Vliv deformace na rozpadové diagramy ocelí

Abstract

The main objective of the work was to investigate the effect of previous deformation on the kinetics of phase transformations during cooling of steel, chemical composition of which differed significantly. In coordination with industrial partners (Třinecké Železárny, a. s., ArcelorMittal Ostrava a. s. and forging shop Kovárna VIVA a. s.) altogether five steel grades were chosen: 20MnCrS5, 32CrB4, 42CrMo4, 51CrV4 and Cr-Mn, i.e. rail steel of the class IH. Using dilatometric module of the plastometer Gleeble 3800, operated at the Regional Materials Science and Technology Centre, at the VŠB - Technical University of Ostrava, as well as metallographic analyses and hardness measurements we compiled for these steels diagrams of anisothermal decay of austenite without influence of the previous deformation (CCT) and with influence of the deformation (DCCT). The obtained diagrams were compared with the results of calculations performed in specialised software QTSteel 3.2, as well as with published transformation diagrams of similar steel grades. Additionally we studied also the influence of austenitic grain size, given by the heating temperature or deformation, on the kinetics of phase transformations during the cooling at different rates. On the basis of the obtained results it was possible to formulate more general conclusions about effect of the input strain on the decay diagrams of steels. The obtained information was used, among others, for optimisation of the operational technology of controlled cooling in order to achieve the desired structural and mechanical properties of the formed products.