Exploring How (Ti + Mo)/C and Ti/Mo Influence the Precipitation Behaviors within Microalloyed Steels: Experimental Evidence and Related Patents Investigation

Abstract

The main objective of the present study was to understand the influences of different atomic ratios of Ti/Mo and (Ti + Mo)/C on the precipitation behaviors in Ti-Mo HSLA steels. It was found that the steel with a higher Ti/Mo atomic ratio possessed a large theoretical volume fraction of precipitated carbides, but the ferrite matrix did not achieve a corresponding higher microhardness. On the other hand, the experimental results also indicated that it was not suitable to assess the precipitation strengthening effect of the ferrite matrix based on only one of the atomic factors, i.e., (Ti + Mo)/C or Ti/Mo. In addition, from the present study, similarity of the (Ti + Mo)/C atomic ratios is a prerequisite for comparing the precipitation hardening effects in steels having different Ti/Mo atomic ratios. Besides experimental data, the main deduction is also supported by related patent information, which further corroborates the reliability of the present study. Furthermore, of the two steels with different M/C atomic ratios, the ferrite matrix of the H-(M/C) steel showed a rising trend in Vickers hardness when the isothermal holding time was increased from 5 min to 60 min at 650-700 °C. This higher strengthening ability, which occurs within ferrite grains after holding at longer times, can be ascribed to the higher austenite decomposition rate occurring in the H-(M/C) atomic ratio steel. Therefore, the hardening mechanisms in both kinds of steel are also discussed in the present study.