TWI Industrial Member Report Summary 192/1982
By R M Rivett and P J Boothby
Welding trials were conducted to assess the weldability of a range of 8 grades of high strength steels with thicknesses in the range 0.65-1.2mm.
It has been established that, with the exception of one solid solution hardened and one dual phase steel, which had the higher alloy contents, 5 root t diameter welds could be produced using the welding conditions recommended for low carbon steel. Of the steels examined only the solid solution steel with the highest C + P level did not give plug failures when testing such welds. The cross-tension of 5 root t diameter welds produced with the recommended weld schedule for low carbon steel were equal to, or up to 20% greater than those made in an equivalent thickness of low carbon steel.
The use of longer time/higher force schedules increased the tolerance to reduction in weld current by a factor of 1.5 to 4. However, the use of such longer time schedules reduced the cross-tension properties of the dual phase steels, whilst the use of higher force schedules reduced the cross-tension properties of the stress-relieved annealed and one of the dual phase steels.
Increasing the electrode tip diameter from 5 to 7mm gave a reduction in the cross-tension properties of 5 root t diameter welds for 3 of the 4 steels examined. Larger unsplashed welds of up to 7 root t diameter could be grown but these did not necessarily give improved cross-tension properties.
Metallurgical examination of 5 root t diameter welds showed that the predominant microconstituent was ferrite with aligned martensite, austenite and carbides (MAC). However, the metallurgical work was insufficient to establish a correlation between joint properties and weld structure.