Selection and Advantages of Welding Methods for Nodular Cast Iron Piston Head and Skirt

Compared with 38MnVS6Ti non quenched and tempered steel and 42CrMo4 quenched and tempered steel, nodular cast iron material has the characteristics of high carbon and silicon content, high sulfur and phosphorus content, and it is difficult to adopt melting welding; However, friction welding is an excellent solid state connection method, especially suitable for the welding of such materials; That is, friction welding is a process in which atoms on the metal surface approach, combine and diffuse to form common crystals by rotating friction and axial compression between metal workpieces; In the whole welding process, the temperature of friction interface generally does not exceed the melting point, so friction welding is called solid welding; Compared with fusion welding, friction welding also has significant advantages in the performance of welded joints; First, the friction welded joint does not produce some welding defects and welding embrittlement related to melting and solidification metallurgy; Second, the axial pressure and torque act on the friction welding surface and its near area together, resulting in some mechanical and metallurgical effects, such as grain refinement, microstructure densification and the “self-cleaning” effect of the friction welding surface; Thirdly, friction welding has the advantages of short welding time, narrow heat affected zone and no obvious coarsening of heat affected zone. The above three aspects are conducive to welding joints with the same strength as the base metal; That is to say, through reasonable friction welding specifications and welding processes, the ferrite nodular cast iron piston head and piston skirt are connected by friction welding to obtain high-quality welding joints, so that the weld can obtain the strength equivalent to or higher than that of the matrix; Thus, the service performance of the piston is guaranteed, and the traditional manufacturing process of the nodular cast iron piston is simplified; The above nodular cast iron with good welding performance, i.e. QT600-7 nodular cast iron, is used as the material for manufacturing split piston, which can not only greatly reduce the material cost, but also greatly reduce the machining cost because the ferritic nodular cast iron has good chip breaking performance and cutting performance.

38MnVS6Ti non quenched and tempered steelQT600-7 Nodular cast Iron
Brinell hardness/HBW250-300150-200
Yield strength/MPa≥520≥400
Tensile strength/MPa≥850≥600
Elongation after fracture/%≥10≥7
MachinabilityDifferenceVery nice
Material price/yuan/kg178

The table shows the specific comparison between 38MnVS6Ti non quenched and tempered steel and QT600-7 nodular cast iron in hardness, mechanical properties, machinability and price.

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