Simulation Of Thermomechanical Processes Research Articles

Clustering and precipitation processes in a ferritic titanium-molybdenum microalloyed steel

Atom Probe Microscopy has been performed on a titanium-molybdenum microalloyed steel after simulation of thermomechanical processing. The results reveal the evolution of clustering and precipitation reactions at the austenite/ferrite interphase interface during isothermal heat treatments of durations ranging between 300 s and 100 h. Shorter isothermal ageing times led to extensive solute clustering at the austenite/ferrite interface, which remained free of precipitates. For ageing times beyond 3600 s, high number densities of interphase nano-precipitates were observed along with extensive solute clustering. Beyond 100 h, there was little evidence of solute clustering at these austenite/ferrite microstructural interfaces, which were instead dominated by a dispersion of coarser nano-precipitates. Both the clusters and nano-precipitates formed during isothermal ageing possessed a disc shape morphology and the growth has taken place in the through thickness direction of the disc without much change in the aspect ratio. The size of clusters and nano-precipitates increased from ∼2 nm after 300 s to ∼15 nm after 100 h of isothermal ageing at 650 °C. The solute clusters contain mainly C, Ti and Mo atoms, while the stoichiometry of the nano-precipitates approached that of MC carbide as their size increased beyond ∼4 nm. It is proposed that Mo controls the process of precipitate growth, resulting in a fine and uniform dispersion of nano-precipitates and a high level of tensile strength after just 300 s ageing at 650 °C. Interestingly, the peak strength was achieved during the very early stages of the precipitation process.

An Extended Age-Hardening Model for Al-Mg-Si Alloys Incorporating the Room-Temperature Storage and Cold Deformation Process Stages

Abstract In this article, a new age-hardening model for Al-Mg-Si alloys is presented (named NaMo-Version 2), which takes into account the combined effect of cold deformation and prolonged room-temperature storage on the subsequent response to artificial aging. As a starting point, the original physical framework of NaMo-Version 1 is revived and used as a basis for the extension. This is permissible, since a more in-depth analysis of the underlying particle-dislocation interactions confirms previous expectations that the simplifying assumption of spherical precipitates is not crucial for the final outcome of the calculations, provided that the yield strength model is calibrated against experimental data. At the same time, the implementation of the Kampmann–Wagner formalism means that the different microstructure models can be linked together in a manner that enforces solute partitioning and competition between the different hardening phases which form during aging (e.g., clusters, β″ and β′). In a calibrated form, NaMo-Version 2 exhibits a high degree of predictive power, as documented by comparison with experiments, using both dedicated nanostructure and yield strength data as a basis for the validation. Hence, the model is deemed to be well-suited for simulation of thermomechanical processing of Al-Mg-Si alloys involving cold-working operations like sheet forming and stretch bending in combination with heat treatment and welding.

Study of the structure and mechanical properties of corrosion-resistant steel with a high concentration of boron at elevated temperatures

Because of the high cost of corrosion-resistant steels, a necessary condition for their production is reducing rejection at all stages of processing, including hot forming, by optimizing process parameters. In this work, the mechanical characteristics of a corrosion-resistant steel with high content of boron have been studied at elevated temperatures. Using a special complex for the physical simulation of thermomechanical processes, it has been shown that the optimum temperature range of hot compressive plastic deformation is 950–1100°C. A mathematical model has been constructed, which relates the yield stress to the parameters of the process of hot plastic deformation. During deformation in the range of 850–1150°C, the boride particles present in the steel become oriented perpendicular to the compression axis; at high temperatures, the spheroidization of titanium diborides occurs, which reduces their size.

The Effect of Mandrel Configuration on the Warpage in Pultrusion of Rectangular Hollow Profiles

Thermo-mechanical process simulation of an industrially pultruded rectangular hollow profile is presented. Glass/polyester is used for the continuous filament mat (CFM) and the uni-directional (UD) layers. The process induced residual distortions together with the temperature and degree of cure are predicted using a three dimensional (3D) thermo-chemical model sequentially coupled with a 2D quasi-static generalized plane strain mechanical model. The predicted deformation pattern at the end of the process is found to agree quite well with the one observed for the real pultruded parts in a commercial pultrusion company. In addition, the predicted warpage behaviour is further analysed by adjusting the mandrel length as well as including the mandrel heating. Using the proposed process model, the effect of the mandrel configurations on the quality of the pultrusion is investigated in terms of temperature, degree of cure and distortions.These unwanted residual distortions may lead to not meeting the desired geometrical tolerances e.g. warpage of pultruded window frames and hollow profiles as well as spring-in of L-shaped profiles, etc.

Optimization of Regimes of Thermodeformation Treatment of High-Strength Aluminum Alloy 019705

The effect of regimes of thermodeformation treatment of high-strength aluminum alloy 019705 developed at the department of physical metallurgy of nonferrous metals of NITU “MISiS” is studied. The modes of fabrication of semiproducts are optimized using a “Gleeble System 380” (Hydrawedge II) facility for physical simulation of thermomechanical processes at deformation rates 0.01 – 10 sec – 1 in a temperature range of 200 – 450 °C. The scheme of fabrication of deformed semiproducts (pressing, rolling) and the rates and temperatures of the deformation are shown to be interrelated.

Physical Simulation of Thermomechanical Processing of Multiphase Mn-Al Steels with Retained Austenite

The thermomechanical processing of certain AHSS still represents a challenge due to the lack of complete data on their hot deformation behaviour. Therefore, the aim of this study was to provide data on the hot-working behaviour of four model steels of the type 0.17C-3Mn-1.5Al and 0.17C-5Mn-1.5Al with or without Nb microaddition. The paper presents the results of hot strip rolling simulated by multi-step compression tests using a Gleeble simulator. Analysis of microstructural features of steels with focusing on Mn and Nb contents was carried out using X-ray, LM (light microscopy) and SEM (scanning electron microscopy). It has been shown that the applied deformation schedule allows to develop very fine-grained transformation products of supercooled austenite and controlled cooling with isothermal holding at 400°C enables to retain from 13 to 18% of retained austenite with the blocky or lath-type morphology. Mn alloying in the amount of 3 to 5 wt.% does not affect hot deformation resistance contrary to Nb microaddition, which raises flow stress levels. Influences of Mn and Nb on the retained austenite content and its carbon content are discussed.

Effects of Processing Parameters on Microstructure and Properties of Ultra High Strength Linepipe Steel

To examine the effect of processing parameters on microstructural evolution and to obtain the excellent combination of strength and toughness, simulation of thermo-mechanical processing was conducted using the Gleeble machine. Trial production was then conducted under the conditions obtained by Gleeble tests. Based on the results of microstructure analysis and mechanical property evaluation, the relationship between microstructural features and mechanical properties was elucidated. The result shows that the volume fraction of constituted phases can be controlled through adjusting the cooling rate and finish cooling temperature in order to get different strength levels. As cooling rate increases, the volume fraction of upper bainite increases, which leads to the increase of strength. The upper shelf energy (USE) increases with increasing volume fraction of acicular ferrite in bainite base because of the small effective acicular ferrite grain size. Ductile-brittle transition temperature (DBTT) decreases with increasing acicular ferrite volume fraction. High reduction in the rough stage has great influence on grain refinement.

MICROSTRUCTURE CONTROL OF HOT ROLLED TRIP STEEL BASED ON DYNAMIC TRANSFORMATION OF UNDERCOOLED AUSTENITE II. Cooling Rate After Dynamic Transformation of Undercooled Austenite

TRIP-aided steels are ideal for lightweight automotive applications due to their high strength and ductility. Thermomechanical processing simulations were performed by hot compression on a Gleeble-1500 machine, in order to develop a comprehensive understanding of the effect of cooling rate after dynamic transformation of undercooled austenite (DTUA) on the microstructure evolution and mechanical properties of 0.2C-1.5Mn-0.5Si-1.0Al (mass faction, %) transformation-induced plas- ticity (TRIP) steel. The results show that the metastable austenite would be transformed to ferrite mainly by means of nucleation during cooling after DTUA. Decreasing the cooling rate after DTUA, the volume fraction of ferrite increase, the static recovery of dislocations in ferrite produced during dynamic transformation could fully take place, thus the density of dislocations in ferrite decreased through by rearranging and merging, but the grain size of ferrite changes little. At the cooling rate of 30 /s, the investigated steel has a moderate volume fraction of ferrite and dislocation density in ferrite and a higher volume fraction of retained austenite, resulting in the steel having a higher strength

Computer Simulation of Thermo-Mechanical Processes at Fusion Welding of Alloyed Steels

Computer Simulation of Thermo-Mechanical Processes at Fusion Welding of Alloyed Steels

Relationship of microstructure and mechanical properties of TRIP-aided steel processed by press forging

Abstract The main emphasis of this study has been placed on thermomechanical processing simulations performed using press forging. In order to develop a comprehensive understanding of the effect of large deformation of bulk specimens, introduced in the austenite recrystallized, nonrecrystallized and intercritical temperature regions, on the microstructure evolution and mechanical properties, the C–Si–Mn transformation induced plasticity (TRIP)-aided steel was used for experimental. The choice of applied strain and thermal parameters had strong impact on austenite transformation kinetics and obtained final multiphase structure, which clearly modified the mechanical properties of TRIP steel. To rationalize the retained austenite volume fraction employing different thermomechanical schedules, the effect of austenite conditioning on ferrite transformation was considered at the first step and the subsequent isothermal bainite transformation treatment was optimized in the second step. The microstructures of treated samples were characterized by optical metallography and scanning electron microscopy. The tensile tests were conducted to characterize the development of TRIP effect with respect to volume fraction of retained austenite in multiphase structure. The volume fraction of retained austenite was measured using X-ray and neutron diffraction methods. The specific design of thermomechanical schedule with varying of strain and temperature values affected multiphase structure development in TRIP bulk steel and yielded in good combination of high tensile strength over 900 MPa and elongation over 20% nearly at all experimental schedules. The complex relationship among the volume fraction of the retained austenite, the morphology and distribution of phases present in the microstructure, and mechanical properties of TRIP steel were revealed. These findings suggested that the intercritical treatment conditions prior austenite transformation appeared to have decisive effect on steel refinement and forming of convenient multiphase structure, which should provide both, the high strength and sufficient ductility of bulky products.

Unified Transformation-Thermoplasticity and the Application

Most constitutive laws for transformation plasticity, which are known to contribute a drastic effect on the simulation of thermo-mechanical processes, have been treated to be independent of ordinal thermo-plasticity. Considering that the mechanisms for both strains are essentially with no difference from metallurgical viewpoint, the constitutive equation for transformation plastic strain rate is expected to be described in relation with plasticity theory. This paper motivates to derive a unified constitutive model including transformation-induced and ordinal thermo-mechanical plastic strain rates by introducing the effect of varying phases during phase transformation into yield function. Thus derived model is applied to simulate temperature-elongation diagram by use of a kinetic rate equation of induced phase.

Quantifying different modes of the late Cenozoic shortening in the central Andes

Abstract Since the late Miocene, the two main segments of the central Andean high plateau, Altiplano and Puna, demonstrate different styles and magnitudes of tectonic shortening. Through numerical simulation of thermomechanical processes, we show that different shortening modes—pure and simple shear accompanied by thin-or thick-skinned tectonics—might be controlled by strength of the foreland uppermost crust and by temperature of the foreland lithosphere. Mechanical weakening and failure of the thick Paleozoic sediments overlying the cold lithosphere in the Altiplano foreland at 13–9 Ma explains the transition from pure to simple shear shortening accompanied by broad thin-skinned thrusting, started before the major uplift of the plateau. However, the high strength of the uppermost crust combined with a relatively warm lithosphere results in the thick-skinned shortening typical for the foreland of the Puna. Failure of Paleozoic sediments in the Altiplano foreland significantly reduces the force required to shorten the lithosphere, which may be the reason for the increased bulk shortening rate in the late Miocene.

New Developments in Physical Simulation of Thermomechanical Processing

New Developments in Physical Simulation of Thermomechanical Processing

Effect of deformation schedule on the microstructure and mechanical properties of a thermomechanically processed C-Mn-Si transformation-induced plasticity steel

Thermomechanical processing simulations were performed using a hot-torsion machine, in order to develop a comprehensive understanding of the effect of severe deformation in the recrystallized and nonrecrystallized austenite regions on the microstructural evolution and mechanical properties of the 0.2 wt pct C-1.55 wt pct Mn-1.5 wt pct Si transformation-induced plasticity (TRIP) steel. The deformation schedule affected all constituents (polygonal ferrite, bainite in different morphologies, retained austenite, and martensite) of the multiphased TRIP steel microstructure. The complex relationships between the volume fraction of the retained austenite, the morphology and distribution of all phases present in the microstructure, and the mechanical properties of TRIP steel were revealed. The bainite morphology had a more pronounced effect on the mechanical behavior than the refinement of the microstructure. The improvement of the mechanical properties of TRIP steel was achieved by variation of the volume fraction of the retained austenite rather than the overall refinement of the microstructure.

Bainite transformation during continuous cooling of low carbon microalloyed steel

The evolution of the final microstructure for a low carbon Nb–Ti microalloyed plate steel was studied during a simulation of thermomechanical processing for hot rolling following by accelerated cooling. The effects of austenite deformation below the non-recrystallisation temperature TNR, cooling rate, and interrupt temperature on the formation of conventional (intergranular) bainite (CB), acicular ferrite (intragranular) (AF), and martensite–austenite (MA) constituents were determined. With increases in austenite deformation and cooling rate, and decrease in the interrupt temperature, the final microstructure changed from a mixture of CB+MA through CB+AF+MA to a dual phase AF+MA.

Simulation of thermomechanical processes in crystallizing polymer

AbstractConstitutive equations are developed to describe the interrelation between thermomechanical behavior and phase transitions in crystallizing polymers. A crystalizing polymer is considered as a two‐component mixture of amorphous and crystalline structures, the fraction of which is defined by the degree of crystallinity. Numerical realization is performed using a variational method and a finite element procedure. The key feature of the calculation algorithm is reduction of a nonstationary problem to a sequence of stationary problems on a nonuniform time mesh. The validity of the proposed mathematical model is supported by the results of experiments performed to study the evolution of the stress‐strain state for a disk‐shaped polyamide 6 plate on crystallization.

Fully coupled thermomechanical behaviour of viscoelastic solids treated with finite elements

The paper is concerned with the numerical simulation of thermomechanical processes for linear viscoelastic solids with special consideration of the dissipative coupling phenomena. A constitutive equation is based on a four-parameter model, the so-called Kelvin-Maxwell model. The fully coupled finite element formulation follows from the mixed thermomechanical boundary- and initial value problem through the usual time and spatial discretization procedures. A simultaneous solution strategy yields the unknown values describing both the mechanical and the thermal field. Illustrative examples, involving static and cyclic loadings, exhibit the viscoelastic behaviour of the material and show the efficiency of the numerical method within the scope of thermomechanics.

Mathematical simulation of thermomechanical processes in bodies of low electrical conductivity in an external quasistationary electromagnetic field

We give a mathematical formulation and computational scheme for the problem of determining the thermoelastic state of bodies of low electrical conductivity caused by an external quasistationary electromagnetic field. We study the characteristics of these processes in a layer and a hollow cylinder.

A Finite Element Analysis of the Thermomechanical Behavior of Fiber Reinforced Composites

Many problems remain unsolved regarding part and mold design for fiber reinforced composites. The thermomechanical processes occur during the mold filling, curing and mold removal stages when compression molding fiber reinforced parts are not very well understood. Irregular thermomechanical properties lead to parts that are warped and that have sink marks and surface waviness. This paper discusses thermomechanical material properties and the theory behind shrinkage and warpage in short fiber reinforced composites. It also presents a thermomechanical process simulation of compression mold ing of short fiber reinforced parts. The simulation is compared to experiments. Numerical experimentation with the simulation program gives us insight into the effect that process ing conditions have on shrinkage and warpage.