Improvement of Long-Term Creep Rupture Strengths of 9-11Cr Ferritic Heat Resistant Steels for Boiler Components

摘要

A well-known problem with 9-11%Cr-W ferritic heat resistant steels is their instability of long-term creep rupture strengths at around 650℃. To improve the instability, a new 9%Cr-W-Co ferritic heat resistant steel was proposed as candidate material for boiler tube and pipe for up to 650℃ application, and its creep rupture property was investigated. The proposed material with very low Al and Ni content showed "Inverse-S" curve on the stress-rupture time diagram at 650℃, and the improvement of creep resistance instability was confirmed by the long-term creep rupture tests. The tube formability of the material was verified by the boiler tube manufacturing test.