Abstract
Oak Ridge National Laboratory and Caterpillar (CAT) have recently developed a new
cast austenitic stainless steel, CF8C-Plus, for a wide range of high-temperature applications,
including diesel exhaust components and turbine casings. The creep-rupture life of
the new CF8C-Plus is over ten times greater than that of the standard cast CF8C stainless
steel, and the creep-rupture strength is about 50–70% greater. Another variant,
CF8C-Plus Cu/W, has been developed with even more creep strength at 750–850°C. The
creep strength of these new cast austenitic stainless steels is close to that of wrought
Ni-based superalloys such as 617. CF8C-Plus steel was developed in about 1.5 years
using an “engineered microstructure” alloy development approach, which produces
creep resistance based on the formation of stable nanocarbides (NbC), and resistance to
the formation of deleterious intermetallics (sigma, Laves) during aging or service. The
first commercial trial heats (227.5 kg or 500 lb) of CF8C-Plus steel were produced in
2002, and to date, over 27,215 kg (300 tons) have been produced, including various
commercial component trials, but mainly for the commercial production of the Caterpillar
regeneration system (CRS). The CRS application is a burner housing for the onhighway
heavy-duty diesel engines that begins the process to burn-off particulates
trapped in the ceramic diesel particulate filter (DPF). The CRS/DPF technology was
required to meet the new more stringent emissions regulations in January, 2007, and
subjects the CRS to frequent and severe thermal cycling. To date, all CF8C-Plus steel
CRS units have performed successfully. The status of testing for other commercial applications
of CF8C-Plus steel is also summarized