No description available.

No description available.

The effect of increasing hot deformation on inclusion parameters such as area fraction (AF), the average inclusion length (Co), the inter-inclusion distance (D), the aspect ratio (FF) and the density of distributions (N);bas been quantitatively analysed by use of Quantimet 720, an image analysing computer and direct microstructural measurements. Two types of X-70 pipeline steel, one a semi-killed conventional (CON) steel, the other a fully killed and calcium treated for inclusion shape control (CAT) steel were examined in this research. Four stages of hot reduction of the CON steel viz. S2 (38% reduced), S3 (70% reduced), S4 (88% reduced) and S6 (97% reduced) and two stages of the CAT steel viz. CI (63% reduced) and C2 (95% reduced) were used in the investigation. The effect of inclusion parameters on the yield strength, total ductility and elastic and elastic-plastic fracture toughness of these materials were investigated to establish the role of inclusions in the ductile, ductile-brittle transition and brittle fracture processes. The elastic and elastic-plastic fracture toughness of the specimens were measured by KJC testing as per ASTM standard E-399-78a method and unloading compliance J-integral technique as per ASTM standard respectively. It was observed that the semi-killed CON steel containing elongated inclusions shows anisotropy in elastic-plastic fracture toughness; whereas the CAT steels with globular inclusions exhibited isotropic elastic-plastic fracture toughness. The inclusion parameters shape, size and distribution do not affect the yield strength of the X-70 steel. The inclusion parameters markedly affect the elastic-plastic fracture toughness properties of the X-70 CON steel, particularly in the ductile and transition temperature region where failure occurs by the mechanism of microvoid coalescence. The effect of inclusions on the elastic fracture toughness in the brittle temperature region, where fracture occurs by cleavage mechanism, is insignificant. The most significent inclusion parameters which affect the elastic-plastic fracture toughness in the ductile fracture regime are the area fraction AF and the inter-inclusion spacing (D). The elastic-plastic fracture toughness of the CON and CAT X-70 pipeline steel at RT has been correlated (i) with AF by the following relation: [figure 1]. (ii) with D by the following relation: [figure 2]. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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.

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published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy

No description available.

No description available.

A method is developed for construction of deflection curves of beam-columns stressed into plastic range by thrusts and equal end moments producing single curvature bending. Actual deflection curves are plotted for 8x8 WF 31 lb/ft section acted upon by moments and thrusts of different magnitudes. These are used for construction of the end moment vs. end slope diagrams and the interaction curves which present in graphical form the ultimate strength of beam-columns of different lengths under various combinations of thrusts and moments. The latter are compared with similar graphs contained in current specifications. The study is based on moment vs. curvature relations developed at Lehigh University. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate