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。     

热变形参数对0.05C-0.13Nb钢相变组织影响

利用Thermecomastor-Z热模拟试验机,研究了含铌0.13%微合金低碳钢奥氏体未再结晶区(超过50%、发生再结晶)变形、并以0.1～50℃/s的冷却速度连续冷却过程的相变。研究了热变形参数对相变组织的影响。结果表明,在未再结晶区变形,在连续冷却条件下,冷却速度≥5℃/s时,90%以上组织为粒状贝氏体;在相同变形温度情况下,随着变形量的增加,先共析铁素体的量增加,贝氏体的量随之减少。     

低碳钢的连续冷却转变

利用Gleeble-1500热力模拟试验机,研究了典型低碳钢在未变形及变形条件下的连续冷却过程的相变规律,并通过光学显微镜对连续冷却后的组织进行了详细观察和分析。结果表明：随着冷却速度的增加,铁素体相变温度降低,相变时间缩短,晶粒细化,贝氏体含量增多;变形加速了钢的连续冷却转变,使CCT曲线左移,贝氏体的临界冷却速度增加。     

17MnNiVNbR钢的连续冷却转变行为研究

利用Formastor-FII型膨胀仪和Gleeble-3800热模拟试验机,结合显微组织观察和硬度测试,研究了压力容器用钢17MnNiVNbR的静态和动态连续冷却转变行为,并分析了热变形对相变行为的影响。实验结果表明:冷却速率较低时,17MnNiVNbR钢的相变组织为先共析铁素体和珠光体;随着冷却速率的增加,依次出现贝氏体和马氏体。热变形能提高铁素体、珠光体和贝氏体的相变温度,并使连续冷却转变曲线向左上方移动。     

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。     

Q500q钢的连续冷却转变行为及生产试制

利用热模拟实验机Gleeble-2000,对Q500q钢连续冷却转变行为以及在650～300℃温度区间的相变行为进行了研究及生产试制.结果表明:当冷速为1～4℃/s时,试验钢的微观组织由铁素体和珠光体组成.当冷速增至4～16℃/s时,发生贝氏体相变;随着冷却速度的增加,贝氏体组织更为细化且体积分数增加.当冷却速度大于4℃/s后,试验钢在650～300℃冷却速度减半时,贝氏体相变的终了温度升高,贝氏体相变区间缩小,与连续冷却转变相比组织差距不大.采用两种不同的冷却方式生产试制后,两组试验钢的力学性能和金相显微组织一致,说明650℃以下可以采用缓冷坑堆冷的方式来提高钢板的探伤合格率.     

变形量对EH40钢连续冷却转变的影响

利用Thermecmastor 100 kN热模拟压缩机进行实验,应用热膨胀法绘制EH40级船板用钢在33.3%、50%变形量下的连续冷却转变曲线,应用OM、SEM和TEM图像并配合硬度法研究了EH40级船板用钢不同变形量的连续冷却转变产物及组织特点。实验结果表明,冷却速度在1～5℃/s时,实验钢组织以多边形铁素体为主;冷却速度在5℃/s以上时,组织为少量铁素体、粒状贝氏体的混合组织;变形量越大,显微组织尺寸越小,贝氏体组织含量越多;在相同变形条件下,冷却速度越大,实验钢硬度值越高。     

12Cr2Mo1R钢相变规律研究

采用热膨胀法并结合金相组织分析及硬度变化来测定12Cr2Mo1R钢变形奥氏体的连续冷却转变温度,研究了钢的相变规律,结果表明,12Cr2Mo1R钢未变形奥氏体连续冷却转变,冷却速度<0.27 ℃/s时,组织为贝氏体+铁素体+珠光体;在0.27～8.4 ℃/s之间时,组织为贝氏体;>8.4 ℃/s时,组织为马氏体+贝氏体。变形奥氏体连续冷却转变,冷却速度<5 ℃/s时,组织为铁素体+珠光体+贝氏体;在5～20 ℃/s之间时,主要为贝氏体组织;>20 ℃/s时,得到的组织为马氏体+贝氏体。形变加速了奥氏体连续相变,使连续冷却相变温度提高。钢中Cr、Mo等合金元素,提高了过冷奥氏体的稳定性,使连续转变过程中出现了亚稳奥氏体区,提高了贝氏体的淬透性。     

低碳贝氏体钢中温转变热模拟试验

研究了一种Mn-Nb低碳贝氏体钢。通过热模拟试验,测定试验钢的相变点温度并绘制其静态CCT曲线,研究试验钢在不同冷速下显微组织及显微硬度的变化规律。在所研究的冷却速度范围内,冷速越高,相变开始温度越低,随着冷速的增加贝氏体钢的显微组织由粒状贝氏体逐渐转变为板条贝氏体,且板条束越来越细小,硬度越高。     

B对高强钢连续冷却相变规律及性能的影响

利用热模拟试验、热轧试验、金相分析等方法,研究了不同B含量高强钢的连续冷却相变规律和性能变化情况.结果表明:B元素可显著提高钢的淬透性,阻止准多边形铁素体形成,促进针状铁素体、粒状贝氏体和贝氏体铁素体等低温相变组织的形成;在相同轧制条件下,不含B试验钢的组织为粒状贝氏体+少量针状铁素体,含B试验钢的组织为板条状贝氏体铁素体+少量粒状贝氏体;B可显著提高试验钢的屈服强度和抗拉强度,但对伸长率和冲击韧性的影响不大.     

In Situ Observation of the Lengthening Rate of Bainite Sheaves During Continuous Cooling Process in a Fe–C–Mn–Si Superbainitic Steel

The evolution of lengthening rate of bainite sheaves during continuous cooling process in a Fe–C–Mn–Si superbainitic steel was investigated by in situ observation on high-temperature laser scanning confocal microscope. The lengthening rates of bainite sheaves in three temperature ranges were calculated. The results indicate that the lengthening rate of bainite sheaves continuously decreases with the decrease of temperature during continuous cooling process. The lengthening rate of bainite sheaf depends on undercooling, transformation temperature, the diffusion of carbon atoms and the carbon content in parent austenite etc. The lengthening rate at high temperature is large due to the favorable carbon diffusion, smaller carbon content and less plastic deformation in untransformed austenite. Additionally, the microstructures after different isothermal holding temperatures were analyzed, indicating that the larger lengthening rate of bainite sheaves due to the high isothermal transformation temperature does not mean more amount of bainite transformation. Lower bainitic transformation temperature results in more and finer bainite plates.     

Bainite Transformation Under Continuous Cooling of Nb-Microalloyed Low Carbon Steel

Utilizing Gleeble-1500 thermomechanical simulator, the influences of hot deformation parameters on continuous cooling bainite transformation in Nb-microalloyed low carbon steel were investigated. The results indicate that bainite starting temperature decreases with raising cooling rate and increases with increasing deformation temperature. Deformation has an accelerative effect on the bainite transformation when the specimens are deformed at 950 ℃. When the deformation temperature increases, the effect of deformation on bainite starting temperature is weakened. The amount of bainite is influenced by strain, cooling rate, and deformation temperature. When the specimens are deformed below 900 ℃, equiaxed ferrites are promoted and the bainite transformation is suppressed.     

Study on transformation behavior of hot- rolled microalloyed TRIP steel

Effects of deformation mode, deformation temperature, deformation rate, cooling rate and slow- cooling stop temperature on the transformation behavior of hot- rolled microalloyed TRIP steel were studied by means of MMS- 300 thermomechanical simulator. The results show that for the samples subjected to the single or double pass deformation, ferrite transformation area is expanded, pearlite transformation area appears, and martensite transformation area disappears in the continuous cooling transformation diagrams. Transformation temperatures of Ar3, Bs and Bf decrease, diffusional transformation is prevented and intermediate temperature transformation is promoted with the increase of deformation temperature or cooling rate. When deformation temperature is 850??, transformation temperatures of Ar3, Bs and Bf increase, the amount of ferrite also increases, and the amount of bainite decreases in the microstructure with the increase of deformation rate. With the decrease of slow- cooling stop temperature, ferrite amount increases, ferrite grains grow and retained austenite amount first increases and then decreases.     

Effect of Cooling Rate and Deformation on Microstructures and Critical Phase-Transformation Temperature of Boron-Nickel Added HSLA H-Beams

 Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy (HSLA) H-beams cooled at different cooling rate, with different deformation were investigated. Continuous cooling transformation (CCT) diagram of this new type of steel was obtained by using Gleeble 1500 thermomechanical simulator. Microstructures and hardness, especially micro-hardness of the experimental steel were investigated by optical microscopy (OM), scanning electron microscope (SEM), Rockwell and Vickers hardness tests. Phase analysis was also studied by X-ray diffraction (XRD). The results indicated that with increase of cooling rate, microstructures of continuous cooled specimens gradually transformed from polygonal ferrite and pearlite, grain boundary ferrite and bainite, bainite and martensite to single martensite. The CCT diagram revealed that slow cooling was needed to avoid austenite-bainite transformation to ensure toughness of this steel. By plastic deformation of 40%, austenite-ferrite transformation temperature increased by 46 ℃, due to deformation induced ferrite transformation during continuous cooling, but Rockwell hardness has little change.     

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。     

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。     

Effect of Thermo‐Mechanical Process on Phase Transformation Behaviors of V–Ti–N Microalloyed Steel

Thermo‐mechanical simulation tests were performed on V–Ti–N microalloyed steel under three hot working conditions by using Gleeble‐3800 thermo‐mechanical simulator to study the effects of hot deformation and post‐deformation holding process on the continuous cooling transformation behaviors of overcooled austenite. The continuous cooling transformation diagrams (CCT diagrams) were determined by thermal dilation method and metallographic method. The effects of the hot deformation, post‐deformation holding, and cooling rate on the microstructure evolution were analyzed. The results show that deformation promotes ferrite and pearlite transformation. In addition, deformation leads to an increase in bainite start temperature, which becomes more markedly with the increase in cooling rate. The post‐deformation holding process is much favorable to promote carbonitride precipitation of the microalloying elements, which contributes to ferrite nucleation and smaller austenite grains. As a result, an increase in ferrite quantity and a decrease in ferrite grain size can be observed. And further more, the post‐deformation holding process reduces the effect of hot deformation on the bainite start temperature.     

热变形和冷却对700 MPa级Mo-Nb微合金化钢组织的影响

通过Gleeble 1500热模拟试验机和光学显微镜，研究了变形及冷却对700MPa级0．04C-0．27Mo-0．047Nb微合金化钢组织和硬度的影响。得出该钢的静态(不变形)和动态(变形)奥氏体连续冷却转变(CCT)曲线，高温转变区，相变产物为先共析铁素体和粒状贝氏体；中温转变区，相变产物主要为贝氏体。热变形促进了铁素体和贝氏体相变，扩大了形成铁素体的冷却速度范围，推迟了羽毛状贝氏体的形成。     

Bainite Transformation of Low-carbon and Boron-containing Steel under Continuous Cooling

The effects of deformation temperature and strain on bainite transformation of low carbon steel and boroncontaining steel were investigated under continuous cooling conditions by means of dilatometric measurement and microstructure observation.The results show that with decreasing the deformation temperature from 1 000to 800 ℃and increasing strains,bainite start temperature for boron-containing low carbon steel increases,whereas it decreases for low carbon steel under the same condition.The bainite microstructures are easily obtained for boron-containing steel deformed at different temperatures and different strains compared with plain low carbon steel.With increasing the continuous cooling rate,the bainite start temperature under deformed condition is about 20 ℃ higher than that under undeformed condition for boron-containing steel,but it changes slightly when the cooling rate is 20℃/s or more.