Modern high-strength low-alloy (HSLA) steels have to fulfill a combination of high strength and toughness. In general, these properties are contrary, due to the fact that a high strength normally decreases the toughness of the material. Nevertheless, a grain refinement increases both, the toughness and the strength of steels. For HSLA steels, thermomechanical rolling is the processing of choice to obtain a finegrained microstructure for industrially relevant applications. [1,2] Adding microalloying elements like niobium, titanium, or vanadium increases the temperature nonrecrystallization (T NR ), which is the temperature below which no complete static recrystallization between two rolling passes takes place. Higher rolling temperatures allow lower rolling forces but have the disadvantage of resulting in grain growth. Titanium as a microalloying element retards the grain coarsening because it leads to the formation of TiN precipitates. These TiN precipitates are stable at temperatures, where Nb is in solution and which often is the starting temperature of the rolling process. [3] The equilibrium temperature for Nb(C,N) in austenite was estimated by Irvine et al. [4,5] and is given in Equation (1). log ðm%NbÞ m%C þ 12 14Nb delays the recrystallization of austenite in two ways. On the one hand, by the solute-drag effect and on the other hand, by precipitates. The solute-drag effect retards the recrystallization when Nb is dissolved in the austenite but is less effective than Nb-enriched precipitates, e.g., carbides, nitrides, and carbonitrides

A tapping process model of the steel from the basic oxygen furnace (BOF) addressing the reactions in the ladle is proposed. In the model, the effective equilibrium reaction zone (EERZ) method is applied to describe the steel/slag interfacial reaction. The equilibrium reactions in the bulk steel (steel/inclusion/lining wear) and slag (liquid slag/slag additions/lining wear) are considered. The thermodynamic library—ChemApp is used to perform thermodynamic calculation. The process model includes most of the actions during the tapping process, such as the additions of ferroalloys and slag formers, carryover slag entrapment and air pick-up. After the calibration by the industrial measurements of two plants, the model is applied to study the influence of the amount of carryover slag.

To achieve higher strength and good hardenability and at the same time use the positive effects of thermomechanical controlled processing, the concept of Nb and Ti microalloyed steels is increasingly used for high‐strength low‐alloy (HSLA) steels with higher C contents. Herein, how the addition of Ti affects the grain growth and static recrystallization behavior of a Nb microalloyed HSLA steel with a C content of 0.23 wt% is investigated. For this reason, alloys with varying Ti and constant Nb content are produced and investigated by means of annealing and double‐hit deformation experiments. Atom probe tomography measurements reveal that the Nb concentration in the matrix decreases with increasing Ti content. Therefore, the static recrystallization behavior is steadily inhibited with decreasing Ti content, as more dissolved Nb is available for the formation of strain‐induced NbC precipitates. The annealing experiments show that the combined addition of Ti and Nb is most effective against grain coarsening, regardless of whether the Ti content is 90 or 180 ppm. To use the positive properties of Ti against grain coarsening and Nb to inhibit recrystallization, a middle content must be chosen when alloying Ti to HSLA steels with higher C content.

The service life of roller bearings strongly depends on nonmetallic inclusions (NMIs). Therefore, these steels request highest metallurgical standards in their production. To determine the effect of the Al2O3 content and a protective atmosphere (N2) on the electroslag remelting (ESR) behavior, laboratory scale experiments are conducted. Changes in the composition of the remelted materials and in the slag are determined. In addition, the amount and composition of the NMI prior and after remelting are investigated, and thermodynamic simulations on the formation of NMI are conducted. Changes in the chemical composition can largely be explained by well‐known equilibrium reactions between the slag and the metal. Lowest Al contents in the remelted steel can only be achieved with the Al2O3‐free slag. Higher Al2O3 contents in the slag lead to higher oxygen and sulfur contents in the steel and corresponding higher amounts of NMI after remelting. The use of a protective gas mainly reduced the loss of Si and led to lower O and S contents after remelting with the Al2O3‐free slag. The composition of the NMI changed from alumina type to MgO–Al2O3 (MA)‐spinel type and finally mixed MgO–SiO2 oxides with decreasing Al2O3 contents. These results are confirmed by thermodynamic calculations.

Dynamic strain-induced transformation (DSIT) enables the formation of fine-grained ferritic microstructures, which are well suited for cold forming processes in the as-rolled condition. In this work, the formation mechanism, chemical composition, and crystallographic orientation of DSIT ferrite were investigated in a micro-alloyed steel and compared to pre-eutectoid ferrite. High-resolution techniques, such as scanning transmission electron microscopy and atom probe tomography (APT), were used for the investigations. To generate DSIT ferrite and pre-eutectoid ferrite, different experimental routes were applied using a compression deformation dilatometer. The results show a large number of NbC precipitates within DSIT ferrite, and show that the formation of DSIT ferrite is accompanied with C diffusion and the formation of retained austenite. APT measurements revealed that the C- and Mn concentration in DSIT ferrite is higher compared to pre-eutectoid ferrite. The crystallographic orientation of DSIT ferrite was examined using electron backscatter diffraction. The crystallographic orientation of DSIT ferrite after the deformation route revealed that the <111> plane normals are parallel to the compression direction with the <110> directions pointing towards the radial direction of the compressed sample. The results suggest that the formation of DSIT ferrite is a displacive mechanism, accompanied by C diffusion.