Deformation behavior of a low carbon steel in α+γ range under electric current heating

The effect of electric current (EC) heating on deformation and phase transformation behavior is studied for plain low carbon steel. It is shown that EC heating does not sensibly influence the deformation resistance of austenite. During deformation at the upper temperatures of the α+γ range the EC-effect is positive (flow stress decreases upon application of EC) while at the lower temperatures of the α+γ range the EC-effect is negative. This is accompanied by variations in the work hardening rate of the same sign. The EC-effect in the α+γ range is more pronounced at lower strain rates when the contribution of the EC heating to the overall temperature of the specimen is higher. EC heating combined with deformation leads to an increase in the A_r3 temperature. The magnitude and the sign of EC-effects on deformation resistance and transformation behavior in the α+γ range are related to the differences in electric resistivity and deformation resistance between the emerging and the parent phases. A negative difference in electric resistivity and deformation resistance accelerates the phase transformation and leads to a positive EC-effect, and vice versa.     

2507超级双相不锈钢的流变应力本构关系及热加工图

采用Gleeble-3800热模拟试验机研究了热变形温度为950~1200 ℃、应变速率为 0.01~10 s^-1条件下2507超级双相不锈钢的热压缩变形行为,并借助光学显微镜观察了不同变形过程中的微观组织演化。基于试验数据分析,建立2507超级双相不锈钢的流变应力本构关系及热加工图。结果表明:流变应力随着变形温度的升高和应变速率的降低而逐渐降低,在高应变速率下,流变曲线出现“类屈服平台”。试验钢的热变形激活能为414.57 kJ·mol^-1,应力指数为4.18,峰值应力本构方程为ε·=3.69×10¹⁵[sinh(0.0101σ)]^4.18exp-414.57RT,根据微观组织分析及热加工图确定出试验钢的最佳热加工区域为热压缩温度1060~1120 ℃,应变速率0.01~0.1 s^-1。     

409L铁素体不锈钢热变形行为

采用热/力模拟实验方法研究了409L铁素体不锈钢(409LFSS)在950～1150℃、应变速率为0.05～2.5 s-1条件下的热变形及组织变化,讨论了热变形参数对流变应力和显微组织的影响.结果表明,409L铁素体不锈钢的表观应力指数及热变形表观激活能分别为4.45、262 kJ/mol;其热变形方程为ε=5.347×1011[sinh(α·σp)]4.45exp(-262000/RT);该钢的铁素体软化机制与Z参数有关,且随着Z值从2.09×108增加到3.92×1011,热变形峰值应力相应从13.73 MPa增加到65.08 MPa.     

21Cr节镍型双相不锈钢高温形变过程的静态软化分析

采用热模拟研究了21Cr双相不锈钢在高温变形道次间隔时间内的静态软化行为,讨论了变形温度、应变速率和变形程度对静态再结晶行为及微观组织的影响。结果表明,变形条件通过影响两相内部应变分配进一步影响双相不锈钢静态软化行为。随着变形温度和变形程度增加,铁素体相内承担的应变增加,铁素体内部再结晶程度增加,促进双相不锈钢的静态软化程度增加;而随着应变速率的增加,试验钢静态软化率的变化规律与奥氏体相承担的应变变化规律相同,都呈现出先降低后升高的变化趋势,奥氏体相在应变速率为1 s^-1时的内部再结晶程度最低。21Cr双相不锈钢静态再结晶激活能约为301 kJ/mol。     

304奥氏体不锈钢热变形行为及热加工图

在应变速率为0.1~10 s~(-1)、变形温度为800~1200℃的变形条件下,利用Gleeble-1500热模拟机对304奥氏体不锈钢进行单向热压缩实验,研究其高温下的流变行为。根据实验数据,304奥氏体不锈钢的流变应力随温度和应变速率变化明显,应变速率越大,变形温度越低,流变应力越大。基于Arrhenius模型推导出材料的热变形本构方程,并算得材料的热变形激活能为486.0 k J·mol~(-1)。建立了真应变为0.7时的热加工图,结合微观组织分析表明:变形温度为1025~1200℃、应变速率为0.1~0.8 s~(-1)时,材料功率耗散系数大于26%,变形过程中发生动态再结晶,此范围为304奥氏体不锈钢的最佳工艺参数。     

316L不锈钢25～350℃中的拉伸行为及流变应力计算

通过高温试验装置在模拟井下工况温度25～350℃范围内进行了316L不锈钢的拉伸试验。结合拉伸试验数据、拉伸后微观结构以及断口形貌对316L不锈钢的25～350℃范围内的拉伸变形行为进行了探讨。应用温加工变形理论,建立了316L不锈钢在井下温度场环境中的形变本构方程。基于拉伸试验数据,计算了应变速率因子Z,变形激活能Q,建立了316L不锈钢温变形过程的流变应力计算模型,为完井设计中膨胀管膨胀施工提供了参考依据。     

X12CrMoWVNbN钢的热变形行为及热加工图

利用Gleeble3180热模拟试验机,在变形温度为950~1100 ℃,应变速率为0.001~1 s^-1,真应变为0.7的条件下,对X12CrMoWVNbN钢进行了高温单向热压缩试验。通过不同条件下的高温流变曲线分析了变形温度和应变速率对试验钢热变形力学行为的影响。以Arrhenius方程为本构模型,建立了能够预测该钢流动应力的本构方程。基于动态材料模型和试验参数、结果,绘制了该钢不同应变量下的热加工图并结合图进行了组织分析。结果表明,流变峰值应力和稳态应力随温度降低或应变速率升高而升高;功率耗散系数随应变速率降低和变形温度的升高而增大;最优热加工区域功率耗散系数η的值都在0.4以上,且这些区域的变形组织晶粒均匀细小;0.3、0.4、0.5和0.6应变下的最优热加工区域都处于变形温度1050~1100 ℃、应变速率0.001~0.003 s^-1的范围。     

基于摩擦-温度双修正的Maraging250钢热变形行为及热加工图

采用Gleeble-3800热模拟试验机,通过热压缩试验研究了变形温度900~1200 ℃、应变速率0.001~10.0 s^-1时,Maraging250钢的热变形行为,综合考虑摩擦效应和变形热效应,对流变应力曲线进行摩擦修正和温度修正,建立双修正条件下的Maraging250钢本构方程和热加工图,并针对真应变为1.2的热加工图分析了试验钢在不同变形条件下的微观组织变化。结果表明,在相同试验条件下,变形温度降低或应变速率升高,摩擦效应对试验钢流变应力影响越显著;变形热仅在低温、高应变速率条件下对流变应力有显著影响。由变形热引起的最大温升约80 ℃、流变应力最大变化约20 MPa。利用双修正的流变应力曲线计算出试验钢的热变形激活能为393.552 02 kJ/mol,并建立了Z参数方程和本构方程,绘制了真应变ε=0.4、0.8和1.2的热加工图。结合微观组织分析,Maraging250钢在1000～1125 ℃、0.001～1.0 s^-1范围内能获得均匀细小的动态再结晶组织,具有较佳的热加工性能。     

13Cr超级马氏体不锈钢热压缩变形行为与组织演变

通过Gleeble-3500热模拟试验机对13Cr超级马氏体不锈钢进行单道次压缩变形试验,系统研究变形温度在950~1150 ℃、应变速率为0.001~10 s^-1条件下的热变形行为。利用双曲正弦模型建立了13Cr超级马氏体不锈钢的流变应力本构方程,求得试验钢的热变形激活能为412 kJ/mol,并基于动态材料模型(DMM)理论绘制了材料的热加工图,得出材料的最佳热变形工艺参数窗口为:变形温度1032~1072 ℃,应变速率0.039~0.087 s^-1。组织演变结果表明,试验钢在高变形温度和低应变速率的条件下,容易发生动态再结晶。当应变速率一定时(0.01 s^-1),变形温度从950 ℃升到1050 ℃,动态再结晶的体积分数从18.7%升高到60.1%,组织的再结晶程度提高,晶粒均匀细小;当变形温度一定时(1050 ℃),随着应变速率的降低,动态再结晶的晶粒长大粗化。     

1Cr22Mn15N不锈钢的高温变形行为研究

采用热／力模拟试验等方法研究了1Cr22Mn15N奥氏体不锈钢在不同温度和应变速率条件下的热变形行为及组织变化，讨论了热变形参数对流变应力和显微组织的影响。结果表明，在上述变形条件下1Cr22Mn15N的软化机制与Zener．Hollomon（Z）参数有关，并建立了变形抗力模型，其应力指数为6．45，热变形激活能为746．5kJ／mol。     

Microstructure Evolution and Strain-Dependent Constitutive Modeling to Predict the Flow Behavior of 20Cr–24Ni–6Mo Super-Austenitic Stainless Steel During Hot Deformation

Hot compression tests were carried out with specimens of 20 Cr–24 Ni–6 Mo super-austenitic stainless steel at strain rate from 0.01 to 10 s~(-1) in the temperature range from 950 to 1150 °C, and flow behavior was analyzed. Microstructure analysis indicated that dynamic recrystallization(DRX) behavior was more sensitive to the temperature than strain rate, and full DRX was obtained when the specimen deformed at 1150 °C. When the temperature reduced to 1050 °C, full DRX was completed at the highest strain rate 10 s~(-1) rather than at the lowest strain rate 0.01 s~(-1) because the adiabatic heating was pronounced at higher strain rate. In addition, flow behavior reflected in flow curves was inconsistent with the actual microstructural evolution during hot deformation, especially at higher strain rates and lower temperatures. Therefore, flow curves were revised in consideration of the effects of adiabatic heating and friction during hot deformation. The results showed that adiabatic heating became greater with the increase of strain level, strain rate and the decrease of temperature, while the frictional effect cannot be neglected at high strain level. Moreover, based on the revised flow curves, strain-dependent constitutive modeling was developed and verified by comparing the predicted data with the experimental data and the modified data. The result suggested that the developed constitutive modeling can more adequately predict the flow behavior reflected by corrected flow curves than that reflected by experimental flow curves, even though some difference existed at 950 °C and0.01 s~(-1). The main reason was that plenty of precipitates generated at this deformation condition and affected the DRX behavior and deformation behavior, eventually resulted in dramatic increase of deformation resistance.     

TC21G钛合金平面应变变形行为及其机理

利用平面应变压缩实验,研究TC21G钛合金在变形温度为870～940℃、应变速率为0.1～1 s-1条件下的变形行为,并分析显微组织的演变过程.同时,研究加工参数对应变硬化指数n值的影响.结果表明:在应变速率一定的条件下,随着变形温度的升高,显微组织中 β 相的含量增加,合金的流变应力降低;而在变形温度一定的条件下,随...     

X65管线钢的高温热变形行为研究

采用Gleeble-3500热模拟试验机研究了X65管线钢的高温热变形行为.结果表明,X65管线钢在给定的试验条件下,随着变形温度降低及应变速率增加,流变应力增加,同时峰值应变增加;实验钢的热变形激活能为276.9kJ/mol,建立了X65管线钢的热变形方程,确立了峰值应力σ_p与Zener-Hollomon因子的关系.     

钛、铌对16%Cr超低碳氮铁素体不锈钢的再结晶和力学性能的影响研究

实验室研究了钛、铌对16%Cr超低碳氮铁素体不锈钢的高温塑性、再结晶温度以及冷轧板力学性能的影响。结果表明,变形温度和应变速率对变形抗力的影响十分显著,而不同含量的钛、铌对钢的变形抗力影响很小。当变形温度达到1 350℃时,三种成分钢的抗拉强度和塑性急剧下降。钛、铌的加入对钢板的完全再结晶温度有一定的影响,即加钛或加铌均延迟再结晶。不加钛、铌的钢在拉伸时有明显的屈服现象,且屈服强度较高,r值较低,而加钛或钛、铌复合加入的钢没有明显的屈服现象,r值较高均达1.50以上。     

316LN奥氏体不锈钢的高温流变行为与本构模型

利用Gleeble-3500热模拟试验机对锻造态316LN不锈钢进行了等温热压缩试验,研究了应变速率为0.001～1 s^-1、变形温度为1223～1523 K、压缩变形量为65%条件下材料的高温流变行为,建立了流变应力本构模型,并将其应用于Deform-3D软件平台,通过导入新材料数据,考虑界面摩擦等尺寸仿真了热模拟试验结果。结果表明:相同应变速率下,随着变形温度升高,316LN奥氏体不锈钢的压缩应力逐渐减小;相同变形温度下,随着应变速率增加,材料的压缩应力逐渐增大;且在真应力-真应变曲线中,随应变量增大,压应力在后期逐渐达到一个稳定值;考虑界面摩擦因数,并利用Arrhenius本构模型进行变形模拟仿真说明了本构方程和仿真模型的有效性和可靠性,可为316LN不锈钢材料的工程应用提供研究基础和理论依据。     

316LN高温热变形行为与热加工图研究

通过Gleeble热模拟实验机在1000~1200℃,应变速率为0.01~10 s~(-1)条件下的近等温热模拟压缩实验,建立了316LN双曲正弦的流动应力预测模型及其热加工图。该流动应力预测模型考虑了实验过程中塑性变形和摩擦引起的温升,对流动应力进行了修正,考虑应变对流动应力预测模型参数的影响,获得了统一流动应力预测模型,模型预测值与实验值的相关系数为0.992,平均相对误差为4.43%;热加工图基于Prasad动态材料模型分别获得了不同应变速率、温度条件下的能量耗散率和失稳系数;分析了应变量、温度和应变速率对于能量耗散率和失稳系数的影响。结果表明:实验条件下最大能量耗散率值为0.38,且高应变速率下失稳,并通过显微组织分析对热加工图进行了验证。     

Continuous dynamic recrystallization of AISI 430 ferritic stainless steel

The high-temperature deformation behavior of AISI 430 ferritic stainless steel was studied by torsion tests. The deformation tests were performed in the temperature range of 900–1100°C and strain rate range of 5.0×10⁻² −5.0/sec. The evolutions of flow stress and microstructure show the characteristics of continuous dynamic recrystallization (CDRX). The flow stress gradually decreased with strain over the peak stress without steady state. Below the 100% effective strain, grains appeared in small angle grain boundaries with a misorientation of 3–9°. In addition, when heavy deformation (>300%) was applied, higher misorientation (∼15°) was achieved. The tendency of CDRX increased with increasing strain rate and decreasing temperature. The dependence of CDRX grain size on the strain rate and temperature was discussed.     

Influence of Vanadium Content on Hot Deformation Behavior of Low-Carbon Boron Microalloyed Steel

Single-pass compression tests were performed to investigate the hot deformation behavior of low-carbon boron microalloyed steel containing three various vanadium contents at 900-1100℃ and strain rate of 0.01-10 s~(-1) using the MMS-300 thermal mechanical simulator.The flow stress curves of investigated steels were obtained under the different deformation conditions,and the effects of the deformation temperature and strain rate on the flow stress were discussed.The characteristic points of flow stress were obtained from the stress dependence of strain hardening rate;the activation energy of investigated steels was determined by the regression analysis;the flow stress constitutive equations were developed;the effect of vanadium content on the flow stress and dynamic recrystallization(DRX) was investigated.The result showed that the flow stress and activation energy(3-6.5 kJ mol~(-1)) of the steel containing 0.18 wt% V were significantly higher than those of the steels with0.042 wt% and 0.086 wt% V,which was related to the increase in solute drag and precipitation effects for higher vanadium content.DRX analysis showed that the addition of vanadium can delay the initiation and the rate of DRX.     

不同热变形条件下310S奥氏体不锈钢动态再结晶行为研究

利用显微组织观察和显微硬度测试两种方法研究了热压缩试验后的310S奥氏体不锈钢动态再结晶行为,热压缩试验在Gleeble-3800热模拟试验机上进行,应变速率采用0.1s-1和1s-1、变形温度在900~1150℃之间。研究结果表明,随着变形温度的升高,310S奥氏体不锈钢的变形抗力降低。在应变速率为0.1s-1时,其完全动态再结晶的变形温度为1000℃;应变速率升高至1s-1时,其完全动态再结晶的变形温度升高至1100℃,高的应变速率可以细化再结晶晶粒。     

微合金元素Nb对高碳合金钢动态再结晶行为的影响

为研究微合金元素Nb对高碳合金钢动态再结晶行为的影响,利用Gleeble-3500热模拟试验机进行单道次压缩试验,测定了高碳合金钢在变形温度为950~1150 ℃、应变速率为0.01~5 s^-1的流变应力曲线,利用Zeiss光学显微镜观察了奥氏体动态再结晶晶粒形态,通过回归计算获得了相应的再结晶激活能,建立了热变形方程。结果表明:较高的变形温度和较低的应变速率有利于含铌高碳合金钢发生动态再结晶;含铌高碳合金钢的动态再结晶晶粒尺寸随着变形温度的升高而增大,当变形温度为1050 ℃时,含铌高碳合金钢已大量出现动态再结晶晶粒;0.040%铌加入到高碳合金钢中,在应变速率为0.1 s^-1,变形温度为1150 ℃时推迟了钢的动态再结晶开始时间约2.23 s,动态再结晶形变激活能增加了52.26 kJ/mol。