In this study, response surface methodology was used to examine the effects of temperature and time on the development of niobium carbide coatings on AISI D3 steel. The effect of niobizing temperature (900–1100∘C) and period (2–6 hours) on coating thickness, hardness, fracture toughness, coefficient of friction and wear rates was investigated. ANOVA was conducted to analyze the experimental data, and it was observed that the coating thickness and microhardness increased with temperature and time. The response surfaces developed for fracture toughness, coefficient of friction and wear rates were found to exhibit a complex structure that is significantly influenced by temperature, time and their interactions. The correlation coefficients of the developed regression models range between 0.82 and 0.99. Using the empirical formulas obtained with these mathematical models, it is predicted that niobium carbide coatings can be obtained with the targeted properties more economically and practically with the thermochemical method.

Although it is an old technique, research on the hot rolling process maintains its importance because of its widespread usage in steel production and its requirement for a vast amount of resources, especially energy. The roll pass design of the hot rolling process considerably affects many operational parameters such as energy requirement, wear of the rolls, working forces, and torques. Furthermore, due to the sequential nature of the rolling process, a design of any number of passes is strictly interrelated with all other passes in the process. This makes it very involved to find optimum design solutions that allow for the compromise between conflicting goals and restrictions. In this paper, a new optimized solution search strategy based on a desirability function is offered to deal with the sequential characteristics of the roll pass design. A novel optimization method utilizing response surfaces and the proposed solution search strategy is presented to reduce the shaping energy of the overall process while minimizing turning moments and radial forces on rolls during the rough rolling process. The method and solution search strategy developed are illustrated and validated via a case study. Comparing the case study's findings to three distinct pass designs used in industrial power plants, it was discovered that significant energy savings, low turning moments, and reduced radial forces had been made compared to the reference designs.

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The hot-rolling process is a very intense energy-consuming process, and deformation energy is one of the major cost items. The deformation energy consumed in the hot-rolling process is highly related to the design of the roll-pass sequence. In this study, the response surface methodology has been utilized to optimize minor geometric parameters – namely, radii and angle – in a box-pass design. Set values of the independent variables of the constructed response surface have been determined by central composite design. Simulation experiments based on the finite-element method have been carried out to estimate deformation energies. The methodology used in the simulations has been verified by modeling an industrial production process and comparing the simulation results with the industrial data. Optimization has been verified by applying the optimized radius and angle values to a roll-pass sequence with five stages. A decrease in deformation energy by 7.44% has been established by optimization with respect to conventional roll-pass design.