Dynamic Recrystallization

Issues in simulation modeling, materials and high-energy explosives have been the three areas of research that have had the most impact on warhead technology. The present study focused on the materials issues and simulations and the relationship between the two in the case of Explosively Formed Penetrators (EFPs). Tantalum (Ta), Armco iron (Fe) and oxygen-free high conductivity copper (OFHC Cu)

In this article, three Compression Continuous Cooling Transformation (CCCT) diagrams of NiCrMoV steel were considered that indicate induced transformations by compression during continuous cooling of austenite. CCCT diagrams of this steel were compared with its Continuous ...

It is important to recognize that this discussion of the effects of alloying elements applies to
situations in which the alloying elements were initially in solution in the austenite. When this is not so, important changes can arise. Let us consider an example to predict the kind of changes that can occur. We select an steel 21CrMoV5-11 ( 1020 ASTM),to which 1 wt.% V has been added and which has a microstructure that contains vanadium carbides. First, let us austenitize the steel at a temperature that is high enough to transform the steel into homogeneous austenite. Then suppose that the steel is successfully transformed to martensite during quenching. Because the vanadium and the carbon are dissolved in the martensite, the events described earlier take place during tempering.
Now suppose we repeat the experiment but this time the steel is held at a temperature that is not far above the A3 point during the austenitization treatment. At this temperature the ferrite is converted to austenite but the vanadium carbides are not dissolved so the austenite contains them when it is quenched. The first effect that we predict is a change in the hardenability of the steel. The hardenability will be decreased in comparison to that of the previous case because the vanadium is not dissolved in the austenite and, also, there is less carbon in the austenite because some resides in the undissolved carbides. The hardenability will also be reduced because the grain size of the austenite will be smaller than in the previous case due to the lower temperature of austenitization and because the vanadium carbides inhibit grain growth. In fact, the hardenability could now be so low that we may fail to produce a uniformly martensitic sample. That could certainly cause problems if a fully martensitic component was a required result of the heat treatment. However, let us suppose that we are fortunate and that the sample is successfully transformed into martensite.
So, the hardness of the as-quenched martensite will be lower than that of the martensite
produced in the first experiment because it has less carbon dissolved in it. Also, it is possible for a reduction in the hardness to arise due to auto-tempering that could occur because of the increase in the Ms temperature due to the absence of Vanadium and the reduction of carbon in the austenite.
When such samples are tempered, the transformations that occur will be very similar to those that would occur in a low/plain carbon steel that contains less carbon than a 1020 steel. Secondary hardening would not take place.
The aim of a quench and temper treatment is to produce a microstructure that has a particular set of mechanical properties. The microstructural changes that take place in low alloy steels during tempering usually cause a reduction in the hardness of the steel unless, of course, secondary hardening occurs. The decrease in hardness is usually accompanied by an increase in the toughness as shown by the results obtained during impact tests. However, there are occasions when this is not so and, instead, the toughness falls. This reduction in the toughness raises the ductile to brittle transition temperature and can reduce the energy absorbed during fracture at and above room temperature. There are two types of embrittlement. One is called tempered martensite embrittlement.
It is also referred to as 500F embrittlement and one step embrittlement. The other is simply called temper embrittlement or, perhaps preferably, two step embrittlement. The one step and two step terminology is less confusing.

In the Veporic Unit building up the central areas of the Western Carpathians, the magnetic fabrics are more or less coplanar and coaxial in metamorphic (Early Palaeozoic in age), granitic (Early to Late Palaeozoic in age) and sedimentary cover rocks (Permian/Triassic in age). The magnetic fabrics in metamorphic and granitoid basement rocks, as well as in sedimentary (-volcanic) cover rocks,

During ductile deformation of marbles under high grade metamorphic conditions on Naxos, Greece, pegmatites enclosed in the marbles were deformed in a brittle fashion forming blocky boudins with quartz crystallized in the interboudin zones. We studied the three-dimensional geometry of the boudins in the field and in two large samples. The first sample was serially sectioned to observe the structural

In order to examine the microstructural evolution during hot-compression deformation of the biomedical Co-29Cr-6Mo (weight percent) alloy without the addition of Ni, hot-compression tests have been conducted at deformation temperatures ranging from 1050 °C to 1200 °C at various strain rates of 10−3 to 10 s−1. The grain refinement due to dynamic recrystallization (DRX) was identified under all deformation conditions by means of field-emission scanning electron microscopy/electron backscattered diffraction (FESEM/EBSD) and transmission electron microscopy (TEM) observations. Although the DRX grain size (d) of the deformed specimens considerably decreased with an increasing Zener–Hollomon (Z) parameter at strain rates ranging from 10−3 to 0.1 s−1, a grain size coarser than that predicted from the d-Z relation was obtained at strain rates of 1.0 and 10 s−1. An ultrafine-grained microstructure with a grain size of approximately 0.6 μm was obtained under deformation at 1050 °C at 0.1 s−1, from an initial grain size of 40 μm. The grain refinement to a submicron scale of biomedical Co-Cr-Mo alloys has been achieved with hot deformation by ~60 pct due to DRX, in which the bulging mechanism is not operative. The ultrafine grains obtained due to DRX without bulging is closely related to the considerably low stacking-fault energy (SFE) of the Co-Cr-Mo alloy at deformation temperatures.

A novel type of duplex microstructure is generated in a single-phase austenitic steel (AISI 316L; X2CrNiMo19-12), consisting of plastically compliant recrystallized austenitic grains as the matrix containing coarse non-recrystallized grains with a nanotwinned austenitic (nt-c) structure as strengthening inclusions. This novel type of single-phase yet duplex microstructured steel exhibits an excellent combination of strength and ductility. We study the plastic co-deformation mechanisms between the nanotwinned and the recrystallized grains under tension using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). At tensile strains below 5%, the nt-c grains nearly deform homogeneously in conjunction with the surrounding statically recrystallized (SRX) grains without generating notable strain localization near their interfaces. The anisotropic plastic deformation of the nt-c grains with predominant shear parallel to the twin boundaries results in a higher dislocation density in the neighboring SRX grains. As the strain exceeds 12%, localized deformation occurs within the nt-c grains in the form of shear banding. A strain gradient is developed in the surrounding SRX grains as a function of distance from the nt-c/SRX interface. Deformation twinning is observed in the SRX grains near the nt-c grains, while away from nt-c grains dislocation slip dominates the deformation. The strengthening effect of the strong and ductile nt-c grains may offer a novel approach to strengthen austenitic steels and related alloys by generating a nanotwinned / recrystallized duplex microstructure.

The deformation behavior and microstructural evolution of a 7075-T6 aluminum alloy have been investigated through applying hot compression tests at different temperatures and strain rates (450, 500, 520, 550, 580°C and 0.004, 0.04 and 0.4 s À1). The peak stress levels in different conditions were extracted from the related true stress-true strain curves. Different dynamic recrystallization (DRX) mechanisms including continuous, discontinuous and geometrical ones were proposed to justify the corresponding results of various thermomechanical processing conditions. Furthermore, the results indicated that the recrystallized structure had been spheroidized in the semi-solid temperature range due to the liquid pressure and their sizes were reduced with increasing the strain rate.

The crystallographic microtexture and microstructure of a β-titanium alloy (Ti–35 wt.% Nb–7 wt.% Zr–5 wt.% Ta) is studied after warm rolling and recrystallization. The main observations are the evolution of partially recrystallized microstructures during warm rolling and the formation of strong through-thickness texture and microstructure gradients at larger strains. Both, the recrystallized volume fraction and the texture depend on the thickness reduction. At small reductions (≤50%) texture gradients are also small showing some αbcc-fiber (crystallographic axis 〈1 1 0〉 parallel to the rolling direction) and γ-fiber (crystallographic axis 〈1 1 1〉 parallel to the normal direction) texture components. At larger strains (70–90%) the texture and microstructure gradients are characterized by shear texture components and dynamic recrystallization particularly close to the surface layers and plane strain texture components which are typical of recovered grains in the center layer.

The hot deformation behavior was studied of two austenitic stainless steels (AISI 304 type) with different carbon contents (0.02 and 0.087%). An analysis of the parameters describing the hot flow curves and their quantification at each strain stage was carried out. The comparative study of the two steels showed no significant effect of the carbon content on the conditions for the onset of dynamic recrystallization or on dynamic recrystallization kinetics, although the Avrami exponent was clearly dependent on the hot forming conditions. Also, peak and steady state stresses were relatively insensitive to the amount of carbon. However, the work hardening and dynamic recovery behavior showed clear differences, depending on the alloy, especially at high temperatures and low strain rates, where the steel with the higher carbon content showed higher work hardening and dynamic recovery rates.

7000 series Aluminum alloys are widely used in the automotive industries for structural lightweight components due to their exceptional high strength to weight ratio. However, this class of aluminum alloy is difficult to join by conventional fusion welding techniques so Friction stir welding (FSW) widely is used for welding this alloys. The process has been demonstrated to be effective and is currently industrially utilized for materials difficult to be welded or “unweldable”, especially aluminum and magnesium alloys. In this paper in order to predict the average grain size occurring in FSW of AA7050 plates due to the dynamic recrystallization (DRX) phenomena due to the welding process, a microstructure evolution model have been implemented in a 3D fully coupled thermo-mechanical FEM in which the tool – workpiece interaction in FSW of butt joint was investigated.