Methods of Cooling Castings in the Design of the LTO Process, Complementing the Technology of Casting and Heat Treatment

Processy litʹâ, 2020, Tom 139, №1, p.42-53

Abstract

Received 06.11.2019

UDK 621.74.02; 621.74.041; 669.13 (03)

In foundry, in the development of methods for controlled cooling of castings after their solidification in sand mold, a combination of casting with heat treatment (HT), which can be called the LTO process, is proposed. The conditions for the development of the LTO process for castings from iron-carbon alloys with medium and high carbon content are considered. PTIMA of the National Academy of Sciences of Ukraine for 2018–2019 obtained a number of patents of Ukraine for methods of complementing casting and HT as varieties of the LTO process, in which Austempering of castings was used. The most convenient for LTO it is casting process in vacuum evacuated sand molds, the sand of which is easily poured out after the end of evacuation, without hindering the removal of the hot casting from the mold. For cases of adhesion of foundry paint to the surface of the casting, sand residues or local areas of the burn, especially for large castings, a method of hardening by supplying an air-sand mixture to a hot casting is proposed, as in sandblasting. A brief review of a number of works published in recent years on the influence of variable technological characteristics, mechanical properties, and microstructure on the manufacturing process of two-phase ductile cast iron (DI) type ADI is performed. Currently, there has been a significant increase in research and development around the world devoted to the production of biphasic and multiphase microand macroinhomogeneous structures containing ferrite, ausferite, bainite, martensite, carbides, carbonitrides, intermetallic compounds, and combinations thereof. Due to this, the properties of known iron-carbon alloys subjected to isothermal quenching according to traditional schemes are improved. Isothermally hardened ADI cast iron with the possibility of controlled introduction of free (proeutectoid) ferrite into the metal matrix improves the machinability of castings, which gives grounds for including the technology of such ADI in the LTO process along with other well-known methods.