Bibliography: pages 96-102. / During the annealing treatment in the production of dual phase steels, partitfoning of alloying elements can occur depending on competitive solubility in the ferrite and austenite for the specific partitioning species. An investigation of the partitioning of substitutional elements was considered paramount in understanding certain anomalies that had been identified by previous researchers in various studies of a dualphase 12% Chromium steel, designated 3CR12. These anomalies concerned observed increases in bulk hardness that could not be attributed to changes in the volume fraction of martensite produced after exposure to a range of temperatures within the dual phase field. Subsequent experiments revealed an unexpected increase in the microhardness of the martensite phase prOduced by heat treatment in the temperature range of interest. In this thesis conventional analytical measurements using Energy dispersive X-ray analysis facilities attached to a Scanning Electron microscope have been utilised to determine the compositions of the two phases in the alloy. A range of temperatures in the dual phase region have been investigated at holding durations of 1, 4 and 20 hours. It was found that partitioning of substitutional elements was occurring, however no changes were observed as a function of holding time. Further empirical data was obtained using dilatometric methods. This strongly suggested that interstitial concentrations were increasing as a function of annealing time and clarified the anomalies observed during previous studies on 3CR12. Further study includes that of substitutional element partitioning in the prior states of the commercially produced hot-rolled and annealed 3CR12 alloy. These include the as cast slab and the hot-rolled slab, as well as the final hot-rolled and annealed slab. Segregation was found to occur in the as cast slab. Subsequent investigation showed the presence of δ-ferrite in the final processing stages of the hot-rolled and annealed product.

The existing design provision in North American Specification for Cold- Formed Steel Structural Member (AISI S100) for the bearing strength of bolted connections were developed from tests on bolted connected sheets which were restrained by bolt nut and head with or without washers. However, in the cold-formed assemblies, particularly in trusses, the single bolt goes through both sides of the connected sections, making the connected sheets on each side unrestrained. the warping of the unrestrained sheet may reduce the bearing strength of the bolted connection. This research investigates the behavior and strength of bearing failure in bolted connections in cold-formed steel trusses. Tensile tests were conducted on trusses connections with various material thicknesses. It was found that the AISI S100 works well for thick connections but provides unconservative predictions for thin materials. Based on the experimental results, a modified bearing strength method is proposed for calculating the bearing strength of bolted truss connections. the proposed method can be used for any cold-formed steel connections with unrestrained sheet.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2018 / The use of austenitic stainless steels in harsh environments at elevated temperatures has increasingly become a global problem, these alloys can fail unpredictably when subjected to tensile stresses and chlorides. Hence the study was focused on understanding the environmentally assisted cracking of Ru enriched laser alloyed layers on 304L stainless steel in a corrosive environment at elevated temperatures. The Ru composition of laser alloyed samples was 0, 0.96, 1.96, 4.74 and 9.2 wt%. Microstructural analysis and microhardness measurements were performed in order to understand the grain orientation and resistance to indentation respectively. The bend beam SCC test was conducted by stressing the samples to 350 MPa and exposing them to 50 ppm sodium chloride with 10 ppm dissolved oxygen at 160°C for 172 hours. The results revealed a significant improvement in the SCC resistance. The samples with lower Ru content (0, 0.98 and 1.96 wt%) were less susceptible to SCC when compared to as-received 304L stainless steel. Cracks initiated from pits and propagated transgranularly on the alloyed layer. The crack growth rate decreased as the Ru content was increased. The samples with 4.74 and 9.2 wt% Ru were immune to SCC. Electrochemical test results showed improved corrosion resistance when the Ru level was increased to 1.96 wt%. Thereafter, there was a gradual increase in corrosion rates for samples with 4.74 and 9.2 wt% Ru. However, these corrosion rates were lower when compared to as-received 304L stainless steel. Another SCC test was conducted to investigate fractography of vacuum remelted samples alloyed with Ru. The results showed ductile failure for most of the samples and the maximum stress threshold of 580 MPa was archived on samples with 1.07 wt% Ru. There was a sudden increase in failure time, % elongation and % reduction in area when the Ru content was increased to 1.07 wt%. In essence, laser surface alloying 304L stainless steel with higher Ru content (more than 2wt%) improves SCC resistance, but does not improve the general corrosion resistance, therefore a careful selection for any application is necessary. However, the cost analysis revealed the laser surface alloying of 304L stainless steel with Ru to be more efficient over other corrosion resistant materials. / MT 2018

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A research report submitted in partial fulfilment of the requirements for the degree of Masters of Science in Engineering to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, 2019 / The report considers survival mechanisms used by Platinum Group Metal (PGM) producers over the period 2008 to 2017 when mining operations were considered marginal for an extended period. Various methods to build cost curves for the PGM industry were tested, with co-product costing, inclusive of sustaining capital, selected. Industry cost curves were developed for the period, showing that a significant portion of producers were marginal from 2014 to 2017, with Impala lease area, Rustenburg mines and Lonmin marginal for more than two years in that period. Survival was achieved through cross-subsidisation, utilising cash reserves, deferring sustaining capital, re-capitalisation and working capital management, before ultimately restructuring through sale or closure took place. While industry cost curves were effective at indicating operational competitiveness in a particular year, a mechanism to indicate relative financial strength (ability to sustain this position) needs to be sought. / TL (2020)

<p> The major emphasis of this paper is to examine technological changes in the steel industry and how these effect employment. The hypothesis is that, "technological changes have contributed significantly to unemployment in the steel industry." The history of the steel industry in Canada is examined. Trends in production, consumption and employment are studied. All are found to be declining in Canada. A regression analysis shows technology to be a significant factor affecting production efficiency in western countries. Data from Canada, Germany, Japan, the United Kingdom, and the United States for the years 1964 to 1982 are used in the regression. More efficient production means lower employment for a given amount of output. The hypothesis is accepted because employment is proven to be lowered as new technology is implemented.</p> / Thesis / Candidate in Philosophy

Fine/nanoscale carbonitrides of microalloying elements such as Nb, Ti, and V play a significant role in the strengthening of HSLA steels. Site-specific analysis of the precipitates in different heterogeneous microstructural areas within realistic alloys is limited and the competition of different precipitates has not been discussed in detail. In this work, the relationship of precipitates/clusters with microstructure has been analyzed by site-specific methods and a simple model has been created to describe the competition between strain-induced precipitation and (Ti, Nb) (C, N). Firstly, the spatial distribution of precipitates and microstructure heterogeneity in an X70 steel were investigated by site-specific analysis method. The quantitative analyze the precipitates reveals that strain-induced precipitation of fine NbC particles (5-20 nm) on dislocations was suppressed by the large (Ti, Nb) (C, N) precipitates. The similarity of precipitates in each location suggests that the local features (such as strain and grain size) in the final microstructure arise from phase transformations during cooling. Secondly, the microstructural evolution during coiling and its effects on the mechanical properties of a vanadium microalloyed steel were investigated. Experimental findings showed that during holding at 500 ºC, nano precipitates (<10 nm) containing V and N nucleated heterogeneously, primarily in areas with high Kernel Average Misorientation (KAM) values. These areas contained a larger number of dislocations, which acted as nucleation sites for the precipitates. The effect of precipitation strengthening was not significant and was offset by softening caused by the aging of bainite and associated recovery of dislocations. Thirdly, in the HSLA steel with both V and Nb additions, nano precipitates were found to preferentially form around dislocations and grain/sub-grain boundaries in high KAM areas associated with bainite. Precipitates were frequently observed around cementite in low KAM areas, which were identified as granular bainite. Interphase clusters were also discovered in low KAM areas behind the ferrite/austenite interface. Analysis of the results indicated that the precipitation of micro-alloyed particles on cementite may reduce the contribution of precipitation hardening achievable through microalloying. Finally, a competition model between strain-induced precipitates (SIP) and epitaxial growth in micro-alloyed austenite has been developed. Using this model, it is possible to estimate the effects of process parameters (T, applied strain), the number density of pre-existing TiN particles, and steel composition on the precipitation process. Through the various studies achieved here, the aim to understand the relationship between the precipitates and different microstructures and develop the competition models has been accomplished. These works provide a relatively new workflow to investigate the precipitates within the steel, especially in site-specific areas, and also allow us to predict the precipitation of NbC by selecting desired temperature range, applied strain, and number density of pre-existing TiN precipitates. / Thesis / Doctor of Philosophy (PhD)