Evaluation of Spatial Distribution of Creep Void in Heat-Affected Zone of Modified 9Cr-1Mo Steel

2 | P a g e Foreword As power plants nowadays tend to push their efficiency to the extremely high level, innumerable new materials have been introduced regularly. One of the recent materials applied to high-pressured steam tubes is modified 9Cr-1Mo steel, commonly used in so-called Ultra Super Critical Power Plant. Modified 9Cr-1Mo steel is known to have superior high temperature strength. There have been, however, several reports regarding problems related to type IV cracking and creep damage taking place in the heat affected zone or the weld joints of the material. To identify the area where creep damage occurred and reveal the cause, we approached the problem in two methods. First, we observed the surface of the heat-affected zone of a cross-section of a weld-joint part of material from Central Research Institute of Electric Power Industry with scanning electron microscope. The data helps us define the area where creep voids and creep damage mainly take place and further out understanding of disputable creep void mechanics. In addition, Vicker’s hardness distribution and grain size distribution were measured; further definition and characteristics of creep damage phenomenon area can be discovered. The other approac