In the mid-1960s, the laboratories of the International Nickel
Company (INCO) initiated the development of a class of low-carbon,
age-hardening Ni-Cu-Cb steels called “NiCuAge” steels. The work focused on the
very low carbon, with changes in Ni, Cu, and Cb content and processing (hot
working schedules and heat treatment) to establish microstructure-mechanical
property relationships. The combinations of strength, ductility, and
processing characteristics exhibited by the Ni-Cu-Cb steels suggested a
variety of applications in transportation, automotive, and oil field
construction. Because of the low carbon content, the steel offered excellent
formability and weldability in the fully strengthened condition.
The key concepts discovered at this stage were the importance of
Ni and Cb additions to the copper steels. The Ni addition and the ratio of
Ni-to-Cu were established as a means to prevent cracking during hot working.
Researchers discovered that small additions of Cb significantly increased
strength, provided grain refinement, and did not degrade any characteristics
of the steel. At this stage, small laboratory melts (30 lb) were used for the
alloy composition optimization.
Hurley, J.L. and C.H. Shelton, “Age-Hardenable Nickel-Copper
Steels,” Metals Engineering Quarterly, ASM, May 1966.