Analysis of Failure in Automobile Spokes Manufactured Using Medium Carbon Steel Wires
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Medium carbon steel wires are used to manufacture spokes for motor vehicles, and the integrity of the spokes is very important from the point of view of safety to the driver of the vehicle. In this paper, analysis of failure of one batch of spokes has been presented. The spokes failed during assembling on to the wheels and also during the field trials. In order to understand the root cause of these failures, metallurgical investigation of these spokes was done. It involved fractography, scanning electron microscopy, EDS analysis, optical microscopy, hardness testing, tensile testing, and chemical analysis. Chemical composition and tensile properties of the material were found to be within the values mentioned in the specification. The cause of failure is concluded to be the wrong microstructure that got developed in the material. The microstructure of the material is coarse lamellar pearlite with ferrite decorated along the grain boundary. Ferrite being softer is preferentially getting deformed in comparison with the rest of the microstructure i.e., pearlite. This preferential deformation in the material is leading to initiation of cracks during the manufacturing of spoke. Additionally, due to higher lamellar spacing in pearlite, ductility of the material has also decreased.
KeywordsSpoke Medium carbon Steel wire Coarse pearlite
The author is grateful to Dr. Sanjay Chandra, Mr. Shishir Desai, Head, and Dr. Sumitesh Das for providing an opportunity to work on this case study. The author is thankful to Mr. K. N. Prabhakar for the discussion on the manufacturing processes at customer end. The author is also thankful to R&D management of TATA Steel Ltd. for their support in carrying out this work.
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