Technology of Welding Joints Mixed with Duplex Steel

Results of the examinations of sample plates of mixed joints with the duplex steel were discussed. Examinations were taken on the sample plates of mixed joints of sheet plates type P355NL1 and X2CrNiMoN22-5-3 welded by the flux-cored wire DW-329A by the Kobelco company of the following category T 22 9 3 NL RC/M3 in the gas shroud M21 (Ar+18%CO2) (plate no.1), and nickel covered electrodes E Ni 6082 by the Böhler company (plate no. 2). Results of the side bend test of welded joint, transverse tensile test, stretching of the weld metal, impact strength, micro and macroscopic metallographic examinations, and measurements of the delta ferrite content were presented.

Effects of Solid Shield and Shroud on Plasma Jet Flame in APS Process

Gas entrainment occurs in atmospheric plasma spray (APS) after plasma jet flows into the cold surroundings, resulting in rapid decaying of speed and unwanted oxidation. Installing a solid shield or inserting a gas shroud at the end of the nozzle may be helpful to reduce air entrainment. Effects of solid shield and inert gas shroud on plasma jet are investigated numerically. It is found that solid shield and gas shroud will expand high temperature field of plasma jet in both axial and radial direction, consequently, enabling a thorough reaction of oxygen content for virtually oxygen free plasma jet. The mass fraction of the O2 gas in the plasma flow outside the shield decreases with the increase of the inert gas velocity, which maintains nearly zero in the solid shield. Inert gas velocity and its injection angle turn out to be important factors to offset the negative effects of solid shield on the main flow. It is demonstrated that the flow field is less affected when the inert gas is axially injected with the inlet velocity of 150m/s. Ar is more appropriate than N2 as an inert gas, which is mainly attributed to its physical properties.

Numerical Modeling of Particle Laden Flow in HVOF Torch with Gas Shroud

A particle laden flow in an HVOF torch is analyzed using Computational Fluid Dynamics (CFD). The torch is similar to the DJ Metco torch with a converging-diverging (de Laval) nozzle, where particles are injected through the center together with nitrogen as a carrier gas. The Eulerian formulation is used for the gas flow whereas the particle motion is described by using the Lagrangian formulation. The flow turbulence is modeled via k-e model with standard wall functions. For modeling the combustion process in the torch, a multi-reaction Eddy-Dissipation Model (EDM) is employed. The computational domain comprised the torch itself and the region outside the torch where our attention is mainly focused. The computations are performed for the torch with and without the gas shroud attachment. The results showed that the presence of the shroud affected to some degree the flow and temperature fields of the main gas and the particle stream, while at the same time, significantly reducing the entrainment of ambient air into the main stream as shown by the lower oxygen concentrations. The results of the numerical computations are compared with experimental results for the same operating conditions and the agreement is found to be good.

A Gas Shroud Nozzle for HVOF Spray Deposition

Properties of MCrAIY coatings obtained by High Velocity Oxy-Fuel (HVOF) thermal spray process operated in a standard configuration were compared with those obtained using a gas shroud attachment to the HVOF gun. Our measurements show that the attached gas (nitrogen) shroud nozzle considerably reduces the oxygen content in the coating without an appreciable change in the microstructure. The particle temperatures were decreased by an average of 100 C at a standoff distance of 0.275 m (11 inches). There was also a large reduction in the particle velocity at this distance. Both these effects were related to the excessive amount of nitrogen used for shrouding.