回火工艺对Aermet100超高强度钢组织与韧性的影响

采用SEM、TEM等方法研究了不同回火温度对Aermet100超高强度钢的显微组织和韧性的影响。结果表明,Aermet100钢经885℃淬火后,在472～492℃温度范围内回火,显微组织为高位错密度的板条马氏体(板条M)和少量逆转变奥氏体(AR)。随着回火温度的升高,板条M宽度略有增加,韧化相AR的含量有所提高。高密度位错马氏体的存在使得Aermet100钢保持较高的韧性水平,而逆转奥氏体含量的增加则导致Aermet100钢的韧性显著提高。     

Aermet100钢的高温变形本构关系与微观组织演变

在变形温度800～1200℃和应变速率0.01～50s-1下,利用Gleeble-3800热模拟试验机对Aermet100钢的高温变形本构关系与微观组织演变进行了研究。结果表明,增加应变速率和降低变形温度都能提高材料的流动应力,延迟动态再结晶发生,使变形材料表现出加工硬化和动态回复。运用位错理论研究了微观组织和流动应力曲线的变化规律并做出了合理的解释。在压缩实验的变形条件下变形激活能为489.10kJ/mol。确定了峰值应力、变形温度和应变速率之间的双曲正弦模型的本构关系。     

Aermet100钢高温变形行为及热加工图研究

通过热模拟压缩试验研究了Aermet100钢在应变速率为0.01~50 s-1,变形温度为1073~1473 K和变形程度为0.05~0.9条件下的热变形行为,并采用正交分析方法研究了工艺参数(应变、应变速率、变形温度)对Aermet100钢热变形流动应力的影响规律,建立了基于正交分析的回归型Aermet100钢的热变形本构方程。综合考虑应变速率和变形温度对材料微观结构及性能的影响,依据动态材料模型(DMM)建立了基于本构方程的Aermet100钢的热加工图,并利用热加工图确定了Aermet100钢热变形时的流变失稳区,分析讨论了不同区域的Aermet100钢的高温变形特征。     

Theoretical and experimental studies of passivity breakdown of Aermet 100 ultra‐high stainless steel in chloride ion medium

Passivity breakdown and pitting behavior in the presence of aggressive Cl^? on ultra‐high strength steel Aermet 100, commonly used for landing gear, has been studied, the data are explained in view of the point defect model (PDM). Cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and X‐ray photoelectron spectroscopy (XPS) were examined to observe corrosion progress and corrosion products in the salt spray tests at 4, 8, 12, 16, and 20 days intervals. The breakdown behavior was studied using CPP, whereas scanning electron microscopy (SEM) and digital confocal microscopy were used to explore the micromorphology and depth distribution of pits. The cumulative distribution basically satisfies a normal probabilistic distribution at the different concentrations of chloride and pH, which is consistent with PDM assuming a near‐normal distribution of potential breakdown sites regarding to the cation vacancy diffusivity.     

55钢CBN砂轮平面磨削的磨削力模型研究

本文建立了基于未变形磨屑厚度的磨削力计算模型。根据55号钢的CBN砂轮平面磨削实验,首先采用随机方向搜索法对切向力模型进行优化拟合,再根据拟合的参数对法向力模型进行优化,得出了CBN砂轮与工件之间的摩擦系数和磨粒顶锥角。分析了摩擦力在磨削力中所占比重的影响因素,结果表明:当切深不变时,随着vs/vw比值的增加,磨削力以及摩擦力在磨削力中所占的比重均下降,但当磨粒间距增加时,磨削力减小,而摩擦力在磨削力中所占比重增加。     

Aermet100钢等温压缩力学行为及正交多项式本构模型的建立

由于Aermet100钢是一种新型超高强度钢,需要对其进行高温流变性能的相关研究。文章通过因果图分析设计试验,再次对各因素(温度、应变、应变速率等)对流变应力的影响进行了分析,并通过正交试验设计和正交多项式理论,建立了Aermet100钢的正交多项式本构模型。结果表明,建立的本构模型误差精度满足工程需要,可以作为后续成形过程控制的基础。     

An analysis of grinding power and surface roughness in external cylindrical grinding of hardened SCM440 steel using the response surface method

The aim of this study was to analyze effectively the grinding power spent during the process and the surface roughness of the ground workpiece in the external cylindrical grinding of hardened SCM440 steel using the response surface method. A Hall effect sensor was used for measuring the grinding power of the spindle driving motor. The surface roughness was also measured and evaluated according to the change of the grinding conditions. Response surface models were developed to predict the grinding power and the surface roughness using the experimental results. From adding simply material removal rate to the contour plot of these mathematical models, it was seen that useful grinding conditions for industrial application could be easily determined.     

钎焊金刚石砂轮磨削硬质合金温度的试验研究

根据半人工热电偶测温原理制备了磨削测温试样,利用感应钎焊金刚石砂轮和电镀金刚石砂轮进行硬质合金YG6的磨削试验,研究了磨削深度、工件进给速度对工件表面磨削温度的影响。试验结果表明:在相同的磨削参数下感应钎焊金刚石砂轮的磨削温度要远低于电镀金刚石砂轮,且随着磨削深度和工件进给速度的增大磨削温度上升较为平缓,钎焊金刚石砂轮磨粒出露高度高、容屑空间大,磨粒呈有序排布是磨削温度较低的主要原因。     

Correlating surface roughness and vibration on plunge cylindrical grinding of steel

Since the wear of a grinding wheel has a direct effect on the workpiece vibration and both have effect on the workpiece quality, the main goal of this work is to study the relation between the process vibration signals and the workpiece quality (mean roughness, circularity and burning) as the grinding wheel gets worn, in an attempt to use these signals to decide the exact moment to dress the wheel. In order to reach this goal, several experiments were carried out in a plunge cylindrical grinding operation of an AISI 52100 quenched and tempered steel, having as input variables the dressing overlap ratio, the spark out time and the workpiece velocity. The output variables were the workpiece surface roughness and circularity and also the process vibration during both, the cutting phase and the spark out phase of the grinding cycle. The main conclusions were: (1) it is possible to have good workpiece quality even with a vibration level much higher than that obtained with a recently dressed wheel; (2) vibration during cutting phase and at the end of complete spark out can be used to monitor the wheel condition at least when high dressing overlap ratio is used; and (3) the decrease in the spark out time makes the vibration at the end of spark out increase a lot, but does not cause such a damage in surface roughness. This fact makes the use of partial spark out feasible in some situations.     

低温冷却磨削机理的研究

磨削是各种加工材料获得精确尺寸和表面完整性的主要加工方法,但在加工过程中,由于磨削区温度过高,经常导致工件表面热损伤、微裂纹和产生残余拉应力,严重影响工件表面质量和完整性的提高。本文通过采用低温CO2和液态氮为磨削冷却介质,有效地控制磨削区温度。实验结果表明,与干磨削和油冷却磨削相比,液态氮低温冷却磨削力、比磨削能、磨削区温度明显降低,工件表面质量和完整性显著提高,同时明显提高了砂轮的使用寿命和减少了冷却液对环境地污染。     

Determination of waviness decrease rate by measuring the frequency characteristics of the grinding force in centerless grinding

In centerless grinding, it is difficult to optimize the grinding conditions for minimizing the workpiece roundness error because of the high number of process parameters such as center height angle, blade angle, and stock removal rate. We had previously proposed a function for evaluating grinding conditions, i.e., the waviness decrease rate, in order to automatically select the optimum process parameters. In order to build a closed-loop control system for the process parameters, however, it is necessary to find a practical way to determine the waviness decrease rate. In this paper, the relationship between the waviness decrease rate and the dynamic components of the grinding force was investigated analytically. It was found that the frequency characteristics of the waviness decrease rate show a similar tendency to those of the grinding force. A grinding force measurement system was built and experiments for measuring the frequency characteristics of the grinding force were carried out. As a result, it was confirmed that the waviness decrease rate can be determined by measuring the frequency characteristics of the grinding force.     

冷轧带钢轧机在线磨辊磨削温度的试验研究

对影响磨削辊面温度的因素进行了系统分析和实验研究,得出轧辊转速,得出轧辊转速、砂轮速度、磨去量等因素对磨削辊面湿度影响的一般规律;同时得出了轧辊表层湿度的分布规律,利用回归分析的方法建立了辊面温度的数学模型。     

GCr15钢的ELID磨削性能实验研究

为了探讨GCr15钢的ELID（Electrolytic In-process Dressing）磨削性能，在基于大量实验的基础上，对GCr15钢采用ELID磨削时磨削力的变化规律进行了详细分析，并将磨削力、磨削表面粗糙度与普通磨削进行了比较。结果表明，采用铸铁结合剂CBN砂轮进行ELID磨削时磨削力几乎不随时间的变化而变化，而采用白刚玉砂轮进行磨削时的磨削力随时间的变化不断增大，在线电解修整使CBN砂轮在磨削过程中始终保持良好的磨削性能，有利于节省砂轮修整时间，提高加工效率。在ELID磨削中，采用微细砂轮进行磨削可以获得很低的表面粗糙度，实现对GCr15钢的超精密镜面磨削。     

Predictive modeling of surface roughness in grinding

The surface roughness is a variable often used to describe the quality of ground surfaces as well as to evaluate the competitiveness of the overall grinding system. This paper presents the prediction of the arithmetic mean surface roughness based on a probabilistic undeformed chip thickness model. The model expresses the ground finish as a function of the wheel microstructure, the process kinematic conditions, and the material properties. The analysis includes a geometrical analysis of the grooves left on the surface by ideal conic grains. The material properties and the wheel microstructure are considered in the surface roughness prediction through the chip thickness model. A simple expression that relates the surface roughness with the chip thickness was found, which was verified using experimental data from cylindrical grinding.     

高体积分数SiCp/Al复合材料平面磨削实验研究

本文使用SiC砂轮和金刚石砂轮对颗粒尺寸大、体积分数高的SiCp/Al复合材料进行了平面磨削实验,研究了磨削深度和工件进给速度对磨削力的影响,并利用扫描电镜对已加工表面形貌进行了研究.结果表明:使用SiC砂轮加工时,磨削力随磨削深度的增加而增大;工件进给速度较低时,磨削力随工件进给速度增加而减小,当工件进给速度超过12...     

预热温度对X100管线钢焊接性的影响

采用插销试验法和热影响区最高硬度法测定了在80,120,160℃三种预热温度下X100管线钢的临界断裂应力以及热影响区的硬度值,并对金相组织以及断口形貌进行分析,综合研究了预热温度对X100管线钢焊接性的影响.结果表明,随着预热温度的升高,X100管线钢临界断裂应力逐渐增大,HAZ区硬度逐渐降低;呈板条束状的BF组织越来越窄小且分布越来越紧密;起裂区氢致开裂的断口特征逐渐减少.     

花岗石异型面高效加工磨削温度场实验研究

石材加工中温度对异型面形成机理和成形刀具的磨破损规律有重要的意义,而理论分析过程比较复杂,准确率还有待修正提高。为有效指导实际生产,掌握金刚石刀具磨削石材的规律,摸索适于高效花岗石磨削的加工工艺,以降低温度对生产的不良影响,提出了基于红外成像的测量和分析方法。实验中,分析了两种石材异型面干切削加工中热量的产生及切削温度的变化,发现花岗石异型面磨削弧区的表面最高温度随主轴转速及刀具切削深度的提高而上升;单独提高刀具的进给速度会使磨削区温度先升后降。     

AerMet100钢力学性能的回火温度敏感性研究

研究了超高强度钢AerMet100在427~510℃范围内回火的力学性能,重点关注了在宇航材料规范AMS6532推荐的482℃附近回火时这一材料力学性能的变化,并从理论上进行了解释。结果表明,AerMet100钢的力学性能对回火温度的敏感性较大,当回火温度由476℃提高到488℃,其抗拉强度从2037 MPa下降到1915 MPa,断裂韧度从115.08 MPa.m1/2升高到145.60 MPa.m1/2。482℃附近温度回火力学性能变化显著的主要原因是基体和M2C中的Cr、Mo比值比其它高Co-Ni超高强度钢高,从而加速了过时效过程,使析出强化相的长大速率加快。     

Study on surface roughness model and surface forming mechanism of ceramics in quick point grinding

The quick-point grinding experiment of fluorophlogopite was conducted by using a MK9025A profile grinder which considered the simple single factor, such as the grinding wheel and table feed speed, grinding depth, inclining angle and deflection angle. The experimental results indicated that the surface roughness was mainly influenced on inclining angle and deflecting angle. Moreover, the modified model of the quick-point grinding process was proposed in the paper, which based on Malkin kinematics model, Snoeys empirical model and grinding thickness empirical model. The inclining angle and deflecting angle was introduced in the modified model. Comparison of the predicted results of these models and experimental ones indicated that the modified model was in well agreement with the experimental data. Further, standard deviation of these models and experiment was studied in the paper, it is found that the modified model was the more ideal. In order to study the effect of various technology factors on the sensitivity of surface roughness, “Relative extremum error” concept was first proposed in the paper. It was found that simple single factor in the modified model were relatively sensitive to surface roughness than other models.     

Experimental investigation of surface/subsurface damage formation and material removal mechanisms in SiC grinding

The difficulty and cost involved in the abrasive machining of hard and brittle ceramics are among the major impediments to the widespread use of advanced ceramics in industries these days. It is often desired to increase the machining rate while maintaining the desired surface integrity. The success of this approach, however, relies in the understanding of mechanism of material removal on the microstructural scale and the relationship between the grinding characteristics and formation of surface/subsurface machining-induced damage. In this paper, grinding characteristics, surface integrity and material removal mechanisms of SiC ground with diamond wheel on surface grinding machine have been investigated. The surface and subsurface damages have been studied with scanning electron microscope (SEM). The effects of grinding conditions on surface/subsurface damage have been discussed. This research links the surface roughness, surface and subsurface damages to grinding parameters and provides valuable insights into the material removal mechanism and the dependence of grinding-induced damage on grinding conditions.