T. Baudin

Influence of the Goss grain environment during secondary recrystallisation of conventional grain oriented Fe-3%Si steels

Abstract Abnormal Goss grain growth in a conventional grain oriented Fe–3%Si steel is analysed using orientation imaging microscopy after several annealing times. Misorientation of boundaries surrounding the growing Goss grains is characterised. It appears that boundaries misoriented by 20–45° are not specially mobile during the secondary recrystallisation.

Influence of the cold rolled reduction on the stored energy and the recrystallization texture in a Fe–53%Ni alloy

Abstract The influence of the cold rolled reduction on stored energy was studied in Fe–53%Ni using neutron diffraction. Measurements of diffraction peak broadening were undertaken to study the influence of stored energy on mechanisms that govern the nucleation and growth of the cube texture in a heavily cold rolled Fe–Ni alloy.

Monte Carlo simulation of recrystallization in Fe–50%Ni starting from EBSD and bulk texture measurements

An improved Monte Carlo approach for simulation of recrystallization from experimental data is presented. The orientation and stored energy maps derived by orientation imaging microscopy and the X-ray bulk texture of a Fe–50%Ni alloy are used as input data. A realistic description of the dependence of grain boundary properties on misorientation is used to simulate the nucleation and growth of the new recrystallized grains. 2002 Published by Elsevier Science Ltd. on behalf of Acta Materialia Inc.

Basement shear zones development and shortening kinematics in the Ecrins Massif, Western Alps

In the Western Alps, Oligocene shortening affected a highly heterogeneous European crust with Liassic half-grabens inherited from the rifting stage and the finite deformation was strongly partitioned between the rigid basement and the weak Jurassic sediments. In the Ecrins massif (Oisans, External Crystalline Massifs, ECM), where the half-grabens are best exposed and preserved, compressional structures within the basement have to date never been described in details. This massif was shortened under moderate metamorphic conditions (250-350°C and 0.1-0.5GPa) and the rheological contrast between the basement and the cover is strong. While the sediments are intensely folded, the cover-basement interface presents apparent open folds underlined by the lower Triassic layers. The basement itself shows a more localised deformation along several brittle-ductile shear zones. We here report new evidences of such brittle-ductile shear zones characterized by anastomosed phyllonitic shear bands rich in phengite and quartz, a low strength material where strain has localized. New detailed maps of reverse shear zones, faults, schistosity and stretching lineations in both the cover and the basement are provided. We show that the Oligocene crustal shortening was mainly E-W to ENE-WSW. Local N-S to NW-SE shortening occurred and was limited to the eastern border of the Ecrins massif, around the Penninic Frontal Thrust, which likely was a sinistral transpressive structure in this area. Finally, new balanced cross-sections show that these basement shear zones have accommodated more than 50% of the Oligocene crustal shortening.

Microstructural characterization in a hot-rolled, two-phase steel

Abstract Orientation Imaging Microscopy allows characterization of the crystallographic orientation of grains in a polycrystal. Consequently, it permits one to define the grain boundary nature in each phase and between the phases when the studied material is a dual-phase material such as an austeno-ferritic steel. Moreover, as is shown in the present paper, this technique allows a good estimation of the surface fraction of each phase and their variation along the radius of a rod that comes from a “round–oval” groove sequence.

Simulation of the anisotropic growth of Goss grains in Fe3%Si sheets (grade HiB)

In classical simulation of abnormal grain growth, the microstructure is generally assumed to be homogeneous in size and the texture randomly distributed on such a theoretical microstructure which characterizes the primary recrystallized state. Experimentally, this last assumption could not be verified in Fe3%Si sheets (grade HiB). Consequently, a new simulation procedure has been implemented using a real microstructure measured by Orientation Imaging Microscopy (OIM) as an input data set. In this first work, the influence of the texture inhomogeneity has been analyzed from a theoretical point of view using Orientation Distribution Function (ODF) calculations and Monte-Carlo simulations without correlation with experimental measurements. The present paper deals with firstly the evolution of both microstructural and textural inhomogeneities and secondly the comparison, grain by grain, at several time steps of the experimental and simulated results obtained during secondary recrystallization.

Study of Inconel 718 weldability using MIG CMT process

Abstract This work investigates the weldability of Inconel 718 using the metal inert gas (MIG) welding process called ‘cold metal transfer’. This arc welding process is reported for working with a lower heat input compared to other arc processes. The consequences are less base metal impaired, low deformation and low residual stress level in assembly. In order to check these abilities, metallographic, texture, chemical and residual stress analyses have been carried out. Results show that MIG cold metal transfer has good properties for the welding of Inconel 718 inasmuch as no defect has been detected and a lower level of residual stresses has been introduced in metal compared to classic MIG.

Orientation correlations in primary recrystallized Fe-50%Ni

Abstract The correlations between orientations of neighboring grains have been investigated in a Fe-50%Ni alloy after primary recrystallization and normal grain growth. Boundary misorientations have been determined by systematic measurement of individual grain orientations by Electron Back-Scattered Diffraction (EBSD). It is shown that the recrystallization process in Fe-50%Ni gives rise to noticeable orientation correlations for Σ 3 n and low-angle orientation relationships. Such correlations result mainly from the non-random spatial distribution of orientations and from the grain size dependence on orientation developed in these alloys during recrystallization. In the present alloy, the grain growth process leads to minor variations in the orientation correlations associated with low-angle misorientations and reduces considerably those related to Σ 3 n orientation relationships.

Deformation textures and plastic anisotropy of steels using the Taylor and nonhomogeneous models

The deformation textures of B.C.C. polycrystals (uniaxial tension, rolling) and the Lankford coefficient are predicted using the Taylor model and a nonhomogeneous model. The mixed glide conditions {110}〈111〉 + {112}〈111〉 are imposed using the yield polyhedron proposed by Orlans-Jolietet al. [1988]. The nonhomogeneous model is based on the Arminjon model [1987]; however, Arminjon used the pencil glide condition. An original calculation is proposed to simulate with a high precision deformation textures (orientation distribution functions O.D.F. F′(g)), without using the harmonic method, which leads to truncation errors. No restrictions are imposed on the eventual symmetry of the initial O.D.F. F(g). Using experimental and calculated textures of low carbon steels, it is shown that the homogeneous Taylor model gives good results for low deformations (uniaxial tension), whereas the nonhomogeneous model improves the Taylor model for high deformations (rolling).

Electron Backscattered Diffraction of Transgranular Crack Propagation in Soft Steel

We consider the crack propagation in a soft steel sheet during the formation. The drawability is considered in relation with the structural anisotropy, the mechanical behaviour is related to both the grain morphology and the texture. The structure heterogeneity could lead to the apparition of micro-cracks. The results show the texture effect on the crack propagation and on the crack arrest in soft steel during the formation. The EBSD technique allows to show that the adjustment of the grain orientation from the initial main component {111}112 towards the deformation orientation {111}110 incites a trans-granular crack through a grain with initial {111}112 orientation in a globally ductile material. It is the presence of grains with {111}110 orientation which permits the closing of micro-cracks.