Local Hardening Research Articles

607 局所通電焼入れ連続処理におけるSKD11の硬化特性(OS7-2 材料と加工(ローテクの中のハイテク(2),OS7 材料と加工(ローテクの中のハイテク)

607 局所通電焼入れ連続処理におけるSKD11の硬化特性(OS7-2 材料と加工(ローテクの中のハイテク(2),OS7 材料と加工(ローテクの中のハイテク)

<i>In Situ</i> Detection of Thermal Cycle in Weld Metal of Cr-Mo Steel

With the self-designed system of welding thermal cycle test, low alloy steel of Cr-Mo series was welded through proper welding procedure according to the phenomenon of cold crack and local hardening in weld metal, and in-situ detection of thermal cycle for deposit metal was realized. The results show that self-designed system is reliable within the error range, the maximum peak temperature during thermal process was above 1700°C, it is largely improved than reported formerly.

Strain gradient effects on steady state crack growth in rate-sensitive materials

Steady state crack propagation produce substantial plastic strain gradients near the tip, which are accompanied by a high density of geometrically necessary dislocations and additional local strain hardening. Here, the objective is to study these gradient effects on Mode I toughness of a homogeneous rate-sensitive metal, using a higher order plasticity theory. Throughout, emphasis is on the toughness rate-sensitivity, as a recent numerical study of a conventional material (no gradient effects) has indicated a significant influence of both strain rate hardening and crack tip velocity. Moreover, a characteristic velocity, at which the toughness becomes independent of the rate-sensitivity, has been observed. It is the aim to bring forward a similar characteristic velocity for the current strain gradient visco-plastic model, as-well as to signify its use in future visco-plastic material modeling.

Microstructure based prediction of strain hardening behavior of dual phase steels

In the automotive industries, dual phase (DP) steels have increasingly used for various car body parts due to their excellent combination of high strength and good formability. The microstructure of DP steel basically consists of a matrix of ferrite embedded by martensitic islands. For the mechanical and fracture behaviors of the DP steel, effects of martensite phase fraction, morphology, and phase distribution play an important role. In this work, dual phase steel sheets with different martensite contents were produced by intercritical annealing process. Subsequently, a Finite Element (FE) based modeling using Representative Volume Elements (RVEs) approach was proposed for predicting overall stress–strain behavior of the investigated DP steels. Two dimensional RVE models were generated from micrographs of the DP steels on the microstructure level. For the individual single phases flow curves based on dislocation theory and local chemical composition were applied. Additionally, Geometrically Necessary Dislocations (GNDs), which accumulates at the phase boundaries due to the austenite–martensite transformation during quenching process, was taken into account. A local hardening effect due to these phase boundary dislocations was applied at the interface layer between ferrite and martensite. The calculated stress–strain responses of the DP steels were verified with experimental results determined from tensile tests. The micromechanics model could be then used to describe the local stress and strain evolution of the individual phases in the DP microstructures.

Adverse Results with PMMA Fillers

Various alloplastic materials have been used for filling depressions and for body contouring. Among them, polymethylmethacrylate (PMMA) has provoked many clinical compilations in both the acute and chronic phases. This study shows the correlation between the clinical application of PMMA and the physiopathology of the acute and late complications. Histological studies were performed on biopsy samples from patients who presented with side effects and acute and late complications after PMMA injections given at other health-care centers or aesthetic services. The histological findings of the samples that were harvested from patients who developed clinical complications or side effects caused by injection of PMMA disclosed not only normal tissues from the implanted areas but also development of capsules that involved individual microspheres of PMMA, and when the capsules were close together they formed concentric capsular groups involving various sets of microspheres and their capsules. The injection of PMMA within the tissues can cause severe complications and side effects in both acute and chronic phases. Initially, the complications are related to vascular compromise, but at the late phase they are a consequence of capsular contracture that involves particles of PMMA. The contracture causes local tissue hardening and clinical nodulation of the implanted areas, ending with extrusion of the filler material. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors at www.springer.com/00266.

In Situ Characterization of Deformation Behavior of Austenitic High Manganese Steels

AbstractThe mechanical properties of high manganese steels are linked to their hardening mechanisms and their intrinsic behavior during deformation. The characterization of mechanical properties is influenced by the localization of plastic flow and the effect of this localization on the material. Depending on grain size, temperature, and extrinsic strain rate localization of strain, adiabatic heating, and hardening vary in spatial and temporal extent. Even at small strain rates the adiabatic heating of samples reaches temperatures more than 100 K over initial testing temperature due to the sharp localization and last but not least this heating is also dependent on the tested sample size. Furthermore, temperature influences the activated mechanisms of plastic flow. The characterization of temperature increase, strain distribution, and local hardening is pursued in tensile tests with application of infrared thermography. With those techniques it is possible to gather correlations between local strain and temperature. The analysis of dynamic strain ageing effects is also carried out by evaluation of the instantaneous strain rate, the strain rate in the gauge length, in dependence of stress in different alloys, as well as at different strain rate regimes. Thus it is possible to distinguish the onset of TRIP, TWIP and DSA.

822 急速通電加熱を用いたダイス鋼の局所焼入れにおける通電条件の焼入れ状態に及ぼす影響

822 急速通電加熱を用いたダイス鋼の局所焼入れにおける通電条件の焼入れ状態に及ぼす影響

Tailored Profiles Made of Tailor Rolled Strips by Roll Forming – Part 2 of 2

AbstractThe main scope of the presented work is to demonstrate the potential of load optimized tubes with a varying thickness distribution in circumferential direction produced by roll forming. As initial material a so called Tailor Rolled Strip (TRS) sheet metal coil produced by Strip Profile Rolling (SPR) method was used instead of plain sheet. The TRS sheet metal is manufactured in a continuously working process by rolling one or more groves in transverse direction into the sheet metal coil. In this paper, the secondary forming of the TRS sheet metal to TRS tubes is investigated by means of FE‐simulations and roll forming experiments. To simulate the manufacturing process of the TRS tube by FEM, an integrated consideration of the process is necessary because of the large local strain hardening in the groves of the initial SPR sheet metal. In experimental roll forming operations welded tubes could be manufactured successfully. The geometrical and material properties of these tubes are analyzed. The reprocessing of TRS tubes by hydroforming is investigated by means of tube bursting tests. It has been found that an additional annealing process is necessary to achieve deformations in the grooved area during the hydroforming process.

Characterization and modeling of heterogeneous deformation in commercial purity titanium

Heterogeneous deformation, including local dislocation shear activity and lattice rotation, was analyzed in microstructure patches of polycrystalline commercial purity titanium specimens using three different experimental methods. The measurements were compared with crystal plasticity finite element simulations for the same region that incorporate a local phenomenological hardening constitutive model. The dislocation activity was measured using techniques associated with atomic force microscopy, confocal microscopy, three-dimensional x-ray diffraction, and nano-indentation. The results indicate that a major challenge for model development is to effectively predict conditions where slip transfer occurs, and where geometrically necessary dislocations accumulate.

Experimental study of W–Eurofer laser brazing for divertor application

This work can be considered as a preliminary evaluation of the potential of laser brazing for joining tungsten based alloys to reduced activation ferritic–martensitic steels (Eurofer). Brazing of tungsten and EUROFER alloys using a 55Ni–45Ti alloy as a brazer and a high power diode laser (HPDL) as a power source has been investigated. The brazed joints showed solidified pools with good superficial aspect and a high degree of wettability with the both parent sheets, presumably because of the active effect of titanium. Metallurgical brazeability was investigated and nanoindentation measurements were done to evaluate local hardening and stiffness effects associated to dilution phenomena.

Quasi-Static behavior as a limit process of a dynamical one for an anisotropic hardening material

We formulate some problems modeling the local hardening behavior of a plastic material following a Prandtl-Reuss law. Directional linear hardening, which is similar to Bauschinger’s effect in metals, is characterized by an anisotropic factor. The flow process of the material is revealed by translation in the direction shown by deformation using an absolutely continuous guiding function. The possibility of choice of a plastic strain component for the mechanical system with hardening requires an algebraic factorization of the space of processes. If the quasi-static deformation is seen as a limit case of the dynamic deformation, corresponding to low speeds and low inertial forces, we obtain an existence and uniqueness result. In this context there exists an admissible plastic strain rate, as follows by choosing a permissible elastic stress as a solution for a sweeping process problem.

Investigation of the deformation behavior of Fe–3%Si sheet metal with large grains via crystal plasticity and finite-element modeling

The purpose of this work is the modeling and simulation of the deformation behavior of thin sheets consisting of large grains of Fe–3%Si and comparison with experiment. To this end, a crystal-plasticity-based finite-element model is developed for each grain, the grain morphology, and the specimen as a whole. The crystal plasticity model itself is rate-dependent and accounts for local dissipative hardening effects. In order to compare model predictions with experiment, the material parameters have been identified with the help of single-crystal data from [1–3]. Identified model predictions are compared with the experimental results of [4] for the deformation behavior of thin sheets of Fe–3%Si loaded incrementally in tension at room temperature. To this end, attention is restricted to the two slip families {110} and {112} expected to be active at room temperature. Comparison of model predictions for grain morphological evolution with the corresponding experimental results up to 19.5% deformation on this basis imply good agreement. In addition, model predictions for the development of the strain field and the grain reorientation field are discussed and evaluated.

Experimental and numerical study on geometrically necessary dislocations and non-homogeneous mechanical properties of the ferrite phase in dual phase steels

The microstructure of dual phase steels can be compared with a composite composed of a matrix of ferrite reinforced by small islands of martensite. This assumption has been used in several attempts to model the mechanical properties of dual phase steels. However, recent measurements show that the properties of the ferrite phase change with distance from the martensite grains. These measurements showed that the grains of the ferrite phase are harder in the vicinity of martensite grains. As a consequence of this local hardening effect, the ferrite phase has to be considered as an inhomogeneous matrix in modeling dual phase steels. This experiment inspired the idea that local hardening is caused by geometrically necessary dislocations. The idea is investigated experimentally and numerically in the present analysis, which for the first time leads to good agreement with experimental observations of the mechanical stress–strain behavior.

Microstructure of as cast reinforced ductile iron

Local hardening of parts made of ductile iron may be achieved by having carbides appearing in appropriate locations. The present work focuses on the study of the as cast microstructure of parts reinforced by Cr containing steel inserts. The presence of such inserts in the mold cavity results in localised chemical changes during the casting process, constituents of the insert (principally chromium) being transferred to the cast iron while carbon penetrates the insert. This leads to the formation of various carbides within and in the surroundings of the insert.

Adjusting Optimized Material Properties for Tailored Heat Treated Blanks

Aluminum alloys have great potential for lightweight construction. In order to achieve an optimized properties distribution for the forming operation and to enhance the formability of aluminum alloys, so called Tailored Heat Treated Blanks (THTB) are developed. In this context, this paper is about the local precipitation hardening of sheet metals for the application of THTB. By using a specific, short-term heat treatment via conductive heating plates the thermal induced hardening of the fast hardenable alloy AA6181PX is quantified and qualified. Considering the processibility of the local precipitation hardening for THTB, a process window for the heat treatment parameters is presented allowing a precise setting of the mechanical material properties.

Effect of CO2 partial pressure on SCC behavior of welded X80 pipeline in simulated soil solution

The stress corrosion cracking (SCC) behavior of welded X80 pipeline steel in simulated Ku′erle soil solution was studied by means of electrochemical impedance spectroscopy (EIS) and slow strain rate tests (SSRT). The microstructure of the welded steel was observed by optical microscopy (OM). It is demonstrated that the microstructure of the weld metal consists of acicular ferrite and grain boundary ferrite, while that of heat affected zone (HAZ) is a mixture of acicular ferrite and bainitic ferrite microconstituents. The microstructure of the base steel is composed of ferrite and pearlite. The anodic dissolution of X80 pipeline steel in simulated Ku′erle soil solution could be enhanced and the SCC sensitivity increased with the increase of CO2 partial pressure. The SCC mechanism of X80 pipeline is a mixing mechanism of hydrogen embrittlement combined with anodic dissolution, and the hydrogen embrittlement plays a leading role. The higher SCC sensitivity of the weld metal was attributed to the metallurgical transformation, local hardening and residual stress.

Analytical and Experimental Determination of Rate- and Temperature-Dependent Length Scales Using Nanoindentation Experiments

This work addresses the temperature and rate indentation size effects (TRISE) encountered in nanoindentation experiments and the corresponding material intrinsic length scales at different strain rates. The same value for the material length scale cannot be used for different rate, temperature, and accumulated plastic-strain conditions. A variable length scale is introduced in this work and used on two different face-centered cubic (FCC) metals. Indentation experiments are performed on copper and aluminum polycrystalline samples for different strain rates. To check the validity of the assumed concept for local hardening in nanoindentation, additional experiments are conducted on single-crystal materials. The existing theories describing the indentation size effects and length scales are reviewed, and a physically based model that depends on strain rate, accumulated plastic strain, and temperature that were scaled with hardness experiments results is proposed for length scales. Furthermore, numerical simul...

The Effect of Texture on the Stability of Retained Austenite in Al-Alloyed TRIP Steels

ABSTRACTSteels with transformation induced plasticity (TRIP) offer an excellent combination of high strength and ductility. The transformation of meta-stable austenite into martensite during straining leads to strong local hardening and prevents early localization of strain. Therefore, the mechanical properties of TRIP steels, including the damage resistance depend to a significant extent on the stability of retained austenite. The aim of this study was to evaluate the effect of texture on the stability of retained austenite. In order to compare the changes in both tension and compression the steel was deformed by a micro 3-point-bending device. The texture development upon bending was followed by electron backscatter diffraction (EBSD) technique. Based on a simple analysis using the relation between face centered cube (FCC) and body centered cube (BCC) shear geometries theoretically expected changes of texture components due to deformation are proposed. Using the results of this analysis the observed changes of the austenite texture due to deformation could be distinguished from those due to transformation, by comparing the experimental results with the theoretically expected behavior. From this comparison, austenite grains with “Brass (B) {011} <211>” and “Goss (G) {110} <100>” texture components were found to transform into martensite much easier than differently oriented grains.

Atomistic modeling of lattice frame effects on laser-induced dislocation behaviors in nanopore mending processes

In recent years, the femtosecond laser technique has emerged as an effective tool for defect mending, especially for fault repairs of the conducting wire in three-dimensional integrated circuits. However, the nanodefect mending mechanism subjected to photothermal and mechanical stress introduced by ultrafast laser dynamics is still not well understood so far. In this paper, the microscopic dislocation behaviors of the lattice mending of metallic nanopore defects induced by femtosecond laser is presented using a modified continuum-atomistic modeling approach and the quantitative dislocation-based analysis. Two different cases of lattice frame effects are elaborated to characterize the dislocation behaviors and the nanopore mending mechanisms. The lattice frame is found to possess a direct effect on controlling the mechanisms of nucleation and growth of dislocation during laser interaction with metallic microdefects. The nanopore defect with a symmetric lattice frame is observed to form a prismaticlike slip structure around the pore region, and the dislocation loop consequently expands along its glide-prism plane. The growth of the loops continues even after they are fully mended to form sessile junctions by creating a local anisotropic hardening structure. On the other hand, the nanopore defect of an asymmetric lattice frame induces drastically irregular lattice glides, forming a tight network of junction loops around the mended area. It was found that the fast shock wave enhanced by the stress concentration factor around the pore that enabled a cooperative movement of sheets of atoms around the pore. This particular mechanism causes a rapid mending of the hole with a metastable lattice structure. The heterogeneous reaction dynamics of dislocation nucleation on the pore defect surface is analyzed in detail in this study. The photomechanical and thermally-activated plastic flow of mending processes is also clearly elucidated. The results provide vital insights into better dynamic behavior characterization of how the ultrafast laser interacts with metallic microdefects.

Hole Expansion by Using Al-Alloy Specimen and 0.45% Carbon Steel Specimen

The enhancement method of fatigue life and the crack initiate and growth behavior of a holed specimen was investigated by using the 2024 Aluminum alloy and 0.45% Carbon steel. The purpose of present study is to propose a simple technical method for enhancement of fatigue life in a notched specimen. Also, the effect of local plastic deformation by cold work on fatigue crack initiation behavior was examined. This paper presents a basic experimental kinematic cold expansion method by inserting and removing a pin through the specimen hole. The shape of cross-section of pin was a circle or an ellipse. It was shown that the fatigue life of the specimen with the cold-worked hole was longer than that of the specimen with non-cold-worked hole for the case of same stress level in aluminum alloy and carbon steel. Also, the fatigue strength was higher in the case of the cold expanded hole. In this study, a methodology of lengthening of fatigue life of holed specimen is shown. Also, the improvement conditions of fatigue life were significantly affected by shape of pin, local hardening and residual stress conditions. The fatigue life improvement of the damaged component of structures was studied.