Medium frequency induction heating gray cast iron induction furnace melting example

Production of HT250 brake drum

Medium frequency induction furnace is used to produce gray cast iron brake drums. Electric furnace smelting has advantages over cupola furnace smelting. The oxidation and burning loss of liquid iron is less, the composition is easy to adjust, the temperature is easy to control, and the cost of furnace materials and the casting scrap rate are reduced.

Scrap steel, a small amount of returned iron, carburizers and ferroalloys are used for the production of charge. Scrap steel and carburizer are the main factors affecting the quality of synthetic cast iron.

The brake drum casting grade HT250 uses more than 60% scrap steel in the ingredients, which can improve the shape of graphite when the molten iron is overheated and kept warm. The use of scrap steel in an appropriate amount increases the N content in the molten iron and stabilizes the pearlite in the matrix. Using carbon steel scrap can stabilize the chemical composition of the molten iron and improve the purity of the molten iron.The brake drum casting grade HT250 uses more than 60% scrap steel in the ingredients, which can improve the shape of graphite when the molten iron is overheated and kept warm. The use of scrap steel in an appropriate amount increases the N content in the molten iron and stabilizes the pearlite in the matrix. Using carbon steel scrap can stabilize the chemical composition of the molten iron and improve the purity of the molten iron.

When choosing a carburizing agent, the fixed carbon should be high and the ash, volatile matter and harmful impurities should be low. Using high-purity graphite electrode fragments as carburizing agent can reduce the balance N amount in the molten iron, reduce the whitening tendency, and increase the carbon absorption rate, thus promoting the formation of A-type graphite. The particle size of the carburizer is 1 to 5 mm.

(1) The chemical composition w (mass fraction) of the production process is: w, 3.4% to 3.6% C: 1.8% to 2.0% Si; 0.6% to 0.8% Mn; 0.15% to 0.3% Cr; ≤ 0.07% P; ≤ 0.1%s, 1.4%-1.6% Si in the original molten iron.

①Carburization operation. When carburizing, it should be ensured that the CE (carbon equivalent) change is small and the carburizing agent absorption rate is high. According to the requirements of low-temperature carburization and high-temperature carbon replenishment, carburization first and silicon addition, the charge for each furnace is divided into 5 batches into the furnace. The feeding sequence is:

The first batch of materials is scrap steel ten-pouring riser

The second batch of materials: scrap steel ten pouring risers ten carburizers

The 3rd and 4th batch of materials: scrap steel, ten pouring risers and ten carburizers.

Batch 5. Ferroalloy ten scrap steel ten pouring riser.

The molten iron is kept at 1450-1500°C for 10 minutes, and the C content is quickly analyzed. If the amount of C is insufficient, add carburizing agent to the clean liquid surface to increase carbonization; if the amount of C is excessive, add scrap steel for decarburization until the amount of C is qualified.

②Incubation treatment. When the temperature of the molten iron is 1480~1500℃, the iron is tapped. Use a compound inoculant of 1.5% RE; 3.0% Ca; 2.0% Ba; 65% Si in the small bag for inoculation treatment. Observe the fracture surface of the triangular test block: the color is light. Gray, white mouth width 0,-2mm, the structure is dense and crystalline.

(2) Mechanical properties and metallographic structure. According to the measured data of the tensile test bar 30 The metallographic structure of the brake drum body: graphite type A, graphite size 4-5, pearlite (95%), ferrite (95%) <5%, cementite and phosphorus eutectic (90%) <1%.

Synthetic gray cast iron produced by scrap steel carburizing electric furnace has good casting performance and better mechanical properties than cupola gray cast iron. It is easy to control, has stable quality, good cutting processability and is widely used.