Prestrain and Its Effect on Low Temperature Toughness of Fe-Cu Alloys

Slow bend test for standard Charpy V notched specimens and tensile test for notched small specimens (30mm×4mm×1mm), were carried out over a range of low temperatures to investigate the effect of prestrain on the low temperature toughness of Fe-Cu alloys by changing the quantity of prestrain and prestraining temperatures. Prestraining of 1 to 6% at room temperature increased ratio of fracture stress (σF) to 0.2% offset stress (σ0.2) over 1 at 143K for notched tensile specimens of aged Fe-1.7%Cu alloy (650°C ×25h) and the prestrained notched specimens were cleaved after macroscopically plastic deformation. Any prestrain at 153K, however, decreased the ratio of σF to σ0.2 to less than 1 at 143K and the specimens were cleavage fractured with macroscopically elastic deformation. Energy transition temperature in slow bend test of Fe-1.1%Cu alloy of as solution-treated did not change with 4% prestrain at room temperature but increased 77K with 40% cold roll at 273K. Energy transition temperature of aged Fe-1.1%Cu alloy (650°C×25h), however, decreased 25K with 4% prestrain at room temperature but increased 30 K with 40% cold roll at 273K.