非等温形变对高强度汽车钢WHT1300HF的马氏体相变的影响

通过非等温形变研究了形变参数(形变温度、形变速率、形变量)对高强度汽车钢WHT1300HF马氏体相变的影响。结果表明:非等温形变导致奥氏体的形变强化,马氏体相变阻力增大,马氏体相变开始温度(MS)下降;形变速率的增大对马氏体相变起到促进作用;形变量的增加加剧了奥氏体的形变强化,导致MS温度下降;形变开始温度对马氏体相变作用不明显。

高速钢形变等温淬火的力学性能及其强韧化机理

对Ｗ６Ｍｏ５Ｃｒ４Ｖ２钢奥氏体化后，在１１５０℃～７５０℃以１．５×１０－２／ｓ的形变速率等温形变０％～６５％，并对２７０℃等温淬火、５６０℃回火后组织与性能进行了研究。结果表明：形变使等温淬火、回火组织的硬度、强度和冲击韧度均有所提高，１０５０℃形变１５％～２０％具有最佳强韧性配合。并根据力学性能与组织变化的关系，提出了组织细化强韧化、位错强化、碳化物沉淀强化和锯齿状晶界韧化的强韧化机理，其中锯齿状晶界韧化对最佳强韧性配合起着关键作用。

TC6合金低压1～4级工作叶片等温成形工艺研究

经过锻造成形工艺摸索,已成功试制出TC6合金低压1～4级工作叶片锻件,并确定出叶片的基本锻造成形工艺过程,即"卧锻机上顶锻制坯→压力机上常规预锻→液压机上等温成形→液压机上等温校形→最终热处理",最终试制出的叶片锻件叶身型面单面余量达到0.4～0.8mm,也获得了比较理想的低倍流线分布,但仍需要对锻件的成形条件、材料的原始组织以及不同的热处理状态等工艺过程的相关参数对合金最终组织性能的影响规律作出进一步的试验研究,以便选择合适的工艺参数,掌握控制叶片最终组织性能的方法。

Effects of non-isothermal annealing on microstructure and mechanical properties of severely deformed 2024 aluminum alloy

Microstructure and mechanical properties of AA2024 after severe plastic deformation （SPD） and non-isothermal annealing were investigated. The non-isothermal treatment was carried out on the severely deformed AA2024, and the interaction between restoration and precipitation phenomena was investigated. Differential scanning calorimetry, hardness and shear punch tests illustrate that static recovery and dissolution of GPB zones/Cu-Mg co-clusters occur concurrently through non-isothermal annealing. Scanning electron microscope and electron backscatter diffraction illustrate that non-isothermal annealing of deformed AA2024 up to 250 ℃ promotes the particle-free regions and also particle stimulated nucleation. Results show that through heating with the rate of 10 ℃/min up to 250 ℃, the ultimate shear strength and the hardness are maximum due to the presence of S＇/S phases which have been detected during non-isothermal differential scanning calorimetry experiment. Also, recrystallization phenomenon occurs in temperature range which includes the dissolution of S＇/S phases. The concurrent recrystallization and dissolution of S＇/S phase at 380 ℃ have been verified by differential scanning calorimetry, mechanical properties, and optical microscope.

Prediction of tri-modal microstructure under complex thermomechanical processing history in isothermal local loading forming of titanium alloy

To control the tri-modal microstructure and performance,a prediction model of tri-modal microstructure in the isothermal local loading forming of titanium alloy was developed.The staged isothermal local loading experiment on TA15alloy indicates that there exist four important microstructure evolution phenomena in the development of tri-modal microstructure,i.e.,the generation of lamellarα,content variation of equiaxedα,spatial orientation change of lamellarαand globularization of lamellarα.Considering the laws of these microstructure phenomena,the microstructure model was established to correlate the parameters of tri-modal microstructure and processing conditions.Then,the developed microstructure model was integrated with finite element(FE)model to predict the tri-modal microstructure in the isothermal local loading forming.Its reliability and accuracy were verified by the microstructure observation at different locations of sample.Good agreements between the predicted and experimental results suggest that the developed microstructure model and its combination with FE model are effective in the prediction of tri-modal microstructure in the isothermal local loading forming of TA15alloy.

Simulation of dynamic recrystallization in 23Co13Ni11Cr3Mo steel using a modified cellular automaton

A modified cellular automaton(CA) program was developed to simulate the process of dynamic recrystallization(DRX) for 23Co13Ni11Cr3Mo ultrahigh strength steel.In this model,influences of deformation parameters on hardening rate and solute drag effect were considered.Moreover,an inverse analysis method was proposed for parameters identification of dislocation model and solute drag effect based on the results of isothermal compression tests on Gleeble-1500.Then,simulated microstructures under different deformation conditions were compared with those of experiments.A good agreement is achieved.Furthermore,influences of deformation parameters on microstructure evolution for 23Co13Ni11Cr3Mo steel were investigated in details.High strain is an effective measure to refine grain and improve homogeneity.Meanwhile,the desired deformation parameters are temperature of 1000-1050 °C and strain rate of 0.008-0.01 s-1 for obtaining grains smaller than 22.5 μm.

Effects of non-isothermal annealing on microstructure and mechanical properties of severely deformed aluminum samples:Modeling and experiment

In order to investigate the evolution of microstructure and flow stress during non-isothermal annealing,aluminum samples were subjected to strain magnitudes of 1, 2 and 3 by performing 2, 4 and 6 passes of multi-directional forging. Then, the samples were non-isothermally annealed up to 150, 200, 250, 300 and 350 ℃. The evolution of dislocation density and flow stress was studied via modeling of deformation and annealing stages. It was found that 2, 4 and 6 passes multi-directionally forged samples show thermal stability up to temperatures of 250, 250 and 300 ℃, respectively. Modeling results and experimental data were compared and a reasonable agreement was observed. It was noticed that 2 and 4 passes multi-directionally forged samples annealed non-isothermally up to 350 ℃ have a lower experimental flow stress in comparison with the flow stress achieved from the model.The underlying reason is that the proposed non-isothermal annealing model is based only on the intragranular dislocation density evolution, which only takes into account recovery and recrystallization phenomena. However, at 350℃ grain growth takes place in addition to recovery and recrystallization,which is the source of discrepancy between the modeling and experimental flow stress.

等温压缩对高强度汽车钢WHT1300HF的马氏体相变及微观组织的影响

通过等温形变研究了形变参数(形变温度、形变速率、形变量)对高强度汽车钢WHT1300HF的微观组织转变和形貌的影响规律。研究结果表明:增加奥氏体等温形变量,有利于铁素体的缺陷形核,促进了形变奥氏体向铁素体转变;奥氏体的形变强化导致马氏体相变阻力增大,马氏体相变开始温度(Ms)下降,细小晶粒数量和小角度晶界数量增多;增加奥氏体等温形变(40%)速率能同时促进马氏体和铁素体相变,但马氏体体积分数和小角度晶界数量减少,细小晶粒数量略有提高;降低等温形变温度加剧奥氏体的形变强化,导致Ms温度下降,马氏体体积分数、小角度晶界比例减少,细小晶粒数量增多,铁素体含量明显增加。