冷速和变形对700MPa超级钢组织和性能的影响

采用Gleeble 1 5 0 0热模拟实验机及Instron试验机研究并分析了 70 0MPa超级钢的连续冷却转变曲线 (CCT曲线 )及冷却和变形工艺对实验钢性能的影响。结果表明 ,热变形显著加速钢的相变过程 ,随着冷却速度的提高 ,钢的抗拉强度提高 ,屈服强度降低     

变形工艺对Q345 GJC高建钢连续冷却相变的影响

借助Gleeble-2000型热力模拟实验机,研究了Q345GJC高建钢奥氏体连续冷却过程的相变规律,结合热膨胀法和金相法,分别构建实验钢奥氏体动态和静态连续冷却相变曲线(CCT),分析了加速冷却、热变形和工艺温度对实验钢相变的影响。结果表明,与静态CCT曲线比较,实验钢的动态CCT曲线整体向左上方移动,γ/α相变开始温度随冷却速度的增大而逐渐降低;高温变形对铁素体和珠光体组织转变有利,扩大了铁素体相变区,但阻碍了贝氏体相变;奥氏体变形对贝氏体转变是双重的,高冷速变形促进贝氏体相变,低冷速变形抑制贝氏体相变。     

0．33C．1．0Mn．0．8Si钢过冷奥氏体的连续冷却转变及组织细化

利用Gleeble-3500热模拟实验机测定了0.33C-1.0Mn-0.8Si钢的静态(不变形)与动态(变形)CCT(连续冷却转变)曲线,并观察了钢的组织.结果可见.形变可以提高铁索体转变的开始温度,但对转变终了温度基本没有影响,变形后过冷奥氏体的铁素体转变区扩大,动态Ar3的值比相同冷却条件下静态时Ar3高出近100℃,形变对Ar3的影响不明显;随着冷却速度的增大,铁素体晶粒由多边形状变成条状或长片状,珠光体团也变得更细小、弥散,且动态连续冷却组织比静态连续冷却组织细小.     

20MnSiV钢变形抗力数学模型和连续冷却转变曲线

在Gleeble-1500热模拟实验机上对20MnSiV钢进行不同变形温度、变形速度、变形程度的压缩变形,得到了该钢种高温轧制过程中的变形抗力模型,采用双道次压缩实验绘制了该钢种的连续冷却转变曲线.     

一种含Nb、Ti微合金钢的连续冷却相变行为

利用MMS -200热模拟试验机对试验钢进行不同变形条件下的连续冷却转变试验.针对不同的冷却速度,采用热膨胀法结合金相法测定试验钢在连续冷却转变中的相变温度,利用光学显微镜及扫描电镜观察试样的显微组织,并测定珠光体的含量,进而绘制出试验钢在变形和未变形条件下的连续冷却转变(CCT)曲线,从而得出不同变形工艺对微合金钢连续冷却转变行为和显微组织的影响规律.     

15MnVB钢160 mm xl60 mm铸坯热变形奥氏体连续冷却转变行为

采用Gleble-1500热模拟机测定了15MnVB钢在0.05～20℃/s冷速下连续冷却转变的膨胀曲线,结合光学显微镜的微观组织观察,测绘了该钢热变形奥氏体连续冷却转变过程中的动态CCT曲线;研究了其连续冷却转变产物的组织形态和硬度。实验结果表明,15MnVB钢在0.05-20℃/s冷却速率下的组织主要由铁素体+珠光体、铁素体+珠光体+贝氏体、铁素体+珠光体+贝氏体+马氏体、贝氏体+马氏体组成。     

15MnVB钢160 mm×160mm铸坯热变形奥氏体连续冷却转变行为

采用Gleble-1500热模拟机测定了15MnVB钢在0.05～20℃/s冷速下连续冷却转变的膨胀曲线,结合光学显微镜的微观组织观察,测绘了该钢热变形奥氏体连续冷却转变过程中的动态CCT曲线;研究了其连续冷却转变产物的组织形态和硬度。实验结果表明,15MnVB钢在0.05-20℃/s冷却速率下的组织主要由铁素体+珠光体、铁素体+珠光体+贝氏体、铁素体+珠光体+贝氏体+马氏体、贝氏体+马氏体组成。     

X70管线钢的组织控制与细化工艺研究

为了解奥氏体在连续冷却过程中的组织演变规律,更好地控制管线钢室温下的组织形态,对X70管线钢进行了静态及动态热模拟试验,绘制出了相应的连续冷却转变曲线(CCT曲线),观察其组织,分析变形和冷却速度等因素对管线钢组织的影响。同时对X70管线钢的入精轧温度、终轧温度等因素控轧控冷工艺进行模拟研究。认为提高变形后的冷却速度能获得针状铁素体组织;在同一冷却速度下,动态连续冷却转变得到的组织更细密;降低入精轧温度、终轧温度,增加冷却速度能细化组织。     

Nb-Ti微合金钢连续冷却相变的研究

利用Gleeble-2000热模拟实验机,测定了Nb-Ti微合金钢变形奥氏体的CCT曲线,研究了冷却速度对连续冷却相变及显微组织的影响,利用碳萃取复型法对第二相析出物进行了分析。结果表明,随冷却速度提高,Nb-Ti微合金钢相变温度降低,组织细化,铁素体的形貌从多边形逐渐向针状转变;随冷却速度的增加,第二相析出物增多且变得细小。     

X70管线钢的组织控制与细化工艺研究

为了解奥氏体在连续冷却过程中的组织演变规律,更好地控制管线钢室温下的组织形态,对X70管线钢进行了静态及动态热模拟试验,绘制出了相应的连续冷却转变曲线（CCT曲线）,观察其组织,分析变形和冷却速度等因素对管线钢组织的影响。同时对X70管线钢的入精轧温度、终轧温度等因素控轧控冷工艺进行模拟研究。认为提高变形后的冷却速度能获得针状铁素体组织;在同一冷却速度下,动态连续冷却转变得到的组织更细密;降低入精轧温度、终轧温度,增加冷却速度能细化组织。     

工艺参数对耐蚀钢12CuCrNiV组织与性能的影响

采用热力模拟试验机、光学显微镜、显微硬度计研究了耐蚀钢12CuCrNiV在不同冷却速率下的连续冷却组织转变规律,并绘制其CCT曲线,同时研究了形变温度和冷却速度对耐蚀钢热变形后的组织和硬度的影响规律。结果表明:连续冷却转变情况下,耐腐蚀钢在冷速小于15℃/s时,有铁素体转变;冷速小于1℃/s时,有珠光体转变;冷速在0.5~20℃/s之间时,有贝氏体转变。控制冷速在5~15℃/s可得到铁素体和贝氏体复相组织。随变形温度的降低,试验钢形变过程中形变诱导铁素体相变现象显著,且伴随有M/A岛生成;随冷却速度的增高,形变诱导相变现象减弱,M/A岛数量减少。与连续冷却试验相比较,形变诱导析出现象明显,其硬度增量为40~50HV,形变可使试验钢的析出向更高冷速移动。     

Effect of hot deformation and Nb precipitation on continuous cooling transformation of a high-Nb steel

In this work, the effects of hot deformation on continuous cooling transformation of a high-Nb steel were investigated on a Gleeble 3500 thermal simulator. The amounts of dissolved Nb were determined by inductively coupled plasma-atomic emission spectrometry. Furthermore, the effects of hot deformation and Nb precipitation on phase transformation were discussed. Results showed that high-Nb steel is suitable for acicular ferrite pipeline steels because the acicular ferrite microstructure can be obtained in a wide cooling rate range. Hot deformation strongly accelerates the polygonal ferrite transformation and increases the critical cooling rate to obtain a full acicular ferrite microstructure. Moreover, hot deformation markedly refines the final microstructure and improves the mechanical properties of acicular ferrite obtained at a high cooling rate. However, hot deformation can also promote Nb precipitation during holding and even cooling at low rates after hot deformation. Nb precipitation dramatically promotes the polygonal ferrite, weakens the effect of Nb in solution on phase transformation and strengthening, and decreases the microhardness.     

含Mo低碳贝氏体钢形变奥氏体连续冷却相变规律研究

在Gleeble-1500热力模拟试验机上,利用热膨胀法测定了两种含Mo低碳贝氏体钢在850℃变形30%后再以不同冷却速度冷却到室温的连续冷却相变曲线(CCT曲线),在Axiovert 200 MAT光学显微镜下检测冷却后的组织.结果表明,奥氏体化的低碳钢低速冷却后的组织主要由粗大的铁素体和少量颗粒状珠光体组成;提高连...     

Influence of Deformation on Transformation of Low Carbon and High Nb-containing Steel during Continuous Cooling

 The effect of deformation in the nonrecrystallized region on the phase transformation for a low carbon and high Nb-containing steel with coarse austenite grain size was investigated by means of dilatometry measurement and microstructure observation. The results show that with the cooling rate increased, both the transformation start and finish temperatures measured by dilatometer are decreased, and the corresponding microstructure is changed from ferrite and pearlite to full granular bainite gradually. The dynamic CCT diagram is plotted according to the dilatometry measurements and microstructure observations. Dilatometry measurements also show that the transformation start and finish temperatures of the tested steel are raised with increasing strain, strain rate and deformation temperature, and the reasons for this are discussed.     

X70管线钢相变规律研究

利用MMS-200热模拟试验机研究了X70管线钢的相变规律,采用热膨胀法及金相法建立了连续冷却转变曲线,分析了工艺参数对组织的影响规律。试验结果表明,试验钢在低冷速下形成的组织主要为多边形铁素铁,随着冷却速度增加,组织变细,当冷速在20～40℃/s时,可以获得理想的针状铁素体组织。     

Phase Evolution and Mechanical Behavior of 0.36 wt% C High Strength TRIP‐Assisted Steel

Phase evolution in a 0.36 wt% C steel has been studied by thermodynamic calculation and dilatometric analysis with an aim to achieve high strength TRIP‐assisted steel with bainitic microstructure. The equilibrium phase fraction calculated as the function of temperature indicated the formation of δ‐ferrite (≈98%) at 1417°C. In contrast, similar calculation under para‐equilibrium condition exhibited transformation of δ‐ferrite to austenite at the temperature below 1300°C. During further cooling two‐phase (α+γ) microstructure has been found to be stable at the intercritical temperature range. The experimentally determined CCT diagram has revealed that adequate hardenability is achievable in the steel under continuous cooling condition at cooling rate >5°C s^?1. In view of the aforesaid results, the steel has been hot rolled and subjected to different process schedule conducive to the evolution of bainitic microstructure. The hot rolled steel has exhibited reasonably good tensile properties. However, cold deformation of the hot rolled sample followed by intercritical annealing and subsequent isothermal bainitic transformation has resulted in high strength (>1000 MPa) with attractive elongation due to the favorable work hardening condition during plastic deformation offered by the multiphase microstructure.     

Hot Deformation Behavior of V-Microalloyed Steel

Through the expansion curve of continuous cooling transformation at different cooling rates measured by THERMECMASTOR-Z thermal simulator for U75V rail steel,the continuous cooling transformation curve was obtained.The influence on steel microstructure and hardness at different cooling rates was studied.The softening behavior of isothermal deforming in austenite area of 850-1000 ℃ in the interval of passes was also studied by double-pass compression test.The results show that the product of austenite transformation is pearlite when the cooling rate is lower than 10 ℃.When the cooling rate was in the range of 10-50 ℃·s-1,only martensite was received.The hardness of the test steel increases with increasing the cooling rate.Under the condition of deformation of 30% and deformation rate of 3 s-1,the relaxation time for complete recrystallization was shorter than 100 s when deformation temperature was higher than 1000 ℃.When deformation temperature was lower than 880 ℃,complete recrystallization of steel was difficult to achieve even if the relaxation time is extended.     

07MnNiMoVDR连续冷却过程相变行为研究

利用MMS-200热模拟试验机测定了07MnNiMoVDR钢的动态CCT曲线,研究了07MnNiMoVDR钢奥氏体连续冷却时的相变行为规律和显微组织。结果表明：随着冷却速度的增大,其组织由铁素体＋珠光体逐渐向贝氏体转变;随冷却速度不同,在CCT图中存在两个相变区,即低冷速的先共析铁素体＋珠光体相变区、中冷速的贝氏体相变区。     

低合金高强钢形变奥氏体相变行为及其模型

 为了研究低合金高强钢的形变奥氏体连续冷却转变行为及组织变化规律,利用Gleeble-3800热力模拟试验机对试验钢进行了多道次轧制工艺模拟试验,并根据试验所得相变温度和各冷却速度下的室温组织相对量,回归出相变模型。结果表明,试验钢在变形后的连续冷却过程中发生铁素体、珠光体、贝氏体和马氏体转变,基于对各转变的温度和组织相对量得到的相变模型分析,证实了模型的可靠性。     

Microstructural Changes after Control Rolling and Interrupted Accelerated Cooling Simulations in Pipeline Steel

The γ‐α transformation and final microstructure in pipeline steel was studied by carrying out a number of physical simulations of industrial hot rolling schedules. Particularly, the effect of the reheating temperature, deformation and cooling parameters on the transformation temperatures and final grain size were considered with a goal to obtain an appropriate thermo‐mechanical processing route which will generate appropriate microstructures for pipeline applications. The CCT diagram of the steel was derived experimentally by means of dilatometric tests. Hot torsion experiments were applied in a multi‐deformation cycle at various temperatures in the austenite region to simulate industrial rolling schedules. By variation of the reheating temperature, equivalent strain, and accelerated cooling, different types of microstructures were obtained. It was found that the deformation increases the transformation temperatures whereas the higher cooling rates after deformation decrease them. Post‐deformation microstructure consists of fine bainitic‐ferrite grains with dispersed carbides and small amount of dispersed martensite/austenite islands which can be controlled by varying the reheating temperature, deformation and post‐deformation cooling. The detailed microstructure characteristics obtained from the present work could be used to optimize the mechanical properties, strength and toughness of pipeline steel grades by an appropriate control of the thermo‐mechanical processing.