Measurement of residual stresses around the notch of tensile specimens of the high-Cr tempered martensitic steel F82H-mod

Vadim Davydov, Nazar Ilchuk, Philippe Spätig, Steven Van Petegem
2014
Conference paper

Abstract

Residual elastic strains were measured by neutron diffraction using POLDI facility at PSI-Switzerland on pre-loaded notched flat tensile specimens made of the high-chromium tempered martensitic steel F82H-mod steel. To calculate the residual stresses using Hooke’s equation, three perpendicular components of the residual strain field were determined. The measured residual strains and stresses were compared with those deduced from finite element simulation calculations. A very good agreement was found for the strains in the loading plane of the specimen while a somewhat larger discrepancy was observed for the out-of-plane residual strain, which was tentatively attributed to an uncertainty in the initial lattice spacing in that direction

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Measurement of residual stresses around the notch of tensile specimens of the high-Cr tempered martensitic steel F82H-mod

Vadim Davydov, Nazar Ilchuk, Philippe Spätig, Steven Van Petegem

Residual elastic strains were measured by neutron diffraction using POLDI materials science diffractometer at PSI-Switzerland on pre-loaded notched flat tensile specimens made of the high-chromium tempered martensitic steel F82H-mod steel. To calculate the residual stresses using Hooke's equation, three perpendicular components of the residual strain field were determined. The measured residual strains and stresses were compared with those deduced from finite element simulation calculations. A very good agreement was found for the strains in the loading plane of the specimen while a somewhat larger discrepancy was observed for the out-of-plane residual strain, which was tentatively attributed to an uncertainty in the initial lattice spacing in that direction.

Trans Tech Publications Ltd2014

Quench-Induced Stresses in AA2618 Forgings for Impellers: A Multiphysics and Multiscale Problem

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In the fabrication of heat-treatable aluminum parts such as AA2618 compressor impellers for turbochargers, solutionizing and quenching are key steps to obtain the required mechanical characteristics. Fast quenching is necessary to avoid coarse precipitation as it reduces the mechanical properties obtained after heat treatment. However, fast quenching induces residual stresses that can cause unacceptable distortions during machining. Furthermore, the remaining residual stresses after final machining can lead to unfavorable stresses in service. Predicting and controlling internal stresses during the whole processing from heat treatment to final machining is therefore of particular interest to prevent negative impacts of residual stresses. This problem is multiphysics because processes such as heat transfer during quenching, precipitation phenomena, thermally induced deformations, and stress generation are interacting and need to be taken into account. The problem is also multiscale as precipitates of nanosize form during quenching at locations where the cooling rate is too low. This precipitation affects the local yield strength of the material and thus impacts the level of macroscale residual stresses. A thermomechanical model accounting for precipitation in a simple but realistic way is presented. Instead of modelling precipitation that occurs during quenching, the model parameters are identified using a limited number of tensile tests achieved after representative interrupted cooling paths in a Gleeble machine. The simulation results are compared with as-quenched residual stresses in a forging measured by neutron diffraction.

Springer2015

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Solutionising and quenching are key steps in the fabrication of heat treatable aluminium parts such as AA2618 compressor impellers for turbochargers. Quenching not only dictates the mechanical characteristics of the product but also induces residual stresses that can cause unacceptable distortions during machining and unfavourable stresses in service. Predicting and controlling stress generation during quenching of large AA2618 forgings is therefore of great interest. Since possible precipitation during quenching may aﬀect the local yield strength of the material and thus impact the level of macro-scale residual stresses, consideration of this phenomenon is required. A phenomenological material model accounting for precipitation in a simple way is used instead of modelling in detail precipitation that occurs during quenching. The required model parameters are identiﬁed using a limited number of tensile tests achieved after representative interrupted cooling paths in a Gleeble machine. This model is used in FE computations of stress generation during quenching of large massive AA2618 forgings for compressor impellers. The residual strain and stress proﬁles are compared with neutron diﬀraction measurements carried out at SALSA and STRESS-SPEC diﬀractometers in as-quenched and in T6 conditions. It turned out that the residual stress predictions by FE modelling might be wrong if precipitation is not taken into account properly in the material model.

Elsevier2017