bluuebunny/crossref_metadata_2025 huggingface dataset:
Crack-Less Wafer-Level Packaging Using Flash Heating Technique for Micro Devices
Authors: Namazu Takahiro , Ohtani Kohei , Yoshiki Keisuke , Inoue Shozo
Published: January 2012

In this article, a new technique for controlling crack position and its propagation direction in solder-bonding using Al/Ni exothermic reaction is described. Sputtered Al/Ni multilayer film is able to produce heat instantly by its self-propagating exothermic reaction, and the reactive film can be used as heat source for solder-bonding. During the reaction, however, volume reduction by approximately 12% occurs due to crystal structural change from fcc to bcc and lattice-spacing reduction. Consequently, cracks are produced in the reacted NiAl structure. The cracks negatively affect the strength of the bonded system. We have found a new technique for controlling crack position and its propagation direction. Multiple ignitions for reaction demonstrated that cracks in reacted NiAl film can be controlled. When applying the flash heating technique to wafer-level bonding, cracks are probably produced. If cracks can be fabricated on dicing cut lines by using the simultaneous multiple reactions technique, crack-less solder-bonded Si hermetic packages would be realized.
Effects of Co Addition on Crystal Structure, Thermal Stability and Magnetic Properties of Ni-Mn-Ga Ferromagnetic Shape Memory Alloys from First-Principles Calculations
Authors: Bai Jing , Raulot Jean Marc , Zhang Yu Dong , Esling Claude , Zhao Xiang , Zuo Liang
Published: January 2012

The effect of Co addition on the properties of Ni8-xMn4Ga4Cox (x=0, 0.5, 1, 1.5 and 2) ferromagnetic shape memory alloys are systematically investigated by means of the first–principles calculations within the framework of density functional theory (DFT) using the Vienna abinitio software package (VASP). The formation energy results indicate that the added Co preferentially occupies the Ni sites in Ni2MnGa alloy. With the increase of the Co content, the optimized lattice parameters of the parent phase decreases regularly, whereas the lattice parameter a of the martensite increases and c decreases, thus leading to a decrease of the c/a ratio. The effects of Co addition on phase stability of the paramagnetic and ferromagnetic austenite are displayed. The difference in the magnetic properties in the investigated series can be explained from the electronic density of states analysis. The aim of this paper is to provide theoretical guidance for the development of new promising ferromagnetic shape memory alloys with optimized properties.
Phase Transformation in Fe Alloys Induced by Surface Treatment
Authors: Sato Hisashi , Nishiura Takayuki , Miura-Fujiwara Eri , Watanabe Yoshimi
Published: January 2012

Difference of the phase transformation behavior at deformation-induced layer depending on surface treatment methods was investigated using Fe-33mass%Ni alloy. As specimens, two kinds of specimens were prepared. One specimen has austenite (γ) single structure, and the other specimen consists of both martensite (α’) and γ phases. Using these specimens, shot-peening tests were performed, and then phase transformation behavior induced by the shot-peening was compared with that by sliding wear reported in previous literature. The deformation-induced layer induced by shot-peening has very fine microstructure consisted of both α’ and γ phases. The microstructure in the deformation-induced layer formed by shot-peening becomes similar with increasing duration of shot-peening regardless of initial microstucture. On the other hand, the deformation-induced layer induced by sliding wear is reported to have γ single structure regardless of initial microstructure. This microstructural difference between shot-peening and sliding wear comes from the difference of heat generation during the surface treatment. Therefore, it is concluded that phase transformation behavior in deformation-induced layer depends on surface treatment method.
Development of Numerical Tool for Analysis of Microstructural Fracture Behavior in Smart & Intelligent Materials
Authors: Serizawa Hisashi , Tomiyama Seigo , Hajima Tsuyoshi , Murakawa Hidekazu
Published: January 2012

As a numerical tool for examining the microstructural fracture behavior in the smart and intelligent materials, a finite element method with the interface element was developed and the applicability of this method was studied through the serial computations using virtual polycrystalline models. As the results assuming the influence of grain orientation on the grain boundary, it was found that the anisotropic mechanical property of grain boundary (interaction between opening and slipping deformations) would be a dominant factor of the fracture process. Also, by employing the theory of crystal plasticity for the mechanical property of grain, it was revealed that the stress concentrations caused by both the mismatch between neighbor grains and the slipping at grain boundary could be demonstrated by using this method.
Electrochemical Characteristics of 410 Stainless Steel Produced by MIM Process through EIS Method under SSRT Test
Authors: Sunada Satoshi , Nunomura Norio , Majima Kazuhiko
Published: January 2012

In this experiment two kinds of 410L stainless steel, i.e., the first one is prepared by the I/M process and the second one is prepared by MIM process were used, and their corrosion behavior under stress in deionized water and the aqueous solution of 0.01kmol·m-3HCl+1.72mol·m-3MgCl2 (pH=2.33) has been investigated by Electrochemical Impedance Spectroscopy (hereafter shortened as EIS) under Slow Strain Rate Tensile (hereafter shortened as SSRT) test. The charge transfer resistance (Rct) of the I/M specimen is larger than that of the MIM specimen irrespective of under stress or non-stress, which means that the I/M specimen has the better corrosion resistance than the MIM specimen in the 0.01kmol·m-3HCl+1.72mol·m-3MgCl2 (pH=2.33) solution. It was also confirmed from the fracture surface observation that hydrogen embrittlement occurred on the MIM specimen in the aqueous solution of 0.01kmol·m-3HCl+1.72mol·m-3MgCl2 (pH=2.33). This result would be confirmed to be due to the existing impurities and defects in the MIM specimen.
Metal-Containing DLC: Toward a Smart Coating on Smart Materials
Authors: Takagi Toshiyuki , Takeno Takanori , Miki Hiroyuki , Luo Yun
Published: January 2012

NiTi shape memory alloys (NiTi-SMA or Nitinol) have successful application thanksto their excellent and unique material properties. However, considering the practical applicationto human body, elution from the toxic Ni ions into human body should be taken into account.Many researchers have dealt with the issue and already proposed various surface treatmenttechniques including the surface oxidation and ion implantation.Our focus is to enhance thefunctionality of Nitinol. We have been developing the smart sensor utilizing metal-containingDiamond-like Carbon (Me-DLC) thin coating. Emphasis can be made on the unique propertiesof Me-DLC deposited on the Nitinol. Strong adhesive strength has been obtained in Me-DLCand Nitinol system. In this paper, we propose a novel Me-DLC coating with multifunctionalityof the suppression of the toxic Ni ions. The paper includes deposition technique, performanceof the coating concerning adhesive strength and suppression of the toxic Ni ions, and ﬁnallymultilayered structure aiming at multifunctionality.
The SMA: An Effective Damper in Civil Engineering that Smoothes Oscillations
Authors: Torra Vicenç , Auguet Carlota , Carreras Guillem , Dieng Lamine , Lovey Francisco C. , Terriault Patrick
Published: January 2012

The properties of SMA (Shape Memory Alloys, smart materials) are associated to a first order phase transition named martensitic transformation that occurs between metastable phases: austenite and martensite. At higher temperature phase or at lower stress the austenite is the metastable phase. The martensite appears at lower temperature phase or higher stresses. The hysteresis of the transformation permits different levels of applications, i.e., in their use as a damper. Two types of applications can be considered in damping of structures in Civil Engineering. The first one is related to diminishing the damage induced by earthquakes. The second one is a reduction of oscillation amplitude associate to an increase of the lifetime for the stayed cables in bridges. Different fundamental behavior of the SMA needs to be guaranteed in each case.
Effect of Third Elements on Pseudoelasticity in Fe3Ga Alloys
Authors: Yasuda Hiroyuki Y. , Furuta Tsuyoshi , Maruyama Takenori
Published: January 2012

Pseudoelasticity of Fe3Ga polycrystals doped with third elements (Ti, V, Cr, Mn, Co, Ni, Si, Ge) was examined. Fe3Ga polycrystals with the appropriate heat treatment were found to exhibit large pseudoelasticity based on reversible motion of dislocation dragging an antiphase boundary (APB). In Fe3Ga crystals with the D03 superlattice structure, paired 1/4<111> superpartial dislocations mainly moved dragging the next-nearest-neighbor APB during loading. During unloading, the APB pulled back the superpartial dislocations resulting in the pseudoelasticity. The D03 ordered phase also developed in Fe3Ga polycrystals with 2at% of the third elements. However, the strain recovery of Fe3Ga polycrystals depended strongly on third element. Fe3Ga polycrystals doped with 2at% of Mn, Cr and Co demonstrated large pseudoelasticity. In contrast, the other doped elements decreased the amount of strain recovery. The frictional stress of 1/4<111> superpartial dislocations and the back stress due to the APB, acting on the dislocations, changed by doping the third elements, which was closely related to the pseudoelastic behavior. It is also noted that there was a good correlation between the APB back stress and the ordering temperature from the B2 to D03 phase.
Embrittlement of a High Manganese TWIP Steel in the Presence of Liquid Zinc
Authors: Beal Coline , Kleber Xavier , Fabrègue Damien , Bouzekri Mohamed
Published: January 2012

In the past decade, new steels have been developed for the automotive industry in the framework of environmental requirements. Among them, high manganese austenitic steels combining exceptional properties of strength and ductility are particularly promising. These exceptional properties stem from a fully austenitic structure at room temperature and a twinning deformation mode in addition to the classical mechanism of dislocation gliding, known as the TWinning Induced Plasticity (TWIP) effect. In this study, the cracking resistance of the Fe22Mn0.6C TWIP steel was investigated in relation to the liquid metal embrittlement (LME) phenomenon. Indeed, liquid zinc has been found to have an embrittling effect on such steels. Electro-galvanized specimens were subjected to hot tensile tests using Gleeble® thermo-mechanical simulator. The influence of different parameters such as temperature and strain rate on embrittlement was studied. The results show that this steel can be embrittled by liquid zinc within a limited range of temperature depending on strain rate. A critical stress for cracking has been defined for each embrittlement condition.
The Formation of Ultrafine Ferrite and Low Temperature Bainite through Thermomechanical Processing
Authors: Beladi Hossein , Timokhina Ilana B. , Hodgson Peter
Published: January 2012

In the current study, a novel approach was employed to produce a unique combination of ultrafine ferrite grains and low temperature bainite in a low carbon steel with a high hardenability. The thermomechanical route included warm deformation of supercooled austenite followed by reheating in the ferrite region and then cooling to bainitic transformation regime (i.e. 400-250°C). The resultant microstructure was ultrafine ferrite grains (i.e. <4μm) and very fine bainite consisting of bainitic ferrite laths with high dislocation density and retained austenite films. This microstructure offers a unique combination of ultimate tensile strength and elongation due to the presence of ductile fine ferrite grains and hard low temperature bainitic ferrite laths with retained austenite films. The microstructural characteristics of bainite were studied using optical microscopy in conjunction with scanning and transmission electron microscopy techniques.
Effect of Wall Thickness Transitions on Texture and Grain Structure in Additive Layer Manufacture (ALM) of Ti-6Al-4V
Authors: Antonysamy Alphons A. , Prangnell Phil B. , Meyer Jonathan
Published: January 2012

In titanium alloys it is known that in bulk sections the solidification conditions in ALM commonly lead to undesirable, coarse, columnar β grain structures. Here, we have investigated the effect of build geometry on the grain structure and associated texture in Ti-6Al-4V ALM components produced by Selective Electron Beam Melting (SEBM). Through reconstruction of the primary β-phase, it has been confirmed that in thick sections large columnar β grains grow with a strong <001>β fibre texture, although there is a significant skin effect. In contrast, in thin walls nucleation off the surrounding powder and growth inwards dominates. Local heterogeneities are also observed within section transitions. It is shown that the weaker α transformation texture arises from a random distribution across the possible habit variants.
Dual Phase Steel Characterization for Tube Bending and Hydroforming Applications
Authors: Oliver Chad , Bowers Randy J. , Green Daniel E.
Published: January 2012

The behaviour of dual phase steel tubes at 600, 780, and 980 MPa strength grades undergoing rotary draw bending and pressure sequence hydroforming is examined. Bending was performed using three different bend ratios. Principal strains were measured at several locations on each tube. It was found that the level of strain experienced by the tubes was independent of steel grade. The outcome of the bending process was stochastic in nature; for a given steel grade and bend ratio, some tubes were successfully formed, while others experienced failure. The proportion of failed tubes was found to increase with higher strength steel grades and tighter bend ratios. Metallographic samples from the extrados of the bent tubes revealed that many of the same microstructural features affecting strength and elongation in uniaxial tensile testing, namely martensite banding and non-metallic inclusions, affected dual phase steel tubes undergoing rotary draw bending. Additionally, a nanoindentation technique was investigated to determine the potential for more detailed microstructural characterization.
Thermo-Mechanical Behaviour of Dual-Phase Steels in Various Structural Morphologies: Experiments and Modelling
Authors: Buchmayr Bruno , Antretter Thomas
Published: January 2012

The thermo-mechanical behaviour of the hot rolled dual-phase steel 10MnSi7 has been determined as a function of temperature and time within the two-phase field α+γ as well as at lower deformation temperatures down to Ms-temperature. The corresponding microstructures, phase hardness, state of recrystallisation have been determined using quantitative metallography. Using this information, a finite element model of a representative volume element (RVE) has been set up. Each element represents a subdomain of a grain that transforms according to the kinetics found in the measurements. The RVE has been subjected to the same loading history as in the accompanying experiments and the overall stress-strain response is monitored during ongoing transformation. The effect of a preferred orientation of the two phase structure has been studied taking into account the effects of a significant plastic deformation. The model is validated by comparison with the experimental evidence.
Metallurgical Design of High Strength/High Toughness Steels
Authors: di Schino Andrea , Guagnelli Mauro
Published: January 2012

The proper balance between yield strength, YS, and ductile to brittle transition temperature, DBTT, has been the main concern during development of high strength engineering steels and the effect of microstructure on impact toughness has attracted a great attention during the last decades. In this paper a review concerning the relationship between strength and toughness in steels will be presented and the effect of different microstructural parameters will be discussed, aiming to improve such properties in designing new high strength steels. Complex microstructures, obtained by quenching and tempering (Q&T) and thermo-mechanical (TM) processing are considered. The steels are low/medium carbon steels (C=0.04%-0.40%) with yield strength in the range YS=500-1000 MPa. Results show that the strength and the impact toughness behaviour are controlled by different microstructural parameters and not, as in the case of polygonal ferritic steels, by the same structural unit (the grain size) and that a “fine” microstructure is required in order to achieve high levels of both strength and toughness. The metallurgical design of high strength steels with toughness requirements is discussed using the same approach for both Q&T and TMCP processes.
Mechanical Properties of Ultra Fine Particle Dispersion Strengthened Ferritic Steel
Authors: Funakawa Yoshimasa
Published: January 2012

The influence of carbides diameter on the mechanical properties of the ferritic steel that was strengthened by the interface precipitated carbides in rows was investigated. Low carbon steel containing titanium as much as carbon in atomic concentration was induction-melt and hot-rolled, followed by the soaking at some temperatures to obtain completely transformed ferrite in which fine carbides precipitated. Lowering holding temperature resulted in fine carbide generation and reduction of the row spacing. Yield strength significantly increased with the decrease in the carbide diameter. The amount of the particle dispersion strengthening was close to the calculation result according to Ashby-Orowan Mechanism. On the other hand, elongation slowly decreased. The decrease in elongation is caused by the reduction of the uniform-elongation. Local elongation did not change by the change of the diameter of the fine carbides in the matrix since voids in the specimen were generated not besides fine carbides but beside large TiN during tensile test.
Development of Reduced Rolling Process for Steel Plate
Authors: Gao Xiu Hua , Lan Hui Fang , Du Lin Xiu , Qiu Chun Lin
Published: January 2012

The low cost Q460 and Q550 steel plates were produced in the 4200mm wide and heavy plate mill using Normal Hot Rolling and High Rate Cooling (NHR+HRC) process. The effect of both rolling processes on microstructure and mechanical property was studied. The results indicate that new type process can realize the good match between microstructure and mechanical properties. Meanwhile the new technology can short rolling time, reduce alloying addition, and improve the output of mill, it is also promote iron and steel industry developing continuously.
Linear Friction Welding of a Forged Near-α Titanium Alloy
Authors: Dalgaard E. , Wanjara Priti , Gholipour Javad , Jonas John J.
Published: January 2012

IMI834 (Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si) is a high-tech near-α titanium alloy with improved creep resistance and mechanical property retention at temperatures up to 600°C [1]. It is used in the aerospace industry for compressor disks and blades due to its excellent balance between creep resistance and fatigue strength [2]. The linear friction welding (LFW) behaviour of IMI834 displaying an initial bimodal α+β microstructure was investigated using varying axial pressures during welding. Electron backscatter diffraction (EBSD) was used to characterize the texture and phase fraction of the welded IMI834 samples in the weld zone (WZ) and thermomechanically affected zones (TMAZ) in relation to the base material. Based on microhardness evaluation of the weldments, the WZ was determined to be slightly harder than the base material.
Effect of Coiling Temperature on Kinetics of Austenite Formation in Cold Rolled Advanced High Strength Steels
Authors: Mohanty R.R. , Girina O.A.
Published: January 2012

A systematic experimental investigation was conducted using lab processed low carbon 0.08C-2.0Mn-Cr-Mo steel microalloyed with Ti/Nb to evaluate the influence of initial hot-rolled microstructures on the kinetics of austenite formation and decomposition after cold-rolling and subsequent annealing. Coiling temperature as a major hot rolling parameter was used to obtain different types of hot-rolled microstructures. Dilatometer and continuous annealing simulator were employed for austenite formation studies and annealing simulations, respectively. It was found that the coiling temperature affects the processes occurring during heat treatment in continuous annealing lines of full hard material: ferrite recrystallization, austenite formation during continuous heating and austenite decomposition during cooling. A decrease in coiling temperature accelerates the recrystallization of ferrite and nucleation of austenite, which results in formation of refined ferrite-martensite structure. The effect of initial hot rolled structure on final mechanical properties after continuous annealing was also investigated.
Study of the Microstructure and Strain Induced Precipitation during Thermomechanical Processing of Low Carbon Microalloyed Steels
Authors: Gómez Manuel , Valles Pilar , Medina Sebastián F.
Published: January 2012

A series of anisothermal multipass hot torsion tests were carried out to simulate hot rolling on three high-strength low-carbon steels with different amounts of Mn, Mo, Nb and Ti and designed for pipeline construction. Mean Flow Stress was graphically represented against the inverse of temperature to characterize the evolution of austenite microstructure during rolling. The effect of austenite strengthening obtained at the end of thermomechanical processing on the final microstructure obtained after cooling was studied. Higher levels of austenite strengthening before cooling promote a refinement of final microstructure but can also restrict the fraction of low-temperature transformation products such as acicular ferrite. This combined effect gives rise to a wide range of final microstructures and mechanical properties depending on the composition, processing schedule and cooling rates applied. On the other hand, the precipitation state obtained at diverse temperatures during and at the end of hot rolling schedule was evaluated by means of transmission electron microscopy (TEM) in two microalloyed steels. It was found that two families of precipitates with different morphology, composition and mean size can coexist in microalloyed steels.
Influence of Nb Microaddition on a Microstructure of Low-Alloyed Steels with Increased Manganese Content
Authors: Grajcar Adam , Lesz Sabina
Published: January 2012

The present study is a first step of a project to obtain thermo-mechanically processed fine-grained increased Mn content TRIP steels with large fractions of retained austenite. Two 0.17C-3Mn-1.6Al-0.2Si-0.2Mo steels with and without Nb microaddition were produced in a vacuum induction furnace. The influence of Nb microaddition on a macrostructure, a grain size and hot-working behavior were examined. The steels are characterized by a slight macrosegregation of Al in the as-cast state, minimized for a Nb-microalloyed steel. After hot forging refined bainitic-martensitic structures with large fractions of γ phase obtained. The steel microalloyed with Nb has finer granules of retained austenite at comparable fractions of this phase. The force-energetic parameters of hot-working were determined in an uniaxial hot-compression test at temperatures of 1150 and 950°C and strain rates from 0.1 to 10s-1. The Gleeble 3800 thermomechanical simulator was used. The hot-working behaviour of the investigated steels is challenging because of higher flow stresses and εmax strains compared to conventional TRIP steels with lower Mn contents.
Quality Analysis of Pig Iron Produced in One of Polish Steelworks
Authors: Kardas Edyta
Published: January 2012

The quality of pig iron from the point of view of the customer, that is steel plant, is one of main factors affecting the quality and cost of steel production. Chemical composition and temperature of pig iron is among the parameters taking into consideration. The constancy of these parameters can result in steelmaking process on optimal level. The paper presents quantitative and quantitative analysis of pig iron produced in one of Polish steelworks. Analysis of the basic quality parameters of pig iron: the content of basic elements will be made. In the analysis statistical methods and quality tools will be applied.
Improvement of Rolling Contact Fatigue Life of Bearing Steel by Quenching and Partitioning Process
Authors: Kim Kwan Ho , Lee Jae Seung , Lee Duk Lak
Published: January 2012

Over the decades, the rolling contact fatigue life of bearing steels has been enhanced mainly by the decrease in total oxygen content in the steels which was accomplished by improving steelmaking processes or facilities. However, it has almost been kept constant in the level of 5 ppm since 1990s and, therefore, it is necessary to find out other methods to enhance the RCFL. It is a well-known fact that the RCFL of bearing steels is maximized with the adequate amount of retained austenite and increasing silicon content results in the increase of the resistance to softening during tempering. In the present study, in order to take advantage of the effects of retained austenite and increasing silicon content, a new through-hardening heat treatment, quenching and partitioning (Q&P), has been chosen in place of the conventional quenching and tempering. One of the distinct differences between tempering and partitioning is no fine carbide precipitation during partitioning, leading to the stabilization of retained austenite due to the diffusion of carbon atoms from martensite, which can be realized by increasing silicon content. On the other hand, the increase of silicon content retarded the spheroidization behavior of cementites, requiring higher annealing temperature to assure the complete spheroidization. A new high carbon chromium bearing steel through-hardened by Q&P process showed superior RCFL characteristics to the conventional steel and process.
The Effect of Time and Temperature Variations during Isothermal Annealing on the Mechanical Properties of High Carbon Bainitic Steel
Authors: Koczurkiewicz Bartosz
Published: January 2012

The industrial development require new materials characterized highest mechanical properties. The conditions of thermo-mechanical treatment proved to highest level of mechanical properties for steels. Another method of making strong materials is to reduce the scale of the microstructure using heat treatment [1]. The paper presents the results of investigation into the effect of time and temperature variations during isothermal annealing on the mechanical properties of high carbon (c.a. 0,8%C) bainitic steel. Chemical composition of that steel (addition Si, Mn, Mo and Cr) obtain high level of tensile strength and good plastic properties. The analyzing of published results of researches of high carbon bainitic steels shown, that transformation of bainite can take between 2 to 60 days within the temperature range 125÷325°C [2,3] Based on results of researches of investigated steel a isothermal annealing in temperature range 200÷300°C were done. The experiments were done for 24, 50 and 100 hours of annealing. After that the mechanical tests were done. A Zwick Z100 testing machine was used for tests. The force and elongation values were recorded. On their basis, the proof stress and tensile strength of the steel tested were determined as a function of annealing temperature. The microstructure were determinated too.
The Effect of Coke Quality on Blast Furnace Working
Authors: Konstanciak Anna
Published: January 2012

The analysis of coke quality and the effect of coke quality on blast furnace process was presented in this paper. The mechanical properties of cokes was determined by the MICUM method, the same coke samples were hot tested in the blast-furnace pre-tuyère chamber model at the Department of the Extraction and Recycling of Metals of the Czestochowa University of Technology to determine their thermo-abrasiveness ξ. Moreover, the permeability of the column of materials in the blast furnace during the use of those cokes was determined. The permeability of the materials column characterizes the “quality” of the materials, including the coke. Separating the coke features in this characteristics is possible with the remaining charge and technological conditions being stabilized. However, the high variability of charge conditions in the blast-furnace under examination distorts the existing permeabilities. Nevertheless, the dependence of the permeability on thermo-abrasiveness was “physically” correct, i.e. it decreased with increasing thermo-abrasiveness ξ, despite the small value of the coefficient of significance of this relationship.
Innovations in Simulation of Microstructure Developments
Authors: Kruse Michael , Schuck Matthias , Borowikow Alexander
Published: January 2012

Today almost all steel production fields use process models on the basis of analytic and numeric simulations. Planning and implementation of modern production in plants strategies can no longer be imagined without simulations in almost all fields of long and flat steel production. For the plant engineering and construction industry, planning of transformation processes and rolling mills can hardly be imagined without the use of modern simulation technology. The possibilities range from the simulation of material transformation behavior to the whole rolling process, extending to the load effected on units and plants as well as the projection of microstructure and material properties when applying different rolling technologies. Thus simulation models increasingly contribute to support future-oriented process development and material related optimization.
Influence of Temperature on Strain Induced Precipitation Kinetics in Microalloyed Steels
Authors: Medina Sebastián F. , Quispe Alberto , Gómez Manuel
Published: January 2012

Starting from the expression of Dutta and Sellars for the beginning of strain induced precipitation in microalloyed steels, the influence of temperature on t0.05 parameter has been studied. Although the equation given by these authors reproduces well the typical “C” shape of the curve of precipitation start time Ps, the expression is not reliable for all cases. The precipitation-time-temperature (PTT) diagrams have been plotted thanks to a new experimental study carried out by means of hot torsion tests on approximately twenty microalloyed steels having different contents of Nb, V and Ti. Mathematical analysis of results recommends the modification of some parameters such as supersaturation ratio (Ks) and constant B, which is no longer a constant but a function of Ks when the latter is calculated at the nose temperature (TN) of curve Ps. The value of parameter B is deduced from the minimum point or nose of the Ps curve, where ∂t0.05/∂T is equal to zero, and it can be demonstrated that B cannot be a constant. The new expressions for these parameters derive from the latest studies developed by the authors and this work supposes an attempt to improve the model. The expressions are now more consistent and predict with remarkable accuracy the PTT curves.
Low C High Mn Cold Rolled TWIP Steel: Kinetics of Isothermal Recrystallization
Authors: Melo Tulio M.F. , Ribeiro Érica , Dutra Lorena , Santos Dagoberto Brandão
Published: January 2012

The increasing demand, mainly from the automobile industry, for materials which combine high strength, high ductility and low specific weight makes steels with the TWIP (TWinning Induced Plasticity) effect a promising material to meet these requirements. This work aimed to study the kinetics of isothermal recrystallization of a TWIP steel (C-0.06%, Mn-25%, Al-3%, Si-2%, and Ni-1%) after cold rolling. The steel was hot and cold-rolled and then annealed at 700°C with soaking times ranging from 10 to 7200 s. Microstructural analysis was performed using light (LM) and scanning electron microscopy (SEM). Furthermore, quantitative metallography was performed in order to evaluate the recrystallized volume fraction and grain size. A JMAK based model was applied to describe the nucleation grain growth process. The restoration of the steel was also evaluated by microhardness tests. A complete recrystallization after 7200 s at 700°C was observed. It was found that with increasing annealing times, the recrystallized volume fraction also increases, while the nucleation and growth rates decrease, in agreement with the results for plain carbon steels.
Fracture Behavior Transition by Change of Strain Rate in Dislocation-Induced Si Steels
Authors: Mizuguchi Takashi , Ueji Rintaro , Miyagawa Hayato , Tanaka Yasuhiro , Shinagawa Kazunari
Published: January 2012

The fracture behavior transition due to the change of strain rate in 5%Si magnetic steel with dislocation microstructures was studied. The Si steel was multi-passed rolled at 800°C to a various reductions up to 50%. The room temperature tensile deformation was conducted at various strain rates from 10-5/s to 100/s. All rolled steels were fractured in ductile manners with local elongation (necking) at slower strain rate. When strain rate was faster, the local elongation disappeared and the fracture manner was turned to brittle. The strain rate at which fracture mechanism changed from ductile to brittle increased with the increasing of the reduction. On the other hand, the almost fully recrystallized Si steel was fractured in the brittle manner at any strain rate and the transition strain rate was not found. The fractured tensile specimen with no local elongations contains deformation twins; whereas these deformation twins were not observed in the fractured specimen with local elongations. This result indicates that dislocation structure evolved during rolling suppressed the twinning and that the dislocation structure is effective for the enhancement of toughness in Si steel.
The Stacking Fault Energy and its Dependence on the Interstitial Content in Various Austenitic Steels
Authors: Mujica Lais , Weber Sebastian , Theisen Werner
Published: January 2012

The stacking fault energy (SFE) is an intrinsic property of metals and is involved in the deformation mechanism of different kind of steels, such as TWIP (twinning induced plasticity), TRIP (transformation induced plasticity), HNS (high nitrogen), and high strength steels. The dependence of the SFE on the content of interstitial elements (C, N) is not yet fully understood, and different tendencies have been found by different authors. In order to study the influence of the interstitial elements on the SFE, experimental measurements extracted from literature were collected and analyzed to predict the individual and combined effect of carbon and nitrogen in different systems. The referenced austenitic steels are Fe-22Mn-C, Fe-30Ni-C, Fe-15Cr-17Mn-N, Fe-18Cr-16Ni-10Mn-N, Fe-18Cr-9Mn-C-N, Fe-18Mn-18Cr-C-N and Fe-(20-30)Mn-12Cr-C-N. The calculation of the SFE is based on the Gibbs free energy of the austenite to ε-martensite transformation (ΔGγàε), which is calculated by means of the Calphad method. The revision of the measured values reveals that on different ranges of interstitial contents the SFE behaves differently. At lower values (C, N or C+N up to 0.4%), a local minimum or maximum is found in most of the systems. At higher concentration levels, a proportional dependence seems to occur. These observations agree with the theory of the dependence of SFE on the free electron concentration. Alloying with Mn or Ni has a strong influence on the electronic configuration and magnetic properties of the austenite and therefore on the SFE. The results of this study provide valuable information for materials design, especially in the context of alloying with C, N or C+N.
Measurement of Deformation-Induced Martensite in Stainless Steel Using Magnetic Contact Force
Authors: Nishihara Tadashi
Published: January 2012

Metastable austenitic stainless steels are attractive industrial materials with excellent corrosion resistance, mechanical properties, and formability. However, during plastic deformation, α’martensite can be formed. The volume fraction of that particular phase influences the mechanical and other properties (such as corrosion resistance) of these steels. Therefore, it is important to determine the amount of α’martensite in the obtained microstructures. Currently, the volume fraction of deformation-induced martensite in stainless steel is most commonly measured by the X-ray diffraction or magnetic permeability methods. In this study, a novel method of measuring deformation-induced martensite using magnetic contact holding force is proposed. Measurement trials were carried out using a prototype measuring system, and the results of measurements taken from SUS301 and SUS304 stainless steels are discussed in terms of deformation and martensite volume fraction.
Mechanical Properties and Wear Resistances of TiC or B4C Reinforced Ti-6Al-4V Prepared by Spark Plasma Sintering
Authors: Ota Akinori , Egawa Hiroki , Izui Hiroshi
Published: January 2012

Titanium and its alloys have excellent specific strength and corrosion resistance. However, they have a high initial cost and high machining cost, and poor wear resistance. Therefore, both factors should be considered in order to reduce the cost and improve the wear resistance of titanium alloy parts. Powder metallurgy (PM) has been taken into account for lowering the their costs. Titanium alloys reinforced with ceramic particle improves their wear resistance and hardness. In this study, we focus on the microstructures, mechanical properties, and wear resistance of TiC or B4C reinforced Ti-6Al-4V composites by using spark plasma sintering. The volume fraction of the reinforcement from 0 to 19.9 vol. %. The tensile strength of TiC/ and B4C/Ti-6Al-4V had 1058MPa (14.9 vol. % TiC) and 1095MPa (1.7 vol. % B4C), respectively. Vickers harnesses of TiC/ and B4C/Ti-6Al-4V increased with increase in the volume fraction of the reinforcement. The wear resistance of B4C/Ti-6Al-4V exhibited superior to that of TiC/Ti-6Al-4V.
Effect of Ferrite Grain Boundary on Strain Aging Behavior in Nb-Bearing Ultra-Low-Carbon Steel Sheets
Authors: Ono Yoshihiko , Okuda Kaneharu , Funakawa Yoshimasa , Seto Kazuhiro
Published: January 2012

Effect of grain boundary on strain ageing behaviour of Nb-bearing ULC steel sheets has been studied at the aging temperature from 70 to 220°C, using 2% pre-strained specimens with different ferrite grain sizes of 9.5μm and 183μm. Two different hardening stages were exhibited in the fine-grain specimen, whereas only a single hardening stage was shown in the large-grain specimen. The increase in YP of the first hardening stage was around 30MPa; the activation energy of this stage was estimated to be from 83 to 86kJ/mol, which is close to that of body diffusion of carbon atoms in α-Fe. The increase in YP of the second hardening stage reached 90MPa; the activation energy was 135kJ/mol, which is close to that of body diffusion of Fe atoms in grain boundary and precipitation of η-carbide. From TEM observations and nanoindentation analyses, it was inferred that the dominant mechanism could be dislocation pinning by carbon atoms for the first hardening stage, and grain boundary hardening or hardening around it for the second.
Austenite Stabilization by Quenching and Partitioning in a Low-Alloy Medium Carbon Steel
Authors: Paravicini Bagliani E. , Anelli E. , Boniardi Marco
Published: January 2012

Innovative treatments like quenching and partitioning (Q&P) have been recently proposed to improve the combination of strength and ductility of high strength steels by stabilization of significant fractions of retained austenite in a microstructure of tempered martensite. The decomposition of austenite into bainite and carbides precipitation are the two main competitive processes that reduce the content of retained austenite achievable at room temperature. A medium carbon low-silicon steel (0.46% C and 0.25% Si) has been studied to identify in which limits the austenite can be enriched in C and stabilized by Q&P, although a silicon content well below 1.5%, commonly used to retard cementite precipitation, is adopted; indeed, high Si contents are detrimental to the surface quality of the product due to the formation of adherent scale in high temperature manufacturing cycles. The heat treatments have been carried out with a quenching dilatometer, investigating the carbon partitioning process mainly below Ms, where cementite precipitation is not activated. The dilatometric curves show the progressive enrichment of carbon in the untransformed austenite and the occurrence of austenite phase transformation during the isothermal holding below Ms. A range of temperatures and times has been found where a content of about 10% of retained austenite can be stabilized at room temperature, a percentage much lower than the theoretical maximum achievable with the carbon content of this steel.
Effect of Interpass Temperature on Microstructure and Mechanical Properties of Weld Metal of 690 MPa HSLA Steel
Authors: Peng Yun , Wang Ai Hua , Xiao Hong Jun , Tian Zhi Ling
Published: January 2012

690 MPa grade HSLA steel has wide application in engineering, such as mechanical equipment and oceanographic platform. Qualified joint is crucial for structure safety. Many factors, such as preheating temperature and interpass temperature, welding heat input and plate thickness, may influence the welding thermal cycle so that microstructure and mechanical properties of weld metal are changed. In this paper, the effect of interpass temperature on microstructure and mechanical properties of weld metal of 690 MPa grade steel are studied. Gas metal arc welding method was used to weld the joint. Four interpass temperatures, 80°C, 120°C, 160°C and 200°C are adopted during welding. Optical microscope, scanning electron microscope, transmission electron microscope and electron back-scattered diffraction (EBSD) were used to analyze the microstructure of weld metal. Tensile test and impact test were used to measure its mechanical properties. Research results show that the weld metal are composed of lath bainite and granular bainite. M-A constituents are found on grain boundary and inside grains. The shape and size of bainite structure and M-A constituent are detailed. The distribution and quantity of residual austenite are also detected. The relationship between microstructure and mechanical properties is discussed. Experiment results show that when interpass temperature is 80°C the yield strength and impact toughness are higher than the other three cases.
Study of the Hydrogen Traps in a High Strength TRIP Steel by Thermal Desorption Spectroscopy
Authors: Pérez Escobar Diana , Duprez Lode , Verbeken Kim , Verhaege Marc
Published: January 2012

Thermal desorption spectroscopy (TDS) is a very important tool in hydrogen related research. It allows to distinguish between the different types of microstructural hydrogen traps based on the analysis of the different temperatures at which hydrogen desorbs from the material during heating. These peak temperatures depend on the metallurgical and microstructural characteristics of the steel under investigation and provide important information on the possible mechanisms for hydrogen embrittlement (HE). In the present work, multiple TDS experiments and an in-depth study of the microstructure were performed on a TRIP steel (TRIP700) that was previously cold deformed in order to make a correlation between the microstructural features of this material, e.g. grain boundaries, dislocations, martensite formation and the peaks that became visible during TDS. The results obtained for the TRIP grade were compared with those obtained for electrolytic pure iron, which only contained a limited amount of possible trap sites such as grain boundaries and an increasing amount of dislocations due to previous application of cold deformation. Significant differences between both materials and a significant impact of the degree of cold deformation for TRIP steels were observed.
Influence of Two-Step Austempering Process on the Fracture Toughness of a Low Carbon Low Alloy (LCLA) Steel
Authors: Putatunda Susil K. , Martis Codrick
Published: January 2012

In this investigation a new low carbon and low alloy (LCLA) (Third generation AHSS) steel with exceptional combination of yield strength and fracture toughness has been developed. The steel has been processed using a novel two step austempering process. The investigation also examined the influence of a two-step austempering process on the microstructure and mechanical properties of this steel. Test results show that by two-step austempering process significant improvement in yield strength and fracture toughness can be obtained in this steel.
Study on the Microstructure and Mechanical Properties of a High Strength Crack-Free Steel
Authors: Qiu Chun Lin , Lan Liang Yun , Zhao De Wen , Gao Xiu Hua , Wen Jing Lin
Published: January 2012

Thermo-mechanical process followed by accelerated cooling and high temperature tempering was applied to investigate the microstructure evolution and mechanical properties of a high strength crack-free steel. Optical microscopy, transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD) technique were employed to analyze the complex microstructural characteristics of the steel. The results indicated that the precipitation strengthening effect played an important role in optimizing the tempered strength. According to EBSD results, the average grain size of as-rolled specimens was about 3.2 μm, and it increased slightly with the tempering temperature. Therefore, the grain refinement wasthe major reason for the good mechanical properties of the crack-free steel.
Microstructure, Mechanical Properties and Formability of a Duplex Steel
Authors: Rana Radhakanta , Loiseaux Jenny , Lahaije Chris
Published: January 2012

A duplex steel with 26Mn-9.7Al-0.47C (wt.%) was investigated for its suitability as an automotive material. The material was processed in the laboratory following standard processing route for steel sheets. It is found that this duplex steel achieves promising mechanical properties at about 22–28 vol.% of ferrite in the microstructure. Control of ferrite volume fraction by optimising annealing temperature appears to be key to monitor the mechanical properties. A tendency of the alloying elements Mn, C and Al to be partitioned in austenite/ferrite bands is observed irrespective of the annealing temperature. The formability (stretchability, bendability and hole expansion coefficient) of the material is better/comparable than conventional automotive steels with similar strength levels.