Abstract
From previous studies on 17-7 PH stainless steel and on Nitralloy-N steel, it had been expected that steels having martensitic or ferritic structure and containing proper amounts of Ni and Al might be hardened by aging at about 500°C, and therefore, age hardening behaviors of low carbon 16% Cr-2 or 3% Ni stainless steel containing 1% Al were investigated. The steel containing 0-19 C-16 Cr-3 Ni-1 Al (R1) exhibited a remarkable hardening by aging at about 500°C after solution treatment at I 100°C, and a tensile strength over 150kg/mm2 was obtained after aging for 1 to 10 hrs at 500°C. This steel, even if tempered at 700°C, was remarkably hardened by aging after the tempering. A steel containing 0.10 C-16 Cr-2Ni-1 Al (Si) also exhibited almost the same age hardening behavior as that of steel RI, but its tensile strength obtained was somewhat less than that of steel R1. A CsC1 type structure with a lattice constant of about 2-9 Å was found in the overaged specimens of steel R1 by means of the electron diffraction technique.
It was concluded that this phase was intermetallic compound NiAl (α′) and the remarkable age hardening properties observed in steels investigated could be attributed to the precipitation of the α′ phase from martensitic or ferritic matrix.
