In Situ Phase Transformation Study in Fine Grained Heat Affected Zone of Grade 91 Steels

摘要: Creep strength-enhanced ferritic (CSEF) steels such as the 9 Cr steel [ASTM A387 Grade 91] are widely used tubing and piping in new generation of fossil fired power plants. Microstructures fine-grained heat affected zone (FGHAZ) may significantly reduce creep strength leading to Type IV failures. Current research suggests that reducing pre-weld tempering temperature from 760 °C (high temper, HTT) 650 (low LTT) has potential double life these welds. To understand this improvement, time-resolved X-ray diffraction (TRXRD) measurement with synchrotron radiation was characterize microstructure evolution during fine grained heat-affected (HAZ) thermal cycling 91 steel. The measurements showed both M23C6 (M = Fe, Cr) MX Nb, V; X C, N) present sample after HTT condition. Near equilibrium fraction measured high condition (HTT, °C). However, amount LTT very low since peaks close background. During simulated FGHAZ cycling, partially dissolved sample. Interestingly, did not dissolve samples. Hypothesis for correlation carbide distribution pre-mature failure will be made.