Mechanisms of strength and toughness enhancement in 23MnNiMoCr54 chain ring steel through V–N microalloying and heat treatment optimization

To meet the urgent demand for high strength and high impact toughness in mining ring chain steels for deep well coal mining, this study developed a new type of high-strength and tough steel based on 23MnNiMoCr54 steel through V-N microalloying. The microstructure evolution and strengthening mechanisms were systematically studied using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and mechanical property testing. The results show that V-N microalloying combined with optimized heat treatment promoted the precipitation of high-density, nano-sized MC-type carbonitrides, effectively suppressing the formation of coarse M 23 C 6 and M 7 C 3 phases. This led to a 29.7% refinement in the size of the precipitates compared to the base steel and significantly increased the high-angle grain boundary fraction to 73.9%. The dispersed nano-sized precipitates promoted grain refinement and significantly increased dislocation density through the pinning effect, leading to an increase of approximately 150 MPa in dislocation strengthening compared to 23MnNiMoCr54 steel. Meanwhile, the fine grains and dispersed small precipitates facilitated uniform stress distribution during impact testing and delayed the accumulation of geometrically necessary dislocations. The high fraction of HAGBs effectively suppressed crack initiation and propagation, significantly improving the impact toughness of the new steel. These findings provide a theoretical basis and technical support for the composition design and microstructure control of high-strength and tough low-alloy martensitic chain ring steels.