TWI Industrial Member Report Summary 122/1980
By D J Abson and P H M Hart
Two-pass tandem submerged arc welds have been deposited in 25mm thick, Si-killed, Al-treated steel plate containing different levels of Nb and V, all of the same base composition, 0.14%C-0.3%Si-1.4%Mn-0.04%Al. Two V-containing steels with a high nitrogen content were also included. The range of plate compositions included those which would be used for controlled rolled and quenched and tempered steels. The effects on weld metal Charpy toughness of the microalloying additions were compared with previous work and COD data were generated for submerged arc welds in such steels. For this, the first phase of a larger programme, a basic agglomerated flux was used and the arc energy (for the second pass) was 4.9kJ/mm. Welding was carried out using S1 (0.5%Mn), S2 (1%Mn) and S3Mo (1.5%Mn, 0. 5%Mo) wire so that the influence of the microalloying additions on different initial microstructures could be studied. Three weld deposit levels of Nb (~0.02%, ~0.03% and ~0.07%) and two of V(~0.06 and ~0.11) were studied.
For the majority of the welds, Charpy and COD properties of the as-deposited weld metal were good (27J temperature generally <-50°C and 0.1mm COD temperature generally <-60°C). The microalloy additions had comparatively little effect on the microstructure except when low levels of Nb (<0.02) were added to lean alloy (1.2%Mn) deposits, when a marked increase in acicular ferrite content occurred. An increase in 27J Charpy temperature and in 0.1mm COD temperature was commonly observed but was generally <15°C for the highest levels of microalloy additions. Hardness increases in reheated weld metal generally became greater with increases in microalloy content and this was reflected in a rise in the 0.1mm COD temperature, particularly for the S3Mo deposits. In contrast, the Charpy tests revealed little influence of microalloying in the S3Mo deposits while in the S2 deposits the effect depended strongly on the level of Nb.