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金属学报  2015, Vol. 51 Issue (11): 1333-1340    DOI: 10.11900/0412.1961.2015.00121
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铁素体球墨铸铁低温冲击断裂裂纹形核及扩展机理*
张新宁,曲迎东(),李荣德,尤俊华
MECHANISM OF CRACK NUCLEATION AND PROPA- GATION OF FERRITE DUCTILE IRON DURING IMPACT FRACTURE UNDER LOW TEMPERATURES
Xinning ZHANG,Yingdong QU,Rongde LI,Junhua YOU
School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870
全文: PDF(1272 KB)   HTML  
摘要: 

在低温下对QT400-18L铁素体球墨铸铁件进行Charpy缺口示波冲击实验, 测试温度对冲击过程中裂纹形核和裂纹扩展能力的影响, 采用OM观察分析不同温度下铁素体球墨铸铁裂纹萌生与扩展路径以及断口附近组织的演变规律. 结果表明, 韧脆转变温度以上, 冲击后断口附近大量石墨-基体界面发生开裂, 石墨界面开裂后产生的孔洞起到钝化裂纹和降低裂纹扩展速率的作用; 韧脆转变温度区间, 冲击试样表现为韧窝和解理混合断口形貌, 断裂模式和裂纹形核均与石墨球有关; 韧脆转变温度以下, 垂直交叉孪晶成核进而导致微裂纹扩展, 解理断裂主要是孪晶起裂, 这种形变孪晶引起的裂纹形核和扩展方式造成了裂纹形成功与裂纹扩展功的剧烈下降.

关键词 石墨球韧脆转变解理断裂形变孪晶    
Abstract

Due to its excellent ductility and moderate strength, QT400-18L ferrite ductile iron has been widely used in producing core components of wind power equipment such as the hub of a wind turbine. Most of the researches have focused on the exploration of mechanical properties at low temperature, but none of them give the explanation on microcosmic mechanism of ductile iron during low temperature impact and the mechanism of crack nucleation and propagation of ferrite ductile iron during impact fracture has not been analyzed. In this work, the impact toughness of QT400-18L ferrite ductile iron was measured by V-notch Charpy impact test at different temperatures, the influence of low temperature impact toughness and the fracture behavior of ferrite ductile iron were discussed. The results show that the cleavage fracture resistance of QT400-18L ferrite ductile iron is reduced with the decrease of impact temperatures. Above ductile-brittle transition temperature (DBTT), most of the total fracture energies are expended during the crack propagation process. Below DBTT, both crack initiation energy and crack propagation energy decrease obviously. By using in situ fracture metallographic observation method, crack initiation and propagation of QT400-18L ferrite ductile iron under different temperatures were analyzed. Above DBTT, graphite nodules play the role of crack blunting and reducing crack propagation rate; in DBTT range, the fracture morphology shows mixed fracture with cleavage and dimples, which are related to graphite nodules; below DBTT, deformation twins lead to the nucleation of microcrack and result in cleavage fracture, the deformation twinning could possibly play a significant role in the ductile to brittle transition of QT400-18L ferrite ductile iron.

Key wordsgraphite nodule    ductile-brittle transition    cleavage fracture    deformation twin
     出版日期: 2015-08-20
基金资助:* 国家自然科学基金项目51274142, 辽宁省自然科学基金项目2014028015和沈阳市科技局项目F15-199-1-15资助

引用本文:

张新宁,曲迎东,李荣德,尤俊华. 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.
Xinning ZHANG,Yingdong QU,Rongde LI,Junhua YOU. MECHANISM OF CRACK NUCLEATION AND PROPA- GATION OF FERRITE DUCTILE IRON DURING IMPACT FRACTURE UNDER LOW TEMPERATURES. Acta Metall, 2015, 51(11): 1333-1340.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2015.00121      或      http://www.ams.org.cn/CN/Y2015/V51/I11/1333

图1  铁素体球墨铸铁的冲击载荷和吸收能量在冲击过程中随位移的变化曲线
图2  铁素体球墨铸铁在不同温度冲击后的断裂路径
图3  铁素体球墨铸铁在-20 ℃冲击后V型缺口下方断口的SEM像
图4  铁素体球墨铸铁在-20 ℃冲击前后断口附近的形貌
图5  铁素体球墨铸铁在-20 ℃冲击后断口附近基体变形的形貌
图6  铁素体球墨铸铁在-20 ℃冲击后石墨球周围显微空洞的形貌
图7  铁素体球墨铸铁在-20 ℃冲击后断裂处纵截面的SEM像
图8  铁素体球墨铸铁在-45 ℃冲击后V型缺口下方断口的SEM像
图9  铁素体球墨铸铁在-45 ℃冲击后靠近断面处的SEM像
图10  铁素体球墨铸铁在-45 ℃冲击前后断口附近石墨形态的形貌
图11  铁素体球墨铸铁在-45 ℃冲击后断口处石墨球周围基体变形的形貌
图12  铁素体球墨铸铁在-80 ℃冲击后断口的SEM像
图13  铁素体球墨铸铁在-80 ℃冲击时的解理断裂示意图
图14  铁素体球墨铸铁在-80 ℃冲击后断口附近组织的形貌
图15  铁素体球墨铸铁在-80 ℃冲击后石墨球周围舌状花样的SEM像
图16  舌状花样模型示意图
图17  铁素体球墨铸铁在-80 ℃ 冲击后形变孪晶的SEM像
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