Na Xu

Fracture Failure of 304 Stainless Steel Connectors on the Isolating Switches

The failure mechanism of the connectors assembled on the isolating switches was analyzed. Under SEM examination, the fracture surface showed obvious crack propagation traces. Beach marks with a reverse bending pattern were found on the fracture surface. Fatigue striations, which were the micro-evidence of fatigue, were observed clearly on the propagation zone. Both the metallurgical examinations and XRD analysis showed that the material of the connector only contained the austenite phase. The collected evidence suggests that that failure of the connectors was induced by fatigue. The vibration of the specimen during transport was the most probable source of the alternating stress. The stretching assembly stress of the connector could increase the fatigue stress ratios of the specimen. Defects existing in the material might destroy the continuity of the material substrate and reduce the fatigue performance of the material.

Corrosion Failure of 304 Stainless Steel Hooks in a Brick Kiln

Failure analysis was carried out on the stainless steel hooks in a brick kiln to confirm its failure mechanism. The collected evidence indicated that chemical composition of the stainless steel hook was consistent with the standard requirements for 304 stainless steel. The metallographic test showed that the microstructure of the stainless steel hook in the non-damaged areas was normal. However, serious chromium segregation which might be caused by secondary phase formation at the high temperature was found in the damaged material. This dramatically reduced the corrosion resistance of the material. The corrosion elements such as oxygen and sulfur were found playing a major role in the corrosion process. Thus, the failure of the stainless steel hook was induced by corrosion due to the chromium segregation and the existence of corrosive elements including oxygen and sulfur.

Analysis of Primary Short Circuited Melted Mark Evidence Identification in Electrical Fire Case

Regardless of fire heat or short circuit high temperature melting, the residual traces which represent the environmental characteristics can be found in copper and aluminum wires. The primary short circuited melted mark identification must be scientific and objective for physical evidence of the electricity fire during detecting, and the conclusions are related to the fire survey process. Currently, identification method of electricity fire, including macroscopic method and metallographic method, is very general and lacking of standard reference map and detailed description. According to the macro and micro characteristics and formation mechanism of various fire wire melted marks and the characteristics of metallographic organization of primary short circuited melted mark, two actual cases were analyzed in detail so as to distinguish the relationship between the melting reason and fire cause and to confirm that these two fires are caused by primary short circuit.

Fracture Failure of Zinc-Plated Hub Bolts by Hydrogen Embrittlement

Abstract In this work, the failure behavior of a batch of zinc-plated hub bolts with high strength was detected and analyzed to determine the failure mechanism. The fracture failure occurred at the head-to-shank transition. The initial region of the crack was at the external edge of the bolts. Brittle fractures containing intergranular and transgranular features were observed using a scanning electron microscope. Yawning grain boundaries as well as micropores on the grain surfaces were observed at many areas of the fracture surfaces. According to the analysis results, hydrogen embrittlement is considered as the probable mechanism of the failed specimens. Poor baking treatment may be the reason leading to the incomplete removal of hydrogen.

Failure Analysis of Water-Wall Tubes in the High-Pressure Boiler

In this case study, the corrosion failure analysis of high-pressure boiler water-wall tubes in a power plant was investigated by means of the chemical analysis, metallographic examination and scanning electron microscope (SEM) observation. Energy dispersive spectroscopy (EDS) was used to examine the changes of test materials and corrosion products. Based on the failure process of the boiler water-wall tubes and the experimental results, a conclusion was drawn that the failure of water-wall tubes was mainly caused by pitting corrosion. Sulfide and chloride attack was the major cause of localized pitting corrosion on the inner surface, and the outer surface damage was mainly due to the synergism of high temperature sulfide corrosion and flue gas erosion.

Corrosion Failure Analysis of a Colored Steel Plate Used as the Workshop Roof

By macro and micro morphology observations, chemical analysis, metallurgical observations, SEM observations and EDS analysis, the failure cause of a colored steel plate used as the workshop roof in a plant was analyzed; then, some improved measures were also proposed in this paper. It is demonstrated that failure of the colored plate is caused by the synergism of high temperature, and sulfur dioxide corrosion. The high concentration sulfur dioxide of the local area on the colored plate is the main failure cause.

Failure Analysis of the Guide Pillar in a Progressive Die

The fracture of the Cr12MoV guide pillar in a progressive die during punching was investigated by SEM observation, metallographic examination, chemical composition analysis, hardness testing. It is showed that the failure of the guide pillar was caused by fatigue. The fatigue crack initiated from the circumferential groove by repeated punching, and propagated throughout about 1/3 of fracture surface, then, instantaneous fracture eventually took place. Besides, there are some bigger eutectic carbides and inclusions in the pillar that made the material worse.