To explore the optimum use of stabilised elements and study the influences of stabilisation in 18Cr–2Mo grades, the Nb and Nb + Ti microalloying investigation focused on the relationships of the microstructure and mechanical properties of the microalloyed 18Cr–2Mo ferritic stainless steel thick plates. Thermo-Calc calculation was performed to predict the equilibrium phase diagrams. Afterwards, the microstructure, i.e. grain size and precipitation, of as-annealed specimens was analysed by means of optical microscopy, scanning electron microscopy and transmission electron microscopy, X-ray diffraction and energy-dispersive spectroscopy. Also, electron backscatter diffraction mapping was constructed to characterise grain boundary. The mechanical properties, including tensile strength and impact toughness, were tested to correlate with the microstructure. The results show that the grain sizes of Nb-stabilised steel are comparatively smaller, which is related to the fine precipitation at the grain boundaries and beneficial to the impact toughness. The increase in its strength is not apparent due to the inhomogeneous grain sizes. The grain boundary characters are similar, which is not the main factor related to their mechanical properties. When Ti is added, TiN forms above the liquidus, and large TiN particles evidently impair impact toughness.

中文翻译：

---

Nb-和Nb + Ti稳定的18Cr-2Mo铁素体不锈钢的组织和力学性能

为了探索稳定元素的最佳使用并研究18Cr-2Mo钢中稳定化的影响，Nb和Nb + Ti微合金化研究着眼于微合金化18Cr-2Mo铁素体不锈钢厚板的组织与力学性能之间的关系。进行Thermo-Calc计算以预测平衡相图。然后，通过光学显微镜，扫描电子显微镜和透射电子显微镜，X射线衍射和能量色散光谱分析退火样品的微观结构，即晶粒尺寸和沉淀。同样，构造了电子背散射衍射图谱来表征晶界。机械性能，包括拉伸强度和冲击韧性，被测试与微观结构相关。结果表明，Nb稳定钢的晶粒尺寸相对较小，这与晶界处的细小析出有关，并且有利于冲击韧性。由于不均匀的晶粒尺寸，其强度的增加并不明显。晶界特征是相似的，这不是与其力学性能有关的主要因素。当添加Ti时，TiN在液相线上方形成，并且大的TiN颗粒明显损害冲击韧性。晶界特征是相似的，这不是与其力学性能有关的主要因素。当添加Ti时，TiN在液相线上方形成，并且大的TiN颗粒明显损害冲击韧性。晶界特征是相似的，这不是与其力学性能有关的主要因素。当添加Ti时，TiN在液相线上方形成，并且大的TiN颗粒明显损害冲击韧性。