steel research international

Cover Photo: Scanning transmission electron microscope image taken from a TEM foil in a scanning electron microscope at an acceleration voltage of 30 kV showing individual stacking faults on different (111) planes forming sessile Lomer-Cotrell-locks.

The deformation mechanisms of high-alloyed cast austenitic steels with 16% of chromium, 6% of manganese, and a nickel content of 3–9% at different temperatures were investigated by scanning electron microscopy. The intensity of the martensitic phase transformation is decreasing by increasing nickel concentration as well as deformation temperature. Thus, low nickel content leads at room temperature to a pronounced formation of α′-martensite, whereas, the highest nickel content leads to a pronounced twinning.

The strain-rate dependence under compressive load of a composite, consisting of 5 vol% MgO-partially stabilized ZrO₂ particles and a TRIP-steel-matrix (CrNiMn steel; Transformation Induced Plasticity), was investigated. The martensitic transformation in both composite components affects the flow behavior significantly, since less martensitic transformation, and adiabatic heating occurred with increasing strain rate.

A mainly martensitic material condition was obtained by compression of a CrMnNi TRIP-steel at cryogenic temperature and its temperature and strain rate dependent deformation behavior was examined. Based on this data and that of a stable austenitic alloy (AIS 316L), the flow stress behavior of the TRIP-steel was modeled for various strain rates using a rule of mixture concept.

Damage evaluation of a new Fe/TiB₂ composite has been studied by in situ three-point bending tests in a scanning electron microscope. This steel composite displays a significant increase in specific stiffness (>20%) and can be produced by continuous casting. The primary mode of damage is particle fracture and this was found to be more common than interfacial debonding.

A feasibility study has been conducted to explore the application of the GTAW process to obtain metal composite functional coating for advanced tribological application. SiC particles in the form of powder was added to the weld pool in autogenous mode as well as with an additional filler wire. The metallurgical characterization of the cladded structures were performed.

This research work investigates the low-cycle fatigue behavior of stainless steel/Mg-PSZ composite materials which have been produced using spark plasma sintering (SPS). The influence of the ceramic reinforcement on the cyclic deformation behavior and fatigue life times is discussed. The resulting deformation microstructures are studied using scanning electron microscopy analyses and electron backscatter diffraction (EBSD) measurements to localize the occurring phase transformations in the metal matrix composite.

In regard to future crash absorber applications, the crushing resistance and the deformation mechanisms of novel honeycomb structures were investigated over a wide range of strain rates. Their mechanical and structural response is significantly affected by the microstructure evolution in the cell walls accompanied by a TRIP effect of the austenitic steel matrix and a particle reinforcement of embedded zirconia.

Mechanical behavior and microstructure evolution during deformation of novel austenitic Cr–Mn–Ni as-cast steels with varied Ni content were investigated at various temperatures. The results were summarized in STT and DTT diagrams. The deformation-induced ε- and α′ martensite formation and twinning occur in these steels depending on the chemical composition and temperature. The nucleation threshold of γ → α′ transformation was determined.

Stability of austenite grains in a TRIP-steel was examined by combining ex situ bending tests and EBSD investigations. Results show that during the initial stage of deformation mainly larger grains deform and later they transform into martensite before reaching higher strain levels as smaller grains. Moreover, higher stresses develop in more elongated grains as shown by a short fiber reinforced composite model.

A ferrite/silicon nitride composite was obtained by nitriding a 1 mm thick Fe–1.5 wt% Si sheet. This treatment resulted in a material consisting in a ferritic matrix containing a large volume fraction of nanosized silicon nitride precipitates displaying a cubic shape. This morphology constitutes an atypical combination with the amorphous crystallography of these precipitates. A brief assessment of mechanical properties and density modification also showed such a method could lead to lightweight strong steel sheet particularly suitable for automotive applications.

The present work is an examination of the fatigue response of quenched and tempered ferritic/martensitic steels at 20°C and at 550°C. The cyclic softening of the commercial steels AISI 410 and AISI 420 is studied and compared with EUROFER 97. The role played by the back and friction stresses on the softening is investigated and correlated with the dislocation structure.