TWI Industrial Member Report Summary 189/1982
By R J Pargeter
Background
This report is concerned with the effects of CaSi2 additions to submerged-arc fluxes on microstructure and toughness properties of unreheated weld metal made in C-Mn steel. It follows a similar report on the effects of Ti bearing additions and forms part of a programme of work investigating effects of deoxidant additions on various aspects of welding behaviour and weld properties.
Two flux types were employed. The alumina basic flux was used with single arc welding over a range of arc energies from 2 to 4kJ/mm on 32mm plate. The basic flux was used with a range of tandem arc welding conditions, two at about 4.5kJ/mm and one using reduced voltages at about 3.9kJ/mm, all on 40mm plate. Microstructures were examined under an optical microscope, and toughness was assessed using the Charpy test and discussed in terms of the 35J transition temperature. The penetration pass was tested in each case.
With both flux types a reduction in transition temperature of between zero and 20°C was observed with the 1.5%CaSi2 flux addition. A slight increase in the proportion of acicular ferrite was also observed, and the lath size of the acicular ferrite was reduced under the basic flux. These microstructural changes could not be directly related to any feature of the weld metal composition other than Si content, which increased with CaSi2 addition. It was concluded that over the range of compositions studied, Si between ~0.15 and 0.4% is beneficial to submerged-arc weld metal toughness