New Method for Evaluating Thermal Wear of Rolls in Rolling Process

Available online at www.sciencedirect.comScienceDirectJOURNAL OF IR0N AND STEEI. RESEARCH, INTERNATIONAL. 2008, 15(6); 52-55New Method for Evaluating Thermal Wear of Rolls in Rolling ProcessLI Chang-sheng, LIU Xiang-hua, WANG Guo-dong(State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 10004, Liaoning, China)Abstract: A new method was developed by a thermal wear machine to evaluate the thermal wear of rolls in steel roll-ing process. The steel strip and rolls were simulated by upper and lower heating disks. The upper heating disk couldbe kept at a temperature of over 900 C by induction heating. The pressure between the disks as high as 323.2 MPacould be achieved and the slpping rate could be 12. 7%. The thermal wear of high speed steel (HSS) roll material, the wearrate of the HSS rll, and the SEM morphology of a worn HSS roll surface were investigated. This method was usefuland could be employed to simulate friction and wear between strip and roll during the strip rolling process.Key words; thermal wear; roll; friction; strip rolling; induction heatingThe roll is one of the most important tools in However, this equipment was a mill and the work-the rolling process. Its surface may get worn out be-piece that needed to be heated and rolled for stud-cause of the relative slip between the roll surface andying the frictional wear. Thus, for some workpieces,steels for the fast changes in both rolling force andit was almost impossible to study the wear under differ-temperature. In designing and calculating the wearent slipping rate and load for a long period.crown of rolls, the roll wear is a very important fac-In this paper, the thermal wear test method istor and has to be taken into consideration, as it candeveloped, which is a disk-like machine. The upperreduce the difficulty in controlling steel shape andand lower disks are used to simulate the workpieceincrease the accuracy in the calculation model of theand the roll, respectively. The upper disk can beroll wear crown. Furthermore, the wear of the rollheated up to 900 C through an induction coil. Thsurface will directly affect the surface quality ofload can be exerted as high as 323. 2 MPa betweensteel. Therefore, it is significant to develop an appro-disks, and the maximum slippage ratio is 12. 7%.priate method to evaluate the roll wear and to study the1 Principlemechanism of roll wear based on friction theory.To date, many studies have been carried out con-To evaluate the thermal wear of rolls, a newcerning roll wear. For example, Kato'1] developed atest machine was developed, which was disk-like onthermal wear equipment, which is a disk- shaped ma-the basis of the 2-high φ160 mm mill, The disk,chine. However, it is difficult to simulate the weardrive shaft, bearing block, and forcing equipmentbetween steel and roll during the rolling process, aswere designed and manufactured, and the inductionthe disk is small and thin, and the load is not veryheating equipment was designed with a special shapelarge. Guo et alL2] and Li et al(3] studied the thermalto heat the upper disk where the temperature couldwear attribution of wear-resistant materials 9Cr2reach higher than 900 C. The upper and lower disksand 3Cr2W8V, and the thermal wear equipmentcould be used to simulate the workpiece and the rollsthey used was a pin-disk machine, which could notduring hot rolling, respectively. The ratio of thebe used to simulate the thermal wear of the roll. Li-slip between disks could be determined by the for-aoleJ used a small mill to roll the wire and studiedward slip. The lower disk with different embeddedthe thermal wear of the roll with high Cr cast iron,mate中国煤化，工tudy the wear of the.Foundation Item :Item Sponsored by National Natural Science Foundation of ChinaMYHCNMHGBlography: LI Chang-sheng(1964-), Male, Doctor, Professort E-mail: lics@ral neu. edu. cn; Revised Date; June 3, 2007Issue 6New Method for Evaluating Thermal Wear of Rolls in Rolling Process,53●roll under some rlling condition.The original 2-high $160 mm mill consists ofmotor-driven equipment, a reducer, and junctor.The devices to be designed are disk, shaft, bearingblock, forcing equipment, balancing spring, end3cap, cushion ring, junction box, back plate, and soon. The high- frequency induction equipment is de-signed as a special heating mode. (1) The dimensionof the upper disk is φ160 mmX 30 mm and that ofthe lower disk is φ160 mmX 50 mm. The disk mate-rial is 45 steel and the dimension of the experimentalroll material is $10 mmX 10 mm, which is embeddedon the periphery of the lower disk. (2) The materialof the drive shaft is 40Cr steel which is hollow for1- High frequency power source; 2- -Induction heater;water cooling. The bearing block, the forcing equip-3 Upper disk; 4- -Lower disk;ment, and the balancing spring are also designed.5 Water box; 6- Water pumpFor this purpose, the GP10-C1 high-frequencyFig 1 Schematic ilustration of thermal wear testerinduction apparatus is employed, and the inductionpower source and the parameters are listed in Table 1.conductor material is T1 or T2 pure copper tube andThe surface of the inverse upper disk is heated the dimension is中10 mmX1 mm.by the GP10 C1 induction power source according to2 Experimentalthe theory of skin effect of electromagnetic inductionheating. The induction coil is specially designed as aTo test the validity of the machine perform-semicircle for a continuous heating of the inverse up- ance, roll material of high speed steel (HSS) wasper disk. The experimental setup for testing thermalembedded in the lower disk[5- 门]。 The chemical com-wear including the heater and water cooling system position of the roll material ( mass percent) is listedof the disks is schematically ilustrated in Fig. 1. Thein Table 2. The original hardness of the experimen-tal material was HRC 51.3 measured by HR-150ATable 1 Parameters of GP10-C1 high-frequencyRockwell hardometer.induction apparatusThe worn amount of HSS roll material underItemsParameter valuedifferent loads and slipping rate was measured usingMaximum fluctuating power10 kWthe SARTORINS BS1 10S electronic balance afterGenerated frequency500- 1 000 kHzcleaning and drying. The morphology of the wornSupply source and consumed power 15 kVA (50 Hz/3q380 V)surface of the specimen was observed through aMaximum electric currents for source 30 Ascanning electron microscope (PHILIPS 505).Table 2 Chemical composition of the materials%M:sisNiCVMo.40.34 0. 260. 0120.025.13.92 0. 753.34 2. 830.12the oxide layer[9-11] did not occur in this experi-3 Results and Discussionment. It could be seen that the wear ratio curve in-The wear ratio curve is presented in Fig. 2, whichcreased with increasing slippage and loads. Loadsindicates the wear ratio as a function of cycles forplayed a more important role than slipping rate forspecimen in different slipping rates of S= 4.8% - -effects were ob-12. 7% and loads of σ= 141.5- 323.2 MPa. In theserve中国煤化工icred slightyexperiment, the temperature of the upper disk wasbeforTYHCNMHGcouldbethatthe900 C，at which the wear was most severe-'l.roll surface was protected from wearing by the thinHowever, a decrease in the thermal wear owing toblack oxide layer generated on it.54●Journal of Iron and Steel Research, InternationalVol. 15HSS roll surface for increased loads, and the wear0.08■S=4.8%, σ=1415 MPa●S=9.6%, σ= 143.4 MPamechanism is of oxidation wear grain-abrasion▲S=12.7%, σ=144.7 MPawear, and adhesive wear at the same time,0.06 t●S-4.8%, σ=316.4 MPa●S=9.6%, σ=320.7 MPaThe effect of abrasion occurs in contact situa-* S=12.7%, σ=323.2 MPation where direct physical contact between two sur-0.04faces is given, and one of the surfaces is considera-bly harder than the other. The harder surface asperi-0.02ties press into the other suface with plastic flow of thesoft surface occurring around the asperities of the hardersurface. When a tangential motion is imposed on theo1 5004500750010 500harder surface, the soft material is removed becauseCycles/rof the combined effect of“micro-ploughing”,“ mi-Fig.2 Wear ratio of the high speed steel rollcro cutting”", and“micro-cracking".The adhesive wear processes are initiated by theThe microstructure of the HSS roll surface hasinterfacial adhesive junctions, which form when sol-been investigated under different rotational speedsid materials come into contact on an atomic scale. Itof the roll between the lower disk at 530 一580 Cis evident that the adhesive wear mechanisms are in-and the upper disk at 880- 930 C. Fig. 3 shows thefluenced by a number of properties of the contactingSEM morphology of the HSS surface under variablesolids. Obviously the process and parameters of ad-rotational speeds when the slipping rate S is 12. 7%hesion as well as those of the fracture must be takenand the load σ is 323. 2 MPa. From Fig.3 (a), it caninto acount, as both the adhesion and fracture arebe seen that there is oxidized frictional wear on the HSSaffected by surface contaminants and environment.roll surface. From Fig.3 (b) and Fig.3 (c), it can beIt is quite difficult to relate adhesive wearseen that it forms grain-abrasion of the cavity forprocesses with elementary bulk properties of materi-the oxide dropping as the rotational speed increases.als. The oxidation wear occurs because of high tem-Fig. 3 (d) shows that there is adhesive wear on theperature of the roll, The oxide is diffused in the matrix.5 um中国煤化工(a) 840 cycles; (b) 1 680 cycles (c) 33HCNMHGFig. 3 SEM morphology of HSS roll surface wearIssue 6New Method for Evaluating Thermal Wear of Rolls in Rolling ProcessThe black oxide layer is exfoliated from the roll sur-2] GUO Xin-cheng. ZENG Qing mei, SHU Delin. Hot Wear andThermal Fatigue Properties of Several Roll Materials [J]. lronface. Plasticity deformation slippage wear is causedand Steel, 1992, 27(11): 37 (in Chinese). .by the deformation of the roll surface and the rela-3] LI Zhi, QU Jing xin, ZHOU Ping-an. Dry Friction Slidingtive motion between the strip and roll.Wear of 3Cr2W8V Steel Under High Temperature and HighLoad [J]. Jourmal of lron and Steel Research, 2000, 12(4):4 Conclusions36 (in Chinese).(1) A new method was developed to test the[4] LIAO Qian- chu, CU1 Pei yong. A Device for Simulating Studyon Roll Wearing Process in Hot Rolling With In-Situ SEM Obroll's thermal wear by a test machine with a diskservation [J]. Iron and Steel, 1990, 25(9): 46 (in Chinese).pattern. High-frequency induction equipment was5] LI Chang sheng. Investigation on Characteristics of Rolls Surused to heat the upper disk. The temperature of theface in HoL Strip Mill [D]. Shenyang: Northeastern UniversityPress, 2001 (in Chinese).disk could be over 900 C.6] LiCs, XuJZ, He X M, et al. Formation and Control for(2) The thermal wear of the high speed steelStrip Scale Pores in Hot Rolling [J]. J Mater Process Technol,roll was investigated. The wear rate curve and the2001, 116(2-3); 201.SEM morphology of the HSS roll surface wear were [幻] Lics, LiuX H. XuJZ, etal. FEM Analyis of Stes onRoll Surface Black Oxide Layers Exfoliation in Hot Strip Roll-obtained.ing [J]. Mater Eng and Performance, 2002, 11(2): 215.(3) It is useful to investigate the mechanism of8] Lundburg, Sven-erik, Gustafsson. Influence of Rolling Tem-roll wear in strip steel rolling process by this method.perature on Roll Wear, Investigated in a New High Tempera-ture Test Rig [J]. J Mater Process Technol, 1994, 42(5):The authors would like to thank the National239] WANG Jiu-bin, LI Qing-chun. Wearing Behavior of High CrNatural Science Foundation of China ( Grant No.Cast lron Roll Caused by Rolling and Sliding Movement [J].50534020) and the Shanghai Baosteel Group forIron and Steel Research, 1994, 77(2); 24 (in Chinese) .their financial support.[10] GAO Cairqiao. Friction Metallography [D]. Harbin: Press ofHarbin lnstitute of Technology, 1988 (in Chinese).References:[11]LUO Hong, LIU Jian-jun, ZHANG Zhi-jun. Sliding Abrasive[1] Kato Osamu. Mechanisms of Surface Deterioration of Roll forWear Characteristics of Steels With Different Hardness [J].Hot Strip Rolling UJ]. ISU International, 1992, 32(11); 1216.Tribology, 1994, 14(3); 213 (in Chinese).中国煤化工MYHCNMHG