Papers by Keyword: Heat Affected Zone (HAZ)

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Authors: Morteza Toloui, Matthias Militzer
Abstract: Three dimensional (3D) phase field modelling is used to simulate austenite grain growth in X80 linepipe steel for thermal paths that are typical in the heat affected zone (HAZ). In the HAZ austenite grain growth is affected by pinning due to precipitates and their potential dissolution. Effective grain boundary mobilities are introduced that are consistent with strong pinning at lower temperatures and weak pinning at higher temperatures separated by the estimated dissolution temperature range of fine NbC precipitates. These mobility relationships are then used to describe austenite grain growth in bulk samples subjected to rapid heating and cooling conditions to replicate thermal cycles at various positions in the HAZ.
Authors: Viboon Tangwarodomnukun, Jun Wang, Philip Mathew
Abstract: Laser micromachining has been widely used for decades to fabricate the micro- and submicro-component structures. However, thermal and physical damages are crucial issues associated with the process. Underwater laser ablation has been developed as a damage-free micro-ablation technique. In this paper, a comparison of the conventional dry and underwater laser micromachining of silicon is presented. It shows that the heat affected zone (HAZ) can be reduced significantly in the underwater laser process, though the material removal rate is reduced due to the energy loss by the water layer. The effects of pulse frequency, traverse speed and laser energy on the obtained kerf width, HAZ and cut surface quality are also analyzed and discussed.
Authors: Bum Joon Kim, Byeong Soo Lim, Sung Jin Song
Abstract: Generally, as the hold time of static load increases, the degradation of material becomes more rapid and the creep-fatigue life decreases. Under the creep-fatigue interaction, the cause of life decrease was mainly the initiation and growth of microvoid with increasing hold time. In this study, using the newly developed alloy of P92, the artificial creep-fatigue degradation tests and its ultrasonic inspection were carried out to evaluate creep-fatigue life. From the relations between the creep-fatigue life and the nondestructive degradation assessment by backscattered ultrasound inspection, the new nondestructive life evaluation parameter, SDA (Slope of Decaying Amplitude) was proposed. Also, to verify the nondestructive life evaluation ability, the life evaluation results by SDA were compared with those of the destructive life evaluation obtained through the fraction of cavity area. From the test result of backscattering Rayleigh surface wave, the linear relationship between SDA and experimental life could be obtained. The good agreement between the experimental life and the predicted life by SDA was also obtained. Finally, it can be stated that the new life evaluation/degradation parameter, SDA (Slope of Decaying Amplitude) could be utilized for the evaluation of the material degradation under creep-fatigue interaction.
Authors: Zhi Gang Hou, Jun Zhao, Li Qiang Xu, Zhong Guo
Abstract: In order to theoretically simulate the welding process of complex structure with large quantities of welding spots, a simplified method for analyzing a single spot welding should be developed firstly. In this paper, a 2D axisymmetric model of thermoelectric Finite Element Method (FEM) is developed to analyze the transient thermal behavior of Resistance Spot Welding (RSW) process using ANSYS. The determination of the contact resistance at the faying surface is moderately simplified to reduce the calculating time, while the temperature dependent material properties, phase change and convectional boundary conditions are taken into account for the improvement of the calculated accuracy. The thermal history of the whole process and temperature distributions for any position in the weldment is obtained through the analysis. The model can also predict the weld nugget size and the width of the Heat Affected Zone (HAZ).
Authors: Hung Hsiou Hsu, Yeong-Maw Hwang
Abstract: Friction stir processes (FSP) are important for enhancing mechanical properties of metal sheets, such as the tensile strength, the elongation, etc. The stress distribution of the tool pin is affected by the thermo-mechanical characteristics of the workpiece in FSP. Recently, magnesium alloy AZ31 is widely used in machine industries due to the light-weight material property. In this paper, a thermo-mechanical model for FSP using three dimensional FEM analyses is proposed for exploring temperature distributions, strain distributions and stress distributions of the workpiece. The heat generated from the plastic deformation and the friction between the head tool and workpiece is considered as the heat source in the simulation of the FSP process. A commercial finite element code – DEFORM 3D is used to carry out the simulation of the plastic deformation of AZ31 sheets during the FSP. The analytical results of temperature, strain and stress distributions of the workpiece and head tool can provide useful knowledge for tool pin design in FSP
Authors: Hsiang Chen Hsu, Wei Yao Chang
Abstract: In this paper, experimental procedures are developed to measure the tensile mechanical property of ultra thin Copper (Cu) wire (=1mil) before and after electric flame-off (EFO). Characteristics of free air ball (FAB), heat affected zone (HAZ) and as-drawn wire on 99.99% Cu wire have been carefully investigated by nanoindentation, microhardness and self-design pull test fixture, respectively. A secondary EFO technique has been conducted to reduce the strength of Cu wire and increase the bondability. The determined accurate material properties can then be applied to finite element analysis (FEA) for further reliability studies. A series of comprehensive parametric studies were conducted in this research.
Authors: Li Jun Yang, Yang Wang
Abstract: Laser forming of metal sheet is a forming technology of sheet without a die that the sheet is deformed by internal thermal stress induced by partially irradiation of a laser beam. In this paper, the bending behavior of common stainless steel 1Cr18Ni9 sheet is studied after being irradiated by straight line with a Nd:YAG pulsed laser beam. The aim of the investigation is to find out the relationship of the physical behaviors of heat affected zone (HAZ) with the pulse parameters of the laser. Through the analysis of the fundamental theory of pulsed laser affected, this paper shows the affected characteristics of metal sheet with pulsed laser forming. The results show that the microstructure of HAZ of pulsed laser scanned is layered, and the micro-hardness is improved than that in matrix. The microstructures show that the deformed grain structure is inhomogeneous, that caused the grain sizes and grain orientations in HAZ to become different. By qualitative analysis of experimental result, the conclusion obtained may provide basis for theoretical investigation and possible industrial application of laser forming process in the future.
Authors: Jacek Górka
Abstract: In this paper an influence of simulated thermal cycle on properties and HAZ structure of 10 mm thick S700MC steel plates. The introduction of thermomechanically processed steels with high yield and relatively low carbon equivalent, will significantly reduce the time of welding works by reducing the preheating temperature, or even complete removal of this processing step, furthermore reduction of cross-sectional areas of structural elements, making welded structures with the same capacity will be more slender and lighter. The simulation of thermal cycles was carried out on a specially built test stand equipped with resistive heating source infrared camera VarioCam Head HR with 50 mm lens and a computer with software IRBIS 3 plus. Simulation was prepared for simple and complex thermal cycle. Simulation studies of thermal cycles consisted of resistive heating of samples prepared for the impact test. Single thermal cycles were simulated at temperatures ranging from 400 to 1300 oC, 100 oC and the cycle complex. For each temperature three repeats were carried out. Specimens were tested on impact, strength test and also hardness and metallographical tests. The study showed that there is a possibility to use a purpose built system to simulate simple and complex thermal cycles of S700 MC steel in specific ranges of the cooling time t8/5. Analysis of the results of the study showed that the welding thermal cycle strongly influences the structural changes and phase in the HAZ zone of S700 MC steel. Areas of HAZ heated to high temperatures above 1000 [°C], show a sudden drop of toughness to unacceptable levels of impact strength (27 [J/cm2]). This sharp decrease in toughness is associated with uncontrolled separation processes of MX phases and dissolution of carbides, niobium and vanadium carbonitrides in austenite during heating. The study also showed that the chemical composition of steel and especially titanium and aluminium content is sufficient to bind in the HAZ free nitrogen and reduce the aging process. The control of the amount of heat introduced into the joint area during welding will reduce the adverse separation processes in the weld and HAZ which will ensure adequate toughness of the connection. Precise knowledge of the phenomena occurring in the HAZ during the thermal cycle can impact the ability to control properties and structure of the welded joint.
Authors: Aniruddha Ghosh, Somnath Chattopadhyaya, S. Mukherjee
Abstract: In Submerged Arc Welding process involves critical set of variables which are needed to control. An attempt has been made in this paper to find out- the influence of the heat input and bead volume on HAZ Hardness for Submerged Arc Welding Process of Mild steel plates. Mild steel plates are welded by changing input variables (current, voltage, travel speed, i.e. heat input) and Rockwell hardness no. has been observed on welded portion and at the zone adjacent to the welded portion. A detailed analysis of the microstructure changes is carried out to understand the HAZ softening phenomenon.
Authors: Jian Ping Zhou, Mamtimin Gheni, Chu Hua Liang, Yan Xu, Bi Sheng Zhou
Abstract: In order to research the surface integrity of SEAM, the surface figure, surface heat-affected zones (HAZ ) and surface hardness are analyzed. The author mainly researches the influence factors of water pressure, air pressure, cathode feed rate and relative line speed on processing indictor. The orthogonal experiment results indicate that the main influence factors of surface roughness and HAZ are air pressure, gap voltage and cutting depth. In SEAM, certain scope pressure atomization of dielectric liquid has deionization and arc-extinguishing effect, and takes away melted metal and heat from the discharge channel in time. Workpiece surface will be smoothness. However, the enlarged air pressure will break normal electrode discharge and make the surface smoothness worse. The research of influence of gap voltage on surface quality are accomplished.
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