奥氏体—贝氏体抗磨钢中共晶体的团球化

用扫描电镜、透射电镜和电子探针研究Ｍｇ－Ａｌ复合变质向－贝钢中共晶体的团球化。结果表明，团球状共晶体是由于Ｃ、Ｍｎ、Ｓｉ偏折、于凝固后期在奥氏体枝晶间形成的渗碳体和奥氏体伪共晶组织，共晶体结晶时的异质核心是ＭｇＳ。团球化是异质核心和变质元素影响共晶体的结晶方式。     

奥氏体─贝氏体抗磨钢中共晶体的团球化

用扫描电镜、透射电镜和电子探针研究Mg－Al复合变质奥─贝钢中共晶体的团球化结果表明，团球状共晶体是由于C、Mn、Si偏析，于凝固后期在奥氏体校晶间形成的渗碳体和奥氏体伪共晶组织，共晶体结晶时的异质核心是MgS．团球化是异质核心和变质元素影响共晶体的结晶方式     

碳化物团球化奥氏体—贝氏体新型抗磨中锰钢

在中锰钢基础上，采用变质处理获得新型铸态抗磨钢：碳化物团球化奥氏体－贝氏体钢，它具有高强韧性，高耐磨性，是一种有广阔应用前景的新型抗磨材料。     

改变Cr—Mn—Mo—B钢冷却速度对其贝氏体转变动力学的影响

用THERMECMASTOR－Z试验装置及H－800型透射电子显微镜研究了一种Cr-Mn-Mo-B钢热变形后中途改变冷却速度对贝氏体转变动力学的影响。试验结果表明,在连续冷却过程中,中途改变冷却速度将发生不同于连续冷却转变曲线所表示的转变特征。     

Si基Si1—x—yGexCy合金生长中C的影响

报道了Si基Si1-x-yGexCy合金生长中C对Ge组分和生长速率的抑制作用,提出一个Si,Ge、C原子的排列构型,从理论上给出了C对Ge组分的抑制度和Ge/C原子比的关系,并指出在富Ge情况下C对Ge的抑制作用会趋向于饱和。     

基体硬度对材质耐磨性的影响—Al—Si合金和Si相锌基复合…

对两种硅相复合的材质耐磨性进行了研究，指出在复合相相同，摩擦工况一致的情况下，基体硬度对材质的磨损性能影响很大，基体硬度大，耐磨性能好，磨损方式都是疲劳磨损。     

不同掺杂对Ba3Y(BO3)3晶体的生长和相变的影响

结合X射线粉末衍射和差示扫描量热法,系统研究了不同格位上的掺杂对Ba₃Y(BO₃)₃晶体的生长和相变的影响. 研究发现,相同掺杂浓度10at%时,掺Nd³⁺的α-Ba₃Y(BO₃)₃晶体的相变温度（1099.6℃）比掺Yb³⁺的晶体的相变温度（1145.3℃）低;且随着掺Nd³⁺浓度的降低,晶体的相变温度升高,晶体在降温过程中更容易发生相变. 在晶体中掺入Sr²⁺离子,可以有效提高Yb³⁺∶α-Ba₃Y(BO₃)₃晶体的稳定性. 随着Sr²⁺掺入浓度的增加,晶体的熔点升高,相变温度降低. 当Sr²⁺掺杂浓度为16at%时,晶体的相变峰消失;当Sr²⁺掺杂浓度分别为5at%、10at%时,晶体仍然发生相变.     

Continuous cooling transformation behaviour and bainite formation kinetics of new bainitic steel

In order to avoid the appearance of soft particles composed of ferrite or pearlite in the actual production of new bainitic steel, the phase transformation behaviour and bainite formation kinetics were investigated by DIL805A dilatometer, optical microscopy, scanning electron microscopy and Vickers-durometer. The results show that the soft particles cannot appear when the cooling rate exceeds 0.025?K?s^?1, and this condition can be ensured by direct spray cooling in production. The local activation energy decreases with increasing transformed bainite volume fraction (f_b), and the average energy is about 136.7?kJ?mol^?1. The local Avrami exponent mainly lies between 0.5 and 3 in a wide f_b range, indicating that the dominating mechanism of bainite formation is two-dimensional and one-dimensional growth.     

Effect of austenite grain size on isothermal bainite transformation in low carbon microalloyed steel

Abstract

The effect of austenite grain size on isothermal bainite transformation in a low carbon microalloyed steel was studied by means of optical microscopy, SEM and TEM. Two widely varying austenite grain sizes, a fine average grain size (～20 μm) and a coarse average grain size (～260 μm), were obtained by different maximum heating temperatures. The results showed that the morphology of isothermal microstructure changes from bainite without carbide precipitation to bainitic ferrite with a decrease in holding temperature. Coarse austenite grain can retard the kinetics of bainite transformation and increase the incubation time of bainite transformation by reducing the number of nucleation site, but it does not influence the nose temperature of the C curve of bainite start transformation, which is ～534°C.     

Effect of microsegregation on carbide-free bainitic transformation in a high-silicon cast steel

ABSTRACT

A high silicon cast steel was studied in the as-cast condition in order to characterise its solidification macrostructure and microsegregation. The steel, poured into 32?mm-keel-block-shaped moulds, has a coarse solidification structure and marked microsegregation, containing low-alloyed areas with a total alloy content (Cr?+?Mn?+?Si) of 2.3 wt-% and high-alloyed zones of 5.3 wt-%. The bainitic transformation behaviour at 300°C was studied at different austempering times. The bainitic reaction occurs at different rates within the specimen volume, because of its chemical heterogeneity. An austempering heat treatment leads to an inhomogeneous carbide-free bainitic microstructure with different phase amounts, morphologies and sizes. The heterogeneous distribution of sizes and chemical compositions of retained austenite is speculated to benefit mechanical properties.     

奥氏体变形对铌微合金钢贝氏体相变的影响

用Gleeb le-1500热模拟机研究了铌微合金钢奥氏体变形后连续冷却条件下贝氏体相变规律.研究表明,随变形温度的升高,先共析铁素体量较少,贝氏体的板条束变宽.在连续冷却条件下,贝氏体的转变量随变形量的增加而减少,随应变速率的增加而减少,但应变速率对贝氏体转变量的影响随冷却速度的增加而减弱.随着变形后保温时间的延长,奥氏体稳定性增加,在较快冷却条件下转变产物中存在残余奥氏体.     

奥氏体变形对22CrSH齿轮钢连续冷却相变的影响

为了研究奥氏体变形对22CrSH齿轮钢连续冷却相变的影响,在Gleeble 1500热模拟机上,将22CrSH钢在950℃变形0.4及未变形处理,然后连续冷却.利用膨胀曲线、光学显微镜、透射显微镜,结合各种腐蚀方法,分析了22CrSH钢相变行为及相变组织.研究表明:奥氏体变形使多边形铁素体加珠光体混合组织的临界冷速增大;当奥氏体变形及降低冷速时,大量的晶界仿晶型铁素体占据了奥氏体晶界,贝氏体相变向针状铁素体相变转变;变形使奥氏体在中温相变区稳定性增加,室温组织中M/A岛的数量增多.     

Effect of molybdenum on continuous cooling bainite transformation of low-carbon microalloyed steel

Through simulation of thermomechanical processing/on-line accelerated cooling processing and observation of microstructure, the effect of molybdenum on continuous cooling bainite transformation of ultra-low carbon microalloyed steel was studied. The continuous cooling transformation curves of the trial steels with or without molybdenum addition were also determined. The result showed that the separate temperature of bainite was obviously reduced and the size of microstructure became smaller as 0.40 wt% Mo was added to the steel. At the same time, the martensitic structure, which formed at some cooling conditions, became finer and dispersed more uniformly. The deformed austenite would transform to finer bainite even when the cooling rate was not too high.     

Effect of B and B + Nb on the bainitic transformation in low carbon steels

Development of new, advanced high and ultra-high strength bainitic steels requires the selection of the optimum balance of bainite promoting elements allowing the production of the desired bainitic microstructure over a wide range of cooling rates. The addition of boron or a combined addition of boron and niobium is well known to retard strongly the polygonal ferrite formation but very little knowledge has been acquired on the bainitic transformation. Therefore, the purpose of this study is to investigate the influence of boron and boron plus niobium on the bainite transformation kinetics, microstructural evolution and mechanical properties in a low carbon steel (Fe-0.05C-1.49Mn-0.30Si). Isothermal and continuous cooling transformation diagrams were determined and followed by a detailed quantitative characterisation of the bainite microstructure and morphology using complementary advanced metallographic techniques (FEG-SEM-EBSD, SIMS and TEM). The relationship between microstructure and hardness has been evaluated. Finally, results of SIMS and TEM analyses coupled with microstructural investigations enable to propose a mechanism to explain the effect of the synergy between boron and niobium on the bainitic transformation and the resultant microstructure.     

Effect of austenite grain size and bainite morphology on overall kinetics of bainite transformation in steels

Abstract

An attempt is made to rationalise some contradictory observations on the effect of austenite grain size on the overall kinetics of the bainite transformation in steels. Experiments have been carried out on two steels which show opposite effects of austenite grain size on the reaction rate. General equations describing the reaction rate are derived by taking into account the morphology of the bainite in each steel. The equations derived can explain the contradictory effects of the austenite grain size on the overall reaction rate. The results are also found to be in good agreement with the published data.     

A study on austenite decomposition during continuous cooling of a low carbon steel

In this work, a model based on the finite element method and assumption of second order phase transformation has been developed to predict temperature history and austenite decomposition kinetics during continuous cooling of a low carbon steel. In order to accurately assess the temperature field and transformation rate the effects of various factors such as work hardening role on the kinetics of transformation, interconnection between austenite phase change and thermo-physical properties of the steel, and initial austenite grain size have been considered in the model. To verify the results of the modelling, time-temperature histories during cooling of a low carbon steel has been determined and microstructural studies have been performed. The comparison between the predictions and the experimental results indicates reliability of the proposed model.     

Effect of bainitic transformation on microstructure of Si-Mn steel

Several Si-Mn steels with similar Si and Mn levels and carbon contents, ranging from 0.25 to 0.75 wt %, were studied to determine the effect of bainitic transformation on the microstructure of Si-Mn steel. The microstructure was categorized by optical metallography, scanning and transmission electron microscopy, and X-ray diffraction. The results showed the existence of an optimum transformation time to produce the maximum content of retained austenite, though the retention of a large amount of retained austenite was encouraged as a result of bainitic transformation. The microstructure consisted of carbon-free upper bainite whose individual ferrite was separated by the thin-film type of retained austenite, while the blocky type of austenite was also found. The results also showed that carbide precipitation occurred in the residual austenite after the optimum time, which decreased the retained austenite content. The retained austenite stability is discussed in relation to the carbon content and morphology of the retained austenite.