Tempering Stability of a 690MPa Grade Ultra-heavy Rack Steel for Offshore Platform

doi:10.12068/j.issn.1005-3026.2022.02.006

Abstract

Abstract: The effects of long-term tempering (2h，4h and 8h) on microstructure and mechanical property of rack steel A514 GrQ for offshore platforms were studied. It is found that during the tempering process， the quenched martensite lath structure recovered， C， Cr， Mo and V elements diffused， and MC， M₂C， and M₂₃C₆ type carbides were precipitated in the martensite matrix. After tempering for 2h， the carbides tended to be stable and the Ostwald ripening occurred. With the increase of tempering time from 0h to 8h， tensile strength of the tested steel decreased from 1100MPa to 813MPa and yield strength decreased from 931MPa to 725MPa. The impact energy at -60℃ increased from 187J of the as-quenched steel to 238J after 2h tempering and then it tended to be stable with a value about 245J for further tempering. The elongation increased from 15.2% of the as-quenched steel to 16.7% after 2h tempering and further increased up to 19.5% for 8h tempering. These results indicate that in the process of tempering at 600℃ for 2-8h， the experimental steel A514 GrQ can perform the good tempering stability and the excellent combination of strength and toughness， associated with the best tempering time of 2h.

Key words: ultra-heavy rack steel； tempering time； carbides； strength and toughness； martensite

CLC Number:

TG156

LIU Geng， LI Hui-jie， WANG Qing-hai， YE Qi-bin. Tempering Stability of a 690MPa Grade Ultra-heavy Rack Steel for Offshore Platform[J]. Journal of Northeastern University(Natural Science), 2022, 43(2): 188-196.

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