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Showing 2 results for Weldability
Volume 7, Issue 2 (9-2007)
Abstract
Thermal fatigue (heat checking), mechanical fatigue, wear and plastic deformation of critical areas of hot forging dies at working temperatures are the main mechanisms that reduce their lifetime. During forging processes the surfaces of the dies reach temperatures of 700-800 ºC. Therefore, hardfacing of these areas with nonferrous elevated temperature hardfacing alloys such as Stellite 6 can improve the performance and lifetime of the dies, many times. Hot hardness, galling resistance, hot corrosion and oxidation resistance, adhesive wear resistance, low friction coefficient and absence of allotropic transformation up to 1100 ºC are the most important properties of Stellite 6. H11 tool steel is widely used as hot forging die material. This steel because of its high alloy contents and, therefore, its hardenability is very sensitive to high cooling rates involved during welding cycles and hydrogen induced cracking (HIC). For this reason, in this research hardfacing parameters of H11 tool steel with Stellite 6 in TIG welding method have been investigated. According to the results, hardfacing of this steel in annealed hardfaced condition isn't feasible and it is recommended that preheating and intermediate temperatures during the hardfacing cycle between 310-370 ºC. The suitable current for TIG hardfacing of this steel by φ3.2mm filler rod was determined to be 80-85 amperes for the first layer and 90-100 amperes for upper layers. The minimum thickness for obtaining maximum hardness in the hardfacing layer (41-42 HRC) under these conditions was determined to be 3mm. It is recommended that the effective heat input for hardfacing of this steel under three-body heat transfer conditions would be less than 455kJ/m. It is also recommended that the Δt8→5 of H11 tool steel hardfacing cycle would be in the range 6 to 15.3s. Finally it is recommended that H11 hardfaced tool steel would be stress relived in the range 425 -500 ºC for 1 hour per 30mm base metal thickness.
Mohammad-Ali Rezaei, H. Naffakh-Moosavy,
Volume 19, Issue 2 (2-2019)
Abstract
Inconel 718 is precipitation strengthened Ni-base superalloy that is strengthened by “γ″ precipitate with the Ni3Nb chemical composition, is widely used for medium and high temperature applications in many industries. The aim of this study is to evaluate the effects of pre-cold treatment on microstructure, geometry of weld, Weldability, and mechanism of HAZ liquation cracking in Inconel 718 superalloy by Nd:YAG pulsed laser welding. Microstructure was investigated, using optical microscope and scanning electron microscope and hardness test was used to investigate mechanical properties. The results of numerical calculations using Rosental relation showed that the length of different welding regions including Mushy Zone (MZ), Partially Melted Zone (PMZ), and Heat Affected Zone (HAZ) decreased by 46%, 46%, and 56%, respectively. The experimental calculations also indicated that the length of PMZ and HAZ, as well as the HAZ area decreased by 2.1, 2.5, and 2.5 times, respectively. Considering that grain boundary liquation was observed in all samples, the possible mechanism for HAZ liquation cracking is constitutional liquation of Nb-rich carbides and delta precipitates that encourages the formation of liquid films in the grain boundaries and causes HAZ liquation cracking in this region. Also, the hardness profile indicates that the hardness of the weld metal increased by using pre-cold conditions.