D310 CHARACTERISTICS OF THE WELDED JOINTS OF FERRITIC HEAT RESISTANT PIPE AND TUBE STEELS FOR ADVANCED STEAM POWER PLANTS

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Effects of welding processes and thermal histories on mechanical properties and failure behaviors have been investigated in P/T91,P92 and P122 steels for utility boiler components. In T/P91 steel, the low hardness value below about 170Hv was remarkably influenced by the abnormal thermal exposure at the inter-critical region between the Ac1 and the Ac3 and subsequent heating at the temperature just below the Ac1. The T/P91 steel with low hardness of 155Hv showed low creep rupture strength below the allowable stresses of T/P91. The continuous fatigue life was similar for both P92 and P122 at the temperature range. The fatigue life of the CFI test with 10 min. hold time also indicated nearly a similar value in the base metal, while lower values by a factor of 2&acd;4 in the weld metal and the HAZ compared to that of the continuous fatigue test. The fatigue crack growth rates at 600℃ and 700℃ were faster in the HAZ than in the base metal at lower values of ΔK. However, the trends was gone into reverse at higher values of ΔK. At a given temperature, the creep crack propagation life of P122 is a little longer than that of P92. The correlation between a^^・ and C_t could be described as a^^.&acd;[C_t]^<1.149> in P92 and a^^.&acd;[C_t]^<0.9567> in P122 at the temperature range of 600℃ to 650℃.

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