To verify the microalloying function and segregation behavior of trace Mg at grain boundary in steel, the 2.25Cr–1Mo steel doped with 0.056% P containing different Mg contents was refined with a vacuum-induction furnace. The effects of trace Mg addition on the temper embrittlement susceptibility of 2.25Cr–1Mo steel were studied by step-cooling test and the segregation behavior of Mg at grain boundary was explored by Auger electron spectroscopy. It is shown that P-induced temper embrittlement susceptibility can be reduced after subjecting to step-cooling treatment with trace Mg addition, mainly benefited from the segregation of Mg at grain boundary. This segregation can decrease the segregation amounts of P and S, especially for P, and increase the grain boundary cohesion, reducing the adverse effect on temper embrittlement caused by P and S.

为了验证钢中晶界微量Mg的微合金化功能和偏析行为，用真空感应炉精炼了掺杂了0.056％P的2.25Cr-1Mo钢，其中P含量不同。通过逐步冷却试验研究了微量镁对2.25Cr-1Mo钢回火脆化敏感性的影响，并通过俄歇电子能谱研究了镁在晶界的偏析行为。结果表明，经过微量添加镁的逐步冷却处理后，P引起的回火脆化敏感性降低，这主要得益于晶界处镁的偏析。这种偏析可以减少P和S的偏析量，特别是对于P而言，并增加晶界凝聚力，减少由P和S引起的对回火脆化的不利影响。