铸态超级双相不锈钢S32750热加工性能

 为研究热变形参数对铸态超级双相不锈钢S32750热变形行为和显微组织的影响,运用Gleeble-3800热模拟试验机对S32750进行不同温度和应变速率下的高温拉伸和压缩试验。结果表明,S32750在1000~1200℃范围内具有较好的热塑性。在变形温度较低、应变速率较低时,流变曲线表现出不同于单相不锈钢的“类屈服平台”特征;当应变速率较高或变形温度较高、应变速率较低时,流变曲线为典型的动态再结晶特征。微观组织演变显示,铁素体和奥氏体两相都发生动态再结晶,且铁素体的再结晶先于奥氏体。降低应变速率,提高变形温度,可促进动态再结晶发生。基于热变形动力学模型建立了本构方程,表观应力指数为3.99,热变形激活能为393.75kJ/mol。S32750的高温软化机制与Zener-Hollomon(Z)参数有关,随Z参数增加,热变形峰值应力增加。     

一种钒氮微合金钢的静态再结晶行为

 通过双道次压缩试验,研究一种钒氮微合金钢道次间隔时间内在奥氏体区变形后的软化行为,采用应力补偿法计算静态再结晶的体积分数,并建立静态再结晶动力学模型。分析变形温度与间隔时间以及钒的析出物对静态软化行为的影响。结果表明,在高于900℃时进行第一道次变形,该钒氮微合金钢很快完成了静态再结晶;在850、800℃变形后的等温阶段,发生了形变诱导析出现象,使再结晶激活能增加,静态再结晶进程受到抑制,导致软化率曲线上出现了平台。     

X70管线钢热变形奥氏体的静态再结晶行为

通过双道次压缩实验,在Gleeble1500热模拟试验机上研究了X70管线钢在不同变形工艺下奥氏体的软化行为,分析了不同变形温度、间隔时间、应变速率、变形量及初始奥氏体晶粒尺寸等参数对静态再结晶行为的影响规律,采用应力补偿法计算了不同变形条件下的静态再结晶百分率.根据实验数据,计算出X70管线钢静态再结晶激活能为435.3kJ·mol^-1,建立了其静态再结晶动力学模型.     

Dynamic Recrystallization Behavior of Medium Carbon Cr-Ni-Mo-Nb Steel during Hot Deformation

Hot compression deformation behaviors of medium carbon Cr-Ni-Mo-Nb steel were investigated at deformation temperatures ranging from 1223 to 1423 Kand strain rates of 0.1,1and 5s^-1.Dynamic recovery（DRV）and dynamic recrystallization（DRX）were observed during the hot compression deformation.For all of the samples,DRX occurred at deformation temperatures above 1323 Kat different strain rates,while below 1223 K,no DRX was observed.The activation energy of the tested steel was determined as 386.06kJ/mol.The ratio of critical stress to peak stress and the ratio of critical strain to peak strain were 0.835 and 0.37,respectively.Kinetic equations interpreting the DRX behavior of the tested steel were proposed,and the corresponding parameters including the volume fraction and the average grain size were determined.Moreover,the microstructures induced under different deformation conditions were analyzed.     

热连轧生产船板钢E36静态再结晶行为研究

基于热模拟双道次压缩试验,研究了热连轧生产过程中船板钢E36奥氏体变形区不同变形温度、变形间隙时间内的软化行为,分析了变形温度和轧制变形间隙时间对静态再结晶软化率的影响,结果表明：变形温度是影响再结晶的最主要因素,在达到轧制变形温度时,随着轧制间隙时间的延长,再结晶软化率呈现逐步递增的趋势。通过金相分析,得出了最佳轧制...     

Dynamic and Static Recrystallization Behaviour of Coarse-grained Austenite in a Nb-V-Ti Microalloyed Steel简

The dynamic recrystallization （DRX） and static recrystallization （SRX） behaviour of coarse-grained aus- tenite in a Nb-V-Ti microalloyed steel were studied by using a Gleeble thermomechanical simulator. Continuous and interrupted compression tests of coarse-grained austenite were performed in the temperature range of 1000-1 150 ℃ at a strain rate of 0. 1- 5 s 1. The peak and critical strains for the onset of DRX were identified with strain hardening rate analysis, and the ratio of critical strain to peak strain was found to be consistent with the one reported for fine- grained austenite. An equation of the time for 50% softening was proposed by considering the activation energy of steel without microalloying elements and the solute drag effect of microalloying elements. Strain-induced precipitation may not take place at the deformation temperature above 1000 ℃, which indicates that SRX of coarse-grained aus- tenite is mainly retarded by coarse grain size and Nb in solution during rough rolling.     

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.     

Hot Compression Behavior of AsCast Precipitation Hardening Stainless Steel

 High temperature deformation characteristics of a semiaustenitic grade of precipitation hardening stainless steels were investigated by conducting hot compression tests at temperatures of 900-1 100 ℃ and strain rates of 0001-1 s-1. Flow behavior of this alloy was investigated and it was realized that dynamic recrystallization (DRX) was responsible for flow softening. The correlation between critical strain for initiation of DRX and deformation parameters including temperature and strain rate, and therefore, Zener Hollomon parameter (Z) was studied. Metallographic observation was performed to determine the as deformed microstructure. Microstructural observation shows that recrystallized grain size increases with increasing the temperature and decreasing the strain rate. The activation energy required for DRX of the investigated steel was determined using correlations of flow stress versus temperature and strain rate. The calculated value of activation energy, 460 kJ/mol, is in accordance with other studies on stainless steels. The relationship between peak strain and Z parameter is proposed.     

Effect of Niobium on Dynamic Recrystallization Behavior of 5%Ni Steel

 The single-pass hot compressions of two 5%Ni steels with and without niobium addition at different temperatures of 800-1150 ℃ and strain rates of 0. 01-1 s-1 were performed by using a Gleeble-3500 thermal simulator and the effect of niobium on the dynamic recrystallization (DRX) behavior was analyzed. The results showed that the niobium addition of 0. 04% can retard DRX in 5%Ni steel significantly by increasing the activation energy for DRX from 394 to 462 kJ/mol. The critical strain required for starting DRX in 5%Ni steel was increased by 0. 04-0. 10 with niobium addition when the steel was deformed at a strain rate of 0. 01 s-1 and temperatures varied from 950 to 1000 ℃. The critical temperature required for starting DRX in 5%Ni steel was also increased from 1000 to 1050 ℃ with niobium addition when the steel was deformed at a strain rate of 0. 1 s-1. Such a retarded DRX occurring in Nb-added 5%Ni steel can be attributed to the pinning effect of precipitates containing niobium.     

Dynamic Recrystallization Behavior of GCr15SiMn Bearing Steel during Hot Deformation

The hot deformation behavior of GCr15SiMn steel was studied through high temperature compression tests on the Gleeble-1500 thermal-mechanical simulator. The initiation and evolution of dynamic recrystallization （DRX） were investigated with microstructural analysis and then the process variables were derived from flow curves. In the present deformation conditions, the curves of strain hardening exponent （n） and the true strain （e） at the deformation temperature of 1423 K and strain rates of 0.1, 1 and 10 s^-1 exhibit single peak and single valley. According to Zener-Hollomon and Ludwik equation, the experimental data have been regressed by using linear method. An expression of Z parameter and hot deformation equation of the tested steel were established. Moreover, the Q values of GCrlSSiMn and GCr15 steels were compared. In order to determine the recrystallization fraction under different con ditions, the volume fraction of DRX as a function of process variables, such as strain rate （ε）, temperature （T）, and strain （ε）, was established. Itwas found that the calculated results agreed with the mierostructure of the steel at any deformation conditions.     

WNQ570桥梁钢的静态再结晶行为

 为了研究轧制工艺对WNQ570桥梁钢再结晶行为的影响,采用Gleeble-3500热模拟试验机模拟了其双道次热变形过程,测试了试验钢的应力-应变曲线,建立了静态再结晶晶粒体积分数随变形温度和道次间隔时间变化的关系模型,分析了应变诱导析出抑制对静态软化行为的影响。研究结果表明：静态再结晶体积分数随变形温度的提高或道次间隔时间的延长而增大,应变诱导析出抑制静态再结晶的进行;静态再结晶激活能为240.47kJ/mol。研究结果为制订试验钢二阶段控轧工艺提供了依据。     

含铌微合金钢低温区静态软化行为

 通过两道次压缩变形实验对含Nb微合金钢静态软化行为进行了研究。结果表明：含Nb微合金钢静态再结晶临界温度随应变量增大而降低;随原始奥氏体晶粒尺寸增加而升高。温度高于静态再结晶临界温度时,含Nb微合金钢的静态再结晶激活能为常数(170589 kJ/mol);温度低于静态再结晶临界温度时,由于Nb的碳氮化物应变诱导析出,含Nb微合金钢的静态再结晶激活能为温度的函数,静态再结晶临界温度可通过再结晶激活能与温度倒数的关系曲线来确定。     

Q345B结构钢的热压缩变形行为及流变应力模型

 利用Gleeble-1500D热模拟试验机对钒、钛、铌微合金化Q345B低合金高强度结构钢（HSLA）进行了高温单道次压缩试验。测量了不同变形温度和变形速率下该钢的变形行为,分析了各变形参数对该钢动态再结晶和变形抗力的影响,得出动态再结晶激活能为451.47kJ/mol。并且建立了高温变形抗力的分段函数流变模型,该模型计算结果与试验值吻合较好。     

GCr15轴承钢静态再结晶行为

在Gleeble-3800热模拟实验机上利用双道次热压缩的实验方法,获得了GCr15轴承钢在不同实验条件下的应力-应变曲线,研究了该钢种在高温变形道次间隔时间内的静态软化行为以及再结晶规律,模拟材料热加工组织性能,为制定合理的轧制工艺提供实验基础和理论依据。分析了变形温度、应变速率和道次间隔时间对其静态再结晶行为的影响,建立了GCr15钢静态再结晶动力学模型,相应的静态再结晶激活能约为118.72kJ/mol。结果表明:静态再结晶体积分数随变形温度的升高、应变速率的提高或道次间隔时间的延长而增大。     

700℃超超临界锅炉材料GH4700合金热压缩行为

利用变形温度为1120~1210℃、应变速率为0.1~20 s^-1以及变形量为15%~60%的等温热压缩实验研究了GH4700合金的热变形行为.通过对低温和高应变速率条件下的形变热效应进行修正,得到准确的流变曲线,推导出描述峰值应力与温度和应变速率等变形参数的本构方程,并得到GH4700合金热变形表观激活能为322 kJ.组织分析表明,动态再结晶是热变形过程中最主要的软化方式,再结晶形核方式为应变诱发晶界迁移,变形温度升高和应变速率增大均有利于再结晶形核.再结晶发展阶段,随着变形量的增大和变形温度的升高,动态再结晶比例增加,在应变速率-温度坐标中,再结晶比例等值线呈反\     

904L不锈钢动态再结晶行为

采用单道次热压缩试验,研究了904L钢在不同变形温度、不同应变速率下的真应力-应变曲线以及组织形貌,阐明了热加工过程中热变形参数对其在变形过程中发生的动态再结晶行为及微观组织演变规律的影响,揭示了其相应的软化机制。结果表明:变形温度越高,流变应力越小,动态再结晶体积分数越高,晶粒尺寸越大;同温度下,变形速率越小,应力峰值越小,晶粒尺寸越大且晶界越平直化;904L钢的动态再结晶行为随着变形温度的升高,应变速率的减小,应变量的增大而进行得越充分且较高的变形温度有利于动态再结晶的进行。     

Effects of Temperature and Strain Rate on Flow Behavior and Microstructural Evolution of Super Duplex Stainless Steel under Hot Deformation

Hot compression tests were carried out in the temperature range of 1 223-1 473 Kand strain rate range of0.01-30s-1 to investigate the flow behavior and microstructural evolution of super duplex stainless steel 2507(SDSS2507).It is found that most of the flow curves exhibit a characteristic of dynamic recrystallization(DRX)and the flow stress increases with the decrease of temperature and the increase of strain rate.The apparent activation energy Qof SDSS2507 with varying true strain and strain rate is determined.As the strain increases,the value of Qdeclines in different ways with varying strain rate.The microstructural evolution characteristics and the strain partition between the two constituent phases are significantly affected by the Zener-Hollomon parameter(Z).At a lower lnZ,dynamic recovery(DRV)and continuous dynamic recrystallization(CDRX)of the ferrite dominate the softening mechanism during the compression.At this time,steady state deformation takes place at the last stage of deformation.In contrast,a higher lnZ will facilitate the plastic deformation of the austenite and then activate the discontinuous dynamic recrystallization(DDRX)of the austenite,which leads to a continuous decline of the flow stress even at the last deformation stage together with CDRX of the ferrite.     

Recrystailization Behavior of Deformed Austenite in High Strength Microalloyed Pipeline Steel

Using methods of single-hit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator,the curves of flow stress and stress relaxation,the microstructure and the recrystallization behavior of Nb-V-Ti high strength microalloyed low carbon pipeline steel were studied,and the influence of the thermomechanical treatment parameters on dynamic and static recrystallization of the steel was investigated.It was found that microalloying elements improved the deformation activation energy and produced a retardation of the recrystallization due to the solid solution and precipitation pinning.The deformation conditions such as deformation temperature,strain,and strain rate influenced the recrystallization kinetics and the microstructure respectively.Equations obtained can be used to valuate and predict the dynamic and static recrystallizations.     

铌、钒对高强钢筋再结晶影响及轧制工艺设计

 为了研究和设计高强钢筋添加铌、钒后轧制过程中对奥氏体区再结晶行为的量化管控,采用Gleeble-3500热模拟机对铌、钒微合金化高强螺纹钢进行单轴热压缩试验,基于再结晶临界条件的热力学原理,通过对不同形变条件下应力-应变曲线分析,采用Avrami方程得到了不同变形条件下的再结晶动力学曲线,并根据再结晶动力学曲线,量化对比分析了铌、钒微合金化对高强螺纹钢再结晶开始、转变及终了过程的影响。结果表明,铌、钒微合金化螺纹钢的热压缩过程均呈现了明显的动态再结晶特征,由于微合金元素Nb/Nb+V的添加,阻碍了20MnSi钢的动态再结晶,变形温度的提高或应变速率的增加可促进再结晶。针对生产中利用动态再结晶而组织调控进行了工艺设计,精轧机组中成品机架前进行冷却和回复,确保830 ℃左右有利再结晶分数达到95%。     

5052铝合金单双道次压缩动态与静态软化行为探讨

实验采用Gleeble-1500D热模拟试验机对5052铝合金进行等温热压缩,研究了该合金动态软化特征和静态软化特征,变形温度330～480℃,应变速0.005～0.05/s。结果表明,5052铝合金在热压缩过程中发生了动态软化和静态软化,首道次压下量显著地影响了道次间的静态软化率。结合流变应力曲线和显微组织分析,揭示了动态软化机制主要为动态回复,而静态软化主要是静态再结晶的结果。