Recently high nitrogen steels (HNS) are known as advanced materials. Nitrogen alloying gives several beneficial effects on the many properties of steels. However, nitrogen loss unavoidably occurs when HNS is welded with fusion welding process, resulting in the reduction of corrosion resistance as well as mechanical properties. Friction welding is a solid-state joining process, and materials do not melt at the bonding interface. Hence defects associated with melting-solidification phenomena, such as nitrogen loss, weld porosity and weld cracking, do not take place. The objective of the present study is to evaluate the weldability of friction welding of high nitrogen stainless steel contained 1.2mass% nitrogen.
This research aims at building a turbulent diffusion combustion model based on chemical equilibrium and kinetics for simplifying complex chemical mechanisms. This paper presents the combustion model based on the chemical equilibrium combined with an eddy dissipation model; this model is validated by simulating a H2-air turbulent diffusion flame. In this model, the reaction rate of fuels is estimated by using the equations of the eddy dissipation model. Here, the reacted fuels are assumed to be in chemical equilibrium; the amounts of the other species are determined by the Gibbs free energy minimization method by using the amounts of the reacted fuels, and air as reactants. An advantage of this model is that the amounts of the combustion products can be determined without using detailed chemical mechanisms. Moreover, it can also predict the amounts of the intermediate species. The obtained results are compared with Takagi's experimental data and the data computed by the EDC model, which uses the detailed chemical mechanisms. The mole fractions of H2, O2, H2O, and the temperature obtained by using our model were in good agreement with these reference data without taking into account the chemical reaction rate of H2. Furthermore, the mole fraction of OH is in good agreement with the results of the EDC model in the high-temperature, post-flame region. The present model can be used to simply calculate the amounts of the chemical species, and the temperature by using the chemical equilibrium method and the overall reaction.