Creep-resistant, cobalt-free alloys for high temperature, liquid-salt heat exchanger systems

An essentially Fe- and Co-free alloy for use in contact with liquid fluoride salts consisting essentially of, in terms of weight percent:

• Cr 6.0 to 7.5
• Al 0 to 0.15
• Mn 0.5 to 0.85
• Mo 11 to 19.5
• Ta 0.3 to 4.5
• W 0.01 to 9
• C 0.03 to 0.08
• Re 0 to 1
• Ru 0 to 1
• B 0 to 0.001
• N 0.0005 to 0.005
• Ni balance, wherein Mo+W is 19.85 or less, and Mo+Cr is 26.37 or less;
• said alloy being characterized by, at 850° C., a yield strength of at least 25 Ksi, a tensile strength of at least 38 Ksi, a creep rupture life at 12 Ksi of at least 25 hours, and a corrosion rate, expressed in weight loss [g/(cm2 sec)]10−11 during a 1000 hour immersion in liquid FLiNaK at 850° C., in a range of 3 to 10, said alloy has a microstructure consisting of γ phase and M6C, wherein M6C is 1 to 2.5 in wt %, and having a corrosion susceptibility index between 0.09 and 0.12.