Evaluation of possibility of using polysiloxane water emulsion as quenching media for metal heat treatment

Thermal effect, or heat treatment, as a part of each technological process for manufacture of metal constructions and components, is one of the most widely distributed methods for transformation and improvement of physicalchemical properties and structural features of metals and alloys. Several technological processes, such as quenching of metals, require cooling media. In comparison with conventional media (water and oil), which are characterized by essential ecological, technological and fire-proof technical restrictions, use of polymeric emulsions as quenching media is actual. This sort of quenching media has several advantages: it allows to control metal cooling rate and provides uniform cooling of product surface, what allows to prevent appearance of internal stresses, cracks, deformations and defects in material structure. To develop colloid-stable emulsion, using as cooling media in metal quenching, it is actual to apply polysiloxane resin as polymeric component, due to hydrophobic ability of emulsified polysiloxane. In this case, obtain of water emulsions of polysiloxane resins needs especial conditions of emulsification. The paper suggests use of polysiloxane water emulsion, which was obtained via the method of phase inversion at the optimal temperature conditions as cooling liquid in metal quenching; these optimal emulsification parameters include speed 9,500–10,000 min-1, temperature 60 ºС and time period 60 min. Obtained emulsion on the base of polysiloxane and polyvinyl alcohol is characterized by small size of particles (about 1–2 μm), low viscosity (0.2 Pa·s), owing to high shifting forces during emulsification and temperature procedure, while metal surface acquires hydrophobic effect after emulsification, with the value of wetting angle up to 146°. It is shown that consequent lowering of polysiloxane concentration in water emulsion provides low viscosity even during temperature rise. When polysiloxane concentration reaches 7.5 %, emulsion displays good heat-exchanging capacity, which provides quenching rates comparative with use of industrial oil and water-polymeric media. The structure with acicular troostite and cementite, which is typical for substantially lower cooling rate, are mainly forming as a result of polysiloxane water emulsion use during quenching of samples made of steel 35Kh. The research was carried out within the framework of realization of the State assignment of RF Ministry of education and science No. FZWN-2023-0006 with use of equipment in the Center of high technologies at Belgorod State Technological University named after V. G. Shukhov.