Microstructure Evolution and Mechanical Properties of Haynes 282
As Haynes 282 has showed sensitivity to heat treatment temperatures within the typical tolerance limits around the conventional heat treatment, the main objective of this research was to understand the microstructural evolution and mechanical properties with changes in heat treatment conditions. The effect of heat treatment variations on microstructure and mechanical properties has been systematically studied. Its influence on microstructure and tensile properties between room temperature and 730 °C are presented.
The results show that γ׳ does not precipitate during rapid cooling but it precipitates as fine spherical particles during air cooling from the carbide stabilization temperature, and it changes to bimodal distribution with square and spherical morphology during slow cooling. During ageing, γ׳ is seen to precipitate intergranularly, as well as along the grain boundaries. The solvus temperature for this phase was above 1010 °C (higher than previously suggested), and depending on the combination of temperatures and times of the heat treatments, the γ׳ morphology changes from spherical to bi-modal to cuboidal. The grain boundary carbide morphology depends strongly on heat treatment temperature and is seen to change from continuous film to brick wall structure and finally to discrete particles. These microstructural changes strongly affect both strength and ductility of the material.
Furthermore, Haynes 282 forgings show ductility variations in short transverse direction. The lower limit of ductility in this direction is close to the design tolerance and thus creates a need to understand the underlying cause. In this part, the study is focused to understand ductility variation by microscopic investigations. Carbide segregation and banding is seen to influence the ductility when oriented perpendicular to the tensile axis. This influence is also qualitatively captured through micromechanical modelling.
Haynes 282, gamma prime, carbides, isothermal transformation, anisotropy ductility, heat treatment, microstructure, solution treatment, carbide stabilization treatment
carbide stabilization treatment
Chalmers, Industri- och materialvetenskap, Konstruktionsmaterial
Bearbetnings-, yt- och fogningsteknik
Metallurgi och metalliska material
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4382
Opponent: Dr. Martin Stockinger