Effects of forming route and heat treatment on the distortion behaviour of case-hardened martensitic steel type S156

The distortion behaviour of carburised and fully heat treated Ni-Cr-Mo martensitic steel (S156) has been experimentally evaluated. Dimensional measurements of Navy c-ring distortion coupons during interrupted heat treatment process for parts manufactured from two forming routes, hot forging and machined from as received bar, was performed. Metallurgical analysis was carried out to attempt to relate the observed microstructural characteristics with measured process induced distortion. The carburisation process was found to be the most severe in terms of inducing distortion. It was found that additional heat treatments during the process results in a larger final distortion. Machining parts from forgings results in higher distortions than that of those machined directly from as received bar due to the added thermal processing history. An FE simulation of the carburisation process for a c-ring coupon is presented

Shinning the spotlight on residual stress

[Abstract unavailable

Evolution of microstructure and residual stress in hot rolled Ti-6Al-4V plates subjected to different heat treatment conditions

Hot rolled Ti-6Al-4V plate samples were taken from three different stages of an industrial heat treatment process; one as-rolled and two heat treated. This was followed by microstructure characterization using optical microscopy. Surface and through-thickness residual stress was determined using a combination of X-ray diffraction (XRD) and the contour method. Measured residual stress distributions showed similarities in distribution with that obtained for rolled Al-7050 alloy; including compressive troughs near the outer thickness on both sides, leading towards a tensile zone around the center with a local minima at the plate center thickness. Microstructure and residual stress data was then used to draw comparisons between the investigated conditions

Optimisation of sample geometry for thermo-mechanical testing of precipitation hardenable nickel-based superalloys with an ETMT machine

Accurate determination of thermo-mechanical properties in precipitation hardenable materials using an electro-thermal mechanical testing (ETMT) system is a well-established challenge. The non-uniform distribution of temperature resulting from heating based on the joule effect (i.e., resistivity heating), leads to heterogeneous deformation along the gauge length, owing to the temperature dependency of mechanical properties, which makes their direct measurements complicated. This study presents an evaluation of four different miniaturised sample geometries which were tested to achieve an optimised sample with acceptable uniform strain and temperature distributions in the gauge volume. In-situ displacement mapping, using digital image correlation (DIC), was utilised to calibrate the optimised sample dimensions with the aim of forcing the deformation to the hottest region of the gauge lengths during the tests. Tests were carried out on Inconel 718 (IN718) at 720˚C, an optimal temperature for the precipitation of γꞌꞌ, the primary strengthening particle in this alloy. The results showed that only in the case of the geometry proposed in this study (i.e., a sample with a short gauge length (~ 2 mm)) did the deformation acceptably localise at the centre, compared to other geometries. A correction methodology is developed which equates the strain measured using DIC over the 2mm gauge length of the modified sample geometry with the strain measured using the Linear Variable Differential Transformer (LVDT) integrated to the ETMT, making future tests on IN718, and other precipitation hardenable materials, possible without the need for use of a DIC system

Material gains : aerospace and AFRC lead the way in controlling residual stress

[Abstract unavailable

Evolution of microstructure and residual stresses in a CP-Ti bioimplant produced by incremental sheet forming

Investigation of material behaviour under different schemes of deformation process is one of the important tasks of modern materials science. Metal manufacturing methods, such as metal forming, related to methods by which material of a simple geometry is transformed into a component of specific shape without any change in mass or chemical composition of the initial material [1]. Metal forming process where the deformation is three-dimensional in nature, is known as bulk deformation [2]. Bulk deformation includes processes such as rolling, extrusion, cold and hot forging, bending, and drawing, where metal is formed by plastic deformation. The term bulk deformation is used to distinguish it from sheet-forming process. In sheet-forming, such as brake forming, deep drawing, and stretch forming, the stresses are usually in the plane of the sheet metal unlike all three coordinate directions of components in bulk deformation

Modelling and experimentation of the evolution of texture in an Al-Mg alloy during earing cupping test

Earing and thinning are often the major manufacturing problems occur during deep drawing processes. Thinning occurs when a section of a part undergoes localised deformation, and earing is the formation of wavy edges at the open end of a drawn part that must be trimmed at final stage leading to higher manufacturing costs. The anisotropic mechanical behavior of the initial sheet metal is the predominant source of thinning and earing problems. This work aims to establish a relationship between the properties of a sheet blank and thinning and earing issues during deep drawing by studying the evolution of crystallographic texture throughout the sheet forming process using crystal plasticity simulation modelling and experimental measurements. Firstly, to understand the impact of individual texture components on the mechanical properties of the material, Lankford coefficients for FCC crystal structure during uni-axial tensile loading were analysed using Visco-Plastic Self Consistent (VPSC) model. Subsequently, Finite Element (FE) analyses were carried out to study the effect of initial state of the material on earing and thinning issues occurred during deep drawing. It was observed that the existing Cube and Goss texture components evolved during annealing heat treatments were responsible for the generation of troughs along 45° to the rolling direction (RD) and peaks along the transverse direction (TD), respectively. Optical 3D scanning of a manufactured part confirmed that earing is less prominent in the case of as-rolled and shear-formed condition due to weakening of Cube and Goss texture components. Furthermore, a combination of FE simulation and the VPSC model has been used to simulate texture evolution during a standard earing cupping test at various points of interest. The results of texture evolution simulations were compared to those measured experimentally by electron backscatter diffraction (EBSD), and a good qualitative agreement is achieved

Finite element modelling of transient behaviours and microstructural evolution during dissimilar rotary friction welding of 316 austenitic stainless steel to A516 ferritic steel

Inertia friction welding (IFW) is a near-net-shape joining process that produces high-integrity welds. The transient nature of this joining process necessitates the availability of reliable computational models to predict the evolution of temperature and deformation throughout welding. In this study, a thermo-mechanical finite element (FE) model, based on an adaptive remeshing technique, is proposed to simulate dissimilar joining of A516 ferritic steel and 316L austenitic stainless steel (SS). The results of FE model were evaluated and verified via comparing the shape/size of the flash, upsetting load and angular velocity profile of a physical weld produced by IFW trials. A good agreement was achieved between the appearance of the weld/flash and those predicted by the FE model, thus verifying the predicted temperature and strain distributions. The microstructural features across different weld regimes were also examined to correlate the concomitant changes with the simulated temperature profile

Effect of deformation heating on microstructure evolution during hot forging of Ti-6Al-4V

The effect of deformation heating on microstructure evolution during hot forging of Ti-6Al-4V was established. For this purpose, right-circular cylinders of Ti-6Al-4V with an equiaxed-α preform microstructure were preheated to a temperature between 1148 K (875 °C) and 1223 K (950 °C), and compressed to a 60-pct. height reduction in a screw press, yielding average true strain rates of ~ 5 to 20 s−1. Thermocouple measurements and corroborating finite-element-method (FEM) simulations quantified substantial deformation-heating-induced temperature increases. For all preheat temperatures, the heating transient led to an exposure above the equilibrium β transus temperature. Despite such temperature excursions, the volume fraction of equiaxed primary α in each forged billet was only slightly lower than that in the corresponding preheated condition. The source of such observations was rationalized on the basis of the (hypothesized) solute-concentration fields that develop during the heating and cooling transients experienced in high-rate deformation processing