电站锅炉冲蚀磨损机理及材料防磨性能的试验研究
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摘要
燃煤电厂锅炉的“四管”泄露问题是影响电厂安全、经济运行的主要原因。其中因对流受热面被飞灰冲蚀磨损引起的泄漏问题占锅炉事故的60％以上。因此，冲蚀磨损问题一直是亟待锅炉行业研究解决的重要课题之一。影响冲蚀磨损的因素很多，材料也是极其重要的一个方面。为了提高管道材料的冲蚀磨损性能，文中通过对锅炉对流受热面的的常用钢材20碳钢和12Cr1MoV合金钢C-N共渗和离子渗N热处理后进行热态飞灰冲蚀磨损试验，以探求这两种热处理方法对提高材料耐磨性能的可能性。
试验结果表明：C-N共渗热处理后，20碳钢耐磨性提高，磨损量减小一半以上，分析其原因是20碳钢表面由于形成了致密而不易脱落的C-N渗层，且组成相晶粒细小，提高了表面硬度，起到保护材料的作用；12Cr1MoV合金钢的耐磨性则未改变，磨损量与未处理时相近，甚至在高温段还比未处理时增大，原因是其表面会形成一种黑色残余奥氏体的非马氏体转变产物，正是这种转变物的存在引起合金钢组织和硬度的不稳定，导致其抗磨损性能并没有得到提高；离子渗N热处理后，两种材料的耐磨性均未显著提高；约490℃之前，磨损率比未热处理时的试验值高，约490℃之后磨损率才低于未热处理时的试验值。分析其原因，是由于形成在两种材料表面的氮化层很脆薄，受冲刷很容易分解脱落，导致前期磨损很大；进一步研究也表明，20碳钢表面形成网状和带状化合物组织，导致材料的耐磨与抗疲劳性能降低；而12Cr1MoV合金钢金相组织中存在大小不一的黑色斑点，这些都是可能导致耐磨性降低的主要原因。
试验中得出，C-N共渗和离子渗N热处理后，两种材料的表面硬度均有所提高。但从试验结果可以看出，硬度增大并非一定会提高材料的耐磨性。材料的耐磨性还与材料本身的性能、热处理工况，材料表面等诸多因素有关。
The "four pipes" leaking of power boilers in coal-fired power plants greatly influence their safely and economically operating. Among these kinds of problems the leaking caused by flying-ash erosion on the contra-flow heated side covers sixty percentages. So the resolve of erosion problems is quite a subject in power boiler industry. There are lots of factors affecting erosion, among which the factor of materials matter a lot. In order to improve the anti-erosion performance of pipe materials, 20 Carbon steel and 12Cr1MoV alloy steel, the common materials used in contra-flow heated side of power boilers, have been carbonitrided and ionodialysized. Then they were tested by flying-ash erosion to find the possibility of improving the anti-eroding performance of materials through these two heat-treating methods.
The results of testing demonstrated such achievements as follow:
After the process of carbonitriding, the wear-resisting property of 20 Carbon steel increased and the wear extent reduced by more than half. The reason is C-N layer produced on the surface of 20 Carbon steel are rigid and not easy to be uncovered, which protect materials very well. The wear-resisting property of 12CrlMoV alloy steel has not changed. Wear extent was as much as the one without being heat treated, and even increased in high temperature stage. The reason is that the black remains of austenitic transmuted to non-marten site on the surface. These transmuting products made the structure and rigidity of alloy steel unsteady, which make the wear-resisting property unchanged. After plasma nitriding, the wear-resisting property of these two materials didn't change. Under the condition of below 490℃, the rate of wear is higher than that without being heat treated, and when over 490℃the rate is lower. This is because the nitration case on the surface of these two materials is thin and easy to break up after being brushed. And wear extent enlarged at the beginning.
Deeper research shows that the structures of reticular and ribbon compound on the surface of 20 Carbon steel made the wear-resisting and fatigue-resisting properties low. And there existed different size blank pots in the structure of 12Cr1MoV alloy steel, which may be the main reason why the wear-resisting property declined.
The conclusion from the research is that the surface hardness of two materials is also enhanced after Carbonitriding and Plasma Nitriding.However, which we can see from the experiment is that the enhancement in hardness can not always improve the wear-resistance of materials. The wear-resistance has relation to the performance of itsself、the condition of heat treatment、the surface of materials and so on.
试验结果表明：C-N共渗热处理后，20碳钢耐磨性提高，磨损量减小一半以上，分析其原因是20碳钢表面由于形成了致密而不易脱落的C-N渗层，且组成相晶粒细小，提高了表面硬度，起到保护材料的作用；12Cr1MoV合金钢的耐磨性则未改变，磨损量与未处理时相近，甚至在高温段还比未处理时增大，原因是其表面会形成一种黑色残余奥氏体的非马氏体转变产物，正是这种转变物的存在引起合金钢组织和硬度的不稳定，导致其抗磨损性能并没有得到提高；离子渗N热处理后，两种材料的耐磨性均未显著提高；约490℃之前，磨损率比未热处理时的试验值高，约490℃之后磨损率才低于未热处理时的试验值。分析其原因，是由于形成在两种材料表面的氮化层很脆薄，受冲刷很容易分解脱落，导致前期磨损很大；进一步研究也表明，20碳钢表面形成网状和带状化合物组织，导致材料的耐磨与抗疲劳性能降低；而12Cr1MoV合金钢金相组织中存在大小不一的黑色斑点，这些都是可能导致耐磨性降低的主要原因。
试验中得出，C-N共渗和离子渗N热处理后，两种材料的表面硬度均有所提高。但从试验结果可以看出，硬度增大并非一定会提高材料的耐磨性。材料的耐磨性还与材料本身的性能、热处理工况，材料表面等诸多因素有关。
The "four pipes" leaking of power boilers in coal-fired power plants greatly influence their safely and economically operating. Among these kinds of problems the leaking caused by flying-ash erosion on the contra-flow heated side covers sixty percentages. So the resolve of erosion problems is quite a subject in power boiler industry. There are lots of factors affecting erosion, among which the factor of materials matter a lot. In order to improve the anti-erosion performance of pipe materials, 20 Carbon steel and 12Cr1MoV alloy steel, the common materials used in contra-flow heated side of power boilers, have been carbonitrided and ionodialysized. Then they were tested by flying-ash erosion to find the possibility of improving the anti-eroding performance of materials through these two heat-treating methods.
The results of testing demonstrated such achievements as follow:
After the process of carbonitriding, the wear-resisting property of 20 Carbon steel increased and the wear extent reduced by more than half. The reason is C-N layer produced on the surface of 20 Carbon steel are rigid and not easy to be uncovered, which protect materials very well. The wear-resisting property of 12CrlMoV alloy steel has not changed. Wear extent was as much as the one without being heat treated, and even increased in high temperature stage. The reason is that the black remains of austenitic transmuted to non-marten site on the surface. These transmuting products made the structure and rigidity of alloy steel unsteady, which make the wear-resisting property unchanged. After plasma nitriding, the wear-resisting property of these two materials didn't change. Under the condition of below 490℃, the rate of wear is higher than that without being heat treated, and when over 490℃the rate is lower. This is because the nitration case on the surface of these two materials is thin and easy to break up after being brushed. And wear extent enlarged at the beginning.
Deeper research shows that the structures of reticular and ribbon compound on the surface of 20 Carbon steel made the wear-resisting and fatigue-resisting properties low. And there existed different size blank pots in the structure of 12Cr1MoV alloy steel, which may be the main reason why the wear-resisting property declined.
The conclusion from the research is that the surface hardness of two materials is also enhanced after Carbonitriding and Plasma Nitriding.However, which we can see from the experiment is that the enhancement in hardness can not always improve the wear-resistance of materials. The wear-resistance has relation to the performance of itsself、the condition of heat treatment、the surface of materials and so on.
引文
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[21] HUTCHINGS. I. M. Amodel for the orosion of metals by spherical particles at normal incidence[J]. Wear 1981(70): 269～281
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[2] 赵宪萍，孙坚荣．15CrMo合金钢热态飞灰冲刷磨损性能的试验研究[J]．动力工程，2000，20(2)：645～649．
[3] 赵宪萍，徐开义，孙家庆等．不同温度下金属氧化膜对灰磨损性能的影响[J]．华东工业大学学报，1996，18(1)：73～79．
[4] 石奇光，马庆，飞灰冲刷角度变化对锅炉常用钢材磨损影响的实验研究[J]．上海电力学院学报，1996，12(1)：1～7．
[5] 赵宪萍，邹辉荣等．12Cr1MoV合金钢热态飞灰冲刷磨损性能的试验研究[J]．热能动力工程，2000，89(15)：502～508．
[6] 张平．热喷涂材料[M]．北京：国防工业出版社，2006：327～328．
[7] XU Lianyong. High-Temperature Corrosion of Protective Coatings for Boiler Tubes in Thermal Power Plants[J]. Transctions of Tianjin University, 2005, 11(3): 183～189.
[8] 姚梅．防止电厂锅炉管道腐蚀和磨损的新技术[J]．江西电力职业技术学院学报，2004，17(4)：92～95．
[9] 胡军志，马世宁．几种高速电弧喷涂层高温冲蚀磨损性能[J]．焊接学报，2005，24(6)：102～105．
[10] Swanekamp, Robert. Thermal-spray coating tames CFB erosion[J]. Power, 1995, 139(8): 458～464.
[11] B. Q. WANG, M. W. Seitz. Comparison in erosion behavior of iron-base coatings sprayed by three different arc-spray processes[J]. WEAR, 2001, 250(31): 755～761.
[12] T. Sundararjan, H. Haruyama. Steam oxidation resistance of thermal sprayed coatings for USC boiler applications[J]. Surface Engineering, 2005, 21(3): 349～359.
[13] V. Rohr, A. Donchev. Diffusion coatings for high temperature corrosion protection of 9～12％Cr steels[J]. Corrosion Engeering,Science and Technoligy, 2005, 40 (3): 632～641.
[14] Strunger. J. Practical experience with wastage at elevated temperatures in coal combustion systems[J]. Wear,1995, 27(3): 203～204.
[15] 马颖，任峻等．冲蚀磨损研究的进展[J]．兰州理工大学学报，2005，31(1)：21～25
[16] FINNIE. I. On the velocity dependence of the erosion of ductile metals by solid particles at low angles of incidence[J].Wear, 1978(48): 181～190.
[17] BITTER J G. A study of erosion phenomena[J]. Wear,1963(6): 5～21.
[18] 邵荷生，曲敬信．摩擦与磨损[M]．北京：煤炭工业出版社，1992．
[19] 董刚，张九渊．固体粒子冲蚀磨损研究进展[J]．材料科学与工程学报，2003，21(2)：307～312．
[20] TILLY G P. A stage mechanism of ductile erosion[J]. Wear, 1973(23): 87～96.
[21] HUTCHINGS. I. M. Amodel for the orosion of metals by spherical particles at normal incidence[J]. Wear 1981(70): 269～281
[22] 刘英杰，成克强．磨损失效分析基础[M]．北京：机械工业出版社，1991．
[23] 陈冠国，张宏亮．关于冲蚀磨损问题[J]．河北理工学院学报，1997，19(4)：56～61．
[24] 张永清．韧性材料冲蚀磨损的机理研究[J]．上海交通大学学报，1989，23(3)：156～162．
[25] M．M．Stack等．高温下合金冲蚀腐蚀机理的探讨[J]．上海电力学院《译文选编》，1995年第1期．
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