Rishabh Shukla

AN APPROACH TO ROBUST PROCESS DESIGN FOR CONTINUOUS CASTING OF SLAB

Continuous casting is a crucial step in the production of a variety of steel products. Its performance is measured in terms of conflicting objectives including productivity, yield, quality and production costs. These are conflicting in the sense that, if the productivity is increased, there is a reduction in other performance parameters. These performance parameters are greatly influenced by operating conditions such as casting speed, superheat, mold oscillation frequency, and secondary cooling conditions. An optimized solution for continuous casting process can be obtained. However uncertainty in operating parameters which affects the performance of caster is rarely considered. Moreover, the solution obtained is optimal with respect to a particular performance measure and does not provide a balance between all. In this paper an integrated design framework has been developed based on metamodels and the compromise Decision Support Problem (cDSP). The framework developed deals with uncertainty and yields robust solutions for performance measures. Further, the design space for continuous casting has been explored for different scenarios to determine satisficing solutions. The utility of the framework has been illustrated for providing decision support when an existing configuration for continuous casting is unable to meet the requirements. This approach can be instantiated for other unit operations involved in steel manufacturing and then may be integrated to simulate the entire production cycle of steel manufacturing. This in turn will enable development of materials with specific properties and reduce the time and cost incurred in the development of new materials and their manufacturing.Copyright

Design Exploration for Determining the Set Points of Continuous Casting Operation: An Industrial Application

To compete with other materials and/or contribute toward light-weighting of vehicles, newer grades of steel are continuously invented and experimented upon. Due to the costs and time involved in such developments, manufacture of new grades of steel at an industrial scale is difficult. We propose a method that is useful for steel manufacturers interested in producing a steel product mix with new grades of steels by predicting the required change in the operating set points of each unit operation in the manufacturing chain of products with the new grade of steel. Here, we demonstrate a method to determine the set points of one unit operation, continuous casting which is measured in terms of conflicting objectives including productivity, quality, and production costs. These parameters are sensitive to the operating set points of casting speed, superheat, mold oscillation frequency, and secondary cooling conditions. To ensure targeted performance and address the challenges of uncertainty and conflicting objectives, an integrated computational method based on surrogate models and the compromise decision support problem (cDSP) is presented. The method is used to explore the design space available for casting operations and determine operating set points to meet requirements imposed on the caster from subsequent downstream processes. This method is of value to the steel industry and enables the rapid and cost effective production of a product mix with a new grade of steel.

Exploring the Design Set Points of Refining Operation in Ladle for Cost Effective Desulfurization and Inclusion Removal

This paper is motivated by a need identified by steel makers, namely, the need to produce steel products with new and often more stringent set of specifications and enhanced performances (such as fatigue life and corrosion behavior) using existing equipment cost-effectively.Manufacturing a steel product involves series of unit operations, each having a significant bearing on the properties of the end product. This paper focuses on studying the effect of one such unit operation, namely, ladle refining. The performance like corrosion behavior and fatigue life and properties of advanced high strength steel are greatly influenced by its cleanliness and by maintaining composition within specified bounds. Cleanliness of steel is assessed in terms of the count and nature of inclusions present and the levels of tramp elements such as sulfur, phosphorus and total oxygen present in the liquid steel. The desired composition is maintained with respect to alloying elements (Ni, Cr, Mn, etc.) that are added to impart certain properties to the steel. The ladle furnace is one of the key unit operations for carrying out deoxidation and desulfurization to maintain the levels of oxygen and sulfur within a tolerable limit. Deoxidation reaction during refining lead to formation of a number of which are deleterious in nature and should be removed. The effectiveness of the ladle operation is thus influenced by conflicting goals such as inclusion removal efficiency, desulfurization and the cost of refining.George Box is reputed to have observed that all models are wrong and some are useful. In keeping with George Box’s observation we suggest that our challenge is to determine the set points for the ladle unit operation using computational models that at best capture the essence of reality but not reality itself. Therefore, the need is to find solutions that are relatively insensitive to the inherent uncertainties embodied in the computational model while satisficing the conflicting goals.In this paper we present a method for visualizing and exploring the solution space using the compromise Decision Support Problem (cDSP) as a decision model. We illustrate the efficacy of our method, for use by steel producers, by determining the set points for a ladle, in an industrial setting.Copyright

ICME for Process Scale-Up: Importance of Vertical and Horizontal Integration of Models

ICME will play a major role in reducing the lead time in development of a new product or component. One of the areas where ICME is likely to play a crucial role is process scale-up of mill products. Process scale-up of a mill product from laboratory to production stage is largely done through hit-and-trial and is a non-trivial exercise. It involves plant level trials which are expensive and time consuming. Use of ICME can significantly narrow down the design search space thereby reducing need for experimentation or plant trial, which in turn will lead to bringing down the cost and time of development. However many challenges need to be addressed to realize the full potential of ICME at an industrial scale. Manufacturing any product/ component involves a host of unit operations and the properties of the end product are intrinsically linked with final as well as intermediate processing steps. To link the material-processing-structure-performance matrix, there is a need to enhance models across various unit operations through multi-scale/multi-phase modelling and integration of models at various length scales. This allows for the information flow across various unit operations and thereby ensures horizontal integration of each process to simulate the entire manufacturing chain. This step is crucial in designing set points and quantifying the influence of various unit operations on end product performance. In this paper, we illustrate the vertical-horizontal integration of models through an example

EXPLORATION OF THE DESIGN SPACE IN CONTINUOUS CASTING TUNDISH

Due to the stringent requirements of industry, it has become extremely important to have a careful control over the required performance and properties of steels. Performance and properties of advanced high strength steel depend significantly on its cleanliness. Cleanliness is achieved by restricting the inclusion count to a permissible limit. Over the past few years, there has been increased use of tundish, a device that acts as a buffer between ladle and mold, for controlling inclusions. Apart from facilitating inclusion removal, tundish also maintains low dead volume and thermal and chemical homogeneity, which is required for smooth casting operation. Thus, performance of the tundish operation greatly influences the properties and quality of the cast slab. Tundish performance is generally assessed using parameters such as inclusion removal efficiency, dead volume within tundish and effectiveness in maintaining the desired amount of superheat. But, the aforesaid parameters are conflicting in nature. Managing the conflict and providing a satisficing solution based on the customer requirements become essential.In this paper, we present an approach to manage the conflicts involved in designing a tundish. An integrated framework, by linking meta-models with compromise Decision Support Problem (cDSP) construct, is developed to determine a satisficing solution considering conflicting requirements.The utility of the framework is illustrated by providing decision support when an existing configuration for tundish is unable to meet the requirements. This has been done by exploring the design space of tundish and coming up with a design and operating set points suitable for a particular purpose. This approach can be instantiated for other unit operations involved in steel manufacturing. In the future, each unit operation can be integrated to provide a complete picture of steel manufacturing which in turn will help in reducing the time and cost incurred in the development of new materials and products.Copyright

A Method for Determining the Set Points of the Ladle, Tundish and Caster for Manufacturing a High Strength Steel Slab

To meet requirements emanating from environmental, safety, and competition, auto manufacturers are demanding improved performance and reduced defect levels from steel makers. The defects are dependent on the design of unit operations, and the processing conditions in the ladle, tundish, and the caster. To improve performance and reduce defect levels, steel makers need to design the process considering multiple unit operations. In this paper, we present a method to determine the design set points of ladle, tundish and casting operation to meet the desired properties of a cast slab, for a given input of molten steel to the ladle. The decisions associated with ladle, tundish and slab continuous casting unit operations are modeled using the compromise Decision Support Problem (cDSP) construct. Within the cDSPs, the required properties and tolerable defect levels for the continuously cast slab and available process window for ladle, tundish and continuous casting are specified. An inductive approach (upstream-downstream design method) is adopted for exploring the solution spaces of the three unit operations as an integrated whole. In this paper, the design set points obtained using this method for ladle, tundish and continuous casting of slab for different set of requirements is presented. The primary advantage of the proposed method is that it enables rapid exploration of the steel slab production process space. The proposed method is extensible and other downstream processes involved in manufacturing of a finished product from steel will also be integrated together.