Synergistic precipitation strengthening effect of copper and niobium in high strength steel weld metal

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:115475

Ramirez, J E; Liu, S; Olson, D L ^[1]

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1. Colorado School of Mines, Golden, CO (United States)

The strengthening effect of copper and niobium in high strength steel weld metals was studied. The strength increase, in the as-welded condition, as function of the alloying content, the kinetics of precipitation, morphology, and distribution of the precipitates, and the associated transformation microstructure was examined in detail. In summary, the dual precipitation concept, with copper and niobium as strengthening agents, showed effective in providing the required hardness/strength and that the dual precipitation scheme reduced the hardness fluctuations commonly observed in welds with single precipitation. Additions of approximately 3.3 wt% copper and up to 0.1 wt% niobium in the weld metal provided the strengthening effect to obtain high strength steel weld metal with acceptable properties, 360 HVN which corresponds to an estimated yield strength of 900 MPa, throughout the entire range of heat input investigated, during single- and multipass welding. To study the fundamental aspects f the synergistic effect of copper and niobium on the precipitation strengthening of the weld metal, systematic additions (individual and combined) of copper from 2.5 to 3.7 wt%, and niobium up to 0.1 wt%, were made via cored an covered electrodes. To investigate the effect of copper-niobium additions on the austenite phase stability, the temperature range of the austenite-to-ferrite transformation was determined using dilstometry as a function of weld copper and noibium content. As expected, only small variations in the austenite decomposition temperature were observed because of the opposite effect of copper and niobium. Higher austenitizing temperatures, however, slowed down the kinetics of the precipitation process and decreased the hardening effect.

• OSTI ID: 115475
• Report Number(s): CONF-9404233--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COPPER
HARDNESS
METALLURGICAL EFFECTS
MICROSTRUCTURE
NIOBIUM
PHASE STABILITY
PRECIPITATION
QUENCHING
STEELS
TEMPERATURE DEPENDENCE
WELDING