Improving Global Quality of Life

4.
Needs and challenges
in welding and joining
technologies
4.1 New materials, weldability and testing
Traditionally welding science and technology are associated with joining of metals and alloys as they form
a substantial part of the material consumed by mankind. Steels, aluminium alloys, nickel-base super alloys
and titanium alloys constitute the major share of these metals and alloys and development in welding
science and testing have been in improving the weldability of these materials and for understanding the
basic metallurgy of their welds. Similarly, processes employed to weld these materials have been confined
predominantly to the arc welding processes and, as in automotive industries, to resistance welding. Today,
however, many more new materials and design methods (e.g multi-material) are available and accordingly
the science and technology of joining them have also undergone revolutionary changes.
The need to improve the quality of life, conserve the natural resources, protect the environment etc. has
been the major driving force for innovations in the field of materials and their application. Some of these
were driven by the desire to take the conventional structural materials like steels, Al alloys etc. up to the
upper limits of their performance. Transformation Induced Plasticity (TRIP) steels used in automobile
industries, advanced ferritic steels in fossil power plants, super austenitic and super duplex stainless steels for
corrosion resistance applications, Al-Li alloys and maraging steels for aerospace applications are successful
examples of these innovations. A paradigm shift in the way the materials are chosen for different application
is another factor that triggered innovation in this field. The choice of ceramics, composites, fibre reinforced
plastic etc. for structural applications, often for very extreme operating conditions, resulted in significant
advances and developments in these new structural materials. These materials now find applications in
gas turbines (structural ceramics), space vehicles (composites) windmills (composites and fibre reinforced
plastics) etc. Development of new technologies, information, communication and bio-technology, triggered
the development in a new generation of materials called advanced materials which are used more for their
special physical properties like biocompatibility, magnetic, electrical and optical properties.
Weldability and performance of the welds in service have been important issues that have to be considered
while developing new structural materials. Often, the welding processes employed for their traditional
counterparts may not be suitable for these new alloys. A good example for this case is the new generation
oxide dispersion strengthened (ODS) ferritic martensitic steels being developed for high temperature
applications in nuclear (both fusion and fission) reactor and fossil power plants. In the case of conventional
ferritic martensitic steels (Cr-Mo steels) weld metals produced by any of the fusion welding processes
possess the desired properties. In contrast, one has to necessarily use solid state welding processes to
join the ODS alloys to ensure that fused weld metal is avoided so that weld joints retain the properties of
the base metal, inherently achieved through dispersion of Y 2
O 3
based nano particles in the steel. Similarly
in materials like TRIP steels and maraging steels, improved properties are attained by controlled thermomechanical
processes which produce the desired microstructure in the base metal. Such a microstructure is
destroyed in the weld metal and the heat affected zone (HAZ) during welding and this has necessitated use
18 Improving Global Quality of Life Through Optimum Use and Innovation of Welding and Joining Technologies