U75V钢相变动力学曲线测定及热处理工艺研究

用Formastor-F型热膨胀仪测定了U75V钢的相变动力学曲线(CCT与TTT曲线);对该钢轨的热处理工艺进行了初步探讨。结果表明:当冷却速度为0.25~6.00℃/s时,组织以珠光体为主,且随冷却速度增加,组织变细,硬度增大;冷却速度大于6.00℃/s时,组织中开始出现马氏体;当转变温度大于525℃时,组织为珠光体,且随温度减小,片间距变细,硬度增大;当温度降到500℃时,开始发生贝氏体相变。U75V钢热处理时,控制转变温度高于525℃并进行等温转变,冷却速度为2.00~6.00℃/s,获得的珠光体片间距最细,硬度可满足钢轨的性能要求。     

耐蚀钢轨U68CuCr连续冷却转变研究

在Formastor-F试验机上进行热模拟试验,采用膨胀法测定了耐蚀钢轨U68CuCr临界点及在0.1～5.0℃/s的冷却速度下连续冷却的温度膨胀曲线,结合微观组织和显微维氏硬度分析,采用Origin软件绘制出连续冷却转变(CCT)曲线。试验结果表明,耐蚀钢轨U68CuCr冷却速度不超过0.1℃/s时,可获得索氏体+珠光体组织;冷却速度达到2.0℃/s时,钢中出现马氏体组织;当冷却速度达到5.0℃/s时,得到片间距更细小的屈氏体组织,过冷奥氏体转变为马氏体+屈氏体组织。根据连续冷却转变曲线,为优化耐蚀钢轨轧后冷却工艺提供理论依据。     

U76CrRE稀土钢轨连续冷却曲线和组织性能研究

用Formastor-F型热膨胀仪测定了U76CrRE钢的CCT曲线;研究了冷却速率对钢组织和硬度的影响。结果表明,U76CrRE钢发生珠光体转变的临界冷速为2.00℃/s;当冷速小于等于2.00℃/s时,得到的组织为珠光体和少量铁素体;当冷速大于2.00℃/s时,转变产物中出现马氏体;实验钢的硬度随冷速的增加而增大。U76CrRE稀土钢轨在温度略高于522℃进行等温转变时可获得片间距细小的珠光体组织,硬度可满足热处理钢轨的性能要求。     

Nb-Ti微碳深冲双相钢的连续冷却转变规律

摘要：通过连续冷却实验研究了Nb Ti微碳深冲双相钢在不同冷却速率下的显微组织变化规律。并结合显微组织、热膨胀曲线以及实验钢的硬度值绘制出实验钢的CCT曲线。结果表明,实验钢的CCT曲线由铁素体、珠光体与贝氏体区组成,其中铁素体和贝氏体的区域较大,覆盖冷却速度范围较广。实验冷却速率下未出现马氏体组织。在05～1℃/s的慢冷速下,组织由铁素体和珠光体组成;当冷速增加至3℃/s时,贝氏体开始出现,珠光体消失。当冷速在5～10℃/s范围内时,获得铁素体+贝氏体双相组织;当冷速大于10℃/s时,铁素体相变消失,此时为纯贝氏体转变。热处理过程中若想获得一定量的马氏体组织,退火温度宜设置在820～900℃双相区较低温度范围,使合金元素充分富集于少量奥氏体中,在随后冷却过程中此奥氏体转变为马氏体组织。     

BT-65MnRE钢的CCT曲线测定与分析

文章通过测定BT-65 MnRE钢在不同冷速下的连续冷却转变曲线,利用金相显微镜观察了不同冷速下的显微组织.结果表明:试验钢BT-65 MnRE的相变点Ac1为707℃,Ac3为764℃,当冷却速度为1～4℃/s时,室温组织为珠光体+先共析铁素体,当冷却速度为5～8℃/s时,室温组织为珠光体+贝氏体+马氏体+少量铁素体,当冷却速度为10～30℃/s时,室温组织为珠光体+马氏体+少量铁素体,当冷却速度大于40℃/s时,室温组织为马氏体.     

胀断连杆用中碳非调质钢的连续冷却转变

通过Gleeble-3800热模拟机,研究了一种胀断连杆用中碳非调质钢的连续冷却转变组织变化规律,分析了冷却速度对转变组织和显微硬度的影响.结果表明,当冷却速度为0.1~3℃/s时,组织为铁素体+珠光体,当冷却速度大于5℃/s时,开始发生贝氏体转变,随着冷却速度提高,贝氏体含量增多,并在速度大于15℃/s时发生马氏体转变.实验钢的显微硬度随着冷却速度的提高而增加.     

51CrV4弹簧钢相变规律研究

利用Gleeble-3800热模拟机研究51CrV4弹簧钢过冷奥氏体连续转变规律,采用热膨胀法测定其相变临界点,同时测定51CrV4钢过冷奥氏体在不同冷却速度下连续转变时的膨胀曲线,绘制其静态连续冷却转变（CCT）曲线.结合金相-显微硬度法,分析不同冷却速度对51CrV4钢组织性能的影响.结果表明：冷却速度为0.5℃/s 时,冷却转变的产物为铁素体和珠光体;当冷速增加,达到1℃/s 后,贝氏体开始生成;马氏体转变冷速区间为2~30℃/s;当冷却速度超过12℃/s后,冷却产物只有马氏体.     

U77CrNb钢轨钢连续冷却转变曲线研究

在Formastor-F试验机上进行热模拟试验,测定了U77CrNb钢轨钢临界点及在0.2~30℃/s冷却速度下连续冷却转变的温度膨胀曲线。试验结果表明:冷却速度≤1℃/s时,可获得屈氏体+珠光体组织;冷却速度达到2℃/s时,钢中出现马氏体组织。测定的连续冷却转变曲线为制定U77CrNb钢轨钢生产及热处理工艺提供了理论依据。     

610 MPa水电用钢连续冷却转变行为研究

采用Formastor-F型全自动相变仪测定610 MPa水电用钢的连续冷却转变曲线(CCT曲线),研究了该钢在不同冷却速度下的过冷奥氏体的组织转变过程及转变产物的组织形态,结果表明,实验钢冷却速度低于5℃/s时,转变产物为F+P,冷却速度高于5℃/s时,出现贝氏体组织,随着冷却速度的加快,贝氏体逐渐增多,珠光体逐渐减少,冷却速度达到20℃/s时,珠光体消失。冷却速度大于150℃/s时,转变产物主要为马氏体。     

U71Mn钢分段式冷却强化工艺试验研究

通过测定U71Mn钢的过冷奥氏体转变动力学曲线,分析其相变规律。基于现场钢轨热处理工艺进行分段式冷却强化热模拟试验,研究冷速和终冷温度对组织及硬度的影响。结果表明,U71Mn钢的珠光体转变临界冷速为7℃/s,允许珠光体转变的温度范围为500～600℃。其分段式冷却合理工艺参数为开始冷却温度为850℃,冷速为6～12℃/s,终冷温度为570℃,此工艺参数下可获得珠光体组织,同时满足钢轨硬度要求。     

奥氏体形变对50CrV4钢相变行为的影响

利用Thermecmastor-Z型热模拟试验机,结合金相显微镜(OM)、扫描电镜(SEM)、维氏硬度计等,系统研究了奥氏体区变形对50CrV4钢连续冷却相变和等温相变规律的影响。建立了试验钢动态CCT曲线。研究结果表明,奥氏体变形能促进连续冷却转变过程中铁素体-珠光体、贝氏体转变,但亦可提高奥氏体的机械稳定性,进而抑制马氏体转变,Ms点由331.6℃(奥氏体未变形)降低至291℃(950℃下变形50%+890℃下变形50%,变形速率均为5s-1,变形后冷速为20℃/s)。当轧后冷速小于0.5℃/s时,试验钢中可获得铁素体+珠光体组织。此外,在研究不同变形量对试验钢等温相变规律影响时发现,650℃等温时,试验钢中发生铁素体-珠光体相变。随着变形量的增加(由30%增加至50%),其等温相变动力学加快(相变完成时间由197.6s减小至136.5s),铁素体体晶粒尺寸、珠光体片层间距减小,硬度增加。     

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The continuous cooling transformation process and the organization performance of transformation product was investigated by means of dilatation test during single pass deformation on Gleeble-3500. The result shows that bainite transition can be happened when the cooling speed about 3??/s on 460B steel with boron, and the grain size is coarse and hardness is higher when the cooling speed (0. 1, 0. 3, 0. 5??/s)is slowly, it is more tiny than without boron. Boron can make the CCT curves shift to right, the transition from austenite to ferrite and pearlite is restrained, the hardenability of the steel are obviously improved, the cooling speed from austenite to martensite is lower and Ac3, Ac1, Ar3, Ar1, Ms is dropped.     

Reheating Austenitizing Temperature of Spring Steel 60Si2MnA for Railway

The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hot rolled state, after reheating treatment at 950 ℃, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 8.5 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 ℃.     

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.     

热形变和钒微合金化对高碳钢组织转变的影响

通过在Gleeble1500热模拟试验机上的热形变和冷却试验,研究了热形变及钒微合金化对高碳钢连续冷却后显微组织及硬度的影响。研究结果表明：未形变的含钒试验钢在5和9℃/s冷速下出现了中低温组织贝氏体和马氏体,950℃变形后的含钒钢,在同样冷速下相变后得到的组织全为珠光体。随钒含量的增加,珠光体转变后的片层间距变小,硬...     

Effect of process parameters on microstructure and hardness of 49MnVS3 steel for automobiles

The thermal compression test of 49MnVS3 steel cylinder specimen was carried out using a Gleeble- 3500 thermal simulation testing machine, and the influence of deformation temperature, deformation degree and cooling rate on microstructure and hardness of 49MnVS3 steel was studied. The results show that the microstructure of 49MnVS3 steel at various deformation temperatures is composed of ferrite and pearlite. The pearlite is obviously homogeneous with 30% deformation than with 20% and 50% deformations, and the distribution of ferrite is more uniform. Under the conditions of deformation temperature of 850??, deformation degree of 30% and cooling rate of 10??/s, the microstructure is uniform, with less ferrite and more pearlite, and the refinement is obvious. However, as the cooling rate increases to 20??/s, martensite microstructure occurs, which affects the performance of the steel.     

Effects of Chromium,Vanadium and Austenite Deformation on Transformation Behaviors of High-strength Spring Steels

The phase transformation behavior during continuous cooling of high-strength spring steels containing dif-ferent amounts of Cr was studied.Furthermore,the effects of combining Cr with V as well as austenite deformation on the transformation kinetics were investigated in the method of dilatometry and metallography hardness.The re-sults showed that,with the increase of Cr,the pearlite transformation field was enlarged,the ferrite transformation field was narrowed,and the entire phase field shifted to the right.With the addition of V,the start transformation temperature of undercooling austenite (Ar3 )was gradually increased,but the ferrite and pearlite transformation fields were not affected.Besides,the minimum critical cooling rate of martensitic transformation was also reduced.In addition,the dynamic continuous cooling transformation (CCT)curve moves to the top left compared with the static CCT curve.The transformed microstructures showed that the addition of V and the deformation not only refined the overall transformed microstructures but also reduced the lamellar spacing of pearlite.The alloying elements Cr and V promoted the Vickers hardness.However,the effect of Cr on the Vickers hardness of martensite was stronger and the influence of V on that of pearlite was stronger.Moreover,the Vickers hardness affected by the austenite deform-ation was more complex and strongly depended on the transformed microstructures.     

冷作硬化非调质钢的连续冷却相变规律

钢的连续冷却相变曲线(CCT)是组织调控的基本依据,为了优化紧固件用冷作硬化非调钢热轧态的组织和力学性能,采用DIL805A相变仪测定了试验钢在0.1～50℃/s不同冷却速率下的热膨胀曲线,结合金相硬度法确定相变类型,并绘制了试验钢的CCT曲线.结果 表明,试验钢马氏体转变点(Ms)为280℃,在不同冷速范围内均有铁素...     

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。     

形变对共析钢连续冷却过程中珠光体相变的影响

摘要：为掌握形变对共析钢连续冷却过程中珠光体相变的影响,研究了共析钢在720～920℃温度范围内进行形变后,在连续冷却过程中奥氏体向珠光体相变的规律,建立了相变时的过冷度和珠光体片层间距的相互关系,并预测了试验钢的力学性能。结果表明：形变储存能促进共析钢在50℃/s高冷速下发生珠光体相变,形成片层间距为129～187 nm的超细片层珠光体,抗拉强度达到近1000MPa,且随着形变温度提高,形变储存能减小,珠光体相变温度降低,珠光体片层间距减小,屈服强度和抗拉强度提高。