Evaluation of porosity in spray deposited A2 tool steel

TLDR: In this article, a heuristic model was proposed to predict porosity of spray forming of tool steels using the effect of relative magnitudes of the fluid flow characteristic time and the solidification characteristic time on the porosity formation process.

Abstract: The objective of the present study is to provide a numerical model to serve as a guide in the determination of optimum processing parameters for the spray forming of tool steels. Porosity is predicted using a heuristic model that incorporates the effect of the relative magnitudes of the fluid flow characteristic time and the solidification characteristic time on the porosity formation process, Two regimes, the 'fast flow' regime and the 'fast salidification regime, are identified a priori. Expressions for porosity as a function of the particle size distribution, the over-age solid fraction of the incident spray, and the solidification contraction are derived, based on these assumptions. The average solid fraction of the incident spray is estimated from the droplet size distribution and the solid fraction of a single droplet of a given size. The fatter is determined by cakulating the droplet dynamics and thermal history. The effects of process parameters (melt superheat, atomization pressure, deposition distance, and melt mass flow rate) on the level of porosity are investigated. By determining the conditions corresponding to a minimom in predicted porosity, optimum processing parameters can be assessed. As a result, processing maps are provided as a reference for achieving spray fermed tool steels with minimum parosity.