Single peak overload retardation of corrosion fatigue crack growth under constant AK control was studied for A537 steel in air and in a 3.5% NaC1 solution at the applied cathodic potential of -1400mV (SCE) and in free corrosion condition. The crack closure behaviour was examined by the speckle interferometry technique at different stages of fatigue crack propagation. Scanning electron microscopy was used to observe the morphologies of fracture surface. The experimental results showed that, in all conditions, overload retardation occurred and the retarded propagation distances of crack were longer than the plastic zone size caused by overload at the crack tip. In air or in 3.5% NaC1 at the cathodic potential, delayed retardation occurred after applying a peak overload, the crack growth consisted of three stages: crack extension due to overload; decelerating in crack growth; and resumption of crack growth rate. Immediate retardation occurred when specimens were tested in a 3.5% NaCl solution in free corrosion conditions. Crack extension due to overload was not observed. Under both cathodic polarization and free corrosion condition, the overload retardation phenomena were not as obvious as that in air. The retarded propagation distance and the retardation degree were both smaller than those in air. The mechanisms for overload retardation of corrosion fatigue crack growth under the control of hydrogen embrittlement and anodic dissolution were discussed on the basis of analyses of crack closure, residual compressive stress and crack tip blunting.

Influence of hydrogen attack on mechanical and fatigue properties of 1020, 15CrMo and 2.25Cr-lMo steels has been studied, which, were exposed to gaseous hydrogen at pressure of 18MPa and 300～480℃ for up to 480h. The results of fatigue test showed that hydrogen attack (HA) resulted in an obvious change in fatigue properties of 1020 and 15CrMo steels, however, 2.25Cr-1Mo steel showed a lower susceptibility to hydrogen attack due to the addition of Cr and Mo. Fatigue crack behaviour for 1020 steel is attributed to hydrogen attack damage and the crack closure induced by the rough cracking surface, which lead to a valley on △Kth～HA% plot. The change in the fatigue behaviour of 15CrMo steel is possibly caused by severe surface decarburization.

Erosion resistance of fusion-bonded epoxy powder coating in emery sand slurry containing 1wt.% NaCl has been investigated by using modified rotating disk rig. The effects of emery sand content, flow velocity and diameter of emery particle on the erosion resistance of the coating have been studied through mass loss test and SEM observation. The results showed that the mass loss rate of the coating increased according to a power law with the flow velocity (V), emery particle content (C) and diameter of emery particle (D). The mass loss rate (E) of the coating could be described by an empirical equation, namely E ∝ V n1Cn-Dn3. The relative large values of n1 and n3 compared with n-indicated that the flow velocity and diameter of emery particle were the dominant factors. The critical flow velocity of the coating in slurry containing 10, 15, 20wt.% emery particle (112μm) was about 7, 6, 5.8m/s, respectively. Under the test conditions, the first critical diameter (FCD) and the second critical diameter (SCD) of emery particle were about 80 and 410μm, respectively. Within 80-410μm, the influence of mean diameter of emery particle on erosion was significant. Therefore, the coating is suitable for the relative mild conditions of liquid-particle two-phase flow such as low flow velocity and small particles.

Fusion-bonded epoxy powder (FBEP) coatings are received wide applications in flow-handling components such as pipelines, slurry pumps. There exists a serious problem in above conditions due to slurry erosion. The purpose of this paper is to improve the erosion resistance of FBEP coatings by controlling curing process and composition of coatings. The slurry erosion behavior of FBEP coatings has been studied by using modified rotating disk rig. The surface morphologies were observed by using SEM. The cross-linked density and microstructure were analyzed by measuring curing degree, glass transition temperature (Tg) and water absorption. The results showed that the slurry erosion resistance increased with increasing curing degree. The coating cured at 160℃ for 60min, had more erosion resistance than the coating cured at 220℃ for 5min, although the curing degree of the former was same as that of the latter. The characteristics of fillers played an important role in the erosion behavior of FBEP coatings. The erosion resistance increased with the increasing of the fraction and size of fillers.