Ultrahigh fatigue strength of gradient nanostructured plain steel

In light of the steel development trend-plainification and high performance, we designed a gradient nanostructured plain steel with ultrahigh mechanical performance and exceptional cost performance. This multiscale design is achieved by using surface mechanical attrition treatment (SMAT) in a plain steel matrix subjected to quenching-partitioning-tempering (Q-P-T) process. The integration of Q-P-T and SMAT processes effectively achieves the gradient surface nanocrystallization on the high mechanical performance matrix. This gradient nanostructure exhibits an environment with gradient compressive stress accompanying with the refinement of grains, which prevent crack formation and propagation effectively. Consequently, an ultrahigh fatigue strength (up to 820 MPa) at high-cycle (107) can be achieved with remarkable cost performance (1653.1 MPa & sdot;kg/USD) at the same time, surpassing maraging steel by 14 times. The multiscale design of gradient nanostructured plain steel not only breaks the endurance-cost trade-off but also paves the way to imparting significant endurance on high carbon plain steel.