Nickeland Nickel Alloy Systems 219

TABLE 7.1 Chronology of Historical Development of Some Austenitic Corrosion-Resistant Alloys

Decade

Alloys

Pre-1950s

300 SS, 200, 400, 600, alloys B & C

1950s

20Cb, 800, 825, alloy F, alloy X

1960s

300L series SS, 20Cb3, 904L, Al-6X alloy 700, 625, G, C-276

1970s

317LM, 254SMo, 28, G-3, C-4, B-2

1980s

A16XN, N06030, 22, 59, 1925hMo, 31

1990s

Controlled chemistry alloy B-2, B-3, B-4, B-10, 686, 2000, 33

metallurgy, melting technology, and thermomechanical processing, along with a better fundamental understanding of the role of various alloying elements, has led to new nickel alloys. These have not only extended the range of usefulness of existing alloys by overcoming their limitations but are reliable and cost-effective and have opened new areas of applications. This chapter briefly describes the various nickel alloy systems developed and in use during the last 100 years with comments as to what the future holds for the newer alloys developed in the last 20 years and the competition faced by these alloys in the new millennium. Table 7.1 gives the chronology of various aqueous corrosion alloys developed in the pre-1950 and post-1950 era. Prior to the 1950s the alloy choices available to material engineers for combating corrosion were very limited. The latter half of this century saw a phenomenal growth in the development of new nickel alloys, including the high-performance Ni-Cr-Mo C family alloys. As is evident from this listing of austenitic alloys, today's corrosion/material engineers have a much wider selection of alloys to meet their specific needs.

Some of the alloys are very recent, developed after the 1980s, whereas some date clearly back to the beginning of the twentieth century. New alloys and refinements of old ones are continually being developed. Typical composition of some of the common wrought nickel alloys of various alloy systems are given at the beginning of individual alloy sections, as described later.

Different from the aqueous corrosion alloys are a class of alloys known as "superalloys," which are intended for elevated temperature service, usually based on periodic table Group VIIIA elements, where relatively severe mechanical stressing is encountered and where high surface stability to various high-temperature modes of degradation is needed. The superalloys are divided into three classes: nickel base, cobalt base, and iron base, and these are utilized at a higher proportion of their actual melting point than any other class of commercial metallurgical materials. This chapter will not delve into the superalloys but direct the reader to many excellent books and articles in the open literature [1-5].

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