The influence of deformation and austenitization temperature on the kinetics of phase transformations during cooling of high-carbon steel

The aim of the performed experiments was to determine the influence of deformation and of austenitization temperature on the kinetics of phase transformations during cooling of high-carbon steel (0.728 wt. % C). The CCT and DCCT diagrams for austenitization temperature 940 degrees C and DCCT diagram for austenitization temperature 1000 degrees C were constructed with the use of dilatometric tests. On the basis of obtained results, a featureless effect of austenitization temperature and deformation on the kinetics of phase transformations during cooling of investigated steel was observed. Critical cooling rates for the transformation of martensite in microstructure fluctuated from 5 to 7 degrees C . s(-1) (depending on the parameters of austenitization and deformation), but only at cooling rates higher than 8 degrees C . s(-1) a dominant share of martensite was observed in the investigated steel, which resulted in the significant increase of hardness.Web of Science6341748174

The influence of cooling rate on phase transformations of C-Mn rail steel

Na základě vyhodnocení laboratorních dilatometrických testů s deformací, které byly provedeny na plastometru Gleeble 3800 s využitím optického bezkontaktního skenovacího dilatometru a na základě vyhodnocení metalografických analýz a zkoušek tvrdosti dilatometricky zkoušených vzorků, byl vytvořen DARA diagram kolejnicové oceli R260. Na vratné kolejnicové trati v Třineckých železárnách, a.s. bylo provedeno měření povrchové teploty hlavy kolejnice při jejím akcelerovaném a volném ochlazování po doválcování. Tyto kolejnice byly také podrobeny metalografickým analýzám a zkouškám tvrdosti. Naměřené ochlazovací křivky v provozních podmínkách ochlazovaných kolejnic byly vloženy do DARA diagramu. Z dosažených výsledků vyplývá, že nežádoucí martenzitická fáze vzniká ve struktuře až při rychlosti ochlazování 5 °C•s-1 nebo vyšší a zvolený akcelerovaný způsob ochlazování hlavy kolejnic z oceli R260 je z hlediska dosažení požadované struktury bezpečný.Based on the evaluation of laboratory dilatometric tests with deformation, which were performed on the plastometer Gleeble 3800 with using optical noncontact scanning dilatometer and based on evaluated metallographic analyses and hardness tests of dilatometric tested samples, the DCCT diagram of rail steel R260 were constructed. On the Reversing rolling mill at Třinecke železarny a.s. was measured the surface temperature of the head of rail during their accelerated or free cooling after finish rolling. These rails were also subjected to metallographic analyses and hardness tests. The measured cooling curves of these rails were inserted to the DCCT diagram. From obtain results ensue that unwanted martensitic phase is generated in the structure at a cooling rate 5 °C•s-1 or higher and selected accelerated manner of cooling the head of rails from steel R260 is safety from point of reaching needed structure.633 - Katedra tváření materiáluvelmi dobř

The high-temperature plastic properties of low-alloy Cr-Mo steels with different carbon content

S využitím simulátoru HDS-20 byly zkoumány plastické vlastnosti za vysokých teplot dvou nízkolegovaných Cr-Mo ocelí, které se lišily obsahem uhlíku a manganu. Speciálním testem byla stanovena teplota nulové pevnosti obou ocelí. V případě oceli 4130 byla teplota nulové pevnosti rovna 1444 °C, v případě oceli 4140 (s vyšším obsahem uhlíku) byla teplota nulové pevnosti rovna 1402 °C. Zkouškami jednoosým tahem do lomu byly zkoumány plastické vlastnosti, resp. tažnost zkoumaných ocelí za vysokých teplot. Ocel 4130 vykazovala nejvyšší tažnost při teplotách 1300 – 1370 °C, oceli 4140 vykazovala nejvyšší tažnost při teplotách 1300 – 1340 °C. Pro ocel 4130 byla stanovena průměrná teplota nulové tažnosti 1405 °C, pro ocel 4140 byla tato teplota rovna 1369,5 °C. Vyšší obsah uhlíku a manganu v oceli 4140 měl tedy, ve srovnání s ocelí 4130, za následek snížení teploty nulové pevnosti o 42 °C a snížení teploty nulové tažnosti o 35,5 °C.By using simulator HDS-20 were investigated plastic properties at high temperature of two low-alloy Cr-Mo steels, which differed to carbon and manganese content. By special test are established the nil-strength temperature of both steels. In case of 4130 steel, the nil-strength temperature was equal to 1444 °C, however in case of 4140 steel (with higher carbon content), the nil-strength temperature was qual to 1402 °C. By means of the uniaxial tensile tests performed on the plastic properties i.e. the steels ductility at high temperature. 4130 steel, reported the highest ductility at 1300 °C up to 1370 °C, but 4140 steel showed the highest ductility from 1300 °C just to 1340 °C. For 4130 steel is average point of the nil-ductility temperature at 1405 °C, in case of 4140 steel is average point of the nil-ductility temperature equal to 1369,5°C. Higher content of carbon and manganese in 4140 steel has resulted decreased by 42 °C nil-strength temperature compared to 4130 steel. Also that has resulted decreased by 35,5 °C nil-ductility temperature.633 - Katedra tváření materiáluvelmi dobř

Racionalizace přípravy obrábění přírubových součástí s využitím systému CAD/CAM

Import 20/04/2006Prezenční výpůjčkaVŠB - Technická univerzita Ostrava. Fakulta strojní. Katedra (346) obrábění a montáž

Innovative approach to monitoring coal pillar deformation and roof movement using 3D laser technology

Monitoring of pillar and roadway deformations is one of the most important issues in geotechnical engineering and mining practice. The use of 3D laser technology is ideal to monitor strata displacements in underground excavations enabling complex spatial data capture of the entire space around monitored pillars including all roof and rib deformation which occurs during the pillar excavation. This method based on repeated scans, can monitor the excavation surface movement ranging from a few mm to more than 600 mm. The 3D laser scanner was used to monitor the coal mine roadways and pillar stability in room and pillar panel trial in the Ostrava-Karvina coal basin (OKD Mines, Czech Republic). The 3D data analysis indicated rib movement that ranged from 250 mm to more than 600 mm, a large floor heave that was regularly brushed and practically no roof movement of very strong roof strata overlaying the whole panel area. All scanned results compared well to the results from the extensometry and other measuring instruments. The results further indicated that the mined roadway cross sectional area decreased between approximately 15-25% during the first 7 months of monitoring and stabilized at 5% after another 7 months. Further monitoring is planned to identify any long term creep in the room and pillar panel

Use of 3D Laser Scanner Technology to Monitor Coal Pillar Deformation

Although the room and pillar mining method is world-known and widely used, in terms of the Czech coal mines located in the Upper Silesian Coal Basin it is still in the testing phase. Unfavourable mining, geotechnical conditions at large depths and the ban by Czech mining authorities prevented this method from being used on rock bolt reinforcement without other roof support. Typically, large amounts of unexploited coal reserves are left in the shaft protective pillars. This coal can be mined if strata subsidence is minimised. Due to its low subsidence characteristics the room and pillar mining method without pillar extraction has been trialled at the CSM Coal Mine at the end of 2014. During the pillar development phase complex geotechnical monitoring was undertaken including the frequent scanning of pillar movement using 3D laser scanning technology. The laser scanner enabled complex capture of the entire space around the monitored pillars during the period of pillar formation and afterwards. The time-lapse scanning method measured changes in the mine roadway surface profiles including pillar displacements, roof movements, floor heave and other dynamic phenomena. The time-lapse scanning indicated variable pillar rib movement ranging from a few cm to a maximum of 50 cm with an average of approximately 25 to 30 cm. The scans indicated that the bottom of the seam displaced more than the top of the rib side due to large floor heave. The weak floor consisting of siltstone and coal beds experienced large floor heave however, due to floor brushing no reliable floor displacements are available. In contrast to the large movements in the rib and the floor, the strong roof strata did not show any significant movements. The purpose of this work is to highlight the importance of terrestrial laser scanning as an essential engineering design tool to evaluate the displacements and deformations of mine excavations at large depths. The 3D scanning results gave relevant information about displacements and deformations that occurred at the tested site and thereby helped to improve safety underground

Possibility of convergence measurement of gates in coal mining using terrestrial 3D laser scanner

The application of laser scanning technology has increased recently in many different branches. The presented paper deals with an application of this technology in the mining environment. To verify the spatial changes (movements and deformations) of mining works this technology was deployed in situ at the selected mining workplace in the Czech part of the Upper Silesian Coal Basin. The main purpose of 3D laser scanning at Lazy Mine was to monitor the deformation of the roadway before approaching the longwall face on the selected tailgate. From the results of performed 3D scanning used it was possible to accurately define and quantify the floor lift area in front of the approaching coalface, observe measurable tilt of middle wooden props, capture documentable changes in floor dinting during the period between campaigns and monitor the deformation of steel arch support, confirming the influence of additional stress away from the goaf of previous longwall

Stress state monitoring in the surroundings of the roadway ahead of longwall mining

Accurate knowledge of the stress-strain state of rock mass, not only in their vicinity but also in the wide surroundings of mine workings, is absolutely critical for precise support designing. Investigation of the rock stress is usually carried out by interpretation of the rock mass deformation processes, which can be relatively precisely observed and measured. In order to verify the stress state of the rock mass and changes in it induced by longwall mining, monitoring of changes in the rock mass stress in connection with the mine out of the longwall No. 371 202 was carried out. The seam extracted by monitored longwall has a thickness of approximately 2 m at a depth about 1100 m and lies within the Czech part of the Upper Silesian Coal Basin. Interpretation of the initial rock mass stress tensor and verification of its changes during longwall mining were the aims of this stress monitoring. A total of five probes were installed on the roof rocks of the main gate. Two compact conical-ended borehole overcoring probes were installed to obtain the pre-mining full stress tensor and afterwards three compact conical-ended borehole monitoring probes were installed to continuously monitor the stress state in the rock mass ahead of the advancing longwall. The monitored stress development contributes to our knowledge of stress distribution and its changes during excavation at great depth in multi-seam sedimentary deposits of the Upper Silesian Coal Basin

Wiki Projects in Czech Medical Education

WikiSkripta jsou příkladem rostoucího wiki projektu. Přestože nebyla prvním, ani jediným wiki projektem na 1. LF UK Praha, je jejich dynamika růstu mezi ostatními projekty výjimečná. V čem jsou rozdíly mezi dynamicky rostoucími a statickými wiki projekty? Lze pozorované jevy zobecnit? Čestmír Štuka, Martin Vejražka, Petr Kajzar, Stanislav Štípek1. LF UK, PrahaWikiSkripta is an example of a growing Wiki project. Although it was not the first and not the only wiki project on the First Faculty of Medicine, its rate of growth among other projects is unique. What are the differences between static and dynamically growing wiki projects?  Can we generalize the observed phenomena? Čestmír Štuka, Martin Vejražka, Petr Kajzar, Stanislav Štípek1. LF UK, Prah

Seismic activity and flooding of hard coal mines in the Ostrava-Karvina Coalfield

The termination of mining activities often results in post-mining problems and risks. One of these issues is the flooding of mines. Long-term mining in the Ostrava and Petrvald sub-basins in the Upper Silesian Coal Basin finished in 1994. Tens of coal seams were mined here, and the depth of mining reached more than 1000 m below the surface. Flooding of the Ostrava sub-basin started in 1994. The Ostrava and Petrvald sub-basins were flooded from one half only to prevent water from flooding into the Karvina sub-basin, where mining continued. The continual pumping of water has been carried out ever since. Only low-energy seismic events (up to 103 J) were recorded during the periods of flooding and water pumping. Only one high-energy seismic event was recorded here (108 J, magnitude of 3.5, 12 December 2017). This study presents the natural and mining conditions regarding the process of mine flooding; and the induced seismicity registered during the flooding of mines and the preservation of water at the stated level. Analysis of the flooding of mines in connection to the registered seismicity is presented. Probable reasons for the low seismic activity during the flooding of mines are also discussed