Combination of a finite element method (FEM) algorithm with ANSYS codes and post image processing of NDT ultrasonic images along with laboratory cooling experiments and microstructural analysis provides a guideline to determine the optimum cooling rate for any grade of steel in which the highest productivity can be achieved without any degradation of the cast steel products. The suggested FEM algorithm with ANSYS codes is introduced to develop a quasi real models to simulate quenching of as-cast steel with any cooling rate from any initial temperature below steel's melting point. The algorithm builds a model which is capable to approximate the thermodynamic stresses generated by thermal strain and possible solid-solid phase transformation for as-cast steel with any chemical composition. The model is applicable for any casting geometry (slab, billet and bloom, bar, etc.) and adaptable for any method of cooling (unidirectional or multidirectional). Cooling with any cooling agent can be simulated with the algorithm in an ideal case. The phase transformation of the steel in the algorithm can be controlled by Continuous Cooling Transformation (CCT) Diagram obtained from analytical calculation or real time-temperature- transformation experiments for the cast steel. A function for optimizing cooling rate is suggested.
Electrical resistance measurements on different rod materials in liquid solutions, molten salts, or molten lead are considered to design a liquid level sensor in a sealed containers when the temperature of the fluid is very high (~1000oC) and conventional measurements are not possible due to properties of the fluid or condition of the container. An analytical solution to the problem is adopted to reduce the cost of the sensor and overcome the difficulties of calibration of sensors at high temperature for prediction of the level of liquid. An electrical circuit model is suggested for analytical solution to compute the resistivity versus height of the electrode rod submerged in the liquid in a narrow container. Good prediction of circuit model for experimental results is verified by comparison of analytical results of different combination of liquid solutions and rods’ material with experimental graphs.
This presentation discusses the main processes of a superplastic forming (SPF) method to form a complex component with eight-pocket from a four-sheet sandwich panel sheetstock. Four sheets of titanium alloys were welded using resistance seam welding based on a defined pattern to manufacture a composite sheetstock of four layers. The composite sheet structures were inflated via SPF process using the Advanced Forming Research Centre’s 200 T SPF press in pockets where the sheets were not welded to each other to form a complex component. Each sheetstock was arranged to consist of four sheets: two core sheets from the same material, which create the inner structure of the panel, two skin sheets from the same material, which form the outer structure of the panel. Ti64 (Ti-6Al-4V) and Ti54 M (Ti-5Al-4Cr-4Mo-2Sn-2Zr titanium alloy sheets were used for the core sheets, whereas Ti64 and Ti6242 (Ti-6Al-2Sn-4Zr-2Mo) titanium alloy sheets were used for the outer sheets of the packs. I will also discuss the manufacture and assembly of the four-sheet packs, and briefly, explain the manufacturing processes adopted to manufacture the dies used in SPF trials. Furthermore, I will go through the applied methodology to define the SPF pressure-time curves to inflate the packs for two SPF gas feeding pipes at specific forming temperature and strain rate. Several samples from selected regions of each inflated pack were investigated via optical and scanning electron microscopy (SEM) to study whether diffusion bonding occurred between the sheets. The optical microscopy images were obtained for three different levels of magnification (x10, x20, and x50) for all samples. The GOM scanning and image analysis demonstrated that during SPF the multisheet packs underwent a degree of diffusion bonding where the adjacent sheets exhibited thickness reduction under compression forces. The thickness reduction to the component surfaces imposed by SPF was found to be up to 59% in some regions of the packs and the elongation was estimated to be up to 134%. The same procedure could be implemented to manufacture sandwich panels with more complex core configurations from sheetstock composed of more than three sheets and made of different titanium alloys
This research work is another step for increasing the efficiency and productivity of the steel making process by enhancing both quality and quantity of the steel produced by the Continuous Casting process. When steels cool from a high temperature, austenite transforms into other phase configurations according to the austenite composition and cooling rate. As result of phase transformation, the steel crystal structure and, consequently, both the shape and the lattice parameter of the unit cell, change. These changes may introduce dilatational strains into the microstructure, which result in the creation of residual stress concentration zones within the microstructure. These stress concentration zones are vulnerable regions to the formation of microcracks or growth of the flaws in these regions. The main objective of this dissertation is to develop a method to define the optimum cooling rate for cooling continuously as-cast steel on industrial level. An FEM algorithm developed with the ANSYS codes is introduced in this dissertation to simulate the cooling of as-cast steel from any temperature below the solidification temperature. The algorithm is capable of being customized to simulate the thermodynamic behavior of as-cast steel microstructure with any chemical composition and any casting geometry imposed to desired cooling method. The phase transformation simulations were based on the CCT diagram and, therefore, they were quasi-real models. The models predict, analytically, the generation of the stress concentration regions due to the thermodynamic strains during cooling a sample from the austenite temperature range with different cooling rates. Another series of FEM models presented in this dissertation and post non-destructive tests (NDT) ultrasonic image analysis tests suggested in this work, can be used in the discussion of the effect of the cooling rate on the altering of the soundness of the tested steel. A combination of the suggested FEM algorithm and post image processing of NDT ultrasonic images along with laboratory cooling experiments and microstructural analysis provide a guideline to find the cooling rate for each grade of steel in the casting steel industry. Results of JMATPRO software also are deployed to increase the accuracy of the experimental set up and to obtain the required input data to run the proposed numerical algorithm cooling simulation.
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