bluuebunny/crossref_metadata_2025 huggingface dataset:
A Variant Selection Rule in Transformation in Steel and Prediction of Transformation Texture
Authors: Tomida Toshiro , Wakita Masayuki , Yoshida Mitsuru , Imai N.
Published: January 2010

Quantitative prediction of transformation textures in steel becomes possible if a variant selection rule is taken into account, in which ferrite nucleating on austenite grain boundaries prefers to have orientation relationship with two neighboring austenite grains at the same time. The mathematical model of the variant selection rule is described and some examples of simulation in transformation textures in hot-rolled steel sheets are presented using the textures of retrained austenite and the misorientation distribution function method. An excellent agreement is attained between the predicted and experimental ferrite textures.
Modelling the Work Hardening Behaviour of AlMgMn Alloys
Authors: Marthinsen Knut , Abtahi Shahriar , Holmedal Bjørn , Friis Jesper , Nes Erik , Furu Trond
Published: January 2010

A recent work hardening model developed by Nes and co-workers at NTNU, Trondheim provides a unified theory for warm and cold stress-strain behaviour which in principle accounts for alloy aspects such as effect of dispersoids (size and number density) and solute content, including dynamic strain aging for Mg containing aluminium alloys. In the present paper the applicability and predictive power of the model are tested for multicomponent alloys to account for the combined effect of different solute elements in solid solution and dispersoids, with a special focus on hot deformation of a range of Al-Mg-Mn alloys. It is demonstrated that the model, without any re-tuning, only accounting for the variations in alloy chemistry and deformation conditions is capable of predicting the stress-strain for a range of compositions, strain rates and temperatures.
Structure/Property Relationship in Intergranular Corrosion of Archaeological Silver Artefacts
Authors: Lejček Pavel , Jäger Aleš , Gärtnerová Viera , Vaníčková Jaroslava , Děd Jiří , Haloda Jakub
Published: January 2010

The knowledge of the structure/property relationship in polycrystalline materials is the basis for successful application of Grain Boundary Engineering. We demonstrate this relationship in the reverse way: from the selective corrosion attack observed in unique sample – loops from excavated necklace dated to the 10th century and manufactured from a Ag–1%Cu alloy – we can deduce the method of manufacturing the objects. Individual grain boundaries in this object were identified by electron back-scattering diffraction. Crystallographic maps of the grain boundaries are confronted with the level of the long-termed selective corrosion attack in the soil electrolyte under conditions of decomposing human body. It is shown that general grain boundaries, which are highly segregated by copper, are preferably attacked by corrosion. The segregated layers represent a less-noble material comparing to the surrounding bulk in this environment. In contrast, the twin and other special grain boundaries are significantly more resistant against this attack.
Grain Boundary Sliding Phenomenon and Its Effect on High Temperature Ductility of Ni-Base Alloys
Authors: Torres E.A. , Caram R. , Ramirez Antonio J.
Published: January 2010

The structural materials phase transformations and failure mechanisms have been under scrutiny for many years. However, the advent of new and more powerful techniques is always making possible to address unsolved problems. Nowadays, the implementation of sophisticated in-situ electron microscopy tests is providing new insights in several fields of chemistry, physics, and materials science by allowing direct observation of a wide variety of phenomena at submicron and even atomic scale. These experiments may involve controlled temperature and atmospheres, mechanical loading, magnetic and/or electric field among other conditions that are imposed to the sample while its response or evolution is studied. An in-situ high temperature deformation experiment was developed and adapted within the vacuum chamber of a scanning electron microscope (SEM). This setup was used to study the grain boundary sliding (GBS) mechanism and its effect on the high temperature cracking phenomenon known as ductility-dip cracking (DDC). The Ni-base filler metals AWS A5.14, ERNiCrFe-7 and ERNiCr-3, which correspond to alloys 690 and 600, respectively, were studied within the temperature range between 700 and 1000 °C. Analysis of the recorded digital videos that registered the high temperature deformation made possible differentiating and quantifying, with submicron resolution, two different components of GBS. The designated pure-GBS and deformation-GBS components were described and quantified. In addition, the GBS relationship with the material high temperature ductility and the DDC failure mechanism was established.
Features of Highly Twinned Microstructures Produced by GBE in FCC Materials
Authors: Xia Shuang , Zhou Bang Xin , Chen Wen Jue , Luo Xin , Li Hui
Published: January 2010

The proportion of low ΣCSL boundaries of single phase brass, Ni based Alloy 690, 304 stainless steel and Pb alloy were enhanced to about 70% (according to Palumbo–Aust criterion) which mainly were Σ3n (n = 1, 2, 3…) types by small amount of deformation and recrystallization annealing. All the resulting microstructures were constituted of large size grain-cluster, in which all the orientation relationships between any two grains (no matter adjacent or not) could be described by Σ3n misorientations according to twin chain analyzing. Twin relationships up to 8th generation (Σ38) were found in one of such clusters. The outer boundaries of grain-clusters were crystallographically random with the adjacent clusters. In the case of high proportion of low ΣCSL boundaries, the connectivity of random boundary network was not fragmented obviously when the Palumbo–Aust criterion was used, whereas substantially interrupted when the Brandon criterion was applied.
Application of Laser Surface Remelting in Grain Boundary Engineering
Authors: Yang Sen , Kokawa Hiroyuki
Published: January 2010

To improve intergranular corrosion resistance of 304 stainless steel, a novel method, laser surface remelting combined with annealing treatment was adopted, which resulted in a high population of low  CSL boundaries, especially, twin boundaries (3) on the surface of the processed specimens. The grain boundary character distribution and effect of laser processing parameters on it were investigated. The experimental results showed that the maximum frequency of the low  CSL boundaries could attain 88.6% under the optimal processing conditions. The high fraction of the low  CSL boundaries led to a high corrosion resistance to intergranular corrosion.
Environmental Cracking and Impact Investigations after Short-Term Temperature Treatments: 7050-T7451 Friction Stir Weld
Authors: Paglia Christian
Published: January 2010

The influence of short-term heat treatments on the environmental cracking and impact properties of a 7050-T7451 friction stir weld were investigated. Prisms, cut transverse to the welding direction, were exposed for minutes at temperatures between 100 oC and 800 oC in an oven or exposed to a propane torch flame and/or water / air quenched. A significant increase in the environmental cracking resistance (ductility ratio from 0.2 to 0.9) was observed for samples exposed to temperatures below the solutionizing limit, but between 240 oC and 280 oC. The fracture location changed from the “soft” heat affected zones to the nugget. Furthermore, the weld exhibited a decrease in the Charpy impact adsorbed energy as compared to the weld unaffected parent metal. An increase in the temperature improved the adsorbed energy, while a temperature decrease promoted the brittleness and reduced the adsorbed energy. The flow contours, also called onion ring bands, present within the nugget, represented a preferential fracture path during impact. The high temperature treatments followed by water quenching did not significantly improved the resistance to impact.
Superplasticity of a Sc and Zr Modified Al-6%Cu Alloy Subjected to ECAE
Authors: Nikulin Ilya , Kaibyshev Rustam , Mironov Sergey , Sato Yutaka S. , Kokawa Hiroyuki , Motohashi Yoshinobu
Published: January 2010

Superplasticity in an Al-6%Cu-0.45%Mg-0.4%Mn-0.16%Sc-0.12%Zr alloy subjected to intense plastic straining through equal-channel angular extrusion (ECAE) was studied in tension at strain rates ranging from 5.6×10-4 to 5.6×10-3 s-1 in the temperature interval 350-450°C. The alloy had a non-uniform microstructure with an average crystallite size of 1.2 m. The volume fraction of high-angle grain boundaries was about 57%. In spite of small crystallite size the alloy shows moderate superplastic properties. The highest elongation-to-failures of 320% appeared at a temperature of ~425°C and an initial strain rate of ~1.410-3 s-1, where the strain rate sensitivity coefficient, m, was about 0.33. The relationship between superplastic ductilities and microstructure stability is analyzed.
Single Crystalline a-Axis Mg Doped ZnO Thin Films Prepared by Sol-Gel Technique for Optoelectronics Applications
Authors: Sonawane Bajirao K. , Bhole Mukesh P. , Patil Dnyaneshwar S.
Published: January 2010

Single crystalline a-axis Mg doped ZnO thin films (MgxZn1-xO) were successfully prepared by sol-gel spin coating method using Zinc acetate, Magnesium acetate as precursors with ethanol as a solvent. The prepared solutions were used to deposit the films on silicon (100) substrate for different mole concentrations (x = 0.1 to 0.33). All deposited films were annealed at 450 0C to get dense crystalline films. X-ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis by X-ray (EDAX), Fourier Transform Infrared Spectroscopy (FTIR), Ellipsometry and semiconductor characterization system with probe station were used to characterize the deposited films for structural, chemical, optical, mechanical and electrical properties. The intense absorption peak was observed in the IR spectra for all deposited films showing bond position of fundamental ZnO peak for all Mg mole concentrations. From the XRD spectra, it revealed that the deposited films were single crystalline and a-axis oriented. EDAX spectra clearly showed the peak of Mg along with Zn and O indicating the successful incorporation of Mg into the ZnO. The refractive index was successfully tailored from 1.6 to 1.11 corresponding to 0.1 to 0.33 Mg mole concentration. The refractive index was found to be decrease with an increase in Mg mole concentration. I-V characteristics shows decrease in current with increase in the Mg mole concentration. Significant effect was not observed on thickness of deposited films due to the varying Mg mole fraction. Through SEM image, it was noted that the uniform film of Mg doped ZnO was deposited on the silicon substrate. Our results explore the applicability of MgZnO as cladding layer material to form effective and efficient heterostructure with ZnO as an active layer for the optical wave-guide applications.
Growth of Cubic AlN Films on Sapphire(0001) with Atomic Scale Surface Smoothness by Pulsed Laser Deposition
Authors: Yoshitake Tomohiro , Yoshitake Tsuyoshi , Sumitani Kazushi , Ohtani Ryota , Nakagawa You , Mohri Satoshi , Nagayama Kunihito
Published: January 2010

We have previously reported that -AlN crystallites with diameters of 0.5–1 µm were occasionally grown on sapphire(0001) by pulsed laser deposition, which implied that the migration mobility of the species deposited on the substrate surface might be an insufficient for the film growth of -AlN. In the present study, in order to enhance the crystal growth of -AlN, sapphire(0001) substrates with an atomically smoothness (step-sapphire) were employed. The growth conditions of - and -AlN extended to higher nitrogen-pressures, as compared to those using normal surface sapphire(0001) substrates (normal-sapphire). This is due to the enhancement in the mobility of the deposited species on the substrate surface.
Effect of Nano-Crystallization on the Mechanical Properties of the (Zr53Cu30Ni9Al8)99.5Si0.5 Bulk Metallic Glass
Authors: Hsiao Z.W. , Fu C.C. , Tsai P.H. , Jang Jason S.C. , Jian S.R. , Huang J.C.
Published: January 2010

The (Zr53Cu30Ni9Al8)99.5Si0.5 bulk metallic glass (BMG) rods, 3 mm in diameter, with different crystallization fraction for compression test were prepared by isothermal annealing the as-cast BMG rods at the temperature in the middle of supercooled temperature region for different time period in vacuum, respectively. The result of compression test revealed that the fracture strength of these samples increases with the crystallization ratio at the beginning, then decreases rapidly at 40 vol.% crystallization fraction. In addition, the best mechanical performance with 1970MPa yield strength and 3 % plastic strain occurs at the sample with 30 vol.% nanocrystalline phase (with an average size about 50 nm). This was suggested these homogeneous distributed nanocrystals which embedded in the matrix may act as obstacles to branch the primary shear band into multiple shear band and result in improving the ductility.
Doping of ZnO Thin Film with Eu Using Ion Beams
Authors: Ionescu Mihail , Photongkam P. , Yu D. , Siegele R. , Li S. , Cohen D.D.
Published: January 2010

Modification of electric and magnetic properties of ZnO thin films was achieved by low energy Eu ion irradiation. The desired doping levels as well as the depth distribution of the dopant was controlled by the ion energy and the ion flux, following a simulated interaction between the doping ion and the host ZnO matrix of epitaxial ZnO (0001) films of approximatelly 200nm, grown on c-Al2O3 by PLD. The properties of the doped ZnO film depend in a critical way on the homogeneity of the doped ions throughout the entire film. The doping levels and the depth distribution of dopants were measured by elastic recoil detection analysis (ERDA). The results show a uniform depth distribution of Eu, as well as some level of Al diffusion from the substrate and the presence of some low levels of H, N and O.
PACS code: 68.49Sf; 74.78Bz
Multiaxial Forging of Super Duplex Steel
Authors: Kleber Siegfried , Hafok Martin
Published: January 2010

The investigated super duplex steel belongs to the group of stainless steels which exhibits an austenitic-ferritic microstructure with a phase fraction of about 50% austenite and 50% ferrite. The alloy shows excellent general corrosion resistance as well as a good resistance against stress corrosion cracking, corrosion fatigue and erosion corrosion. Due to these outstanding properties, the super duplex alloy is used in components for sea or waste water applications and in the offshore and chemical industry. In addition, the investigated super duplex steel exhibits a good weldability and a high strength in comparison to pure austenitic steel grades
In order to optimize the production process and to provide a suitable microstructure to satisfy the customer’s requirements multiaxial forging test at various temperatures were performed in the Gleeble Maxstrain system. The force and the displacement after each anvil stroke were measured and used to distinguish the mechanical behaviour in the forging process at different thermal conditions. The recorded force and displacement is also compared with a multi step compression test to show the influence of change in the deformation direction. A certain number of samples were exposed an in-situ heat treatment after the deformation while other samples were immediately quenched after the forging to preserve the deformed microstructure, which was measured by optical microscopy and electron microscopy. Furthermore, electron back scatter diffractions scans were applied to characterize the degree of dynamic recrystallization during the forging process.
Next Decades’ Challenges for Terrestrial Vehicles’ Materials and Manufacturing to Reduce CO2 Emissions
Authors: Friedrich Horst E. , Steinle Philipp , Kopp Gerhard , Schöll Roland
Published: January 2010

The history of terrestrial transport systems on road and rail has always been influenced by material-related developments. These developments gave rise to various construction methods, taking into account the different requirements that transport systems had to fulfil and providing new approaches. The urgency of the CO2 problem will result in alternative power trains also establishing themselves on the market, in turn giving rise to new requirements and possibilities in the field of vehicle construction, over and above the established light weight design. Further development of materials is supported and supplemented by new material systems able to actively respond to the particular state of the system.
Recrystallization of Coarse-Grained Nb-Containing AISI-430 Ferritic Stainless Steel
Authors: Siqueira Rodrigo P. , Sandim Hugo Ricardo Zschommler , Oliveira Tarcisio R.
Published: January 2010

Ferritic stainless steels (FSSs) have excellent corrosion resistance and good mechanical properties. Applications include heaters, houseware, and automotive exhaust systems. Alloying, even in small amounts, affects the recrystallization behavior of FSSs by selective dragging or pinning effects. In the present study, we present the main results regarding the recrystallization of a coarse-grained Nb-containing AISI 430 ferritic stainless steel. The material was processed by hot rolling and further annealed at 1250oC for 2 h to promote secondary recrystallization. Following, the material was cold rolled to a 80% reduction in thickness and annealed at 400-1000oC for 15 min. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to characterize the microstructure. Recrystallization of this steel begins at 700oC. Important orientation effects were observed in both as-rolled and annealed conditions. Recrystallization kinetics was strongly dependent on the initial orientation of the coarse grains. Results show that grain boundaries, transition bands and coarse Nb(C,N) particles are preferential sites for nucleation at moderate annealing temperatures.
The Activity of Nitrogen in the Liquid Fe-N-Cr Alloy Based on the Non-Random Solubility Model by Schmid - Fetzer
Authors: Siwka J. , Hutny A.
Published: January 2010

The values of nitrogen solubility in the liquid Fe-N-Cr alloy and in liquid chromium were determined experimentally. The alloy of a chromium content of 8; 13; 18; 25; 35; and 69, respectively, and chromium of purity of 99.7 wt % were subjected to experiment. The original data on nitrogen solubility in liquid iron and the data on nitrogen solubility in liquid chromium (the authors' own studies) were converted in relation to the new standard state that is represented by pure nitrogen. The energy parameter, h Fe-Cr, was determined based on literature data.
Using the coefficient values for the Fe-Cr alloy, calculated on the basis of our own investigation results, the values of the energy parameter h were determined. The determined energy parameter h in the form of a temperature function relationship will enable the determination of the numerical values of the for the Fe-Cr alloy of any arbitrary composition.
Dissolution and Precipitation of Excess Phases in High-Nitrogen Steels
Authors: Svyazhin A.G. , Kaputkina Liudmila M.
Published: January 2010

Cast structure of ferric, austenitic and dual-phase high-nitrogen alloys and steels saturated with nitrogen at pressures of up to 3.2 MPa and solidified at cooling rates of 2 to 4•104 K/s has been investigated. Increasing the nitrogen concentration in the alloy and decreasing the cooling rate results in smaller nitrogen content in α and γ solutions and in larger content of crystallization nitrides.
Applicability of Adaptive Neural Networks (ANN) in the Extrusion of Aluminum Alloys and in the Prediction of Hardness and Internal Defects
Authors: Campana Rodrigo C. , Vieira P.C. , Plaut Ronald Lesley
Published: January 2010

Adaptive Neural Networks (ANN) can be used in the analysis of a complex panorama of interconnected input/output industrial data, even when they present substantial noise.
The ANN, despite presenting substantial mathematical complexity associated with non-linear parameterization (which includes transfer equations and corresponding “training”), are largely used under industrial conditions in several engineering areas (such as in steelmaking), with substantial success.
This work shows the applicability of the ANN in a specific case related to the analysis of internal defects of extruded aluminum sections (occurring both at the head and at the extrusion tail), and the associated bar hardness as a function of process parameters such as: billet temperature, extrusion ratio, ram speed and billet length.
Results were analyzed in terms of the adhesion to an ANN built upon the collected industrial data, as well as the relevance of each variable within the ANN.
Recent Progress and Application of Bainite Steels for High Strength Linepipe up to X120
Authors: Asahi Hitoshi , Shinohara Yasuhiro , Hara Takuya
Published: January 2010

For the constant transmission of gas through a pipeline, steel weight decreases linearly with an increase in the strength of the linepipe irrespective of pipe size and internal pressure. Thus, high-strength large-diameter linepipe up to X120 has been developed and is now being applied to reduce pipe costs, transportation costs and construction costs. To meet the excellent weldability and low production costs required for the linepipe application of bainite produced through using Thermo-Mechanical Control Processing (TMCP) from low carbon chemistry is essential. Dual phase steel made by means of the introduction of ferrite in the bainite matrix mitigates the inferior properties of bainite. Herein, the production parameters affecting the microstructure and the properties are overviewed.
Mn-Series Low Carbon Air Cooling Bainitic Steels Containing Niobium
Authors: Feng Chun , Bai Bing Zhe , Zheng Y.K. , Fang Hong Sheng
Published: January 2010

The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper.
The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical property of the thick plate (30mm) is: σb>1050MPa, σ0.2>700MPa, δ5>17%, Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4) It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5) Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6) This steel is with low production cost since the alloying element Mn is cheap.
Key Factors in Grain Refinement of Martensite and Bainite
Authors: Furuhara Tadashi , Takayama Naoki , Miyamoto Goro
Published: January 2010

Grain refinement in lath martensite and bainite structures, which is important for strengthening and toughening, are discussed in various aspects. Strain accommodation plays important roles to determine final crystal sizes of bainitic ferrite (BF) and martensite. There is strong variant selection of BF by natures of the austenite grain boundary where it nucleates. For small undercooling, such variant selection leads to coarse bainite block and packet sizes. More BF variants are formed by increasing undercooling, which leads to nucleation of BF variants of less potency, and by increasing strength of materials, which results in more self-accommodation of transformation strain due to suppression of plastic accommodation. In lath martensite, there seems to be similar variant selection at austenite grain boundaries. However, packet/block sizes in lath martensite decreases with an increase in carbon content because of more extensive self-accommodation due to lower transformation temperatures than bainite.
Cyclic Deformation and Fatigue Crack Behavior of Extruded AZ31B Magnesium Alloy
Authors: Morita Shigeki , Tanaka Shingo , Ohno Nobuyoshi , Kawakami Yuji , Enjoji Takashi
Published: January 2010

Pseudoelastic behaviors were observed in compressive and tensile loading-unloading tests at room temperature. The large anelastic strains were observed in compressive stress-strain hysteresis loops. The fatigue limit of axial load-controlled fatigue test at 107 cycles was 90MPa at room temperature. The deformation twins were observed in the specimen subjected to the higher stress amplitude of fatigue limit and free deformation twins were observed in the specimen subjected to the lower stress amplitude of fatigue limit. Stress-strain hysteresis loops were linear in tensile and compressive phases at the lower stress amplitude of fatigue limit and the complicated pseudoelastic deformations were observed in tensile and compressive phases at the higher stress amplitude of fatigue limit of axial load-controlled fatigue tests. Compressive mean strain generated by cyclic pseudoelastic deformations at the higher stress amplitude of fatigue limit. Fatigue cracks initiated at the secondary particle/matrix interface or broken secondary particle near the surface. Subsequently, small cracks tended to grow through transgranular.
Effect of Thermomechanical Processing Parameters on the Final Microstructure of Pipeline Steels
Authors: Mouriño Nuria Sánchez , Petrov Roumen H. , Bae Jin Ho , Kim Ki Soo , Kestens Leo A.I.
Published: January 2010

The phase transformation and the final microstructure were studied in a pipeline steel grade API-X80 by carrying out a number of physical simulations of the industrial hot rolling schedules. The deformation and the cooling parameters were simulated by means of hot torsion and dilatometry experiments. Torsion deformations in the same range as in the hot rolling schedule were applied in a multi-deformation cycle at various temperatures in the austenite region. Subsequently the following parameters were varied with respect to a reference status: the reheating temperature from 900 to 1200°C, the deformation step from 0.6 to 0.15 von Misses strain, the strain rate from 1 to 10 s-1, the inter-pass time from 0.4 to 2 s, the deformation temperature from 1,100 to 850°C, the cooling rate from 0.1 to 100°C/s and the cooling stop temperature from 650 to 25°C. The transformation product microstructures were observed with optical microscopy, scanning electron microscopy and electron backscatter diffraction.
The experimental data were used to study the microstructure evolution of none-deformed austenite and highly deformed austenite (Von Misses strain of 3.2), and the corresponding CCT diagrams were constructed. The detailed microstructure characteristics obtained from the present work as well as the data from the CCT diagrams for undeformed and deformed austenite could be used to optimize the mechanical properties, strength and toughness of pipeline steel grades by thermo-mechanical control process.
Formation of Martensite Austenite Constituent in Continuously Cooled Nb-Bearing Low Carbon Steels
Authors: Takayama Naoki , Miyamoto Goro , Kamikawa Naoya , Nako Hidenori , Maki Tadashi , Furuhara Tadashi
Published: January 2010

Fe-0.15%C-1.5%Mn-0.2%Si (Nb-free alloy) and Fe-0.15%C-1.5%Mn-0.2%Si-0.03%Nb (Nb-added alloy) were continuously cooled to room temperature at constant cooling rates in the range from 0.1 to 20K/s. At lower cooling rates, such as 0.1K/s, the Nb addition retards the ferrite transformation, resulting in a decrease in the transformation temperature and an increase in the volume fraction of bainite. The fraction of martensite-austenite constituent (MA) increases by the Nb addition and the largest fraction of MA, about 0.5 %, is observed in the Nb-added specimen cooled at 5K/s. In the specimens cooled at 5K/s, relatively coarse bainite without cementite precipitation is formed near the austenite () grain boundary in both alloys. Most of MA is localized between such relatively coarse bainitic ferrite (BF). On the other hand, MA is hardly observed in the bainite formed with cementite precipitation in  grain. Based on microstructure observation of the continuously cooled specimens down to intermediate temperatures followed by quenching, it is concluded that small-sized untransformed  near  grain boundary partly remains as MA whereas relatively larger untransformed  in the  grain decompose into bainite with cementite precipitation.
Effect of Cold Deformation on Thermal Stability of Bainite in Nb-Bearing Microalloyed Steels
Authors: Yang Shan Wu , Lv H.Q. , Zhang R. , He Y. , He Xin Lai
Published: January 2010

Bainite in microalloyed steel possesses excellent synthetic mechanical properties. However, it will probably evolve towards equilibrium microstructure when it is subjected to thermal disturbance. In addition, bainite frequently undergoes more or less deformation during manufacture of steel structure. In the present investigation, cold deformation test, isothermal heat treatment, hardness measurement, optical microscopy and transmission electron microscopy were employed to detect evolution behavior of bainite isothermally held below A1 temperature. It was found that hardness of samples drops in generally during the isothermal heat treatment. Meanwhile, bainite evolves gradually into polygonal ferrite. Cold deformation enhances the initial hardness of samples while it largely accelerates softening and evolution of microstructure towards equilibrium one during heating. Almost same effects are produced by tensile strain and compressive strain. Higher solubility product of carbon and niobium results in higher thermal stability of bainite. Cold deformation cause dislocations in bainitic laths to distribute heterogeneously and most dislocations pile up along boundaries. During isothermal holding, dislocations redistribute further followed by extending of low dislocation density areas across lath boundaries. Finally, polygonal ferrite nucleates in those areas and grows gradually.
Hot Deformation Behavior of Near-α Ti-Fe Alloy in (α+β) Two-Phase Region with Different Fe Content
Authors: Poorganji Behrang , Yamaguchi Makoto , Itsumi Yoshio , Matsumoto Katsushi , Tanaka Tomofumi , Asa Yusuke , Miyamoto Goro , Furuhara Tadashi
Published: January 2010

In the present study, microstructure evolution of Ti-Fe alloys with different Fe content between 0.2-1.5mass% during hot deformation in (α+β) two-phase region is studied with focusing on effect of phase volume fraction at different deformation temperatures and strain rates. Hot deformation was conducted on the specimens quenched after β solutionizing at 1173K for 1.2ks at 1108, 1073 and 948K, by uniaxial compression by 50% at various strain rates ranged from 1 to 10-4 s-1. Initial structures are (α+β) lamellar structures of fine interlamellar spacing and colony sizes. Increase in Fe content results in increasing the fraction of the β phase at the given deformation temperature. Either colony size or interlamellar spacing is coarser at higher temperatures. At the higher deformation temperature where β phase fraction is larger, dynamic recovery of β phase is a major deformation mechanism while at a lower temperature, i.e., a higher α fraction, dynamic recrystallization of α phase occurs predominantly. It is concluded that critical strain needed for occurrence of dynamic recrystallization is decreased by increasing fraction of the α phase at the same deformation temperature, i.e., by decreasing Fe content. Furthermore, by increasing strain rate grain size of the recrystallized α is decreased.
Investigation of Bar-Like Carbides in HR3C Boiler Steel
Authors: Cheng Shi Chang , Liu Zheng Dong , Bao Hang Sheng , Wang Jiing Zhong
Published: January 2010

After the heat treatment at 1200 oC 30 minutes followed by water cooling and 700 oC 4 hours for HR3C (S31042) boiler steel, the bar-like carbides precipitate in grain boundaries and within grains. It was found that the bar-like carbides nucleate in the grain boundaries and grew into grains in a parallel manner. With the help of TEM, the carbides were characterized to be M23C6, with a length of about 6μm and width of 0.6-0.8μm. Through observing crept specimens after testing at 700 oC, it was found that fine and dispersed MX (about 20nm) as well as dislocation walls exist inside grains, except bar-like and granular M23C6 carbide.
Design of Modern Steels for Automotive Application
Authors: Hofmann Harald , Heller Thomas , Sikora Sascha
Published: January 2010

Advanced high-strength steels offer a great potential for the further development of automobile bodies-in-white due to their combined mechanical properties of high formability and strength. New types of grades – multi-phase steels, superductile steels and density reduced steels – are under development at ThyssenKrupp Steel with tensile strength levels of up to 1000 MPa in combination with excellent formability for the high demands of cold formed structural automobile components. New forming technologies at increased temperatures – hot forming, semi-hot forming and superplastic forming - enable the processing of complex parts with extreme high strength. ThyssenKrupp Steel identifies potential future steels and technology concepts by technology monitoring and evaluates their potential for future applications in pre-development projects. University research institutions are significantly involved in this essential future oriented challenge. Seminal concepts are being implemented together with automotive manufactures by simultaneous engineering processes with coordinated phases of production and testing.
Refinement of CFB/M High Strength Steel Micro-Alloyed with Nb
Authors: Bai B.Z. , Yu Y. , Liu D.Y. , Gu J.L.
Published: January 2010

A novel carbide free bainite/martensite (CFB/M) high strength steel of 1500MPa grade is micro-alloyed with Nb in order to refine the microstructure and improve the toughness. After the steel containing Nb was forged, coarse microstructure and strong transmissibility of structure were found. It is suggested that the large numbers of precipitates of Nb(CN) in the steel makes the structure transmissibility more serious. After solution treatment at 1200°C, both complete annealing twice and isothermal treatment at 600°C twice can eliminate the structure transmissibility and refine the structure. Investigation on refinement of cycle phase transformation shows that excellent effect of the grain refinement is obtained when the heating velocity exceeds some threshold. In addition, the temperature of austenitizing is of little influences on the size of refined austenite grain.
Through Process Prevention of Recrystallization in Hot Formed Aluminium Structural Car Components
Authors: Sandvik Jon , Jensrud Ola , Gulbrandsen-Dahl Sverre , Hallem Håkon , Moe John Ivar
Published: January 2010

Aluminium is increasingly used in structural components in cars. The advantages are many, and recyclability, weight saving and energy absorption during impact and are often considered as the most important. There are also several disadvantages compared to iron and steel, i.e. material cost, low stiffness, lack of fatigue limit, high thermal conductivity, high thermal expansion coefficient, corrosion susceptibility and others.
To enhance the advantages and to minimize the disadvantages, several actions can be made. To prevent recrystallization is one of them, and has to be dealt with from the melt through all thermo-mechanical, mass reducing and assembly processes – “from the ore to the car”.
As recrystallization may reduce the static strength and fatigue life time in a finished component considerably, preventing recrystallization is as important as to optimize component geometry. Additionally, there is considerable risk of inter-granular cracking or melting during thermo-mechanical processing, especially those involving very high strain and forming temperatures above eutectics.
To prevent recrystallization, a well balanced budget on chemical composition, strain, strain rates and temperatures is essential. Examples of successes and failures are vital ingredients of the base of knowledge in development of highly utilized aluminium car components.
All process steps, from alloying and melt treatment of wrought aluminium alloys to the assembly of a finished component, can influence on product performance. AlMgSi1 alloys are used as examples in evaluating recrystallization in this paper. By focusing on recrystallization, other major factors influencing performance are not neglected, but not further discussed here.
Analysis of the Redundant Deformation Factor in the Axisymmetric Drawing of AISI 304 Stainless Steel Bars through Experimental Techniques
Authors: Siqueira Corrêa Elaine Carballo , Paulino Aguilar Maria Teresa , Cetlin Paulo Roberto
Published: January 2010

One of the most significant aspects of the axisymmetric drawing operation is the occurrence of non-homogeneous deformation in the cross section of the metal. This phenomenon is associated with an internal distortion process that takes place in the bar as it flows through the die, leading to the development of higher drawing forces and affecting the subsequent mechanical behavior of the material. An adequate analysis of the process and of the work hardening of the drawn metal, therefore, must involve a detailed study of the deformation features in the forming operation. In the present work, the deformation in the single-pass drawing of AISI 304 stainless steel bars was investigated through the evaluation of the relationship between the redundant deformation factor and the parameter . Two experimetal procedures were employed in the study: the visioplasticity and the stress-strain curves superposition techniques. The first one, previously considered as the method leading to the most realistic solutions to various forming processes, allowed the establishment of an increasing linear relationship between de redundant deformation factor and the parameter . A similar behavior was observed through the stress-strain curves superposition technique. In this case, however, the redundant deformation factor values were lower or higher than those obtained through visioplasticity according to the drawing conditions and more sensitive to variations of the parameter . The results were compared to those exhibited by the AISI 420 stainless steel, revealing the influence of the structural features on the behavior of the metal.
Numerical Simulation of Steel Flow and Behaviour of Non-Metallic Inclusions in the Six-Strand Tundish with Stopper Rod System
Authors: Cwudziński Adam , Jowsa Jan
Published: January 2010

The numerical modelling technique is successfully used for simulation of steel flow and behaviour of non-metallic inclusions in the tundish. The CFD (Computational Fluid Dynamic) method allows information on steel motion, flow, flow turbulence and steel temperature distribution in the tundish to be obtained. In the continuous steel casting process, where the tundish performs the function of a device batching steel to the mould, the monitoring of steel flow is very essential because steel flow has influence on the behaviour of non-metallic inclusions. The paper presents the results of computing simulation steel flow and flotation of non-metallic inclusions in the six-strand tundish with stopper rod system. The subject of simulation was a six-strand tundish unprovided with flow control devices. The tundish is used in the polish steel mill to process of continuous casting billets. The Fluent program was used for solved mathematical model of casting process. The numerical simulation of steel flow was performed for whole test facility without the “symmetry” boundary condition. As a results of numerical simulation maps of directions flow and temperature of steel, Residence Time Distributions curve type of (F) and (E) and distributions of non-metallic inclusions between slag phase and particular tundish outlets has been obtained.
Dissolution of Precipitates in Hot Rolled Low Mn, Ti Added Pipeline Steels
Authors: Dehghan-Manshadi Ali , Dippenaar Rian
Published: January 2010

The dissolution of different sulphides, carbides, carbo-sulphides and nitrides during re-heating of hot rolled low carbon, low manganese, titanium added steel have been studied using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analysis. In addition, the chemical composition and size distribution of the different precipitates have been determined before and after reheating to analyze the modification of these precipitates in the course of the reheating cycle.
The TEM and EDS analyses showed the presence of a wide variety of simple and/or complex precipitates in as rolled samples. The reheating of these samples to temperatures as high as 1350 °C, caused dissolution of most particles, although titanium nitride (TiN) did not dissolve even after reheating. By decreasing the reheating temperature more and more precipitates remained un-dissolved, but some spherodization occurred at higher temperatures.
Creep Behavior of an Oxide Dispersion Strengthened Iron with Ultrafine Grain Structure
Authors: Dudko Valeriy , Kaibyshev Rustam , Belyakov Andrey , Sakai Yoshikazu , Tsuzaki Kaneaki
Published: January 2010

The creep behavior of oxide-bearing Fe-0.6%O steel was studied in the temperature range of 550-700°C at stresses ranging from 100 to 400 MPa. The creep data showed high values of an apparent stress exponent n close to 16 for power-law creep. In addition the apparent experimental activation energy was much higher than that for the lattice diffusion in -iron. Analysis of creep data revealed that the deformation behavior was strongly affected by the threshold stresses, which are associated with the interaction between moving dislocations and fine incoherent oxide particles. Analysis of deformation behavior in terms of threshold stress leads the true stress exponent of 8; the activation energy for creep became close to value of activation energy for lattice diffusion at 700°C and for pipe-diffusion in the temperature range of 550–650°C.
Polynomial vs. Mechanism-Based Response Surface Analysis of the Thermomechanical Treatment of Al-Sn Alloys
Authors: Schouwenaars Rafael , Cortéz H. A. , Jacobo V. H. , Ortiz A.
Published: January 2010

The effects of strain, annealing time and temperature during the processing of an Al-Sn-based triboalloy were researched by response surface analysis. A second-degree polynomial in strain-time-temperature space was compared to a formulation based on generally accepted physical models for recrystallisation, recovery and grain growth, using the rule of mixtures for a microstructure consisting of recovered, recrystallised and second-phase grains. The polynomial approach provides interesting information on the role of rolling reduction in the optimisation of the alloy. The mechanism-based approach yields higher precision with less fitting parameters and provides insight into the relative importance of the physical phenomena involved in the processing of an alloy which has rarely been studied from the viewpoint of physical metallurgy.
Microstructure Evolution of C-Mn-Si-Al-Nb High-Manganese Steel during the Thermomechanical Processing
Authors: Dobrzański Leszek Adam , Grajcar Adam , Borek Wojciech
Published: January 2010

The aim of the paper is to determine the influence of hot deformation conditions on σ-ε curves and microstructure evolution of new-developed high-manganese C-Mn-Si-Al-Nb austenitic steel. The force-energetic parameters of hot-working were determined in continuous and multi-stage compression tests performed in a temperature range of 850 to 1100°C by the use of the Gleeble 3800 thermomechanical simulator. Evaluation of processes controlling work-hardening were identified by microstructure observations of the specimens water-quenched after various conditions of plastic deformation. Multi-stage compression tests with true strain of 0.29 permit to use the dynamic and metadynamic recrystallization for forming the fine-grained, austenite microstructure of steel in the whole range of deformation temperature.
Microstructure and Mechanical Properties of Cooled and Tempered Cu and Nb-Bearing Ultra-Low Carbon Steels
Authors: Guo Hui , Yao Zhi Qiang , Yang Shan Wu , He Xin Lai
Published: January 2010

To improve the toughness and weldability, the carbon content of the steels has to be deduced, and more and more attention has been attracted to the low carbon and ultra-low carbon steels. To strengthen the microstructure Cu and Nb-bearing steels are developed. However, the knowledge on influence of combined addition of Cu and Nb is still in lack. The microstructure and mechanical properties are studied in the 6-mm thick as-rolled and tempered ultra-low carbon steel plates with varied copper and niobium content. The microstructure and mechanical properties are studied in the 6-mm thick as-rolled and tempered ultra-low carbon steel plates with varied copper and niobium content. The experimental results show that if niobium is added without copper, the increase of niobium addition does not have a significant influence on the phase transformation and mechanical properties before tempering. The strength and toughness of those copper-free niobium steels do not vary significantly after tempered at different temperatures, while the strength of niobium steels with 1.8% copper added increases after tempered in the range of 450-650°C and reaches a peak at 500-550°C. If combined with 1.8% copper, the increase of niobium addition from 0.08% to 0.16% improves the hardenabililty and strength significantly, and the strength peak after tempering moves to a lower temperature. The strength of air-cooled niobium steels with 1.8% copper added is usually higher than those water-cooled, while after tempered at a proper temperature, the strength of the latter becomes higher than the former.
Microstructure and Mechanical Properties of Ultra-High Strength Steel Plates with High Deformability
Authors: Hwang Byoung Chul , Lee Chang Gil , Lee Sung Hak
Published: January 2010

High deformability has been considered as a critical factor of ultra-high strength steel plates subjected to compressive, tensile, and bending deformation induced by large ground movements. In this paper, various dual phase microstructures consisting of soft ferrite and strong low-temperature transformation phases without deformation in the (austenite + ferrite) two-phase temperature region after controlled rolling were introduced and then the mechanical properties were discussed with emphasis on deformability such as yield ratio and uniform elongation. Ultra-high strength steel plates fabricated by a modified thermo-mechanical control process showed lower yield ratio of under 0.75 and higher uniform elongation of 5% as a minimum, as compared to commercial API X100 and X120 grade pipeline steels, without much sacrifice of Charpy impact properties because of an appropriate formation of soft ferrite and strong low-temperature transformation phases.