NEEP 541 Swelling II Fall 2002 Jake Blanchard

NEEP 541 – Swelling II Fall 2002 Jake Blanchard

Outline n Contemporary Swelling Theories

Contemporary Swelling Theory n n n Many now believe that swelling rates in austenitic steels are universally 1%/dpa, independent of just about everything Variations only reside in the incubation dose Rate theories are thought to be inadequate

Crystal Structure Effects n n n Ferritic steels swell at rates more like 0. 1%/dpa Structure alone is not sufficient to explain the difference between ferritics and austenitics BCC vanadium alloys can swell at rates more like austenitic steels

Base Composition n At low temperatures, there is no composition dependence of swelling in Fe-Cr-Ni alloys At high temperatures, only incubation duration is affected At high Ni levels, the incubation can be quite long

Varying Base Composition

Fe-Cr-Ni alloys

Fe-Cr-Ni alloys

Varying Ni Content

Comparison for different Ni

Effect on Incubation

Solute Additions n n n Many minor and major solutes are present in most steels Phosphorous has the strongest demonstrated effect Increasing P delays onset of swelling Carbon can both increase and decrease incubation dose Solutes only affect incubation

Varying Cr Content and Temperature

Varying P Content

Varying Si Content

Varying C Content

Thermomechanical Treatment n n Cold work increases incubation Aging below annealing temperatures encourages precipitate formation and stress relief Aging decreases incubation Aging seems to accelerate carbide formation (and intermetallic phases)

CW Effects 316 SS Temperature (C)

CW Effects 304 SS 450 C

Dose Rate n n Increased dose rate generally increases incubation dose This is thought to be due to precipitation and dislocation evolution effects

Rate Effects – 316 SS Annealed – 562 C 20% CW

Stress n Stress tends to enhance swelling by lowering the incubation dose