Due to the intro protection layer, in the process of the self-protective paste boronizing,parts local boronisation can be achieved. When the boron temperature decreased effectively, the economizer steel pipe’s online instant boronisation could be achieved and this technology can be applied to the strengthening treatment of the surface of other boiler heat pipes and other high- temperature resistant and corrosion resistant parts. 4 conclusion With no rare earth added, self-protective paste boronizing can only be carried out when the temperature was over 800 . Within a certain range, rare earth could speed up the boronisation and ℃ make the boronizing layer be well-distributed and closely integrated. Therefore, the binding force between the boronizing layer and matrix was increased and the performance of the steel pipe was improved. Rare earth was used to assist boron, when the boriding technology was properly handled, the temperature of the economizer self-protective paste borinisation can be decreased to 700 , the ℃ addition of 9wt％ rare earth could achieve good boron effect. The protective paste in which quartz powder, the covering layer of fly ash and coal gangue were as the main ingredients, has the characteristics of high strength, good sealing and easy peeling in boronizing temperature, could also achieve good boron effect. Acknowledgements This research supported by national natural science foundation of China(51275058) and Hunan provincial natural science foundation of China（09JJ3097）. References [1] W.L. Cheng, Y. Zhou, A Model to be Used for Monitoring the Wear of Boiler Economers, Power Engineering, 26（2006）646–649. [2] J.M. Ye, Power plant boilers principle and equipment, China Electric Power Press, Beijing, 2004. [3] W.P. Yan, Y.Z. Liu, Y.H. Gao, Comparing Study on Styles of Exetended Heating Surfaces of Economizers in Utility Boilers, Boiler Technology, 37(2006) 26-30 [4] X.H. Yi, F.H. Li, Z.G. Fan, Technology for Solid- State Pack Boronizing of Q235 Steel and Kinetic Study of Boron Diffusion in Steel, MATERIALS PROTECTION,42（2009）13-16. [5] J.S. Hu, Z.Y. Li, J.M. Hao et al., Development and applications of self-protective boronising paste based on thermodynamic analysis, Ordnance Material Science and Engineering, 25 （2002）38-40. [6] S.Roumiana, Petrova, S. Naruemon., S. Veljko, The Effect of Boronizing on Metallic Alloys for Automotive Applications, Journal of Materials Engineering and Performance, 17(2008) 340-345. [7] D.C. Loua, J.K. Solbergb, O.M. Akselsena, N. Dahlc, Microstructure and Property Investigation of Paste Boronized Pure Nickel and Nimonic 90 Superalloy, Materials Chemistry and Physics, 115 (2009) 239-244. [8] X.M. Ou, Z.Y. Ni, Study and Analysis on Process of Paste Boronization Without Boxing, Journal of China University of Mining & Technology, 27(1998)200-203. [9] Y.Z Gong, L.D. Zhang Research on Self-protective Rare Earth-Boronizing Pasty Agent[J]. ELECTRONICS PROCESS TECHNOLOGY, 7(2001) 161-165. [10] J.S. Hu, Z.Y. LI, J.M. Hao, et al. Application and Thermodynamic Analysis on Self-Shield Boronizing Pasty, HEAT TREATMENT OF METALS, 27(2007) 26-28. [11] Z.S. Ji, Multivariate Boronizing Technology and Applications, Metallurgical Industry Press, Beijing,2004. [12] I. Campos, M. Islas, E. González, et al.. Use of fuzzy logic for modeling the growth of Fe2B boride layers during boronizing, Surface & Coatings Technology, 201(2006)2717-2723.
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