Effect of kolsterising treatment on surface properties of a duplex stainless steel

In recent years, attempts of engineering the surface of duplex stainless steels were made in order to enhance their hardness and tribological properties, without affecting their corrosion resistance. A possibility of improving these properties is provided by a family of processes developed by Prof. B.H. Kolster in the Netherlands in the late 1980’s. These processes (usually referred to as Kolsterising® treatments) consist in a low temperature surface carburizing, which involves the diffusion of large quantities of carbon atoms (up to 6-7 wt.%) into the steel at a diffusion temperature below 450 °C. In the present paper a characterization of the surface layer of Kolsterised duplex SAF 2205 stainless steel was carried out to study the effects of this treatment on surface properties. The characterization includes optical metallographic examination, microhardness tests and SEM-EDS investigation on the Kolsterised steel in the as treated condition and after annealing treatments at 200, 250, 300 350 and 400°C for 10 hours, to evaluate the stability of Kolsterised layer’s properties with a moderate increase in temperature. Moreover, complying with ASTM G48-03 Method E Standard, in order to evaluate the effect of the Kolsterising® treatment on steel pitting resistance, the critical pitting temperature was obtained for Kolsterised duplex SAF 2205 stainless steel compared with the base metal

On the crack path of rolling contact fatigue cracks in a railway wheel steel

The objective of the present paper is to give some preliminary results obtained in the frame of a more wide investigation on the rolling contact fatigue (RCF) behavior of a railway wheel steel. The effect of different test parameters on the RCF fatigue strength of the railway wheel steel was evaluated. RCF tests were conducted using two cylindrical contact specimens under different Po/k ratio (where Po is the maximum Hertzian pressure, k is the yield stress in shear of the material), under dry contact conditions or with water lubrication, and at varying slip ratio. In the present study crack initiation location and crack growth direction were carefully investigated; microscopic examination showed that the cracks were initiated at the surface, propagated obliquely in the depth direction and then occasionally branched into two directions. Usually multiple cracks are initiated, at the rolling contact surface, caused by the accumulation of shear deformation due to repeated rolling–sliding contact loading. Subsequent crack growth has been found to occur along specific sloped directions. The influence of Po/k ratio, dry or wet contact, and slip ratio on crack slope angle to the radial direction and the depths at which slope changes occur has been investigated. Observed crack slopes and slope change position have been discussed according to crack path prediction criteria in the literature

Automatic optimization of array queries

Non-trivial scientific applications often involve complex computations on large multi-dimensional datasets. Using relational database technology for these datasets is cumbersome since expressing the computations in terms of relational queries is difficult and time-consuming. Moreover, query optimization strategies successful in classical relational domains may not suffice when applied to the multi-dimensional array domain. The RAM (Relational Array Mapping) system hides these issues by providing a transparent mapping between the scientific problem specification and the underlying database system. This paper focuses on the RAM query optimizer which is specifically tuned to exploit the characteristics of the array paradigm. We detail how an intermediate array-algebra and several equivalence rules are used to create efficient query plans and how, with minor extensions, the optimizer can automatically parallelize array operation

A Case Study on Array Query Optimisation

The development of applications involving multi-dimensional data sets on top of a RDBMS raises several difficulties that are not directly related to the scientific problem being addressed. In particular, an additional effort is needed to solve the mismatch existing between the array-based data model typical for such computations and the set-based data model provided by the RDMBS. The RAM (Relational Array Mapping) system fills this gap, silently providing a mapping layer between the two data models. As expected though, a naive implementation of such an automatic translation cannot compete with the efficiency of queries written by an experienced programmer. In order to make RAM a valid alternative to expensive and time-consuming hand-written solutions, this performance gap should be reduced. We study a real-world application aimed at the ranking of multimedia collections to assess the impact of different implementation strategies. The result of this study provides an illustrative outlook for the development of generally applicable optimisation techniques

Evolution of prototyping in automotive engineering: a comprehensive study on the reliability of Additive Manufacturing for advanced powertrain components

Additive manufacturing (AM) could be used to reduce the production times of prototypes; however, further research is required to address metals structural parts. To obtain the correct properties, some relevant factors to be considered are the build volume, shape factor, and the need for specific heat treatments. This study aims to evaluate the reliability of AM prototypes applied at a new powertrain system developed to reduce vehicle emissions. Firstly, it was investigated the mechanical behavior, microstructure, and the effect of sample size and heat treatments on both specimens and prototypes made of AM 17-4PH steel. Finite Element Analysis (FEA) was performed to evaluate the structural resistance. Finally, the prototypes were produced, analyzed, and tested on a functional engine test bench to evaluate their reliability. The mechanical properties decreased with an increase in the sample volume. After heat treatment, the yield strength increased, due to the transformation of δ-ferrite in martensite and the reduction of retained austenite. The engine test bench was successfully completed. The conclusions set the basis for similar future applications of time-effective prototypes that can be dimensioned owing to appositely developed postprocesses that guarantee the required resistance

Distribution Rules for Array Database Queries

Non-trivial retrieval applications involve complex computations on large multi-dimensional datasets. These should, in principle, benefit from the use of relational database technology. However, expressing such problems in terms of relational queries is difficult and timeconsuming. Even more discouraging is the efficiency issue: query optimization strategies successful in classical relational domains may not suffice when applied to the multi-dimensional array domain. The RAM (Relational Array Mapping) system hides these difficulties by providing a transparent mapping between the scientific problem specification and the underlying database system. In addition, its optimizer is specifically tuned to exploit the characteristics of the array paradigm and to allow for automatic balanced work-load distribution. Using an example taken from the multimedia domain, this paper shows how a distributed realword application can be efficiently implemented, using the RAM system, without user intervention

Investigating post-processing impact on fatigue performance of LPBF Ti6Al4V with heat treatment, high pressure heat treatment, and dry electropolishing strategies

This study investigates the impact of post-processing techniques on the fatigue behaviour of specimens in Ti6Al4V made by laser powder bed fusion (LPBF) for relevant applications, such as motorsport. Despite the LPBF advantages in terms of complex design and weight reduction, challenges such as reduced fatigue performance persist. Therefore, the application of post-processing treatments can play a critical role. In addition to traditional sandblasting (SB), three post-processing conditions were investigated to enhance mechanical properties under quasi-static and fatigue loading conditions: heat treatment (HT) and the innovative High Pressure Heat Treatment (HPHT) along with dry electropolishing (EP) treatment. The results indicate that both the HT and HPHT treatments produced a macrostructure with equiaxial grains composed of fine α + β lamellae. Mechanical analyses demonstrated that the HPHT-SB-EP condition exhibits properties comparable to those of forged Ti6Al4V used in the automotive field, with a good balance between strength and ductility. The EP treatment effectively reduced surface roughness and inherent surface irregularities caused by the LPBF process. The best fatigue results were achieved with the HPHT-SB-EP condition, despite data scattering. An increase in fatigue resistance was observed by using SB at a higher pressure

Non linear fields in the SPS and their compensation

Tight tolerances were placed upon non-linearities in the SPS magnet system and sextupoles installed to adjust the chromaticity of the machine. These sextupoles together with octupoles and active damping were used to adjust the SPS beam dynamics and to damp and suppress both multibunch and single bunch transverse instabilities up to 10/sup 13/ protons per pulse. (4 refs)