Numerical investigation on stress distribution and evolution in 9Cr/2.25Cr dissimilar welded rotor undergoing welding and heat treatment

Abstract

Numerical investigation has been employed to analysis stress distribution in 9Cr/2.25Cr dissimilar welded rotor undergoing welding and heat treatment in order to help optimize structural design. The simulated residual stress on inner and outer cylindrical surface has been validated with experimental data. Distribution and evolution of welding residual stress along weld center line through thickness has also been investigated. It is found that expansion due to martensitic phase transformation in cap weld and shrinkage in nominal HAZ determines the distribution of residual stress on outer cylindrical surface. Meanwhile, expansion caused by martensitic phase transformation and bending effect in annular structure is responsible for the evolution and distribution of through-wall residual stress. Distribution and peak value of through-wall welding residual stress remains after the weld height reaches a certain value (it is about 30% thickness from the inner cylindrical surface in this work), which provides a possibility to predict stress distribution with less time. Meanwhile, post weld heat treatment (PWHT) can release residual stress effectively. Hence, more attention has been paid to as-welded residual stress. Compared with 2.25Cr weld filler, 9Cr weld filler induces greater compressive hoop stress in the newly deposited weld metal and decreases the peak value of tensile hoop stress under it because of greater martensitic phase transformation expansion in cooling process and smaller yield stress at low temperatures.