INFLUENCE OF THE POURING DIRECTION ON THE QUALITY OF THE MELT ENTERING THE MOLD AND OBTAINING A GOOD STANDARD CAST IRON SAMPLE

The paper presents the results of computer simulation (on the example of grey cast iron of SCH 20 grade) of the influence of melt pouring direction on the degree of defects of shrinkage origin in the axial zone of the neck of a tensile sample when filling the mold cavity with a standard cast sample for optimal values of melt mass flow rate.

Stressstrain state of metal at the initial stage of railway rails rolling

Based on the studies of stress­strain metal formation during railway rails rolling in roughing stands of a universal rail­and­beam mill, carried out using the DEFORM­3D software package, the authors have determined the features of distribution of the Cockcroft­Latham criterion over the cross­section of the rolled stock of various shapes. An extremely uneven distribution of the Cockcroft­Latham criterion over the roll section has been established. According to the data obtained, values of the specifed criterion are minimal in the axial zone, and in the near­surface layers the greatest value of the Cockcroft­Latham criterion and, accordingly, the highest probability of defects formation occur near the gauge vertical axis. In gauges of complex shape (“trapezium”, “recumbent trapezium”, rail gauges), the authors have revealed the presence of local zones with maximum Cockcroft­Latham criterion, located in the places where the foot of the rail profle is formed. And rolling in gauge of the “trapezium” type is marked by the presence of such a zone in the near­surface area near the gauge vertical axis. Within the framework of determining formation regularities of the diagram of metal stress­strain state at the initial stage of rail rolling, direct relationship was established between the uneven temperature distribution over the section of rolling and the values (maximum and average over the section) of the Cockcroft­Latham criterion. At the same time, it was shown that uneven temperature distribution over the cross­section of the roll tends to decrease with an increase in the coefcients of extracts along the passes and increase in tilting frequency, regardless of the shape of the used gauges. For gauges of complex shape, in addition to the listed parameters, an increase in similarity of shape of the roll and gauge used also has a signifcant effect on reducing temperature inhomogeneity. Based on the results of theoretical studies, a new mode of railway rails rolling has been developed. Its pilot testing in the conditions of a universal rail­and­beam mill of JSC “EVRAZ ZSMK” has shown a decrease in rail rejection by 0.78 % compared to the previously used rolling mode.

Development of Advanced Technologies for the Production of Innovative Materials with a Submicrocrystalline Structure by Methods of Severe Plastic Deformation

A promising direction for the development of steel and alloy processing processes is the intensification of plastic deformation by creating zones of localization of shear strains not only in the longitudinal but also in the transverse directions of the deformed metal flow. Intensification of alternating deformations along the entire cross-section and, especially, in the axial zone of the billet by creating new deformation schemes is an effective way to increase the physical, mechanical and functional properties of the metal with the maximum approximation of the finished product size to the original billet size. The paper shows that a promising idea is the development of new technological schemes that implement severe alternating deformation in existing metal forming processes. A continuous rolling method of wide strips is proposed, which provides severe alternating deformation with minor changes in the size of the billet. Based on this method, a scheme of continuous rolling of the strip with the intensification of plastic deformation of the metal is designed. The results of computer simulation showed that the new rolling method increases the strain uniformity in height and the value of the strain degree in the plane of symmetry of the billet.

Posets pluton: a geochronological piece in the puzzle of the Axial Zone of the Pyrenees

A detailed geochronological study was conducted on zircons from a diorite sample of the Posets pluton (Axial Zone, Pyrenees). The extracted igneous zircons constrain the emplacement of the pluton to 302 ± 2 Ma and 301 ± 3 Ma, by means of U–Pb sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses, respectively. Considering the syn- to late-tectonic emplacement of the Posets pluton during the main Variscan deformation event (D2), the obtained ages constrain the long-lasting D2, associated with the dextral transpression registered through the Axial Zone of the Pyrenees.

THE INFLUENCE OF EXTERNAL FORCES ON THE CHARACTERISTICS OF HARDENING AND THE CHARACTER OF CONVECTIVE FLOWS DURING THE CURING OF INGOTS

The paper describes the influence of external influences on the features and nature of convective flows during the solidification of ingots. It is shown that topping up the profitable part of the ingot with hot portions of the melt changes the nature of the convective motion of the melt in the body of the model ingot. Laminar movement is observed before refilling, after turbulent. The change in the nature of the movement of the liquid in the body of the ingot contributes to an increase in the speed of the front of the solid phase, as evidenced by the results of calculating the rate of solidification throughout the solidification process of the model ingot. The analysis of the structural zones showed an increase in the zone of columnar crystals from 58.6% to 72.3% and the zone of the deposition cone, from 6.5% to 9.1% in refilled ingots compared to the classic ingot. There is also a decrease in the zone of differently oriented crystals from 26.8 to 13.7% and the crustal zone from 5.9% to 2.8%. The length of the axial zone increased from 36 to 54%, with a decrease in its diameter from 6.5 to 5.1%.

Recycling of stainless steel bar scrap by radial-shear rolling to obtain an ultrafine-grained gradient structure

This work is devoted to the study of the possibility of recycling bar scrap of stainless metals using radial-shear rolling. In the course of studies on the deformation of bar scrap in the form of pins made of 12X18N9T stainless austenitic steel on a radial-shear rolling mill, the resulting bar was obtained microstructure of two different types: on the periphery an equiaxed ultrafine-grained structure with a grain size of 0.4–0.6 microns was formed; in the axial zone anoriented, banded texture was obtained. This discrepancy in the structure of the peripheral and axial zones, together with the results of cross-section microhardness measurements of samples made of 12X18N9T austenitic stainless steel with a total degree of deformation of 44.4 %, indicates the gradient nature of the resulting microstructure.

Paleomagnetism from multi-orogenic terranes is "not a simple game": Pyrenees' Paleozoic warning

Paleomagnetism is a versatile tool in the Earth sciences: it provides critical input to geological time scales and plate tectonic reconstructions. Despite its undeniable perks, paleomagnetism is not without complications. Remagnetizations overprinting the original magnetic signature of rocks are frequent, especially in orogens which tend to be the areas with better rock exposure. Unraveling the magnetic history of the rocks is a complicated task, especially in areas that underwent several orogenic pulses. In turn, constraining the timing of remagnetization represents an opportunity to solve post-magnetization structural and tectonic kinematics. Here, we evaluate the magnetization history of Silurian-Devonian carbonates from the Axial Zone of the Pyrenees. The Pyrenees are a multi-orogenic mountain belt where Silurian-Devonian rocks have seen the Variscan collision (late Paleozoic), the opening of the Atlantic / Bay of Biscay (early Cretaceous) and the Alpine orogeny (late Cretaceous to Miocene). Our results show widespread remagnetization(s) carried by magnetite and pyrrhotite in the Silurian-Devonian series of the Pyrenees. The majority of the samples show a post-folding but pre-alpine tilting magnetization. Considering the equatorial inclinations found in such samples, we suggest that they likely acquired their magnetization during the late Carboniferous and early Permian times. Two of the studied sites (located at the western Axial Zone) were subsequently remagnetized at the end of the Alpine orogeny. The paleomagnetic results constrained that the Variscan orogeny was responsible for the main folding event affecting Paleozoic rocks in the Axial Zone, whereas the Alpine orogeny produced the large-scale thrusting and antiformal stacking of these units. In addition, we observed a general clockwise rotational pattern which could be related with the formation of the Cantabrian Orocline and/or rotations associated with the Alpine orogeny. The Silurian-Devonian carbonates are thus useful to understand the tectonic evolution of the Pyrenean mountain range after a systematic combination of paleomagnetism with structural and petrological observations. In contrast, the secondary character of magnetization and complications associated with the Variscan tectonics indicate that a reassessment of Siluro-Devonian poles from the Variscan elsewhere in Europe might be appropriate.

Analysis of Deformation, the Stressed State and Fracture Predictions for Cogging Shafts with Convex Anvils

In this article, a new manner of cogging a forging (type: shaft), consisting in the application of a two-stage process composed of preliminary shaping in convex anvils, and also principal forging in flat or shaped anvils, is presented. A new manner of forging brought about the formation of favorable conditions for achieving the maximum values of the effective strain in the central part of a forging, accompanied by a simultaneous absence of tensile stresses, which was exerting a favorable influence upon reforging the axial zone of an ingot. What was determined, was the effective geometric shapes of convex anvils; the efficiency of different technological parameters in the case of the intensity of reforging the axial zone of an ingot was analyzed as well. The investigations were complemented by means of predicting the formation of ductile fractures in the course of forging with the application of three different ductile fracture criteria. The comparison of theoretical and experimental outcomes of investigations indicates a good level of being commensurate.

A heterogeneous subcontinental mantle under the African–Arabian Plate boundary revealed by boron and radiogenic isotopes

The northern and northwestern margins of the Arabian Plate are a locus of a diffuse and long-lasting (early Miocene to Pleistocene) Na-alkali basaltic volcanism, sourced in the asthenosphere mantle. The upwelling asthenosphere at the Africa–Arabia margin produces very limited magma volumes in the axial zone. Therefore, portions of hot, fertile mantle continue their eastward migration and are stored at shallower depths under the 100-km thick Arabian lithosphere, which is much thinner than the African one (≈175 km): this causes the occurrence and 20-Ma persistence of magma supply under the study area. Erupted basalts sampled a continuous variation of the mantle source, with a striking correlation among temperature, pressure and isotopic composition shifting between two end members: a 100 km-deep, more depleted source, and a 60 km-deep, more enriched one. In particular, we observed an unusual variation in boron isotopes, which in the oceanic domain does not vary between more depleted and more enriched mantle sources. This study shows that, at least in the considered region, subcontinental mantle is more heterogeneous than the suboceanic one, and able to record for very long times recycling of shallow material.