ductile iron heat treatment
In the structure of spheroidal graphite cast iron, graphite is spherical, and its weakening and destructive effect on the matrix is weaker than that of flake graphite. The performance of ductile iron mainly depends on the matrix structure, and the influence of graphite takes a second place. By improving the matrix structure of ductile iron with various heat treatment methods, its mechanical properties can be improved to varying degrees. The purpose of heat treatment is to obtain the required structure, thereby improving the mechanical properties.
The commonly used heat treatment methods for ductile iron are as follows：
（1）Low temperature graphitization annealing, heating temperature 720~760℃. Cooled with the furnace to below 500 ℃, air-cooled out of the furnace. The eutectoid cementite is decomposed to obtain ferrite matrix ductile iron to improve toughness.
（2）High temperature graphitization annealing 880~930℃, transfer to 720~760℃ for heat preservation, and then cool to below 500℃ with furnace and air cooling. Eliminate white-mouth structure, obtain ferrite matrix ductile iron, improve plasticity, reduce hardness, and increase toughness.
（3）Fully austenitizing normalizing 880~930℃, cooling method: mist cooling, air cooling or air cooling, in order to reduce stress, increase the tempering process: 500~600℃, obtain pearlite + a small amount of ferrite + spherical graphite, improve Strength, increase hardness and wear resistance.
（4）Incomplete austenitizing normalizing heating at 820~860℃, cooling method: mist cooling, air cooling or air cooling, in order to reduce stress, increase the tempering process: 500~600℃ to obtain pearlite + a small amount of dispersed ferrite structure , Get better comprehensive mechanical properties.
（5）Tempering treatment 840~880℃ heating, cooling method: oil or water cooling, tempering temperature after quenching: 550~600℃, to obtain tempered sorbite structure and improve comprehensive mechanical properties.
（6）Austempering Heating at 840~880℃ and quenching in a salt bath at 250~350℃ to obtain comprehensive mechanical properties, especially to improve strength, toughness and wear resistance.
During heat treatment heating, the casting temperature is generally less than 350℃, and the heating speed depends on the size and complexity of the casting, and it can be selected between 30~120℃/h. The temperature of entering the furnace for large and complex parts should be low, and the heating speed should be slow. The heating temperature depends on the matrix structure and chemical composition. The holding time depends on the wall thickness of the casting.
Anyang Huatuo Metallurgy Co.,Ltd in the raw materials of ductile iron for more than 20 years, own rich experience in the product and production, if any confused just consult.