Impact toughness of QT400-18L ductile iron is measured by V-notch Charpy impact test at room and low temperatures. scanning electron microscope(SEM) is used to analyze the impact fracture morphology. The dislocation density near impact fracture surfaces at different temperatures is calculated by X-ray diffraction(XRD) diffraction method. Experimental results show that the energy absorbed by impact test decreases significantly with the decrease of graphite grade. Three damage models of graphite nodules are found during impact fracture. Cracks mainly form at grain boundaries under low temperatures due to dislocation pile-up. Inclusions on grain boundaries lead to the formation of microcavities on dimple fracture. As the temperature decreases, both the density of dislocation and the number of mobile dislocation are decreased. The density of dislocation is about 1.32×1015 m-2 at room temperature, and the density of dislocation is about 0.39×1015 m-2 at -60 ℃.
LI Rongde
,
ZHANG Xinning
,
JIANG Lipeng
,
JIANG Ke
. Influence Factors of Ferrite Cast Iron of Low-temperature Impact Fracture Behavior[J]. Journal of Mechanical Engineering, 2016
, 52(10)
: 25
-31
.
DOI: 10.3901/JME.2016.10.025
[1] CAI Qizhou,WEI Bokang. Recent development of ductile cast iron production technology in China[J]. China Foundry,2008,5(2)：82-91.
[2] LABRECQUE C,GAGNE M. Ductile iron：Fifty years of continuous development[J]. Canadian Metallurgical Quarterly,1998,37(5)：343-378.
[3] 张新宁,曲迎东,李荣德. 铁素体球墨铸铁低温冲击断裂裂纹形核及扩展机理[J]. 金属学报,2015,51(11)：1333-1340.
ZHANG Xinning,QU Yingdong,LI Rongde. Mechanism of crack nucleation and propagation of ferrite ductile iron during impact fracture under low temperatures[J]. Acta Metallurgica Sinica,2015,51(11)：1333-1340.
[4] SERTUCHA J,LACAZE J,SERRALLACH J,et al. Effect of alloying on mechanical properties of as cast ferritic nodular cast irons[J]. Materials Science and Technology,2012,28(2)：184-191.
[5] IBRAHIM O H,ELSHAZLY E S. Microstructural effects on fracture behavior of ferritic and martensitic structural steels[J]. Journal of Materials Engineering and Performance,2013,22(2)：584-589.
[6] 唐振廷. 冲击试样断口与力-位移曲线之间的关系[J]. 物理测试,2004(4)：1-5.
TANG Zhenting. Relationship between fracture and force-displacement curve of impact specimen[J]. Phys. Exam. Testing,2004(4)：1-5.
[7] 原田昭治,小林俊郎. 球墨铸铁的强度评价[M]. 沈阳：东北大学出版社,2002.
HARADA S,KOBAYASHI T. Evaluation of the strength of nodular cast iron[M]. Shenyang：Northeastern University Press,2002.
[8] 周继扬. 铸铁彩色金相学[M]. 北京：机械工业出版社,2002.
ZHOU Jiyang. Iron color metallography[M]. Beijing：China Machine Press,2002.
[9] 周继扬. 球状石墨的形核与孕育–球墨铸铁基础理论的最新发展(一)[J]. 现代铸铁,2002(3)：7-12.
ZHOU Jiyang. Nucleation of spheroidal graphite and inoculation:Recent development of the basic theory of spheroidal graphite cast iron(Ⅰ)[J]. Modern Cast Iron,2002(3)：7-12.
[10] HUNG Maolin. A study on the cycilc heating induced intergranular fracture of ferritic spheroidal graphite cast irons[D]. Taiwan,China：Cheng Kung University,2004.
[11] HISASHI I,KIYOHIKO I,TOSHIO O. The yield condition of nodular cast iron subjected to triaxial stress[J]. Bulletn of the JSME,1981,24(6)：902-912.
[12] YANAGISAWA O,LUI T S,Effect of carbon content and ferrite grain size on the tensile flow stress of ferritic spheroidal graphite cast iron[J]. Metall. Trans. A,1985,16：667-673.
[13] HEINE R W. The Fe-C-Si solidification diagram for cast irons[J]. AFS Trans.,1986,94：391-402.
[14] SUO Z. Zener’s crack and the M-integral[J]. Transaction of the ASME,2000,67(6)：417-418.
[15] HAUŠILD P,NEDBAL I,BERDIN C. The influence of ductile tearing on fracture energy in the ductile-to-brittle transition temperature range[J]. Materials Science and Engineering：A,2002,335(1)：164-174.
[16] TAKEBAYASHI T K S,YOSHINAGA N,USHIODA K,et al. Comparison of the dislocation density in martensite steels evaluated by some X-ray diffraction methods[J]. ISIJ International,2010,50：875-882.
[17] 贾仁需,张玉明,张义门,等. XRD法计算4H-SiC外延单晶中的位错密度[J]. 光谱学与光谱分析,2010,30(7)：1995-1997.
JIA Renxu,ZHANG Yuming,ZHANG Yimen,et al. Calculation of dislocation destiny using X-ray diffraction for 4H-SiC homoepitaxial layers[J]. Spectroscopy and Spectral Analysis,2010,30(7)：1995-1997.
[18] 王晓强,崔凤奎,燕根鹏,等. 40Cr冷滚打成形中位错密度变化研究[J]. 中国机械工程,2013,24(16)：2248-2252.
WANG Xiaoqiang,CUI Fengkui,YAN Genpeng,et al. Study on dislocation density change during cold roll-beating of 40Cr[J]. China Mechanical Engineering,2013,24(16)：2248-2252.
