The influence of deformation and austenitization temperature on the kinetics of phase transformations during cooling of high-carbon steel

The aim of the performed experiments was to determine the influence of deformation and of austenitization temperature on the kinetics of phase transformations during cooling of high-carbon steel (0.728 wt. % C). The CCT and DCCT diagrams for austenitization temperature 940 degrees C and DCCT diagram for austenitization temperature 1000 degrees C were constructed with the use of dilatometric tests. On the basis of obtained results, a featureless effect of austenitization temperature and deformation on the kinetics of phase transformations during cooling of investigated steel was observed. Critical cooling rates for the transformation of martensite in microstructure fluctuated from 5 to 7 degrees C . s(-1) (depending on the parameters of austenitization and deformation), but only at cooling rates higher than 8 degrees C . s(-1) a dominant share of martensite was observed in the investigated steel, which resulted in the significant increase of hardness.Web of Science6341748174

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 degrees 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 mu m; the other set of samples was uniformly preheated at the temperature of 1200 degrees 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.Web of Science6341792178

Flow stress and hot deformation activation energy of 6082 aluminium alloy influenced by initial structural state

Stress-strain curves of the EN AW 6082 aluminium alloy with 1.2 Si-0.51 Mg-0.75 Mn (wt.%) were determined by the uniaxial compression tests at temperatures of 450-550 degrees C with a strain rate of 0.5-10 s(-1). The initial structure state corresponded to three processing types: as-cast structure non-homogenized or homogenized at 500 degrees C, and the structure after homogenization and hot extrusion. Significantly higher flow stress appeared as a result of low temperature forming of the non-homogenized material. Hot deformation activation energy Q-values varied between 99 and 122 kJ.mol(-1) for both homogenized materials and from 200 to 216 kJ.mol(-1) for the as-cast state, while the Q-values calculated from the measured steady-state stress were always higher than those calculated from the peak stress values. For the extruded state of the 6082 alloy, the physically-based model was developed to reliably predict the flow stress influenced by dynamic softening, temperature, strain rate, and true strain up to 0.6.Web of Science912art. no. 124

Extension of experimentally assembled processing maps of 10CrMo9-10 steel via a predicted dataset and the influence on overall informative possibilities

Processing maps embody a supportive tool for the optimization of hot forming processes. In the present work, based on the dynamic material model, the processing maps of 10CrMo9-10 low-alloy steel were assembled with the use of two flow curve datasets. The first one was obtained on the basis of uniaxial hot compression tests in a temperature range of 1073-1523 K and a strain rate range of 0.1-100 s(-1). This experimental dataset was subsequently approximated by means of an artificial neural network approach. Based on this approximation, the second dataset was calculated. An important finding was that the additional dataset contributed significantly to improving the informative ability of the assembled processing maps in terms of revealing potentially inappropriate forming conditions.Web of Science911art. no. 121

Study of the effect of deformation on transformation diagrams of two low-alloy manganese-chromium steels

The work deal with an assembling and comparing of transformation diagrams of two low-alloy steels, specifically 16MnCrS5 and 20MnCrS5. In this work, diagrams of the type of CCT and DCCT of both steels were assembled. Transformation diagrams were assembled on the basis of dilatometric tests realized on the plastometer Gleeble 3800, of metallographic analyses and of hardness measurements. In addition, for comparison, the transformation diagrams were assembled even with use of the QTSteel 3.2 software. Uniform austenitization temperature of 850°C was chosen in case of both steels and even both types of diagrams. In case of both steels, an influence of deformation led to expected acceleration of phase transformations controlled by diffusion and also of bainite transformation. In both cases, the kinetics of martensitic transformation was not significantly affected by deformation.Web of Science6341741173

The combined effect of chemical composition and cooling rate on transformation temperatures of hypoeutectoid steels

The transformation temperatures A(r3) and A(r1) of four unalloyed hypoeutectoid steels with a carbon content of 0.029-0,73 % were determined using dilatometric tests. Unusually high cooling rates of 2 and 8 degrees C s(-1) were used intentionally, corresponding to the conditions in the wire rod rolling mills The developed regression models are phenomenological and allow a simple prediction of transformation temperatures, depending only on the cooling rate and the chemical composition of the steel represented by the carbon equivalent (in the case of A(r1)), respectively by the A(c3) temperature (for A(r3)). When calculating the A(c3) temperature, it was worth considering its non-linear dependence on carbon content. It has been verified that the derived equations are applicable even at relatively low cooling rates when the austenite decomposes exclusively on ferrite and pearlite.Web of Science56317016

Transformation diagrams of selected steel grades with consideration of deformation effect

The aim of this article was to assess the effect of previous plastic deformation on the transformation kinetics of selected steels with a wide range of chemical composition. Transformation (CCT and DCCT) diagrams were constructed on the basis of dilatometric tests on the plastometer Gleeble 3800 and metallographic analyses supplemented by measurements of HV hardness. Effect of previous deformation on transformation was evaluated of the critical rate of formation of the individual structural components (ferrite, pearlite and bainite) in the case of formation of martensite respect to M-s temperature. Previous plastic deformation accelerated especially diffuse transformations (ferrite and pearlite), temperature of M-s was lower after previous plastic deformation and bainitic transformation was highly dependent on the chemical composition of steel.Web of Science631605

The influence of a cooling rate on the evolution of microstructure and hardness of the steel 27MnCrB5

The aim of the performed experiments was to determine the influence of a cooling rate on the evolution of microstructure and hardness of the steel 27MnCrB5. By using dilatometric tests performed on the plastometer Gleeble 3800 and by using mathematical modelling in the software QTSteel a continuous cooling transformation diagram for a heating temperature of 850 degrees C was constructed. Conformity of diagrams constructed for both methods is relatively good, except for the position and shape of the ferrite nose. The values of hardness, temperatures of phase transformations and the volume fractions of structural phases upon cooling from the temperature of 850 degrees C at the rate from 0.16 degrees C.s(-1) to 37.2 degrees C.s(-1) were determined. Mathematically predicted proportion of martensite with real data was of relatively solid conformity, but the hardness values evaluated by mathematical modelling was always higher.Web of Science63291490

Phase transformation and cooling curves of the mild steel influenced by previous hot rolling

Rods from mild steel S235JR were intensively rolled in the laboratory continuous mill. Specifically defined temperature of phase transformation Ar was determined from the free cooling curves measured by the temperature scanner. The Ar value increased from 763 to 786 °C with rolling temperature descending from 1 200 to 800 °C. The value of Ar = 730 °C was obtained at free cooling of the non-deformed rod of the same diameter 9,8 mm from heating temperature 1 000 °C. The obtained results were compared with continuous cooling transformation (CCT) and deformation continuous cooling transformation (DCCT) diagrams based on the dilatometric tests.Web of Science55465865

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.Web of Science54347246