A Comprehensive Case Study of Macrosegregation in a Steel Ingot

This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/s11663-015-0386-yA case study is presented that examines the macrosegregation and grain structure present in a 12-tonne steel ingot, which was cast for experimental purposes. Details of the casting procedure were well documented and the resulting ingot was characterized using a number of techniques that measured chemical segregation, shrinkage, and porosity. The formation of the porosity and segregation patterns is discussed in reference to the particular grain structure observed in the ingot. It is hoped that this case study can be used as a tool for the validation of future macromodels.This work was undertaken as part of a Project sponsored by Rolls-Royce Power Nuclear plc in collaboration with Sheffield Forgemasters International

Microstructural and Chemical Rejuvenation of a Ni-Based Superalloy

This is an open access article published by Springer and distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), http://creativecommons.org/licenses/by/4.0/The microstructural evolution of the Ni-based superalloy CMSX-4 including the change in gamma prime morphology, size and distribution after high temperature degradation and subsequent rejuvenation heat treatments has been examined using field emission gun scanning electron microscopy (FEGSEM) and transmission electron microscopy (TEM). In this paper it is shown that there are significant differences in the size of the ‘channels’ between gamma prime particles, the degree of rafting and the size of tertiary gamma prime particles in each of the different microstructural conditions studied. Chemical analysis has been carried out to compare rejuvenated and pre-service samples after the same subsequent degradation procedure. The results indicate that although the microstructure of pre-service and rejuvenated samples are similar, chemical differences are more pronounced in the rejuvenated samples, suggesting that chemical segregation from partitioning of the elements was not completely eliminated through the applied rejuvenation heat treatment. A number of modified rejuvenation heat treatment trials were carried out to reduce the chemical segregation prior to creep testing. The creep test results suggest that chemical segregation has an immeasurable influence on the short-term mechanical properties under the test conditions used here, indicating that further work is required to fully understand the suitability of specific rejuvenation heat treatments and their role in the extension of component life in power plant applications

About one stable and three metastable eutectic microconstituents in the Fe-W-C system

International audienceThe Fe–W–C system has been the subject of numerous investigations and the findings have led to quite different interpretations in the iron-rich corner, justifying the need for new experimental studies. In the present study, some 12 compositions are prepared using both the powder metallurgy technique and the casting of melted alloys. DTA experiments, long time annealing supplemented by the phase separation technique and controlled solidification experiments are carried out. The micrographs of the corresponding specimens reveal significant sedimentation of WC carbides, an observation which must be carefully taken into account in interpreting the micrographs. The liquid/solid equilibria between 1423 and 1543 K are investigated and the corresponding partial isothermal sections of the Fe–W–C system are compared to the calculated phase equilibria based on thermochemical models. Four ternary eutectic microconstituents γ/M6C/cementite, γ/WC/cementite, γ/M6C/graphite and γ/WC/graphite, are observed by experiments. The microstructures are characterised and the four eutectic temperatures are established both experimentally and by calculations. The experimental eutectic temperatures lie within a range of 10 K but well below the temperatures predicted by thermodynamic modelling and the calculated temperatures within a range of 20 K. This explains why metastable microconstituents can so readily be formed

Practical aspects of carbon content determination in carburized steels by EPMA

International audienc