Influence Of Dynamic Recrystallization Research Articles

Numerical Investigation of the Damage Effect on the Evolution of Adiabatic Shear Banding and Its Transition to Fracture during High-Speed Blanking of 304 Stainless Steel Sheets.

This paper investigates numerically the effect of damage evolution on adiabatic shear banding (ASB) formation and its transition to fracture during high-speed blanking of 304 stainless steel sheets. A structural-thermal-damage-coupled finite element (FE) analysis is developed in LS-DYNA considering the modified Johnson-Cook thermo-viscoplastic model for both plasticity flow rule and damage law, while further, a temperature-dependent fracture criterion is implemented by introducing a critical temperature. The modeling approach is initially validated against experimental data regarding the fracture profile and ASB width. Next, FE simulations are conducted to examine the effect of strain rate and temperature dependence on damage law, while the effect of damage coupling is also evaluated, aiming to highlight the connection between thermal and damage softening and attribute them a specific role regarding ASB formation and transition to fracture. Also, the influence of dynamic recrystallization (DRX) softening is studied macroscopically, while further, a parametric analysis of the Taylor-Quinney coefficient is conducted to highlight the effect of plastic work-to-internal heat conversion efficiency on ASB formation. The results revealed that the implementation of damage coupling reacts to reduced ASB width and provides an S-shaped fracture profile, while it also decreases the peak force and results in an earlier fracture. Both findings are enhanced when accounting further for DRX softening and a higher value of the Taylor-Quinney coefficient. Finally, the simulations indicated that thermal softening precedes damage softening, showing that the temperature rise is responsible for ASB initiation, while instead, damage evolution drives ASB propagation and fracture.

Effects of dynamic recrystallization and strain-induced dynamic precipitation on the corrosion behavior of partially recrystallized Mg–9Al–1Zn alloys

Abstract The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed (ECAPed) Mg–9Al–1Zn (AZ91) alloys immersed in chloride containing media was investigated through immersion testing and an electrochemical microcell technique coupled with high resolution techniques such as scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). During ECAP, dynamic recrystallization (DRX) and strain-induced dynamic precipitation (SIDP) simultaneously occurred, resulting in a bimodal grain structure of original elongated coarse grains and newly formed equiaxed fine grains with a large volume fraction of β-Mg17Al12 precipitates. Corrosion preferentially initiates and propagates in the DRXed grains, owing to the greater microchemistry difference between the β-Mg17Al12 precipitates formed at the DRXed grain boundaries and the adjacent α-Mg matrix, which induces a strong microgalvanic coupling between these phases. Additionally, the weaker basal texture of the DRXed grains also makes these grains more susceptible to electrochemical reactions than the highly textured un-DRXed grains. The influence of dynamic recrystallization and dynamic precipitation was also studied in ECAPed alloys with different levels of deformation strain through corrosion and electrochemical techniques. Increasing the strain level led to a more uniform corrosion with a shallow penetration depth, lower corrosion rate values, and higher protective ability of the oxide film. Furthermore, higher levels of strain resulted in greater hardness values of the ECAPed alloys. The superior corrosion resistance and strength of the ECAPed alloys with increasing strain level was attributed to the combination of smaller DRXed grain size, higher DRX ratio, and higher volume fraction of uniformly distributed fine β-Mg17Al12 precipitates.

Grain refinement in laser powder bed fusion: The influence of dynamic recrystallization and recovery

During laser powder bed fusion (LPBF) the powder bed undergoes several thermal cycles incorporating complex thermo-mechanical processing. Different restoration mechanisms such as dynamic recovery, dynamic recrystallization and grain growth can be activated at different thermal cycles, leading to a very fine average grain size. This is modelled via classical and thermostatistical approaches for an austenitic stainless steel. Four subsequent thermal cycles in each layer induce various microstructural transitions for each individual grain. The high cooling rate solidification in the first two thermal cycles leads to the formation of a highly deformed cellular microstructure. Discontinuous and continuous dynamic recrystallization are activated in the third thermal cycle to induce grain refinement. The fourth thermal cycle undergoes dynamic recovery and grain growth. The as-built alloys exhibit an excellent combination of high yield and ultimate tensile strength. The high strength is attributed to the activation of the various dynamic recrystallization mechanisms, as well as to the development of the cellular structures resulting from a high cooling rate upon solidification. A methodology to design alloys with tailored microstructures is presented.

Influence of dynamic recrystallization on microstructure and mechanical properties of welding zone in Al–Mg–Si aluminum profile during porthole die extrusion

Abstract The effect of dynamic recrystallization (DRX) on the microstructure and mechanical properties of 6063 aluminum alloy profile during porthole die extrusion was studied through experiment and simulation. The grain morphology was observed by means of electron backscatter diffraction (EBSD) technology. The results show that, at low ram speeds, increasing the ram speed caused an increase in DRX fraction due to the increase of temperature and strain rate. In contrast, at high ram speeds, further increasing ram speed had much less effect on the temperature, and the DRX faction decreased due to high stain rates. The microhardness and fraction of low angle boundaries in the welding zones were lower than those in the matrix zones. The grain size in the welding zone was smaller than that in the matrix zone due to lower DRX fraction. The decrease of grain size and increase of extrudate temperature were beneficial to the improvement of microhardness.

Dynamic recrystallization-dependent damage modeling during hot forming

Hot forming processes are extensively used to produce semi-finished and finished components. At elevated temperatures, dynamic recovery and recrystallization processes occur that enable large shape changes at low forming forces. In steel, non-metallic inclusions cannot be avoided during metallurgical processes. They may induce damage in the same way as at room temperature, but the softening of the matrix due to dynamic recrystallization may be used to control the initiation and progression of damage. Damage models do not take into account that dynamic recrystallization reduces the local stresses at the interface of matrix–inclusion. The purpose of the presented study is to analyze the interaction between dynamic recrystallization and damage initiation. Using representative volume elements, the influence of dynamic recrystallization on damage initiation is studied at different temperatures, strain rates, and stress states. Based on this study, a damage model is devised that couples dynamic recrystallization and damage on the macro level and hence can be used in macroscopic process simulations.

Influence of dynamic recrystallization and shear banding on the localized corrosion of severely deformed Al–Mg–Si alloy

The low intergranular corrosion resistance of extruded aluminum alloys is a limiting criteria for several applications. In this work, we investigated the effects of shear deformation, dynamic recrystallization and peak aging on the corrosion susceptibility of an AA6061 alloy up to seven ECAP passes following route Bc. We assessed intergranular corrosion susceptibility using the standard ISO test 11846 (Method B). Our results show that dynamic recrystallization improves the localized corrosion resistance of severely deformed AA6061 by reducing the fraction of shear bands in the material. We found a clear difference in surface reactivity between the recrystallized grains inside and outside the shear bands, suggesting that in this material grain-stored energy influences corrosion more than grain boundary precipitation. In parallel, we characterized the degradation of conventionally extruded AA6061-T6. The results reveal that shear deformation is a promising process for extruded aluminum alloys with improved strength and intergranular corrosion resistance.

Dynamic Recrystallization of Spheroidal Graphite Iron during Hot Cutting Operations

The objective of the present paper is to analyse the dynamic recrystallization process occurring during the hot cutting of spheroidal graphite iron. In the first instance, hot cutting tests are performed with an orthogonal cutting test bench. The emergence of dynamic recrystallization is highlighted thanks to microstructural observations. Then, a finite element model of the hot cutting operation is introduced. The material behaviour is modelled with a specific constitutive model considering the influence of dynamic recrystallization on the plastic flow stress. Finally, the predictive response of this model is compared to the experimental observations.

The Law of the Grain Size Changing in the Warm Tension Test for the B340/590DP Dual-Phase Steel

Based on the warm tension test and metallurgical microstructure observations, the change of the microstructure of B340/590DP dual-phase steel, especially the change of grain size in different strain rates and temperatures, was studied in this paper. The results of the experiment show that: in the warm tension tests of the dual-phase steel, both the dynamic recovery and dynamic recrystallization affect the grain size, and the influence of dynamic recrystallization is stronger. In different rates of extension, the microstructure all has the minimum grain sizes in the medium term of the dynamic recrystallization. In the medium term of the dynamic recrystallization under different rates of extension, the minimum grain sizes increase as strain rate drops. The temperature in which the minimum grain size forms decreases as strain rates drops.

Influence of Dynamic Recrystallisation on Texture Formation in ECAP deformed Nickel

3N nickel has been deformed by equal channel angular pressing (ECAP) at 400°C up to 3 passes using route A. The texture with respect to position in the deformed billet, i.e. from top to bottom, has been measured with high-energy synchrotron radiation. It is characterized by texture components typical for simple shear in the intersection plane of the square-shaped 90° bent channel. Besides, an oblique cube component is observed. Orientation imaging microscopy clearly shows that this component is due to partial recrystallization. Intensities of the texture components as well as deviations from their ideal shear positions vary from the top to the bottom of the billet and with the number of passes. The change of the intensity of texture components and the texture gradient investigated is discussed. Special emphasis is put on the influence of dynamic recrystallization on texture and microstructure formation during ECAP of fcc metals.

The influence of dynamic recrystallization on the grain size distribution and rheological behaviour of Carrara marble deformed in axial compression

AbstractStrain localization and associated rheological weakening are often attributed to grain size reduction resulting from dynamic recrystallization. Most studies investigating rheological changes due to dynamic recrystallization regard recrystallized grain size as a single value that is uniquely related to stress during steady-state deformation. However, rock materials invariably exhibit a grain size distribution with distribution parameters that may be altered by dynamic recrystallization during transient deformation, affecting the rheological behaviour. This study aims to investigate the effect of deformation conditions on the evolution of grain size distribution and rheological behaviour during dynamic recrystallization in the approach to steady state. To study this, we have deformed Carrara marble to natural strains of 0.15–0.90 in axial compression at temperatures of 700–990°C, stresses of 15–65 MPa, strain rates of 3.0 × 10−6–4.9 × 10−4 s−1 and a confining pressure of 150 or 300 MPa, and analysed the grain size distribution of each sample. The results show that during dynamic recrystallization, grain size distributions evolve by a competition between grain growth and grain size reduction. The relative importance of grain-size-sensitive creep increases as the average grain size is reduced with strain. Minor weakening is observed, which is probably insufficient to cause strain localization in nature.

Influence of Dynamic Recrystallisation on the Tensile Ductility of Steels in the Temperature Range 700 to 1150.DEG.C..

The role of dynamic recrystallisation (DRX) in influencing the hot ductility of plain C-Mn and microalloyed steels was examined by comparing the critical strain for Dynamic recrystallisation with the fracture strain in a hot tensile test. The temperature range examined was 700 to 1150°C and the strain rates were varied from 3×10–2 to 3×10–4 s–1.For coarse grained plain C-Mn and C-Mn-Al steels solution treated at 1330°C and cooled to the test temperature, the presence at the γ grain boundaries of thin films of deformation induced ferrite at temperatures between the Ae3 and the undeformed Ar3, leads to strain concentrations which give rise to poor ductility. The presence of these thin films prevents the occurrence of DRX. For these steels, the Ae3 temperature, which marks the onset of good ductility is generally high enough to lead to DRX, so that it is not possible to assess its independent contribution to restoring the hot ductility. In coarse grained C-Mn-Nb-Al steels, DRX and the full recovery of ductility are often not observed until the test temperature is higher than 1000°C. This is related to the strain-induced precipitation of NbCN below 1050°C. However, even when recrystallisation is not possible, the ductility can be improved if the amount of strain-induced NbCN is reduced.For fine grained plain C-Mn and microalloyed steels heated directly to the test temperature, DRX often occurs in the trough. Grain boundary migration rates have to be sufficiently high to prevent crack linkage from occurring, and this often necessitates the resolution and coarsening of particles so that they are no longer effective in pinning the boundaries. Finally, of interest in this work was the observation that as the initial grain size do is refined, its influence in encouraging DRX becomes more marked than that given by the simple do1/2 relationship in the equation εp=Ado1/2Zn, where εp is the critical strain to the peak stress, Z is the Zener-Hollomon parameter and A and n are constants.

Influence of dynamic recrystallisation on hot ductility of aluminium killed mild steel

Torsion tests at strain rates of 10−3, 0·16, and 1 s−1 and at temperatures between 850 and 1100°C have been carried out on an aluminium killed mild steel after either heating directly to the testing temperature or soaking for 30 min at 1200°C, then cooling the specimen to the testing temperature. During direct heating, a dispersion of small AlN particles was present and after soaking a coarser distribution of AlN particles was observed. Compared with the latter, the former microstructure seriously retarded the completion of dynamic recrystallisation. The effect of the two different particle distributions was examined for the following parameters: peak and steady state stress, peak strain, and dynamically recrystallised grain size. The retardation of completion of dynamic recrystallisation has the additional effect of impairing the hot ductility.MST/997

Influence of dynamic recrystallisation on hot ductility of aluminium killed mild steel

Torsion tests at strain rates of 10−3, 0·16, and 1 s−1 and at temperatures between 850 and 1100°C have been carried out on an aluminium killed mild steel after either heating directly to the testing temperature or soaking for 30 min at 1200°C, then cooling the specimen to the testing temperature. During direct heating, a dispersion of small AlN particles was present and after soaking a coarser distribution of AlN particles was observed. Compared with the latter, the former microstructure seriously retarded the completion of dynamic recrystallisation. The effect of the two different particle distributions was examined for the following parameters: peak and steady state stress, peak strain, and dynamically recrystallised grain size. The retardation of completion of dynamic recrystallisation has the additional effect of impairing the hot ductility.MST/997