Effect of Stored Energy on Corrosion Fatigue Properties of Ultrafine Grained Fe-20%Cr Steel by Equal Channel Angular Pressing
Muhammad Rifai (a*), Hiroyuki Miyamoto (b)
a) Center of Science and Technology for Advanced Material, National Nuclear Energy Agency
Kawasan Puspiptek, Serpong, Tangerang 15314, Indonesia.
*iamrifai[at]yahoo.com
b) Department of Mechanical Engineering, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0394, Japan.
Abstract
Corrosion fatigue properties of ultrafine grained (UFG) Fe-20%Cr steel by equal channel angular pressing (ECAP) was investigated in term of grain refinement and stored energy. Iron chromium alloy as referred to as stainless-steel has been wide used as a material for cardiovascular stents, orthopedic and different implants used as biomedical application because of the plasticity and corrosion resistance. The improvement of strength was related to the grain refinement by ECAP process, however the decreasing of ductility is occurred. Effect of the grain boundary status can be examined by comparison between equilibrium dan non-equilibrium by annealing at 698 K. Under annealing temperature of 698 K, due to the recovery stage, there was a little difference in microstructure from the four passes ECAP. The corrosion fatigue life of the ECAP processed and the post-ECAP annealed sample was analyzed. Two mechanisms for crack propagation have been well recognized for stainless steel. One is slipping step dissolution mode. In this model, the slip step formed by active dislocation at a crack tip is anodic dissolution reaction, so that crack tip advance to further distance. The other is stress adsorption mechanism. The corrosion fatigue cracks initiation and cracks propagation process of iron-chromium alloy can be characterized by corrosion pits and intergranular fracture, respectively.
Keywords: Iron chromium; grain refinement; ECAP; Corrosion fatigue
Topic: Materials Science