13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Hydrogen Effect on Fatigue Crack Initiation Behavior of Structural Materials Ryuichiro Ebara* Institute of Materials Science and Technology, Fukuoka University, Fukuoka-city, 814-0180,Japan * ebara@gold.megaegg.ne.jp Abstract Hydrogen effect on fatigue crack initiation behavior of structural materials related to the internal hydrogen embrittlement and hydrogen environment embrittlement is reviewed. Mechanisms of hydrogen effect on fatigue crack initiation behavior of structural materials are briefly summarized. The emphasis is focused upon the hydrogen related corrosion fatigue crack initiation behavior of structural materials in aggressive gas and sour crude oil environments. Finally recommended researches in hydrogen effect on fatigue crack initiation of structural materials are touched on briefly. Keywords Hydrogen, Fatigue, Corrosion fatigue, Corrosion pit, Crack initiation 1. Introduction Hydrogen effect has been investigated on structural materials used for important machinery components in oil and energy related industries so far. It is well recognized that hydrogen drastically accelerate crack propagation rate of structural materials [1]. However hydrogen effect on crack initiation behavior of structural materials is not well understood. Prevention of hydrogen related fatigue crack initiation of structural materials is indispensable for safety use of fuel cell vehicle and hydrogen fueled internal combustion engine yet to come[2,3]. In this paper hydrogen related fatigue crack initiation behavior of structural materials is reviewed mainly on the basis of the author’s experimental results. First the proposed mechanisms of hydrogen effect on fatigue crack initiation and propagation behavior of structural materials are briefly summarized. Then the corrosion related fatigue crack initiation behavior of structural materials in steam, humid air and aqueous solution including industrial gas such as H2S, SO2 and CO2 are summarized. Hydrogen related corrosion fatigue crack initiation behavior of ship hull structural steels in sour crude oil environment is also emphasized. Finally recommended studies in hydrogen effect on fatigue crack initiation behavior of structural materials are touched on briefly. 2. Mechanism of hydrogen effect on fatigue crack initiation behavior of structural materials It has been well recognized that fatigue strength of structural materials is affected by oxygen and humidity in air. Therefore oxygen effect on fatigue crack initiation of structural materials has been well investigated. The mechanisms for oxygen effect on fatigue crack initiation such as the oxygen intake mechanism with dislocation motion [4] were proposed so far. However the decisive mechanism for hydrogen effect on fatigue crack initiation has not yet proposed so far. Hydrogen effect on fatigue strength of mild steel with round notched plate specimen was not significant as compared with effect of oxygen and humidity [5]. Suzuki et al. conducted low cycle fatigue tests for normalized S45C round bar specimens with different purity with P,S,N,O and Al in order to investigate the pre-charged hydrogen effect [6]. The pre-charged hydrogen effect on low cycle fatigue life was not significant for high purity S45C steel. On the contrary low cycle fatigue life of low purity S45C steel was 50 to 90 % lower than that of conventional normalized S45C steel. They concluded that cyclic softening reduce the dislocation density in S45C steel with high purity and make the steel insensitive to hydrogen. Low cycle fatigue tests were also conducted for 21/4 Cr-1Mo steel in high temperature and
RkJQdWJsaXNoZXIy MjM0NDE=