Validated prediction of weld residual stresses in austenitic steel pipe girth welds before and after thermal ageing, part 1: Mock-up manufacture, residual stress measurements, and materials characterisation

A series of engineering-scale multi-pass pipe girth weld mock-ups were manufactured using conventional manual metal arc techniques from Esshete 1250 austenitic steel. They were characterised in detail, in order to provide validation benchmarks for finite element prediction of weld residual stresses. The fabrication sequence comprised initial solution heat treatment and quenching, manufacture of five closely spaced girth welds in a single assembly, and then separation into five individual weldments. Detailed welding records were kept, to allow subsequent calibration of weld heat source models. Residual stresses were measured using diverse methods (incremental deep hole drilling and the contour method), in both the as-welded condition and after thermal ageing at 650 °C. The measurements showed good agreement, providing reliable validation targets for predicted residual stresses in both states. Detailed mechanical property characterisation was performed on both parent material and weld metal, comprising monotonic and isothermal cyclic testing over a range of temperatures from ambient up to 1000 °C. The test data were used to derive a range of Lemaitre-Chaboche mixed isotropic-kinematic model parameter sets for use in finite element simulation. These welds and their supporting characterisation comprise a reliable benchmark for weld residual stress simulation in an engineering-scale weldment

Design of Thermo Mechanicaln Processing and Transformation Behaviour of Bulk Si-Mn Trip Steel

In the last decade, a lot of effort has been paid to optimising the thermomechanical processing of TRIP steels that stands for transformation induced plasticity. The precise characterization of the resulting multiphase microstructure of low alloyed TRIP steels is of great importance for the interpretation and optimisation of their mechanical properties. The results obtained in situ neutron diffraction laboratory experiment concerning the austenite to ferrite transformation in Si-Mn bulk TRIP steel specimens, displaying the transformation induced plasticity (TRIP), are presented. The advancement of ferrite formation during transformation in conditioned austenite is investigated at different transformation temperatures and has been monitored using neutron diffraction method. The relevant information on transformation proceeding is extracted from neutron diffraction spectra. The integrated intensities of austenite and ferrite neutron diffraction profiles developed during the transformation are then assumed as a measure of the phase volume fractions of both phases in dependence on transformation temperature and austenite conditioning. According to the yielding information on ferrite volume fractions from isothermal transformation kinetics data the thermo mechanical processing of bulk specimen was designed in order to support austenite stabilization through bainitic transformation. The volume fractions of retained austenite resulting at alternating transformation conditions were measured by neutron and X-ray diffraction respectively. The stability of retained austenite in bulk specimens during room temperature mechanical testing was characterized by in situ neutron diffraction experiments as well

On the irradiation tolerance of nano-grained Ni-Mo-Cr alloy: 1MeV He+ irradiation experiment

The irradiation damage behavior is surveyed in the nano-grained GH3535 condition irradiated by He ion to various dose. The evolution of defects and hardness changes are characterized by transmission electron microscopy and nanoindentation respectively to explore the irradiation tolerance of the nano-grained GH3535 condition, with the annealed GH3535 condition as reference material. The results show that though both the average size and number density of He bubbles increase with an increase in the irradiation dose, the smaller volume fraction is found in the nano-grained GH3535 condition compared with the annealed GH3535 condition under the same irradiation condition. This indicates that the nano-grained GH3535 condition possess better irradiation swelling resistance than the annealed GH3535 condition. However, the increase in the hardness of the nano-grained GH3535 condition is more significant than in the annealed GH3535 condition under the same irradiation dose. This suggests stronger irradiation-induced hardening of the nano-grained alloy comparing to coarse-grained alloy, due to the impeding effect caused by grain boundaries decorated with He bubbles. This study provides insight into the design of irradiation-tolerant nickel-based alloys for nuclear industry applications

Numerical analysis of the effect of weld-induced residual stress and plastic damage on the ballistic performance of welded steel plate

The current paper presents numerical analyses that elucidate the effects of post-weld residual stress and associated plastic damage on the ballistic performance of 316L austenitic steel plate. Impact simulations of an 18 mm thick plate with a centreline three-pass slot weld by hemispherical-nosed and flat-nosed projectiles are performed, with initial velocities in the range of 300-800 m/s. The numerical framework consists of three interdependent stages: (i) a weld model was developed in Abaqus/Standard and validated using two independent experimental data sets; (ii) a Johnson-Cook material model is calibrated and validated along with the shear failure fracture criterion available in Abaqus/Explicit for impact models; and (iii) the weld modelling results were transferred to an impact model built in Abaqus/Explicit, which employs the validated material and fracture models to predict the ballistic performance of welded plate. It is shown that the associated plastic strain damage accumulated during the welding process - and its distribution - has an adverse effect on the ballistic performance. It has also been determined that a fracture criterion that accounts for pre-existing damage in the weldment must be used for accurate impact analyses of welded structures. Crown Copyright (C) 2012 Published by Elsevier B.V

In situ neutron diffraction studies of deformation and transformation processes in modern types of steels

Matematicko-fyzikální fakultaFaculty of Mathematics and Physic

Mitigating cutting-induced plasticity in the contour method, part 1: Experimental

Application of the contour method for the measurement of weld residual stresses (WRS) is prone to inaccuracy due to plastic deformation resulting from the redistribution of typically high (close to yield) WRS during the cutting process. The current work, seeks ways to mitigate cutting-induced plasticity by controlling stress redistribution through optimisation of the contour cutting configuration. The idea of using a stress-informed fracture mechanics approach to find the optimal cutting configuration is introduced. The level of plasticity associated with different cutting configurations is then assessed, allowing control of the location and magnitude of cutting-induced plasticity to occur during the cutting process. A conventional edge-crack cutting configuration is compared with a proposed double-embedded cutting configuration by measuring the longitudinal WRS in two three-pass slot weld specimens (NeT TG4) produced using identical weld procedures. The experimental results show that a novel double-embedded cutting configuration leads to greater accuracy in WRS measurements relative to conventional edge-crack cutting configurations at the expense of higher levels of plasticity being introduced local to small ligaments

Mitigating Cutting-Induced Plasticity in the Contour Method, Part 2: Numerical Analysis

Cutting-induced plasticity can have a significant effect on the measurement accuracy of the contour method. The present study examines the benefit of a double-embedded cutting configuration that relies on self-restraint of the specimen, relative to conventional edge-crack cutting configurations. A series of finite element analyses are used to simulate the planar sectioning performed during double-embedded and conventional edge-crack contour cutting configurations. The results of numerical analyses are first compared to measured results to validate the cutting simulations. The simulations are then used to compare the efficacy of different cutting configurations by predicting the deviation of the residual stress profile from an original (pre-cutting) reference stress field, and the extent of cutting-induced plasticity. Comparisons reveal that while the double-embedded cutting configuration produces the most accurate residual stress measurements, the highest levels of plastic flow are generated in this process. This cutting-induced plastic deformation is, however, largely confined to small ligaments formed as a consequence of the sample sectioning process, and as such it does not significantly affect the back-calculated residual stress field

Duplex stainless steel welds: residual stress determination, magnetic force microscopy and susceptibility to intergranular corrosion.

Not availabl