Evaluation of thermal aging embrittlement in CF8 duplex stainless steel by small punch test

Small punch test was performed on CF8 duplex stainless steel aged at 370 and 400 degrees C for up to 5,000 h to characterize thermal aging embrittlement. At room temperature, i the small punch (SP) load-displacement curve was similar in shape to those of ferritic steels and exhibited a good reproducibility in spite of ferrite-austenite structure. As the test temperature was lowered to a certain temperature depending on the degree of aging, the SP load showed a sudden drop followed by curve serration before the SP specimen fractured, resulting from the cracking of ferrite phase While the aging heat treatment led to a slight increase of the yield strength, the transition appearing in the SP energy versus temperature curves shifted to higher temperature-due to the hardening of ferrite phase. Additionally, phase boundary separation was an important factor in the degradation of the steel aged at 400 degrees C.