Friction Welding Case Study

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COMPARATIVE STUDY ON FRICTION WELDED AND ELECTRON BEAM WELDED JOINTS MADE BY 20VNiMoCr120 STEEL

Gabriela IANCULESCU*, Lucia Violeta MELNIC, Marian Andrei GURĂU
Ovidius University of Constanta

Abstract: In the paper there are presented experimental results concerning mechanical characteristics of friction-welded joints in comparison with electron beam welded joints, made by 20VNiMoCr120 heat-resistant steel, which are part of some elements working at high pressure and temperature. The paper represents a study which suggests non-conventional welding and heat-treatment procedures for water and steam-supply pipes, large cylindrical recipients with high values of wall thickness, boiler pipes, steam turbines which compose thermo-energetic installations,
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Presentation of non-conventional welding procedures applied
a. Friction welding
Friction welding is a pressure welding procedure, at which the energy necessary for welding is obtained by transforming the friction mechanical energy into heat. [1]
Welding process includes the following phases: [1]
 driving one of the welding components in rotating, with constant or variable speed and the other one (fixed) pressing on it, with an axial force;
 heating the components ends, because of the friction of the two surfaces in contact, under the axial force action (constant or variable in time); the relative components rotation under the axial pressure action is maintained until the temperature necessary to plastic deformation of the components in contact is reached;
 pressing the components in order to weld them is realized using an axial force higher than the heating force.
Economical factor represents an advantage of friction welding procedure, considered to be more economical than pressure electrical welding, because of the consumption power lower about 22.5 times.
Another advantage is considered to be that friction welding procedure allows the welding of materials with different chemical composition, as well as the welding of materials with different melting
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[2], [7]

2.4. Metallographic analysis
Metallographic analysis is a physical research method which consists in examination of a component surface that has been polished and attacked, thus being studied the alloy structure. This analysis includes two important study methods: micrograph and macrograph.
Metallographic analysis of welded joints can highlight the defects of weld and it may leas to the causes that produced them, the influence of the welded process above the added material and base material, heat treatment etc. This analysis can be done macro as well as microstructural. [6]
Macro or microstructure of a component can be highlighted by metallographic reactive attack. Metallographic reactives are water or alcohol dilutions of some chemical substances which, in some concrete determined conditions, in contact with metallographic component, highlight macro or microstructure of the metal.

a. Macroscopic examination
Macroscopic analysis of polished specimens can

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