Metal Science and Heat Treatment最新文献

The effect of heat treatment modes under conditions of phase pre-transformation on the structure and properties of electron-beam-welded joints of titanium alloy VT20 is investigated. It is shown that heat treatment at 980°C for 120 – 150 sec makes it possible to remove residual stresses and to increase the tensile strength of the welded joints to 1230 MPa, as well as to ensure a uniform chemical composition over the volume of the joints to meet the requirements of OST 1 90013–81. The suggested method of heat treatment may be used for local treatment of the heat affected zone and of the welded joint in air environment.

Diffusion kinetics of boron in AISI 1050 steel is investigated. AISI 1050 steel samples are borided for 2, 4 and 6 h at 850, 900 and 950°C by the powder-pack boriding method using Ekabor-II boriding powder. After the powder-pack boriding, about 25.4 – 118.9 μm thick FeB/Fe₂B boride layers are obtained on the surfaces of the samples. The boride layers have a typical tooth morphology and their hardness is 1071 – 1460 HV_0.1. The growth rate constants for the boriding temperatures of 850, 900 and 950°C for the AISI 1050 steel are determined to be 1.522 × 10 ^–12, 2.964 × 10 ^–13 and 6.354 ×10 ^–12 m² · sec ^–1, respectively. The boron diffusion activation energy in the AISI 1050 steel is 162.93 kJ · mol ^–1.

The results of metallographic and x-ray phase studies of 35Kh2N3 steel samples after two-component thermal diffusion saturation with chromium and vanadium in mixtures of different compositions are presented. It is shown that when metallic chromium is replaced by ferrochromium, the structure and the phase composition of the coating change; the amount of carbide and nitride phases decreases and the amount of the Cr – Fe – V solid solution increases. The use of serpentine in the saturating mixture (an emitter of oxygen anions, which creates a flow of charged particles directed to the saturated part) elevates the depth of diffusion of chromium into the metal from 20 to 50 μm. The hardness of the coatings due to chromizing in metallic chromium powder with ferrovanadium and in a mixture of ferrochromium with ferrovanadium amounts to 2000 HV and 1750 HV, respectively.

The effect of the temperature and duration of boriding on the nanohardness and modulus of elasticity of 16MnCr5 steel is studied. Pack-boriding is carried out in a solid medium at temperatures of 1123 – 1223 K for 2–6h using the Ekabor II reagent. The obtained experimental results prove effectiveness of the nanoindendation method for assessing the quality and properties of the borided surfaces of 16MnCr5 steel. It is shown that the values of the nanohardness and of the Young’s modulus of the steel range within 587.5 – 3716.4 MPa and 63.3 – 159.7 GPa, respectively.

The processes of formation of carbide-free bainite and the effect of the temperature-time parameters of isothermal hardening in the range of bainitic transformation on the structure and impact toughness of low-alloy structural steels are studied. A method for nondestructive testing of the impact toughness of medium-carbon steels heat-treated by isothermal quenching is developed on the basis of identified patterns of changes in the properties of retained austenite and in the impact toughens of the steels.

The effect of hot forging and heat treatment parameters (austenitization temperature, quenching medium and tempering temperature) on the microstructure and mechanical properties (hardness, impact strength and wear resistance) of AISI D2 steel has been studied. It has been established that during hot forging, the primary M₇C₃ carbides in the steel structure are transformed into secondary M₂₃C₆ carbides. This leads to hardening of the steel, since the secondary M₂₃C₆ carbides are the main factors in its increased strength and wear resistance. Carrying out of quenching after forging contributes to an increase in the number of secondary carbides and their more uniform distribution in the steel structure, which leads to an increase in its hardness, toughness, and wear resistance.

The results of a study of structural-phase transformations and kinetics of decomposition of supersaturated solid solution that occur during heat treatment (aging) of a new-generation magnesium alloy with an elevated ignition temperature are presented. The microstructure of the alloy in cast, quenched and aged states is studied. The physical and mechanical properties of magnesium alloy VML26 after aging at different temperatures and time parameters are determined. Dependence of the mechanical properties and hardness of alloy VML26 on the aging modes is established.

The effect of powder feed rate (PFR) on the structure, phase composition, and mechanical properties of Stellite 6 coating deposited on SS316L steel substrate by plasma welding is studied. It is shown that a high powder feed rate leads to delamination of the coating, and a low PFR leads to an extreme melting depth of the substrate due to the high thermal energy. It is shown that a cobalt-rich fcc phase is formed at low PFR, while the M₂₃C₆, M₆C, MC, and M₇C₃ phases (M is W, Cr, Co, and Mo) are metastable. At high PFRs, a cobalt-rich hcp phase is formed in the coating structure. The cobalt-based hcp phase is more resistant to sliding wear than the other phases. The coatings deposited at higher PFRs increase the hardness and the wear resistance due to formation of an hcp cobalt phase in the structure, but the bond between the substrate and the coating is worse than when using low PFRs. Therefore, for critical components used in the petrochemical industry, Stellite 6 coatings deposited on stainless steel at lower powder feed rates are recommended.

Coatings on a titanium alloy are prepared by electrospark deposition with a non-localized anode consisting of titanium and aluminum granules with addition of chromium diboride powder. With increase of the CrB₂ concentration from 2 to 10 vol.%, the gain in the weight of the cathode increases monotonically from 4.10 to 9.56 mg/cm². According to the data of polarization tests and electrochemical impedance spectroscopy, the Ti – Al – Cr – B coatings reduce the corrosion rate of the VT3-1 alloy. The highest oxidation resistance of the coatings is observed for a CrB₂ concentration of 2 vol.%. Deposition of Ti – Al – Cr – B coatings makes it possible to increase the surface hardness of the VT3-1 alloy by a factor of 2.7 – 4. The deposited Ti – Al – Cr – B coatings increase the wear resistance of the surface of titanium alloy VT3-1 by up to a factor of 6.