The geomorphology at Adršpach-Teplice, Czech Republic is dominated by vertical-walled, fracture-controlled features including slot canyons, gorges and pillars. Surfaces of canyon walls in Adršpach are case-hardened and more resistant to erosion than the bulk of the sandstone, which appears to be fundamental to the formation and preservation of canyons. Core and whole rock samples from Adršpach-Teplice were analyzed in thin section, including SEM analysis with cathodo luminescence. XRF and XRD analyses indicated that silica case-hardened surfaces are chemically and mineralogically similar to the rock interior, while iron case-hardened surfaces have an increase in iron present at the surface as the mineral goethite. Permeability analysis indicates a decrease in porosity in case-hardened surfaces. The rock at Adršpach-Teplice is poorly cemented yet has the strength to maintain vertical faces because of a locked sand structure, which was formed by pressure solution. Fracture faces contain disaggregation and cataclastic bands that reduce porosity and increase strength. Case-hardening exists on fracture faces and other surfaces as either silica or iron. Silica case-hardening is ubiquitous in the area and consists of a slight increase in abundance of silica overgrowths and sometimes an increase in clay content. It can form on fresh surfaces in as little as five years, creating what is essentially a self-repairing material. Iron case-hardening is composed of goethite, is much less prevalent than silica case-hardening, and does not appear to be actively depositing. Lichens, fungi, and other biological material are present on case-hardened surfaces and may add to the strength of the material. The internal structure of the rock lends the strength to form and maintain the features seen at Adršpach-Teplice, while case-hardening helps to protect them from erosion.

This thesis presents an engineering geological and geotechnical investigation of the proposed Terrace Opencast Coalmine highwall in the Reddale Valley, Reefton. The proposed pit will target the 4-11m thick No. 4 Seam coal, which exists on the Valley floor beneath outwash gravels and Brunner Coal Measures (BCM) overburden dipping at 15-30° to the northwest. Rock coatings are providing friable sandstone units with protection from weathering in existing cut faces and may contribute to short term pit wall stability. The BCM core was divided into four geotechnical units for rock material testing purposes: unit 1 siltstone, unit 2 carbonaceous mudstone, unit 3 interbedded sandstone and carbonaceous mudstone and unit 4 loose sandstone. The average results for units 1-3 gave classifications within the medium to high porosity (9-13%) and dry density (2250-2470kg/m³) ranges, and medium to medium high slake-durability Id2 values (72-94% retained). Unit 4 (loose sandstone) recorded very low dry density (1694 kg/m³) and slake-durability Id2 (9%) average values. Strength testing confirmed that the units can be classed as weak rocks, with average UCS values of 12.8-13.7MPa for units 1-3, and for all four units Is(50) from point load testing of 0.26-0.62MPa with low cohesion values (0-6.2MPa) from triaxial testing. Friction angles from triaxial tests gave high values of 32-45°, while direct shear tests established 15° internal friction for bedding planes in carbonaceous mudstone and 37° for a high angle defect in interbedded sandstone/carbonaceous mudstone. The average Young's modulus values ranged from 0.82 to 10GPa, and Poisson's ratio between 0.39 and 0.50. Eight scanline defect surveys established that the major discontinuities in existing cut faces consist of high angle tension joints, shallow dipping bedding, and faults related to regional uplift. The defect orientations from the scanlines located in the southwest were significantly different from those in the northeast, and may be due to the faults that cross the Valley. In general the majority of defects displayed low persistence (less than 3m), were clean and tight, and had low joint roughness coefficients (JRC less than 6). Joint wall compressive strengths gave an average of 32MPa, but were affected by case-hardening on weathered faces. The results from the 8 drill holes analysed show that 37% of core was within the excellent rock quality designation class (RQD = 90-100%), while 29% was in the very poor quality rock (RQD = 0-25%). A semi-confined aquifer in the outwash gravels that will drain into the proposed pit was found to have a transmissivity of 58m²/day and hydraulic conductivity of 3.1 x 10⁻⁵ m/s. Kinematic feasibility assessment determined an optimum highwall orientation of 65° dip to 120° (dip direction), which is within at least 20° of the coal seam strike. The likelihood of planar, wedge or toppling failure depends on whether the structural conditions are similar to those encountered in the southwest or northeast scanlines, as well as the persistence of the defects present. The occurrence of small scale (less than 1m offset) 'step-up' normal faults, and the three larger faults that cross the valley, all of which are related to regional uplift, will also affect which failure mode will be kinematically feasible. Other crucial slope stability considerations include groundwater inflow from the saturated overburden and bedding parallel failures on the footwall dip slope of the pit. An investigation into case hardening on existing cut faces identified three interconnected rock coatings: iron films, lithobiontic (biological) and clay-dominated crusts. Jarosite was found at sites with abundant pyrite and the oxidation of iron may have been aided by microbial activity. A green algae inhabiting pore spaces approximately 1mm below the surface was noted beneath an iron film and it is suggested to be similar to that found in arid environments. Although lithobiontic and clay-dominated crusts did not provide the weathered surface with any additional strength, they were observed to form relatively quickly (from months to less than 5 years) and will aid short term stability by providing the batters with protection from weathering processes. This project concluded that the overburden material in the proposed highwall can be expected to behave like weak rock and in some cases (such as the loose sandstone) can be expected to have soil characteristics. Highwall stability is more likely to be affected by substantial inflows of groundwater than highly persistent joint sets. Establishment of the highwalls in their final position in the early mining stages will enable development of rock coatings that are expected to aid short and long term stability.

Case hardened Uddeholm Orvar® Superior (Orvar) has the potential to replace currently used materials in shafts inside transmissions, which would lower the overall weight and thus result in lower fuel consumption while maintaining the necessary mechanical properties. However, previous studies have failed to reliably carburize the steel during the case hardening process. The case contains tempered martensite, which has high wear resistance, hardness, and good fatigue properties, and will be affected by the absence of the additional carbon. The presence of passive oxide layers such as chromia and silica is believed to inhibit the carburization, this by their impact of the adsorption and diffusion. One suggested solution is a preoxidation step before the carburization, to promote the formation of iron oxides which are preferential for carburization due to higher diffusion. To evaluate the impact of preoxidation different times, temperatures, and cooling methods were used and analyzed by LOM, XRD, SEM, and hardness measurements. The results indicate that reliable carburization can be obtained by preoxidation performed at 600 °C for 24 hours followed by immediate case hardening. / Sätthärdat Uddeholm Orvar® Superior (Orvar) har potential att ersätta nuvarande material i drivaxlari växellådor, detta skulle minska vikten och därmed sänka bränslekonsumtionen medan de nödvändiga mekaniska egenskaperna behålls. Tidigare studier har emellertid misslyckats med att tillförlitligt uppkola stålytan under sätthärdningen. Ytan består utav tempererad martensit som har hög slitstyrka, hårdhet, och bra utmattningsegenskaper, och påverkas utav avsaknaden av tillfört kol. Närvaron av passiva oxidskikt som kiseldioxid och kromoxid tros hindra uppkolningen, detta på grund utav deras påverkan på adsorption och diffusion. En föreslagen lösning är ett föroxideringssteg innan sätthärdningen, för att gynna bildandet utav järnoxider vilka är fördelaktiga för uppkolningen på grund utav högre diffusion. För att utvärdera påverkan av föroxideringen användes olika tider, temperaturer, och kylningsmetoder som blev analyserade utav LOM, XRD, SEM, och hårdhetsmätningar. Resultaten indikerar att tillförlitlig uppkolning kan uppnås med föroxideringutförd vid 600 °C i 24 timmar följt utav omedelbar sätthärdning.

High rolling contact fatigue parts are vital for the long service life of fuel pumps. Cummins Fuel Systems are currently using an M2 tool steel for one of the most important roller bearing application in their pumps, namely the cam follower. The future design of the cam follower is a pin-less tappet roller. The wear and fatigue properties of the roller is vital to ensure reliability of the fuel system. M2 tool steel is an expensive material and becomes even more so if diamond like coating (DLC) is needed to decrease the friction coefficients. To cut costs of the fuel pump it might be possible to replace the M2 tool steel with 52100 steel (100Cr6). Competitive methods have proven that carbonitrided 52100 can reach excellent wear and fatigue properties making it a candidate to replace M2 tool steel. How the properties of hardness, toughness and compressive residual stresses are developed in 52100 and how they affect the fatigue and wear resistance has been researched from the literature. A big part of this project was to do an extensive analysis of a roller bearing that was believed to have gone through one of these competitive methods that produce excellent wear and fatigue resistance. The analysis was done with background to the knowledge gathered from the literature. Finally process trials were set up to carbonitride 52100 steel samples. The trials were done to develop a better understanding of how adding carbon together with nitrogen to the surface of 52100 steel will influence the metallurgical parameters that results in good wear and fatigue resistance. From this analysis Cummins hope to create a process recipe that can be used for carbonitriding the cam follower and maybe other components in their fuel systems.

Orientador: Itamar Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-04T09:29:09Z (GMT). No. of bitstreams: 1 Sandor_LeonardoTaborda_M.pdf: 9634671 bytes, checksum: 3b7603db85e265d8bd0e3fc244928942 (MD5) Previous issue date: 2005 / Resumo: Este trabalho propõe um modelo para avaliar pontualmente as variações de tenacidade à fratura ao longo da camada cementada de um aço SAE 5115. A pequena espessura dessas camadas impede a retirada de corpos de prova nas dimensões especificadas pelas normas de ensaios de tenacidade à fratura. Assim, para simular uma camada cementada retirou-se corpos de prova de tração e de tenacidade à fratura de amostras de aços SAE 5115, 5140, 5160 e 52100 assumindo a influência local apenas da variação do teor de carbono e considerando que os teores dos demais elementos de liga são essencialmente constantes. Os corpos de prova após eletrodeposição de cobre foram tratados termicamente numa carga industrial de cementação, têmpera e revenimento para serem submetidos aos efeitos térmicos sem absorção de carbono. Os resultados da análise microestrutural, dos ensaios de microdureza, de tração e de tenacidade à fratura foram agrupados em um único gráfico e comparados com o perfil de cementação de peças de aço SAE 5115 tratadas nas mesmas condições. Foi confirmado que a tenacidade à fratura varia inversamente proporcional à microdureza (HV1) e que a previsão do comportamento de uma trinca numa camada cementada pode ser feita por meio de equação ou diagrama que relacionam a miicrodureza HV1 com a tenacidade à fratura (K1c ou CTODc) / Abstract: The purpose of this work is to propose a model for evaluating the fracture toughness along the SAE 5115 steel carburized layer. Due to the small thickness of those layers, it is impossible to machine specimens from those layer in accordance with standards. For simulating the microstructures of the carburized layer in order to get samples for tensile and the fracture toughness testing, specimens of SAE 5115, 5140, 5160, and 52100 steels assuming the local influence just of the variation of the content of carbon and considering that the contents of the other alloy elements are essentially constant. The specimens after electroplated copper layer were heat treated in an industrialload of carburizing, quenching, and tempering for they be submitted to the thermal effects without absorption of carbono The results of the microstructure analysis and microhardness, tension, and fracture toughness tests were placed in a single graph and compared with the profile of the carburizing of the steel SAE 5115 heat treated in the same conditions. It was confirmed that the fracture toughness varies inversely proportional to the microhardness (HV1) and that the forecast of the behavior of a crack in a carburized layer can be made through equation or it designs that relate the microhardness (HV1) with the fracture toughness (KIC or CTODc) / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

The increasing demands for lightweight designs with high strength call for improved manufacturing processes regarding heat treatment of steel. The manufacturing process has considerable potential to improve the mechanical performance and to obtain more reliable results with less variation. The goal of this thesis is to establish new knowledge regarding improved manufacturing processes in industrial heat treatment applications. Three research questions with associated hypotheses are formulated. Process experiments, evaluation of the mechanical performance, and modelling of the fatigue behaviour assist in answering the questions. The gas quenching procedure following low-pressure carburising differs from the conventional procedure of gas carburising and oil quenching. It is shown that the introduction of a holding time during the low-temperature part of the quench has a positive effect on mechanical properties, with some 20 percent increase in fatigue strength. This is attributed to increased compressive surface residual stress and stabilisation of austenite. Tempering is a common manufacturing process step following hardening in order to increase the toughness of the steel. However, the research shows that the higher hardness from eliminating tempering from the manufacturing process is beneficial for contact fatigue resistance. The untempered steel showed not only less contact fatigue damage but also a different contact fatigue mechanism. Straightening of elongated components is made after heat treatment in order to compensate for distortions. The research shows that straightening of induction hardened shafts may lead to lowering of the fatigue strength of up to 20 percent. A fracture mechanics based model is developed to estimate the effects of straightening on fatigue strength. / Ökande krav på höghållfasta lättviktskonstruktioner kräver förbättrade tillverkningsprocesser för värmebehandling av stål. Det finns stor potential att förbättra mekanisk prestanda och att erhålla mer tillförlitliga resultat med mindre variation genom att förbättra tillverkningsprocessen. Målet med denna avhandling är att etablera ny kunskap kring tillverkningsprocesser inom industriella värmebehandlingsapplikationer. Tre forskningsfrågor med tillhörande hypoteser formuleras. Processexperiment, utvärdering av mekanisk hållfasthet och modellering av utmattningsbeteende bygger upp besvarandet av frågorna. Gaskylning som följer lågtrycksuppkolning skiljer sig från det konventionella förfarandet med gasuppkolning och släckning i olja. Resultaten visar att en hålltid i den nedre delen av kylningsförloppet har positiv inverkan på utmattningshållfastheten. Orsaken till förbättringen hänförs till ökade tryckrestspänningar samt stabilisering av austenit. Anlöpning är en vanlig tillverkningsprocess som efterföljer härdning för att öka stålets seghet. Forskningen visar däremot att den högre hårdheten för oanlöpt stål är fördelaktig för motstånd mot kontaktutmattning. Oanlöpt stål visade mindre mängd kontaktutmattningsskador och även en annan skademekanism. Riktning av långa komponenter görs efter värmebehandling för att kompensera för de formförändringar som uppstår. Forskningen visar att riktning av induktionshärdade axlar kan leda till sänkning av utmattningshållfastheten med upp till 20 procent. En brottmekanisk modell som uppskattar effekten av riktning på utmattningshållfasthet presenteras. / <p>QC 20150410</p>

Hardening distortions are unwanted changes in shape and dimension that arise during hardening of steel components. Uncontrolled distortions induce random errors to the manufacturing process, and have a strong negative impact on manufacturing costs. The distortions are not only caused by the hardening process, several factors from previous manufacturing steps including the component geometry itself contribute to varying extent. The aim of the current work is to investigate the main influencing factors on hardening distortions for serial produced gears. The investigations were done on two different types of gears for heavy-duty transmissions, crown wheels for the rear axle central gear and main shaft gears for the gearbox. The steel was produced using either continuous casting or ingot casting. For rectangular continuously cast steel, the effect of disabling magnetic stirring of the steel melt during casting was investigated, finding a strong reduction of gear runout for crown wheels. Segregations in crown wheels produced from the top and bottom of ingots were shown to go in opposite directions, producing opposite back-face tilts. For crown wheels quenched one at a time, influences of stacking level on the hardening tray were found, indicating an impact from small variations in the carburizing process, despite identical quenching conditions. For main shaft gears, horizontal loading gave considerably less roundness and runout errors but increased flatness errors compared to vertical loading. This thesis shows the complexity of the distortion phenomenon and how several factors interact and contribute to the final result. It is shown that factors with significant impact on hardening distortions for one component may be less important for another component. With this in mind, each type of component to be hardened should be produced by a manufacturing chain where each process step is carefully chosen with respect to minimizing distortions. / <p>QC 20170516</p>

No description available.

Corrosion fatigue is a common failure mechanism in rock drilling components and many othermechanical parts subjected to cyclic loads in corrosive environments. A crucial part in the design ofsuch components resides in the selection of the right materials for the application, which ideallyinvolves testing and comparison of their performance under working conditions. The present work was performed with the purpose of designing a corrosion-fatigue testing methodthat would allow the designer to compare the performance of different materials exposed to corrosionfatigue, permitting also the comparison with results from dry fatigue testing. The method was designedfor rotating-bending machines. Two different steel grades were used during the work, one throughhardened and one case hardened. The effect of these heat treatments and of shot peening overcorrosion-fatigue behaviour were studied using the proposed method. It was proven that the testing speed has a strong impact on the fatigue life of steel. It was found that,at a fixed stress level, the case hardened and shot peened steel reached 3X10^6 cycles at 2300 rpm,while it failed at only 5X10^5 cycles with a testing speed of 500 rpm. A large beneficial influence of theshot peening was demonstrated. It was also observed that, at fixed testing speed, the shot peening onthe through hardened steel can increase its fatigue strength from 190 MPa to 600 MPa under corrosionfatigue. Many cracks were found at the surface of the shot peened parts, which are arrested near thesurface by the compressive stress layer from the shot peening. It was also found that, for the non-shotpeened parts, case hardening had a slightly higher corrosion-fatigue strength than the throughhardened. This might be a result of the compressive stresses from carburization, or due to the highercore toughness of this steel grade.

The thesis dwells about methodics of processing an order in the company: Hardening shop Frydrych s.r.o. while respecting all the demands on the technological process of thermal and thermo-chemical manipulation as annealing, tempering and cementing. On the bases of the analyse and documental procedures the thesis is unraveling a concept for elimination of absences in the sphere of processing the order also as booking, invoicing and evaluating.