G. Barbieri

Electron Beam Welding of IN792 DS: Effects of Pass Speed and PWHT on Microstructure and Hardness

Electron Beam (EB) welding has been used to realize seams on 2 mm-thick plates of directionally solidified (DS) IN792 superalloy. The first part of this work evidenced the importance of pre-heating the workpiece to avoid the formation of long cracks in the seam. The comparison of different pre-heating temperatures (PHT) and pass speeds (v) allowed the identification of optimal process parameters, namely PHT = 300 °C and v = 2.5 m/min. The microstructural features of the melted zone (MZ); the heat affected zone (HAZ), and base material (BM) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD), and micro-hardness tests. In the as-welded condition; the structure of directionally oriented grains was completely lost in MZ. The γ’ phase in MZ consisted of small (20–40 nm) round shaped particles and its total amount depended on both PHT and welding pass speed, whereas in HAZ, it was the same BM. Even if the amount of γ’ phase in MZ was lower than that of the as-received material, the nanometric size of the particles induced an increase in hardness. EDS examinations did not show relevant composition changes in the γ’ and γ phases. Post-welding heat treatments (PWHT) at 700 and 750 °C for two hours were performed on the best samples. After PWHTs, the amount of the ordered phase increased, and the effect was more pronounced at 750 °C, while the size of γ’ particles in MZ remained almost the same. The hardness profiles measured across the joints showed an upward shift, but peak-valley height was a little lower, indicating more homogeneous features in the different zones.

Welding of Automotive Aluminum Alloys by Laser Wobbling Processing

The scope of this paper is to examine the improvement from laser welding by an innovative beam wobbling head towards the welding of tailored blanks parts, widely used in automotive to develop different stiffness aluminum components. For this purpose, butt joints and overlapping joints were produced from sheets made out of two industrial grades, i.e. AA-6082 T6 and AA-5754 H111 of different thickness. The technique was evaluated both with and without the use of a filler wire (AA-5556). The qualification of the welding process encompassed Non Destructive Testing (NDT) and mechanical testing. The results indicate that butt joints tend to fail within the base material (BM) of sheet with smaller thickness. On the contrary, the shear tests on lap joints highlighted a rupture mode occurring in the heat affected zone (HAZ) of the thin sheet. Remarkably, the wobbling process generally allows avoiding porosity when combined with an optimized set of welding parameters. Yet, a residual porosity was always detected in lap joints, varying with the size of the fused zone.

IN792 DS superalloy: Optimization of EB welding and post-welding heat treatments

Electron beam (EB) welding has been used to realize the seams on 2 mm thick plates of directionally solidified (DS) IN792 superalloy. A grid of the samples has been prepared by varying the pass speed v from 1 to 2.5 m/min, while the other process parameters (power P = 1 kW, acceleration voltage T = 50 kV, beam current I = 20 mA) were kept constant. Experiments were carried out both at room temperature and with pre-heating at 200 °C or 300 °C.Once found the best process conditions (pre-heating at 300 °C; v = 2.5 m/min) the effect of post-welding heat treatments at 700 and 750 °C for increasing time up to 2 hours has been investigated.

Welding of IN792 DS Superalloy by High Energy Density Techniques

Laser (LBW) and Electron Beam (EBW) welding have been used to produce seams on 2 mm thick plates of directionally solidified (DS) IN792 superalloy. For each welding technique a grid of samples were prepared by varying the pass speed (v) and keeping constant the other process parameters. The experiments were carried out at room temperature and with pre-heating (PHT) at 200 °C and 300 °C to find the best process conditions. The microstructural changes in molten zone (MZ) and heat affected zone (HAZ) were investigated finding that EBW guarantee a better quality and efficiency of the process without any macro defects. About the microstructure, the amount of ordered γ’ phase in the MZ is similar (≈ 25 %) for both welding techniques and quite lower than the value (70 %) of the original alloy.

Welding of high-resilience martensitic stainless steel for hydrodynamic components in innovative seacraft: a comparison of traditional and HDE technologies

For the designer, the production of innovative seacraft involves the use of atypical materials at the shipyard. This article presents a comparison between traditional (SMAW) and innovative [LBW, electron beam welding (EBW)] welding technologies to illustrate the feasibility and suitability – also in economic terms – of the penetration of new welding technologies in the shipbuilding sector. In particular, the material considered for the production of submerged bearing components in an innovative submerged-wing hydrofoil is X4CrNiMo13-4, a martensitic stainless steel presenting improved resilience chosen by the shipbuilding company (Rodriquez Cantieri Navali), above all, on account of its high mechanical strength. In order to avoid costly PWHT, which, given the large size of the components, has a heavy influence on production costs, welding procedure specifications were developed using an austenitic filler material that, while inducing a limited reduction in performance in the melt zone, allows for conspicuous economic advantages. Research has shown how EBW technology undoubtedly allows for better results, while – although it would be more suitable for large-size components – LBW technology requires a more critical optimization of parameters.