汽车悬架用弹簧钢铁素体全脱碳行为研究

为掌握汽车悬架用60Si2MnA弹簧钢的铁素体全脱碳行为,利用Gleeble1500热模拟机、金相显微镜、扫描电镜和电子探针等研究了加热温度、保温时间、热轧后的冷却速率对铁素体全脱碳层形成的影响.研究结果表明,加热温度对铁素体全脱碳行为影响最大,影响区间为725～925℃,850℃对应的脱碳层厚度达到最大;保温时间和冷却速率对铁素体脱碳行为也有较大影响,脱碳层厚度与时间的平方根呈线性关系;冷却太慢会形成较厚的脱碳层,冷却速率达到0.2℃/s时,实验钢基本不会发生脱碳行为.因此,避开脱碳层峰值温度,减少在(α+γ)两相区停留时间,均可有效阻止60Si2MnA弹簧钢的铁素体全脱碳.     

吐丝机螺栓断裂的失效分析

采用化学成分分析、宏观扣微观检验、金相组织分析和力学性能测定等方法分析了吐丝机用高强度螺栓发生断裂的原因。结果表明,由于机加工不当而在螺纹根部产生表面缺陷,并且这些表面缺陷周围在随后的热处理过程中发生全脱碳,大大降低了螺栓的疲劳强度,导致螺栓在使用过程中早期疲劳断裂。     

DJ4热卷弹簧纵向裂纹的原因分析和解决措施

采用表面形态、金相组织、硬度和冲击断口分析等方法对淬火纵向开裂DJ4弹簧进行了分析。结果表明，制扁后表面缺陷、脱碳及夹杂物的纵向分布，是产生纵向裂纹的诱因；卷制前加热温度过高，晶粒粗大，是产生纵向裂纹的主要原因。提出了整改措施，即对热处理工艺的调整和卷制后空冷到600℃重结晶细化晶粒，抑制了纵向裂纹的产生，使冲击断裂韧性得到较大提高。     

齿座裂纹分析

采用金相分析方法分析了齿座表面裂纹的性质和产生原因。根据齿座表面裂纹主要呈沿晶扩展,裂纹两侧无脱碳和氧化现象,认为该裂纹为淬火裂纹。渗碳温度过高、晶粒粗大、材质不良是产生淬火裂纹的原因。     

Q235表面预处理中温渗碳特性

将Q235表面脱碳处理后,进行氧化还原处理,对其表面进行SEM观测,在处理试样的表面出现亚微米晶粒及在晶粒中存在纳米层状结构。在滴注式渗碳炉中,在750℃温度中进行不同时长的渗碳,升温至900℃保温5 min后淬火。测量显微硬度,用SEM、金相显微镜进行组织观察,测量渗碳厚度。结果表明,表面预处理对渗碳有明显的加速作用。     

大锻轴表面裂纹分析

采用光学金相和电子金相分析方法，对大锻轴的表面裂纹性质和产生原因进行了分析。结果表明，大锻轴表面裂纹为锻造裂纹。锻造时加热温度过高或加热时间过长是其产生的主要原因。     

汽车钢板弹簧断裂失效分析

采用金相及断口分析等方法,对早期疲劳断裂失效的汽车钢板弹簧进行了综合分析,得出,钢板弹簧产生疲劳断裂的主要原因是由于喷丸工艺控制不当,致使弹簧表面存在较多较多较深的弹坑,这些凹坑在弹簧工作时成为应力集中点而形成疲劳源,另上,弹簧表面局部区域存在脱碳,降低了材料的疲劳强度。     

含硅中碳钢热轧过程中表面脱碳的控制

研究了分别经历三种加热轧制工艺过程的含硅中碳钢表面的脱碳行为以及碳和硅元素对脱碳的影响.应用金相显微分析方法观察钢的表面脱碳层组织,测定由表及里的显微硬度值,找出了用还原性介质保护加热轧制的方法防止该钢表面脱碳的最佳工艺.所用还原介质的碳浓度应为钢中碳、硅元素含量之和的15倍左右.     

Q345R受火后力学性能及组织的变化

通过对Q345R材料在不同受火温度、保温时长及冷却方式条件下进行热处理来模拟其受火损伤的热暴露试验,进一步评定材料的力学性能及相应的微观组织。研究表明:在20℃～649℃受火温度下,材料力学性能均满足要求,732℃～816℃受火温度下,与空冷条件下相比,水冷对其力学性能影响较大;受火温度低于649℃时,材料组织为铁素体+珠光体,高于649℃时,金相组织明显发生变化,水冷下晶粒度与空冷条件下相比较为不均匀;热处理温度不高于649℃时,材料无明显脱碳现象,在816℃时材料表面脱碳层最大深度约0.20 mm;随着受火温度的升高,热处理后表面颜色呈红褐色、灰褐色、暗红、亮红色变化。     

Q235钢板表面裂纹形成原因分析

采用宏观检验、化学成分分析、金相检验、扫描电镜及能谱分析的方法,对Q235钢板表面纵裂纹的产生原因进行了分析。结果表明:裂纹附近组织存在脱碳现象,且裂纹附近基体中分布有颗粒夹杂物,除了裂纹内部主要含铁的氧化物,基体附近中还存在硅和锰的二次氧化颗粒以及钠元素,说明此类裂纹是在连铸结晶器中形成的,最终在钢板表面形成裂纹。     

钽铌酸钾晶体相结构和相变的研究

本文采用 X 射线粉末衍射法研究了不同组分钽铌酸钾的相结构、高温相变特征和温度与组分的关系等。并讨论了相变的过程。     

Effect of heating rate on the hysteresis in the phase transition in silver telluride thin films

The electrical resistance of vacuum deposited silver telluride thin films was measured in the temperature range from 300 to 430 K at different heating rates. It is found that silver telluride films undergo a structural phase transition, with a hysteresis. The phase transition occurs over a wide temperature range of about 30 K and the transition temperature as well as the hysteresis width are found to be influenced by the heating rate. The effect of heating rate on the phase transition temperature and the hysteresis are discussed.     

Effect of boron oxide on the cubic-to-monoclinic phase transition in yttria-stabilized zirconia

Specimens of yttria fully stabilized zirconia with different amounts of boron oxide have been studied by X-ray diffraction at room temperature and at higher temperatures up to 1250 °C. A boron oxide-assisted cubic-to-monoclinic phase transformation was determined in the temperature range 800-1250 °C. In situ high temperature X-ray diffraction experiments gave evidences of the dependence of the phase transformation on the heating rate. The possibility of tuning the cubic-monoclinic phase ratio by suitable addition of boron oxide before pressing and sintering is proposed.     

A computational study of kinetic phase diagrams for CoPt alloy films during epitaxial growth

We have studied the kinetic processes of the epitaxial growth for CoPt alloy films using the master equation method. The kinetic phase diagrams of CoPt alloy films which show the phase formation conditions during the epitaxial growth are determined. From the kinetic phase diagrams, we find that the [001] ordered structure is much easy to be grown at high temperature while the [100] ordered structure is easy to be grown at low temperature although both the [001] and [100] ordering could be the equilibrium ground states. The atomic deposition, ordering and surface segregation lead to a rich variety of phases in epitaxial growth. The surface segregation is found to enhance the [001] ordering and leads to the formation of the [001] ordered phase at high temperature.     

Crystallite size and phase transition demeanor of ceramic steel

Zirconia is an important oxide of zirconium used in variety of field ranging from dentistry, fuel cells, and thermal barrier coatings. Phase transition of zirconia is an important phenomenon controlling its fracture strength, low temperature degradability and ion conductivity. In the present study, effect of molar concentration of precursor and calcination temperature on phase transition and crystallite size of zirconia was investigated. All the samples were characterized by X-ray diffractometry (XRD), Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). In sample having lowest precursor concentration crystallite size of monoclinic zirconia was found to be lower than that of tetragonal zirconia, simultaneously with the higher proportion of tetragonal zirconia (67.62%) as compared to all other samples (42.75%–58.04%). In all cases, monoclinic to tetragonal phase transition occurs with raise of temperature but in the sample with lowest precursor concentration, tetragonal to monoclinic phase transition occurred on raising the temperature.     

Phase Transition at High Heating Rate and Strain Rate During Maraging Steel C250 Grinding

In this study, maraging steel kinetics of both diffusion-controlled and diffusionless phase transitions under thermo-mechanical conditions was predicted using a physics-based model via the investigation of heating rate, stain rate, and contact zone temperature during grinding. It was assumed that high heating rate and high strain rate will affect phase transition. The theory of phase transition nucleation was combined with analysis of heating rate, stain rate, and contact zone temperature to predict phase transition during the grinding. The effects of heating rate and strain rate on phase transition were verified through maraging steel grinding experiments, X-ray diffractometry, and regression analyses. The results of post-grinding phase volume fractions of martensite and ferrite were compared with the results predicted from the neural network model, and models without consideration of heating rate or strain rate. Validation tests proved that the proposed physics-based model successfully predicted the occurrence and extent of phase transition associated with heating rate and strain rate. This physics-based model can be used to reduce phase transition during grinding of maraging steel, or to cause a predefined phase transition by controlling the thermo-mechanical loading.     

Intergrowth of C phase within μ phase in a Re-containing Ni-base single crystal superalloy

Precipitation of topologically close-packed phases in a Re-containing Ni-base single crystal superalloy was studied under elevated temperature by in situ transmission electron microscopy.Above 1150?C,a new intergrowth structure called C phase was found within μ phase with a defined crystallographic orientation relationship.Elements mapping analysis reveals that C phase has a similar element composition as μ phase,but contains a lower level of Cr,W and Re.With increasing temperature,the proportion of C phase increases gradually.At 1250?C,C phase becomes the dominant precipitate.It is demonstrated that C phase is more thermodynamically stable than μ phase above 1150?C that leads to an intergrowth pathway from μ phase to C phase.     

K_2O-MgO-Al_2O_3-P_2O_5-B_2O_3系统玻璃分相和光色性之间的关系

为了获得一种具有良好光色性能的磷酸盐光色玻璃,选择了 K_2O-MgO-Al_2O_3-P_2O_5-B_2O_3系统作为基础玻璃,以 AgX 为光敏成分,研究了玻璃分相和光色性之间的相互关系。用分子光谱、SEM,EDAX 和 XRD 等研究了2~#分相玻璃的相组成、相形貌。实验结果表明,光色玻璃中光敏相不仅是 AgCl 和 NaCl 固溶相组成,而且富集于液滴相中。玻璃的热处理以及相应热处理条件下分相形貌的观察结果表明:在一定的温度范围内,随着热处理温度升高,玻璃的分相程度增大,增强了玻璃的变暗程度,但相应地降低了光色玻璃的退色速率。     

Modelling of Phase Transformation of Plain Carbon Steels during Continuous Cooling

A model based on Avrami equation and Scheil‘s additivity rule was proposed to simulate the phase transformation in plain carbon steels during continuous cooling in hot strip mill. In this model, a wide range of composition, cooling rate, primary austenite grain size and retained strain has been taken into account. It can be used to calculate the phase fraction transformed at different temperatures during continuous cooling. The phase equilibrium and transformation starting temperature can be determined by using Thermo-Calc and DICTRA. The simulated results containing the transformation at starting and finishing temperatures, Ae1, Ae3 and the maximum volume fraction for Q235B, were obtained. The calculated phase volume fractions are in good agreement with the experimental results.