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Mehdi Fattahi - One of the best experts on this subject based on the ideXlab platform.
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Effect of Ti-based inclusions and acicular ferrite on the corrosion performance of Multipass Weld metals
Materials Chemistry and Physics, 2014Co-Authors: Mehdi Fattahi, N Nabhani, E. Rafiee, Nasibi, E. Ahmadi, Y FattahiAbstract:Abstract This paper reports the effect of Ti-based inclusions and acicular ferrite on the corrosion performance of carbon steel Multipass Weld metals. The Weld metals containing Ti-based inclusions have been prepared by addition of different quantities of titanium oxide nanoparticles to the electrode coating, which was dispersed using the ultrasonication process. After Welding, the relationship between microstructure and corrosion performance of the Weld metals was studied through full metallographic, potentiodynamic polarization and electrochemical impedance spectroscopy methods. It was observed that the use of titanium oxide nanoparticles in the coated electrodes grain refined the Weld metals, which is attributed to the beneficial role of nanostructured inclusions as heterogeneous nucleation sites of acicular ferrite. It was also deduced from the corrosion tests of the Weld samples that increasing the Ti-based inclusion content and grain refinement can deteriorate the corrosion resistance of the Weld metals.
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a new technique for the strengthening of aluminum tungsten inert gas Weld metals using carbon nanotube aluminum composite as a filler metal
Micron, 2013Co-Authors: Mehdi Fattahi, N Nabhani, E Rashidkhani, Y Fattahi, S Akhavan, N ArabianAbstract:The effect of multi-walled carbon nanotube (MWCNT) on the mechanical properties of aluminum Multipass Weld metal prepared by the tungsten inert gas (TIG) Welding process was investigated. High energy ball milling was used to disperse MWCNT in the aluminum powder. Carbon nanotube/aluminum composite filler metal was fabricated for the first time by hot extrusion of ball-milled powders. After Welding, the tensile strength, microhardness and MWCNT distribution in the Weld metal were investigated. The test results showed that the tensile strength and microhardness of Weld metal was greatly increased when using the filler metal containing 1.5 wt.% MWCNT. Therefore, according to the results presented in this paper, it can be concluded that the filler metal containing MWCNT can serve as a super filler metal to improve the mechanical properties of TIG Welds of Al and its alloys.
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Effect of Ti-containing inclusions on the nucleation of acicular ferrite and mechanical properties of Multipass Weld metals.
Micron (Oxford England : 1993), 2012Co-Authors: Mehdi Fattahi, N Nabhani, N Arabian, M. Hosseini, Ebrahim RahimiAbstract:In the present study, the influence of Ti-containing inclusions on the development of acicular ferrite microstructure and mechanical properties in the Multipass Weld metals has been studied. Shielded metal arc Weld deposits were prepared by varying titanium content in the range of 0.003-0.021%. The variation in the titanium content was obtained by the addition of different amounts of titanium oxide nanoparticles to the electrode coating. The dispersion of titanium oxide nanoparticles, composition of inclusions, microstructural analysis, tensile properties and Charpy impact toughness were evaluated. As the amount of Ti-containing inclusions in the Weld metal was increased, the microstructure of the Weld metal was changed from the grain boundary allotriomorphic ferrite structure to acicular ferrite with the intragranular nucleation of ferrite on the Ti-containing inclusions, and the mechanical properties were improved. This improvement is attributable to the increased percentage of acicular ferrite due to the uniform dispersion of Ti-containing inclusions and the pinning force of oxide nanoparticles against the growth of allotriomorphic ferrite and Widmanstätten ferrite from the austenite grain boundaries.
Kazutoshi Nishimoto - One of the best experts on this subject based on the ideXlab platform.
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Influences of phosphorus and sulphur on ductility dip cracking susceptibility in Multipass Weld metal of alloy 690
Science and Technology of Welding and Joining, 2012Co-Authors: Kazuyoshi Saida, Hiroyuki Ogiwara, Y Nomoto, H Okauchi, Kazutoshi NishimotoAbstract:The influence of P and S on ductility dip cracking susceptibility in the reheated Weld metal of alloy 690 was evaluated by the spot Varestraint test using different alloy 690 filler metals, while varying the contents of P and S. The ductility dip cracking susceptibility was reduced with a decrease in the content of P and S in the filler metal; the amount of (P+1·2S) in the Weld metal should be limited to 30 ppm in order to prevent microcracking in the Multipass Weld metal. A numerical simulation of cosegregation behaviour of P and S revealed that both elements were segregated at the grain boundary in the ductility dip temperature range during Multipass Welding. A molecular orbital analysis has suggested that ductility dip cracking can be attributed to grain boundary embrittlement due to grain boundary segregation of P and S.
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metallurgical mechanism of ductility dip cracking in Multipass Welds of alloy 690
Transactions of JWRI, 2010Co-Authors: H Okauchi, Hiroyuki Ogiwara, Kazuyoshi Saida, Y Nomoto, Kazutoshi NishimotoAbstract:A Ni-base superalloy, alloy 690 is highly susceptible to ductility-dip cracking, and the primary cause of ductility-dip cracking in the reheated Weld metal of alloy 690 is likely to be the reduction of hot ductility attributable to grain boundary segregation of impurity elements such as P and S (1). The objective of the present study is to clarify the cause of the increased ductility-dip cracking susceptibility with an increase in the P and S contents based on a grain boundary segregation analysis and a molecular orbital analysis of the binding strength of the grain boundary. 2. Materials and Experimental Procedures The base metal used is a commercial alloy 690. Several kinds of commercial filler metals (FM1-FM3), lab-melting filler metals (FF1-FF5) and extra high-purity filler metal (EHP) were employed for comparison. The chemical compositions of base metal and filler metals used are shown in Table 1. The ductility-dip cracking susceptibility in the reheated Weld metal was evaluated by the spot-Varestraint test. 3. Effects of P and S on Ductility-Dip Cracking The relationship between (P+1.2S) content in the Weld metals and the DTR evaluated is shown in Fig. 1. Open and filled symbols indicate crack-free and cracking in the Multipass Weld cracking test, respectively. There is a good linear relationship between the compositional parameter of (P+1.2S) and the DTR for all Weld metals. According to the Multipass Weld cracking test results, the critical DTR where microcracks didn't occur during Multipass Welding could be estimated as approx. 200K. It follows that the amount of (P+1.2S) in the Weld metal should be limited to 30ppm in order to prevent ductility-dip cracking in the Multipass Weld metal.
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microcracking behaviour and mechanism in Multipass Weld metal of alloy 690
Quarterly Journal of The Japan Welding Society, 2010Co-Authors: Kazuyoshi Saida, Y Nomoto, Akira Taniguchi, Masashi Sakamoto, Kazutoshi NishimotoAbstract:Microcracking behaviours in the Multipass Welds of alloy 690 were investigated. The effect of impurity elements such as P and S on ductility-dip cracking susceptibility in the reheated Weld metal was evaluated by the spot-Varestraint test using different filler metals varying the contents of P and S. The ductility-dip cracking susceptibility was reduced with a decrease in the content of impurity elements in the filler metal, and the amount of (P+1.2S) in the Weld metal should be limited to 30ppm in order to prevent the microcracking in the Multipass Weld metal. Numerical calculation of microsegregation and molecular orbital analysis have suggested that ductility-dip cracking was attributed to the grain boundary embrittlement due to the grain boundary segregation of P and S. FEM analysis of thermal strain predicted that ductility-dip cracks would occur during Multipass Welding when the plastic strain-temperature curve intersected the ductility-dip temperature range (DTR). The effect of the addition of rare earth metals (REM) to the Weld metal on the microcracking susceptibility was examined by using the La or Ce containing filler metals. The ductility-dip cracking susceptibility could be significantly improved by adding 0.01-0.025mass%REM to the Weld metal. Microstructural analyses revealed that the ductility-dip cracking susceptibility decreased as a result of lowering the grain boundary segregation P and S due to the scavenging effect of REM. The Multipass Welding test confirmed that microcracks in the Multipass Welds of alloy 690 were completely prevented by using the filler metals containing approx. 0.03mass%REM.
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effect of ce addition to filler metal on microcracking susceptibility of alloy 690 Multipass Weld metal
Quarterly Journal of The Japan Welding Society, 2009Co-Authors: Kazuyoshi Saida, Akira Taniguchi, Masashi Sakamoto, Kazutoshi NishimotoAbstract:The effect of Ce addition on microcracking susceptibility in the Multipass Weld metal of alloy 690 was investigated in order to improve the microcracking susceptibility in it. The ductility-dip cracking susceptibility in the reheated Weld metal could be greatly improved by adding 0.015-0.025mass%Ce to the Weld metal. Conversely, the excessive Ce addition to the Weld metal led to liquation and solidification cracking in the Weld metal. Hot ductility of the Weld metal at the cracking temperature was greatly improved by adding 0.01-0.03mass%Ce, implying that the ductility-dip cracking susceptibility was decreased as a result of the desegregation of impurity elements of P and S to grain boundaries due to the scavenging effect of Ce. The excessive Ce addition to the Weld metal resulted in the liquation and solidification cracking attributed to the formation of liquefiable Ni-Ce intermetallic compound. The Multipass Welding test confirmed that microcracks in the Multipass Welds were completely prevented by using the filler metal added 0.032mass%Ce.
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amelioration of microcracking in Multipass Weld metal of alloy 690 by adding rare earth metals
PROCEEDINGS OF THE ASME PRESSURE VESSELS AND PIPING CONFERENCE VOL 6 PTS A AND B, 2009Co-Authors: Kazutoshi Nishimoto, Kazuyoshi Saida, Yasuyuki FujiyaAbstract:The effect of the addition of rare earth metals (REM) to the Weld metal on the microcracking susceptibility in the Multipass Welds of alloy 690 was examined by using the La or Ce containing filler metals. The amounts of the La and Ce in the filler metal were varied in several levels. The microcracking susceptibility of the reheated Weld metal was evaluated by the spot and transverse-Varestraint tests using pre-Welded specimens made by GTAW. The augmented strain levels were varied from 0.50–2.44%. Cracks that occurred in the reheated Weld metal evaluated by the Varestraint test could be classified into three types; ductility-dip, liquation and solidification cracking. The ductility-dip cracking susceptibility could be significantly improved by adding 0.01–0.025mass%REM to the Weld metal. Adversely, the excessive REM addition led to the liquation and/or solidification cracking in the Weld metal. Microstructural analyses revealed that phosphide and sulphide of La or Ce were formed in the REM containing Weld metals, and Ni-La or Ni-Ce intermetallic compound was additionally identified in the excessively REM containing Weld metals. High temperature tensile test indicated that hot ductility of the Weld metal was ameliorated by adding 0.01–0.03mass%REM, implying that the ductility-dip cracking susceptibility was decreased as a result of lowering the grain boundary segregation of impurity elements such as P and S due to the scavenging effect of REM. The liquation and solidification cracking in the excessively REM containing Weld metals were considered to be due to the formation of liquefiable intermetallic compounds of Ni and REM. The Multipass Welding test confirmed that microcracks in the Multipass Welds of alloy 690 were completely prevented by using the filler metals containing approx. 0.03mass%REM.Copyright © 2009 by ASME
H Madaah R Hosseini - One of the best experts on this subject based on the ideXlab platform.
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influence of peak temperature during simulation and real thermal cycles on microstructure and fracture properties of the reheated zones
Materials & Design, 2010Co-Authors: Sadegh Moeinifar, A H Kokabi, H Madaah R HosseiniAbstract:Abstract The objective of this paper is to study the influence of the second peak temperature during real and simulated Welding on properties of the subcritically (S), intercritically (IC) and supercritically (SC) reheated coarse grained heat affected (CGHAZ) zones. The X80 high strength pipeline microalloyed steel was subject to processing in a double-pass tandem submerged arc Welding process with total heat input of 6.98 kJ/mm and thermal cycles to simulate microstructure of reheated CGHAZ zones. This involved heating to a first peak temperature ( T P1 ) of 1400 °C, then reheating to different second peak temperatures ( T P2 ) of 700, 800 and 900 °C with a constant cooling rate of 3.75 °C/s. Toughness of the simulated reheated CGHAZ regions were assessed using Charpy impact testing at 0 °C, −25 °C and −50 °C. The microstructure of the real and simulated reheated CGHAZ regions was investigated using an optical microscope and field emission scanning electron microscope. Morphology of the martensite/austenite (MA) constituent was obtained by the use of a field emission scanning electron microscope. The blocky and connected MA particles, along prior-austenite grain boundaries, act as a brittle phase for the initiation site of the brittle fracture. Charpy impact results indicated that IC CGHAZ had less absorbed energy with higher transition temperature and hardness. The SC CGHAZ region showed higher absorbed impact energy with lower hardness. Design of Multipass Weld joints with less IC CGHAZ regions can result in a higher toughness property.
N Nabhani - One of the best experts on this subject based on the ideXlab platform.
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Effect of Ti-based inclusions and acicular ferrite on the corrosion performance of Multipass Weld metals
Materials Chemistry and Physics, 2014Co-Authors: Mehdi Fattahi, N Nabhani, E. Rafiee, Nasibi, E. Ahmadi, Y FattahiAbstract:Abstract This paper reports the effect of Ti-based inclusions and acicular ferrite on the corrosion performance of carbon steel Multipass Weld metals. The Weld metals containing Ti-based inclusions have been prepared by addition of different quantities of titanium oxide nanoparticles to the electrode coating, which was dispersed using the ultrasonication process. After Welding, the relationship between microstructure and corrosion performance of the Weld metals was studied through full metallographic, potentiodynamic polarization and electrochemical impedance spectroscopy methods. It was observed that the use of titanium oxide nanoparticles in the coated electrodes grain refined the Weld metals, which is attributed to the beneficial role of nanostructured inclusions as heterogeneous nucleation sites of acicular ferrite. It was also deduced from the corrosion tests of the Weld samples that increasing the Ti-based inclusion content and grain refinement can deteriorate the corrosion resistance of the Weld metals.
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a new technique for the strengthening of aluminum tungsten inert gas Weld metals using carbon nanotube aluminum composite as a filler metal
Micron, 2013Co-Authors: Mehdi Fattahi, N Nabhani, E Rashidkhani, Y Fattahi, S Akhavan, N ArabianAbstract:The effect of multi-walled carbon nanotube (MWCNT) on the mechanical properties of aluminum Multipass Weld metal prepared by the tungsten inert gas (TIG) Welding process was investigated. High energy ball milling was used to disperse MWCNT in the aluminum powder. Carbon nanotube/aluminum composite filler metal was fabricated for the first time by hot extrusion of ball-milled powders. After Welding, the tensile strength, microhardness and MWCNT distribution in the Weld metal were investigated. The test results showed that the tensile strength and microhardness of Weld metal was greatly increased when using the filler metal containing 1.5 wt.% MWCNT. Therefore, according to the results presented in this paper, it can be concluded that the filler metal containing MWCNT can serve as a super filler metal to improve the mechanical properties of TIG Welds of Al and its alloys.
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Effect of Ti-containing inclusions on the nucleation of acicular ferrite and mechanical properties of Multipass Weld metals.
Micron (Oxford England : 1993), 2012Co-Authors: Mehdi Fattahi, N Nabhani, N Arabian, M. Hosseini, Ebrahim RahimiAbstract:In the present study, the influence of Ti-containing inclusions on the development of acicular ferrite microstructure and mechanical properties in the Multipass Weld metals has been studied. Shielded metal arc Weld deposits were prepared by varying titanium content in the range of 0.003-0.021%. The variation in the titanium content was obtained by the addition of different amounts of titanium oxide nanoparticles to the electrode coating. The dispersion of titanium oxide nanoparticles, composition of inclusions, microstructural analysis, tensile properties and Charpy impact toughness were evaluated. As the amount of Ti-containing inclusions in the Weld metal was increased, the microstructure of the Weld metal was changed from the grain boundary allotriomorphic ferrite structure to acicular ferrite with the intragranular nucleation of ferrite on the Ti-containing inclusions, and the mechanical properties were improved. This improvement is attributable to the increased percentage of acicular ferrite due to the uniform dispersion of Ti-containing inclusions and the pinning force of oxide nanoparticles against the growth of allotriomorphic ferrite and Widmanstätten ferrite from the austenite grain boundaries.
Ebrahim Rahimi - One of the best experts on this subject based on the ideXlab platform.
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Effect of Ti-containing inclusions on the nucleation of acicular ferrite and mechanical properties of Multipass Weld metals.
Micron (Oxford England : 1993), 2012Co-Authors: Mehdi Fattahi, N Nabhani, N Arabian, M. Hosseini, Ebrahim RahimiAbstract:In the present study, the influence of Ti-containing inclusions on the development of acicular ferrite microstructure and mechanical properties in the Multipass Weld metals has been studied. Shielded metal arc Weld deposits were prepared by varying titanium content in the range of 0.003-0.021%. The variation in the titanium content was obtained by the addition of different amounts of titanium oxide nanoparticles to the electrode coating. The dispersion of titanium oxide nanoparticles, composition of inclusions, microstructural analysis, tensile properties and Charpy impact toughness were evaluated. As the amount of Ti-containing inclusions in the Weld metal was increased, the microstructure of the Weld metal was changed from the grain boundary allotriomorphic ferrite structure to acicular ferrite with the intragranular nucleation of ferrite on the Ti-containing inclusions, and the mechanical properties were improved. This improvement is attributable to the increased percentage of acicular ferrite due to the uniform dispersion of Ti-containing inclusions and the pinning force of oxide nanoparticles against the growth of allotriomorphic ferrite and Widmanstätten ferrite from the austenite grain boundaries.