Study of White Patch Defect in Automotive Grade Interstitial Free Steel
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CASE HISTORY—PEER-REVIEWED
Study of White Patch Defect in Automotive Grade Interstitial Free Steel Sachin Pawar . Subho Chakraborty . Hrishikesh Jugade . Goutam Mukhopadhyay
Submitted: 24 July 2020 / Accepted: 3 September 2020 ASM International 2020
Abstract Surface of cold-rolled steel intended for automotive body panel applications is expected to be defect free. The presence of surface defects hampers the aesthetics and average surface roughness and thereby deteriorates the paintability of the steel sheet. This study aims to investigate the source of white patch defect in cold-rolled and skin-passed interstitial free steel sheets. Macroscopic observations of as-received white patch sample revealed the presence of blackish deposit having cracks inside the deposits, suggesting that these deposits were heated up possibly during annealing process. Further during macroscopic observation, it was revealed that the black deposits were of near round shape. If deposit is present before rolling, then it is expected that it will elongate during rolling and will not retain round shape. Round shape of the deposits under investigation suggested that it is not before rolling. Electrolytic cleaning line (ECL) is the only inbetween process. Surface characterization techniques such as SEM–EDS, Raman spectroscopy, Fourier transform infrared spectroscopy were used to analyze the defect and good region of the steel sheet. Overall analysis indicated grease contamination on cold-rolled steel sheet at the entry of ECL caused generation of white patch defect. Regular cleaning and preventive maintenance of plant machinery were recommended to avoid such leakages to arrest the defect generation in the future.
S. Pawar (&) H. Jugade G. Mukhopadhyay Scientific Services, Tata Steel, Jamshedpur 831001, India e-mail: [email protected]; [email protected] S. Chakraborty Research and Development, Tata Steel, Jamshedpur 831001,, India
Keywords White spot Steel defects Raman spectroscopy FTIR
Introduction Automotive Steel—Manufacturing Process Automotive sector in India was estimated to be third largest automotive market in the world, by volume in 2016. It contributes about 49% of India’s manufacturing gross domestic product [1, 2]. For this reason, automotive sector is a major consumer of steel and it accounts for 12% of overall steel consumption [3]. Of the total steel used in a vehicle, 34% of it is used in the body structure, panels, doors and trunk closures [4]. All these parts are mostly coated to enhance their life by providing corrosion resistance from exposed atmosphere. Additional benefit of coating is improved aesthetic value [5]. For coating to be effective, it is important to have ideally defect-free steel surface. Before proceeding further, it is important to understand the manufacturing process flow of the steel sheet investigated here. Raw material for cold rolling used in this study was hotrolled (HR) sheet of * 3 mm thickness and pickled in hydrochloric acid solution to remove the oxide scale (refer
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