含有Cu、Mo、Sn的高强度蠕墨铸铁的蠕变行为
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摘要
研究了一种含有Cu、Mo、Sn的高强度蠕墨铸铁在623～823 K、40～150 MPa的蠕变行为,观察了不同形态的蠕变损伤组织并分析了蠕变变形及断裂机理。当T/Tm>0.5(T为使用温度,Tm为蠕墨铸铁熔点)、载荷大于150 MPa时这种蠕墨铸铁的蠕变变形显著,且变形主要来自基体变形、蠕变空洞的形核长大以及石墨/基体界面的开裂。随着温度的提高和载荷的增加,蠕变变形逐渐由晶界移动转变为晶内变形。在蠕变过程中有两种开裂机制:(I)微裂纹在石墨/基体开裂处形核长大并优先沿铁素体向基体扩展,与邻近石墨/基体开裂连接而逐渐形成主裂纹;(II)晶界处的蠕变空洞形核长大转变成蠕变裂纹。氧原子通过石墨的连通性向组织内部扩散,造成上述两种裂纹表面氧化。由于,石墨、铁素体、珠光体三者性能的差异,石墨/铁素体界面比石墨/珠光体界面更易发生开裂。另外,在773 K、823 K组织中的珠光体分解明显,层片状渗碳体逐渐转变为短棒状,在晶界附近则以颗粒状为主。
The creep behavior of a high strength compacted graphite cast iron(CGI) containing Cu,Mo and Sn under tensile load of 40～150 MPa in air at 623～823 K was investigated, while the creep damage was observed and the relevant mechanism of deformation and fracture during creep test was further analyzed. When the ratio T/Tm>0.5(T represents test temperature, Tm melt point of CGI) and the load is greater than 150 MPa, the creep deformation is significant. The creep deformation consists of matrix deformation, initiation and development of creep cavities at grain boundaries and debondings of the interface graphite/matrix. With the increasing temperature and tensile load, the creep deformation is gradually changing from grain boundary sliding to intragranular deformation. Two kind of cracks were observed in the microstructure of CGI:(1) cracks propagated preferentially in ferrite phase and connected with adjacent debondings of the interface graphite/matrix,(2) microcracks caused by nucleation and growth of creep cavities along grain boundaries. It is worthy to mention that the 3D network of the vermicular graphite in CGI may facilitate the inward diffusion of oxygen atoms throughout the sample of CGI, therewith induces the oxidation of the above mentioned two type cracks. Due to the difference in properties between graphite with ferrite and pearlite respectively, the debonding occurance for the inerface of graphite/ferrite may be easier than that of graphite/pearlite. In addition, pearlite in the microstructure may decompose significantly at 773 K and 823 K for 100 h, as a result, the lamellar cementite should be converted to short rods and granules at grain boundaries.
The creep behavior of a high strength compacted graphite cast iron(CGI) containing Cu,Mo and Sn under tensile load of 40～150 MPa in air at 623～823 K was investigated, while the creep damage was observed and the relevant mechanism of deformation and fracture during creep test was further analyzed. When the ratio T/Tm>0.5(T represents test temperature, Tm melt point of CGI) and the load is greater than 150 MPa, the creep deformation is significant. The creep deformation consists of matrix deformation, initiation and development of creep cavities at grain boundaries and debondings of the interface graphite/matrix. With the increasing temperature and tensile load, the creep deformation is gradually changing from grain boundary sliding to intragranular deformation. Two kind of cracks were observed in the microstructure of CGI:(1) cracks propagated preferentially in ferrite phase and connected with adjacent debondings of the interface graphite/matrix,(2) microcracks caused by nucleation and growth of creep cavities along grain boundaries. It is worthy to mention that the 3D network of the vermicular graphite in CGI may facilitate the inward diffusion of oxygen atoms throughout the sample of CGI, therewith induces the oxidation of the above mentioned two type cracks. Due to the difference in properties between graphite with ferrite and pearlite respectively, the debonding occurance for the inerface of graphite/ferrite may be easier than that of graphite/pearlite. In addition, pearlite in the microstructure may decompose significantly at 773 K and 823 K for 100 h, as a result, the lamellar cementite should be converted to short rods and granules at grain boundaries.
引文
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[17] Kachanov L M. On Creep Rupture Time[A]. Proceeding of the Academy Sciences of USSR, 1958, 8, p 26-31
[18] Rabotnov Y N, Leckie F A, Prager W. Creep Problems in Structur‐al Members[J]. Journal of Applied Mechanics, 1969, 37(1):249
[19] Wu X J, Quan G, MacNeil R, et al. Thermomechanical fatigue of ductile cast iron and its life prediction[J]. Metallurgical and Mate‐rials Transactions A, 2015, 46:2530
[20] Wu X J. A model of nonlinear fatigue-creep(dwell)interactions[J].Journal of Engineering for Gas Turbines and Power, 2009, 131:032101-1-032101-6
[21] Wu X J, Quan G, MacNeil R, et al. Failure mechanisms and dam‐age model of ductile cast iron under low-cycle fatigue condi‐tions[J]. Metallurgical and Materials Transactions A, 2014, 45(11):5085
[22] Wu X J, Williams S, Gong D. A true-stress creep model based on deformation mechanisms for polycrystalline materials[J]. Journal of Materials Engineering and Performance, 2012, 21(11):2255
[23] Jing G X, Zhang S Y, Fu W Q, et al. Loading characteristics of cast iron cylinder head for high-strengthened diesel engine[J]. Vehicle Engine, 2017,(01):42(景国玺,张树勇,付文清等.高强化柴油机铸铁缸盖承载特性研究[J].车用发动机, 2017,(01):42)
[24] Chen I W. Cavity growth on a sliding grain boundary[J]. Metallur‐gical Transactions A, 1983, 14(11):2289
[25] Frost H J, Ashby M F. Deformation Mechanism Maps[M]. Per‐gamon Press, 1982
[26] Wu Y, Li J P, Zhang Y J, et al. Effect of heat treatment on mechani‐cal properties and thermal conductivity of RuT300 vermicular graphite cast iron[J]. Transactions of materials and heat treatment,2017,(02):143(武岳,李建平,张延京等.热处理工艺对RuT300蠕墨铸铁力学性能与导热性能的影响[J].材料热处理学报, 2017,(02):143)
[2] Yang Z, Tao D, Guo Y C, et al. Effect of multi-component microalloying on microstructure and properties of compacted graphite cast iron[J]. Foundry, 2014,(02):115(杨忠,陶栋,郭永春等.多元低合金化对蠕墨铸铁组织与性能的影响[J].铸造, 2014,(02):115)
[3] Moonesan M, HonarbakhshRaouf A, Madah F, et al. Effect of al‐loying elements on thermal shock resistance of gray cast iron[J].Journal of Alloys and Compounds, 2012, 520(Supplement C):226
[4] Imasogie, B I Microstructural features and mechanical properties of compacted graphite iron treated with calcium-magnesium based master alloy[J]. Journal of Materials Engineering and Perfor‐mance,2003, 12(3):239
[5] Ghodrat S, Janssen M, Kestens L A I. et al. Volume expansion of compacted graphite iron induced by pearlite decomposition and the effect of oxidation at elevated temperature[J]. Oxidation of Metals, 2013, 80(1-2):161
[6] Dawson S. Compacted graphite iron-a material solution for mod‐ern diesel engine cylinder blocks and heads[J]. Foundry Technolo‐gy, 2009,(04):455(史蒂夫·道森.蠕墨铸铁—现代柴油发动机缸体和缸盖的材料[J].铸造技术, 2009,(04):455)
[7] Yuan Y L, He G Q, Fan K L, et al. Low cycle fatigue behavior of gray cast iron used for engine[J]. Chinese journal of materials re‐search, 2013,(05):469
[8] Selin M. Tensile and thermal properties in compacted graphite irons at elevated temperatures[J]. Metallurgical and Materials Transactions A, 2010, 41(12):3100
[9] Qiu Y, Pang J C, Yang E N, et al. Transition of tensile strength and damaging mechanisms of compacted graphite iron with tempera‐ture[J]. Materials Science and Engineering:A, 2016, 677(Supple‐ment C):290
[10] Qiu Y, Pang J C, Li S X, et al. Influence of thermal exposure on microstructure evolution and tensile fracture behaviors of compact‐ed graphite iron[J]. Materials Science and Engineering:A, 2016,664(Supplement C):75
[11] Ma Z J, Tao D, Yang Z, et al. The effect of vermicularity on the thermal conductivity of vermicular graphite cast iron[J]. Materials and Design, 2016, 93:48
[12] Zhang J S. High temperature deformation and fracture of materi‐al[M]. Beijing:Science Press, 2007:3(张俊善.材料的高温变形与断裂[M].北京:科学出版社,2007:3)
[13] Tu S D, Xuan F Z, Wang W Z. Some critical issues in creep and fracture assessment at high temperature[J]. Acta metallurgica sini‐ca, 2009,(07):781(涂善东,轩福贞,王卫泽.高温蠕变与断裂评价的若干关键问题[J].金属学报, 2009,(07):781)
[14] Norton F H. The Creep of Steel at High Temperatures[M]. Mc‐Graw-Hill, London, 1929
[15] Bailey R W. The utilization of creep test data in engineering de‐sign[J]. Proceedings of the Institution of Mechanical Engineers,1935, 131:131
[16] Evans R W, Wilshire B. Creep of Metals and Alloys[M]. The Insti‐tute of Metals, London, 1985
[17] Kachanov L M. On Creep Rupture Time[A]. Proceeding of the Academy Sciences of USSR, 1958, 8, p 26-31
[18] Rabotnov Y N, Leckie F A, Prager W. Creep Problems in Structur‐al Members[J]. Journal of Applied Mechanics, 1969, 37(1):249
[19] Wu X J, Quan G, MacNeil R, et al. Thermomechanical fatigue of ductile cast iron and its life prediction[J]. Metallurgical and Mate‐rials Transactions A, 2015, 46:2530
[20] Wu X J. A model of nonlinear fatigue-creep(dwell)interactions[J].Journal of Engineering for Gas Turbines and Power, 2009, 131:032101-1-032101-6
[21] Wu X J, Quan G, MacNeil R, et al. Failure mechanisms and dam‐age model of ductile cast iron under low-cycle fatigue condi‐tions[J]. Metallurgical and Materials Transactions A, 2014, 45(11):5085
[22] Wu X J, Williams S, Gong D. A true-stress creep model based on deformation mechanisms for polycrystalline materials[J]. Journal of Materials Engineering and Performance, 2012, 21(11):2255
[23] Jing G X, Zhang S Y, Fu W Q, et al. Loading characteristics of cast iron cylinder head for high-strengthened diesel engine[J]. Vehicle Engine, 2017,(01):42(景国玺,张树勇,付文清等.高强化柴油机铸铁缸盖承载特性研究[J].车用发动机, 2017,(01):42)
[24] Chen I W. Cavity growth on a sliding grain boundary[J]. Metallur‐gical Transactions A, 1983, 14(11):2289
[25] Frost H J, Ashby M F. Deformation Mechanism Maps[M]. Per‐gamon Press, 1982
[26] Wu Y, Li J P, Zhang Y J, et al. Effect of heat treatment on mechani‐cal properties and thermal conductivity of RuT300 vermicular graphite cast iron[J]. Transactions of materials and heat treatment,2017,(02):143(武岳,李建平,张延京等.热处理工艺对RuT300蠕墨铸铁力学性能与导热性能的影响[J].材料热处理学报, 2017,(02):143)
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