Vanadium and niobium additions in pressure vessel steels

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:5094091

Xu, Peiyuan

A statistically designed series of vanadium and niobium microalloyed C-Mn HSLA steels was used for an investigation of heat-affected zone (HAZ) toughness in multipass welds. The vanadium additions were in the range 0.005 to 0.097 Wt.% and the niobium additions were in the range 0.004 to 0.06 Wt.%. GMAW processes with welding heat inputs of 3kJ/mm and 5kJ/mm and post-weld heat treatments (PWHT) at additions of microalloy elements V and Nb on multipass HAZ toughness in the as-welded and PWHT conditions was confirmed. the 50 Joule transition temperature (TT50J) for HAZs in all weld conditions correlated with maximum HAZ hardness. Increases in HAZ hardness and TT50J caused by PWHT were observed. Hence PWHT is not recommended for V/Nb microalloyed HLSA steels. The randomly distributed precipitation of V and Nb carbides (V,Nb)C, including dislocation precipitation and matrix precipitation with particle sizes of 5-15nm, is the predominant alloy carbide precipitate morphology in these steels. Banded morphology of (V,Nb)C precipitation is rarely observed in the HAZ. The volume fraction of (V,Nb)C precipitates increases as increasing V and/or Nb contents in the experimental heats. The volume fraction of precipitates also increases with increasing the PWHT time. The crack initiation sites in Charpy specimens of HAZs tested at the approximate transition temperature are shifted from the highest stress triaxiality location to a higher hardness location. This is found to be characteristic of fracture in the multipass HAZ of the microalloyed steel. An analytical study shows that the influences of additions of microalloy elements V and Nb on yield stress, [sigma][sub y8], and fracture stress, [sigma][sub f], eventuate in the increase of transition temperature in these materials.

• Research Organization: Lehigh Univ., Bethlehem, PA (United States)
• OSTI ID: 5094091
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CARBON STEELS
CONTAINERS
FRACTURE PROPERTIES
HEAT AFFECTED ZONE
IRON ALLOYS
IRON BASE ALLOYS
MECHANICAL PROPERTIES
NIOBIUM ADDITIONS
NIOBIUM ALLOYS
PRESSURE VESSELS
STEELS
VANADIUM ADDITIONS
VANADIUM ALLOYS
ZONES