爆炸硬化处理对高锰钢冲击磨损性能影响的研究

对Mn13Cr2高锰钢进行了爆炸硬化处理。并分别以玻璃砂、鹅卵石为磨料，在MLD．10动载磨料磨损试验机上对比研究了爆炸前、后Mn13Cr2高锰钢的冲击磨损性能。实验结果表明：在低硬度磨料（玻璃砂）冲击磨损时，爆炸硬化使高锰钢的冲击耐磨性提高20％-40％。在高硬度磨料（鹅卵石）冲击磨损时，在冲击功小于1．7J的条件下，爆炸硬化使高锰钢的冲击耐磨性提高30—50％。在冲击功大予1．7J的条件下，爆炸硬化则使高锰钢的冲击耐磨性降低。爆炸硬化使高锰钢表层硬化和冲击韧性降低是冲击耐磨性发生变化的主要原因。在冲击磨损条件下，爆炸硬化前、后高锰钢磨损面均出现磨料嵌入物及犁沟、凿削坑和剥落坑等形貌特征。爆炸硬化高锰钢适用予低硬度磨料的冲击磨损及高硬度磨料的低冲击功冲击磨损的工况条件。     

多冲接触载荷下涂层零件低应力宏观塑性行为

对高强度Co基、Ni基合金为表面涂层的中碳钢、不锈钢试样进行低应力多冲试验和测试,结果表明,在远低于材料屈服强度的低应力多冲接触载荷下,涂层和其下部一段基体材料将发生塑性变形,平均每次冲击造成的塑性变形量随冲击周次增加先大后小,累积可出现宏观塑性变形并伴随材料硬化现象。塑性变形量和变形区域大小与冲击应力值和材料强度有关。形变硬化程度由表及里衰减,并且只在冲击接触表面及以下一段长度上发生,形成一"易变形区"。分析认为多冲低应力变形是一种累积疲劳损伤。当峰值应力相同时,材料在多冲接触载荷下比静载荷和静疲劳载荷下吸收的能量多,且吸收量与离冲击点的距离成反比。多次冲击使原子易动性增强,临界切应力下降,位错易于启动和增殖。     

High rate crushing of wood along the grain

The results of tests carried out to measure proximal end and distal end loads during dynamic crushing of oak along the grain over a velocity range of 20–260 m/s are presented. A stress enhancement factor of roughly 2 is seen in the distal end loads for impact velocities from 34 to 225 m/s. Further enhancements in stress measured at the proximal end are the result of inertia effects associated with the dynamic localisation of crushing. The crushing behaviour is analysed using shock wave theory together with rigid, softening, hardening and elastic, softening, hardening material models. The results of the analyses compare well with load histories recorded experimentally.     

冷作模具表面硬化层的耐磨性研究

用多弧离子镀及离子氮碳共渗技术对基体钢表面进行了硬化处理。对表面硬化层在不同冲击功下(0J、0.2J、1J)的耐磨性进行了研究,两种表面硬化技术分别应用于不同品种的冷作模具,达到了显著提高模具使用寿命的效果。     

Wave propagation in an elastic/viscoplastic hollow sphere

An analysis of the dynamic problem of a hollow sphere is presented. The medium is assumed elastic/viscoplastic, satisfying Mises condition, isotropic hardening and viscoplastic incompressibility. The cavity is subjected to a radially applied and continuously maintained impact load. The analysis for viscoplastic waves is based on the method of characteristics and a generalized form of Malvern's theory for strain-rate dependent materials. A bilinear shear stress-shear strain curve is considered and calculations are carried out on the IBM 7094 computer. The paper examines the influence of the important parameters governing spherical wave propagation on the response of the sphere; these parameters include the level of strain hardening, the viscosity coefficient, Poisson's ratio and the geometry of the sphere. It is shown that the degree of strain hardening has a significant effect on the amplitude of the oscillations with the period unaffected. The viscosity coefficient becomes more influential as the wall thickness of the sphere increases.     

Impact of plasma hardening on the wear resistance of 38XC steel

The impact of plasma hardening on the wear resistance of 38XC steel was studied. It has been found that the wear resistance increases by 53.7 times under the condition of dry friction compared to the normalized state and by 12.7 times compared to the improved state. During plasma hardening, the wear of 38XC steel under dry friction is equal to the normalized steel 15 with lubrication; and the wear is not increased in case of a 1.5-fold increase in the load. The addition of HADO revitalizant to oil contributed to an approximately twofold decrease in the wear of 38XC steel with plasma hardening during wearing-in after cutting off the lubricant.     

The influence of strain hardening on steel erosion wear studied by analytical modelling of impeller testing

ABSTRACT

Abrasive wear of steel is a common problem in the mining industry. It was tackled by many researches using analytical and numerical approaches. Despite the advantages of the analytical models to provide quick and elegant solutions, they were derived using several assumptions limiting their applicability, such as e.g. rigid-plastic flow. However, the consideration of strain hardening during impact is crucial to depict a real behaviour of tool material, which changes its mechanical properties during collision. In this research, a new analytical model is invented describing the impact of steel plate with a solid rock, while the material of the steel plate is hardening during penetration and scratching. The model provides a frame of analytical equations based on the second Newton law and equations of motion in vertical and horizontal directions. The motion in vertical direction is considered as an indentation problem and the motion in the horizontal direction as a scratch problem. This model incorporates the most general Holloman representation of strain-hardening law to capture the relationship between microstructural characteristics of steels and wear resistance. It was shown that the indentation depth, the pile-up height, length of the scratch and erosion ratio directly dependant on the strain-hardening parameters in Holloman equation. The model predicts the maximum indentation depth and scratch length as a function of strength coefficient and strain hardening exponent, but also of impact angle, mass of the rock, position of impact at the surface of steel plate and coefficient of friction during metal movement. The model was tested qualitatively by comparison with impeller-tumbler experiments using different steel plates. The solution obtained from this model could be used for quick and easy evaluation of the steel for mining tools in an industrial environment.     

高速滚子链的多冲磨损特性

汽车链条的高速多冲特性不同于其它高速滚子链，高速下的多冲特性以及速度与载体交变特性的双重效应，对其耐磨性能提出了荷刻的要坟，而速度与载荷交变特性的影响尤为重要。销轴、套筒零件表层的抗多冲过载能力和抗多冲磨损能力以及心部的抗塑变能力和表层的循环软化与硬化特性是汽车用高速滚子链磨擦学设计的关键因素。     

高应变率下Cu-P/M摩擦材料正向和反向应变率效应

研究了冲击载荷下铜基粉末冶金(Cu P/M)摩擦材料不同的应变率效应。试验在分离式Hopkinson压杆 (SHPB)上完成。应变率范围为:102/s～103/s。通过试验得到了该材料的动态应力应变曲线,发现该材料在应变率 1000/s以下,表现为应变率强化效应;在应变率1000/s以上,表现为应变率弱化效应。也就是说,应变率1000/s是 该材料的临界应变率。为了与静态时的情况比较,在MTS试验机上又做了10-4/s～10-3/s应变率范围内的准静态 实验。比较动静态试验结果,发现动态时的屈服极限大于静态的;而屈服后的应变硬化率是静态大于动态的。通过 对样品进行微观组织分析,发现在压制烧结时有硬质颗粒破碎。在冲击载荷下材料内部的损伤演化形成大范围的 多源裂纹及孔洞分布群导致裂纹迅速扩展,同时伴随硬质颗粒破碎。     

Parameter optimization of laser die-surface hardening using the particle swarm optimization technique

A method of multiple-objective optimization is proposed for parameter designing of laser die-surface hardening. The mechanical properties (wear resistance and hardness) and the geometrical properties (hardening depth and surface roughness), which control the hardening effect, are taken as the optimization objectives. A regression analysis is applied to build a non-linear equation for mapping the hardening parameters to the optimization objectives. Multiple constraints are analysed and a model of non-linear multi-objectives is established to optimize the parameters of laser die-surface hardening. The particle swarm optimization (PSO) technique is used for solving this optimization problem. The objectives are contradictive, since the laser die-surface hardening increases the surface hardness of the die, but increases the surface roughness as well. To overcome this problem, the surface roughness is set not only as an objective, but also as a constraint, so that a special fitness function is designed for the iteration of the optimal solution. The die of an auto body is used as an example to test the optimization of parameters. The optimization results show that the optimal parameters can be obtained using this method for laser die-surface hardening which satisfy the hardening requirement, and reduce the hardening time and cost.     

奥氏体中锰钢的耐磨性与形变诱发马氏体及位错强化的关系

本文利用电镜和X射线等检验手段及磨损与现场运行实验,研究了非强烈冲击工况下奥氏体中锰钢的耐磨性与形变诱发马氏体和位错强化的关系。实验结果表明：奥氏体稳定性低的中锰钢,由于形变诱发马氏体的产生及其与位错交互作用促进了加工硬化能力和耐磨性的提高,而奥氏体稳定性高的中锰钢则是由于溶质原子和第二相粒子与位错产生的交互作用所致。因此降低碳、锰含量,大量形成第二相弥散硬粒子或增加溶质原子深度是提高奥氏体中锰钢加工硬化能力和耐磨性的有效途径。     

电火花线切割中热效应现象及其对模具质量影响

热效应是电火花线切割加工模具时的固有现象,将热效应影响范围分为7个区,并分析对模具质量的影响,指出模具热效应区中的过热区和淬火区产生的残余应力和微裂纹是影响模具制造质量的重要原因,并制定相应的解决办法与对策.实例表明,用热效应现象分析和解决模具电火花线切割的质量问题是非常有效的.     

一种超细晶材料的混合硬化模型及其数值模拟

针对超细晶材料强度高、塑性能力不佳以及饱和应力跟晶粒尺寸和应变率等因素有关的特点,在Johnson-Cook模型的基础上引入Hall-Petch关系式,再与Armstrong-Frederick非线性随动硬化规律进行叠加,提出一种同时包含各向同性硬化和非线性随动硬化的混合硬化模型。该数学模型不仅考虑了超细晶材料的尺寸效应,还计及了加工硬化和包辛格效应的组合效应。在推导出该混合硬化模型的积分算法的基础上进行有限元数值分析和试验数据的对比分析。对比结果表明,不同晶粒大小与不同应变率下的超细晶材料的数值仿真结果与试验数据均吻合较好,进而证明该数学模型的合理性。因此,该混合硬化模型不仅丰富了塑性力学的内容,也可为超细晶材料的结构件设计提供一定的理论依据。     

TC4合金冲击磨损性能与机制的研究

固定冲击频率,在3组大小不同的冲击力下,在自制的小载荷冲击磨损实验机上对TC4合金进行了系列周次的冲击试验,研究了TC4合金的冲击磨损性能与磨损机制.结果表明:试样的整个冲击磨损过程可分为3个阶段,即无磨损阶段、微量磨损阶段和严重磨损阶段,增加冲击力将缩小前2个阶段的进程,加速材料的磨损;在各冲击力下磨痕轮廓及形貌的变化规律基本一致.TC4合金的磨损过程是接触表面硬化、启裂、疲劳剥落的过程,其磨损机制主要表现为塑性变形和疲劳剥落.     

热轧高锰钢Mn13的冲滚磨料磨损性能

在M2000摩擦磨损试验机上,研究以煤矸石为磨料时热轧高锰钢Mn13冲滚耦合的磨料磨损性能,利用XRD和SEM分析其组织转变及磨损机制。实验结果表明,在较高冲滚载荷下,热轧Mn13钢表现出更好的抗冲滚磨料磨损性能;冲滚磨料磨损表面存在一定厚度的硬化层,且随冲滚载荷的增加,磨损面硬度增加,硬化层厚度增大,形变孪晶和马氏体相变是其加工硬化和耐磨损性能改善的主要原因;低载荷冲击时,磨损机制主要表现为凿削磨损并伴随犁沟切削磨损,较高载荷冲击时,磨损机制凿削磨损和犁沟划伤过渡到疲劳剥落和凿削磨损。     

不同强化模型下的板料成形极限

介绍Hill48屈服准则下基于不同强化模型的屈服方程。推导出能够用来确定随动强化模型和混合强化模型中参数的方程。采用单向拉伸曲线上所取得的数据,对所得方程进行拟合,得到参数值,并使用所得参数值得出三种强化模型下的单向拉伸曲线。结果表明采用上述方法能够准确地确定强化模型中的参数。给出随动强化模型和混合强化模型下成形极限的计算方法。基于三种强化模型,针对分散性失稳准则、Hill集中性失稳准则、凹槽失稳准则和平面应变漂移失稳准则,得到简单加载路径下的成形极限图和成形极限应力图。从这些图中可以看出,强化模型对成形极限图和成形极限应力图影响明显。因此应当确定板料在成形过程中的强化规律,选择合适的强化模型进行成形极限预测。     

General analytical shakedown solution for structures with kinematic hardening materials

The effect of kinematic hardening behavior on the shakedown behaviors of structure has been investigated by performing shakedown analysis for some specific problems. The results obtained only show that the shakedown limit loads of structures with kinematic hardening model are larger than or equal to those with perfectly plastic model of the same initial yield stress. To further investigate the rules governing the different shakedown behaviors of kinematic hardening structures, the extended shakedown theorem for limited kinematic hardening is applied, the shakedown condition is then proposed, and a general analytical solution for the structural shakedown limit load is thus derived. The analytical shakedown limit loads for fully reversed cyclic loading and non-fully reversed cyclic loading are then given based on the general solution. The resulting analytical solution is applied to some specific problems: a hollow specimen subjected to tension and torsion, a flanged pipe subjected to pressure and axial force and a square plate with small central hole subjected to biaxial tension. The results obtained are compared with those in literatures, they are consistent with each other. Based on the resulting general analytical solution, rules governing the general effects of kinematic hardening behavior on the shakedown behavior of structure are clearly.     

混合硬化弹塑性本构关系及其在环件冷辗扩模拟中的应用

采用数值模拟方法和混合硬化弹塑性本构关系,提出了基于弹性张量的应力补偿更新算法,引入等向强化系数,给出了有限元计算步骤,基于ABAQUS/Explicit平台开发了子程序VUMAT,并在单个单元模型中验证了其可靠性。将其应用于环件冷辗扩过程模拟中,着重研究了等向强化系数对环件冷辗扩成形的影响规律。结果表明,随着等向强化系数的增大,辗扩力、辗扩力矩增大,鱼尾形状系数减小,环件外圈金属受各向异性硬化影响较大,进而从理论上进行了解释。研究结论指出该研究对环件冷辗扩成形工艺具有指导意义。     

组织结构对应变硬化的影响

研究了不同类型材料应变硬化的变化特征，结果表明：存在应变诱发马氏体转变的亚稳奥氏体不锈钢、TRIP钢平均硬化率最高，硬化指数随应变的增加呈抛物线型变化；变形后无相变但组织转变为孪晶结构的奥氏体锰钢硬化率次之，硬化指数n随应变量呈线性变化；组织无变化的稳定态材料硬化率最低，n是常数。     

基于CAD技术的调质钢亚温淬火工艺

介绍基于CAD技术的调质钢亚温淬火工艺参数的确定原理 ,根据钢的化学成分及有关参数 ,利用热处理中的临界点数学模型 ,计算出各临界点的数值 ,并由此确定出钢的亚温淬火加热温度和回火温度 ,同时根据钢的淬透性数学模型计算出钢的淬透性数值 ,以此来判断此亚温淬火工艺是否可行。对 40Cr钢齿轮轴套进行亚温淬火试验研究 ,结果表明 ,利用CAD技术设计调质钢的亚温淬火工艺切实可行