TWI Industrial Member Report Summary 194/1982
By D J Abson
Background
An investigation has been carried out on the effect of weld metal manganese content (0.9 to 1.9%) on the as-welded, tensile and toughness properties and microstructure of vertically-up manual metal arc welds in 38mm thick C-Mn steel plate. Welds were produced using 4mm diameter basic coated experimental electrodes, two levels of preheat and interpass temperatures (100/150°C and 250/30O°C), and an arc energy of ~1kJ/mm.
Increasing manganese gave a progressive refinement of the microstructure in as-deposited and reheated regions, and an increase in strength with the root regions being of higher strength than the sub-surface regions. Charpy toughness generally increased with increasing manganese. For the lower preheat and interpass temperatures, the root toughness was substantially lower than in the sub-surface region only at manganese levels less than ~1.6%.
For B x B crack tip opening displacement (CTOD) specimens tested at -10°C, toughness and scatter increased with increasing manganese; however, the scatter in log CTOD was independent of manganese. Scatter was greater for surface-notched specimens than for through-thickness-notched specimens, as a consequence, in some instances, of the fatigue crack tip sampling only regions of high toughness in the former case.
The welds produced with the higher preheat and interpass temperatures generally showed similar behaviour to those welded at lower temperatures, except that they were of lower strength and had coarser microstructures. The highest levels of Charpy toughness occurred at ~1.9%Mn, where (at sufficiently high test temperatures) toughness was substantially higher for these deposits than for those produced with the lower preheat and interpass temperatures.