Quantitative Characterization of a Belt-cast High-Manganese Steel Microstructure

The description of the solidification process in casting processes with varying product thickness is characterized based on solidification structures, segregations as well as the primary and secondary microstructure. In near-net-shape casting processes, it is particularly challenging to achieve microstructure homogeneity in the as-cast condition, since the degree of forming in production processes up to hot or cold strip is lower than in the production of slabs or thin slabs. The density of shrinkage porosity in belt-cast high-manganese steel (HMnS) will be determined quantitatively using polished microsections. Following the visualization of the primary cast structure, light microscopic images will be obtained using different tint etches. For the evaluation of secondary dendrite arm spacing (SDAS), internally developed software based on ImageJ and Matlab will be used.

Acceleration of Plasma Nitriding at 550 °C with Rare Earth on the Surface of 38CrMoAl Steel

In order to explore the effect of the addition of rare earth (RE) to a steel microstructure and the consequent performance of a nitrided layer, plasma nitriding was carried out on 38CrMoAl steel in an atmosphere of NH3 at 550 °C for 4, 8, and 12 h. The modified layers were characterized using an optical microscope (OM), a microhardness tester, X-ray diffraction (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), and an electrochemical workstation. After 12 h of nitriding without RE, the modified layer thickness was 355.90 μm, the weight gain was 3.75 mg/cm2, and the surface hardness was 882.5 HV0.05. After 12 h of RE nitriding, the thickness of the modified layer was 390.8 μm, the weight gain was 3.87 mg/cm2, and the surface hardness was 1027 HV0.05. Compared with nitriding without RE, the ε-Fe2-3N diffraction peak was enhanced in the RE nitriding layer. After 12 h of RE nitriding, La, LaFeO3, and a trace amount of Fe2O3 appeared. The corrosion rate of the modified layer was at its lowest (15.089 × 10−2 mm/a), as was the current density (1.282 × 10−5 A/cm2); therefore, the corrosion resistance improved.

Campo del Cielo – an Iron Meteorite found in Argentina

Fragments of the “Campo del Cielo” meteorite were first reported by conquistadores in Argentina in as early as 1576. This meteorite belongs to the group of iron meteorites and is classified as a group IA coarse octahedrite. The use of meteoric iron to make objects of daily use or hunting weapons in prehistoric times is only confirmed by very few finds. Metallographic examinations were performed to assess if it was realistic and in fact feasible to process meteoric iron. The bulk of the examined “Campo del Cielo” meteorite fragment found in Argentina is kamacite (α-Fe) with approx. 5.3 wt.% of dissolved Ni. Graphite was also detected in addition to various non-metallic phases. Due to high temperatures during processing, graphite can dissolve and a steel microstructure would form as a result.

Influence of thermomechanical processing parameters on critical temperatures to develop an Advanced High-Strength Steel microstructure

A good selection of the thermomechanical processing parameters will optimize the function of alloying elements to get the most of mechanical properties in Advanced High-Strength Steels for automotive components, where high resistance is required for passenger safety. As such, critical processing temperatures must be defined taking into account alloy composition, in order for effective thermomechanical processing schedules to be designed. These critical temperatures mainly include the recrystallization stop temperature (T5%) and the transformation temperatures (Ar1, Ar3, Bs, etc.). These critical processing temperatures were characterized using different thermomechanical conditions. T5% was determined through the softening evaluation on double hit tests and the observation of prior austenite grain boundaries on the microstructure. Phase transformation temperatures were measured by dilatometry experiments at different cooling rates. The results indicate that the strain per pass and the interpass time will influence the most on the determination of T5%. The range of temperatures between the recrystallized and non-recrystallized regions can be as narrow as 30 °C at a higher amount of strain. The proposed controlled thermomechanical processing schedule involves getting a severely deformed austenite with a high dislocation density and deformation bands to increase the nucleation sites to start the transformation products. This microstructure along with a proper cooling strategy will lead to an enhancement in the final mechanical properties of a particular steel composition.

Effects of Heat Treatment on Microstructure Parameters, Mechanical Properties and Cold Resistance of Sparingly Alloyed High-Strength Steel

This study considers the influence of various heat treatment conditions on the change of steel microstructure parameters, mechanical properties and cold resistance at a temperature of-60 °C. The common behavior of these properties is considered depending on the heating temperature used for quenching and subsequent tempering. Based on the obtained results, heat treatment conditions are proposed that provide a combination of a guaranteed yield point σ0.2 ≥600 N/mm2 with a low-temperature impact toughness KCV-60 ≥50 J/cm2 and plasticity δ5 ≥17%. The obtained research results are intended for industrial use at the mill "5000" site of MMK PJSC.