Enhancement of the Mechanical Properties of a V–Ti–N Microalloyed Steel Treated by a Novel Precipitation-Quenching & Partitioning Process

In this study, a novel precipitation-quenching & partitioning (P-Q&P) process was proposed by combining a proper intermediate holding treatment with the Q&P process, which successfully increased the strength of a V–Ti–N microalloyed steel without sacrificing the plasticity. However, the impact toughness of the P-Q&P samples is lower than that of the Q&P sample. Compared to the Q&P sample, the P-Q&P samples have more retained austenite. In addition, coarser substructures of martensite and bainite were formed in the P-Q&P samples. All the P-Q&P and Q&P samples contain two types of carbonitrides, which are the large-size particles (enriched in Ti) formed or undissolved in austenite and the small-size particles (enriched in V) formed in martensite and bainite. The P-Q&P samples have a smaller size and larger volume fraction of the large-size particles than the Q&P sample. The increase in the strength of the P-Q&P samples is attributed to the precipitation strengthening of the carbonitrides formed in austenite during the intermediate holding treatment. And the maintained elongation is mainly caused by the higher austenite content in the P-Q&P samples. The poor toughness of the P-Q&P samples is mainly resulted from the coarser substructures.