Investigations into fatigue failure in e-type fastening clips used in railway tracks

This study describes the investigations of failure in an e-type clip at the inside of rear arch, where the stresses are maximum owing to in-service loading and bending that occurs during forming operations. Visual inspection, stereomicroscopy, optical-microscopy and Scanning Electron Microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) have been used as the characterization techniques. The microstructural, morphological changes were compared both in the central area and close to the location of failure in e-clip. During primary heating for forming steel rod into e-clip shape, the oxidation and decarburization occurs which caused the formation and penetration of iron oxide. The average thickness of oxide layer was found to be 20 µm with localized areas, where the oxides penetrated up to depth of 50 µm. During forming and shot peening operations, the iron oxide ingested in material at the inside circumferential region of rear arch, which triggered the initiation and propagation of fatigue phenomenon in service. The SEM-EDS analysis and fractography confirmed the presence of iron oxide and pearlite lamellar tearing at the crack initiation site, respectively. It is suggested to use electric induction heating for forming of steel rod into e-clip shape or increased the silicon content from two to three weight percent, which minimize the thickness of oxide layer. The finishing process by adding air spray or tapping of the rod after heating will further help to remove the scale at the critical region before taking it up for mechanical forming operations.

Weldability and Lamellar Tearing Susceptibility of High-Strength SN 490C Steel Plates

In this study, weldability and cracking susceptibility of SN 490C steel were firstly investigated. For this study, SN 490C thick plates which had been developed for anti-seismic steel of building structures were welded by flux-cored arc welding (FCAW) and submerged arc welding (SAW) processes based on welding conditions of actual construction site. Weldments using the plates with different thickness were produced using E71T-1C and EH14 filler wires, respectively. For the weldability tests, various welded joints such as butt and T-joints were examined. After welding, microstructure analysis was performed. Various microstructures were found depending on the location of the weldments. Heat effects by multi-pass welding were correlated with the microstructure. The microstructure was correlated with the hardness profile and the impact test result. In addition, the through-thickness tensile test, window test, and Cranfield test were conducted to evaluate sensitivity of lamellar tearing, which may occur during tensile restraint stress of welds. As a result of the tests, it was found that the SN 490C steel was sufficiently resistant to lamellar tearing.

Lamellar Tearing Observations Regarding the Application of European Standards in the Field of Welded Steel Constructions

The problem of corrosion for old steel bridges in operation is often solved by direct replacement of elements or structure. Only a few studies have been done to determine the efforts influenced by corrosion in those elements. In general, it is considered that a corroded element has exceeded the bearing capacity and should be replaced, but if the corroded element is secondary it could be treated and kept. A factor in the rehabilitation of an old steel bridge in operation is the aspect of structure. If the structure is corroded, rehabilitation decision is taken is easier. Lamellar tearing describes the cracking that occurs beneath the weld and can be characterized as a brittle failure of steel, in the direction perpendicular to the plane of rolling. The paper presents a comprehensive study on lamellar tearing and summarizes some conclusions about the prevention of them. The conclusions will be exemplified in the case of a railway bridge, with a main truss girder. The paper presents also some observations regarding the stress analysis in fillet welds, resulting from the engineering practice.

Effect of Finish Rolling Process on Improvement of Lamellar Tearing Resistance of High-Rise Building Steel

A process of finish rolling was researched to enhance lamellar tearing resistant of the high-rise building steel EH36. Experimental results indicate that gain size decreased with the decrease of finish temperature. When the finishing temperature on 840/810/780/750°C respectively, microstructure is finest with the size of 11.4μm. Moreover, the size of TiC precipitation turned ideal as the coiling temperature decreased. When coiling temperature is 550°C, the average size of TiC precipitation is only 0.09μm, refined by 40% relative to the conventional process. The microstructure and precipitation phase size of test steel are both effectively controlled because of the improved process. Therefore, high-rise building steel EH36 is finally prepared, and the lamellar tearing resistance reaches up to 78.2%.

Microstructure and Properties of Q345E Lamellar Tearing Resistant Steel SAW Welding Joints

The Q345E lamellar tearing resistant steel with 140mm thickness was welded by submerged arc welding (SAW). The microstructure and properties of the welded joints were investigated. Affected by the long-term welding thermal cycle, microstructure at different thickness has great differences. The hardness in the weld center is higher about 55 HV than the base metal. Due to the grains refinement of the microstructure at 1/2 thickness was more obvious, the microhardness of this zone has a more obvious dispersion degree. The average grain size of ferrite at the 1/4 thickness is about 10 μm, which resulted in two samples at this thickness obtain a higher tensile strength (496.568 MPa and 496.36 MPa). Moreover, part of the pearlite lamellar in the HAZ at 1/4 thickness had been fragmented and spheroidized.