| 摘要 |
PURPOSE:To obtain the titled piston which has no possibility of having cracks in the part where the resistance to thermal impact and thermal fatigue is required in the piston head part of said piston by partially reinforcing the sur face layer of said part to specific structure. CONSTITUTION:The part where the temp. is made highest by the direct receipt of fuel injection and particularly the resistance to thermal impact and thermal fatigue is required in the head part 2 of the piston 1, for example, a hot spot part 4, is partially reinforced. More specifically, a fine graphite dispersed layer which consists of a ferrite phase as the matrix and in which finely lumped graphite of <=20mu average grain size is dispersed and crystallized is formed on the part 4 down to >=0.2mm depth from the surface. A rough shape material for the piston is cast of a cast iron for the above-mentioned purpose and there after high-density energy such as laser is irradiated on the surface of the part 4. The irradiated position is moved or the irradiation is stopped to quickly melt and quickly solidify the surface layer, by which a chilled layer is formed. After the layer 11 is hated for 1min-3hr at 800-110 deg.C, the layer is cooled at a rate of <=50 deg.C/min. |
