The influence of flow-forming parameters and microstructure on the quality of a D6ac steel

The influences of how-forming parameters and the state of the microstructure on the quality and mechanical properties of a D6ac steel were studied. The effects of feed rate, the shape of the contact line, the roller angle and the percentage reduction on the elimination of spinning defects such as a wave-like surface, microcracks and bore were studied. Also, the influence of the preheat temperature, the holding time and the cooling rate on the microstructure and mechanical properties of the material was investigated. The experiments were carried out on a 3-roller spinning machine and the optimum conditions for the elimination of the above-mentioned defects were determined. Both optical and electron microscopy were used for the study of the microstructure, and the appropriate heat-treatment leading to the best strength-toughness combination was found. The results obtained are interpreted within the framework of metal working theories and examined critically with existing models. (C) 2000 Elsevier Science S.A. All rights reserved.