Investigation on Microstructures of Multipass Deposited Metal for 9Cr-1Mo Ferritic Steels

Abstract

The microstructures of multipass deposited metal for 9Cr-1Mo ferritic steels were investigated. Columnar martensites and a number of film austenites retained along the lath of martensite comprised primary microstructure. -ferrite was formed and the volume fraction of -ferrite increased as the chromium equivalent (Creq) of steel composition increased. Subjected to weld heating, the primary microstructure transformed. “Weld bead heat-affected zone (WBHAZ)” was thus formed. The morphology of -ferrite changed and columnar martensite grains were broken in sub-zone I and II of WBHAZ. The size and amount of -ferrite reduced because of austenitization and growth of austenite in sub-zone III of WBHAZ. Retained austenite morphology changed from film into island-like in sub-zone IV and martensite tempered to some degree in sub-zone V of WBHAZ. The precipitation and evolution of M23C6, MX and Laves phase by means of neutron diffraction is to be conducted in the future.