Improved fatigue life for cylinder heads

Purpose and goal

The main objective of the project was to develop a new alloy suitable for cylinder heads with improved fatigue performance compared to the materials used today. It has been found that an alloy of compacted graphite iron with a ferritic, silicon hardened, matrix can lead to improved fatigue strength. The silicon content affects the mechanical and thermal properties and by varying this, the alloy can be optimized against different types of loads. The project has been successful and has provided improved knowledge of the relationship between microstructure and mechanical properties.

Expected results and effects

The project has shown how casting parameters such as chemical composition and solidification rate affect the microstructure and the mechanical properties of compacted graphite iron (CGI) intended for cylinder heads. The project has also developed a material model that qualitatively describes the relation between microstructure and mechanical properties. The project has been successful and a new CGI alloy with a silicon hardened ferritic matrix has been developed with promising properties. In a next step, it is proposed that cylinder heads are cast and tested in full-scale tests.

Planned approach and implementation

The project was initiated with a literature study and a review of the various load cases that are relevant for cylinder heads. Based on this, an extensive experimental series of 9 different compacted graphite iron alloys was cast. After initial microstructurural studies and mechanical experiments, extensive studies were carried out on the fatigue properties of the most interesting alloys. In parallel with this, a micromechanical model was developed that qualitatively links microstructure to mechanical performance.