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 5000 h to characterize thermal aging embrittlement. At room temperature, 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 show ed 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. (C) 2000 Elsevier Science B.V. All rights reserved.