NEW ALLOYING CONCEPT FOR FINISHING MILL ROLLS INCLUDING RESULTS IN APPLICATION AND SURFACE TESTS
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.
1 Roll F. Handbuch der gießerei-technik. Berlin: Springer-Verlag; 1960. p. 321-328.
2 Lee G. Rolls for the metalworking industries. Warrendale, USA: Iron & Steel Society; 2002. p. 41-47.
3 Göbel H. Neue Gußeisenwerkstoffe für Walzen. ihre Eigenschaften und Verwendungsmöglichkeiten. Stahl und Eisen. 1957;77:143-157.
4 Feistritzer B, Schröder KH, Windhager M, Ziehenberger KH. Indefinite chill: Upgrading an old HSM work roll grade. In: Proceedings of the 41st MWSP Conference; 1999 Oct 21-24; Baltimore, USA. Warrendale, PA: Iron and Steel Society. p. 103-108
5 Paar AM, Brandner L, Elizondo T, Trickl C, Sommitsch C. Béal: from ICDP to (graphitized) HSS: sophisticated work roll grades for highest demands in rolling mills for flat products. In: Proceedings of the Rolling 2016 Conference; 2016 June 6-9. Graz, Österreich. Leoben, Austria: ASMET, Austrian Society for Metallurgy and Materials.; 2016.
6 Bravo SV, Yamamoto K, Miyahara H, Ogi K. Control of carbides and graphite in cast irons type alloy’s microstructures for hot strip mills. Materials Science Forum. 2007;561-565:1023-1026.
7 Hattori TN, Oda N. Meada: latest development of cast rolls for hot strip mill finishing trains and other rolling mills. Proceedings of the Rolls 5th Conference; 2015Apr 22-24; Birmingham; Großbritannien. London: The Institute of Materials, Minerals and Mining.; 2015.
8 Oda N, Fleiner P, Toshiyuki H. Latest developments of a new technology hss work roll for later stands (F4-F7) in hot strip mill finishing trains. In: Proceedings of the AISTech 2013 Conference and Expo. 2013 May 6-9; Pittsburgh; USA. Warrendale: AIST; 2013. p. 1977-1984.
9 Zybill C, Goryany V, Neumann M, Buch J, Römschmied M. New graphitised hss materials for rolls in finishing stands. Stahl und Eisen. 2015;135(10):61-64.
10 Feistritzer B, Schröder KH, Windhager M, Ziehenberger KH, inventors; Eisenwerk Sulzau-Werfen R, Weinberger AG, applicants. Casting material for indefinite rollers with a sleeve part and method for producing the same. WO 00/65118. 2000.
11 Paar A, Brandner M, Aigner M, Elizondo L, Trickl T. Anzeigen bei der Ultraschallprüfung von Verbund-IndefiniteWalzen und deren Ursachen. Giesserei Rundschau 2018;65(5):6-12.
12 Flament S, Walmag G, Lemaire M, Sinnaeve M. Development of a new grade for rear finishing stands based on modeling and evaluation of specific degradations. In: Proceedings of the AISTech 2017 Conference and Exposition; 2017 May 8-11; Nashville, USA. Warrendale: AIST; 2017. p. 2667-2676.
13 Nylén T. Niobium in cast iron. In: Proceedings of the International Symposium Niobium; 2001 Dec 2-5; Orlando, USA. Bridgeville, PA : Niobium 2001 Ltd., ©2002.; 2001.
14 Theisen W. Hartphasen. In: Berns HH, org. Hartlegierungen und Hartverbundstoffe. Berlin: Springer-Verlag; 1998. p. 28
15 Girschowitsch N. Kristallisation und Eigenschaften von Gußeisen in Gußstücken. Moskau: Verlag Maschinostroenie; 1996. 562 p.
16 ASM International. ASM handbook Vol. 3 - Alloy Phase Diagrams. Ohio: AST International; 1992.
17 Pavlina E, van Tyne C, Speer J. Effects of combined silicon and molybdenum alloying on the size and evolution of microalloy precipitates in HSLA steels containing niobium and titanium. Materials Characterization. 2015;102:35-46.
18 Cöl M, Koc F, Öktem H, Kir D. The role of boron content in high alloy white cast iron (Ni-Hard 4) on microstructure, mechanical properties and wear resistance. Wear. 2016;348-349:158-165.
19 Cen Q, Jiang Z, Fu H. Effect of Ti addition on the microstructure and properties of a high speed steel roll. Materials Testing. 2013;55(11-12):871-876.
20 Ciesla M, Ducki K. Effect of increased nitrogen content on the structrue and properties of tool steels. Journal of Achievements in Materials and Manufacturing Engineering. 2008;29(1):15-22.
21 Jonck J, Moema J, Jooste J, van Tonder P. Investigation of the ‘tiger skin’ defect on indefinite chill rolls. Journal of the Southern African Institute of Mining and Metallurgy. 2016;116:907-913.
22 van Kollenburg R, van den Elzen SM. Practical results of the next generation eddy current technology for roll inspection. In: Proceedings of the AISTech; 2016; Pittsburgh, USA. Warrendale: AIST; 2016.