Many engineering materials call for increasing strength and ductility. Unfortunately, the material properties of high ductility and high strength are usually mutually contradictory. These conflicting requirements have generated interest in transformation induced plasticity or TRIP steels, which mainly consist of a mixture bainite, ferrite and retained austenite. The superior strength and ductility of these types of steels is due to the strain induced transformation of retained austenite to martensite. Intercritical deformation (i.e. deformation in the austenite + ferrite two phase region) has been extensively studied on C-Mn and microalloyed steels, but not on TRIP steels. Intercritical rolling increases the volume fraction and decreases the grain size of ferrite. These characteristics may be beneficial to the ductility of TRIP steels, since the volume fraction of retained austenite may increase with ferrite volume fraction by increasing the level of C segregation to the untransformed austenite. As well, the size of the retained austenite may decrease with decreasing ferrite grain size, thus increasing the stability of retained austenite against strain induced transformation. The aim of this study was to investigate the effect of the intercritical deformation on the characteristics of retained austenite and resulting mechanical properties of a TRIP steel.

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Source: Dissertation Abstracts International, Volume: 33-05, Section: B, page: 2115. / Thesis (Ph.D.)--The Florida State University, 1972.

A novel and accurate method of chemical analysis was developed to identify and assay the products of the hydrolysis that occurred when magnesium chloride hexahydrate was heated and held at temperature and reacted with its own liberated waters of hydration. The novel method took advantage of the solubility of magnesium chloride and magnesium chloride hydrates in methanol and the concomitant insolubility of magnesium oxide and magnesium hydroxychlorides in methanol. The method was found to have a precision of 5-7 % and represents a substantial improvement over previous analytical methods. The method is also readily applied to any methanol soluble salt containing insoluble impurities, meaning that it can also be used for the monitoring of the fused salt electrolyte present the magnesium electrolysis cells. [...] / Une nouvelle méthode d'analyse chimique a été développée pour identifier et tester les produits d'hydrolyse qui se forment quand le chlorure de magnésium hexahydrate est chauffé, maintenu à température constante et qu'il réagit avec les eaux d'hydratation qu'il libère. La nouvelle méthode tire avantage de la solubilité du chlorure de magnésium, hydraté ou non, et en parallèle de l'insolubilité de l'oxyde et des hydroxychlorures de magnésium dans le méthanol. Il s'avère que la méthode a montré une précision de 5-7 %, ce qui apporte une importante amélioration aux méthodes analytiques précédentes. La méthode est aussi facilement applicable a tout sel soluble, qui contiendrait des impuretés insolubles, dans le méthanol, ce qui signifie qu'elle peut aussi être utilisée pour le suivi de l'électrolyse de sel fondu présent dans les cellules d'électrolyse du magnésium.[...]

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Distinct serrations had been observed on the stress-strain curves of various steels tested previously at high temperatures (950--1100°C) at McGill University. An explanation proposed for this behavior was that dynamic strain aging (DSA), caused by the presence of substitutional elements, was taking place. To investigate the possibility that the jerky flow was caused by an interaction between dislocations and substitutional elements, the conditions of temperature and strain rate under which serrated yielding had previously been observed were explored. In addition, some of the same material was utilized in the testing. / Much of the previous work on DSA in steel has focused on the effect of interstitials, namely, carbon and nitrogen, rather than that of substitutional elements. These studies have been conducted in the blue brittle region (i.e. 100--400°C), where the diffusivity of the interstitial elements is sufficiently rapid for them to keep up with the moving dislocations. However, for substitutional elements to obtain enough mobility to induce DSA, the temperature range must be significantly higher. / The effect of substitutional elements on DSA in steel was examined in torsion and, although numerous tests were formulated and carried out in an attempt to gather evidence for this phenomenon, no firm data for the occurrence of DSA were obtained. Further experiments and analysis will be required to gain a better understanding of the behavior of DSA at elevated temperatures, particularly for the case where dynamic recrystallization is taking place. A testing method might then be devised that could make the effect of DSA more evident.

In the presence of air and oxygen, oxidation of a molten aluminum alloy will easily take place. The oxidation not only harms the operation by contributing to melt losses, but the processing of the oxides present in the melt and refractory is also costly in time and money. Refractory accretions formed due to the interactions between the oxide-layer and base refractory material, especially alumina-lined ones, are a significant problem for the industry. Aluminum alloys containing magnesium are known to oxidize much more easily and rapidly. In the foundry, oxidation of molten aluminum-magnesium alloy is more prominent than that of pure aluminum. Magnesium has a higher affinity for oxygen, causing it to oxidize more easily than aluminum. In previous studies of oxidation of aluminum alloys, it has been found that strontium additions to the alloy reduce the amount of oxidized layer in an undisturbed melt. / The effects of strontium additions on the oxidation behavior of commercial A356, A357 and 5182 aluminum alloys were investigated by monitoring sample weight gains with time with a thermo-gravimetric balance at 700, 750, and 800°C. Sample surfaces were examined using electron microscope and x-ray diffraction techniques. It was found that in the absence of Sr, the A356 and A357 samples gained substantial amounts of weight through the preferential oxidation of magnesium. Samples containing strontium had significantly lower weight gains. For the high magnesium-containing 5182 alloy, an increase of incubation period before the onset of significant oxidation is associated with the presence of strontium. This change in oxidation behavior was linked to the presence of strontium containing oxide species in the oxidizing surface.

The effect of chemical composition and cooling rate on the static strain aging (SSA) and dynamic strain aging (DSA) behaviors of four IF steels was investigated after reheating to different temperatures and cooling to room temperature at various rates. In the case of DSA, tensile tests were carried out over the range from room temperature to 450°C and at strain rates of 10-4 to 10-1 s-1 . The DSA behavior was also studied in torsion in the austenite and ferrite regions. Aging index (AI) tests were carried out to evaluate the response to SSA and to estimate the amount of carbon in solution after employing various cooling rates. In all cases, although the atomic Ti/C ratio was greater than one, even still air cooling (3°C/s) led to a supersaturated/unstabilized material and to the occurrence of both DSA and SSA. By contrast, there were no signs of SSA and DSA after furnace cooling (0.05°C/s). / The three Ti and the Ti-Nb IF grades studied displayed serrated flow behavior at all strain rates in the blue brittleness temperature range (100 to 300°C). A simple model is described that predicts whether or not DSA will occur at the strain rates and temperatures involved in the processing of IF steels. It was found that the higher the Ti/S ratio, the higher the solute C. Steels with different chemistries but equal Ti/S ratios displayed the same aging behavior. Internal friction measurements were executed to establish a calibration between the AI values and solute C levels. Two novel techniques for the strengthening of IF steels by dynamic bake hardening (BH) are presented. These techniques lead to much higher BH values compared to those produced by conventional BH methods. The observations also show that when C supersaturation results from cooling after coiling, lower annealing temperatures after cold rolling lead to higher solute C levels.

Grain refinement of Al-Si casting alloys is commonly assessed by the presence of Ti and B in the melt, but in the last decade, thermal analysis has become an alternative control tool for the determination of the degree of refinement in the melt prior to casting. The objective of this work is to determine the best optimum method to predict the grain size in 319 and 356 Al-Si casting alloys by the use of the thermal analysis technique. Different time and temperature parameters from the cooling curve and its derivatives have been analyzed for a variety of grain refined samples. Four different master alloys (Al-6%Ti, Al-5%Ti-1%B, Al-2.5%Ti-2.5%B and Al-5%B) and two salt fluxes (AlTab-75%Ti and TiLite75BC-75%Ti-l.5%B) were used as grain refiners and samples were frozen at two different cooling rates (1.0 and 0.1°C/s). The effect of type of refiner and cooling rate on the thermal analysis parameters has been analyzed. / A time parameter, t1, which is the duration of the recalescence period, and the maximum undercooling and recalescence temperatures, TU and TR respectively, yield the best correlation with grain size. These results are consistent irrespective of the type of grain refiner, for both 319 and 356 alloys, but only when the alloy solidifies at a cooling rate of 1.0°C/s). Lower cooling rates produce scattering in the results. / Grain growth velocity, as calculated from the dendrite coherency point, correlates well with grain size for both alloys. A grain growth model is proposed to explain the effectiveness of these thermal parameters, where the duration of the recalescence period is related to a free growth period of the grains. Thermal analysis parameters related to the nucleation period seem to be sensitive to the type of grain refiner used and do not show good correlation with grain size.