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Aspects of the electroslag welding process

University of British Columbia

The electroslag welding (ESW) process has been investigated utilizing consumable guide welding procedures. Electroslag welding employing large square cross-section electrodes was also studied. The study of the process parameters is of importance in understanding the role which they play in determining the grain size attained in the heat affected zone of the resultant weld. The large grain size adversely effects the impact strength: the grain size is a direct consequence of the thermal history. The thermal history of the base metal was determined during welding for various physical configurations and welding schedules. The welding parameters having the major effect on the thermal history are: mode of welding, electrode immersion depth, slag depth, welding velocity and specific power input. The penetration of the parent metal and size of the heat-affected zone as well as the grain size have been shown to be a consequence of the thermal history. The quazi-steady state electrical and temperature distributions in the slag are seen to determine the temperature distribution in the metal. The preferred modes of welding are alternating current (AC) and direct current reverse polarity (DCRP) with direct current straight polarity (DCSP) being unacceptable due to the high inclusion content of the weld when DCSP is employed. The electrode immersion depth, or interelectrode gap, has been found to determine the volume of the effective heat source and thus the temperature and electrical distributions. The slag depth and electrode velocity are the principal factors which determine the interelectrode gap when the slag chemistry and physical configuration are constant. There exist ranges of slag depth and electrode velocity values outside of which welding is not achieved. An analytical model has been employed which adequately describes thick plate welding practice, but which only applies to thin plate welds in a qualitative manner. In this model, an empirical equation has been used to calculate electrode immersion values which compare favourably with the measured values. In addition,the Bastein method of grain size calculation has been applied to the thermal histories obtained experimentally and has been found to be applicable. In welds where impact strength is an important design criteria the weld/HAZ grain size is an important variable. We conclude that no combination of ESW process parameters will lead to an acceptable HAZ grain size giving HAZ impact values comparable with the parent plate. In such cases full heat treatment of the HAZ would be mandatory.

Text

2010-03-11

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http://hdl.handle.net/2429/21795

Metals and Materials Engineering

University of British Columbia

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