研究了回火温度对含15% δ铁素体(体积分数)的热轧高铝中锰钢显微组织和力学性能的影响。结果表明，钢中长300 μm的δ铁素体经热轧再结晶可被细化分割至大量长3 μm左右竹节状晶粒，且在回火温度高达700℃时尺寸不变。400~500℃回火后，马氏体基体依然维持较高的位错密度且析出细小渗碳体和纳米级VC粒子，屈服强度最高；同时C由马氏体向奥氏体的大量配分提高了奥氏体稳定性，获得了相对持久的加工硬化，最终获得了屈服强度约1500 MPa、抗拉强度1800 MPa和断后延伸率14%的最佳力学性能组合。该钢δ铁素体相一方面由于析出强化、晶粒细化和位错强化而得到显著硬化；另一方面δ铁素体体积分数不高且呈孤岛状嵌在马氏体基体中，这些特征导致该钢屈服强度由马氏体基体而非δ铁素体所决定，因此相比于其他类似Al含量的含δ铁素体中锰钢，屈服强度大幅度提高。

Automobile industries require advanced high-strength steels (AHSSs) that possess high strength and good formability and are light; automobiles manufactured using AHSSs have reduced fuel consumption and enhanced safety compared to automobiles manufactured using traditional materials. Al-containing medium Mn steels, which are a typical example of 3rd generation AHSSs, have attracted much research attention with an aim of meeting these requirements as they possess extraordinary work hardening ability, which leads to high strength and excellent elongation at a low density. However, such steels often exhibit low yield strength resulting from the formation of coarse δ-ferrite grains due to the high Al content. In this study, the influence of tempering temperatures on the microstructure and mechanical properties of hot-rolled medium Mn steel containing 15% (volume fraction) δ-ferrite due to the addition of 3%Al (mass fraction) is studied. δ-ferrite with a length of 300 μm was refined and divided into a large number of bamboo-like grains having a length of about 3 μm due to dynamic recrystallization caused by hot rolling. The grain size of these refined δ-ferrite grains remained unchanged when the tempering temperature was increased to 700^oC. In the case of tempering at 400-500^oC, although the dislocation density in martensite decreased, the precipitation of fine cementite and nanosized VC particles compensated for this effect, leading to high yield strengths, which was almost the highest among all the tempering temperatures. Meanwhile, many C atoms could be partitioned from martensite to austenite, leading to the steel acquiring the enhanced chemical stability of austenite, which contributed to the higher work hardening rate and more durable strain hardening. Finally, the best mechanical combination consisting of a yield strength of about 1500 MPa, an ultimate tensile strength of 1800 MPa, and a total elongation of 14% was achieved after tempering at 400-500^oC. The resultant yield strength is much higher than that of other medium Mn steels having similar Al content because it is dependent on the tempered martensitic matrix rather than δ-ferrite. This is due to two factors: first, δ-ferrite in the studied steel is strengthened due to precipitation, dislocation, and grain refinement hardening; second, δ-ferrite grains have a small fraction of 15% and a refined size of 3 μm; thus, they are actually embedded in the martensite matrix as isolated islands. These results open a path for the designing and manufacturing of new low-density steels having high yield strengths.