NEW ALLOYING CONCEPT FOR FINISHING MILL ROLLS INCLUDING RESULTS IN APPLICATION AND SURFACE TESTS

• Published in: Tecnologia em metalurgia, materiais e mineração Vol. 17; no. 2; pp. 137 - 148
• Main Authors: Brandner, Michael, Paar, Armin, Mul, Sander
• Format: Journal Article
• Language: English
• Published: Sao Paulo Associação Brasileira de Metalurgia, Materiais e Mineração 2020
• Subjects: Alloying; Alloys; Analytical chemistry; Cemented carbides; Cementite; Chill rolls; Eddy currents; Finishing mills; Graphite; Hot rolling; Hot strip mills; Inspection; Microstructure; Nodular cast iron; Rolling mills; Rolls; Strip mills; Supports; Surface properties; Surface waves; Tempered martensite; Test equipment; Wear resistance
• ISSN: 2176-1515; 2176-1523
• DOI: 10.4322/2176-1523.20202277

ESW’s brand VANIMO can be considered as the latest development in Graphitic HSS roll grades for the last finishing stands in hot strip mills. These grades are based on the alloying concept of carbide enhancement of Indefinite Chill work roll materials. The amount and types of carbide forming elements are varied and adjusted according to the experience of cast HSS roll grades. The microstructure of these roll grades therefore consists of tempered martensite, cementite and several different carbide types as well as a well-defined amount of free graphite. The main goal of graphitic HSS roll grades is the combination of the high surface quality of ICDP alloys as well as the high wear resistance of HSS roll grades. Systematic steps were tested to increase the wear performance from earlier made Carbide-Enhanced ICDP grades to the more advanced VANIC grade and ended now in the highest alloyed roll grade VANIMO. In every trial, the surface quality of the roll and the strip was carefully monitored. The investment in new testing equipment at ESW’s plant was decided to get more information about microstructural effects of different alloys in a macroscopic dimension. Samples taken from cast rolls and investigation is done in comparably small areas in relation to the total surface of a roll. Strip rolling is and surface quality of the strip is in strong relation to the barrel surface quality. Effects of alloy and microstructure can appear anywhere on the barrel surface. To get a better understanding and knowledge about alloying trials in relation to surface quality, we decided to install the last version of LRI (Lismar Roll Inspection). LRI is the latest technology of Eddy Current with a higher resolution compared to existing systems. Depending on matrix and free graphite and the balancing formation of carbide precipitations and carbide network the EC test can detect smallest differences. Different results of EC and UT surface wave inspection give the possibility to analysis and discussion. Rolls applied in the mill have given different results in respect of surface quality. A few examples of surface effects will be discussed and improvement strategies explained.