Solidification microstructure and sources of type II grain boundary disponding in CRA cladding

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

OSTI ID:115469

Wu, Y; Patchett, B M

Hydrogen-related disbonding of austenitic stainless steel cladded overlay is a problem encountered in the use of hydrogenation pressure vessels in petrochemical industries. One of the major factors contributing to the disbonding is the microstructure developed during solidification of the weld metal. This study investigated the microstructure along the interface between an overlay and base steel and set out to establish the mechanism of the formation of crack-susceptible microstructures. Eight corrosion resistant alloys, with primary solidification crystals as {delta} only, {delta} + {gamma}, and {gamma} only, were submerged arc welded on plates of Cr-Mo low alloy steel by two procedures with the same nominal heat input: one was low current (750 amp) at a low travel speed (140 mm/min), and the other high current (1500 amp) at a high travel speed (280 mm/min). under the influence of patterns developed. After postweld heat treatment and hydrogen-charged autoclave testing, disbonding was revealed by ultrasonic C-scan and metallographic examinations. The most susceptible microstructure to hydrogen-related disbonding is the Type II grain boundary. The standard industrial cladding of type 309L stainless steel is prone to hydrogen-related disbonding, due to the mixed {delta} + {gamma} solidification mode, which tends to form Type II boundaries. Duplex stainless steel with primary solidification crystals as {delta}-ferrite eliminates Type II grain boundaries and disbonding. High current welding will reduce the chance of forming Type II boundaries in overlays with primary crystals as a {delta} + {gamma}, but will increase the chance of forming planar grain boundaries in nickel-based alloy overlay, due to the high dilution effect.

• OSTI ID: 115469
• Report Number(s): CONF-9404233--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CORROSION RESISTANT ALLOYS
CRACK PROPAGATION
HYDROGEN
LATTICE PARAMETERS
LOW ALLOY STEELS
METALLURGICAL EFFECTS
MICROSTRUCTURE
PHASE TRANSFORMATIONS
PRESSURE VESSELS
SOLIDIFICATION
SUBMERGED ARC WELDING