Research of modification influence on cracking resistance of cast iron in moulds

The main feature of thermal mould work during its operation is presence of quick cyclically repeated one-side heats induced by liquid steel cast in a mould internal space, as well as consequent cooling processes (including the period after stripping of solidified ingot) [1–4]. A mould wall is subjected to thermal shock during ingot casting and solidification, which is accompanied by its thermal elastic and thermal plastic deformation (buckling). As a result, the high temperature gradient appeared in the mould wall, and essential temperature stresses are arisen; they reach the value of tensile strength of mould material, where gray cast iron is usually used. At the same time, the temperature effect of liquid steel leads to variation in the structure of metallic base, corrosion development, variation of thermal physical and mechanical properties, thermal fatigue of mould cast iron [5–9]. Multiple iterations of very intensive thermal effects on a mould (both on its construction and materials presented by cast iron) are considered as the main causes of its destruction and breakdown. The effect of thermal procedures on a mould can be assessed mostly correct only via joint analytical and experimental approach for solving this problem. Trustworthy description of the temperature field of mould wall is mandatory condition for determining the temperature effect of ingot on a mould; this is the main parameter of temperature stresses and variation of mechanical and thermal physical properties of material [10–12]. Overwhelming majority of the works manufacturing cast iron with spheroidal graphite uses the treatment technology in an open casting ladle with location of modifying additive on its bottom in the special cavity. This cavity is fenced by refractory barrier, and the process itself is known as SandwichVerfahren or “Sandwich process”. The methods of liquid cast iron processing are improved gradually [13–17]. Buckling investigation of the moulds for consumable electrodes in the process of vacuum arc remelting was conducted on the cast iron physical models in the form of hollow cylinders with internal diameter 22 mm, external diameter 32 mm and height 210 mm (scale 1:10) [18]. It is recognized at present time that computer-aided simulation of complicated tasks about heat exchange and stressed state of materials, dynamics of plastic appearances is often more acceptable than experimental investigations [19–22]. Research of modification influence on cracking resistance of cast iron in moulds