Investigation of creep damage in advanced martensitic chromium steel weldments using synchrotron X-ray micro-tomography and EBSD

Abstract

In recent years, a design concept for the stabilisation of the microstructure by addition of boron and nitrogen was developed. This so called martensitic boron-nitrogen strengthened steel (MARBN) combines boron strengthening by solid solution with precipitation strengthening by finely dispersed nitrides. Welded joints of MARBN steels showed no formation of a uniform fine grained region in the heat affected zone (HAZ) which is in general highly susceptible to Type IV cracking. In this work, the crossweld creep strength of a newly developed MARBN steel was analysed and the evolution of damage was investigated using synchrotron microtomography supported by electron microscopy. Three-dimensional (3D) reconstructions of the tested samples together with electron backscatter diffraction investigations revealed an intense void formation in a restricted area along small grains at prior austenite grain boundaries in the HAZ as the main reason for premature creep failures in the HAZ of welded joints.

The development of creep damage constitutive equations for high Cr steel

“…The number density of cavities at failure for CB8 under a range of stress level has been researched by Xu et al [1], which the set of 3D cavity data referenced by X-ray micro-tomography. Fortunately, there is another set of 3D cavity data that the number density of cavities at failure for MARBN-heat 1 crosswelds under a range of stress levels from 70 MPa to 130 MPa are available [13,25]. The relevant data were extracted by reading the published graph and table.…”

Cavitation studies in materials: New insights from modern techniques in 2D/3D/4D characterisation

“…al. 4 provided the insight that individual fine grain at the local scale can act as sites for intense cavitation promoting the failures at stresses below 100 MPa. This typically illustrates the need to investigate damage contained in the microstructure in a multi-scale and multi-modal manner.…”

Creep behavior and microstructure evaluation of welded joint in dissimilar modified 9Cr–1Mo steels

“…And hence, the materials with more excellent creep property and oxidation resistance are required to adapt to such kind of severe service conditions. Modified 9Cr-1Mo steels are the candidate structural materials for turbine and boiler components in power plants, attributing to their excellent comprehensive properties of high temperature mechanical and oxidation resistance properties [5,6]. In the past 30 years, martensitic creep resistant 9Cr steels have been modified and introduced into power plants successively.…”