TWI Industrial Member Report Summary 45/1977
By R E Dolby
Experiments on submerged arc and electroslag welds are described in which the effect of niobium levels up to 0.06% on the heat affected zone (HAZ) toughness of 25mm thick 0.16C-1.3Mn steels was investigated. The welding conditions covered heat inputs in the range 5-25kJ/mm with cooling times from 800-500°C in the range 35-200sec. The crack opening displacement (COD) test results showed that the niobium containing steels had a lower HAZ cleavage resistance than the niobium free steels and metallurgical studies confirmed that this was associated with the development of bainitic structures of higher yield strength in the former case. Charpy V tests on the electroslag HAZs showed similar trends to the COD tests.
The implications of the results are discussed and a diagram presented enabling critical COD values for HAZs to be derived for welding conditions within the range investigated, appropriate to 25mm thick plate.