Evolution of substructure during continuous rolling of microalloyed steel strip

Abstract

ith the aim of investigating the evolution of the substructure, the rolling of a steel strip containing 0•13%C, 0•75%Mn, and 0•048%Nb (all wt-%) was interrupted and the partially rolled strip water quenched. Using X-ray diVraction spectra, subgrain size and dislocation density were determined for specimens taken before and after the rolling passes. Both these microstructural characteristics were related to the rolling temperature and the amount of NbC precipitation. T he distribution of precipitates was investigated via T EM. At lower rolling temperature, particles precipitated in rows in the austenite temperature range.MST /3964

The Interdependence of the Degree of Precipitation and Dislocation Density during the Thermomechanical Treatment of Microalloyed Niobium Steel

“…In the last passes of the final thermomechanical processing in both variants, the degree of total deformation decreases ( Figure 6) while dislocation density increases, as is the case with the degree of precipitation (Figure 4a). In investigations of the same steels [10] it was proven that the low temperature rolling schedule leads to considerably higher rolling forces in the last three passes. In order to determine the quantitative amount of changes in the structure, a study of the diffraction line profile was carried out.…”

“…where D is the subgrain size [10]. The microstructure of metallographically prepared samples after etching in nital was observed using a light microscope (Leitz Ortholux, Wetzlar, Germany), and images were taken using an Olympus digital camera.…”

“…During the heating and steel austenitization stages, the heating temperature is very important. It is determined by the chemical composition of the steel and must ensure complete solubility of the niobium precipitates to provide sufficient niobium, carbon, and nitrogen content for precipitation during thermomechanical treatment [9,10]. A higher temperature than the complete solubility temperature of niobium carbonitride is not desirable because a longer austenitization time at high temperatures results in a heterogeneous increase in austenitic grains, resulting in poor mechanical and technological properties [8].…”

“…TEM micrograph of niobium precipitates in pre-deformation, reproduced from[10], with permission from Taylor&Francis, 2013.…”

The Application of a Factorial Experiment with Repeated Measurements in the Investigation of Parameters Influencing the Properties of Niobium Microalloyed Cold Drawn Welded Steel Tubes

“…It is well known that a small addition of a microalloying element with a proper selection of hot rolling parameters results in a significant improvement in the mechanical and technological properties of a rolled product [1][2][3]. The optimal addition of the microalloying element niobium is about 0.05% [4]. During hot deformation, niobium in combination with carbon or nitrogen produces solid compounds of niobium nitrides, niobium carbides or niobium carbonitrides.…”