Wire-arc additive manufacturing (WAAM) is considered as a rather promising alternative to conventional subtracting production process for manufacture of large expensive metal components with complicated geometrical shape. Up-todate direction of WAAM investigations is aimed on production of functional metallic components with complicated geometrical shape and high accuracy, surface processing and mechanical properties meeting the strict requirements of aerospace, automotive and instrumental industries. At the same time, structural application of metal components based on their mechanical properties is studied insufficiently. It is necessary to understand additionally influence of technological conditions (such as energy input, protective gas role, speed of wire feed, welding speed, facing features and its sequence etc.) on the thermal initial parameters and finishing mechanical properties. The paper displays that mechanical properties of low-alloyed silicon-manganese composition of C-Mn-Si type with ferrite-pearlite structure is higher comparing with conventional steel 09G2S. It is shown that impact strength values for C-Mn-Si-type composition, which id formed via WAAM method, is higher by 2 times in comparison with welded joints which are faced by Sv-08G2S wire.
Investigations of the structural components of rail joints, obtained by contact butt welding using burning-off, which are revealed on the surface of kinks after the destruction of the compounds during static bending tests and after destruction in operating conditions, were carried out. Analysis of the microstructure and chemical heterogeneity of the fracture surface was carried out with the help of a scanning electron microscope JEOL JIB-Z4500, equipped with an attachment for energy-dispersive analysis. The analysis showed that the main structural defects were poor penetration and inclusions of iron-manganese silicates that significantly reduced the parameters for mechanical tests of welded joints. Their presence in welded joints is unacceptable. Clusters of inclusions of aluminosilicates, so-called matte spots, and oxide films of a more complex composition are formed in the compound on the basis of non-uniformly distributed nonmetallic inclusions of the metal of the rail.
In the process of plasma surface hardening, a surface layer that consists of zones of different sizes with different phase and structural composition is formed. The minimum grain size for plasma surface heating is determined by the initial austenitic grain. Its size depends on the dispersion of the initial structure. The rate of plasma heating at 200-1000 °C/s affects the size of the initial grain. The further growth of austenite crystallites with an increase of temperature essentially depends on the heating rate: small rates and high temperatures of plasma surface heating can lead to a significant enlargement of the grain. Increase of the heating temperature in the zone of thermal influence during welding from 900 to 1040 °C of rail steel 76F leads to the growth of the austenitic grain from No. 9 to No. 7 and individual grains – from No. 8 to No. 3. The largest austenite grains while heated at 1000 and 1040 °C form separate zones where conglomerates of large grains predominate. Stiffness of 76F steel, heat-strengthened on the troosto-sorbitol structure, deteriorates substantially when the temperature of rapid heating increases from 900 to 1040 °C. This also increases the instability of stiffness.
This study presents the development of a novel equipment for carburizing, by means of a plasma arc and a graphite paste based on liquid glass. After processing by this method, the microstructure and microhardness of the hardened layer were studied. The assay revealed that during a brief plasma exposure, the surface layer was saturated with carbon to a concentration level, which corresponds to white cast iron. The microstructures and characteristics of the metal surface post plasma cementation were also studied. The main parameters of the cemented layer were determined: the depth of the cemented layer was 150-200 μm, microhardness was up to 1000 HV0.2.
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