Affordable Access

Publisher Website

Structural changes in a ferritic heat-resistant steel after long-term service

Materials Science and Engineering
Publication Date
DOI: 10.1016/0025-5416(84)90274-x


Abstract The microstructures of ASTM A335-P11 1Cr-0.5Mo steel specimens removed from tubes which operated in a crude oil reformer for 1.05 × 10 5 and 1.22 × 10 5 h at about 520°C were examined by transmission electron microscopy. The main structural elements, ferrite grains, post-pearlite grains and ferrite grain boundaries, were investigated. It is shown that ferrite grains after 1.05 × 10 5 h in service contain mainly needle-like Mo 2C precipitates and a very small amount of M 23C 6 carbides. The amount of M 23C 6 carbides in ferrite grains is significantly higher after 1.22 × 10 5 h is service. At ferrite grain boundaries after both service periods a large amount of M 7C 3 and M 23C 6 carbides was found. After 1.22 × 10 5 h in service, M 6C carbides were also observed at some ferrite grain boundaries. Some specimens were also normalized at 930°C after 1.05 × 10 5 h service and then tempered at 725°C. Transmission electron microscopy of heat-treated steel revealed small spherical precipitates in ferrite grains instead of needle-like molybdenum carbides and the majority of ferrite grain boundaries were free of precipitates. The results of microstructural investigations are discussed in terms of the eventual changes in creep properties.

There are no comments yet on this publication. Be the first to share your thoughts.