The precipitation of titanium nitride in undeformed solid carbon-manganese steel has been investigated by means of metallography and electron microscopy at in-situ melted samples the cooling of which was interrupted at different temperatures for a defined time. The deformation-induced precipitation of titanium nitride was studied on samples which were in-situ melted in a torsion plastometer, deformed after solidification, re-deformed after a holding time, and quenched. Additionally, 50 mm slabs were investigated after direct rolling in a pilot plant, partially with a preceding soaking. In the range of delta ferrite fast homogenization of segregated titanium takes place. No TiN nuclei were formed. In undeformed austenite some large precipitates were formed indicating the solidification structure. In the 1200 to 1100 "C range particle sizes between 20 and 70 nm were reached. A high density of deformation-induced particles smaller than 10 nm could be obtained at or below 1050 "C. The density of the particles increased with decreasing deformation temperature. After fast cooling, below 1000 "C also in undeformed material finely dispersed precipitates were formed.Ausscheidung von Titannitrid in niedriglegiertem Stahl wiihrend des AbkOhlens und Umformens. Die Bildung von Titannitrid in unverformtem festem Kohlenstoff-Mangan-Stahl wurde metallographisch und elektronenoptisch an Proben, deren AbkOhlung nach dem Erstarren bei unterschiedlichen Temperaturen fOr vorgegebene Zeiten unterbrochen wurde, untersucht. Eine verformungsinduzierte Ausscheidung von Titannitrid erfolgte an Proben, die in einem Torsionsplastometer in-situ geschmolzen, nach dem Erstarren umgeformt, nach einer Haltezeit nochmals verformt und abgeschreckt wurden. Zusatzllch wurden 50-mm-Platinen nach Direktwalzen in einer Versuchsanlage untersucht, teilweise mit AusgleichsglOhung vor dem Walzen.
Laboratory melts of microalloyed low carbon steels with an increased silicon content of about 1 % and manganese contents between 0.3 and 1.3 % were thermomechanically rolled in a laboratory two‐high rolling stand to plates of about 10 mm in thickness. The influence of chemical composition and finish rolling temperature (FRT) on the ferrite‐pearlite structure of the plates (tensile and Charpy impact tests) was investigated. The choice of the temperature range of finish rolling with respect to the γ/α transformation start temperature strongly influences the ferrite‐pearlite structure and the mechanical properties. The most fine‐grained and homogeneous ferrite‐pearlite structure and the best combination of strength and toughness have been obtained with steels containing about 1 % Mn and 1 % Si rolled with a finish rolling temperature of about 850°C.
For the modelling of microstructure development during hot deformation operations as well as for the prediction of deformation loads stress‐strain data are required. For this purpose various laboratory deformation techniques are employed. On two steel grades (medium carbon Cr‐Mo steel and austenitic Cr‐Ni steel) axisymmetric and plane strain compression tests as well as torsion tests were applied with the aim of comparing equivalent stress‐strain curves determined by such different deformation tests. The results showed that for the calculations of deformation loads during multi‐deformation industrial operations with rather small individual deformation steps, the choice of laboratory deformation test is not a critical point. Nevertheless, conflicting results are expected by an exact interpretation of stress‐strain curves concerning microstructural development by using different testing methods.
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