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2,000 4,000 6,000 8,000 10,000 Exposure Time (h)

FIGURE 7.6 Metal wastage of nickel base alloys 602CA, 600, and 601 due to metal dusting after exposure in strongly carburizing CO — H2 — H2 gas at 650°C.

coupons. In the real world the components exposed to metal dusting environments are stressed and hence have certain amount of strain. Alloy 602CA, even with 1% strain, maintained its passive oxide layers, thus preventing any accelerated attack, whereas in alloy 690 the passive layer is damaged leading to accelerated metal wastage. Figure 7.6 shows the comparison between alloys 600, 601, and 602CA.

The combination of excellent high-temperature strength at temperatures greater than 1000° C and the excellent oxidation resistance up to 1200° C with good carburization/metal dusting resistance led to the selection and good performance of alloy 602CA in several diverse applications, as described later.

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