Roman Kuziak

Identification of rheological parameters on the basis of various types of plastometric tests

Abstract Axisymmetric compression and plane-strain compression tests have been performed on specimens of carbon–manganese steel containing 0.17% of carbon. Load–displacement relationships were monitored for each test and the inverse analysis method used to determine the material flow stress for constant strain rate.

Modelling of the influence of thermomechanical processing of Nb-microalloyed steel on the resulting mechanical properties

Abstract Two-stage compression tests were performed at various temperatures and reductions. The influence of finish deformation temperature in the range of 650–820°C and strain on microstructure and final mechanical properties of Nb steel is investigated. Starting from detailed simulation of microstructure development, i.e. recrystallization, precipitation and grain growth kinetics, the material behaviour was modelled. An empirical model of yield strength, developed in previous work, is employed to predict mechanical properties of microalloying steel during hot deformation above and below the γ–α transformation temperature. The comparison of simulated and measured results shows that the real thermomechanical behaviour as well as the microstructure development of Nb-steel has been correctly implemented. The results provided by both finite element analyses and microstructure modelling were compared with earlier similar investigations of C–Mn steel.

Softening Kinetics in Nb-Microalloyed TRIP Steels with Increased Mn Content

Two 5Mn-1.5Al TRIP steels with and without Nb microaddition were developed in the present study. The steels contain bainite, martensite, interlath retained austenite and martensite- austenite islands. The paper presents the results of the compression tests carried out at various temperatures using the Gleeble simulator. To analyze the kinetics of static recrystallization in these steels, a softening kinetics were determined in a double-hit compression test. It was found that the dynamic recovery is a main thermally activated process occurring during hot deformation. The Nb microalloyed steel has higher flow stresses and peak strains than the Nb-free steel. A solute drag effect of Nb results in a slower softening kinetics of Nb containing steel. The effects of Mn on the retardation of Nb(C,N) precipitation and hot deformation characteristics are also discussed.

The Use of ADINA Software to Simulate Thixocasting Processes

The main purpose of work was to develop a methodology of physical and numerical simulation of the thixocasting processes. For the purpose of the studies an experiment was conducted using a GLEEBLE 3800 simulator. In this work, the GLEEBLE 3800 system was adapted for physical simulation of the processes of light metal alloy forming in the solid-liquid state. The physical simulations of thixoforming processes and characterization of thixotropic materials were supported by computer simulations using ADINA software. The numerical model of thixoforming processes was developed in order to estimate values of the rheological model parameters.

Use of the computer simulation to predict mechanical properties of C-Mn steel, after thermomechanical processing

Abstract The objective of the paper is to demonstrate the ability of a computer simulation to analyse the development of microstructure and finally to the predict mechanical properties of C-Mn steels. The microstructure of ferrite is the main parameter which controls the mechanical properties of steels after hot deformation. This microstructure depends on the grain size and morphology of austenite just before the transformation. However, when the last deformation takes place below the γ-α transformation temperature, the mechanisms connected with substructure and dislocation forest becomes a significant part of the strengthening process. The microstructural model makes it possible to separate the relative contributions of solid solution, ferrite microstructure, substructure and dislocation strengthening. The change in microstructure at lower temperatures requires an improvement in the model which will allow to account for the substructure and dislocation density. In the present work hot deformation conditions were simulated using Finite Element Method. The investigation was focused on the case when the last deformation takes place in the two phase or ferrite region. The two stage constant strain rate compression tests were conducted, in continuous cooling condition, at the temperature range 1050 – 650 °C. The material after deformation was investigated to obtain the microstructure and verify the model of substructure and dislocation strengthening mechanisms. The experimental results were used to validate and improve the empirical equations that were employed to the general model. The computer simulation suggested in the work can be used to predict mechanical properties, including all the events that occur under industrial processing conditions which cannot be reproduced in the laboratory.

From High Accuracy to High Efficiency in Simulations of Processing of Dual-Phase Steels

Searching for a compromise between computing costs and predictive capabilities of metal processing models is the objective of this work. The justification of using multiscale and simplified models in simulations of manufacturing of DP steel products is discussed. Multiscale techniques are described and their applications to modeling annealing and stamping are shown. This approach is costly and should be used in specific applications only. Models based on the JMAK equation are an alternative. Physical simulations of the continuous annealing were conducted for validation of the models. An analysis of the computing time and predictive capabilities of the models allowed to conclude that the modified JMAK equation gives good results as far as prediction of volume fractions after annealing is needed. Contrary, a multiscale model is needed to analyze the distributions of strains in the ferritic-martensitic microstructure. The idea of simplification of multiscale models is presented, as well.

Conventional and Multiscale Modeling of Microstructure Evolution During Laminar Cooling of DP Steel Strips

Physical and numerical simulations of the hot rolling and laminar cooling of DP steel strips are presented in the paper. The objectives of the paper were twofold. Physical simulations of hot plastic deformation were used to identify and validate numerical models. Validated models were applied to simulate the manufacturing of DP steel strips. Conventional flow stress model and microstructure evolution model were used in the hot deformation part. The approach to the complex systems analysis based on global thermodynamic characterization and detailed microstructure characterization was applied to determine equilibrium state at various temperatures. Finally, two numerical models were used to simulate kinetics of austenite decomposition at varying temperatures: the first, conventional model based on the Avrami equation, and the second, the discrete Cellular Automata approach. Plastometric tests and stress relaxation tests were used for identification of the hot rolling model for the DP steel. Dilatometric tests were performed to identify the phase transformation models. Verification confirmed good accuracy of all models. Validated models were applied to simulate the manufacturing of DP steel strips. Influence of technological parameters (e.g., strip thickness and velocity, active sections in the laminar cooling, and water flux in the sections) on the DP microstructure was analyzed. The cooling schedules, which give required microstructures were proposed. The numerical tool, which simulates manufacturing chain for DP steel strips is the main output of the paper.

Experimental Evidence of the Effect of Alloying Additions on the Stagnant Stage Length During Cyclic Partial Phase Transformations

Cyclic phase transformation experiments are performed in a series of Fe-C-xMn, Fe-C-Mn-xNi, and Fe-C-Mn-xCo alloys to study the effect of alloying elements on the length of the stagnant stage during a cyclic partial phase transformation in the austenite–ferrite two-phase region. The length of stagnant stage increases linearly with the increasing Mn or Ni concentration, while Co has no effect. It was experimentally proven that the effects of alloying elements on the length of stagnant stage are additive, and the experimental results matched the predictions of the local equilibrium model very well.

Rheological model of Cu based alloys accounting for the preheating prior to deformation

Development of the rheological model of copper based alloys, accounting for the state of the solid solution prior to deformation, is the objective of the paper. Two alloys are considered, Cu-1%Cr and Cu-0.7%Cr-1%Si-2%Ni. Plastometric tests were performed at various temperatures and various strain rates. Different preheating conditions before the tests were applied aimed at investigation of the effect of the initial microstructure on the flow stress. Three different rheological models for the investigated alloys were developed using inverse analysis of the tests results. Accuracy of the inverse analysis for various models was compared and the best model was selected. This model allowed comparison of the flow stress for various preheating schedules at different temperatures and strain rates, including also those which were not applied in the plastometric tests. Developed models were implemented into the finite element code FORGE based on the Norton-Hoff visco-plastic flow rule and simulations of forging of the alloys were performed.

System for design of the manufacturing process of connecting parts for automotive industry

The proposition of complex hybrid system, dedicated to modelling of life cycle of materials and optimization of their in use properties, is presented in the paper. The approach is based on the conventional optimization algorithms, FE simulations of industrial production process and knowledge base, containing both theoretical and practical data in form of rules, facts and equations. Simulation and optimization of the manufacturing of the connecting part used in automotive industry was selected for the purposes of this work. The particular emphasis is put on control of selected in use properties of products by proper design of technological parameters for consecutive stages of the production chain. The concept of the life cycle modelling used in the proposed system, as well as results obtained from simulations, are also presented in the paper.