Effect of tungsten addition on high-temperature properties and microstructure of alumina-forming austenitic heat-resistant steels

High-temperature tensile and creep properties of W-added Alumina-Forming austenitic (AFAW) heat-resistant steel were investigated as compared with AFA steel without W. High-temperature tensile properties of two steels were similar to each other, but creep lifetime of AFAW steel was increased. Microstructural examination using SEM and TEM revealed that creep rate rapidly decreased when Laves phase initially precipitated. This indicated that the precipitation of Laves phase played an important role in hardening of AFA steel. It is also found that AFAW steel exhibited finer and denser Laves phase compared with AFA steel, which is due to partial substitution of W for Mo. The finer and denser distribution of Laves phase contributed to improved creep properties of AFAW steel by enhancement in precipitation hardening.