TWI Industrial Member Report Summary 119/1980
By R J Pargeter and N Bailey
Background
Tests have been made with two commercial submerged arc consumables containing boron and titanium to explore the resultant weld toughness, tensile properties and microstructures when welding 32mm thick mild and C-Mn steels.
Sufficient titanium and boron transferred from a rutile-boron flux used with a 1.5%Mn (S3) wire on low Si, carbon steel plate in two-pass welds at 5.5kJ/mm to reduce the proportion of grain boundary ferrite and to refine both the prior austenite grain size and the transformed microstructure. The as-welded toughness was therefore good and better than would be expected from either a similar weld composition or from a weld microstructure containing similar proportions of less refined constituents but containing no titanium and boron. Stress relieved at 610degC, a weld made from these consumables showed only a small drop in proof stress and the Charpy and COD transition temperatures were some 20-30degC higher than as-welded.
With a Mo-Ti-B wire and a basic flux, detectable transfer of boron was only obtained with a very low oxygen (0.001%) C-Mn-Si-Al plate in a two-pass weld. This weld showed reduction in grain boundary ferrite content and an increase in proof stress compared with what would be expected from a similar composition without molybdenum or boron. The microstructure was not, however, refined and the toughness was similar to that expected from a similar microstructure containing neither molybdenum nor boron.
Multipass and two-pass welds made on C-Si-Al plate (0. 002%O) with the Mo-Ti-B wire gave good combinations of strength and toughness due, in part, to their molybdenum content but a two-pass weld on low silicon, carbon steel plate gave a weld of very low silicon content containing little acicular ferrite, with much coarse lamellar products. The Charpy transition temperature of this weld was about ambient, although a low COD transition was achieved.