The last group of
nickel-base CRA is the group of Ni-Cr-Fe alloys.
These alloys also may contain smaller amounts
of molybdenum and/or copper. Nickel-chromiumiron
alloys, in general, are less resistant to corrosion
than Ni-Cr-Mo alloys; however, they could
be less expensive and therefore find a wide range
of industrial applications. Figure 1(a) shows that
the corrosion rate of alloy 600 in sulfuric acid is
higher than the corrosion rate of alloy 825. The
latter contains small amounts of molybdenum
and copper (Table 2), which are beneficial alloying
elements for resistance to sulfuric acid. Also,
alloy 825 has a lower corrosion rate in nitric acid
(Fig. 1b), because it contains larger amounts of
chromium. One of the most common applications
of Ni-Cr-Fe alloys, such as alloy 33 and
N06030, is in the industrial production of phosphoric
acid and in highly oxidizing media such
as nitric acid.