Research achievements of Austempered Ductile Iron in China

In terms of molten iron melting and spheroidizing treatment, Shen Yonghua has produced high-quality Austempered Ductile Iron blanks by using sand coated iron mold casting technology. It is found that sand coated iron mold casting can speed up the cooling rate of molten iron in the mold cavity. At the same time, the existence of coated sand ensures that the molten iron will not produce white spots due to the rapid cooling rate. In addition, the casting spheroidization effect is good and the mold dimension precision is high, which can ensure the stable production of the blank for austempered ductile iron.

Wang Haiquan spheroidized ADI blank by wire feeding method and punching method respectively. It is found that under the same austempering process and equipment, the nodular cast iron produced by wire feeding method has higher spheroidizing quality, smaller fluctuation of WMG residue and WS residue, stable production process, higher quality of austempered ductile iron blank, and the tensile strength of ductile iron treated by wire feeding method is better than that by punching method.

In terms of heat treatment process, microstructure and properties, zufangqiu found that the two-step austempering process can refine the austenite structure in ADI matrix, and improve its strength, toughness and hardness significantly.

Jiang Likun studied the double equal temperature quenched ductile iron, and found that the increase of austenitizing temperature (820 ℃ ~ 880 ℃) can reduce the amount of ferrite in ADI matrix, but increase the amount of austenite; with the increase of isothermal transformation temperature (250 ℃ ~ 390 ℃), the structure of ADI coarsens, and the amount of untransformed austenite increases; the austempering time is 0.5h ~ 1.5h When the isothermal transformation time is more than 1.5h, the carbon rich austenite is prone to γ HC  α + ε transformation.

Wei Bingqing found that there are a lot of dislocations in ferrite and austenite in Austempered Ductile Iron by TEM. The dislocation density of ferrite needle in ADI decreases with the increase of isothermal transformation temperature under different technological conditions.

Cui Junjun found that with the increase of tempering temperature (300 ℃ ~ 450 ℃), the hardness and tensile strength of low alloy Austempered Ductile Iron gradually decreased, and the amount of austenite and martensite in the matrix decreased, and a and Mo2C were further decomposed.

With the joint efforts and practice of many experts and enterprises, the technology of Austempered Ductile Iron in China has made great progress. It is believed that in the near future, austempered ductile iron will show its brilliance in various fields in China.