Mechanical Properties of Alloy A286 at Cryogenic Temperature

Abstract

The strength and the toughness of Fe-base superalloy A286, which has been used as the structural material in cryogenic environments, were investigated at temperature range from room temperature to 4.2K by comparing with stainless steel SUS 304LN and Ni-base superalloy Inconel 718.The influence of grain size on mechanical properties of alloy A286 was also discussed.
The temperature dependence of the strength and toughness of alloy A286 was smaller than that of steel SUS 304LN, and similar to that of alloy Inconel 718.Therefore, the strength of alloy A286 was higher than that of steel SUS 304LN at room temperature, but almost the same as that of the steel at 4.2K.The fracture toughness K_1c(J) of alloy A286 was lower than that of steel SUS 304LN at room temperature but slightly higher than that of the steel at 4.2K.The strength of alloy Inconel 718 was higher, but the toughness of the alloy was lower than alloy A286 in the test temperature range.
The tensile strength, ductility and toughness of alloy A286 decreased with increase of the grain size, especially at 4.2K.From the results of microstructure observations and fracture mode analysises, low ductility and toughness of the specimen having a large grain size were attributed to the carbides precipitations at grain boundaries.However, the K_1c(J) of the specimen having even a coarse grain size of GS No. 1.5 was as high as 700 kgf·mm^-3/2 at 4.2K.