DRUŠTVO LIVARJEV SLOVENIJESLOVENIAN FOUNDRYMEN SOCIETY
Član The World Foundry OrganizationMember of World Foundry Organization

Abstract

New ductile iron grades are required to meet the challenges arising from engine downsizing and subsequent temperature increase. This paper describes the development of new ferritic, temperature resistant ductile iron grades, their properties, serial applications and newest achievements in material development. Downsizing of gasoline and Diesel engines helps to reduce CO2 emissions. Constructing smaller engines with increased power levels leads to higher exhaust gas temperatures. In passenger cars, these exceed 850°C in Diesel engines and even 1050 °C in turbocharged gasoline engines. Thermal insulation protects the engine's surroundings, but tightens the operating conditions of the insulated hot parts even further. Ferritic silicon and molybdenum-alloyed ductile iron grades are standardized in Europe in EN- 16124. However, these materials' properties are not sufficient for being applied in the newest downsized engines. Based on SiMo ductile iron, new ferritic materials are developed with the aim to raise ferrite/austenite transition temperature, high temperature (HT) strength and scaling resistance.

Keywords ductile iron, SiMo, temperature resistance, exhaust manifold, turbocharger, ferrite-austenite transformation.

 

The economic efficiency of the whole high-pressure die-casting process is essentially influenced by the lifetime of the used die casting die. Such dies are constantly exposed by high thermal, mechanical, chemical, and tribological cyclic loads during the operation. These loads might cause different defects on or in the mould and thereby reduce the die lifetime significantly. In the case of an unexpected production stop caused by a critical defect in the mould, repair welding is often the only way of reinstating the casting tool during the production. Currently, the TIG or plasma welding processes are mainly used for such repair welding routines. Nevertheless these conventional repair welding techniques constitute an insufficient process reliability and therefore achieve an insufficient life extension. A repair welding process instead of a remanufacture of a die is, however, economically and technically feasible, if the welding is done immediately and reliably and results in a sufficient lifetime.

The primary objective is thus the development of a technology for an economic regeneration of locally damaged die casting tools, focusing on the metallurgical properties with improved properties compared to conventional repair welding techniques such as TIG or plasma welding. The electron-beam welding technique allows a variable, needs-adapted design of the overall heat balance and the use of filler material; therefore it is going to be qualified as a repair welding technology for industrially used hot-work steels. This article starts with an overview of the typical types of damages to die casting moulds. Furthermore, common repair welding methods for die casting moulds, like TIG- or plasma welding will be explained for a comparison to the electron-beam welding. The article also explains the technique and potential of the electron-beam welding as a repair welding method. To sum up this article, the current achieved results and the following researches will be presented.