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低碳Nb-Ti二元微合金鋼析出過程的演變

Evolution of precipitates in Nb-Ti binary low-carbon microalloyed steels

  • 摘要: 建立規則溶液亞點陣模型計算了不同溫度(1073~1523 K)下低碳Nb-Ti二元微合金鋼(Nb質量分數為0.023%,Ti質量分數為0.012%)中碳氮化物析出相的平衡摩爾分數、化學驅動力和各組元摩爾分數,對微合金鋼中析出粒子演變規律進行研究,并利用透射電鏡觀察及能譜分析驗證這種析出模式.計算結果表明,1523 K下析出粒子化學式組成為(Nb0.15Ti0.85)(C0.16N0.84),由富Ti的析出物逐漸過渡至Nb-Ti均勻析出,析出粒子演變順序為(Nb0.15Ti0.85)(C0.16N0.84)、(NbxTi1-x)(CyN1-y)和(Nb0.5Ti0.5)(C0.56N0.44),與實驗結果符合較好.隨著溫度降低,Ti/Nb質量比逐漸減小,得到的TiC比NbC更難溶.對均勻形核及位錯處形核的臨界核心尺寸和相對形核速率進行計算,得到最大形核率即可獲得最細小第二相尺寸的溫度.

     

    Abstract: A thermodynamic model of binary low-carbon microalloyed steel with 0.023% Nb and 0.012% Ti additions was established to calculate the equilibrium molar fraction and chemical driving force of carbonitride precipitation as well as the molar fraction of each element in austenite at temperatures from 1 073 to 1 523 K. The evolution of precipitation in the microalloyed steel was studied, and the precipitation pattern was verified by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The calculating results show that the chemical formula of precipitation particles is (Nb0.15Ti0.85) (C0.16N0.84) at 1523 K, Ti-rich precipitates gradually transit to Nb-Ti uniform precipitates. The evolution order of precipitation particles is (Nb0.15Ti0.85) (C0.16N0.84), (NbxTi1-x) (CyN1-y) and (Nb0.5 Ti0.5) (C0.56 N0.44), which accord with the experimental results. The Ti/Nb mass ratio decreases gradually with decreasing temperature, and TiC is more insoluble than NbC. The critical core size and the relative nucleation rate were computed under two nucleation conditions, and the temperatures at which the size of the second phase is the smallest, i. e. the nucleation rate is maximum are 1 198 K and 1 123 K for homogeneous nucleation and dislocation nucleation, respectively.

     

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