IMPROVEMENT OF CREEP RUPTURE STRENGTH OF HIGH STRENGTH 12CR FERRITIC HEAT-RESISTANT STEEL

摘要

Recently, steam temperature in USC(ultra super critical) power plant has been increasing in order to improve the efficiency. Superior high temperature mechanical properties such as creep rupture strength are required for materials applied for turbine blades and bolts of USC power plant above 600-650°C. A high strength 12% chromium ferritic heat-resistant steel, TAF650, which contains W, Co, and B, was developed for these applications. Chemical compositions of TAF650 were determined to make the microstructure stable at elevated temperatures. But the creep rupture strength of TAF650 at longer time than 1,000 hours deviated from the estimation from Larson-Miller curve obtained from the data within 2,000 hours. The present study is aimed at improving the long time creep rupture strength of TAF650 at 600-650°C. The effect of the contents of Ni, Co, B, etc. on the creep rupture strength of TAF650 was investigated. It is found that the decrease of the austenite forming elements such as Co and Ni and the increase of B suppress the degradation of long time creep rupture strength of TAF650.