利用光学显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)、透射电镜(TEM)结合析出动力学和冲击实验,研究了不同Mn含量(4.3％,6.9％,9.7％,质量分数,下同)对22％Cr节镍型双相不锈钢700℃时效析出相形成和韧性的影响.结果表明:随Mn含量由4.3％增加至9.7％,时效76h,析出形貌分别为铁素体/奥氏体(δ/γ)界面细小σ相颗粒析出和铁素体晶内σ相/二次奥氏体(γ2)共析组织.Mn含量增加使Avrami指数n减小,反应常数B增大,Mn元素参与并促进σ相析出,σ相开始析出和完全析出时间均提前,开始析出与完全析出的时间间隔增大,析出速率降低.时效过程中δ相分解量低于1％(体积分数,下同)对冲击韧度影响不大,δ相分解量由1％增至5％会显著降低冲击韧度.Mn含量增加在时效前期对冲击韧度有利,时效中期则会促使δ相分解量更早超过1％,导致冲击韧度快速下降.
The effect of different Mn contents on the σ 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 σ phase in δ/γ phase boundary to σ/γ2 eutectoid structure within δ phase with the addition of Mn from 4.3５ to 9.7％ and 76 hours aging.The increase of Mn content can decrease Avrami exponent n and increase reaction constant B,and the accelerating of σ-phase precipitation with higher Mn addition is due to the participation of Mn.Increasing Mn content can make initial time and ending time of σ-phase precipitation earlier and expand the interval between the initial time and ending time of σ-phase precipitation,that is,the more Mn addition,the earlier precipitation beginning time of σ-phase and the lower precipitation rate of it.The impact toughness is not sensitive to 1％ transformation fraction of δ-ferrite,but it drops rapidly while the transformation fraction of δ-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 δ-ferrite more than 1％ earlier at the middle stage of aging time.
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