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Genzel C.,Helmholtz Center Berlin | Krahmer S.,Helmholtz Center Berlin | Klaus M.,Helmholtz Center Berlin | Denks I.A.,Salzgitter Mannesmann Forschung GmbH
Journal of Applied Crystallography | Year: 2011

For a feasibility study of energy-dispersive residual stress analysis under laboratory conditions, an X-ray diffractometer that has been operated so far in the angle dispersive diffraction mode was equipped with a commercial tungsten tube and an energy-dispersive solid-state germanium detector. Starting from systematic investigations to find the optimum configuration regarding geometrical resolution, measuring time and stability of the applied detector system, different materials were characterized with respect to the near-surface residual stress state. The results achieved with the modified laboratory equipment within reasonable measuring times are in good agreement with synchrotron measurements performed on the same samples. With the example of a shot-peened Al2O3 ceramic with a highly non-uniform near-surface residual stress distribution it is furthermore shown that the different size and shape of the diffracting gauge volume used for the laboratory and synchrotron measurements might have a significant influence on the experimentally obtained Laplace-space residual stress depth profiles θ||(r). © 2011 International Union of Crystallography Printed in Singapore-all rights reserved. Source

Bendick W.,Salzgitter Mannesmann Forschung GmbH | Cipolla L.,Centro Sviluppo Materiali S.p.A | Gabrel J.,Vallourec Research Center | Hald J.,Technical University of Denmark
International Journal of Pressure Vessels and Piping | Year: 2010

A first assessment of creep rupture strength for steel grade X10CrMoVNb9-1 (Grade 91) was performed by ECCC in 1995. The results were included in the European standard EN 10216. Due to a significant increase of test data and test duration it was decided in 2005 to make a re-assessment of the extended database. Different procedures have been used independently by different assessors. The method with the best overall fit of the data set has found to be the ISO CRD method. This is characterized by a two steps procedure: in the first step the mean isotherms are evaluated from the test data, afterwards the evaluated isotherms are used for averaging by a Manson-Haferd master-curve. The results have been chosen as the basis to specify long term creep rupture strength values in a new ECCC data sheet for X10CrMoVNb9-1 (Grade 91). © 2010 Elsevier Ltd. Source

Panait C.G.,MINES ParisTech Center of materials | Panait C.G.,Vallourec Research Aulnoye | Bendick W.,Salzgitter Mannesmann Forschung GmbH | Fuchsmann A.,Vallourec Research Aulnoye | And 2 more authors.
International Journal of Pressure Vessels and Piping | Year: 2010

This paper presents results on the evolution of microstructure (both matrix and precipitates) of an ASME Grade 91 steel that has been creep tested for 113,431 h at 600 °C under a load of 80 MPa.The microstructure was investigated using transmission electron microscopy (TEM) and revealed chromium rich M23C6 carbides, MX-type precipitates, Laves phases and modified Z-phases. Only a small amount of modified Z-phase was found. In order to quantify coarsening of precipitates and growth of new phases during creep, the size distributions of the identified precipitates were determined by analysis of TEM images. In addition to this, the size distribution of Laves phases was determined by image analysis of scanning electron micrographs.Substructure modifications and creep damage were investigated on cross sections of the creep specimen using Electron Backscatter Diffraction and Scanning Electron Microscopy. © 2010 Elsevier Ltd. Source

Calcagnotto M.,Max Planck Institute Fur Eisenforschung | Calcagnotto M.,Salzgitter Mannesmann Forschung GmbH | Ponge D.,Max Planck Institute Fur Eisenforschung | Raabe D.,Max Planck Institute Fur Eisenforschung
ISIJ International | Year: 2012

An ultrafine grained (UFG) ferrite/cementite steel was subjected to intercritical annealing in order to obtain an UFG ferrite/martensite dual-phase (DP) steel. The intercritical annealing parameters, namely, holding temperature and time, heating rate, and cooling rate were varied independently by applying dilatometer experiments. Microstructure characterization was performed using scanning electron microscopy (SEM) and high-resolution electron backscatter diffraction (EBSD). An EBSD data post-processing routine is proposed that allows precise distinction between the ferrite and the martensite phase. The sensitivity of the microstructure to the different annealing conditions is identified. As in conventional DP steels, the martensite fraction and the ferrite grain size increase with intercritical annealing time and temperature. Furthermore, the variations of the microstructure are explained in terms of the changes in phase transformation kinetics due to grain refinement and the manganese enrichment in cementite during warm deformation. © 2012 ISIJ. Source

Calcagnotto M.,Max Planck Institute Fur Eisenforschung | Calcagnotto M.,Salzgitter Mannesmann Forschung GmbH | Ponge D.,Max Planck Institute Fur Eisenforschung | Raabe D.,Max Planck Institute Fur Eisenforschung
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2012

Two plain carbon steels with varying manganese content (0.87 wt pct and 1.63 wt pct) were refined to approximately 1 μm by large strain warm deformation and subsequently subjected to intercritical annealing to produce an ultrafine grained ferrite/martensite dual-phase steel. The influence of the Mn content on microstructure evolution is studied by scanning electron microscopy (SEM). The Mn distribution in ferrite and martensite is analyzed by high-resolution electron backscatter diffraction (EBSD) combined with energy dispersive X-ray spectroscopy (EDX). The experimental findings are supported by the calculated phase diagrams, equilibrium phase compositions, and the estimated diffusion distances using Thermo-Calc (Thermo-Calc Software, McMurray, PA) and Dictra (Thermo-Calc Software). Mn substantially enhances the grain size stability during intercritical annealing and the ability of austenite to undergo martensitic phase transformation. The first observation is explained in terms of the alteration of the phase transformation temperatures and the grain boundary mobility, while the second is a result of the Mn enrichment in cementite during large strain warm deformation, which is inherited by the newly formed austenite and increases its hardenability. The latter is the main reason why the ultrafine-grained material exhibits a hardenability that is comparable with the hardenability of the coarse-grained reference material. © 2011 The Minerals, Metals & Materials Society and ASM International. Source

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