The Effects of Prior Austenite Grain Refinement on Strength and Toughness of High-Strength Low-Alloy Steel

The effects of prior austenite grain (PAG) refinement on the mechanical properties of bainitic/martensitic steels not only come from itself, but also have more complex effects by affecting the substructure formed by coherent transformation. In this study, the samples of a low-alloy steel were water quenched from different austenitizing temperatures and the bainitic/martensitic microstructures with different PAG sizes were obtained. Electron back-scattered diffraction was used to characterize the microstructure and different types of boundaries were identified and quantitatively analyzed. The tensile tests and series temperature Charpy impact tests of different heat treatment were also carried out and comprehensively analyzed with microstructure characterization works. The results show that the uniform refinement of prior austenite grain can increases the density of packet boundary and block boundary, which leads to microstructure refinement with higher density of high-angle grain boundaries with misorientation >45°. The contribution of this microstructure refinement to toughness is significant, but its contributions to strength and elongation are relatively limited. Compared to uniform refined PAG, if the PAGs are mixed crystal, the density of block boundary will be reduced, which leads to a lower density of the high-angle boundary with misorientation >45° and the positive effects of microstructure refinement on toughness improvement are weakened. The observation of fracture surface of impact specimens indicates that refining the PAG can delay the tendency of brittle fracture with the decrease in test temperature, and even in the case of brittle fracture, the cleavage facet of the fracture surface is relatively smaller. This result also verifies that PAG refinement can effectively improve toughness by inhibiting cleavage fracture.

The Importance of Seismic Attributes in Complex Area, Case Study from Vodianivske Field, Dnieper-Donets Basin, Ukraine

The Dnieper-Donets Basin (DDB) is the principal producer of hydrocarbons in Ukraine and reserves are found in lower Permian and in Visean-Serpukhovian from Lower Carboniferous. The Vodianivske field is located halfway between Poltava and Kharkiv in east Ukraine with proven reserves at depth of 5-6km. Previous studies based on legacy seismic data show thickness changes of the upper Visean towards the main structure and dim small-scale structures on the block boundary. A recent 3D data reprocessing using 5D interpolation and advanced prestack time migration provides a broad frequency content image and imparts detailed high-resolution geological events. While traditional exploration is focused on gas traps in the Visean and below, current study aims to scan for potential traps in the Serpukhovian and above. In order to reveal thin section features, multiple seismic attributes were tested, and spectral decomposition was found to be a powerful tool that delineated thin sand bodies in river valleys and allowed interpretation of high-resolution small-scale faults and pinch-outs not seen before. Frequency tuning analysis on mapped horizons associated with upper Serpukhovian supported the presence of a large deltaic structure revealing SE-NW thin ∼1km wide sand body and developed set of crossing meanders. Similar approach was applied on legacy data expanding to the east and while seismic quality was limited, it was possible to identify a narrow ∼25km length meander and highlight a fault set. Upon seismic attribute study we were able to identify and map thin units associated with sands that can be considered as future targets in hydrocarbon exploration in the area.

An Efficient Lossless Compression algorithm for Medical images

Medical image compression plays a vital role in diagnosis of diseases which allowing manipulation, efficient, transmission and storage of color, binary and grayscale image. Before transmission and storage, a medical image may be required to be compressed. The objective of the study is to develop an efficient and effective technique for digital medical images which alleviates the blocking artifacts from grayscale image while retaining all relevant structures. In this paper, we demonstrate a highly engineered postprocessing filtering approach has been designed to remove blocking effects from medical images at low bit rate. The proposed technique is comprised of three strategies i.e. 1) a threshold valve scheme which is used to capture the pixel vectors containing blocking artifacts. 2) Blocking artifacts measurement techniques. The blocking artifacts are measured by three frequency related modes (low, Moderate and high frequency model). 3) A directional filter which is used to remove over-smoothing and ringing artifacts near edges of block boundary. The algorithm is tested on digital medical grayscale images from different modalities. The experimental results illustrate that the proposed technique is more efficient on the basis of PSNR-B, MSSIM, and MOS indices than the state-of-the-art methods. The proposed algorithm can be seamlessly applied in area of medical image compression which high transmission efficiency and acceptable image quality can be guaranteed.