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Friction Welding
Friction Welding
"Friction welding can produce high quality welds between two components with either similar or different compositions"
Friction welding (FW), as a solid-state joining process, is now well established as a means of joining many different types of materials because it has proved to be a reliable and economical way of producing high quality welds. The joint has a narrow heat affected zone and shows plastically deformed material which is subject to severe plastic deformation due to the high local temperature and internal pressures. Three variants of FW are rotary, linear and orbital FW. The subject has been reviewed thoroughly in: "Science and Technology of Welding and Joining, 12 (8),(2007), 738-759"
A wide variety of materials that cannot be joined by conventional welding techniques can be bonded using friction welding. For example fusion welding of high carbon steels such as eutectoid steel is extremely difficult, if not impossible, due to the possibility of formation of unwanted brittle phases. By means of friction welding process formation of those unwanted phases can be minimized.
The main advantages of the process:
- Due to the highly concentrated heat at the weld interface, the heat affected zone (HAZ) is very narrow. (i.e. minimal welding distortion and non-uniformity).
- The process is very energy efficient and fast, joining time on the order of seconds. The required power is as low as 10-25% of that used in butt welding.
- Since it is a solid-state process, defects associated with melting-solidification phenomenon are not present.
- An airtight weld is made across 100% of the joint interface, eliminating the risk of porosity, voids, leaks or cracks (superior strength).
- Joint preparation in FW is minimal and filler metal, flux and shielding gas are not required (i.e. cost reduction).
- The process is environmentally friendly, producing minimum smoke, fume and slag.
That's why engineers show increasing interest in using the FW processes in vast variety of applications.
Different variants of friction welding
Friction welded high carbon steel bars
Welding Metallurgy
Welding Metallurgy
“Welding is an inevitable part of every engineering and manufacturing sector and a welded joint covers the entire field of metallurgy”.
The development of new materials to improve the operational efficiency will also need the development of new welding techniques and it is very important to understand the welding metallurgy and associated mechanical properties in order to ensure their weldability. For example, growing environmental concerns, the need for low fuel consumption vehicles, and high safety performance are driving automotive manufacturers towards new innovations in advanced high strength steels (AHSS). The development of AHSS with complex structure imposes a great challenge for welding technology. A great understanding and knowledge of welding metallurgy of these materials is required in order to retain the properties of the carefully designed original base material and thus securing the hold of the welds established in the base design.
Welding of pipeline steel
Welding of pipeline steel
Increasing demand for energy worldwide implies continued growth of oil and gas pipeline installation with the highest possible transport efficiency. High strength micro-alloyed linepipe steels are of great attention to reduce the cost by making thinner wall thickness and enhance the transportation efficiency by increasing operating pressure.
Microstructure process models for the weld heat affected zone (HAZ) have been proposed with an emphasis on austenite grain growth. Large austenite grain sizes are of particular concern during welding where the HAZ experiences rapid thermal cycles with high peak temperatures. In general, martensite formation in the HAZ is a concern as it may lower the weld toughness and increase the risk of hydrogen cracking. It also increases the vulnerability to cold cracking and reheat cracking in welds. Further, the grain structure in the HAZ influences the grain size in the weld metal where the grains grow epitaxially from the HAZ.
A critical aspect of building pipelines to transport natural gas will be development of suitable high strength steels and new economic welding procedures, e.g. dual torch welding, without compromising the pipeline’s structural integrity during its in-service performance. The objective of this project is to predict the microstructure and mechanical properties of the weld heat affected zone (HAZ) of an X80 linepipe steel as a function of its temperature-time history. The approach taken involves a combination of experimental techniques and advanced modelling approaches. On the experimental side, dual-torch weld trials for assessment of spatial and temporal variations of temperature in the HAZ were conducted. To simulate and investigate the microstructure evolutions in the HAZ, i.e. precipitate dissolution, austenite formation, grain growth and decompositions, Gleeble thermo-mechanical simulations were performed. These simulations include rapid heating and cooling tests at rates of up to 1000 °C/s. Notably, real-time monitoring of austenite grain growth was possible by using a novel laser ultrasonic technique. Further, bulk samples were produced using the Gleeble adopting the experimentally determined temperature time history. These bulk specimens were subsequently subjected to tensile and fracture resistance tests.
Schematic austenite grain size of microalloyed steel with precipitates as a function of temperature in the heat affected zone (HAZ). The motion of grain boundaries driven from the curvature of boundary (reduction of surface energy) is retarded by pinning force of precipitates. At temperatures well above the dissolution temperature of precipitates grain growth is significant (adapted from ASM Handbook, Vol. 6A)
Measured and calculated austenite grain size in the HAZ of X80 linepipe steel
Microstructure modelling results in the HAZ of X80
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