Selection of lining (crucible) materials for medium frequency furnace steelmaking and alloy steel

1. Refractory adhesive for furnace lining

Refractory adhesive is a heat-resistant and insulating material. Usually, apply a circle on the inner wall of the induction coil, with a thickness of 1.5-2.5cm. After solidification and drying, it is a material that protects the induction coil and improves the mechanical strength of the coil. At the same time, it can make the furnace lining smoothly expand and contract in the vertical direction, so it is sometimes called permanent furnace lining. At present, the refractory mortar in China can withstand temperatures of 1800 ℃ for half an hour, effectively preventing furnace leakage.

2. Introduction to furnace lining (crucible) materials

Furnace lining material

There are three common types of intermediate frequency furnace crucibles: alkaline crucible, acidic crucible, and neutral crucible.

The main material used to make alkaline crucibles is magnesium oxide;

The only material used to make acidic crucibles is silicon oxide;

The materials used to make neutral crucibles are only aluminum oxide, MgO · Al2O3 composite oxide, graphite, etc.

Induction furnace crucibles are required to have the following characteristics:

(1)High fire resistance. The steelmaking crucible requires a temperature of 1700 ℃, and the melting of cast iron crucible requires a temperature of 1500 ℃;

(2)table physicochemical properties. Require crucible products to be resistant to slag and molten steel corrosion;

(3)Has good thermal shock resistance and high temperature strength;

(4)Has certain insulation performance;

(5)Small thermal conductivity;

(6)Low cost and pollution-free.

3. Selection of crucible materials

Alkaline crucible materials are suitable for melting special steels, precision alloys, and alloy steels. Such as stainless steel, etc.

Acidic crucible materials are suitable for melting carbon steel and low-alloy steel, and are not suitable for steel grades containing active wave elements such as Al, Ti, B, and rare earths.

4. Sintering of Induction Furnace Crucible

The sintering process involves the formation of a continuous sintering network by the combination of liquid phases on the contact surface of the sand material at high temperatures, which connects the entire sand material into a cohesive whole through the network.

After sintering, the cross-section of the crucible should be divided into unsintered layer, semi sintered layer, and sintered layer from the outside to the inside. The sintered layer requires high density, high strength, few surface cracks, complete melting between sand particles, and a uniform and complete sintered network. The thickness of the sintered layer accounts for about 30% to 50% of the total wall thickness, and transverse cracks in the sintered layer should be avoided as much as possible. The semi sintered layer is the transition zone between the sintered layer and the unsintered layer, where the contact surfaces of some particles begin to melt and the sintered network is incomplete. The function of this layer is to buffer the stress of the sintered layer and prevent cracks generated inside the sintered layer from extending outward. The thickness of the semi sintered layer accounts for about 35% to 40% of the thickness of the crucible wall. The unsintered layer is a layer of raw sand material between the semi sintered layer and the induction coil that has not been sintered at all. This layer of sand serves as insulation and also expands and contracts the volume of the crucible during heating and cooling. The thickness of the unsintered layer accounts for about 25% to 30% of the thickness of the crucible wall.