Metallurgical variability Subject

It is notable that while it is possible to produce maraging steels with consistently uniform mechanical properties, the stress corrosion properties are subject to scatter, as indicated in Fig. 3.34. To a large extent this scatter is an indication of the greater sensitivity of s.c.c. resistance to metallurgical variables. Although the variation in cracking resistance is not well understood, and the reaction to certain treatments not always consistent, certain observations may be used to indicate guidelines for improved properties. 

The actual mechanism of radiation embrittlement is not completely understood. For example, in low alloy RPV steel, radiation embrittlement is a function of both environmental and metallurgical variables. Fluence or dpa, and copper and nickel content have been identified as the primary contributors in US NRC Regulatory Guide 1.99, Revision 2 [5.1]. Other important variables include flux, temperature and phosphorus content. There is evidence that other variables such as heat treatment may also influence embrittlement. Therefore, mathematically based statistical data correlation are subject to uncertainty. 

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