EFFECT OF MICROALLOY ADDITIONS ON THE HEAT AFFECTED ZONE NOTCH TOUGHNESS OF A C-Mn-Mo LINE PIPE STEEL.

Fourteen heats with variations in columbium, titanium and titanium-columbium and titanium-vanadium additions were controlled rolled to plate. Strengths equivalent to those required for Grade 483 pipe were achieved only in the columbium-bearing (less than 0. 04 percent) and high titanium (0. 11 percent) chemistries. HAZ toughness was evaluated using fatigue precracked Charpy tests and CTOD tests on Gleeble samples that simulated the single pass coarse grained HAZ of a 2 KJ/mm submerged arc weld. Small titanium additions (0. 01 percent) resulted in refinement of prior austenite grain size and an improvement in CTOD and impact toughness. Columbium additions to 0. 01 and 0. 005 percent titanium steels resulted in improved HAZ grain refinement but deterioration in toughness associated with higher HAZ strength. The 0. 11 percent titanium addition was not as effective as a small titanium addition in restricting austenite grain coarsening and it lowered HAZ toughness.