Numerical study of TRIP transformation in 35NCD16 steel-effects of plate orientation and some criteria

This study aims to analyze the effect of thermo mechanical coupling damage in the presence of a phase change (austenite/martensite) in 35NCD16 steel. The impact of increasing mechanical traction load, accompanied by a martensitic transformation on the scale of a single grain with boundary has been studied. The prediction transformation of induced plasticity (TRIP) was evaluated by taking into account the following parameters: twenty shear directions of the martensitic plates, two values of the shear deformation of the martensitic plates, energetic and thermodynamics criteria for getting in order the transformation of the martensitic plates, elastoplastic behavior of the two areas in the first case (martensitic plate and grain boundary) and elastic behavior for the grain boundary in the second case. The numerical calculation is carried out using the finite element method (FEM), implemented in the Zebulon calculation code. The developed approach is validated using the available experimental results reported in the literature. The numerical results showed that the estimation of TRIP given by the energetics criteria with the values of the shear deformation (γ0 = 0.16) are closer to the experiment results.

Internal Stresses and their Sources in BCC and FCC Steels

The present work summarizes and presents separate results obtained by the authors when investigating mesoscopic and microscopic internal stresses formed under the conditions of thermal and mechanical treatment of martensitic, pearlitic and austenitic steels. Internal stresses were investigated using the method based on the analysis of bend extinction contours. The results obtained on industrial steels were presented. The sources were described and examples of internal stresses induced by these sources were given. The nature of bending-torsion of the crystal lattice depending on the averaging volume was determined. It has been shown that in martensitic steels along with the increase in the averaging volume (carbide particle → separate martensitic lath → martensite packet→ martensitic plate → grain) the amplitude of bending-torsion of the crystal lattice decreases. The nature of distortions also changes. At large amplitudes and low volumes of averaging they are completely or partly elastic, at large volumes of averaging they are completely plastic. Thereby, distortions are fully driven by the excess dislocation density.

Analysis of the crystallogeometry of tetragonal martensite in indium-cadmium alloys by the method of electron back scattering diffractions

It was shown in the work using electron back scattering diffractions analysis that when cooling lower than temperature of the martensitic fcc-hct transformation in the alloy In - 4.5 wt% Cd a packet structure is formed consisting of colonies of tetragonal lamella plates. At the next packages there are always three grades of the plates of a tetragonal martensite which are in twinning situation and differing with the direction of the tetragonality axis. Each martensitic plate consists in turn of a set of more shallow submicrotwinning plates alternating in the direction of an axis of tetragonality. On the basis of the obtained data it is possible to conclude that the structure of the package consisting of twinning plates and the structure of the separate martensitic plate consisting, in turn, of submicro-twins submits to the general regularities. At each structural level in group of the neighboring areas the building blocks of three grades differing with the direction of a tetragonality axis are found.

A Multi-Scale Model of Martensitic Transformation Induced Plasticity at Finite Strains

A physically-based multi-scale model for martensitic transformation induced plasticity is presented. At the fine scale, a model for one transforming martensitic variant is established based on the concept of a lamellae composed of a martensitic plate and an austenitic layer. Next, the behaviour of 24 potentially transforming variants is homogenized towards the behaviour of an austenitic grain. As a simple example, the model is applied to deformation and transformation of a single austenitic grain under different deformation modes.