Process Optimization and Property of Novel Tunnel Boring Machine Cutter Ring Material to Prevent Fracture Failure

During the excavation of upper-soft and lower-hard strata, many disc cutter rings on the tunnel boring machine fractured in a subway tunnel project in Guangzhou. To improve the tunneling efficiency, the fracture causes of the field cutter ring were analyzed. A systematic study was then performed to investigate the microstructure, mechanical properties, and wear resistance of the improved novel material DQ2 steel under various heat treatment processes. The tunneling performance of the cutter ring made of DQ2 steel was explored through the industrial test. The results showed that a high quantity of primary carbides with chain distribution seriously reduced the impact toughness of the field cutter ring. This structural defect was the main cause of the field cutter ring fracture. The excellent comprehensive properties of DQ2 steel quenched at 1070 °C and tempered at 530 °C were obtained. In comparison to the field fracture cutter ring, the hardness of DQ2 steel was increased by 1.2 HRC, and the impact absorption energy was increased by nearly 20 times, reaching 196.89 J. When tunneling the compound strata, the failure mode of DQ2 cutter rings is uniform wear, without the common fracture issue of the field cutter ring.