The sizes of chondrules are a valuable tool for understanding relationships between meteorite groups and the affinity of ungrouped chondrites, documenting temporal/spatial variability in the solar nebula, and exploring the effects of parent body processing. Many of the recently reported sizes of chondrules within the CM carbonaceous chondrites differ significantly from the established literature average and are more closely comparable to those of chondrules within CO chondrites. Here, we report an updated analysis of chondrule dimensions within the CM group based on data from 1937 chondrules, obtained across a suite of CM lithologies ranging from petrologic subtypes CM2.2 to CM2.7. Our revised average CM chondrule size is 194 μm. Among the samples examined, a relationship was observed between petrologic subtype and chondrule size such that chondrule long‐axis lengths are greater in the more highly aqueously altered lithologies. These findings suggest a greater similarity between the CM and CO chondrites than previously thought and support arguments for a genetic link between the two groups (i.e., the CM‐CO clan). Using the 2‐D and 3‐D data gathered, we also apply numerous stereological corrections to examine their usefulness in correcting 2‐D chondrule measurements within the CM chondrites. Alongside this analysis, we present the details of a standardized methodology for 2‐D chondrule size measurement to facilitate more reliable inter‐study comparisons.

In this study, the deformation-induced α-martensite formation in AISI 304L steel was investigated in the temperature range between 75 °C and − 196 °C in the light of the temperature-dependence of hydrogen embrittlement phenomena. For this purpose, tensile tests with in-situ and ex-situ magnetic measurement of the α-martensite volume content as a function of plastic strain were carried out. In addition, a theoretical assessment of the temperature-dependence of the austenite stability was undertaken, evaluating chemical and non-chemical driving force contributions to the martensitic γ → α transformation as proposed by Ghosh and Olson. The experimental results clearly show an increase in the α-martensite volume content and a shifting of the phase transformation to lower strain levels upon reducing the temperature to − 75 °C. A further reduction of the temperature to − 196 °C revealed to have no significant impact on the α-martensite formation. The theoretical assessments indicate a similar temperature-dependence of the austenite stability as observed experimentally and suggest contributions of the thermal friction work at the fcc/bcc interface to be responsible for a constant austenite stability in low-temperature regimes. Additional investigations of deformed microstructures showed that element segregation effects on the local austenite stability are pronounced around room temperature, but become less relevant at low temperatures.

In the paper industry, machine circular knives are used in the cutting process to provide industrial quality cuts on a variety of products. In the production of paper rolls, they cut the long-rolled paper products into commercial sizes. For this application, the high-alloyed ledeburitic cold work tool steel, DIN EN 1.2379 (X153CrMoV12; AISI D2), in the secondary hardened heat-treated condition has become the widely used industry solution. However, its heat treatment is a very energy-intensive production process. It consists of a quenching from an austenitizing temperature above 1050 °C, followed by three high-temperature tempering steps of more than 500 °C. In the study, the heat treatment process was optimized for energy efficiency, resulting in superior material properties with lower energy consumption. The most promising low energy heat treatment developed in the laboratory was reproduced in the industrial scale, and the required energy consumption was quantified. Subsequently, the resulting properties of the tools such as hardness, wear resistance and fracture toughness were determined. The energy production costs and mechanical properties of the tool steel were evaluated in comparison to conventional production methods. The newly applied heat treatment condition showed very promising and positive results in all analyzed parameters.