2.08.2.4.1 Chemical compositions, physical properties, and mechanical properties

The chemical compositions of other nickel-based alloys not already described in the previously men­tioned categories are shown in Table 3, along with those of the alloys mentioned above.

Alloy G (UNS N06007) has excellent corrosion resistance to hot sulfuric acid and hot phosphoric acid. The alloy has superior corrosion resistance to oxidizing environments compared to Alloy C-276, due to its higher chromium content (about 22%) than that of Alloy C-276 (about 18%). On the other hand, Alloy G has inferior corrosion resistance to reducing environments such as sulfuric acid com­pared to Alloy C-276, due to its lower molybdenum content (about 6.5%) than that of Alloy C-276 (about 18%). A copper content of ^2% is included in Alloy G to improve its corrosion resistance in sulfuric acid. Alloy G can be welded because of its niobium content, which stabilizes carbon. However, the alloy is highly susceptible to hot cracking during welding.

Alloy G-3 (UNS N06985) is improved in terms of the bending characteristics of welded joints due to a reduced carbon and niobium content. This alloy has a lower susceptibility to hot cracking during welding.

Alloy G-30 (UNS N06030) was originally devel­oped to improve corrosion resistance in wet phosphoric acid. This alloy shows excellent corrosion resis­tance to oxidizing acids, such as nitric acid, and also to oxidizing halogen-ion-containing environments such as nitric and fluoric acid, due to its increased chromium content (about 30%).38

The chromium content in this alloy leads to delete­rious effects in molten fluoride. However, Alloy N shows excellent corrosion resistance to molten fluoride due to its reduced chromium content (about 7%).3

Alloy 230 (UNS N06230) shows excellent resis­tance to oxidation and nitriding as well as high strength at high temperatures. This alloy has been applied as a heat-resistant material in industrial fur­naces and gas turbines.40

Alloy X (UNS N06002) is a solid-solution-hardened alloy owing to the presence of molybdenum. This alloy has high strength at high temperatures and good resistance to oxidation in high-temperature air.41

Alloy XR was originally developed as a structural material for high-temperature gas-cooled reactors (HTGR) and is a modified version of Alloy X. It is produced by vacuum double melting with optimized contents of manganese, silicon, and boron as inten­tional additives, while minimizing the aluminum, titanium, and cobalt content, as these are undesirable

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impurities.

The mechanical and physical properties of the above alloys are shown in Tables 4 and 5, respectively, together with those of other nickel-based alloys.