Research on Fatigue Performance of 550MPa Grade Engineering Machinery Steel

• 1、School of Metallurgy and Ecological Engineering, University of Science and Technology Beijing,Beijing 100083

Abstract：The quenched and tempered steel Q550D for construction machinery has good comprehensive properties. Through microstructure observation, mechanical performance testing and rotating bending fatigue experiment, the high cycle fatigue performance of Q550D has been studied, and the S-N curve has been obtained, the influencing factors of fatigue strength are analyzed. The results show that after quenching at 920~930 C and tempering at 545~555 C for 110 minutes, the experimental Q550D has good comprehensive mechanical properties and fatigue properties, and its average rotating bending fatigue strength is 390MPa; according to the S-N curve function with a failure probability of 0.1% and a confidence level of 95%, the maximum alternating load that it can withstand under the requirement of a fatigue life of 10^7 cycles is 312.4MPa; observing the fatigue fracture through SEM, it is found that the fatigue crack source of Q550D used in the experiment is mainly caused by processing defects on the sample surface and stress concentration caused by the surface slip zone; the addition of alloying element Cr improves the comprehensive performance of the experimental Q550D, and generates small-sized spherical inclusions, which can effectively hinder the initiation and propagation of cracks, and improve the fatigue performance of the material, but due to the small size, fatigue is not formed in the end crack source.

Keywords： tempered martensite steel construction machinery Q550D S-N curve fatigue properties