A Comparative Study of Microstructures and Properties of Two Types of Nickel-Base Alloy Covered Electrodes
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JMEPEG (2017) 26:94–104 DOI: 10.1007/s11665-016-2434-4
A Comparative Study of Microstructures and Properties of Two Types of Nickel-Base Alloy Covered Electrodes Huang Wang and Guo He (Submitted February 17, 2016; in revised form November 2, 2016; published online November 17, 2016) Two types of nickel-base alloy covered electrodes, ENiCrMo-6 and ENiCrFe-9, were investigated and compared among their deposited metal compositions, microstructures, strengths, and cryogenic impact values. They all exhibited dendritic microstructures which were composed of dendritic fcc nickel-base solid solution, interdendritic phases, and grain boundary carbides. The molybdenum in the deposited metals tended to migrate and aggregate toward the edges of the dendrite arms during solidification. The niobium preferred to form oxide and/or carbide and aggregate in the interdendritic regions. The grain boundaries were filled with the continuous carbides and oxides. The differences in the tensile mechanical properties of the deposited metals of the two types of electrodes were relatively minor. The impact values of ENiCrMo-6 at 2196 C were above 80 J; while that of ENiCrFe-9 were in the range of 54-66 J. The relatively high level of carbon and sulfur and more grain boundary precipitates should be responsible for the lower cryogenic impact value of the ENiCrFe-9 covered electrode. Keywords
9 percent nickel steel, cryogenic impact, ENiCrFe-9, ENiCrMo-6, nickel-base alloy
1. Introduction The Ni-base alloy welding consumables can be used for welding the structures that serves from cryogenic to high temperatures due to their stable austenitic structure over the large temperature interval. ENiCrMo-6 and ENiCrFe-9 are two typical nickel-base alloy covered electrodes, both which have been recommended to be used for welding 9 percent nickel steel and other similar applications to produce excellent aswelded strength and impact toughness at liquid nitrogen temperatures (Ref 1, 2). According to the specification of AWS A5.11/A5.11M, both welding materials have very similar composition ranges of most major elements (i.e., Ni, Cr, Nb, W, Mn) in their deposited metals, but different compositions in molybdenum, iron, and carbon (Ref 2). For ENiCrMo-6 covered electrode, the molybdenum in its deposited metal is in range of 5.0-9.0 wt.%, and the maximum limits of iron and carbon are 10.0 and 0.10 wt.%, respectively. But for ENiCrFe9 covered electrode, the molybdenum is in range of 2.55.5 wt.%, and the maximum limits of iron and carbon are 12.0 and 0.15 wt.%, respectively. The different chemical compositions would influence as-welded microstructures, mechanical properties (especially the impact energy at cryogenic temperatures), as well as corrosion resistance. Comparison of those differences may provide valuable data and basis for the design Huang Wang, Shanghai Key Lab of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240, China; and Guo He, Shanghai Key Lab of Materials Laser Processing and Modification, Shanghai Jiao T
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