Process Study Of Laser Surface Hardening For Cylinder Liner Of High Power Marine Diesel Engine

Cylinder liner, one of the critical components of high-power marine diesel engine, has a great influence on working performance and service life of diesel engine. As one of the main failure modes of cylinder liner, abrasion is a major problem that restricts the quality of cylinder liner. With ring-liner fit clearance increasing and airtightness decreasing, Abrasion results in less power, higher fuel consumption, louder noise, more vibration, and lower working efficiency. Therefore, improving the wear resistance ability of cylinder liner is essential to prolong its service life and to improve the quality of diesel engine. In this paper, the cylinder liner of SEMT PA6V280 marine diesel engine is taken as the research object, and laser surface hardening process is used to strengthen the surface of the cylinder liner and to improve the friction and wear properties. The following results are obtained from the theories and experiments:In theory aspects, parameter calculation of thermal-physical properties of the liner cast iron specimen with known composition has been completed. On the base of existing thermal field calculation method, calculation for thermal field distribution of the laser heating zone and preliminary calibration of the quenching parameter range have been finished. Cylinder liner material database creation and secondary development of uniform energy distribution heat source model with rectangular outline have been completed. Laser surface hardening temperature field simulation under different parameters has been carried out with finite element method, and the parameter range of laser surface hardening process is finally determined by contracting calculation and simulation results.In experiment aspects, test for laser surface hardening, test for hardness and its distribution of laser hardened zone, test for metallographic structure of laser hardened zone, and test for friction and wear properties between different samples with various hardened area ratio have been carried out. With input power of 1500 w and scanning speed of 40mm/s, a hardened zone with width of about 4.1mm and depth of about 0.43 mm is obtained. The hardening metallographic phase of hardened zone is mainly composed of phosphorus eutectic and cryptocrystalline martensite and the hardness of hardened zone is about 2 times higher than that of the matrix. The abrasion loss of the laser hardened specimens with respectively 21.5%, 31.7%, 42.3% and 52.8% hardened area ratio are decreased by 47.11%, 38.84, 28.93% and 27.27%. The ratio range of hardened area is determined as 30%-40%. The interval-distributed laser hardened zone forms a hard and wear-resistant "skeleton", which significantly improves the overall wear resistance of the specimen.