Comparison between new type ductile iron piston and steel piston after isothermal quenching

(1) A new generation of high-performance piston is manufactured by using ferrite ductile iron, such as QT600-7 profile split method. That is, use ductile iron pipes to process the piston head, use ductile iron bars to process the piston skirt, and then use inertial friction welding to obtain the piston semi-finished products. Further machining and surface treatment will result in a new type of finished ductile iron, which can greatly reduce the material cost, At the same time, because the ferritic ductile iron has good chip breaking property and cutting property, the machining cost can be greatly reduced;

(2) After the ferritic ductile iron friction welding annealing treatment, further increase the quenching+tempering or isothermal quenching process, so as to eliminate the hardness difference between the welding heat affected zone (weld area) and the non weld area, keep the hardness of the weld area and the non weld area consistent, reduce the intermittent cutting of tools, and effectively reduce the processing and production costs;

(3) For QT600-7 ductile iron piston after friction welding and stress relief annealing, further increase the quenching+tempering or isothermal quenching process. Although the cost of heat treatment is slightly increased, its tensile strength and yield strength can be greatly improved, thus reaching or exceeding the existing mechanical property level of 38MnVS6Ti non quenched and tempered steel;

(4) As the density of this new type of isothermally quenched ductile iron is smaller than that of steel, and its thermal conductivity is lower than that of steel, but its mechanical properties are consistent with those of existing steel piston materials, it can further reduce the weight of the engine, reduce the heat loss of the engine, and improve the thermal efficiency. It is the best material for a new generation of high-performance, low-cost national VI piston.

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