139
Through Optimum Use and Innovation of Welding and Joining Technologies
Improving Global Quality of Life
above however, the retained austenite reduces the mechanical strength, and so an optimum microstructure
control is necessary to obtain a weld metal with required mechanical properties and resistance to hydrogen-
induced cracking.
As mentioned above, the MIG welding is suitable for producing the weld metal for the HSLA steel of more
than 780 MPa classes, in which the contents of both oxide inclusion and hydrogen must be low. The heat
input of the MIG welding, however, controlling the productivity, is practically limited to a significantly lower
level than most of other conventional welding processes, and this is an obstacle to its wider application.
It was believed that the practical heat input was limited by the instability of the arc plasma due to the
scattering of the cathode spot in the weld pool. Hiraoka et al., however, showed that the arc instability could
be resolved by stabilising the wire electrode rather than the cathode spot. Therefore, it can be expected that
the MIG welding can be carried out at much higher heat input by stabilising the wire cathode and thus the
obstacle to the wider use of the MIG welding to the advanced steel can be removed.
In Japan, a national project on the innovation of welding for advanced steels has been undertaken with the
cooperation of universities, governmental research institutes, and industries. As exemplified by the HSLA
steel of more than 780 MPa classes, the desired microstructure of the weld metal is different from those of
lower strength steels, and the weldability, a measure of hydrogen embrittlement susceptibility of weldment,
depends on factors other than the carbon equivalent of the base metal. Thus, one needs to establish a new
paradigm of the weldability for advanced steels like HSLA steel of 780 MPa class. It is also required to develop
a welding process that enables one to produce a weld metal with low oxygen content at high productivity. A
comprehensive approach based on the microstructural design and control of the weld metal, development of
the welding process involving high energy density beam welding, and the control of residual stress and strain
will contribute to solving these problems and eventually to the improvement of the quality of global life.
9.13.4
Hot topics
Research and development of welding processes and technologies for the joining of advanced steels
e.g. high strength low alloy.
Research in the metallurgy, preheat and residual stress of advanced steels.
9.14
Electronics sector
(
Images in Section 9.14, 9.15 and 9.16 reproduced courtesy of TWI Ltd
).
Electronics, combined with sensing technology, form the fundamental operating
systems for nearly all modern industrial products and systems frommobile phones
to power stations. As electronics becomes more sophisticated its integration
into products is increasing, to a point where many systems (e.g. automotive,
aerospace, assembly equipment, welding power supplies) cannot be operated
without electronic/computer/sensor assistance.
The electronics sector is also a key influencing factor
in environmental issues. On one side it can be used
to significantly save energy through intelligent system management (e.g. motor
controls, consumer product energy usage) and renewable energy controls (e.g.
solar, wind and tidal). Conversely, it is the major contributor to the growth in landfill
waste (e.g. consumer products - mobile phones, TVs, games machines etc.). Future
developments in terms of materials and assembly processes will influence the overall
balance of electronics’ environmental sustainability.
High density electronic
package
Electronics for landfill waste
9
Needs and challenges of major industry sectors for future applications
