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A Study on Longitudinal Cracks in Steel Billets

Author(s):

Mukesh Kumar , PEC university of technology, Chandigarh; Prof. R. K. Mahajan, PEC university of technology, Chandigarh

Keywords:

Longitudinal Cracks, FESEM, EDS, Continuous Casting, Nitride Embrittlement

Abstract

Longitudinal crack (LC) is a complex type of defect found in continuous casted steel and the consequences of longitudinal cracked product to go into service could be disastrous. Thus billets affected by longitudinal cracks are almost universally rejected and scraped, which affect the total yield of industry. The origin of longitudinal crack (LC) defect is not analysis evident from visual examination alone, since defect from different sources can appear essentially identical on the surface. This defect is primarily caused by nitride embrittlement which is caused by precipitation of nitrides of Aluminum, Boron or Niobium on the crack boundary. It may also cause by uneven cooling, both primary cooling and secondary cooling, and includes molten steel qualities, such as the chemical composition being out of specification, cleanliness of the material, and homogeneity. The nature of crack, severity of crack and causes of crack has investigated by different testing and characterization techniques such as magnetic particle inspection, optical microscopy, FESEM and EDS. Surface crack has been detected in magnetic particle inspection. In optical microscopy we found crack of varying depth in mm, decarburized zone and ferrite finger at the end of crack. Aluminum, Boron and nitrogen has been found at crack boundaries, which confirms the precipitation of nitride of aluminum or / and boron. Possible solution has been proposed to prevent the occurrence of longitudinal cracks in billet during Continuous casting. Addition of Ti, V, Zr or Mo, which has high affinity to nitrogen than aluminum prevent precipitation of aluminum nitride at grain boundaries. Longitudinal cracks can also be preventing by lowering nitrogen content in molten steel by vacuum degassing process.

Other Details

Paper ID: IJSRDV5I50939
Published in: Volume : 5, Issue : 5
Publication Date: 01/08/2017
Page(s): 890-894

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