Abstract: Effects of Si and Mn content on microstructure and properties of steel for construction machinery were studied by means of optical microscope, scanning electron microscope and tensile testing machine. The results show that although the increase of Mn content promoted the grain growth, but the grain size is still low because the structure genetic effect is significantly higher than that caused by the change of Mn content, while the increase of Si content has little effect on the primary austenite grains. The increase of Mn content has no obvious effect on the precipitation of carbides in the quenched and tempered steel for construction machinery. Although the carbides in the specimens with increased Si content are still mainly granular, and has also a small amount of short rod carbides, the number of carbides is obviously less and the size is smaller. With the increase of Mn content, the tensile strength, yield strength and Brinell hardness of steel for construction machinery are improved, while the elongation, section shrinkage and impact absorbed energy at -40 ℃ are reduced to varying degrees. After adding Si content, the tensile strength, yield strength and Brinell hardness of steel for construction machinery are decreased, while the elongation, section shrinkage and impact absorbed energy at -40 ℃ are increased significantly, but the strength and Brinell hardness do not meet the standard requirements of steel for construction machinery; the appropriate Si and Mn content of steel for 1000 MPa grade construction machinery steel for test are 0.35 wt% and 1.12 wt%, respectively.

Key words: steel for 1000 MPa grade construction machinery, Si and Mn content, quenching and tempering, microstructure, properties