Search Results (4)

The lattice parameters of both the product phase and the matrix phase have determined using in situ X-ray and neutron diffraction measurements during forward and reverse transformations in steels. The lattice parameters are well known to be influenced by various factors, including temperature, internal stresses induced by transformation strains, partitioning of alloying elements, crystal defects, and magnetic strains. Therefore, it is crucial to accurately disentangle the contributions of these factors to the observed changes in lattice parameters. This review examines the evaluation of internal strain (stress) associated with ferrite, pearlite, bainite, martensite, and reverse austenite transformations, with a particular emphasis on the distinction between diffusional and displacive transformations. Additionally, the effects of plastic deformation of austenite on the bainite or martensite transformation are discussed. In this context, the roles of dislocations and vacancies are highlighted as key areas for further investigation. Full article

The effects of strain on the microstructure and mechanical properties of 0.81C-0.22Si-0.31Mn (wt%) high-carbon steel were investigated by thermal simulation, scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), and an electron backscatter diffractometer (EBSD). It was found that when the steel was deformed at 670 °C (a temperature between A₁ and A_r1), a deformation-induced pearlite transformation and cementite spheroidization occurred. The volume fraction of pearlite and the spheroidization ratio of cementite increased with a strain increase from 20% to 75%. The microstructure mainly consisted of pearlite when the deformation strain exceeded 40%. The aspect ratio was at its maximum (5.3) at 40% strain and decreased to 1.4 at 75% strain. In addition, the strength of the steel decreased and the elongation increased rapidly with the increase in strain from 20% to 60% due to the spheroidization of cementite. However, as the strain further increased to 75%, the strength increased slightly due to the refinement of the ferrite matrix. The comprehensive performance of the investigated steel can be improved by applying a strain between A₁ and A_r1. Full article

In the work, the results of the research concerned with the TRIP (Transformation Induced Plasticity) steel wire drawing process in experimental and theoretical ways are shown. The wire drawing process tests on the experimental way were conducted in both laboratories as well as industrial conditions, with the use of two drawing speeds (1.6 and 6 m/s) and two drawing schemes (low and high single reductions). The mechanical properties of wires drawn with high drawing speed equal to 6 m/s showed higher values of mechanical properties for wires drawn with low single reductions than for wires drawn with high single reductions. Such a phenomenon contradicts the theory of drawing wires from steel with a ferritic-pearlitic structure and must be related to TRIP structure and the presence of retained austenite in it, which is transformed into martensite during the deformation process. In order to explain this phenomenon, the theoretical wire drawing process analysis was conducted with the use of the Drawing 2D program based on the finite element method. On the base of the simulation, a large increase in temperature was found on the surface for wires drawn with high drawing speed and low single reductions, which can cause the blocking of transformation retained austenite into martensite and thus a decrease in R_m. To confirm this thesis, further studies will include tests of the amount of retained austenite in wires obtained during experimental tests. Full article

In order to investigate the influence of vanadium microalloying on deformation-induced pearlite transformation (DIPT) of eutectoid steel, thermomechanical simulation tests were carried out in this study. The following four compositions of vanadium microalloying were applied in the tests: vanadium free in Steel A, vanadium content of 0.1 mass% in Steel B, vanadium content of 0.27 mass% in Steel C, and vanadium content of 0.1 mass% with the addition of 0.02 mass% N in Steel D. The dissolution of vanadium and precipitation of vanadium carbides, nitrides, or carbonitrides and the effect of vanadium microalloying on the fraction and morphology of deformation-induced pearlite for different magnitudes of strain were examined, and the mechanism of the effect was elucidated. The results revealed that DIPT could be significantly improved by vanadium microalloying with the addition of N but decreased and postponed without the addition of N because vanadium nitrides or carbonitrides were precipitated in austenite under a small strain and facilitated the nucleation of pearlite both along the boundary of austenite grain (AG pearlite) and intragranular (IG pearlite). Moreover, transformation kinetics of DIPT was fitted and compared. The results further revealed that the rate of DIPT in vanadium-microalloyed steel with the addition of N was twice as fast as that in the vanadium-free steel. In order to ensure the complete spheroidization of lamellar cementites in vanadium-microalloyed steel, a comparison of the morphology of cementites revealed that a greater magnitude of strain was required. Full article