THE MICROSTRUCTURAL, MECHANICAL, AND FRACTURE PROPERTIES OF AUSTENITIC STAINLESS STEEL ALLOYED WITH GALLIUM

摘要

Diffusion of Ga into austenitic stainless steel storage containers housing plutonium-gallium compounds is likely during fifty-year storage at temperatures as high as 250 deg C. Thus, the mechanicar and fracture properties of austenitic stainless steels alloyed with gallium require assessment in order to determine the likelihood of premature failure following Ga uptake. AISI 304 L SS (UNS S30403) was cast with 1, 3, and 12 wt percent Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having a nearly identical composition to the austenitic phase. Room temperature tests indicated that small additions of Ga (less than 3 wt percent) were beneficial to the mechanical behavior of 304 L SS but that 12 wt percent Ga resulted in a 95 percent loss in ductility. Small additions of Ga are beneficial to the cracking resistance of stainless steel also. 3 wt percent Ga alloys showed the greatest resistance to crack initiation and propagation as measured by fatigue crack growth rate, fracture toughness, and tearing modulus. 12 wt percent Ga alloys were least resistant to crack initiation and propagation and these alloys failed by transgranular cleavage. It is hypothesized that the embrittlement is attributable to composition (i.e., Ga in solid solution) and not microstructure (i.e., the presence of ferrite), per se.