检索结果-南通市图书馆

Dynamic Recrystallization and Precipitation Behavior of Mn-Cu-V Weathering Steel

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2011年第12期27卷 1131-1138页

作者： Hongyan Wu Linxiu Du xianghua liu State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 China

The hot deformation behavior of a Mn-Cu-V weathering steel was investigated at temperatures ranging from 850 to 1050℃ and strain rates ranging from 0.01 to 5 s-1 using MMS-300 thermal-mechanical simulator. The activation energy for dynamic recrystallization and stress exponent were calculated to be 551 kJ/mol and 7.73, respectively. The accurate values of critical strain were determined by the relationship between work hardening rate and flow stress （θ-σ） curves. The hyperbolic sine constitutive equation was employed to describe the relationship between the peak stress and Zener-Hollomon parameter during hot deformation. The interaction between dynamic recrystallization and dynamic precipitation of V（C,N） at a low strain rate was analyzed. The results showed that precipitation particles size of weathering steel increased with increasing strain at deformation temperature g50~C and strain rate 0.1 s-I. The calculation results of the recrystallization driving force and pinning force showed that dynamic precipitation could retard the progress of dynamic recrystallization but not prevent it while the pinning forces is less than driving force. On the contrary, dynamic precipitation can effectively prevent the progress of dynamic recrystallization.

关键词： Weathering steel Critical strain Dynamic recrystallization Dynamic precipitation

Enhanced mechanical stability of ultrafine grained steel through intercritical annealing cold rolled martensite

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2012年第6期25卷 443-452页

作者： Huifang LAN xianghua liu Linxiu DU The State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 China

The ultrafine grained ferritic steels possess shortage of work hardening. Fine grained high strength but low ductility due to the ferrite-martensite dual phase microstruc- ture was obtained in a microalloyed steel and low carbon steels through intercritical annealing of the cold rolled martensite. The dual phase microstructure was uniform and the ferrite grain size was smaller in the microalloyed steel resulted from the pin- ning effect of microalloyed precipitates. But ferrite grown apparently and the volume fraction of the martensite was much higher without the addition of microalloying el- ements. By introducing martensite into the fine grained ferrite, the work hardening was effectively improved, leading to better mechanical stability. As a result of the fine ferrite grain size as well as uniform distribution of the martensite, the work harden- ing was enhanced, showing better strength-ductility balance in the microalloyed dual phase steel.

关键词： Mechanical stability Fine grained dual phase steel Work hardening Strength-ductility balance

Springback characteristics in U-channel forming of tailor rolled blank

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2012年第3期25卷 207-213页

作者： Huawei ZHANG Lizhong liu Ping HU xianghua liu School of Automotive Engineering Faculty of Vehicle Engineering and Mechanics State Key Labora- tory of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian 116024 China Research Institute of Science and Technology Northeastern University Shenyang 110819 China

Residual stress developed during the rolling process of tailor rolled blank （TRB） can affect the springback of finished parts considerably. Springback characteristics of unannealed and annealed TRBs were investigated by means of numerical simulation and experiments taking U-Channel as an example. TRBs were annealed by the annealing process （700 ℃, holding time 10 h）, then stamping and springback processes of unannealed and annealed TRBs were simulated, and corresponding experiments were also carried out. Effects of the transition zone length, the blank thickness, the friction coefficient and the die clearance on the springback of TRB were analyzed. The results demonstrate that the springback of TRB annealed at 700 ~C for 10 h re- duces significantly. For unannealed and annealed U-Channels, the springback of TRB U-Channel is in direct proportion to the die clearance and is in inverse proportion to the transition zone length, the blank thickness and the friction coefficient. Spring- backs of the thinner monolithic （uniform thickness） blank, the thinner side of TRB, the thicker side of TRB and the thicker monolithic blank are sorted in descending order.

关键词： Tailor rolled blank Springback Annealing

Microstructure and mechanical properties of X80 pipeline steels in different cooling schedules

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2010年第3期23卷 171-175页

作者： Min ZHOU Linxiu DU xianghua liu State Key Laboratory of Rolling Technology and Automation Northeastern University Shenyang 110819 China

The microstructures and mechanical properties of three X80 pipeline steel plates were investigated in this *** plates were hot rolled by two stages, and cooled by three different cooling schedules to obtain different microstructures and mechanical *** electron microscope（TEM） was used to observe the *** results indicated that the amount of polygonal ferrite（PF） and quasi-polygonal ferrite（QPF） decreased with decreasing of the finish cooling temperature（FCT）, while the amount and size of M-A islands were *** promoted the Charpy V-notch（CVN） impact toughness at-20℃, but not the drop weight tear testing（DWTT） property at-15℃, and decreased the strength of the steel.

关键词： Microstructure Mechanical properties Cooling schedule Relaxation

Growth behavior of ultrafine austenite grains in microalloyed steel

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2009年第1期22卷 7-12页

作者： Linxiu DU Shengjie YAO xianghua liu Guodong WANG State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 China

Ultrafine austenite gains （UFAGs） with size of 1-5 μm were prepared through repetitive treatment, four times, of rapid heating and quenching, and the growth behaviors of these UFACs during both the reheating and cooling stages were investigated. The results indicated that UFAGs without pinning particles appeared with significant coarsening when the reheating temperature reached 1000 ℃. Although coarsening still occurred in the cooling stage, the growth was obscured during the isothermal holding process at temperatures between 900 ℃ and At3.

关键词： Ultrafine austenite grain Growth Microalloyed steel Second-phase particle

High performance low cost steels with ultrafine grained and multi-phased microstructure

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2009年第8期52卷 2245-2254页

作者： liu xianghua LAN HuiFang DU LinXiu liu WeiJie State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110004China Graduate Institute of Ferrous Technology Pohang University of Science and TechnologyPohang790-784Korea

Ultrafine grained ferrite was obtained through tempering cold rolled martensite with an average grain size of 200―400 nm in a low carbon and a microalloyed steel. Thermal and mechanical stability of the two steels was studied. Due to the pinning effect of microalloyed precipitates on the movement of dislocations and grain boundaries, the recrystallization and grain growth rate were retarded, and the thermal stability of ultrafine grained microstructure was improved. The ultrafine grained ferritic steel was strengthened, but its strain hardening rate was reduced. It seems that the tiny carbide precipitates have no significant effect on work hardening rate. The ultrafine grained ferrite+martensite dual phase microstructure was obtained in the microalloyed steel through intercritically annealing cold rolled martensite. The resulting multiphase microstructure has a tensile strength higher than 1.0 GPa with a yield ratio lower than 0.7. Another type of multiphase microstructure with nanoscaled lath bainite+ retained austenite was obtained through an isothermal heat treatment in low temperature bainite transformation region in high carbon steel. The tensile strength was as high as 1.64 GPa with a yield ratio of 0.84.

关键词： ultrafine grained steel multiphase high strength yield ratio

Simulation of Fluid Flow, Heat Transfer and Micro-Segregation in Twin-roll Strip Casting of Stainless Steel

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2006年第3期22卷 295-300页

作者： Xiaomin ZHANG Zhengyi JIANG xianghua liu Guodong WANG State Key Laboratory of Rolling Technology and Automation Northeastern University Shenyang 110004 China

In twin-roll strip casting process, metal flow and temperature distribution in the molten pool directly affect the stability of the process and the quality of products. In this paper, a 3D coupled thermal-flow fenite element modeling （FEM） simulation for twin-roll strip casting of stainless steel was performed. Influences of the pouring temperature and casting speed on the temperature fields were obtained from the numerical simulation. The micro-segregation of the solutes during the strip casting process of stainless steel was also simulated. A developed micro-segregation model was used to calculate the micro-segregation of solutes in twin-roll casting of stainless steel. The relationship between the solidus fraction in solidification and temperature was given, which was used to determine the LIT （liquid impermeable temperature）, ZST （zero strength temperature） and ZDT （zero ductility temperature） in the period of non-equilibrium solidification. The effect of temperature on the micro-segregation was discussed. According to the computational results, the solidification completion temperature in the twin-roll strip casting of stainless steel was then determined, which can provide a basis for controlling the location of solidification completion temperature and analysing the crack of the casting strip.

关键词： Casting speed Micro-segregation Twin-roll strip casting Simulation

Dynamic Recrystallization Behavior of a Heat-resistant Martensitic Stainless Steel 403Nb during Hot Deformation

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2011年第10期27卷 913-919页

作者： Zhouyu Zeng Liqing Chen Fuxian Zhu xianghua liu State Key Laboratory of Rolling and Automation Northeastern University 3-11 Wenhua Road Shenyang 110819 China

Dynamic recrystallization （DRX） behaviors of a heat-resistant martensitic stainless steel 403Nb during hot deformation have been investigated by single-pass thermo-mechanical simulative experiment at temperatures of 900-1150℃ and strain rates of 0.01-1 s-1 The results show that the true stress-true strain curves of this alloy can be classified into two types, one is of dynamic recovery and the other is of dynamic recrystallization. The DRX in 403Nb alloy is easy to occur at strain rates lower than 0.5 s-1 and deformation temperatures higher than 1000℃. Using regression analysis, the stress multiplier （a） and apparent stress exponent （n） were calculated to be 0.0153 and 3.22, respectively, while the activation energy （Qd） for DRX of 403Nb was calculated to be 367.293 kJ/mol. The constitutive equation of peak stress for DRX was also obtained. Based on P-J method, the critical strain for DRX was accurately determined. The mathematical models of peak strain and kinetic equation for DRX of 403Nb steel were finally established.

关键词： 403Nb steel Dynamic recrystallization Hot deformation Critical strain

Effect of Austempering Route on Microstructural Characterization of Nanobainitic Steel

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2014年第1期27卷 19-26页

作者： Huifang Lan Linxiu Du Na Zhou xianghua liu State Key Laboratory of Rolling and Automation Northeastern University Hebei Shougang Qian'an Iron & Steel Co. Ltd

A low-temperature nanobainitic steel was obtained through one-step and two-step austempering. The effect of austempering temperature, time, and route on bainitic lath width, volume fraction of retained austenite, carbon concen- tration in retained austenite, and nanohardness of bainitic lath and retained austenite was studied. Results showed that the transformation kinetics was slowed down and the bainitic lath was refined as the austempering temperature decreased from 300 to 250 C. Both coarser and finer bainitic laths were obtained with the two-step austempering, which was consistent with the lath size at 300 and 250 C austempering, respectively. X-ray diffraction analysis showed that both volume fraction of retained austenite and its carbon concentration decreased with the decrease of austempering temperature for the one-step austempering, and especially the carbon concentration is obviously increased when the two-step austempering is adopted. The nanohardness of the bainitic lath in the sample after two-step austempering treated lies between that of the samples after 300 and 250 C austempering treated. The product of tensile strength and total elongation of the two-step austempered sample is the highest, which increases monotonously with the product of retained austenite fraction and its carbon concentration. Higher strengthluctility balance may be resulted by the fine bainitic lath, high volume fraction, and high stability of retained austenite in the sample after two-step austempered.

关键词： Nanobainitic steel Stability Retained austenite Nanohardness Strength-ductility balance