High nickel-based alloy

Most nonferrous metals are suitable for low temperature service. Essentially, all copper, aluminum, and high nickel based alloys remain tough and ductile in the cryogenic range. Low temperature applications also utilize low nickel alloys, such as 2-1/4 Ni and 3-1/2 Ni. Cryogenic apphcations utilize 9% Ni, stainless steel and aluminum. Austenitic stainless steels are capable of exposure to temperatures to absolute zero, (—) 459°F. 

Also, relatively new are the 6% molybdenum super-austenitic stainless steels, which possess the strength of duplex stainless steels and corrosion resistances about midway between the duplex stainless steels and the high-nickel-based alloys. Welding super-austenitic stainless is not a problem with molybdenum-enriched filler metals. Examples of high-molybdenum alloys are AL-6XN (Allegheny Ludlum Corp.) and 254 SMO (Avesta Sheffield, Inc.). Sorell (1994) and Kane (1993) present concise reviews of the various alloy groups. 

Plain Carbon and Low Alloy Steels. For the purposes herein plain carbon and low alloy steels include those containing up to 10% chromium and 1.5% molybdenum, plus small amounts of other alloying elements. These steels are generally cheaper and easier to fabricate than the more highly alloyed steels, and are the most widely used class of alloys within their serviceable temperature range. Figure 7 shows relaxation strengths of these steels and some nickel-base alloys at elevated temperatures (34). 

The greatest use of cubic boron nitride is as an abrasive under the name Bora2on, in the form of small crystals, 1—500 p.m in si2e. Usually these crystals are incorporated in abrasive wheels and used to grind hard ferrous and nickel-based alloys, ranging from high speed steel tools and chilled cast-iron to gas turbine parts. The extreme hardness of the crystals and their resistance to attack by air and hot metal make the wheels very durable, and close tolerances can be maintained on the workpieces. 

The cubic BN crystals may also be bonded into strong bodies that make excellent cutting tools for hard iron and nickel-based alloys. Such tools produce red-hot chips and permit the wider use of tough, high temperature alloys which would otherwise be prohibitively difficult to shape (12,20,21) (see... 

Silver-palladium-manganese brazes possess excellent creep characteristics and have been developed for high-temperature applications involving the use of cobalt or nickel-based alloys, heat-resistant steels, molybdenum and tungsten. Their liquidus temperatures lie in the range 1 100-1 250°C. 

In the gas-cooled reactor, reaction.between the coolant and the moderator results in formation of a proportion of carbon monoxide in the atmosphere. This gas can be carburising to nickel-base alloys but the results of tests in which CO2 was allowed to react with graphite in the furnace indicate that the attack on high-nickel alloys is slight, even at moderately high temperatures and is still mainly due to simple oxidation. 

Recent industrial experience for alloys in waste incineration plants has indicated the superiority of nickel-base alloys compared with iron-base and iron-containing alloys as would be expected from the previous discussion of the volatility of chlorides. Nickel-base alloys with no addition of iron and relatively high chromium contents have significantly improved performance in these applications (see Tables 7.33 and 7.34.) . 

Compared with ferritic carbon and low-alloy steels, relatively little information is available in the literature concerning stainless steels or nickel-base alloys. From the preceding section concerning low-alloy steels in high temperature aqueous environments, where environmental effects depend critically on water chemistry and dissolution and repassivation kinetics when protective oxide films are ruptured, it can be anticipated that this factor would be of even more importance for more highly alloyed corrosion-resistant materials. 

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