Abstract The mechanism of formation of reverted austenite in a low carbon low alloy system was comprehensively studied by 3D atom probe tomography and Thermo-Calc simulation. It was observed that low C-content provided the condition for nucleation of reverted austenite at lath boundaries, while the alloying elements, Mn, Ni and Cu led to the growth of reverted austenite. Mo provided diverse impact on mechanical properties of steel at high temperature. (1) The diffusional direction of Mo atoms was controlled by the partitioning of Mo; (2) Mo C co-segregation layers, nano Mo C clusters, nano Mo clusters and MoC precipitates were formed at two-phase interfaces; (3) Mo formed nano Mo C clusters and MoC precipitates at lath boundaries or in the matrix; (4) Mo promoted the formation of Nb carbides and was dissolved in carbides to produce (NbxMo1-x)C precipitates. High resolution transmission electron microscopy images of (NbxMo1-x)C precipitates showed that they had face-centered cubic structure and the lattice constant was in the range of 0.440–0.445 nm. Nano Cu precipitates were observed in reverted austenite. Mo C co-segregation layers, nano Mo C clusters, nano Mo clusters and MoC precipitates formed at γ/α interfaces effectively enhanced the grain boundary strength. Nano Mo C clusters, MoC precipitates and (NbxMo1-x)C precipitates in the matrix effectively pinned dislocations and prevented movement of dislocations. The combined effect led to good fire resistance and heat resistance properties of studied steel.

中文翻译：

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低碳低合金体系中回复奥氏体形成机制和Mo行为的原子尺度研究

摘要 通过3D原子探针断层扫描和Thermo-Calc模拟，综合研究了低碳低合金体系中回复奥氏体的形成机制。观察到低C含量为板条边界处的回复奥氏体形核提供了条件，而合金元素Mn、Ni和Cu导致回复奥氏体的生长。钼对钢在高温下的机械性能有不同的影响。(1) Mo原子的扩散方向受Mo的分配控制；(2)两相界面形成Mo C共偏析层、纳米Mo C团簇、纳米Mo团簇和MoC析出物；(3) Mo形成纳米Mo C团簇，MoC在板条边界或基体中析出；(4) Mo促进Nb碳化物的形成并溶解在碳化物中产生(NbxMo1-x)C析出物。(NbxMo1-x)C 析出物的高分辨率透射电子显微镜图像显示它们具有面心立方结构，晶格常数在 0.440-0.445 nm 范围内。在回复奥氏体中观察到纳米铜沉淀。在γ/α界面形成的Mo C共偏析层、纳米Mo C团簇、纳米Mo团簇和MoC析出物有效地增强了晶界强度。基体中的纳米 Mo C 簇、MoC 沉淀和 (NbxMo1-x)C 沉淀有效地固定位错并防止位错移动。综合作用导致所研究的钢具有良好的耐火性和耐热性。(NbxMo1-x)C 析出物的高分辨率透射电子显微镜图像显示它们具有面心立方结构，晶格常数在 0.440-0.445 nm 范围内。在回复奥氏体中观察到纳米铜沉淀。在γ/α界面形成的Mo C共偏析层、纳米Mo C团簇、纳米Mo团簇和MoC析出物有效地增强了晶界强度。基体中的纳米 Mo C 簇、MoC 沉淀和 (NbxMo1-x)C 沉淀有效地固定位错并防止位错移动。综合作用导致所研究的钢具有良好的耐火性和耐热性。(NbxMo1-x)C 析出物的高分辨率透射电子显微镜图像显示它们具有面心立方结构，晶格常数在 0.440-0.445 nm 范围内。在回复奥氏体中观察到纳米铜沉淀。在γ/α界面形成的Mo C共偏析层、纳米Mo C团簇、纳米Mo团簇和MoC析出物有效地增强了晶界强度。基体中的纳米 Mo C 簇、MoC 沉淀和 (NbxMo1-x)C 沉淀有效地固定位错并防止位错移动。综合作用导致所研究的钢具有良好的耐火性和耐热性。在γ/α界面形成的Mo C共偏析层、纳米Mo C团簇、纳米Mo团簇和MoC析出物有效地增强了晶界强度。基体中的纳米 Mo C 簇、MoC 沉淀和 (NbxMo1-x)C 沉淀有效地固定位错并防止位错移动。综合作用导致所研究的钢具有良好的耐火性和耐热性。在γ/α界面形成的Mo C共偏析层、纳米Mo C团簇、纳米Mo团簇和MoC析出物有效地增强了晶界强度。基体中的纳米 Mo C 簇、MoC 沉淀和 (NbxMo1-x)C 沉淀有效地固定位错并防止位错移动。综合作用导致所研究的钢具有良好的耐火性和耐热性。