Christian Doppler Laboratory

          Early Stages of Precipitation

Christian Doppler Laboratory

          Early Stages of Precipitation

 

Structure-Properties Relationship of Maraging Steel

 

Project manager: Ronald Schnitzer

 

Maraging steels exhibit an excellent combination of high strength and ductility, which make them attractive for aircraft applications and as plastic mould steels. T he microstructure of maraging steels consists of a martensitic matrix which is strengthened by nm-sized intermetallic precipitates. Additionally, small amounts of austenite can be present in this type of alloys. However, the austenite is not stable during deformation, which results in a back-transformation to martensite (TRIP effect). Each of the microstructure constituents has a significant influence on the properties, and therefore basic knowledge and understanding of their formation and effects are required. Thus the aim of this project is to describe the microstructure constituents of maraging steels and to determine their influence on the mechanical properties.

The microstructure is characterized in this study by high-resolution methods like transmission electron microscopy (TEM) and three-dimensional atom probe tomography (APT). Figure 1 shows exemplarily results from APT measurements on a PH 13-8 Mo maraging steel. The methods which are used to characterize the mechanical behaviour are tensile tests, notched impact tests and dynamic compression tests on a split-Hopkinson-pressure-bar. Furthermore, the transformation behavior from austenite to martensite is investigated during tensile loading by in-situ X-ray diffraction using synchrotron radiation.

Based on the characterization of the microstructure and simulations the aim is to develop models which describe the microstructure evolution and predicts mechanical properties.

 

Figure 1: Three-dimensional reconstruction of a maraging steel PH 13-8 Mo measured with the 3D atom

probe (LEAP 3000X HR). In the left image the different phases are marked. The large rectangle shows a

detail of the measured volume and the distribution of the Ni, Al and Cr atoms. The Ni and Al enriched

areas in the martensitic matrix correspond to NiAl precipitates.