A STUDY OF PRECIPITATION IN AS-WELDED 316LN PLATE USING 316L 317L WELD METAL/

A study was undertaken of the precipitation in multi-pass 316L and 317 L weldments in as-welded conditions. A feature of the work was that th e microstructure of the welds was compared by trepanning 3 mm discs fr om specific positions. Specimens for transmission electron microscopy (TEM) were prepared from the discs. The volume percentages of delta(de lta)-ferrite and intermetallics were determined by taking the mean of values obtained from 30-40 fields of view. Selected area electron diff raction (SAED) and energy dispersive X-ray analysis (EDAX) were used t o identify the phases present in the various positions within each wel d. In regions where overlapping of two welding passes occurred and hen ce where there was some remelting of the initial pass, the chi(chi) ph ase was identified. This precipitated usually at the delta/austenite p hase boundary in the size range 0.05-0.1 mu m probably due to the high er Mo and Cr, and lower N in these regions. The higher Mo content resu lted in a higher volume % of chi phase in the overlapped pass region o f the 317L welds compared to the 316L welds. One case was observed of sigma(sigma) phase which was probably transformed from the chi phase.