Analysis of solidification microstructures in single crystal stainless steel melt pools

The microstructural analysis of stationary-melt or "weld"pools provides important information concerning the relationships between the weld-pool shape, the crystallography of the sample, and the resulting microstructural properties of the weld. A detailed microstructural analysis of stationary melt pools made using oriented stainless steel single crystals with a composition of 70%Fe-15%Ni-15&Cr (wt%) was performed in order to investigate the resulting microstructure and the effects of crystallography in determining microstructural development. Stationary melt pools were formed by employing electron-beam and gas-tungsten-arc heating methods on the (001), (011), and (111) oriented planes of the austenitic, FCC-alloy crystals. The characterization and analysis of the resulting microstructure was carried out for each crystallographic plane and welding method. The results showed that crystallography which favors "easy growth" along the <100> family of directions is a controlling factor in the microstructural formation along with the melt-pool shape. The microstructure was found to depend on the melting method, since each method forms a unique melt-pool shape. These results are used in making a three-dimensional reconstruction of the microstructure for each plane and melting method employed. This investigation also suggests avenues for future research into the microstructural properties of electron-beam welds as well as providing an experimental basis for mathematical models for the prediction of solidification microstructures.