High-temperature oxidation phenomena play a crucial role in steel production and processing. The development of new alloying concepts, the modification of production routes due to the decarbonization of steelmaking, and increasing quality demands will additionally stimulate research activities on high-temperature oxidation. Within the scope of this publication, the oxidation behavior of an unalloyed steel was investigated by means of thermogravimetric (TG) and metallographic analysis. The TG measurements were performed with a simultaneous thermal analyzer in combination with a water vapor generator and a mass spectrometer for quality control. Experiments were conducted in a temperature range from 900 to 1200 °C under various oxidation atmospheres, containing synthetic air and water vapor, with different linear flow rates of the oxidizing medium. According to the thermogravimetric data, an evaluation method is introduced to obtain direct kinetic data for linear and parabolic scale growth. The influence of the experimental parameters on high-temperature oxidation is discussed in detail.

Oxidation processes are unavoidable in continuous casting and further hot processing of steel. A deeper understanding of the occurring phenomena such as intergranular oxidation and liquid metal infiltration of grain boundaries is essential to continuously improve the quality of the products. In this study, oxidation experiments were performed with simultaneous thermal analysis for two thin slab casting and rolling applications under near-process conditions up to the point prior to the first reduction stage. The experiments were performed for two low-carbon steels contaminated with undesirable tramp elements (Cu, Sn, …). In addition, the two steels contain Silicon at different levels. The results show that for the "Endless Strip Production" process (ESP), intergranular oxidation is significantly less pronounced compared to a "Thin Slab Casting and Rolling process" with a gas-fired tunnel furnace (TSCR TF). Due to the short process time at high temperatures in the ESP process, hardly any liquid metal infiltration by copper appears. In low silicon steel, intergranular oxidation results from various oxides, and liquid metal infiltration appears simultaneously in the TSCR TF process. Furthermore, the yield loss from oxidation is significantly higher in the TSCR TF process. The change from a natural gas combustion atmosphere to a hydrogen combustion atmosphere further increases the oxidation rate and results in a higher mass loss.

In the course of the decarbonization of steel production, electric steel production will continue to gain importance. The processing of low‐quality scrap will also play an important role, which may lead to an increase in the content of so‐called tramp elements in steel production and further processing. This article examines the effect of the elements Cu, Sn, and Ni on the formation of surface cracks under the conditions of the continuous casting process. Results of an in situ bending test are compared with the results of the experimental simulation of high‐temperature oxidation and thermodynamic analysis based on the CALculation of PHase Diagrams (CALPHAD) approach. For a temperature of 900 °C, an equivalent Cu content of 0.20 wt% must be considered as the critical upper limit. The presumable reason is the existence of Cu‐ and Sn‐rich liquid phases at the austenite grain boundaries. The results clearly show the effect of the investigated elements but also point to the importance of the gas atmosphere and cooling conditions on the results. This can be a groundbreaking result for extending the process window for casting steels with increased tramp element contents.

The surface quality in continuous casting of the semi-finished product is one of the most important criteria for the successful processing into a finished product. Any defects that may occur should be completely avoided and therefore parameters have to be defined by external experiments. However, this presupposes that the examination is as close to the process as possible. A new approach is to determine the crack sensitivity using the in situ material characterization by bending (IMC-B) test. The advantage of this test method is that the entire process, from the solidification to the bending of the sample in a 3-point bending test, offers conditions close to the continuous casting process. The occurring microstructure, the oxidation processes during controlled cooling, and the bending parameters are similar. Therefore, the obtained results regarding the necessary strain for crack formation can be transferred directly for quality prediction in continuous casting. Within the scope of this publication, the crack susceptibility for a low-carbon and medium-carbon steel in a temperature range of 650 °C to 1100 °C is analyzed in detail for different parameters such as maximum strain or strain rate. Furthermore, the influence of the tramp elements Cu and Sn is investigated for expected future concentrations. The most critical temperature range for all investigated steels is from 850 °C to 1000 °C and it is aggravated by the presence of Cu and Sn. The strain required for cracking is then reduced to less than 1 pct.

Oxidation-related surface defect formation in continuous casting is an under-researched topic, as most of the experiments, which aim to define surface defect mechanisms, are performed under a protective atmosphere. However, intergranular oxidation or the formation of low-melting Cu-rich phases at the grain boundaries may lead to tremendous problems during straightening. This study exclusively addresses the impact of oxidation-related pre-defects on surface crack formation in continuous casting and how different parameters, such as cooling cycle and cooling atmosphere, affect the outcome. The investigations were performed using in-situ material characterization by bending tests (IMC-B) to evaluate crack susceptibility and simultaneous thermal analysis (STA) to analyze oxidation mechanisms in detail. Both the damage of grain boundaries by intergranular oxidation due to a low-melting fayalite-wustite eutectic and due to low-melting Cu-rich phases favor crack formation at lower temperatures significantly. A stronger external oxidation can have both positive and negative effects on surface crack formation, depending considerably on the specific steel composition. Regarding intergranular oxidation, increased external oxidation helps minimize internal and intergranular oxidation, thereby reducing potential nuclei for surface defect formation in subsequent processing steps. However, in the presence of Cu and Sn, which do not readily oxidize due to their low oxygen affinity, enhanced external oxidation promotes their enrichment, consequently increasing the risk of defect formation.