Metal Science and Heat Treatment最新文献

The method of non-vacuum electron beam cladding is used to obtain coatings based on a high-entropy Cantor alloy reinforced with Cr₃C₂ particles. The microstructure of the coatings is studied; the chemical and phase compositions are determined; microhardness measurements, wear resistance and heat resistance tests are performed. The structure of the coatings is represented by an fcc matrix with Me₇C₃ carbides. Increase in the percentage of reinforcing particles leads to elevation of the proportion of the carbide phase in the cladding layer. The addition of carbide particles results in growth of the microhardness, wear resistance and oxidation resistance. The structure of the coating obtained from a powder mixture with 50 wt.% Cr₃C₂ exhibits a 60% volume fraction of carbides. The properties have the highest values in the coating obtained from a mixture with 50 wt.% carbide particles in the initial composition. Its hardness is 1071 ± 114 HV_0.1, and the wear resistance and the oxidation resistance increase with respect to the unreinforced coating by a factor of 15.3 and 3.3 respectively.

The weldability and mechanical properties of welded joints of pipeline steels of grades API 5L (X52, X60, X65 and X70) manufactured by submerged arc welding (SAW) are investigated. It is shown that the SAW process makes it possible to obtain high-quality welded joints. It is shown that such welded joints fracture during tensile tests over the base metal region. The weld region has the highest hardness and ultimate tensile strength, which are 214 HV₁₀ and 713 MPa for steels X70 and X65 respectively. These values are higher than that of the base metal.

The creep behavior of high-chromium martensitic steel 10Cr9Co3W2MoVNbB (ASTM A335 P92) at a temperature of 650°C and stresses 100 – 180 MPa is studied. The effect of creep on the subgrain structure and the characteristics of secondary particles are determined using transmission electron microscopy. Thermodynamic calculations are performed to determine the volume fraction of precipitates after heat treatment and creep. Precipitation of (Fe, Cr)₂(W, Mo) Laves phase particles and of (Fe, Cr)₂₃(C, B)₆ and (Nb, V)(C, N) particles is observed after short-term creep for 243 h. It is shown that pronounced coarsening of the Laves phase particles leads to a decrease in dispersion strengthening under conditions of long-term creep. Creep is accompanied by a decrease in dislocation density and an increase in the subgrain size. It is concluded that the change in the creep power-law exponent upon transition to long-term tests at 650°C is associated with degradation of microstructure, namely, with a pronounced increase in the subgrain size due to a decrease in the density of secondary particles which inhibit the migration of subgrain boundaries.

A technique for through prediction of microstructure and mechanical properties of metal in the heat affected-zone is suggested. It is based on calculated thermal cycles, diagrams of anisothermal decomposition of austenite and dependences of mechanical properties on the cooling time or the cooling rate. An analytical relationship between the cooling time in the specified temperature range and the cooling rate at the specified temperature is presented. The stages of the technique are considered for an example of welding of a structural steel in air and under water. Satisfactory agreement between the calculated and experimental thermal cycles and hardness distributions is demonstrated.

Comparative tests of mechanical characteristics of aluminum and steel pipes under static and cyclic loading are described. The mechanism of fatigue failure of drill pipes made of aluminum alloy 1953T1 and steel G-105 is analyzed. The endurance limit of the drill pipes made of 1953T1 alloy and G-105 steel is 192 and 507 MPa, and the ratio of the endurance to the yield strength is 32 and 66%, respectively. However, the strength/density ratio under cyclic loading of aluminum alloy 1953T1 is at the same level as that of steel G-105, and under static loading it significantly exceeds the values for steel G-105. This makes it possible to recommend the use of aluminum alloys for manufacturing drill pipes instead of steel ones for service under rigid operating conditions.

The process of formation, the structure, and the phase composition of coatings based on copper and zinc and deposited by cold gas-dynamic spraying are studied. It is shown that a multiphase structure is formed in the coating based on a solid solution of copper in zinc, a solid solution of zinc in copper and solid solutions based on electron compounds CuZn₃ and Cu₅Zn₈. At a low spraying temperature (270°C), the formation of the structure is mainly influenced by interboundary diffusion. The total diffusion rate is D_c = 0.15 × 10^–12 m²/sec. When the spraying temperature is increased to 360°C and higher values (450°C), the vacancy diffusion mechanism prevails. The diffusion rate increases to D_c = 0.56 × 10^–12 m²/sec, which is accompanied by an increase in the mass fraction of the transformation products. A model of formation of the multiphase gradient coating structure is suggested and the influence of the spraying parameters on the formation of the structure is discussed.

The possibility of using plasma-liquid welding with direct current electric discharge at atmospheric pressure to manufacture products from electrical steel E-310 is studied. The samples are welded by immersing a metallic cathode (the welded parts) into a liquid (non-metallic) anode. The electrophysical parameters of the welding process are determined, including the current-voltage characteristic and the current and voltage fluctuations. The results of the analysis of the morphology and of the microhardness of the weld are presented. The prospects of plasma-liquid welding of parts from electrical steel E-310 are demonstrated at an appropriately chosen mode of the variable resistor.

The effect of plastic deformation on the structure, phase composition, and magnetic parameters of maraging steel 08Kh15N5D2T was studied. The hysteresis, electromagnetic, and magnetostrictive characteristics were measured both in a closed magnetic circuit using the Remagraph C-500 hysteresis graph and by means of attached magnetic transducers. The regions of plastic deformation are experimentally determined in which the behavior of the magnetic parameters and their relationship vary with changes in structure and phase composition. Informative parameters are proposed that can be used to control variations in the structure and phase composition of the studied steel.

Pipe steel 06Mn2MoNb is studied after hot rolling and subsequent heat treatment, i.e., austenitizing at 980°C, 30 min and cooling at different rates. By means of orientation microscopy and crystallographic analysis using various orientation relationships the possibility is demonstrated of creating structural and textural characteristics based upon transformation products (martensite, bainite) of deformed austenite within the steel. It is shown that the crystallographic texture resulting from a multivariant γ → α-transformation may be explained by α-phase generation at crystallographically ordered boundaries between deformed γ-phase grains.

Structure and mechanical properties for experimental heat-resistant steels with 12% Cr with a ferritic or ferritic- martensitic structure, as well as austenitic steel 08Kh18N10T after quenching from different temperatures (950 – 1250°C), are studied. The behavior of steels of different groups, classified according to structural features (grain size and phase content), under these conditions is analyzed. The effect of heating temperature for hardening on yield strength of steels at 20 and 720°C during static compression tests is demonstrated.