Failure analysis used for remanufacturing of steel rolling components

Vol.12 Suppl 2J. CENT. SOUTH UNIV. TECHNOL.Oct.2005Article ID: 1005 - 9784(2005)S2 - 0030 - 04Failure analysis used for remanufacturing ofsteel rolling components"WANG Hai-dou(王海斗)，XU Bin-shi(徐滨士),WEI Shi-cheng(魏世丞) , ZHANG Xian-cheng(张显程) ,JIN Guo(金国), JIANG Yi(姜神)(National Key Laboratory for Remanufacturing, Beijing 100072, China)Abstract: The guide pieces, used in the process line of steel rlling. were the important components. The guidepieces, which were slide contacting with the rolled-piece, had a high temperature and high speed. The wear wasvery serious. The results from failure analysis showed that there were three failure forms in the guide-pieces: thefirst was the wear during heat friction, the second was the heat fatigue under the cycle of deep heating and deepcooling, and the third was the impact rupture. Among them, the wear was the main reason. To the wear of guidepieces, there were four mechanisms, namely abrasive wear, adhesive wear, fatigue wear and corrosion wear. Thefailure analysis to the guide-piece laid the foundation for its remanufacturing.Key words: guide-picces; failure analysis; remanufacturing; steel rlling; wearCLC number: TG174. 442Document code: AINTRODUCTIONerally by the steel wires, and were impacted by thesteel wires one by one when they entered into theThe guide-pieces are the important auxiliaryguide-pieces.device in the process line of steel rolling. It ismainly used to induce and grip the rolled- piece2 EXPERIMENTAL(steel wires) to pass through. There are 38 pairsof guide-pieces with different calibers in theThere are mainly three kinds of failure formsprocess line. The guide pieces analyzed in the pa-in the guide piecesl1. The first is the wear underper worked within No.5 and No. 6 rolling mills ofthe hot condition, the second is the thermal fatiguethe process line of steel rolling. The orifice shapecracks owing to the deep cooling and deep heating,of No.5 rolling mill is flat oval, and that of No. 6and the third is the impact rupture.rolling mill is edge oval, meaning that the guideWear is the most important failure form. In apieces must grip the steel wires that were twistedshort time, the wear values are more than the av-at 90° between the two rolling mills. The workingerage values. Some guide-pieces have the 3 mmcondition was very serious. In the condition, de-deep scars, see Fig. 1. The thermal fatigue cracksspite the guide-piece made by the chilled cast ironare from huge thermal stress due to the large tem-with high hardness (HRC63) and good wear-re-perature gradient, from the alternate action fromsistance, their wear is still serious. It was counteddeep cooling to deep heating， on the surface 0that the operating life of a pair of guide-piece wasguide- pieces. The thermal fatigue cracks can bonly up to 20 b1.seen in Fig. 2. After the occurrence of the thermalThe steel wires, passing through guide piecefatigue cracks, the performance of the guide pieceswith a high velocity of 6 s/m，has a high tempera-metal decreased rapidly. Impact rupture is the.ture (1 100 C). The contact between the guidemost severe failure form due to the continuous im-pieces and steel wires is the sliding contact withpact from steel wires to guide-pieces. If ruptured,high temperature and high speed. although cooledthe guide-pieces are unremanufacturable, seby water, the temperature of the guide piece sur-Fig.3face is as high as 600 - 800 C. Meanwhile accord-Among the three failure forms， the thermaling to the processing need, the process line of steelfatigue crack and impact rupture belong to the se-rolling is not a straight line, but the serpentine1nufactured, con-line. Therefore the guide pieces were pressed lat-trary中国煤化工-exces. The follow-YHCNMHGD Foundation item; Project(50235030) supported by the National Natural Science Foundation of ChinaReceived date: 2005 -07 - 12: Accepted date: 2005 - 08 - 08Correspondence: w ANG Hairdou, Associate Professor, PhD; Tel: +86-10-66718541; E mail: wanghaidou@ tsinghua. org. cnWANG Hai-dou, et al; Failure analysis used for remanufacturing of steel rlling components●31●ing is the failure analyses to the wear of guide-pieces.3 RESULTS AND DISCUSSIONFig. 4 and Fig. 5 are the worn surface andcrOss-. section morphologies of the guide-pieces re-Womn scarsspectively. In Fig. 4(a) it can be found that the fla-king off was serious. There had been flaking off inthe top half, and there would be flaking off in the._2cm_bottom half. The obvious fatigue cracks could beseen, meaning the fatigue wear was the main rea-Fig.1 Serious wear of guide piecesson of the guide pieces. Fig. 5 shows that the obvi-ous plastic yielding took place within the hard ce-mentite in the sub-surface of guide-pieces, furtherillustrating the serious fatigue wear. Meanwhilethe evident adhesive scars were on the worn sur-face. It can be thought that there occurs strong ad-hesive wear between guide pieces and steel wires.In Fig.4(b), mass of loose materials was on theThermal fatigue cracksguide pieces, illustrating the corrosion wear was2cmanother reason for the failure of guide- pieces. InFig. 4(c), the clear micro furrows could be seen onFig. 2 Thermal fatigue of guide-piecesthe surface, showing the abrasive wear to theguide-pieces.Therefore the wear modes of the guide-piecesincluded abrasive wear, adhesive wear, fatiguewear and corrosion wear.3.1 Influence from abrasive wearDuring the friction between guide pieces andsteel wires, there were much abrasive dusts, suchImpact ruptureas oxidation husks, caducous adhesive scars, andthe micro towers on the steel wires on the contactsurface. The wear of guide-pieces occurred due toFig. 3 Impact rupture of guide piecesthe composite action. Owing to the high tempera-9988625KV x608e8un99200825KV xi 0oP.89200725KV x1.00K 30um中国煤化工Fig.4 Worn surface morpholoI YHCNMHG(a)- -Flaking off from fatigue; (b)- - Loose surface from corrosion; (c)- Furrows trom abrasive wear●32●Journal CSUT Vol. 12 Suppl 2 2005strain fatigue. The appearance of the fatigue cracksaccelerated the fatigue wear. Meanwhile, duringthe course of smelting, many non-metal inclusionsHardened layerremained in the white cast iron. The inclusions ob-structed the metal's continuity, and then inducedthe stress concentration to result in fatigue cracks.3.4 Influence from corrosion wearThe recyeling water was used to cool theguide pieces. Thewater was the industrial waterPlastic deformationwith poor cleanliness and subacidity. When cycly-ing, the cooling water was continuously pollutedby different lubrication oils. The acidity and corro-sivity increased, and the destructiveness to guide-pieces increased too. In Fig. 4(b) the corrosionproduct was the loosen corrosion shape. The cor-_9um1rosion dissolution was dominant in the corrosionwear, showing the strong acidity of the coolingFig.5 Worn cross-section morphologywater.The guide-pieces were composed of chilledture of 600 - 800° on the surface of guide pieces,cast iron which had the multi-phase wear-resistancethe wear the abrasive dusts acting to the guide-containing carbides. In the corrosive medium con-pieces was not the micro-cutting and micro-furrowsisting of the acidic cooling water, due to the elec-at room temperature, but the typical thermaltrode potential of carbides was much higher thanwear. A thin layer of melting metal, like lubri-that of the substrate, the interphase corrosion cellcant, was produced at high temperature. Duringvas formed between the carbides and substrate,friction, the abrasive dusts and micro-towers actedand the "interphase corrosin?[9, 10] happened. Theas the scratching board to scratch some metal awaybonding between carbides and substrate was ruinedthe melting layer(2], resulting in the wear of theseriously. Under the mechanical action of abrasiveguide pieces acceleratedly.dusts or micro-towers, the carbides were easilyseparated from the substrate or ruptured them, so3.2 Influence from adhesive wearas to deteriorate the wear of guide-pieces. The ad-In Fig.5，on the surface of plastic yieldinghesion, oxide skin, or mirco-towers on steel wires,area, there was a strip of white zone. It's the .which played the role of abrasive dusts, all pos-white layer. The appearance of the white layersessed electric- activity. Therefore they formed theshowed that the frictional temperature on the sur-“metal materials and dusts galvanic couple corro-face of guide- pieces was over the critical tempera-sion ell"11, 12] together with guide-pieces. As theture[3.1. The thermal adhesive wear, namely theanode, the metal materials could be dis-second gluing, occurred.solved[3, 140.Once the occurrence of the second glueing, thelocal interfusion of metals appeared in the contact4 CONCLUSIONSarea between guidepieces and steel wiress.61.When the steel wires moved ahead, the interfusion1) As the important auxiliary device in thewas cut away, some metals stayed on the guide-process line of steel rolling, the guide pieces havepieces, and the others were brought away by steelbeen working in the serious condition of high tem-wiresperature, high velocity, corrosion, and so on. Itswear was severe.3.3 Influence of fatigue wear2) There were mainly three kinds of failureThe fatigue cracks of strain fatigue resultedforms in the guide-pieces. The first was the wearfrom the great plastic deformation. In the area ofunder the hot condition, the second was the ther-the crack's burgeoning and enlarging, the obviousmal fatigue cracks owing to the deep cooling andplastic deformation could be seen. The dominantdeep heating, and the third was the impact rup-course of the strain fatigue was the crack's enlarture中国煤化工wear, the guide-ging perid'.8.piecMHCNMHG。; included abrasiveThe chilled cast iron possessed good hardnessat room temperature, but the plasticity was poor.wear, adhesive wear, fatigue wear and corrosionThus, the guide-pieces were easily subject to thewear. .WANG Hai-dou, et al; Failure analysis used for remanufacturing of steel rlling componentsAcknowledges[8] Magalha SeabraJ, Sa C. Experimental observations ofThe authors are grateful to Prof. Tan Ye-fa,contact fatigue crack mechanisms for austempered duc-tile iron (ADI) discs [J]. Wear,2000, 246(1 - 2):from Nanjing Engineering Institute, for his help in134- 148.microscopic analysis.[9] ZhangSY, LiSJ, LuoX W, Zhou W F. 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