With two pilot plants in operation, the Direct Strip Casting (DSC) technology has reached a state from which it can be concluded that a DSC production process is feasible. The core of the process consists of a caster in which liquid steel is fed on an intensively cooled revolving belt. After solidification in a protective atmosphere, the yielded strip of about 10 mm in thickness is directly hot rolled without intermediate reheating. Thus, due to the reduced expenditures for hot rolling and reheating, substantial energy savings compared to conventional slab casting can be achieved. Moreover, the production of new high‐strength, light‐weight steels with an increased content of manganese, aluminium and/or silicon is enabled by the special features of the DSC process. The use of these steels in automotive applications would lead to further energy savings induced by significant weight reductions and an enhanced life cycle of the car body. Furthermore, also a higher share of scrap based strip steel production, requiring less than half of the energy needed for the blast furnace route, becomes conceivable for quality steel grades, as a higher content of tramp elements, e.g. copper and tin, is tolerable without quality losses (surface cracks). Finally, the compact design and the high productivity of the DSC process save capital and processing costs. In the paper, process development steps, material properties and energy saving potentials are outlined.

The microalloying with niobium (Nb) and titanium (Ti) is standardly applied in low carbon steel high-strength low-alloy (HSLA) steels and enables austenite conditioning during thermo-mechanical controlled processing (TMCP), which results in pronounced grain refinement in the finished steel. In that respect, it is important to better understand the precipitation kinetics as well as the precipitation sequence in a typical Nb-Ti-microalloyed steel. Various characterization methods were utilized in this study for tracing microalloy precipitation after simulating different austenite TMCP conditions in a Gleeble thermo-mechanical simulator. Atom probe tomography (APT), scanning transmission electron microscopy in a focused ion beam equipped scanning electron microscope (STEM-on-FIB), and electrical resistivity measurements provided complementary information on the precipitation status and were correlated with each other. It was demonstrated that accurate electrical resistivity measurements of the bulk steel could monitor the general consumption of solute microalloys (Nb) during hot working and were further complemented by APT measurements of the steel matrix. Precipitates that had formed during cooling or isothermal holding could be distinguished from strain-induced precipitates by corroborating STEM measurements with APT results, because APT specifically allowed obtaining detailed information about the chemical composition of precipitates as well as the elemental distribution. The current paper highlights the complementarity of these methods and shows first results within the framework of a larger study on strain-induced precipitation.

Die komplexe Technik heutiger Kraftfahrzeuge und Antriebsstränge macht einen immer größer werdenden Fundus an Informationen notwendig, um die Funktion und die Arbeitsweise von Komponenten oder Systemen zu verstehen. Den raschen und sicheren Zugriff auf diese Informationen bietet die Reihe ATZ/MTZ-Fachbuch, welche die zum Verständnis erforderlichen Grundlagen, Daten und Erklärungen anschaulich, systematisch, anwendungsorientiert und aktuell zusammenstellt.Die Reihe wendet sich an Ingenieure der Kraftfahrzeugentwicklung und Antriebstechnik sowie Studierende, die Nachschlagebedarf haben und im Zusammenhang Fragestellungen ihres Arbeitsfeldes verstehen müssen und an Professoren und Dozenten an Universitäten und Hochschulen mit Schwerpunkt Fahrzeug-und Antriebstechnik. Sie liefert gleichzeitig das theoretische Rüstzeug für das Verständnis wie auch die Anwendungen, wie sie für Gutachter, Forscher und Entwicklungsingenieure in der Automobil-und Zulieferindustrie sowie bei Dienstleistern benötigt werden.

No abstract

Actual multiphase steels guarantee tensile strengths in different grades between 500 and 1000 MPa. Specifications and standards permit a wide field of chemical compositions. On one hand, carbon amounts higher than 0.12% are not seldom for grades exceeding 600 MPa tensile strength. However, frequently encountered difficulties during body manufacturing, due to limited formability, like enhanced crack formation at trim edges, increased springback, or deteriorated fracture behavior of weld joints are typically related to unfavorable microstructures. On the other hand, a strict limitation of the carbon content to below 0.1 wt % across all strength classes up to 1000 MPa allows avoiding the mentioned manufacturing difficulties. Carbon reduction as well as grain refinement and precipitation hardening by means of Nb-microalloying and solid solution hardening through further addition of manganese, silicon, chromium, or molybdenum are the major key factors on metallurgical site. A more homogenous combination of ferrite and martensite with certain amounts of bainite is adjusted by heat treatment to defuse the critical interfaces to increase forming properties measured by bending angle and hole expansion.