Results of studying the effect of a calcium modifier of 10KhSND low-alloy steel on its physicomechanical characteristics are presented. The rolled sheets of commercially produced shipbuilding steel, ...wherein before teeming during melting a ferroalumocalcium alloy was added, were used for investigation. The corrosion rate of examined steel in a model aggressive medium, as well as its fatigue resistance in salt water in torsion, axial loading, and bending tests against the calcium concentration, was elucidated. The effect of calcium concentrations on the austenite grain sizes and dispersity of nonmetallic inclusions, as well as the fracture toughness characteristics (critical stress intensity factor and crack opening) at different temperatures was examined. The microstructure of fracture facets of shipbuilding steel specimens of long-term service on brittle fracture along pearlite grains and ductile fracture along ferrite ones for as-received steel was revealed. Nonmetallic inclusions in specimen fractures of shipbuilding steel at different calcium concentrations were studied. Their quantity grows considerably with its service terms, which exerts negative influence on the corrosion and mechanical properties of the metal. The calcium alloying of steel is shown to contribute to its corrosion resistance and fracture toughness on long-term service in seawater. The recommendations are given as regards optimal modifier concentrations in the shipbuilding metal, which is consistent with minimum austenite grain sizes and dispersity of nonmetallic inclusions.
It was established that with increased concentrations of chlorides, sulfate-reducing bacteria, heterotrophic bacteria, thionic and iron bacteria the corrosion rate of the studied specimens of ...reinforcing steels sharply increases. The 40KhN and 09G2S steels had the highest resistance to corrosion, and the St.20 steel had the lowest resistance. The obtained data correlate with the results of numerical experiments reported in the publications of domestic and foreign researchers. For the first time, the data obtained from a series of experimental tests of reinforcing steels for cyclic strength showed that the steels characterized by low corrosion resistance also have a low resistance to cyclic strength, which can be explained by their degradation. The authors believe that, in the process of long-term operation of reinforced concrete structures in an aggressive environment, carbonization and chloritization of concrete, that is, its destruction occur. Further hydrogen charging of reinforced concrete causes embrittlement and reduction of the visco-plastic properties of the reinforcement, which in turn leads to the destruction of metal. The obtained results make it possible to develop metallurgical and technological measures to increase the durability of reinforced concrete structures: the use of chromium, nickel, and manganese alloyed steels for the manufacture of reinforcement with subsequent proper heat treatment; the use of modern high-strength concrete, which will ensure strong adhesion of concrete mortar to the surface of reinforcing bars.
A mechanophysical model for crack growth kinetics computation on stress corrosion fracture of modified 06G2BA and 08KhMCHA pipe steels is adequately expressed through the plane stress-strain state
dα
.../
dt
and
dJ
/
dt
ratios that are dependent on the strain crack tip rate. The crack growth accelerated by an aggressive environment occurs under static and cyclic loading due to transient dissolution and repassivation processes at the crack tip. Such accelerations are divided into three categories, determined by the strain rate: mechanical cracking (fatigue crack and stationary plastic crack), corrosion-accelerated mechanical cracking (corrosion fatigue and corrosion-accelerated plastic crack), and sulfide stress corrosion fracture. Metallographic studies revealed the change in the crack nucleation and propagation mechanisms, from transcrystalline to intercrystalline, related to the viscoplastic and brittle structure of steel specimens cyclically loaded and simultaneously affected by a corrosive environment.
The results of the experimental study of the degradation of steel structures of sewer underground constructions are presented. The distribution of harmful gas elements (sulfur, hydrogen, oxygen) over ...the wall thickness of sewer pipes along corrosion defects in the form of pits, as well as the character of changes in the microhardness of the metal depending on the hydrogen content and service life, are shown. To confirm the metal softening with increasing hydrogen concentration, the stresses of the crystal lattice (distortion stresses) were measured.
Previous studies have shown that with increasing service life of shipbuilding steels, a strong hydrogen charging of their internal near-surface layers occurs, especially if the service life exceeds 3 ...years or more. This is known to cause changes in the mechanical properties of steels. Therefore, there is a need to conduct additional experimental studies on the effect of hydrogen in a wide temperature range on the degradation of the structural and phase states of steels, in particular, on changes in the crystal lattice and redistribution of cementite, which directly leads to a decrease in the ductile and deformation properties of the metal, especially at subzero air temperatures. The effect of service life and subzero temperatures on the stress state of the a-matrix lattice and its parameters for the 10KhSND and D32 steels was investigated. A tendency to increase in the value of lattice distortion stresses and decrease in the mass fraction of cementite in specimens of these steels after long-term operation was revealed. Metallographic studies showed that with decrease in the temperature of the cooling medium, the volume fraction of hydrides increases significantly, which leads to embrittlement and softening of steels.
The results of experimental research of low temperatures influence on mechanical characteristics of structural steels of long-term operation in chemically aggressive environments of cooling systems ...are presented. It is shown that such characteristics of pipe steel as impact toughness (according to Charpy), critical coefficient of stress intensity (fracture toughness), critical crack opening, and microscopic resistance significantly decrease when temperature changes from 20 to -50°C, which indicates a significant decrease in crack resistance of the material. It has been established that the indices of ductile-plastic properties – yield strength, relative longitudinal and transverse deformations decrease sharply in the process of prolonged (up to 30 years) operation of pipe steel. At the same time, intensive flooding of metal takes place.
We present the results of corrosion testing of austenitic-martensitic steel deposited on 40Kh steel samples under a layer of AN-26 flux with the help of a Pd-Np-30Kh22MN flux-cored wire with a ...diameter of 2.2 mm in a single layer with 50% overlapping of the rollers for two modes of delivery into the welding bath (0.5 and 0.7 Hz). It is found that the best operating characteristics under the influence of corrosive media are attained as a result of surfacing with pulses of electrode wire supply of 0.7 Hz.
The progressive nature of type 2 diabetes mellitus leads to the need for insulin therapy in a significant proportion of patients. Very often start of insulin therapy in type 2 diabetes mellitus ...(T2DM) is associated with weight gain and a significant increase of hypoglycemia’s risk. However, innovative options, such as fixed ratio combinations of glucagon-like peptide 1 receptor agonists (GLP-1RA) and basal insulin, minimize weight gain and hypoglycemia risks and allow a greater proportion of patients to achieve individual glycemic control goals without compromising safety parameters. This review includes a description of the randomized clinical trials, as well as the results of real clinical practice of the use of two currently existing fixed ration combinations of GLP-1RA and basal insulin — iDegLira and iGlarLixi.
The paper deals with a significant extension of the recently proposed class of relatively strongly convex optimization problems in spaces of large dimension. In the present paper, we introduce an ...analog of the concept of relative strong convexity for variational inequalities (relative strong monotonicity) and study estimates for the rate of convergence of some numerical first-order methods for problems of this type. The paper discusses two classes of variational inequalities depending on the conditions related to the smoothness of the operator. The first of these classes of problems contains relatively bounded operators, and the second, operators with an analog of the Lipschitz condition (known as relative smoothness). For variational inequalities with relatively bounded and relatively strongly monotone operators, a version of the subgradient method is studied and an optimal estimate for the rate of convergence is justified. For problems with relatively smooth and relatively strongly monotone operators, we prove the linear rate of convergence of an algorithm with a special organization of the restart procedure of a mirror prox method for variational inequalities with monotone operators.
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