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This paper discusses permanent deformation of the fuel assembly of pressurized water reactors that can satisfy a drop time requirement of the control rod assembly. During a seismic event, the fuel assemblies and the reactor core exhibit transient vibration. When the fuel assemblies collide, they develop impact forces in the spacer grids along the fuel assemblies. If the impact forces on some spacer grids of the fuel assembly exceed an allowable strength, the buckling occurs in the corresponding spacer grids, followed by permanent deformation. The geometry change of the buckled spacer grids leads to the movement of the guide tube positions in the fuel assembly. Therefore the geometry change is associated with the distortion of the control rod drop path. In this study, the permanent deformation of the spacer grids was measured during the impact tests, and the maximum deviation of the guide tube from the original position was reviewed. Control rod drop tests were also performed to measure the change in drop time according to the deformation of the fuel assembly. Using actuators in the loop test facility, the authors realized the first and second bending mode shapes of the fuel assembly under the flowing water condition. Based on a series of drop tests, the critical fuel assembly deformation was identified that could lead to a violation of an allowable drop time of the control rod.

The cell-type continuous electromagnetic radiation system is a demonstration device capable of generating high-power millimeter electromagnetic waves of a specific wavelength and observing their effects on living organisms. It irradiates a biological sample placed in a 30 × 30 × 50 cm3 cell with electromagnetic waves in the 3.15-mm-wavelength region (with an output of ≥1 W) and analyzes the temperature change of the sample. A vacuum electronic device-based coupled-cavity backward-wave oscillator converts the electron energy of the electron beam into radiofrequency (RF) energy and radiates it to the target through an antenna, increasing the temperature through the absorption of RF energy in the skin. The system causes pain and ultimately reduces combat power. A cell-type continuous electromagnetic radiation system consisting of four parts—an electromagnetic-wave generator, a high-voltage power supply, a test cell, and a system controller—generates an RF signal of ≥1 W in a continuous waveform at a 95-GHz center frequency, as well as a chemical solution with a dielectric constant similar to that of the skin of a living organism. An increase of 5 °C lasting approximately 10 s was confirmed through an experiment.

High-power microwave sources applied to a directed-energy weapon can lead to permanent damage by radiating concentrated energy in a specific direction to disturb or overload electronic equipment. The effect analysis on the target, such as electronics exposed to electromagnetic pulse, should be considered as an important factor in determining the performance of high-power microwave sources and conducting experimental evaluations. In this study, a magnetically insulated transmission line oscillator, one of the representative high-power microwave sources based on vacuum electronics device, was constructed and experimental analysis with respect to electromagnetic pulse effects was performed. The specification of the magnetically insulated transmission line oscillator used in this study corresponded to 3 GW of high-power electromagnetic wave pulses operating at L-band. The power efficiency was approximately 10 – 15%. For effective targeting, a Vlasov antenna that converts TM01 mode to TE11 mode was designed and fabricated. The radiation pattern was confirmed via fluorescent lamps, and to confirm the effect of the directed-energy weapon on the target, an effect analysis was performed using a portable electronic device as a sample. Furthermore, the electric field was measured with a D-dot probe and quantified and compared. This study presents a future blueprint of the value of the directed-energy weapon by predicting the radiant output power of the weapon in the far-field region after it is mounted on a movable ground vehicle or unmanned aerial vehicle.

Versatile high-power pulsed electron-beam accelerators that meet the requirements of pulsed high-power specifications are needed for appropriate applications in medical industry, defense, and other industries. The pulsed electron beam accelerator comprising a Marx generator and Blumlein pulse forming line (PFL) is designed to accelerate the electron beams at the level of 1 MeV when electrostatically discharging. The performance specifications of Marx generators consisting of a 100 kV DC power supply, R-L-C circuit, and high voltage switch are at a maximum 800 kV. At this time, by using the capacitance mismatching principle between the Marx generator and the Blumlein PFL under the law of preserving the amount of charge, it is possible to generate a high voltage in the form of a square pulse up to about 1.1 MV, as much as 1.37 times the charged voltage of the Marx generator. As a result, energy transmission from the Marx generator with a high efficiency of about 85% to the Blumlein PFL is possible. The aim of this study is that the pulsed high-power electron-beam accelerator can be used to change the diode impedance, and the energy of the accelerated electron beam reaches a level of 1 MeV with the square pulse width of about 100 ns at the flat-top in the range of relativistic electron beam generation. Performance tests were securely carried out by installing a dummy load based on CuSO4 solution varying the diode impedance to deter damage to the circuit by preventing reflected waves from being generated in the load.

An analysis of the effects of electromagnetic pulses from a high-power microwave (HPM) radiation technique is conducted using a relativistic backward-wave oscillator (RBWO) which uses relativistic ...

Researchers have investigated plasma-related phenomena and internal breakdowns in the gigawatt–terahertz relativistic backward wave oscillator (RBWO) caused by field emissions from the surfaces of the waveguide circuits in these oscillators. In order to increase the power-handling capability of relativistic electron beam devices, an RBWO is proposed in the form of an oversized structure in which the diameter ( $D$ ) of the electrodynamic structure is increased to several times the free-space wavelength ( $\lambda )$ . An optimal periodic rectangular corrugation structure of which the axial mode is matched to the $\pi $ mode is designed in order to determine only the TM01 mode without mode competition in a slow-wave structure (SWS). The oversized RBWO has a fairly large diameter and uses a resonant reflector to achieve optimum efficiency while also preventing mode competition in the SWS. Absorption of a decelerated electron beam is achieved by the collector, which protects against breakdown and damage. The results of 0.5–0.1 THz from 500 kV–5 kA in the relativistic region are observed by means of a particle-in-cell simulation, and the dispersion relationship is determined by a finite-difference time-domain simulation. The outcomes show that a high-power oversized RBWO can control the selection of the mode and the interaction efficiency.

Generally, as the operating frequency of the electromagnetic wave increases, the maximum output becomes smaller and the wavelength of the wave becomes smaller, so that the size of the circuit cannot but be reduced. Particularly, fabrication of a circuit with a high-power terahertz (THz) wave frequency band of kW or more is limited due to the problem of circuit size on the order of μm to mm. In order to overcome these limitations, this paper proposes a source design technique of 0.1THz-0.3GW levels with a cylindrical shape with a diameter of about 2.4cm. Modeling and computational simulation were performed to optimize the design of high power electromagnetic sources based on the Cherenkov radiation generation technology using the principle of plasma wake-field acceleration with ponderomotive force and artificial dielectrics. An effective design guideline has been proposed to facilitate the fabrication of large-power terahertz wave vacuum devices of large diameter that are less restricted in circuit size through objective verification.

The automodulation processes in backward-wave oscillator with an inclined electron beam (the clinotron) operating at low-focusing magnetic fields have been studied. The automodulation behavior has been analyzed in the clinotron for different angles of the beam inclination. It has been shown that at low magnetic fields, the RF transverse electric field may cause significant changes in electron trajectories, and hence in the beam–wave interaction power that leads to the automodulation.

A multimode theory of the resonant backward-wave oscillator (BWO) with an electron beam inclined with respect to the surface of a periodic structure—a clinotron—is presented. It is shown that mode interaction provides phase velocity variation in the interaction space. The beam–wave interaction power increases at a favorable phase velocity profile along the interaction space, which manifests as power peaks in the clinotron zone. In contrast, when it is nonfavorable, there is power drop in the bandwidth. Developed multimode theory results are in satisfactory agreement with the theory of a BWO with reflections and with particle-in-cell simulations.

The emission capability of as prepared reduced graphene oxide (rGO) and tungsten doped reduced graphene oxide (W-rGO) film field emitter (FE) cathodes are investigated experimentally. It is observed that W-rGO films showed a highest emission current density of ∼ 800 A/cm2 at an applied DC electric field of 6.6 V/μm, which is far superior than the current density of ∼ 390 A/cm2 from an as prepared rGO film. Short stability test also showed that emission current is much more stable than the rGO films. These excellent improvements can be attributed to the doping of tungsten into the rGO film, which helped to repair the broken bonds thus lowering the turn on field. Also, tungsten gives the film an excellent mechanical stability and higher thermal load handling capability, which is very important to achieve a stable, high performance operation and long life.

Non-thermal irreversible electroporation (NTIRE) to avoid thermal damage to cells during intense DC ns pulsed electric fields (nsPEFs) is a recent modality for medical applications. This mechanism, related to bioelectrical dynamics of the cell, is linked to the effect of a DC electric field and a threshold effect with an electrically stimulated membrane for the charge distribution in the cell. To create the NTIRE condition, the pulse width of the nsPEF should be shorter than the charging time constant of the membrane related to the cell radius, membrane capacitance, cytoplasm resistivity, and medium resistivity. It is necessary to design and fabricate a very intense nanosecond DC electric field pulser that is capable of producing voltages up to the level of 100 kV/cm with an artificial pulse width (∼ns) with controllable repetition rates. Many devices to generate intense DC nsPEF using various pulse-forming line technologies have been introduced thus far. However, the previous Blumlein pulse-generating devices are clearly inefficient due to the energy loss between the input voltage and the output voltage. An improved two-stage stacked Blumlein pulse-forming line can overcome this limitation and decrease the energy loss from a DC power supply. A metal oxide silicon field-effect transistor switch with a fast rise and fall time would enable a high repetition rate (max. 100 kHz) and good endurance against very high voltages (DC ∼ 30 kV). The load is designed to match the sample for exposure to cell suspensions consisting of a 200 Ω resistor matched with a Blumlein circuit and two electrodes without the characteristic RC time effect of the circuit (capacitance =0.174 pF).

A klystron is an important vacuum device which is useful in medical linear accelerators because it amplifies the radio-frequency (RF) signals required to produce high-energy particle beams. The properties of the nonlinear input and output dynamics in the klystron circuit arouse distortion in various types of parameters pertaining to the beam voltage, beam current, RF power, and operating frequency from unpredictable external factors. Therefore, low-level RF (LLRF) control systems can facilitate the regulation of the output of the klystron to a desired level. Low-level RF control system of the klystron is designed to stabilize the applied voltage and control the resonance frequency of the cavity of the klystron. In this work, an infallible low-level RF control system, the most suitable for a klystron, is designed to use a beam monitoring and an interlock system with components that include an isolator and a phase shifter. Moreover, with regard to pulse distortion at the flap top at the RF output power, the stability of the RF power pulse at the flap top part was improved somewhat by a variable inductor which controlled the inside of the pulse modulator. In this LLRF control experiment, the pulse modulator generated 140kV-95A and succeeded in generating RF output power of 2.856GHz-6MW level of an S-band klystron. During this process, the efficiency of the RF power was approximately 42∼45% and the pulse repetition rate was 10 Hz. The flattop pulse width was measured and found to be 1 µs.

Background and Objectives: The impacts of prophylactic central compartment neck dissection (pCCND) on the prognosis of papillary thyroid cancer (PTC) are controversial. The aim of this study is to evaluate the relationship between nodal factors of pCCND and the prognosis of PTC patients. Materials and Methods: A total of 1754 patients who underwent thyroidectomy with pCCND were retrospectively reviewed. Nodal factor was defined as the number of metastatic lymph node (MLN), lymph node yield (LNY) and lymph node ratio (LNR). In regarding the cutoff of nodal factors, patients were categorized as low/high MLN, LNR and LNY group. The correlation of clinicopathologic characteristics including nodal factors and recurrence free survival (RFS) were anlalyzed. Results: Of these, 1195 patients underwent thyroidectomy with unilateral pCCND and 559 patients underwent total thyroidectomy with bilateral pCCND. During follow-up, 45 (2.57%) patients showed recurrent disease. Of these, 19 patients underwent bilateral pCCND and 26 cases were unilateral pCCND. Gross extrathyroidal extension (ETE), high MLN and LNR showed statistically significant on RFS in univariate analysis in unilateral pCCND. In multivariate analysis, gross ETE and high LNR were independent risk factor of recurrence in unilateral pCCND. In bilateral pCCND, larger tumor size, minimal ETE, high MLN and LNR were significant correlation with RFS in univariate analysis. However, in multivariate analysis, multiple larger tumor and high LNR showed significant correlation with RFS. LNY was not statistically significant in both unilateral and bilateral pCCND. Conclusion: In regarding nodal factors, high LNR was only independent risk factor to worse RFS in both unilateral and bilateral pCCND in cN0 PTC patients.

Purpose: A laparoscopic approach, rather than conventional laparotomy, is the well-accepted first choice for excision of an adrenal or perinephric retroperitoneal mass. The purpose of this study was to investigate the factors that affect surgical outcomes and analyze the clinical effectiveness of this surgical treatment modality. Methods: W e conducted a retrospective analysis of 62 patients who underwent laparoscopic adrenalectomies from September 2007 to February 2013. These operations were performed by a single surgeon. Demographic characteristics, operative data, tumor characteristics, and surgical outcomes were analyzed. Results: Of 62 patients, 21 were men and 41 were women. The mean operative time was 151.16±48.58 minutes and the mean amount of blood loss was 179.51±161.66 ml. There were two cases of metastatic adrenal tumors that were resected completely with prolonged survival. There was one case of recurrence during the postoperative period. Preoperatively, it was only a tumor measuring 3.5 ㎝ without evidence of malignancy. Postoperative complications occurred in three patients. However, there was no case of conversion to laparotomy. Previous history of open abdominal operation did not affect post-operative outcomes. Conclusion: Laparoscopic approach for adrenal tumors is indicated regardless of its type or past history of abdominal surgery. Unless greater than 10 ㎝, relatively large tumors can be safely removed using this method. In particular, due to the possibility of malignant potential, aggressive surgical intervention is recommended for tumors measuring between 3 and 5 ㎝. Use of a laparoscopic approach is associated with low risk of surgical complication and the benefits outweigh the disadvantages.

The possibility of the efficient operation of a backward-wave oscillator (BWO) with an electron beam inclined with respect to the surface of a periodic structure-a clinotron-is analyzed here. The beam inclination provides the possibility of effective interaction by all particles of a thick electron beam with the slow evanescent harmonic of the cavity modes. The problem of electron-beam-wave interaction is treated in a self-consistent formulation. A theoretical analysis shows that the inclination of the electron beam to the grating surface decreases the demand of the clinotron for magnetic field magnitude and beam velocity spread compared to a conventional BWO. It is demonstrated that, for an optimal inclination angle and an optimal beam thickness, the clinotron efficiency exceeds the efficiency of a conventional BWO considerably given the same electron beam parameters. The developed multimode theory results are in satisfactory agreement with the theory of a BWO in terms of reflections and particle-in-cell simulations.

Metallic glass alloys have been considered as attractive materials due to their excellent mechanical and magnetic properties. However, commercial application of metallic glasses has been limited not only because of high production cost, but because of low market demands. A critical production cost factor was raw material since ferrous metallic glasses were made from high purity electrolytic iron. An idea to reduce the cost was to utilize the raw materials which were taken directly from molten iron and steel manufactured at the existing steel plants. Investigations have been performed to find whether metallic glasses made of molten iron and steel demonstrated appropriate mechanical and magnetic performance. Pilot scale equipments were designed to produce amorphous metallic fibers and strips continuously under the atmospheric condition. Process conditions were optimized by controlling process variables such as alloying and nozzle design, feeding temperature, speed and so on. The glass formability was tested by XRD and DSC analysis. Possibilities of application of Fe-based metallic glasses to reinforced concrete were also evaluated. It was confirmed that a small addition of metallic glass fibers in concrete increased the mechanical performance compared to that of commercial concrete reinforced with steel wires. In addition, amorphous strips were manufactured to apply them to the transformer core. It has been demonstrated that the magnetic properties were equivalent to those of commercial products.

Thermal analysis of an L-band 60-kW (continuous-wave) double-ring strapped magnetron for optimizing the design of a cathode support structure and cooling system is presented. This magnetron consists of an oxygen-free copper anode with ten built-in cooling channels and a directly heated tungsten cathode. The operating temperature of the cathode is greater than 2000°C; therefore, proper thermal design of the cathode support structure is essential for reliable operation. The heat convection coefficient for the forced air is estimated by simulations comparing the simulated temperatures for different heat convection coefficients with the measured one. It is observed that the comparison between simulations with measurement is in good agreement for various temperatures from 1000°C to 2000°C when the estimated heat convection coefficient of the forced air is used.

Recently, newly developed bake-hardenable (BH) steel sheets strengthened by copper sulfide (CuS) have been successfully employed in commercial production lines that supply automotive outer panels. The metallurgical concepts governing fabrication of these new BH steel sheets require keeping carbon content as low as 0.0015 wt.% without any additional amount of titanium and/or niobium for solute carbon scavenging. The role of CuS precipitates has turned out to raise the yield strength acting as a barrier against dislocation movement. In this paper, we studied the effects of chemical compositions and manufacturing process variables on the microstructure and mechanical properties of newly developed BH steel sheets. We found that the control of carbon and nitrogen showed a good balance between bake-hardenability (BH) and yield point elongation (YP-El). We identified the crystallographic relationship between the nano-size CuS precipitates and the ferrite matrix of (001)sulfide//(001)α-Fe and [001]sulfide//[001]α-Fe. We also found that the BH and YP-El were affected by the formation of aluminium nitride (AlN) and the annealing temperature.

When a semiconductor element is irradiated with radiation in the form of a transient pulse emitted from a nuclear explosion, a large amount of charge is generated in a short time in the device. A photocurrent amplified in a certain direction by these types of charges cause the device to break down and malfunction or in extreme cases causes them to burn out. In this study, a pulse-type γ-ray generator based on a relativistic electron beam accelerator (γ=2.2, β=0.89) which functions by means of tungsten impingement was constructed and tested in an effort to investigate the process and effects of the photocurrent formed by electron hole pairs (EHP) generated in a pMOSFET device when a transient radiation pulse is incident in the device. The pulse-type γ-ray irradiating device used here to generate the electron beam current in a short time was devised to allow an increase in the irradiation dose. A precise signal processing circuit was constructed to measure the photocurrent of the small signal generated by the pMOSFET due to the electron beam accelerator pulse signal from the large noise stemming from the electromagnetic field around the relativistic electron beam accelerator. The pulse-type γ-ray generator was installed to meet the requirements of relativistic electron beam accelerators, and beam irradiation was conducted after a beam commissioning step.

The body design with light weight and enhanced safety is a key issue in the car industry. Corresponding to this trend, POSCO is developing various automotive steel products with advanced performance. Conventional advanced high strength steels such as DP and TRIP steels are now expanding their application since the steels exhibit higher strength and ductility than those of conventional solution and precipitation strengthened high strength steels. Efforts have been made to enhance the mechanical performance of these steels such as ductility, hole expansion ratio, deep drawability, etc. Current research is focused on development of extra- and ultra-AHSS. Extra-AHSS are designed to utilize nano-scale retained austenite embedded in fine bainite and martensite. Ultra-AHSS are designed to have austenite as the major phase, and the ductility is enhanced primarily by continuous strain hardening generated during forming. These steels including extra- and ultra-AHSS are believed to be the next generation automotive steels which will replace the existing high strength steels due to their extremely high strength and ductility combinations.

In recent years, for automotive applications, the need for new advanced high-strength sheet steels (AHSSs) with high ductility has rapidly increased. This is mainly related to the need for more fuel-efficient (and therefore more environmentally friendly) cars, and the increasing consumer demand for safer vehicles. In this research, the transformation-induced plasticity (TRIP) that accompanies the mechanically induced martensitic transformation (MIMT) in TRIP-aided multiphase steel was analyzed. The analysis was performed using a computational model that takes the ductile fracture during tensile deformation into account. The TRIP and MIMT phenomena were calculated using the concept of variant selection, which is based on the Kurdjumov–Sachs (K–S) orientation relationship. To consider the localization of the plastic flow in the deforming material, the increase in void nucleation due to the martensitic transformation and the void growth based on the yield criterion for porous material were studied. The feasibility of the extra advanced high-strength sheet steel (X-AHSS) was assessed by analyzing the results obtained using various initial volume fractions and various stabilities of the retained austenite in the TRIP-aided multiphase steel. Subsequently, the optimum volume fraction and stability of the retained austenite in the TRIP-aided multiphase steel could be determined.

Our recent efforts suggest that there exists strong electromagnetic field enhancement in our recently proposed metallic metamaterial. Of particular importance here is the potential for the realization of compact terahertz free-electron lasers (THz-FELs) using this structure. We present the capability of controlling electromagnetic field enhancement, which must be one of the main issues in developing the compact THz-FELs. Moreover, switching and sensing abilities of this structure could also be investigated for other metal-based THz applications. The numerical and experimental works will be presented in the conference.

Terahertz vacuum sources with high power are in immediate need for several applications like medical, security, communication, etc. The power and performance of these devices mainly depends on cathode. As structure become smaller, it is very much difficult to obtain high power at terahertz frequency, using conventional low current density thermionic cathodes. As a result development of non-conventional field emission cathode is in progress, which may produce a very high current density with comparatively high current and can help in terahertz research and application. In this work our main aim is to develop and analyze high current density (>103A/cm2) sheet beam film cathode using reduced graphene oxide (rGO)-nano particle composite.

Tensile tests were conducted in order to study the effects of nitrogen on the mechanical properties of the 0.2C–1.5Mn–1.5Si–0.04Al–(0.003–0.015)N steels often annealing at 800–830°C, followed by the austempering at 400–450°C. The results show that both tensile strength and elongation increase and the balance of tensile strength×elongation are improved upon nitrogen addition to the TRIP steel. It was found that the density of AlN precipitates increases with addition of nitrogen. The volume fraction of retained austenite increases due to AlN precipitation, because the precipitates retard the transformation of austenite during cooling and austempering. As a larger volume fraction of austenite remained after annealing has been transformed to martensite during deformation, elongation as well as strength has increased in the nitrogen added steel. It is also observed that the average grain size of ferrite and bainite decreases because of AlN precipitation that hinders grain growth. The refinement of ferrite and bainite by AlN precipitates also contributes to the increase in the strength of nitrogen added steels.

This paper presents the confidence assessment algorithm of lane mark detected by a vision sensor for lane change decision and its application to lane-level localization. The lane mark information is critical to determine whether driving maneuver is either lane following or lane change. Furthermore, it should be considered that the detected lane mark could be wrong due to its worn-out or soil/snow/obstacles on the mark. Thus it is necessary to assess the confidence of lane. By using detection results of each side of lane from vision sensor and vehicle state measured by in-vehicle sensor, lane confidence assessment algorithm based on probabilistic data association filter (PDAF) is proposed. And by using estimation results from PDAF, lane change decision algorithm is also proposed. The proposed algorithms are validated experimentally via field test data.

The suppression of TE mode oscillations in a PPM-focused S-band sheet beam klystron amplifier using a method of loading distributed losses is presented. This method allows us to make a reasonable attenuation of unwanted modes relative to the operating TM mode and can be used to improve the stability of beam-wave interaction circuit with high aspect ratio.

Tensile and dilatation tests were conducted in order to study the effects of Mn, Si and Nb on the transformation behavior in the 0.14C-(2.1∼2.4)Mn-(0.5∼1.0)Si-(0.00∼0.02)Nb TRIP steels. All the specimens for dilation tests were annealed under the condition to form the same austenite fraction, followed by cooling to the austempering temperature. The volume fraction of bainite transformed during austempering, ΔV B , and the martensite start temperature, M s , were measured. ΔV B was dependent on the austempering temperature and a minimum in ΔV B was obtained at 450°C for all the examined steels. The M s temperature was linearly decreased as ΔV B was increased. The decreasing rate of M s to ΔV B was not dependent on the steel composition, but on the austempering temperature, exhibiting the maximum value when the austempering temperature was 450°C. It was also observed that volume fraction of retained austenite was linearly increased with the decrease of M s for the steels austempered at various conditions. The highest elongation was obtained when the rate of M s to ΔV B was the maximum. M s was increased when the amount of Mn was increased from 2.1 % to 2.4 %. It was because Mn retarded the ferrite transformation rate, so that the soluble C diffused from the ferrite to the austenite was decreased. The addition of Si decreased M s because it activated the diffusion of C to austenite during the cooling to the austempering temperature. The addition of Nb was observed to give little influence on ΔV B and the M s .

The effect of sheet thickness on shear deformation and texture for the ferrite rolling has been studied. The shear deformation was estimated from the distorted shape of inserted wire before rolling and FEM simulation. The deformed shape of inserted wires and FEM results showed that the shear strain decreased with increasing initial sheet thickness. The measured and simulated textures also showed that the Goss component changed to Dillamore component as the thickness increased. From rolling simulation of 20 % reduction, the minimum shear deformation was found to exist for the given roll bite geometry and friction coefficient.

A new equation was proposed to investigate the heat transfer in the hot rolled coils by taking account of the variation of contact between coiled layers. The proposed equation was represented by the equivalent radial thermal conductivity as a function of radial normal pressure. It was found that the analytical results were in good agreement with the experimental data. The cooling times of the hot rolled coils of various dimensions cooled by air or water have been calculated by using the proposed equation. It was shown by finite element analyses that the cooling time was decreased from 32–53 hours to 6–13 hours for spray water cooling.

Effects of centerline macrosegregation on necking was examined by the stretching experiment for cold rolled P-added extra low carbon steel sheets. The centerline macrosegregated zone containing high concentration of Mn and P was elongated in the rolling process. The elongated macrosegregated zone induced instability in the strain state when the sheet was stretched, thus resulted in the waved sheet surface. The formability of cold rolled steel sheet was deteriorated due to the wave formed by the macrosegregation. The waved surface was thought to be caused by the higher hardness in the macrosegregated zone compared to the segregation free zone. The experiments on the stretching of sheet including macrosegregation showed that the macrosegregation was the important source of instability in that of the cold rolled steel sheets. A 3D FEM analysis was carried out for the quantitative evaluation of waved surface. It was confirmed that the main source of the waved surface was the macrosegregation. Stretching in the transverse direction under the plane strain condition made the cold rolled steel sheet more inhomogeneous than stretching in any other strain condition. The thickness difference in the stretched sheet was linearly increased when the ratio of hardness in the macrosegregated zone to that of the segregation free zone was increased. The macrosegregation formed in the internal crack close to the surface was more harmful to the formability in the cold rolled steel sheet than the centerline macrosegregation.

Design of weld line in tailor welded blanks is indispensable for good manufacturing of stamped parts as assigned, since the initial weld line is distorted severely during the forming process. The initial weld line has to be determined such that desired weld line in a formed part can be obtained. The initial weld line can be predicted by inverse finite element analysis from the desired weld line in a formed part. In this paper, the multi-step inverse approach is employed to calculate more accurate initial blank shapes and initial weld line of tailor welded blanks for a cylindrical or square cup drawing. The applications demonstrates that the approach is useful for design of weld line in tailor welded blanks.