Plastometric study of hot formability of hypereutectoid C – Mn – Cr – V steel

Formability of hypereutectoid C-Mn-Cr-V steel in hot condition was investigated with use of plastometric methods. A wide range of deformation temperatures 1 300 - 640 °C for hot tensile tests was proposed with use of nil-strength temperature (NST), determined by special plastometric method, and as well as with use of the calculated temperatures of phase transformations during heating of the investigated steel. Ultimate tensile strength of the investigated steel was increasing exponentially with the decreasing deformation temperature. Ductility of the investigated steel in hot condition increased with the increasing deformation temperature up to the temperatures ranging from 1 150 to 1 250 °C, after which a sharp decline of formability took place in investigated material

Transformation kinetics of selected steel grades after plastic deformation

The aim of this article was to assess the impact of previous plastic deformation on the kinetics of transformations of four selected steels. The research was conducted with use of the universal plastometer GLEEBLE 3800, when Continuous Cooling Transformation (CCT) and Deformation Continuous Cooling Transformation (DCCT) diagrams of selected steels were constructed on the basis of dilatometric tests. The research confirmed that the strain accelerates the particularly the transformations controlled by diffusion. Bainitic transformation was accelerated in three of the four steels. In the case of martensitic transformation the effect of the previous deformation was relatively small, but with clearly discernible trend

Effect of deformation on the continuous cooling transformation (CCT) diagram of steel 32CRB4

CCT and DCCT steel diagrams of the steel 32CrB4 were determined by the universal plastometer GLEEBLE 3 800 on the basis of dilatometric tests. Dilatometric analysis showed that compared to the diagram provided by the software QTSteel th e noses of individual curves are in fact shifted towards shorter times. Preceding deformation significantly affected the decay diagram of the investigated steel. Shorter times, which were available for recovery of the deformed structure during more rapid cooling, resulted in a significant shift of the curves in the DCCT diagram towards shorter times. At low cooling rates the effect of deformation was practically negligible, since recrystallization took place between the deformation and beginning of the phase transformation

Influence of Heating Parameters on Flow Stress Curves of Low-Alloy Mn-Ti-B Steel

Influence of the initial grain size on hot deformation behavior of the low-alloy Mn-Ti-B steel was investigated. The uniaxial compression tests were performed in range of the deformation temperatures of 900-1200°C and strain rates of 0.1-10 s-1. One set of samples was heated directly to the deformation temperature, which corresponded to the initial austenitic grain size of 19-56 μm; the other set of samples was uniformly preheated at the temperature of 1200°C. Whereas the values of activation energy, peak stress and steady-state stress values practically did not depend on the initial austenitic grain size, the peak strain values of coarser-grained structure significantly increase mainly at high values of the Zener-Hollomon parameter. This confirms the negative effect of the large size of the initial grain on the dynamic recrystallization kinetics, which can be explained by the reduction in nucleation density

Hot flow stress models of the steel C45

Flows stress of the steel C45 were predicted on the basis of experimentally obtained flow stress curves, using uniaxial hot compression tests on the plastometer HDS-20, by two completely different types of mathematical models, moreover with comparison to a model comprised in the FEM database of the FORGE software. The tests were carried out within the temperature range from 900 to 1 280 °C, at the strain rate from 0,1 to 100 s^-1 and deformations up to 1,0. It follows from the results of flow stress prediction that models designed on the basis of experimental measurements have much better information capability than the generated model implemented into the database of the FORGE software, however, their extrapolation for larger deformations is limited

Hot Deformation Activation Energy of Metallic Materials Influenced by Strain Value

Suitable and complete sets of stress-strain curves significantly affected by dynamic recrystallization were analyzed for 11 different iron, copper, magnesium, titanium or nickel based alloys. Using the same methodology, apparent hot deformation activation energy Qp and Qss values were calculated for each alloy based on peak stress and steady-state stress values. Linear dependence between quantities Qp and Qss was found, while Qp values are on average only about 6% higher. This should not be essential in predicting true stress of a specific material depending on the temperature-compensated strain rate and strain