Secondary ledeburite formation during various welding techniques

The occurrence and formation sequence of secondary ledeburite in the heat affected zone of chromium ledeburitic tool steel W.Nr. 1.2379 (OCR12 VM) after welding with SAW, TIG, microplasma and laser welding techniques is presented in this paper. Special attention was paid on the behaviour of carbides. The occurrence of secondary ledeburite is a result of local enrichment of the austenite matrix with alloying elements, due to partial or complete dissolution of primary/eutectic carbides. The results show that the largest amount of secondary ledeburite is formed during submerged arc welding, followed by TIG and microplasma welding technique. Welding by laser technique, with appropriate technological parameters, could prevent secondary ledeburite formation.

Visual Evaluation of Cast Dental Alloys Welds Discontinuities in the Field of Fixed Prosthodontics

It is essential for a weld to satisfy the requirements of certain standards in the field where it is applied. The aim of the study was to highlight the discontinuities which can appear in the joints achieved by laser and microplasma welding of base metal dental alloys used in fixed prosthodontics. All types of discontinuities which are visible from visual inspection were searched: inclusions, inadequate joint penetration, incomplete fusion, undercuts, overlaps, underfills. Recognizing the defects and discontinuities and their delimitation was essential in determining the weld quality. The obtained results were satisfactory for the purpose both for microplasma and laser welding. Using these methods, welds without defects, which meet minimum acceptable standards for each case, could be obtained.

Marginal Adaptation of Cast Metallic Dental Crowns Using Microplasma Welding Procedures

Modern welding proceedings can be a beneficial method for repairing marginal adaptation defects in fixed prostheses technology. The aim of the study was to conduct experimental investigations to determine the optimal microplasma welding parameters according to the defect type. Different Ni-Cr alloy cast metal restorations with marginal defects were selected and divided depending on the repair possibility. A microplasma welding device, Welder, was used and as filling material a specific Ni-Cr wire was chosen. The process parameters were determined for each case. Introducing the practice of welding in dental technology requires prior experiments to determine the process parameters for the individual processes and their reproducibility.