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High-cycle Fatigue Fracture Behavior of Ultrahigh Strength Steels 被引量:2
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作者 Weijun HUI Yihong NIE +2 位作者 Han DONG Yuqing WENG Chunxu WANG 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2008年第5期787-792,共6页
The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the hi... The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the high-cycle regime up to 107 cycles of loading. The fracture surfaces were observed by field emission scanning electron microscopy (FESEM). It was found that the size of inclusion has significant effect on the fatigue behavior. For AtSI 4340 steel in which the inclusion size is smaller than 5.5 μm, all the fatigue cracks except one did not initiated from inclusion but from specimen surface and conventional S-N curve exists. For 65Si2MnWE and Aermet 100 steels in which the average inclusion sizes are 12.2 and 14.9 μm, respectively, fatigue cracks initiated from inclusions at lower stress amplitudes and stepwise S-N curves were observed. The S-N curve displays a continuous decline and fatigue failures originated from large oxide inclusion for 60Si2CrVA steel in which the average inclusion size is 44.4 pro. In the case of internal inclusion-induced fractures at cycles beyond about 1×10^6 for 65Si2MnWE and 60Si2CrVA steels, inclusion was always found inside the fish-eye and a granular bright facet (GBF) was observed in the vicinity around the inclusion. The GBF sizes increase with increasing the number of cycles to failure Nf in the long-life regime. The values of stress intensity factor range at crack initiation site for the GBF are almost constant with Nf, and are almost equal to that for the surface inclusion and the internal inclusion at cycles lower than about 1×10^6. Neither fish-eye nor GBF was observed for Aermet 100 steel in the present study. 展开更多
关键词 High-cycle fatigue Ultrahigh strength steel INCLUSION S-N curve Fish-eye fracture
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Microstructure and Mechanical Properties of Gear Steels After High Temperature Carburization 被引量:10
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作者 YANG Yan-hui WANG Mao-qiu +1 位作者 CHEN Jing-chao DONG Han 《Journal of Iron and Steel Research International》 SCIE EI CAS CSCD 2013年第12期140-145,共6页
High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity. However, the commonly used gear steels which are microalloyed by Al are n... High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity. However, the commonly used gear steels which are microalloyed by Al are not suitable for high temperature carburization due to abnormal grain coarsening. The gear steel 20CrMnTiNb, which is microalloyed with 0. 048% Nb and 0. 038% Ti, has been compared with the gear steel 20CrMn in terms of microstructure in the case of hardened layer and in the core after carburizing at 1000 ℃ for 4 h and mechanical prop- erties after carburizing and pseudo-carburizing. The results indicate that the fine austenite grains exist in the carbu- rized case of 20CrMnTiNb steel, while there is abnormal coarsening and duplex grain structure in the case and core of steel 20CrMn. The average prior austenite grain sizes are 19.5 and 34.2 μm for the steels 20CrMnTiNb and 20CrMn, respectively. In addition, the mechanical properties of 20CrMnTiNb steel are superior to those of 20CrMn steel. In particular, the HV hardness of the former is higher than that of the latter by about 40--70 in the range of less than 0. 7 mm in depth. Therefore, the steel 20CrMnTiNb is suitable for high temperature carburization. 展开更多
关键词 gear steel high temperature carburization austenite grain size effective case depth
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Effect of Sulfur Content and Sulfide Shape on Fracture Ductility in Case Hardening Steel 被引量:6
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作者 XIAO Guo-hua DONG Han WANG Mao-qiu HUI Wei-jun 《Journal of Iron and Steel Research International》 SCIE EI CAS CSCD 2011年第8期58-64,共7页
The effects of sulfur content and calcium addition on smooth axisymmetric tensile fracture ductility of case hardening steel DIN 18CrNiMo7-6 have been investigated. The quantitative metallographic analysis of sulfide ... The effects of sulfur content and calcium addition on smooth axisymmetric tensile fracture ductility of case hardening steel DIN 18CrNiMo7-6 have been investigated. The quantitative metallographic analysis of sulfide inclusions and the correlations between sulfide inclusions and fracture ductility were examined. Sulfide inclusions were found to have deleterious effect on fracture ductility, whereas the effect can be offset to some extent by calcium-treat- ment due to less easily deforming of sulfides during hot-working. The product (AA·λAW) of sulfide inclusion area fraction (An) and its area-weighted aspect ratio (λAW) can be used as a parameter to describe the effect of sulfide inclusions on fracture true strain. 展开更多
关键词 case hardening steel calcium treatment SULFIDE fracture ductility
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Influence of Hydrogen on GBF in Very High Cycle Fatigue of High Strength Steel 被引量:4
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作者 ZHOU Chao ZHANG Yong-jian +1 位作者 HUI Wei-jun WANG Lei 《Journal of Iron and Steel Research International》 SCIE EI CAS CSCD 2013年第12期92-97,共6页
The relationship of hydrogen, GBF (granular bright facet) and very high cycle fatigue properties of high strength spring steels 60Si2CrV with three different hydrogen contents were studied using hydrogen thermal des... The relationship of hydrogen, GBF (granular bright facet) and very high cycle fatigue properties of high strength spring steels 60Si2CrV with three different hydrogen contents were studied using hydrogen thermal desorp- tion analysis and ultrasonic fatigue test. The results showed that the influence of hydrogen on the relationship between fatigue life and the ratio of GBF to inclusion size was obvious, and the expression between fatigue life and with different hydrogen contents can also be obtained. In addition, based on the research of hydrogen diffusion and GBF, it was explained why the GBF cannot form below 106 cycles. At last, the estimated critical fa tigue life of GBF formation can be expressed accurately. 展开更多
关键词 HYDROGEN granular bright facet very high cycle fatigue
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Effect of austenization temperature on the microstructure evolution of the medium manganese steel (0.2C-5Mn) during ART-annealing 被引量:1
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作者 Jie SHI Haifeng XU +5 位作者 Jie ZHAO Wenquan CAO Chang WANG Cunyu WANG Jian LI Han DONG 《Acta Metallurgica Sinica(English Letters)》 SCIE EI CAS CSCD 2012年第2期111-123,共13页
Microstructure evolution during ART-annealing (austenite reverted transformation annealing) of 0.2C-5Mn steel processed by austenitation at different temperatures was examined by SEM, TEM and XRD. It was demonstrate... Microstructure evolution during ART-annealing (austenite reverted transformation annealing) of 0.2C-5Mn steel processed by austenitation at different temperatures was examined by SEM, TEM and XRD. It was demonstrated that the initial mi- crostructures resulted from austenization at different temperatures strongly affect the microstructure evolution during followed ART-annealing, even the ultrafine grained ferrite/austenite duplex structure with about 30% austenite could be obtained af- ter long time ART-annealing in all cases. Austenization in the intercritical region (between Ad and At3) gave a duplex structure after quenching, which was nearly not affected by followed annealing process. However, high temperature austenization (above A^3) resulted in a full martensite structure after quenching, which gradually transformed into a ferrite/austenite duplex structure during the following anneal- ing process. Based on the analysis of austenite fraction and carbon concentrate, it was found that not only carbon partitioning but also manganese paxtitioning in the austenite affected the stability of austenite and even dominated the development of lamellar ferrite and austenite duplex structure during intercritical annealing with different times. At last an austenite lath nucleation and thickening model was pro- posed to describe the microstructure evolution of medium mangenese steel during ART-annealing. 展开更多
关键词 Austenization temperature ART-annealing Microstructure evolution Carbon and manganese partitioning Lamellar duplex structure
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Hydrogen Absorption and Desorption during Heat Treatment of AISI 4140 Steel 被引量:1
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作者 Ming-da ZHANG Mao-qiu WANG Han DONG 《Journal of Iron and Steel Research International》 SCIE EI CAS CSCD 2014年第10期951-955,共5页
Hydrogen plays an important role in the formation of quench cracks of structural steels. To clarify hydrogen ab- sorption and desorption during heat treatment of AISI 4140 steel, thermal desorption spectrometry (TDS... Hydrogen plays an important role in the formation of quench cracks of structural steels. To clarify hydrogen ab- sorption and desorption during heat treatment of AISI 4140 steel, thermal desorption spectrometry (TDS) analysis was carried out for the specimens in the as-rolled, as quenched, and quenched and tempered conditions. Results show that hydrogen content increased from 0. 127 ×10 6 in the as-rolled specimen to 0. 316 × 10-6 in the as-oil-quenched specimen. After tempering at 200 ℃, the hydrogen content in the oil-quenched specimen decreased to 0. 155 × 10-6 , and the peak temperature of hydrogen desorption increased from 200 to 360 ℃. From the dependence of hydrogen content in the as-quenched specimens on austenitizing time, it can be deduced that hydrogen absorption occurs during austenitizing. The simulation of hydrogen absorption contributes to a better understanding on the distribution of hy- drogen during the heat treatment in structural steels. 展开更多
关键词 STEEL hydrogen absorption heat treatment thermal desorption spectrometry
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Mechanism of Austenite Evolution During Deformation of Ultra-High Carbon Steel 被引量:1
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作者 ZHANG Shu-lan SUN Xin-jun DONG Han 《Journal of Iron and Steel Research International》 SCIE EI CAS CSCD 2008年第3期42-46,共5页
The mechanism of transformation of austenite to cementite and pearlite during the deformation of ultra-high carbon steel was discussed. The results indicate that the pearlite and cementite can be induced by deformatio... The mechanism of transformation of austenite to cementite and pearlite during the deformation of ultra-high carbon steel was discussed. The results indicate that the pearlite and cementite can be induced by deformation between Acm to Arcm The transformation during deformation is still considered as a diffusion-controlled process. With the increase of time and reduction, the pearlite fraction increased. At the beginning of the transformation, the pearlite was lamelliform. When the rate of reduction was increased to 70%, some of the induced lamellar pearlite was broken up under deformation. 展开更多
关键词 ultra-high carbon steel microstructure DEFORMATION TRANSFORMATION
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Effects of Cold Rolling Reduction on Retained Austenite Fraction and Mechanical Properties of High-Si TRIP Steel
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作者 FU Yong-tao LIU Jing +2 位作者 SHI Jie CAO Wen-quan DONG Han 《Journal of Iron and Steel Research International》 SCIE EI CAS CSCD 2013年第5期50-56,共7页
Transformation-induced plasticity-aided steel was rolled at room temperature to different thickness reductions (0, 4%, 10%, 20%, 40%, and 60%). The mechanical properties, microstructure and austenite fractions of th... Transformation-induced plasticity-aided steel was rolled at room temperature to different thickness reductions (0, 4%, 10%, 20%, 40%, and 60%). The mechanical properties, microstructure and austenite fractions of the rolled samples were measured by tensile test, electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) for each rolling. The deformation behavior was studied based on the analysis of the mechanical properties and microstructure of steel after tensile deformation, aiming at understanding the effects of cold rolling reduction on the decay behavior of the austenite and the change of mechanical properties of the TRIP steels. It was found that increasing rolling reduction increases the yield stress gradually but decreases the total elongation significantly. It is very interesting that after 10% rolling reduction the yield stress is about 1 000 MPa but still with 20% total elongation, which gives an excellent combination of yield strength and ductility. Based on the XRD results, it was revealed that in both rolling and tension the austenite volume fraction monotonically decayed with the increase of rolling strain, but the decaying rate is faster in tension than in rolling, which may be ascribed to the higher temperature in rolled specimens than in the tensioned ones during deformation. Experimental results and theoretical reasoning indicate that the decreasing trend of austenite volume fraction with strain can be formulated by a unique equation. 展开更多
关键词 TRIP steel cold rolling mechanical stability austenite fraction
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Ultrafine Grained Duplex Structure Developed by ART-annealing in Cold Rolled Medium-Mn Steels 被引量:6
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作者 Jie SHI Jun HU +3 位作者 Chang WANG Cun-yu WANG Han DONG Wen-quan CAO 《Journal of Iron and Steel Research International》 SCIE EI CAS CSCD 2014年第2期208-214,共7页
The microstructural evolutions of the cold rolled Fe-0.1C-5Mn steel during intercritical annealing were ex- amined using combined advanced techniques. It was demonstrated that intercritical annealing results in an ult... The microstructural evolutions of the cold rolled Fe-0.1C-5Mn steel during intercritical annealing were ex- amined using combined advanced techniques. It was demonstrated that intercritical annealing results in an ultrafine granular ferrite and austenite duplex structure in cold rolled 0.1C-5Mn steel. The strong partitioning of manganese and carbon elements from ferrite to austenite was found during intercritical annealing by scanning transmission elec- tron microscopy (STEM) and X-ray diffraction (XRD). Strong effects of boundary characters on the austenite for- mation were indicated by austenite fast nucleation and growth in the high angle boundaries but sluggish nucleation and growth in the low angle boundaries. The ultrafine grained duplex structure in 0.1C-5Mn was resulted from the the sluggish Mn-diffusion and the extra high Gibbs free energy of ferrite phase. Based on the analysis of the micro- structure evolution, it was pointed out that the intercritical annealing of the medium Mn steels could be applied to fabricate an ultrafine duplex grained microstructure, which would be a promising approach to develop the 3rd genera- tion austomobile steels with excellent combination of strength and ductility. 展开更多
关键词 intercritical annealing partitioning SEGREGATION ultrafine grained duplex structure boundary character Gibbs free energy
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An ultrahigh strength steel produced through deformation-induced ferrite transformation and Q&P process 被引量:3
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作者 CHEN MingMing WU RiMing +4 位作者 LIU HePing WANG Li SHI Jie DONG Han JIN XueJun 《Science China(Technological Sciences)》 SCIE EI CAS 2012年第7期1827-1832,共6页
In this work,DIFT technology and Q&P process were combined in order to introduce ultrafine-grained ferrite into the matrix of martensite and retained austenite to develop a new kind of advanced high strength steel... In this work,DIFT technology and Q&P process were combined in order to introduce ultrafine-grained ferrite into the matrix of martensite and retained austenite to develop a new kind of advanced high strength steel,and two kinds of steels were investigated by this novel combined process.The newly designed process resulted in a sophisticated microstructure of a large amount of ferrite(about 5 m in diameter),martensite and a considerable amount of retained austenite for TRIP 780 steel.The ultimate tensile strength can reach about 1200 MPa with elongation above 16% for TRIP 780,that is much higher than the one solely treated by Q&P process.Tensile tests showed that both steels with the novel combined process achieved a good combination of strength and ductility,indicating that the new process is promising for the new generation of advanced high strength steels. 展开更多
关键词 deformation induced ferrite transformation(DIFT) quenching and partitioning(Q&P) MICROSTRUCTURE mechanical property
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