An assessment of cold work effects on strain-controlled low-cycle fatigue behavior of type 304 stainless steel
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I.
INTRODUCTION
AUSXENrrIc stainless steels (types 304 and 316) are currently being used in liquid metal cooled fast breeder reactors (LMFBRs) as cladding and structural materials. In these applications, the components o f the structures are often subjected to repeated thermal stresses as a result o f temperature gradients w h i c h o c c u r on heating and cooling during startups and shutdowns o r during variations in operating conditions. Therefore, the resistance to l o w cycle fatigue (LCF) is an essential requirement in the design o f LMFBR components. In LMFBRs, f o r the core components, cold-worked austenitic stainless steels are often recommended to reduce radiation-induced void swelling. Furthermore, cold work may be introduced in the components unintentionally during the fabrication o f plates and sheets into vessels, tanks, pipings, heat exchangers, e t c . However, only a limited amount o f information pertaining to the influence o f p r i o r cold work ( P C W ) on LCF behavior o f austenitic stainless steels has been available,tl,2,3] The pausity o f the information on the effects o f PCW on LCF behavior o f austenitic stainless steels is a serious limitation, as cold work is recognized to be an important metallurgical variable for nuclear components. Detailed investigations have been performed in the K. B H A N U S A N K A R A RAO, H e a d , Mechanical Properties Section, M . VALSAN, Scientific Officer-SE, R. SANDHYA, Scientific Officer-SC, S.L. MANNAN, Head, Materials Development Division, and P . RODRIGUEZ, Director, are with the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam 603 1 0 2 , Tamil N a d u , India. Manuscript submitted December 2 7 , 1991. METALLURGICAL TRANSACTIONS A
present study to characterize the effects o f PCW on LCF life, cyclic stress response, and cyclic stress-strain behavior o f type 304 stainless steel in the temperature range o f 300 to 1023 K. A detailed examination o f the microstructural changes and the c r a c k initiation and propagation modes has also been conducted with a view to understanding the features w h i c h may influence the fatigue life and cyclic stress response at different temperatures. The results reported here form a part o f an extensive investigation on the effects o f grain size, cold work, and thermal aging on LCF and time-dependent f a tigue behavior o f type 304 stainless steel, t4]
II. A.
E X P E R I M E N T A LD E T A I L S
Material
The material chosen for the investigations conducted here was a nuclear grade type 304 stainless steel o f chemical composition (weight percent) 18.2Cr, 9.2Ni, 0.042C, 0.38Si, 1.65Mn, 0.024P, 0.003S, and balance Fe. Material was supplied by M / s Avesta Ltd., Degerfors, Sweden, in the form o f 5000 × 2000 × 2 5 - m m plates in mill-annealed condition. Bars 1000 mm in length and 24 mm in diameter were machined from plates with their longitudinal axis parallel to the plate rolling direction. These rods were given a solution annealing treatment at 1323 K for 1 / 2 hour. Solution-annealed material
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