La metallografia ottica nello studio di cricche e tensioni nei giunti saldati

To detect defects and residual stresses in a welded joint, is a fundamental aspect to determine the final product quality. Non-destructive tests highlight dimensions and positions of macroscopic defects but the best way to collect helpful data is the investigation of appropriate metallo graphic section. The selected investigation method to apply must be simple, accurate, reproducible and cheap both in time and money. Well consolidate sciences as optic and electronic metallography, allow, by a "sacrificial sample" to gain a big part of those fundamental information necessary to carry on with the research. To use and to tweak chemical etchings to obtain detailed observation of defective areas complete the aim. The goal of this work is the investigation, by tint metallography, of "hot tearing " and of hardening phenomena due to the residual stresses in artistic tin-bronzes during post-welding cooling processes. The selected chemical etching is a modified Klemm III which, producing a coloured micro structure, allows to recognize second phases or inclusions, hardening phenomena, residual stresses.