A high strength steel with Nb-V-Ti addition was heat treated by a series of isothermal bainite holding (IBH) processes and quenching and partitioning (Q&P) processes with different intercritical annealing temperatures. The microstructure observation showed that some martensite was formed during quenching in IBH condition with annealing temperature above 850 °C, mainly ascribed to heterogeneous carbon content distribution in parent austenite with relatively large size. Meanwhile, film-like RA in martensite, relatively coarser lath-like RA in bainite and blocky RA located in grain boundaries or phase boundaries were observed in both IBH and Q&P treatments. Moreover, Q&P process was proved to be more beneficial to retain austenite than IBH process, while the ability of austenite retention was similar in IBH conditions. An excellent combination of strength and ductility was obtained in Q&P process annealed at 880 °C with tensile strength of 1126 MPa and total elongation of ~ 18%, attributing to TRIP effect mainly occurred in the latter part of strain and fine microstructure with homogeneous distribution.

通过一系列等温贝氏体保持（IBH）工艺以及淬火和分配（Q＆P）工艺（具有不同的临界退火温度）对添加Nb-V-Ti的高强度钢进行了热处理。显微组织观察表明，在IBH条件下，退火温度高于850°C时，淬火过程中形成了一些马氏体，这主要归因于母体奥氏体中具有较大尺寸的碳含量分布不均。同时，在IBH和Q＆P处理中均观察到马氏体中的薄膜状RA，贝氏体中的板条状RA相对较粗，且在晶界或相界中存在块状RA。此外，事实证明，Q＆P工艺比IBH工艺更有利于保留奥氏体，而在IBH条件下，奥氏体的保留能力相似。