Role of residual elements on through-thickness properties of carbon steel plates

While the importance of through-thickness ductility in minimizing lamellar tearing during the welding of carbon steel plates is well known, the importance of through-thickness toughness has not yet been fully realized. Examination of several cracked fillet weldments has clearly identified two distinct modes of lamellar tearing, one dependent on ductility and the other on toughness. Correlations with multiple linear regression techniques were established for throughthickness elongation, reduction of area, fracture strength and toughness with chemistry, inclusion characteristics and microstructure. About 80 cracked weldments and plates were examined and it was found that both inclusion characteristics such as size, thickness and area and chemical characteristics such as Al, Mn, P and Si influence the through-thickness mechanical properties of the plates. To examine further, the effect of sulphur content, 333 plates from 185 different heats were analysed and tested. The beneficial effect of lower sulphur content (fewer sulphides) on through-thickness elongation, reduction of area, fracture strength and charpy V-notch impact strength was confirmed.