A model based creep equation for 9Cr–1Mo–0·2V (P91 type) steel

Abstract

The isothermal constant stress creep tests data for a 9Cr–1Mo–0·2V (P91 type) steel were submitted for a phenomenological analysis in order to obtain the relevant creep equation for such steel. Namely, the minimum creep strain rate of P91 type steel cannot be described by the simple Arrhenius type power law constitutive model. The incorporation of the threshold stress concept in the analysis of creep data leads to a modified power law, which satisfactorily describes the creep behaviour of the examined P91 steel. However, the threshold stress is not a good material parameter, as it often varies with temperature and/or applied stress. This adds uncertainty to the extrapolation of the creep rates into ranges where experimental data are not available. Besides the fact that the physical foundation for a threshold stress is questionable from a scientific point of view, this is a serious practical limitation of the modified power law creep equation. The second creep equation proposed in the present paper is the improved stress dependent energy barrier model. The improvement of the standard model is based on two assumptions: first, on the hypothesis that the application of a stress also affects the energy barrier to be overcome when a local region transitions from the initial to the final state, and second, by applying a simple power function of stress instead of a hyperbolic sin function in the model based equation. The obtained value of stress exponent, n=5·5, is too high for entirely climb controlled creep. The apparent activation energy of approximately 510 to 545 kJ mol^?1, which is considerably higher than the activation energy for lattice diffusion, is the stress dependent activation energy of the slowest, dominant rate controlling process of the supposed multiple creep mechanisms.     

A haptic representation system for a virtual plain wall

The purpose of this study is to develop a virtual wall display system for a walk simulator to grope its way in an 'invisible' situation, such as in a building filled with dense smoke, etc. To reproduce the realistic haptic sense of a building wall, the implementation of the wideness and the rigidity of wall are essential. Wideness of a virtual wall was realized by a hand-tracking control combined with a small wall panel which is mounted on a three-axis Cartesian manipulator. A 6-d.o.f. magnetic tracking system was utilized for the hand position tracking in the non-contact situation of the hand and the panel. In the contact situation, high rigidity of the wall was attained as stiffness in the normal direction is provided to the wall panel to represent the haptic sense of a rigid wall. Force-based tracking provides the low stiffness in the tangential direction to make the wall panel move easily along the direction of hand movement to represent a wide plain wall. A three-axis force sensor is attached on the wall panel to detect the contact force. The realization of smooth switching between both tracking controls provides the user with the haptic feel of the presence and continuity of a virtual wall. In addition, the frictional sensation has the effect of giving the system more reality. Experimental results have shown the effectiveness of the hybrid tracking method for the virtual wall system.     

Two body type abrasion wear behaviour in hypoeutectic 16%Cr cast irons with Mo

Abstract

Hypoeutectic 16%Cr cast irons, both Mo free and 1–3%Mo containing specimens were prepared to investigate their abrasion wear behaviour. Annealed specimens were hardened at 1323 K and then tempered at three temperatures from 673 to 873 K for 7·2 ks, the temperature giving the maximum hardness (H_Tmax) and the lower and higher temperature, (L-H_Tmax, H-H_Tmax). The abrasion wear behaviour was investigated using a two body type Suga abrasion wear tester. A linear relation was obtained between wear loss and wear distance. The highest wear resistance or the lowest wear rate (R _W) was obtained in H _Tmax specimens except for the Mo free specimen. The lowest wear resistance or the highest R _W was obtained in H-H_Tmax specimens. The R _W was decreased with an increase in macrohardness. The lowest R _W appeared around 25% retained austenite (V _γ ). The R _W was decreased with an increase of Mo content, and the V _γ value at the minimum R _W shifted to the high V _γ side.     

基于Pro/E Wildfire 3.0和立式加工中心铣削平面型腔的研究

在模具加工中,型腔是一种常见的对象,它的结构形状比较复杂,含有大量自由曲面及岛,所以通常用数控机床加工。如何设计型腔加工的NC刀具轨迹和走刀方式是实际工作中的难题。研究和讨论了基于Pro/E软件模拟型腔加工时的NC刀具SCAN-TYPE和型腔铣削加工"ROUGH-OPTION"方式的选择。     

Weld porosity in containers for storage of plutonium containing materials

Abstract

An autogenous gas tungsten arc closure weld was developed for the US Department of Energy's primary container for the storage of plutonium bearing materials. The occurrence of porosity at the tie-in point of the closure weld was investigated. The primary cause of the porosity was linked to the geometry at the root of the closure weld joint. The present paper describes the mechanistic model that was developed to describe and predict the porosity.     

Influence of ferromanganese additions on microalloyed engineering steel

Abstract

Plant trials with the addition of four different low carbon and medium carbon ferromanganese alloys to microalloyed engineering steels have been carried out at Ovako Steel, Hofors, Sweden. The process route for this type of steel at Ovako is electric arc furnace (EAF), ladle arc furnace (LAF), ASEA-SKF vacuum degasser, LAF and finally uphill teeming. For each ferromanganese alloy type, five experiments were accomplished by adding alloy at the ladle furnace station, i.e. 20 charges in total. During the experiments, liquid steel rapid solidification samples were taken to study the behaviour of inclusion formation and removal during ladle treatment. Also, samples for LSHR testing (liquid sampling hot rolling) were acquired for one heat of each of the ferromanganese containing alloys. Microinclusion assessments were carried out according to the method described in Swedish standard SS 111116. Macroinclusion assessments were carried out using immersed ultrasonic testing. Element analysis and mappings were done using a scanning electron microscope to establish the effect of ferromanganese addition on the composition of inclusions present in the steel. In samples taken 3 min after the ferromanganese addition to the LAF, about 30% of the analysed inclusions contain Al₂O₃, MnO and MnS. The Al₂O₃ content is concluded to originate from the deoxidation practice, while MnO and MnS contents are likely to originate from the addition of ferromanganese. The results also show that the addition of ferromanganese alloys leads to an increased amount of macroinclusions in the LAF up to 9 min after alloy addition. Steel samples taken after degassing but just before casting indicate that all the tested ferromanganese alloys give the same result with respect to the studied microinclusion characteristics at the end of ladle treatment. Last, the inclusion composition in the final steel samples is unrelated to the type of ferromanganese alloy used. In this case, the main compositions are Al₂O₃-MgO and MnS.     

Effects of weld preheat temperature and heat input on type IV failure

Abstract

Type IV cracking refers to the premature failure of a welded joint due to an enhanced rate of creep void formation in the fine grained or intercritically annealed heat affected zone. A great deal of research effort has been directed at understanding the underlying mechanisms for this type of failure, but most have approached the problem from a metallurgical standpoint, and comparatively little effort has been directed at understanding the effects of welding variables. Here the effects of parameters such as the preheat temperature and heat input on the tendency for type IV failure in 9–12%Cr steels have been quantitatively estimated. These calculations have subsequently been verified experimentally to form the first systematic study of welding parameters on type IV cracking. The joint geometry and preheat temperature have been found to ameliorate type IV failures, while the effect of heat input is less significant.     

载频为13.56MHz的IC卡PCD发送通道技术

介绍了13.56MHzPCD发送通道的电路结构和设计思路 ,给出了一种适合TYPEA、TYPEB、RFID等多种非接触式IC卡的PCD发送通道的设计方法     

TCP／IP跨平台通信的研究

跨平台数据传输一直是研究TCP／IP协议的一个重要方向，同时跨平台数据传输也是OSI通信的瓶颈。为了解决不同系统之间的通信，就需要研究TCP／IP协议关于跨平台数据传输方面的关键技术及原理，并在此基础上对当前各种解决方法的基本原理进行了比较分析。最后，详细分析了为实现跨平台传输目标的类型缓冲区技术，从而使我们对网络高层软件的开发和应用由一个清晰的了解。     

TCP/IP跨平台通信的研究

跨平台数据传输一直是研究TCP/IP协议的一个重要方向,同时跨平台数据传输也是OSI通信的瓶颈。为了解决不同系统之间的通信,就需要研究TCP/IP协议关于跨平台数据传输方面的关键技术及原理,并在此基础上对当前各种解决方法的基本原理进行了比较分析。最后,详细分析了为实现跨平台传输目标的类型缓冲区技术,从而使我们对网络高层软件的开发和应用由一个清晰的了解。