How to heat treat ductile iron?

After spheroidisation treatment of cast iron liquid, after pouring graphite crystallisation spherical, obtain ductile cast iron, thus improving the mechanical properties of cast iron. In order to make the strength, plasticity and toughness of ductile cast iron are as visible as possible, it is necessary to use heat treatment to change the matrix organisation of ductile cast iron

Heat treatment of ductile iron

1、Annealing

Ductile iron annealing is divided into stress relief annealing, low temperature annealing and high temperature annealing. Stress relief annealing process is the same as grey cast iron. The purpose of low temperature annealing and high temperature annealing is to make the organisation of carburite decomposition, access to ferrite ductile iron, improve the plasticity and toughness, improve the cutting performance.

2、Normalising

The purpose of normalising ductile iron is to increase the number of pearlite in the matrix, or to obtain all pearlite matrix, to refine the grain, improve the strength of castings and wear resistance. Normalising is divided into low temperature normalising and high temperature normalising.

3、Tempering treatment

The casting will be heated to 860 ~ 920 ℃, insulation 2 ~ 4 hours after quenching in oil, and then tempered at 550 ~ 600 ℃ 2 ~ 4 hours, to get the tempered Sohnite plus spheroidal graphite organisation, with good overall mechanical properties, for the complexity of the force and the overall mechanical properties of the important requirements of the castings, such as crankshafts and connecting rods.

4, Isothermal quenching

The casting will be heated to 850 ~ 900 ℃, insulation and then quickly into the 250 ~ 350 ℃ salt bath isothermal 60 ~ 90 minutes, and then out of the air-cooled, to obtain the lower bainite matrix plus spheroidal graphite organisation, so that the overall mechanical properties of the good, for the shape of the complexity of the heat treatment of the deformation of the easy to crack, the requirements of high strength, plasticity and toughness of the good, not large cross-section size of the parts.

Summary

Ductile iron heat treatment is an important means to improve its performance and life, need to take into account the raw materials, processing and subsequent treatment and other factors in order to achieve good results.