Experimental and Numerical Study on the Effect of ZDDP Films on Sticking During Hot Rolling of Ferritic Stainless Steel
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SINCE hot rolling is a mill process that involves rolling the metal at a high temperature in an open atmosphere, oxidation of the metal is inevitable. The oxide scale can deform plastically or fracture, and its behavior will have a considerable impact on the surface quality of the formed products. According to the reports,[1] approximately 30 pct of the surface defects can be related to the behavior of the oxide scale. One surface defect is called ‘‘sticking,’’ which refers to a phenomenon where fragments of the rolled strips are detached and get stuck to the work roll surface, causing surface defects on the mill products and scoring on the roll surface, which frequently occurs during hot rolling of ferritic stainless steels.[2] It has been found that sticking did not occur in the surface region containing oxides, whereas it occurs in the surface region without oxides.[3] During hot rolling, a large reduction proceeded. The extension of the thin oxide scale formed on ferritic stainless steels cannot fully cover the substrate. Therefore, the fresh substrate is bound to make contact with the work LIANG HAO, Lecturer, is with the School of Electro-Mechanical Engineering, Xidian University, Xi’an, 710071, P.R. China. ZHENGYI JIANG, Professor, and XIAWEI CHENG and JINGWEI ZHAO, Research Fellows, are with the School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522, Australia. Contact e-mail: [email protected] DONGBIN WEI, Senior Lecturer, is with the School of Electrical, Mechanical and Mechatronic Systems, University of Technology Sydney, Sydney, NSW 2007, Australia. DIANYAO GONG, Associate Professor, is with the State Key Laboratory of Rolling and Automation, Northeastern University, Shengyang 110004, P.R. China. SUZHEN LUO, Director, and LAIZHU JIANG, Vice President, are with the Stainless Steel Research Centre, Research Institute (R&D Centre), Baoshan Iron & Steel Co., Ltd., Shanghai 200431, P.R. China. Manuscript submitted May 25, 2015. Article published online August 1, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
roll surface. In addition, the higher the content of Cr in alloys, the more likely it is to suffer sticking because a thinner oxide scale was formed.[4] With the development of new ferritic stainless steels with higher content of Cr in the future, it is very significant to put forward the effective measure against sticking in practice. Extreme pressure (EP) agents are one of the most important constituents in lubricants,[5] which can form a solid film, acting as a boundary lubricant and preventing the substrate from directly contacting the work roll surface. Zinc dithiophosphates (ZDDPs) are arguably the most successfully lubricant additives ever invented. They were introduced over 60 years ago, have been in continuous use ever since, and are still being employed in practically all current engine oils. As well as being remarkable in their performance, ZDDPs have also been astonishingly successfully in their ability to inspire research.[6] In the previou
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