Journal of Casting & Materials Engineering

Theoretical Possibilities of Controlling the Cooling Rate in the Heat Treatment of Cast Iron with Water Mist

Piotr Stręk — 2024-12-24

The goal of the cooling procedure after austenitizing in the austempering heat treatment process applied to ausferritic ductile iron (ADI) castings is to rapidly reduce the temperature throughout the casting volume to the temperature range of the process window in which the proper metal matrix structure is formed. The lower limit of this range must be higher than the temperature at which the martensitic transformation starts. The upper limit is selected to eliminate the possibility of diffusion decomposition of austenite while holding castings at austempering temperature. Most often in heat treatment practice, salt baths are used for this purpose. Such a solution makes it possible to realize in one device both the procedure of cooling down to a given temperature and the procedure of isothermal heat treatment at this temperature. Unfortunately, the presence of molten salt in the process equipment has a very unfavorable impact on working conditions and ecology. The purpose of this research is to analyze the possibility of replacing the salt bath cooling procedure in the manufacturing process of ADI castings with a water mist spray cooling procedure on the surfaces of the heat-treated casting. If such cooling is effective, subsequent procedures of heat treatment operations can be carried out with traditional furnace equipment without the use of molten salt, which will clearly improve the environmental performance of the enterprise. The article, using analytical and numerical methods, analyzes the possibility of cooling objects made of cast iron with the help of a high-efficiency heat receiver such as water mist spraying. The limiting conditions for carrying out the process for the assumed cooling curve were considered. It was proposed to use a PID controller realizing the function of controlling the intensity of water mist spray, which corresponds to the intensity of the heat flux received from the heat-treated casting. The theoretical analysis carried out allows us to conclude that water mist cooling according to the assumed cooling curve is practically feasible.

A Characterization of the Impact Toughness of Hot-rolled HSLA Steel

Tomasz Hamryszczak — 2024-12-02

Due to the wide use of HSLA steels in difficult conditions, e.g. at low temperatures, it is extremely important to test the impact strength of these steels. This is equally important because most of those structures are made by welding these steels, and the welding process itself has a significant impact on the properties of joints and welding zones. In this work, the authors analyzed two selected representative HSLA steels rolled in the Krakow branch of ArcelorMittal Poland S.A. – the only place in Poland where HSLA steels in the form of hot-rolled strips can be produced on an industrial scale. Impact tests were performed in accordance with technical acceptance standards, and then the fracture surfaces after impact tests were characterized using light and scanning microscopy. In the next part of the work, a set of previously gathered data were analyzed to determine the influence of thermomechanical rolling process parameters on the level of impact strength and the influence of chemical composition on it.

Bactericidal Properties of the Sol-gel Layer on Polymer Substrates in Medical Applications

Paulina Armatys — 2024-12-02

Polymeric biomaterials are a group of plastics used in medical devices, implants, and artificial organ components. In order to maintain the higher asepticity of the products, solutions based on the modification of the volume or surface of a plastic with biocidal agents, e.g. antibiotics, nanoparticles, are used. One of the methods used to impart biocidal properties to the material can be the use of layers applied by the sol-gel method. The aim of this study was to produce homogeneous and durable coatings on inert and hydrophobic silicone surfaces based on polysiloxane sols with biocidal activity against model bacteria: Gram negative (Escherichia coli, Klebsiella pneumoniae) and Gram positive (Staphylococcus aureus, Enterococcus faecalis). This paper presents results of investigations on a commercial biomedical silicone material (DEMED Sp. zoo) modified with eight sols; siloxane (TD), phenol-siloxane (FD), siloxane-aluminum (TD-Al), siloxane-titanium (TD-Ti), titanium (Ti), zinc (Zn), and TD and TD-Al sols modified with green tea extract (TD-GT, TD-Al-GT). The reference for the tested materials was unmodified silicone. In order to be prepared for coating, the siloxane samples were etched with hydrofluoric acid. Residual acid was removed from the silicone by washing and the substrates were then coated with sols by means of dip coating. The modified materials were then polymerized at 100°C for one week. The produced layered composites were subjected to microstructural, physicochemical, structural and microbiological analysis by contacting them with Gramm negative and Gramm positive bacteria. It was shown that the strongest biocidal properties were exhibited by samples modified with the sols based on - Zn, TD-Ti, Ti, TD-Al-GT and TD-GT.