Influence of cooling rate on the ferrite content and microstructures in CD3MWCuN castings

TLDR: In this paper, the influence of cooling rates on the ferrite content of duplex stainless steels was investigated and it was found that cooling rate can influence the overall ferrite/austenite ratio and achieving the proper balance of phases is crucial in producing a casting with suitable mechanical and corrosion properties.

Abstract: Highly alloyed CD3MWCuN was chosen to investigate the influence of cooling rates on the ferrite content of duplex stainless steels. It is known that cooling rate can influence the overall ferrite/austenite ratio, and achieving the proper balance of phases is crucial in producing a casting with suitable mechanical and corrosion properties. Initial experiments were carried out to study the ferrite/austenite ratio as a function of cooling involved samples obtained using different cooling rates through the solidification temperature as well as different cooling rates from the homogenization temperature. A single keel bar was obtained, sectioned, and recast at six different solidification cooling rates. Each of the six castings was then sectioned into six pieces and each piece cooled from the homogenization temperature to produce six different homogenization cooling rates. Backscattered electron imaging was used to measure the phase percentages and observe the microstructures. The ferrite content was found to increase with increasing homogenization cooling rates. It was also found that the homogenization cooling rate should be higher than 200 °C/h in order to get high ferrite contents (> 40%). As the cooling rate slows, intermetallic phases such as sigma start to precipitate at the grain boundaries.