763 Thermal Stability

The superior thermal stability characteristics of alloy 59 are shown in Tables 7.10A and 7.10B. The data clearly demonstrates the detrimental effects of tungsten and copper on the thermal stability behavior of various alloys of the C family. Figure 7.2 shows the attack on the tungsten-containing Ni-Cr-Mo alloy C22 after aging at 1600°F for one hour. This phenomenon was also observed on other tungsten-containing Ni-Cr-Mo alloys, C-276, and alloy 686 along with the copper-containing alloy C2000.

In the real world, during welding of heavy-walled vessels and/or hot forming of heavy-walled materials, this phenomenon takes on an added importance in maintaining the superior corrosion resistance behavior. Other corrosion resistance data and information on physical metallurgy, fabricability, and weldability of alloy 59 have been adequately covered elsewhere [36-38].

TABLE 7.10B Thermal Stability per ASTM G28B after Sensitization at 1600°F (871°C)

Corrosion Rate (mpy)a

TABLE 7.10B Thermal Stability per ASTM G28B after Sensitization at 1600°F (871°C)

Corrosion Rate (mpy)a

Sensitization

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