Influence of nitrogen on 475°C embrittlement of high-chromium ferritic steels
Influence of nitrogen on 475°C embrittlement of high-chromium ferritic steels
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氮对高铬铁素体钢475℃脆性的影响
DOI：
10.1179/030634579790438327
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
MSc Tyne. Z. F. Mazur
中科院分区：
文献类型：
--
作者：
A. Hendry;Z. Mazur;K. Jack;MSc Tyne. Z. F. Mazur
铬含量大于13wt -%的铁铬合金在550-800℃范围内的硬化是众所周知的，这归因于σ-FeCr的形成。较低温度下的严重脆化，通常被称为“475℃脆化”，人们对其了解较少，并将其归因于σ相、有序的Fe-Cr超晶格和富cr铁氧体的相干析出。叙述了控制氮浓度变化对fe - 22wt -%Cr合金的组织和性能的影响。通过显微硬度测量和透射电镜观察合金在500℃时效下力学性能随时效时间的变化。当超过临界氮浓度时，微观结构会发生明显的变化，并伴有严重的脆化。然后合金含有高密度的相干盘状颗粒和高相关应变，并且与所提出的模型一致，其中脆化是取代-间隙溶质-原子聚类的结果。由于Fe-Cr体系中存在混相隙，高铬合金的团簇倾向因氮的存在而增强，并且与间隙团簇相关的晶格应变导致脆化。Cr-N团簇剪切的化学强化模型令人满意地解释了所观察到的硬度增加。团簇的形貌取决于合金相对于Fe-Cr体系中相干旋轴的时效温度。
The hardening of iron-chromium alloys containing more than 13 wt-%Cr in the temperature range 550–800°C is well known and is ascribed to the formation of σ-FeCr. Severe embrittlement at lower temperatures, commonly referred to as ‘475°C embrittlement’, is less well understood and has been variously ascribed to σ-phase, ordered Fe-Cr superlattices, and coherent precipitation of Cr-rich ferrite. The microstructure and properties of Fe-22 wt-%Cr alloys resulting from controlled changes in nitrogen concentration are described. The variation of mechanical properties with ageing time at 500°C was followed using microhardness measurements, and corresponding changes of microstructure were observed by transmission electron microscopy. A pronounced change in microstructure accompanied by severe embrittlement occurs when a critical nitrogen concentration is exceeded. The alloy then contains a high density of coherent disc-shaped particles with high associated strain and is consistent with the proposed model in which embrittlement is a result of substitutional-interstitial solute-atom clustering. The tendency of high-Cr alloys to cluster as a result of the miscibility gap in the Fe-Cr system is enhanced by the presence of nitrogen, and the lattice strains associated with interstitial clusters result in embrittlement. A chemical-strengthening model for the shearing of Cr-N clusters accounts satisfactorily for the observed increase in hardness. The morphology of the clusters depends on the ageing temperature of the alloy relative to the coherent spinodal in the Fe-Cr system.