Cracking of Electrolytic Tough Pitch Copper Plates During Hot Rolling
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TECHNICAL ARTICLE—PEER-REVIEWED
Cracking of Electrolytic Tough Pitch Copper Plates During Hot Rolling George Pantazopoulos
. Athanasios Vazdirvanidis . Ioannis Contopoulos
Submitted: 21 April 2019 / Published online: 18 June 2019 Ó ASM International 2019
Abstract Failure analysis is performed in electrolytic tough pitch copper plates that have been severely fractured during the initial hot rolling passes. A comprehensive investigation was conducted, including mainly macroscopic examination, fractographic and metallographic evaluation. Moreover, numerical simulation of the solidification front using a computational fluid dynamics software was also employed to analyze the influence of the variation of casting parameters on the solidification front development. Fracture areas manifested poor ductility, while in many cases a prior cast pattern consisting of coarsely solidified dendritic crystals was revealed. The obtained evidence is suggestive of microstructural embrittlement caused by the synergistic contribution of the manufacturing process conditions and the potential elemental and particle segregation, such as cuprous oxide aggregation, that might promote failure susceptibility. Keywords Hot-rolled plates Electrolytic tough pitch copper Low-ductility fracture Solidification front
This paper is based on a presentation at MS&T 2018 in Columbus, Ohio, in the ASM International Failure Analysis Society symposium ‘‘Manufacturing-Related Failures.’’ G. Pantazopoulos (&) A. Vazdirvanidis I. Contopoulos ELKEME Hellenic Research Centre for Metals S.A., 61st km Athens – Lamia National Road, 32011 Oinofyta Viotias, Greece e-mail: [email protected]
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Introduction and Background Information Copper alloy strips are produced following a sequence of casting and thermomechanical processing, consisting of hot and cold rolling processes and thermal treatment to achieve the required temper (hardness, tensile properties) and electrical conductivity. Hot rolling performed usually at a temperature above 0.6 Tm (Tm: absolute melting point) of slabs is a key manufacturing process which breaks down the coarse and non-uniform as-cast structure to a fine and homogeneous grain structure coming from the dynamic recrystallization process occurred during processing [1]. Several defects could be generated due to the uncontrolled rolling conditions and/or abnormal cast structure, resulting in significant material irregularities and degradation [2]. Severe cracking failures were reported in a copper alloy hot rolling mill raising the amount of scrap and quality rejections. These failures occurred at the initial hot rolling passes leading to immediate material loss and interruption of the process continuity and production sequence. Cracks appeared mostly at the edges of hot-rolled plates which also propagated internally, with destructive consequences of the entire feedstock, raising the production rejections and the returns to the cast shop for recasting. Metallographic and fractographic investigation of representative section
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