Metal Science and Heat Treatment

Degtyareva, S. P.; Kodzhaspirov, G. E.; Peskishev, S. A.; Tikhomirova, E. A.

doi: 10.1007/s11041-024-01027-zpmid: N/A

Analysis of published results of thermal fatigue studies carried out by various methods of thermocycling testing is presented. The widely used Coffin’s method and its feasibility for describing the dependence of the durability on the plastic deformation in a cycle (εpl) is considered. It is shown that the range of the variation of εpl provided by the method is too narrow for covering the processes occurring in the materials during operation of the articles. This fact is confirmed by evaluation of εpl in testing of corset samples at the I. I. Polzunov Scientific and Development Association on Research and Design of Power Equipment, the test portion of which repeats the shape of failure areas frequently occurring in actual articles due to thermal fatigue. It is shown that during the testing process, cracks appear already in the first loading cycles and are a manifestation of the structural changes in the material. This is a result of an excessively high εpl, which is confirmed by a theoretical estimation. It is recommended to use a similar approach to simulate thermal fatigue in articles and to vary the plastic strain in them by changing the shape of the shoulders of corset samples without changing the thermal regime in testing.

Tkachev, E. S.; Borisov, S. I.; Borisova, Yu. I.; Kaibyshev, R. O.

doi: 10.1007/s11041-024-01028-ypmid: N/A

The effect of air quenching and subsequent tempering on the structure, mechanical properties and fracture mechanism of steel 10Kh9K3B2MFBR alloyed with tantalum and boron is studied. Transmission electron microscopy is used to show that after the air quenching, the steel acquires a structure of lath martensite with nanosize particles of (Nb, Ta)(C, N) carbonitride and cementite. Residual film-like austenite morphology is located over the boundaries of laths and blocks. The steel in this state is characterized by a high strength (σ0.2 = 1020 MPa) and an impact toughness of 24 J ∙ cm2. During the low-temperature tempering, dispersion hardening and decomposition of retained austenite with precipitation of cementite chains along the lath boundaries lead to embrittlement. Increase of the tempering temperature in the range of 500 – 750°C is accompanied by a monotonic decrease in the strength characteristics. However, a significant increase in the impact toughness occurs only at tempering temperatures ≥ 780°C. It is concluded that the relatively high tempering temperature required to ensure a satisfactory impact toughness is explainable by enhanced precipitation of particles of a M23C6-type carbide and (Nb, Ta)(C, N) carbonitride, which retards the retrogression processes in the lath martensite structure.

Shvetsov, O. V.; Alfimov, A. D.; Ermakov, B. S.; Kondrat’ev, S. Yu.

doi: 10.1007/s11041-024-01029-xpmid: N/A

The effect of microstructure on fatigue properties and fracture mechanisms in drill pipes made of aluminum alloys 1953 and 2024 (D16) has been studied experimentally. It is shown that the more hardened α-solid solution and the presence of reinforcing intermetallics MgZn2 and Al2CuMg in the structure of alloy 1953 provide more effective resistance to fatigue crack nucleation as compared to alloy 2024 with Al2CuMg and Al2Cu intermetallics and a less hardened matrix α-solid solution. Accordingly, the fatigue limit of the pipe made of alloy 1953 is 192 MPa, and that of alloy 2024 is 179 MPa. However, the ratio of the fatigue limit to the yield strength of the aluminum alloy 2024 is 40%, while for the 1953 alloy it is 32%. This is explained by a higher fracture toughness of alloy 2024 as compared to 1953, a greater degree of deformation and uniformity of the structure of alloy 2024.

Illarionov, A. G.; Karabanalov, M. S.; Shabanov, M. A.; Stepanov, S. I.; Soundappan, P.; Raman, K. H. Thulasi; Suwas, S.

doi: 10.1007/s11041-024-01030-4pmid: N/A

Electrode-induction gas atomization (EIGA) is a promising and cost-effective method for producing spherical intermetallic titanium powders used in additive manufacturing. The present study investigates the morphology, microstructure, chemical and phase compositions, nanoindentation properties of a commercial pre-alloyed TiAl-based EIGA alloy powder. The Ti – 48Al – 2Cr – 2Nb powder is characterized by a spherical shape and dendritic structure with the dendrites enriched with Nb and the interdendritic areas enriched with aluminum and chromium. The temperature ranges of the phase transformations in the powder with precipitation/dissolution of phases α2 , α, γ, B2, (TiNb)Cr2 are determined using thermal analysis during heating and cooling in an inert atmosphere of argon at a rate of 50 K/min. Development of an oxidation process at the temperatures above 500°C and significant increase in its rate at the temperatures above 900°C is detected.

Konovalov, M. S.; Konovalov, I. S.; Lad’yanov, V. I.

doi: 10.1007/s11041-024-01032-2pmid: N/A

Metal matrix composites based on Fe – Cr – Mn – Mo – N – C system and obtained by the aluminobarothermic variant of self-propagating high-temperature synthesis (SHS) are studied. The possibility of uniform carburizing of a melt obtained by aluminobarothermic synthesis in the cooling crucible is shown. An artificial neural network model is suggested, which makes it possible to predict the carbon content in the studied composite during carburization in the cooling crucible of an SHS reactor (the average approximation error is 9 – 14% depending on the training method). The results of training of the artificial neural network model using the Adam optimization algorithm and the Levenberg–Marquardt method are compared. It is shown that under the conditions of a limited set of initial data, it is effective to use a perceptron with one hidden layer containing three target neurons and one displacement neuron.

Evgenov, A. G.; Shurtakov, S. V.; Prager, S. M.; Zaitsev, D. V.

doi: 10.1007/s11041-024-01031-3pmid: N/A

Refractory high-chromium alloy VZh159 (Haynes 282) obtained by the method of selective laser melting (SLM) is studied. C-curves of the precipitation of particles of a topologically closed-packed (tcp) phase are plotted for the temperature range of heat treatment and operation. It is shown that the content of the tcp-particles of unfavorable morphology increases and the ductility of the synthesized material during synthesis in a protective nitrogen environment decreases with increase in the chromium content in the alloy. The intensification of the precipitation of the particles of the tcp-phase is associated with decrease in the solubility of chromium in the solid solution at high temperatures due to elevation of the nitrogen content in the alloy. To stabilize the alloying system, the chromium content in alloy VZh159 is reduced by 1 wt.% with respect to the upper and lower alloying limits as compared to the deformable counterpart, which makes it possible to prevent marked lowering of the ductility of VZh159 fabricatedby SLM.

Efron, L. I.; Stepanov, P. P.; Bagmet, O. A.; Smetanin, K. S.

doi: 10.1007/s11041-024-01033-1pmid: N/A

Impact bending tests of rolled products, base metal and welded joints of pipes manufactured from low-carbon microalloyed steels are performed. The structure of different parts of welded joints is studied. Fractures of impact samples and compositions of nonmetallic inclusions on fracture surfaces are analyzed. The embrittling mechanisms and the causes of scattering of the impact toughness are considered. These may include coarse bainite within a large (deformed) austenite grain, a region near the fusion line with an unfavorable orientation of crystallographic cleavage planes {001} in a HFC welded joint, and large grains of grain-boundary ferrite in the weld and in the HAZ under arc welding. The critical grain size of the α-phase (the maximum fraction), at which the embrittling effect of the nonmetallic inclusions begins to be observed in the steels is 50 – 80 μm.

Kumar, Adarsh; Mahto, Mithlesh Kumar; Vashista, Meghanshu; Yusufzai, Mohd Zaheer Khan

doi: 10.1007/s11041-024-01034-0pmid: N/A

The effect of current pulsing during gas tungsten arc welding (GTAW) of titanium alloy Ti – 6Al – 4V on the structure and properties of the weld is studied. Beads on plate welds are prepared on 2-mm-thick Ti – 6Al – 4V sheets using continuous- and pulse-current GTAW(keeping the heat input the same in both conditions). When welding, an indigenously developed shielding setup is used for protection against atmospheric contamination without any external shielding. The weld characteristics are determined by visual inspection, metallographic analysis, and microhardness testing. It is established that the use of current pulsing during GTAW provides finer grains, deeper weld penetration, and increased hardness in the weld zone and in the HAZ. The weld bead has acceptable quality and a silver color on the top and root sides.

Kotov, S. A.; Kudryavtseva, T. S.; Naumova, Z. V.

doi: 10.1007/s11041-024-01035-zpmid: N/A

The chemical and phase compositions of rolling scale of low-carbon sheet steel at the Izhora Plant are studied experimentally. The results are compared to the data of the scale studies at various metallurgical enterprises reported by other authors. It is shown that the main chemical elements in the scale composition in all the cases are Fe and O plus some Mn, Cr, Al, Ca, and C. The phase compositions of the scale are also similar and contain hematite, magnetite, and wustite. However, the proportion of the phases over cross-section of the scale varies significantly and depends on the oxidation conditions. It is inferred that in order to reuse the scale in steelmaking, its preliminary study is required in each specific case.

Kondrat’ev, S. Yu.; Tsemenko, A. V.

doi: 10.1007/s11041-024-01036-ypmid: N/A

The process of high-temperature oxidation of multicomponent multiphase HP40NbTi alloy at 1150°C with duration of up to 500 hours in air is studied experimentally at the micro level using SEM and x-ray mapping. It is shown that the process occurs under the influence of various interrelated mechanisms. The changes in the composition and structure of the surface multilayer scale and of the subsurface diffusion zone in the alloy after oxidation of various durations are studied consistently. It is demonstrated that after a long-term exposure, conditional equilibrium is established in the alloy subsurface area; the formation of scale and the internal oxidation deplete the diffusion zone of chromium and silicon. This is compensated by the diffusion of Cr, Ni and Fe from the bulk of the metal to the surface. The process slows down with time due to the increase in the depth of the diffusion zone and formation of a “barrier” layer of silicon oxides.