Improved low-temperature mechanical properties of FH36 marine steel after ultrasonic surface rolling process

The ultrasonic surface rolling process (USRP) was adopted to improve the low- temperature mechanical properties of FH36 marine steel for strengthening the service performance of marine steel in the lowtemperature environment between - 30 & DEG;C and - 60 & DEG;C, such as polar regions. The results indicated that the surface integrity of FH36 marine steel was restructured as a result of the severe plastic deformation induced by USRP. The surface average grain diameter was refined from 10.92 & mu;m to 5.86 & mu;m with the number of nanoscale grains increased significantly and a nanostructured surface layer formed. The surface roughness decreased greatly with Ra not more than 0.074 & mu;m. The surface residual compressive stress with an affected layer depth of not less than 2.6 mm was produced. The surface microhardness increased significantly with a large-depth work hardening layer of not less than 580 & mu;m. The yield strength and ultimate tensile strength of FH36 marine steel after USRP at room temperature and low temperatures were enhanced. The combined effects of fine grain strengthening, dislocation strengthening, modified surface roughness, induced residual compressive stress, work hardening, and changed heat transfer performance caused by USRP were the main reasons for the improved low-temperature mechanical properties of FH36 marine steel. & COPY; 2022 Elsevier B.V. All rights reserved.