Rationale

In harmony with other product forms of Grade 91 Type 2, such as A213, A335 and A336, a new supplement S64 for Minimum Cooling Rate will be added in response to EPRI guidelines and ASME Code Case 2864-3. The rapid cooling is required to maintain the proper tempered martensite microstructure with fine dispersion of precipitates necessary for meeting the tensile properties and long-term creep strength.