Change in Structural-Phase States and Properties of Lengthy Rails during Extremely Long-Term Operation

The regularities and formation mechanisms of structural-phase states and properties at different depths in the rail heads along the central axis and fillet after differential quenching of 100-meter rails and extremely long operation (with passed tonnage of 1411 million tons gross weight) have been revealed by the methods of the state-of-the-art physical materials science. As revealed, the differential quenching is accompanied by the formation of morphologically multi-aspect structure presented by grains of lamellar perlite, ferrite–carbide mixture, and structure-free ferrite. The steel structure is characterized by the α-Fe lattice parameter, the level of microstresses, the size of coherent-scattering region, the value of interlamellar distance, the scalar and excess dislocation densities. As shown, the extremely long operation of rails is accompanied by the numerous transformations of metal structure of rail head: firstly, a fracture of lamellar pearlite structure and a formation of subgrain structure of submicron (100–150 nm) sizes in the bulk of pearlite colonies; secondly, a precipitation of carbide phase particles of nanometer range along the boundaries and in the bulk of subgrains; thirdly, a microdistortion growth of steel crystal lattice; fourthly, a strain hardening of metal resulting in the increase (by 1.5-fold) in scalar and excess dislocation densities relative to the initial state. A long-term operation of rails is accompanied by the formation of structural constituent gradient consisting in a regular change in the relative content of lamellar pearlite, fractured pearlite, and structure of ferrite–carbide mixture along cross-section of railhead. As the distance to the rail fillet surface decreases, a relative content of metal volume with lamellar pearlite decreases, and that with the structure of fractured pearlite and ferrite–carbide mixture increases. As determined, the characteristic feature of ferrite–carbide mixture structure is a nanosize range of grains, subgrains and carbide-phase particles forming it. The size of grains and subgrains forming the type of structure varies in the limits of 40–70 nm; the size of carbide-phase particles located along the boundaries of grains and subgrains varies in the limits of 8–20 nm. A multiaspect character of steel strengthening is detected that is caused by several factors: firstly, the substructural strengthening due to the formation of fragment subboundaries, whose boundaries are stabilized by the carbide-phase particles; secondly, the strengthening by carbide-phase particles located in the bulk of fragments and on elements of dislocation substructure (dispersion hardening); thirdly, the strengthening caused by the precipitation of carbon atoms on dislocations (formation of Cottrell atmospheres); fourthly, the strengthening being introduced by internal stress fields due to incompatibility of crystal-lattices’ deformation of α-phase structural constituents and carbide-phase particles.

Differential quenching of the angular momentum of the B and Q bands of a porphyrin as a result of extended ring π-conjugation

A novel porphyrin, whose [Formula: see text]-system has been extended via the presence of two additional carbon–carbon triple bonds on opposite meso-positions and by fusion of a single naphthalene unit simultaneously bridging the third meso-position and the [Formula: see text]-carbon of one of the pyrroles, has been synthesized in good yield. Absorption, magnetic circular dichroism, emission, and theoretical spectra are reported for the fused and unfused trans-naphthalene free base and zinc porphyrins. The fusing of one of the naphthalene moieties results in significant changes to the absorption spectrum and, very unusually, the bridged meso-[Formula: see text]-pyrrole fusion results in quenching of the MCD Faraday pseudo-A term in the porphyrin’s B band (S2). This unique effect was interpreted as resulting from the origin of the electronic structure of the second excited state (the B state). The [Formula: see text] and [Formula: see text] polarizations are completely mixed by the electronic effects of the non-symmetric extended conjugation of the [Formula: see text] ring. Analysis of the origin of the MCD signal indicates that the presence of this novel mixed polarization leads to negligible angular momentum in the important B state. To our knowledge, this is the first report in which the magnetic moment in a porphyrin’s intensely absorbing B band has been quenched while the angular momentum in the Q band, the first excited state, remains as normal. This implies that the photophysical properties of the B state are likely very different than those of the Q state, which has novel and significant implications for applications, especially in non-linear spectroscopy.

The effect of block braking on the residual stress state of a solid railway wheel

A finite element, numerical model of a solid railway wheel was perfected permitting the simulation of a block braking operation. The analyses performed, backed by experimental tests, permitted the degree of variation in the residual stress state (induced by differential quenching heat treatment and successive tempering) caused by particularly heavy braking to be evaluated. The results highlight the influence of the main braking parameters (force and time) and the thermal history previously suffered by the wheel. Finally, the thermal fatigue strength of the component, although in an approximate way, was checked on the basis of the calculated stress state and through the introduction of the data of a real and particularly significant route into the model. This demonstrated the broad safety margin with which the wheel operates and also brought to light the dangerous nature of particularly severe braking which can drastically modify the residual stresses induced by the heat treatment, moving them towards tensile stresses.