rios Paulo Rangel
Published: January 2010

During the life cycle of an API steel there are occasions when it will be submitted to thermal cycle. For tubes produced by the UOE process, for the oil and gas industry, severe thermal cycles occur during the welding procedure and when the tube requires hot induction bending. It is therefore of interest to learn about the influence of different cooling rates on the microstructure of these steels, produced by TMCP (Thermomechanical Controlled Process), since these changes can be reflected in a variation in the mechanical properties and hence in the performance of the pipeline.
In this work three steels of class API 5L X80, with additions of, Nb-Cr, Nb-Cr-Mo and Nb-Cr-Mo-V, and otherwise similar alloy content, produced by TMCP without accelerated cooling were investigated. These alloys were submitted to austenitization at 900oC for 1 hour followed by three different cooling rates of 1.5oC/s, 30oC/s, 115oC/s, in air, oil and water respectively.
It is well known that the main strengthening mechanism in TMCP, which allows a simultaneous increase in strength and toughness, is the reduction of the grain size. Other mechanisms such as solid solution hardening, precipitation and increasing dislocation density also contribute. For the steels in this study, all having a similar base chemical composition and yield strength, all the different thermal cycles applied promoted a reduction in the grain size, and only for the higher cooling rate (115oC/s) were there significant observable phase transformations. The Nb-Cr-Mo-V system exhibited a higher percentage of martensite than the Nb-Cr and Nb-Cr-Mo systems.
Hot Deformation and Ductility Analysis of Continuous Cast C40 Steel by Means of Tensile and Compression Tests
Authors: Rodriguez-Calvillo Pablo , Hernandez-Exposito Ana , Boulaajaj Ahmed , Cabrera Jose María
Published: January 2010

The steel production from scrap using continuous cast technology has increased in last decades. Sometimes, steels processed via this route display poor ductility at high temperature. This feature is associated to cooling conditions and chemical composition, which in turns affect the segregation pattern and vary the transformation temperatures and the phase transformation kinetics.
The material under study was a C40 steel with a dendrite solidification microstructure coming from an industrial continuous casting plant. The high temperature ductility was evaluated by means of tensile tests up to fracture at strain rate of 0.001 s-1 in a temperature range of 1100 to 710°C. The reduction in area at fracture as a function of temperature graphs show a clear reduction of the steel ductility in the intercritical region, but also after the pearlite transformation.
Single deformation compression tests were also carried out on the steel in the austenitic temperature domain, 900 to 1100°C, and at strain rate of 0.001 to 1 s-1. A modification of the Garofalo hyperbolic sine equation has been employed to derive the peak and steady stresses of the flow curve. The work hardening, U, and dynamic recovery, Ω, parameters which describe the flow curve before dynamic recrystallization takes place and the k and t50 parameters, based on the JMAK model, to describe the recrystallization kinetics were also calculated for every test and expressed as a function of the Zener Hollomon parameter, Z.
Comparative Study of Various Data Conversion Methods for Torsion Tests Applied to a HSLA Steel
Authors: Castellanos Jesus , Rieiro Ignacio , Carsí Manuel , Muñoz Julio , Ruano Oscar
Published: January 2010

The influence of methods for converting torsion data (torque, number of turns and speed rotation) into equivalent variables (true stress, true strain and true strain rate) on the Garofalo equation parameters is studied. Torsion tests for a high strength low alloy steel at temperatures in the range 900 to 1150°C and strain rates in the range 0.5 to 30 s-1 were conducted. The flow behavior of the material was analyzed by means of the Garofalo equation which is especially adequate for the correlation of torsion data in wide ranges of temperatures and strain rates. The Garofalo equation was fitted at different strains: from peak strain to a value of strain where a steady-state is assumed. The parameters of this equation, A, Q, n, , were determined by the RCR method which does not need initial values and provides coefficients indicating the quality of the fitting. Finally, the Garofalo equation parameters were related to creep mechanisms operating in this steel.
Microstructure and Cleavage Resistance of High Strength Steels
Authors: di Schino Andrea , Guarnaschelli Claudio
Published: January 2010

The relationship between microstructure and cleavage resistance in quenched and tempered high strength bainitic and martensitic steels is investigated by means of Charpy-V three-point bending tests, uniaxial tensile test on unnotched specimens and EBSD. Steels under investigation are low/medium carbon (C=0.10%-0.40%) steels with yield strength in the range YS=500-1000 MPa. Results show that the tensile strength and the cleavage resistance of Q&T steels appear to be controlled by different structural parameters and not, as in the case of polygonal ferritic steels, by the same structural unit. In particular, yield strength is controlled by the mean subgrain size, whereas the structural unit controlling the critical cleavage stress is the covariant (bainitic or martensitic) packet, whose size is slightly lower than the average unit crack path (UCP). The critical stage in the fracture process appears to be the propagation of a Griffith crack from one packet to another, and the resistance offered by high-angle boundaries is approximately the same as that of low-C steels with bainitic or polygonal ferrite microstructure.
Towards Understanding the Development of Grain Boundary Clusters in Austenitic Stainless Steel
Authors: Engelberg D.L. , Rahimi S. , Marrow T.James
Published: January 2010

The development of global microstructure characteristics has been compared to the local distribution and extent of Σ3 and Σ3n (1 n 3) grain boundary clusters as a function of thermo-mechanical processing in Type 304 stainless steel. A cold reduction of 5% produced GBE modified microstructures on annealing at 1050°C, containing almost one order of magnitude longer maximum cluster lengths than the corresponding annealing treatments for a reduction of 15%. Differences in the development of the distributions of cluster length scales were observed between the thermo-mechanical treatments. A re-conversion of the longest cluster obtained after GBE processing was observed with long annealing times. The local distribution of Σ3n boundary clusters was assessed, and regions with a low density of clusters are indicative of the onset of GBE conversion of microstructure.
Isothermal and Thermal Fatigue of Tool Steel AISI H11
Authors: Grüning Alexander , Lebsanft Markus , Scholtes Berthold
Published: January 2010

Lifetime of hot-work tool steels is often limited by the development of crack nets as a consequence of thermal or mechanical fatigue loading. In this paper, the isothermal and thermal fatigue behaviour of tool steel AISI H11 (German grade X38CrMoV 5-1) in the temperature range between room temperature and 650°C is investigated. In addition to stress controlled isothermal tension-compression fatigue tests, out-of-phase thermal fatigue tests were carried out using a servohydraulic testing system, keeping the macroscopic total strain of the gauge length constant, while triangular time-temperature cycles were applied. The temperature range was chosen in such a way that numbers of cycles to fracture between 1,000 and 10,000 were achieved. The development of stress amplitudes, plastic strain amplitudes as well as of mean stresses was analysed during the tests. Results of isothermal and thermal fatigue tests are compared and discussed.
Recrystallization Behaviors of an Al-Zn-Mg-Cu Alloy during Multi-Pass Hot Compression
Authors: Shen Jian , Li Ju Peng , Yan Liang Ming , Yan Xiao Dong
Published: January 2010

Dynamic recovery (DRV) and dynamic recrystallization (DRX) play important roles during thermomechanical processes of light metals and alloys because they have obvious influence on microstructure evolution and finally on the mechanical properties of the worked material. Hot compression tests of 7050 aluminum alloy was carried out on Gleeble1500D thermomechanical simulator to modeling multi-pass hot rolling process. Microstructure evolution features of the alloy deformed to a reduction up to 80% were investigated through OM, TEM and EBSD observations. DRX behavior of the alloy during hot compression was emphasized. Some evidence of continuous DRX can be found in the alloy deformed at different temperatures and reductions. The main nucleation mechanisms of DRX are subgrain coalescence and subgrain growth. However, static recrystallization takes place in the material during slow cooling after hot compression.
Microstructure and Texture Evolution in a High Manganes Austenitic Steel During Tensile Test
Authors: Jiménez José A. , Frommeyer Georg
Published: January 2010

The evolution of microstructure and texture in a Fe-22wt%Mn-0.6C% steel during plastic deformation was studied by interrupted tensile tests at plastic strain levels ranging from 5 to 40% at 10-3 s-1. The steel present in as-received condition a fully recrystallized austenitic microstructure and almost random texture. A microstructural analysis of deformed samples reveals the presence of thin bands. As no martensite was detected by X-ray diffraction, these striations must correspond to deformation twins. The amount of twins increases progressively with plastic strain. At lower deformation, these bands are parallel and start and terminate at the grain boundaries. As the strain level increases, the number of the twins band increases and they intersect each other. This evolution of the microstructure is accompanied by the appearance a fiber texture with the <111> and <100> directions parallel to the tensile direction
Static Strain Ageing in Some Austenitic Stainless Steels
Authors: Juuti Timo J. , Karjalainen L. Pentti , Ruoppa Raimo , Taulavuori Tero
Published: January 2010

The yield strength in austenitic stainless steels can be improved by cold rolling. Recently, it has been realized that a considerable further increase can be achieved through static strain ageing (SSA). The effect of SSA in four austenitic stainless steel grades was studied. The test materials were formerly cold rolled to three different reductions of 15%, 30% and 40%. Subsequently, the steels were aged at temperature range between 160 and 400 °C with ageing times from 15 to 15000 seconds. Owing to SSA, increments over 200 MPa in yield strength were observed, while elongation decreased only slightly or even improved by 1 to 2%-units. The influence of ´-martensite on the strength increase was apparent. The maximum strength increase with relatively small drop of elongation was achieved in the steels cold rolled to 30% reduction while approximately 50% of ´- martensite was formed. However, a small increase in the yield strength was detected even in steels cold rolled to 15% reduction and containing 0 to 2% of ´-martensite only. Therefore, SSA seems also to take place in the austenite phase. To clarify the reason for improvement of the ductility in the instance of strengthening, work hardening rates were determined and found to differ considerably between aged and non-aged structures. The activation energy of the SSA process determined was found to be almost equal to the activation energy of carbon and nitrogen diffusion in the austenite phase. A mechanism resembling the Suzuki effect was suggested as the main mechanism of the SSA process.
Calculation of Stress-Strain Curve of Two-Phase Microstructure on the Basis of the Extended Secant Method
Authors: Koyama Toshiyuki , Onodera Hidehiro
Published: January 2010

The secant method proposed by Weng [1] is a practical calculation method to evaluate the stress-strain curve of the two-phase materials, but the shape of the inclusion phase has been often assumed to be a sphere or an ellipsoid in the calculation. In this study, we modified the secant method by utilizing the phase-field micro-elasticity theory [2,3] so as to be able to calculate the SS-curve of the materials consisting arbitrary morphology of microstructure, and applied this method to the conventional microstructures in steels, i.e., the ferrite-bainite two-phase microstructure.
Modeling of Phase Transformation and Carbon Behaviors after Holding at γ/α Region and Controlled Cooling in Low Carbon Steels
Authors: Choi J.M. , Park B.J. , Lee K.S. , Lee K.J.
Published: January 2010

It is very important to understand interstitial carbon behaviors in cold rolled steel to get the good formability as well as the high strength. In low carbon steel, most of carbons are consumed by the formation of grain boundary cementite during cooling. During heating and holding between Ae1 and Ae3, cementite is dissolved and consequently carbon enriched austenite is formed. By controlled cooling, retained austenite as well as bainite and martensite are formed. In this study, the effect of silicon, intercritical annealing, isothermal bainite transformation on the formation of ferritic bainite, cementite and retained austenite are modeled by nucleation and growth, diffusion and dissolution. In addition, the formation of retained austenite and their carbon contents are modeled and compared with experimental data.
Ductility of Microalloyed Steels during Hot Deformation
Authors: Mannucci A. , Anelli E. , Armengol M. , Vedani Maurizio
Published: January 2010

The ductility behaviour experienced by steels for linepipe (LP) applications in a temperature range generally from 700°C to 1200°C is a widely studied subject in steel research, especially for its implication on cracking during continuous casting and rolling. Hot tensile / torsion tests on as-cast products, conducted until fracture, are normally used to characterise the hot deformability behaviour.
Depending on the industrial hot deformation process within which the steel aptitude is being investigated, other types of tests can be more adequate.
With the aim to characterize the hot deformability behaviour in terms of the damages each steel presents at moderate strain levels (i.e. far from the onset of necking), a special device for interrupted hot tensile tests, followed by immediate quenching (i.e. to “freeze” the microstructure) was developed.
Various industrial steels with different starting microstructures (ad hoc in-lab heat treatments performed before testing) were tested by this method, and subsequent metallurgical investigations of the strained samples were carried out to identify, for each case, the damage mechanism and the microstructure features having the major influence on ductility loss.
As a result, it was found that (i) microstructural damages at moderate strain levels can be much better described throughout interrupted hot tensile tests, (ii) different compositions and starting microstructures within the industrial LP scenario lead always to microstructural damages at relatively high deformation temperatures (e.g. 950°C) and moderate strains (e.g. 0.1 to 0.2, very far from the onset of necking), (iii) the common mechanism by which LP steels start voiding is the grain boundary sliding and (iv) the intergranular voids, once formed, grow longer in coarser microstructures.
Temperature Dependence of Austenite Nucleation Site on Reversion of Lath Martensite
Authors: Nakada Nobuo , Tsuchiyama Toshihiro , Takaki Setsuo , Miyano Naoki
Published: January 2010

The temperature dependence of austenite nucleation behavior within lath martensitic structure was investigated in an ultralow carbon 13%Cr-6%Ni martensitic stainless steel partially reversed at (austenite + ferrite) two phase region. The shape and nucleation site of the reversed austenite grains were varied depending on the reversion temperature; fine acicular austenite grains frequently formed along the lath boundaries at a temperature lower than 915 K, while the granular ones tended to nucleate mainly on the prior austenite grain boundaries at a higher temperature. In order to explain the temperature dependence of nucleation site transition, the difference in energetics of austenite nucleation between the lath boundary and the prior austenite grain boundary was discussed on the basis of the classical nucleation theory and FEM analysis. The calculation of the changes in interfacial energy and elastic strain for austenite nucleation suggested that the lath boundary acts as more preferential nucleation sites for austenite rather than the prior austenite grain boundary to reduce the increment of elastic strain when the reversion temperature is low.
Genetic Alloy Design of Ultra High Strength Stainless Steels: From Thermodynamics to Quantum Mechanics
Authors: Rivera-Díaz-del-Castillo Pedro E.J. , Xu Wei , van der Zwaag Sybrand
Published: January 2010

The design of novel ultra high strength steels for aerospace applications is subjected to stringent requirements to ensure their performance. Such requirements include the ability to withstand high loads in corrosive environments subjected to temperature variations and cyclic loading. Achieving the desired performance demands microstructural control at various scales; e.g. fine lath martensite is desired in combination with nanoprecipitate networks at specified volume fractions, and controlled concentrations of alloying elements to prevent alloy embrittlement. The design for a specified microstructure cannot be separated from the processing route required for its fabrication. Alloys displaying exceptional properties are subjected to complex interactions between microstructure and processing requirements, which can be described in terms of evolutionary principles. The present work shows how genetic alloy design principles have been utilised for designing stainless steels displaying strength exceeding that of commercial counterparts. Such designed alloys become feasible for fabrication by tailoring their microstructure employing thermodynamic and kinetic principles, while fracture toughness properties can be controlled via performing quantum mechanical cohesion energy computations.