Ultrasonic Forging Research Articles

Фазовые превращения в нержавеющей стали Сr-Mn-N, активированные наноструктурирующей поверхностной обработкой, и их влияние на деформационное поведение и разрушение при криогенной температуре

The structure of stainless austenitic Cr-Mn-N steel after deformation treatment of its surface by ultrasonic forging strain (UFS) has been studied. It is shown that UFS activates strain aging in the near-surface layer with the formation of CrN particles. Preliminary ultrasonic treatment of the steel surface contributes to an increase in the yield strength during tensile tests at a temperature of -196 ° C and provides ductile fracture of the near-surface layer.

Phase Transformations in Stainless Cr-Mn-N Steel Activated by Nanostructuring Surface Treatment and Their Influence on Deformation Behavior and Fracture at Cryogenic Temperatures

The structure of stainless austenitic Cr-Mn-N steel after deformation treatment of its surface by ultrasonic forging strain (UFS) has been studied. It is shown that UFS activates strain aging in the near-surface layer with the formation of CrN particles. Preliminary ultrasonic treatment of the steel surface contributes to an increase in the yield strength during tensile tests at a temperature of -196oC and provides ductile fracture of the near-surface layer. Keywords: high nitrogen steel, austenite, ultrasonic forgingstrain, strain aging, cryogenic temperature, martensitic transformation.

Effect of ultrasonic forging strain processing on the surface layer microstructure and temperature-dependent mechanical properties of high nitrogen austenitic steel

The paper presents the research results on the effect of ultrasonic forging strain (UFS) processing of the high-nitrogen Cr–Mn–N austenitic stainless steel on the surface layer microstructure and tensile properties in the temperature range from −80 up to 20 °C. The high dispersion microstructure, strain aging with the formation of both CrN and Fe2N nitrides, as well as twinning were revealed in the surface layer 2–3 μm thick using a transmission electron microscope (TEM). In addition, ε-martensite with the hcp lattice was observed at a depth of more than 80 μm from the surface after UFS processing. Tensile tests showed that UFS processing had increased the yield strength. Elongation level of about 40% did not differ over the entire test temperature range. A ductile type of the fracture surfaces was observed for all test temperatures down to −80 °C.

Applying Digital Image Correlation Technique for Studying the Growth of a Fatigue Crack in VT23 Titanium Alloy Welded Joints

We present results of applying a combined approach to studying fatigue fracture processes in VT23 titanium alloy with a laser-welded joint. The approach involves fractographic examination using scanning electron microscopy and analysis of strain fields at the sample surface (using digital image correlation technique). Samples with permanent connections are presented in two forms: in the initial state and subjected to post-welding treatment by ultrasonic forging and pulsed high-energy impact. It is shown that applying the proposed integrated approach to the analysis of fatigue fracture has allowed identifying features in the development of processes of nucleation and propagation of cracks and locating them in the bulk of the material, as well as determining running times after which transition from one stage to another takes place: crack initiation, stable growth, and rupture. The results have made it possible to explain the mechanisms of how post-welding treatment of permanent joints affects their fatigue properties.

Structural Scale Levels of Plastic Deformation and Fracture of High-Strength Titanium Alloy Welds

Structural scale levels of plastic deformation and fracture of welded joints have been studied for two high-strength titanium alloys with a low (VT18U alloy) and a high (VT23 alloy) content of the bcc s phase. Ultrasonic forging and its combination with high-current pulsed electron beam treatment were used to activate nanoscale structural levels of deformation and fracture in welds in order to increase the fatigue life of welded structures. Ultrasonic forging provides an effective dispersion and nanostructuring of surface layers in the VT18U welded joints with a 4.6-fold increase in their fatigue life. The dispersion and nanostructuring of the VT23 laser welded joints is achieved only by ultrasonic forging combined with high-current electric pulse treatment, in which longitudinal dispersion of s bands occurs with the formation of orthorhombic a " nanolaths. In so doing, the fatigue life of the VT23 welds increases twice, but the effect depends on the power of the high-current generator and electrical pulse parameters. The fracture micrographs of the treated VT23 welded joints reveal nanofibrous bands responsible for ductile fracture and for the reduction of the fatigue crack growth rate. The structural changes and the increase in the fatigue life of the studied titanium alloy welds are associated with the activation of nanoscale structural levels of deformation and fracture induced by ultrasonic forging or by its combination with high-current pulsed electron beam treatment.

Structure and Mechanical Properties of Nitrogen Austenitic Steel after Ultrasonic Forging

Electron microscopy and X-ray diffraction have been used to investigate a nitrogen 07Kh17AG18 steel with an austenitic structure after the surface deformation treatment—ultrasonic forging. During ultrasonic forging, an austenitic structure transforms into a new structure with an elevated concentration of deformation-induced stacking faults, a lot of deformation microtwins, e-martensite crystals. The austenite lattice parameter is found to be decreased in the surface layer. After ultrasonic forging, nitrided steel exhibits enhanced strength properties with retained high plasticity.