低碳9Ni钢的动态再结晶数学模型

利用MMS-300热模拟实验机对9Ni钢进行了温度范围为800～1150℃、应变速率范围为0.05～1s-1的单道次压缩实验.通过应力-应变曲线研究了9Ni钢的动态再结晶规律,采用硬化率-应力(θ-σ)曲线较精确地确定了动态再结晶的临界条件和峰值应力应变.采用回归法确定了双曲线本构方程中的材料常数和动态再结晶激活能(269kJ/mol),并建立了临界应变、峰值应变和峰值应力与无量纲参数Z/A之间的关系.利用Avrami方程和应力应变曲线建立了9Ni钢动态再结晶动力学模型.     

基于40Cr高温动态力学性能的磨削表面动态再结晶行为

通过分离式霍普金森压杆(SHPB)实验得到了40Cr合金钢在高温高应变率下真应力-真应变曲线，据此确定了材料发生动态再结晶的临界条件.采用解析法和实验法分别求解了磨削强化层的温度场和塑性应变场分布.结果表明，磨削强化层在磨削深度方向具有较大的温度和塑性应变梯度;150μm强化层内会发生奥氏体转变;磨削表面最高温度可达1060℃.在磨削亚表面60μm内会产生剧烈的塑性变形，达到了再结晶的临界条件.较大的磨削深度使磨削强化层塑性应变增大，再结晶现象越充分，微观组织细化程度越高.     

Nb-Ti微合金钢高温变形软化行为力学分析及析出物电镜分析

研究了Nb-Ti微合金钢高温变形时的软化行为和微合金钢动态和静态析出物的电镜分析.通过双道次恒应变速率压缩实验,从流变应力曲线用卸载法求出了不同热变形条件下的软化分数,并建立了静态再结晶、亚动态再结晶动力学模型,计算出静态再结晶、亚动态再结晶的表观激活能.同时,还对静态和动态析出行为进行了探讨,讨论了析出对软化行为的影响,并通过透射电子显微镜对析出物的形貌、大小、分布进行了观察,用衍射图谱进一步确定了析出物的成份.     

S38MnSiV非调质钢热变形行为及组织演变

利用MMS-300热模拟试验机开展单道次压缩实验和光学显微组织观察,研究了S38MnSiV非调质钢在温度为1173~1423K及应变速率为001~10s-1条件下的热变形行为,获得了应变速率和变形温度对该钢动态再结晶行为及组织的影响规律,按照双曲正弦方法确定了实验钢的热变形激活能和本构方程.结果表明:变形温度越高,应变速率越低,越有利于动态再结晶的发生;随着动态再结晶的进行,奥氏体平均晶粒尺寸随应变的增加逐渐减小;当应力达到稳态时,奥氏体晶粒尺寸不再随应变而发生变化.     

高级别X80/X100管线钢的包辛格效应

利用单轴压缩-拉伸试验研究了炉卷轧机生产X80/X100管线钢不同变形情况下的包辛格效应.结果表明:随着预压缩变形量的增大,包辛格效应绝对值增大,X100管线钢的包辛格效应在1.5%的预压缩变形量下达到饱和;包辛格效应绝对值随着板卷强度的提高而上升;在试验范围内,X80、X100管线钢分别表现出了瞬时软化和永久软化.分析X80/X100管线钢的化学成分与显微组织特点,认为管线钢组织中的软、硬相(如M/A岛)的强度差、硬相的体积分数以及初始组织中的位错密度是不同包辛格现象的关键因素.     

Dynamic recrystallization behavior of the Ti–48Al–2Cr–2Nb alloy during isothermal hot deformation

The hot deformation behavior of the as-cast Ti–48Al–2Cr–2Nb alloy was investigated by isothermal compression tests at deformation temperatures ranging from 1000℃ to 1200℃,and strain rates from 0.001 s~(-1)to 0.1 s~(-1).The single peak stress features common to all flow curves indicate that DRX is the dominating softening mechanism.The calculated values of the hot deformation activation energy Q and stress index n are 296.5 kJ mol~(-1)and 3.97,respectively.Based on this,the Arrhenius type constitutive equation was successfully established.The DRX critical condition model and relationship among DRX volume fractions,deformation temperatures and strain rates were obtained to optimize the process.Combined with microstructure analysis,it's concluded that 1200℃/0.01s~(-1)is the optimization parameter.Besides,both DDRX and CDRX were observed in theγphase evolution.The deformation mechanism from the inter-grain dislocation motion to the grain boundary migration and grain rotation was discussed.     

Hot deformation characteristics of as-cast high-Cr ultra-super-critical rotor steel with columnar grains

Isothermal hot compression tests of as-cast high-Cr ultra-super-critical (USC) rotor steel with columnar grains perpendicular to the compression direction were carried out in the temperature range from 950 to 1250°C at strain rates ranging from 0.001 to 1 s-1. The softening mechanism was dynamic recovery (DRV) at 950°C and the strain rate of 1 s-1, whereas it was dynamic recrystallization (DRX) under the other conditions. A modified constitutive equation based on the Arrhenius model with strain compensation reasonably predicted the flow stress under various deformation conditions, and the activation energy was calculated to be 643.92 kJ·mol-1. The critical stresses of dynamic recrystallization under different conditions were determined from the work-hardening rate (θ)–flow stress (σ) and -?θ/?σ–σ curves. The optimum processing parameters via analysis of the processing map and the softening mechanism were determined to be a deformation temperature range from 1100 to 1200°C and a strain-rate range from 0.001 to 0.08 s-1, with a power dissipation efficiency η greater than 31%.     

钢中动态再结晶力学测定及其数学模型

采用物理模拟的方法，对W18Cr4V高速钢和H13热作模具钢热变形过程中的动态再结晶规律进行了研究，提出采用加工硬化率-应变图可以判断动态软化的开始和结束所对应的应变．与传统的采用应力-应变图的方法相比，该方法具有准确、直观的优点．采用该方法，可以判断动态软化的类型．建立了W18Cr4V高速钢和H13热作模具钢的动态再结晶的动力学、晶粒尺寸的数学模型．     

Effect of compression direction on the dynamic recrystallization behavior of continuous columnar-grained CuNi10Fe1Mn alloy

The dynamic recrystallization (DRX) behavior of continuous columnar-grained (CCG) CuNi10Fe1Mn alloy was investigated by hot compression along the solidification direction (SD) and perpendicular to the solidification direction (PD). Specimens were compressed to a true strain of 0.8 at temperatures ranging from 25℃ to 900℃ and strain rates ranging from 0.01 to 10 s-1. The results indicate that DRX nucleation at grain boundaries (GBs) and DRX nucleation at slip bands (SBs) are the two main nucleation modes. For SD specimens, C-shaped bending and zig-zagging of the GBs occurred during hot compression, which made DRX nucleation at the GBs easier than that at the SBs. When lnZ ≤ 37.4 (Z is the Zener–Hollomon parameter), DRX can occur in SD specimens with a critical temperature for the DRX onset of ~650℃ and a thermal activated energy (Q) of 313.5 kJ·mol-1. In contrast, in PD specimens, the GBs remained straight, and DRX nucleation occurred preferentially at the SBs. For PD specimens, the critical temperature is about 700℃, Q is 351.7 kJ·mol-1, and the occurrence condition of DRX is lnZ ≤ 40.1. The zig-zagging of GB morphology can significantly reduce the nucleation energy at the GBs; as a result, DRX nucleation occurs more easily in SD specimens than in PD specimens.     

热连轧生产厚规格X80管线钢的静态再结晶行为及工艺优化

通过双道次压缩实验对首钢迁安公司2160热连轧生产的厚规格X80管线钢形变奥氏体静态再结晶行为进行了研究,依据实验规律对生产工艺进行了改进与优化.通过力学拉伸、冲击及落锤实验,对改进工艺后生产的X80钢的综合性能进行了检测,利用光学显微镜、扫描电镜和透射电镜对X80钢卷显微组织进行了观察分析.结果表明:变形温度是影响奥氏体静态再结晶行为的主要因素;微合金碳氮化物的析出抑制了再结晶的进行,使软化率曲线出现了平台;利用实验结果回归计算出了X80管线钢的静态再结晶激活能为380kJ·mol-1,并根据文献研究讨论了结果的合理性.通过工艺改进与优化,所生产X80钢卷的显微组织细小均匀,呈现典型的针状铁素体特征;析出相中主要包含复合的(Ti,Nb)(C,N)以及单个的NbC;X80钢卷棒状试样的拉伸性能较相关标准均有较大富余量,尤其在冲击、落锤性能方面表现出了良好的低温韧性.     

低Ni，Cr，Cu和Mo高性能桥梁钢的动态再结晶行为

采用单道次压缩实验研究了一种低Ni,Cr,Cu和Mo高性能桥梁钢的动态再结晶行为.同时,采用9次多项式对实测真应力-真应变曲线进行了拟合,消除了实测曲线上的波动,进而确定了不同条件下的加工硬化率-真应力曲线.加工硬化率-真应力曲线特征表明,在所研究的不同热压缩变形工艺条件下,均发生了动态再结晶.通过计算将常数α修正为0009MPa-1,得到了实验钢的动态再结晶激活能,确定了εc=063εp关系式,建立了动态再结晶临界应变模型.而且降低Ni,Cr,Cu和Mo含量将显著降低动态再结晶激活能.     

X80管线钢微孔洞形核

利用扫描电镜和透射电镜等手段,观察了X80管线钢中的夹杂物和MA岛,获得了它们的尺寸统计特征.应用不同颈缩程度的拉伸试验,探明了X80管线钢中微孔洞萌生的机理：第一阶段微孔洞的形核是围绕钙处理夹杂物,在颈缩初期已经开始;第二阶段属高应变量阶段,此时孔洞是通过MA岛/基体界面脱离形核.通过有限元法分析了拉伸过程,确定了试样的真实应力--应变曲线,计算了钙处理夹杂物/基体界面强度和MA岛/基体界面强度.     

形变量和冷却速度对低碳微合金管线钢晶粒细化的影响

以管线钢X52为研究对象,在Gleeble1500热模拟机上,主要进行了在奥氏体未再结晶区不同形变量和冷却速度对X52的相变行为及显微组织影响的研究·通过光学显微镜、扫描电镜分析技术可以发现,随形变量和冷却速度的增加,晶粒明显变细·实验结果表明,在奥氏体未再结晶区轧制可以大大地增加铁素体的形核位置,使晶粒细化;同时冷却速度的增大,使铁素体的形核驱动力加大,形核率增加,也使晶粒明显细化·另外,与低碳钢不同的是,在铁素体晶粒边界和铁素体晶粒内部可以观察到有第二相的析出,在奥氏体未再结晶区轧制时,第二相的析出可以抑制再结晶,并且,析出物的存在不仅阻碍位错的运...     

Static Recrystallization Behavior of SCM435 Steel

The static recrystallization behaviors in SCM435 steel were investigated by two-pass hot compression tests on MMS-200 thermosimulation machine. Effects of deformation temperature, strain rate,deformation degree and the initial austenite grain size on static softening were analyzed. The stress compensation method was used to calculate the static recrystallization. The kinetics model of the static recrystallization of SCM435 steel was established and the obtained activation energy for static recrystallization was 182. 8 kJ /mol. Results showed that within a certain time interval( 1-100 s),the static recrystallization fraction X of SCM435 steel increased as the deformation temperature,the deformation rate and the amount of deformation increased,and it decreased as the initial grain size increased and increased as the time interval increased.     

X100管线钢的高温变形力学行为

采用Gleeble-3500热模拟试验机对X100管线钢进行单道次压缩试验,研究其变形抗力与应变量、应变速率和变形温度的关系,利用回归分析确立合适的变形抗力数学模型,并将模型预测值与试验值进行比较。结果表明,变形温度对X100管线钢变形抗力影响显著;高温低应变速率更有利于X100管线钢回复和再结晶的发生;应变速率过高会引起非稳态变形,不利于X100管线钢轧制过程的控制;利用回归分析确定的变形抗力模型能够准确预测X100管线钢的变形抗力,相关系数为0.986。     

316L不锈钢动态再结晶行为

在Gleeble-1500热模拟试验机上, 通过高温压缩实验对316L不锈钢的动态再结晶行为进行了系统研究. 结果表明:316L不锈钢热变形加工硬化倾向性较大, 在真应力应变曲线上没有出现明显的应力峰值σ_p;316L不锈钢在热变形过程中发生了动态再结晶, 但只是在局部区域观察到了动态再结晶晶粒. 对动态再结晶的实验数据进行拟合, 得到316L不锈钢的热激活能和热变形方程, 并给出了发生动态再结晶的临界应变和临界应力以及Zener-Hollomon参数和稳态应力的关系.     

低碳、Ti-V复合微合金化钢的流变应力模型

通过单道次压缩实验,研究了一种低碳、Ti-V复合微合金化钢在温度为1 173~1 373 K及应变速率为0.1~10 s-1条件下的奥氏体应力-应变行为;基于Akben等对溶质阻碍动态再结晶的量化研究工作,获得了本实验钢的近似的形变激活能Qdef及Zener-Hollomon参数;采用Jonas等的分析方法,计算得到回复参数r和r’、屈服应力σ0、饱和流变应力σsat和动态再结晶临界应力σc与Z参数的关系;获得了动态再结晶动力学,并最终建立流变应力数学模型.     

ZK31+0.3Yb镁合金的热力模拟

通过热压缩变形实验, 利用光学显微镜观察, 对ZK31 0.3Yb镁合金变形过程的流变应力和组织演变进行研究. 研究结果表明: 663 K/0.1 s-1是最佳的变形条件, 在此条件下, 合金的流变应力低, 动态再结晶充分激发, 合金的塑性好;当变形温度降至623 K和573 K时, 动态再结晶不能充分激发, 合金变形的流变应力明显提高, 尤其是573 K变形时流变应力达到185 Mpa;而变形温度提高到723 K时, 晶界处形成楔形裂纹, 合金的塑性差;在663 K时变形, 尽管应变速率降低至0.001 s-1, 合金的动态再结晶充分激发, 流变应力下降, 但变形的进程被减缓;当变速率提高到1.000 s-1时, 晶粒间的协调变形不能发挥作用, 合金的塑性最差.     

Hot ductility behavior of V-N and V-Nb microalloyed steels

The hot ductility of V-N and V-Nb microalloyed steels was investigated on a Gleeble-1500 thermomechanical simulator, and the results were compared with those of V and Nb microalloyed steels. A ductility trough is found in both the steels in the temperature range of 700 to 1050℃. Compared to the V steel, the V-N steel has a wider and deeper ductility trough with the increase of N content, due to the increased precipitation of V(C, N) in the steel. Above 930℃, when 0.047wt% V is added to the 0.028wt% Nb-containing steel, the ductility becomes worse, owing to the rise of the onset dynamic recrystallization temperature. However, the ductility gets better at 800 to 930℃ because of the coarsening of precipitates in austenite. With the improvement in ductility, the fracture mechanism is changed from intergranular to high ductile fracture in the temperature range of 800 to 1050℃.     

Thermal and microstructural characterization of a novel ductile cast iron modified by aluminum addition

In high-temperature applications, like exhaust manifolds, cast irons with a ferritic matrix are mostly used. However, the increasing demand for higher-temperature applications has led manufacturers to use additional expensive materials such as stainless steels and Ni-resist austenitic ductile cast irons. Thus, in order to meet the demand while using low-cost materials, new alloys with improved high-temperature strength and oxidation resistance must be developed. In this study, thermodynamic calculations with Thermo-Calc software were applied to study a novel ductile cast iron with a composition of 3.5 wt% C, 4 wt% Si, 1 wt% Nb, 0-4 wt% Al. The designed compositions were cast, and thermal analysis and microstructural characterization were performed to validate the calculations. The lowest critical temperature of austenite to pearlite eutectoid transformation, i.e., A1, was calculated, and the solidification sequence was determined. Both calculations and experimental data revealed the importance of aluminum addition, as the A1 increased by increasing the aluminum content in the alloys, indicating the possibility of utilizing the alloys at higher temperature. The experimental data validated the transformation temperature during solidification and at the solid state and confirmed the equilibrium phases at room temperature as ferrite, graphite, and MC-type carbides.