Research and application of combined pressure relief technology of roof hydraulic fracturing and deep hole blasting

In order to realize the smooth collapse of high-strength composite roof in 1311 working face of Zhaozhuang Coal Industry company and avoid strong ground pressure disaster caused by large-area roof suspension, firstly, the composite pressure relief mechanism of “cross cutting and longitudinal explosion” is analyzed theoretically, in other words, the secondary propagation radius r of blasting crack is greatly increased on the basis of fracturing damage length R and explosion crack radius a0, which improves the effect of roof pre-cracking, then, based on the industrial test of 1309 working face, the pressure relief process parameters of “cross cutting and longitudinal explosion” are reasonably determined and applied in the field. The results show that: the “cross cutting and longitudinal blasting” composite pressure relief process can increase the density of borehole axial fractures and borehole radial fractures, and the roof separation of roadway in the application area is low; it shows that the “cross cutting and longitudinal blasting” pressure relief process can effectively destroy the integrity of the roof, reduce the stress concentration of the surrounding rock of the roadway, and play a preventive effect on the strong ground pressure disaster

Effect of hot isostatic pressing and heat treatment on the evolution of precipitated phase and mechanical properties of GH3230 superalloy fabricated via selective laser melting

In this paper, the microstructure and mechanical properties of SLM-GH3230 superalloy treated by different post treatments (single hot isostatic pressing and heat treatments after hot isostatic pressing) were studied. The micro-morphologies show that the grains along building direction after HIP + HT are mainly columnar grains, which is consistent to that after single HIP. The granular precipitates distribute intergranularly and intragranularly after HIP, but gradually re-dissolve into matrix with the increase of the temperature of the post HT processes. XRD and EDS analyses results indicate that the matrix mainly consists of austenitic γ phase and the granular precipitates are mainly M6C carbides enriched in W element. The average grain size decreases after HT compared to that after HIP, and the crystallographic orientation of grains tends to be more uniform. The Vickers hardness decreases after HIP and HIP + HT processes within a certain degree. According to tensile test results, the sample shows a better combination of strength and plastic performance under HIP+1250 °C/30 min processing, which can also be verified by the characteristic of the fracture morphology with more tearing dimples