690MPa级海洋平台用特厚齿条钢的回火稳定性

研究了长时间回火(2，4和8h)对海洋平台用齿条钢A514 GrQ显微组织及力学性能的影响.结果表明，回火过程中，淬火态马氏体板条组织发生回复，C，Cr，Mo和V等元素扩散，析出MC，M₂C和M₂₃C₆型碳化物，回火2h后碳化物类型趋于稳定，并发生Ostwald熟化现象；随着回火时间的增加，实验钢的抗拉强度由淬火态的1100MPa逐渐降低到回火8h时的813MPa，屈服强度由淬火态的931MPa逐渐降低至回火8h时的725MPa；淬火态实验钢回火2h后，-60℃冲击功由淬火态的187J增加至238J，继续增加回火时间，冲击功趋于稳定，约为245J；延伸率由淬火态的15.2%增加至回火2h时的16.7%，并且随着回火时间的增加，升高至回火8h时的19.5%.实验钢在600℃回火2~8h过程中，具有良好的回火稳定性和强韧性匹配，最佳回火时间为2h.

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

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.