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The effect of different Mn contents on the <i>σ</i> phase and toughness of 22%Cr (mass fraction, the same below) low-nickel DSS by means of OM, XRD, SEM, TEM, precipitation kinetics and Charpy impact tests was studied. The results show that the morphology of precipitated phases changes from tiny granulated <i>σ</i> phase in <i>δ</i>/<i>γ</i> phase boundary to <i>σ</i>/<i>γ</i>₂ eutectoid structure within <i>δ</i> phase with the addition of Mn from 4.3% to 9.7% and 76 hours aging. The increase of Mn content can decrease Avrami exponent <em>n</em> and increase reaction constant <em>B</em>, and the accelerating of <i>σ</i>-phase precipitation with higher Mn addition is due to the participation of Mn. Increasing Mn content can make initial time and ending time of <i>σ</i>-phase precipitation earlier and expand the interval between the initial time and ending time of <i>σ</i>-phase precipitation, that is, the more Mn addition, the earlier precipitation beginning time of <i>σ</i>-phase and the lower precipitation rate of it. The impact toughness is not sensitive to 1% transformation fraction of <i>δ</i>-ferrite, but it drops rapidly while the transformation fraction of <i>δ</i>-ferrite increases from 1% to 5%. More addition of Mn is good to impact toughness at the early stage of aging treatment, but the impact toughness decreases rapidly by accelerating the transformation fraction of <i>δ</i>-ferrite more than 1% earlier at the middle stage of aging time.