Mechanism of carburizing defect in lost foam steel casting

The filling process of lost foam casting is the replacement process of metal liquid and foam pattern. Because the pouring temperature of molten steel is high (above 1550 C), the gasification and cracking of foam pattern are relatively sufficient, resulting in a large amount of elemental carbon. Carbon diffuses into the soft moving molten steel and solidified casting, resulting in the carburization defect of steel casting.

The mass transfer equation of carbon into the casting is expressed as follows:

Where CW ⎯ carbon content of casting, unit%;

K ∑⎯ mass transfer pouring number, unit: s · m-2;

The contact area between the pyrolysis product of S foam and the liquid metal, m2;

CE ⎯ carbon content of pyrolysis products, unit%;

C0 ⎯ initial carbon content of molten metal, unit%;

τ⎯ contact time between molten metal and pyrolysis products, unit s.

According to the formula, the larger the contact area, the longer the contact time, and the greater the carbon concentration gradient (ce-c0) between molten metal and pyrolysis products, the higher the carbon content of casting.