Advanced High Strength and Nanostructured Steels

We review microstructures and properties of metal matrix composites produced by severe plastic deformation of multiphase alloys. Typical processings are wire drawing, ball milling, roll bonding, equal-channel angular extrusion, and high-pressure torsion of multiphase materials. [more]

For 5000 years, metals have been mankind’s most essential materials owing to their ductility and strength. Linear defects called dislocations carry atomic shear steps, enabling their formability. We report chemical and structural states confined at dislocations. In a body-centered cubic Fe–9 atomic percent Mn steel, we found Mn segregation at dislocation cores during heating, followed by formation of face-centered cubic regions but no further growth. [more]

Dual-phase (DP) steel is the flagship of advanced high-strength steels, which were the first among various candidate alloy systems to find application in weight-reduced automotive components. On the one hand, this is a metallurgical success story: [more]

Grain refinement through severe plastic deformation enables synthesis of ultrahigh-strength nanostructured materials. Two challenges exist in that context: [more]

Grain boundary segregation leads to nanoscale chemical variations that can alter a material's performance by orders of magnitude (e.g., embrittlement). To understand this phenomenon, a large number of grain boundaries must be characterized in terms of both their five crystallographic interface parameters and their atomic-scale chemical composition. [more]

Carbon partitioning between ferritic and austenitic phases is essential for austenite stabilization in the most advanced steels such as those produced by the quenching and partitioning (Q&P) process. [more]

LAM involves rapid melting and solidification with only a small melt pool volume existing at any time during the manufacturing process. This offers the opportunity to manufacture materials that cannot be cast conventionally, e.g. oxide-dispersion strengthened alloys.  [more]

B₂NiMn and Ni₂MnAl Heusler nanoprecipitates are designed via elastic misfit stabilization in Fe–Mn maraging steels by combining transmission electron microscopy (TEM) correlated atom probe tomography (APT) with ab initio simulations. [more]

In this project we investigate the kinetics of the deformation structure evolution and its contribution to the strain hardening of a Fe–30.5Mn–2.1Al–1.2C (wt.%) steel during tensile deformation by means of transmission electron microscopy and electron channeling contrast imaging combined with electron backscatter diffraction. [more]

This project is about the fundamentals of the martensite to austenite reversion transformation. [more]

In this project we study partitioning at phase boundaries of complex steels which is important for their properties. We present atom probe tomography results across martensite/austenite interfaces in a precipitation-hardened maraging-TRIP steel (12.2 Mn, 1.9 Ni, 0.6 Mo, 1.2 Ti, 0.3 Al; at.%). [more]

Quench and Partioning (Q&P) steels are 3rd generation advanced high strengths (AHS) steels. They consist of a martensite-austenite microstructure created during a quenching process. However, due to the subsequent partitioning treatment the martensite is relatively soft and the austenite relatively stable against phase transformation which makes the alloy strong (tensile strength up to 1000 MPa) and ductile (uniform tensile elongation up to 20 %) at the same time. We aim at improving the microstructure by obtaining finer austenite dispersion. [more]

This project is about the understanding and optimization of the microstructure and properties of thin strip cast austenitic stainless steel (AISI 304, 1.4301). Concerning the processing steps the relevance of different thin strip casting parameters, in-line forming operations, and heat treatments for optimizing microstructure and properties have been studied. [more]

 Steels with a high ultimate tensile strength (UTS) above 1 GPa and good ductility (total elongation (TE) of 15-20% in a tensile test) are of greatest relevance for lightweight engineering design strategies and corresponding CO₂ savings. In this project we work on a novel design approach for precipitation hardened ductile high strength martensitic and austenitic-martensitic steels (up to 1.5 GPa strength). [more]

Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite results in an ultra-high strength ferritic stainless steel with excellent ductility. [more]

In this project we pursue recent developments in the field of austenitic steels with up to 18% reduced mass density. The alloys are based on the Fe-Mn-Al-C system. [more]

Carbon partitioning from martensite into austenite in the quenching and partitioning (Q&P) process has been suggested to be controlled by the constrained carbon equilibrium (CCE) criterion. [more]