large diameter internal thread of high-strength steel（LDITHSS） manufactured by traditional methods always has the problems of low accuracy and short life. Compared with traditional methods, the cold extrusion proces...large diameter internal thread of high-strength steel（LDITHSS） manufactured by traditional methods always has the problems of low accuracy and short life. Compared with traditional methods, the cold extrusion process is an effective means to realize higher accuracy and longer life. The low-cycle fatigue properties of LDITHSS are obtained by experiments, and the initiation and propagation of fatigue cracks are observed by scanning electron microscope（SEM）. Based on the mechanical properties, surface microstructure and residual stress, the strengthening mechanism of cold extruded large diameter internal thread（LDIT） is discussed. The results show that new grains or sub-grains can be formed on the surface of LDIT due to grain segmentation and grain refinement during cold extrusion. The fibrous structures appear as elongated and streamlined along the normal direction of the tooth surface which leads to residual compressive stress on the extruded surface. The maximum tension stress of LDIT after cold extrusion is found to be 192.55 k N. Under low stress cycling, the yield stress on thread increases, the propagation rate of crack reduces, the fatigue life is thus improved significantly with decreasing surface grain diameter and the average fatigue life increases to 45.539×10~3 cycle when the maximum applied load decreases to 120 k N. The low cycle fatigue and strengthening mechanism of cold extruded LDIT revealed by this research has significant importance to promote application of internal thread by cold extrusion processing.展开更多
In this study,the scale and internal oxidation of hot-rolled ultra-high strength steel sheets were characterized.It was found that both the formation of the scale and the internal oxidation of Si and Mn depended on th...In this study,the scale and internal oxidation of hot-rolled ultra-high strength steel sheets were characterized.It was found that both the formation of the scale and the internal oxidation of Si and Mn depended on the coiling temperature and position of the steel sample on the strip coil.At a relatively high coiling temperature,a large amount of internal oxidation was observed on the samples cut from the middle of the coil.The depth of the internal oxidation zone exceeded 10 μm and a thin iron layer covering the scale was observed in some cases.Pickling and cold-rolling experiments were conducted on selected samples.Scale pickling was found to be greatly delayed by the formation of an iron layer,which frequently resulted in under-pickled defects.In addition,pickling of the entire internal oxidation zone was difficult,except at the grain boundaries,where the degree of internal Si and Mn oxidation was enriched.The surface of the cold-rolled steel sheet was ruined by the remaining oxidation zone in the subsurface of the pickled steel.The internal oxidation of hot-rolled ultra-high strength steel must be precisely controlled to improve the subsequent surface quality of cold-rolled steel.展开更多
European literary criticism was rapidly transformed into literary theory through the United States after Rene Wellek and Austin Warren’s textbook Theory of Literary Theory by Harcourt,Brace and Co.(1949).Within a sho...European literary criticism was rapidly transformed into literary theory through the United States after Rene Wellek and Austin Warren’s textbook Theory of Literary Theory by Harcourt,Brace and Co.(1949).Within a short period of time,American new criticism,European psychoanalysis,semiotics,structuralism,hermeneutics,deconstructivism,and so on,as well as the western Marxism,feminism,new historicism,post-colonial criticism,and cultural studies,all the critical methods little referenced to postwar Western ideology and Soviet Ideology,and are even known for their profound criticism of some problems in capitalist society.These intuitively scientific or neutral literary theories flourished during the Cold War years that contained the Soviet Union.During this period,“political correctness”not only influenced the direction of social development in the West,but also directly influenced the academic pattern and the development trend of universities at that time,so that“literary criticism”,which was originally only based on personal experience,benefited and became“literary theory”in the discipline and curriculum system.As a result,the discipline of literary theory,which benefited from the Cold War pattern,is often in conflict with the specific literary theory that transcends ideology.However,the Cold War ended with the failure of the Soviet Union and its socialist realism theory system,and the western literary theory unexpectedly gained full legitimacy like Fukuyama’s“the end of history”.In the post-Cold War era,Western literary critics reasonably expanded the controversial theories and this has become the most concerned topic for 30 years.Thus,the international politics of the disguised Western literary theory was highlighted.Such Western literary theory has been generalized in China in the last 40 years,because Chinese academic yet has not understood the difference between theory as discipline and theory as doctrine,even anti-western in recent years.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51372216)Jiangsu Science and Technology Plan Project of China(Grant No.BE2015113)Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.BKJB460016)
文摘large diameter internal thread of high-strength steel（LDITHSS） manufactured by traditional methods always has the problems of low accuracy and short life. Compared with traditional methods, the cold extrusion process is an effective means to realize higher accuracy and longer life. The low-cycle fatigue properties of LDITHSS are obtained by experiments, and the initiation and propagation of fatigue cracks are observed by scanning electron microscope（SEM）. Based on the mechanical properties, surface microstructure and residual stress, the strengthening mechanism of cold extruded large diameter internal thread（LDIT） is discussed. The results show that new grains or sub-grains can be formed on the surface of LDIT due to grain segmentation and grain refinement during cold extrusion. The fibrous structures appear as elongated and streamlined along the normal direction of the tooth surface which leads to residual compressive stress on the extruded surface. The maximum tension stress of LDIT after cold extrusion is found to be 192.55 k N. Under low stress cycling, the yield stress on thread increases, the propagation rate of crack reduces, the fatigue life is thus improved significantly with decreasing surface grain diameter and the average fatigue life increases to 45.539×10~3 cycle when the maximum applied load decreases to 120 k N. The low cycle fatigue and strengthening mechanism of cold extruded LDIT revealed by this research has significant importance to promote application of internal thread by cold extrusion processing.
文摘In this study,the scale and internal oxidation of hot-rolled ultra-high strength steel sheets were characterized.It was found that both the formation of the scale and the internal oxidation of Si and Mn depended on the coiling temperature and position of the steel sample on the strip coil.At a relatively high coiling temperature,a large amount of internal oxidation was observed on the samples cut from the middle of the coil.The depth of the internal oxidation zone exceeded 10 μm and a thin iron layer covering the scale was observed in some cases.Pickling and cold-rolling experiments were conducted on selected samples.Scale pickling was found to be greatly delayed by the formation of an iron layer,which frequently resulted in under-pickled defects.In addition,pickling of the entire internal oxidation zone was difficult,except at the grain boundaries,where the degree of internal Si and Mn oxidation was enriched.The surface of the cold-rolled steel sheet was ruined by the remaining oxidation zone in the subsurface of the pickled steel.The internal oxidation of hot-rolled ultra-high strength steel must be precisely controlled to improve the subsequent surface quality of cold-rolled steel.
文摘European literary criticism was rapidly transformed into literary theory through the United States after Rene Wellek and Austin Warren’s textbook Theory of Literary Theory by Harcourt,Brace and Co.(1949).Within a short period of time,American new criticism,European psychoanalysis,semiotics,structuralism,hermeneutics,deconstructivism,and so on,as well as the western Marxism,feminism,new historicism,post-colonial criticism,and cultural studies,all the critical methods little referenced to postwar Western ideology and Soviet Ideology,and are even known for their profound criticism of some problems in capitalist society.These intuitively scientific or neutral literary theories flourished during the Cold War years that contained the Soviet Union.During this period,“political correctness”not only influenced the direction of social development in the West,but also directly influenced the academic pattern and the development trend of universities at that time,so that“literary criticism”,which was originally only based on personal experience,benefited and became“literary theory”in the discipline and curriculum system.As a result,the discipline of literary theory,which benefited from the Cold War pattern,is often in conflict with the specific literary theory that transcends ideology.However,the Cold War ended with the failure of the Soviet Union and its socialist realism theory system,and the western literary theory unexpectedly gained full legitimacy like Fukuyama’s“the end of history”.In the post-Cold War era,Western literary critics reasonably expanded the controversial theories and this has become the most concerned topic for 30 years.Thus,the international politics of the disguised Western literary theory was highlighted.Such Western literary theory has been generalized in China in the last 40 years,because Chinese academic yet has not understood the difference between theory as discipline and theory as doctrine,even anti-western in recent years.
