In the coarse grain heat-affected zone (CGHAZ) of a low carbon Mo–V–Ti–B steel subjected to a simulative welding thermal cycle with a heat input as high as 75 kJ/cm, the influence of an increase in nitrogen content from 0.0085 to 0.0144 wt% on the microstructures and impact properties of the steel was comparatively estimated using Gleeble-3800 simulation, microstructure characterization and impact testing. With a rise in the nitrogen content, the number of fine and coarse particles also increased. An increase in the number of fine precipitates can effectively pin the prior austenite grain (PAG) boundary and inhibit the grain growth, resulting in the refinement of PAG in the CGHAZ. The intragranular and intergranular V-containing coarse particles effectively promoted the nucleation of intragranular acicular ferrite (IGAF) and grain boundary polygonal ferrite (GBPF). Accordingly, the contents of heterogeneously-nucleated IGAF and polygonal ferrite (PF) increased; however, the bainite content decreased with a rise in N content, leading to a prominent microstructure refinement in this CGHAZ with a high heat input. Furthermore, the nitrogen addition led to the formation of finer and more dispersed martensite-austenite (M/A) constituents in the CGHAZ. Therefore, the impact toughness of this CGHAZ was enhanced. This can be attributed to the microstructure refinement of the CGHAZ, which in turn was ascribed to an increasing nitrogen.

在热输入高达 75 kJ/cm 的模拟焊接热循环下，低碳 Mo-V-Ti-B 钢的粗晶热影响区 (CGHAZ) 中，氮含量增加的影响使用 Gleeble-3800 模拟、微观结构表征和冲击测试，比较估计钢的微观结构和冲击性能的 0.0085 至 0.0144 wt%。随着氮含量的增加，细颗粒和粗颗粒的数量也增加。细小析出物数量的增加可以有效地钉住原奥氏体晶粒（PAG）边界并抑制晶粒长大，从而使 CGHAZ 中的 PAG 细化。晶内和晶间含钒粗颗粒有效地促进了晶内针状铁素体（IGAF）和晶界多边形铁素体（GBPF）的形核。相应地，异相成核IGAF和多边形铁素体（PF）的含量增加；然而，贝氏体含量随着 N 含量的增加而降低，导致该高热输入的 CGHAZ 显着的微观结构细化。此外，氮的添加导致在 CGHAZ 中形成更细、更分散的马氏体 - 奥氏体 (M/A) 成分。因此，该CGHAZ 的冲击韧性得到了增强。这可归因于 CGHAZ 的微观结构细化，而这又归因于氮的增加。异相成核IGAF和多边形铁素体（PF）的含量增加；然而，贝氏体含量随着 N 含量的增加而降低，导致该高热输入的 CGHAZ 显着的微观结构细化。此外，氮的添加导致在 CGHAZ 中形成更细、更分散的马氏体 - 奥氏体 (M/A) 成分。因此，该CGHAZ 的冲击韧性得到了增强。这可归因于 CGHAZ 的微观结构细化，而这又归因于氮的增加。异相成核IGAF和多边形铁素体（PF）的含量增加；然而，贝氏体含量随着 N 含量的增加而降低，导致该高热输入的 CGHAZ 显着的微观结构细化。此外，氮的添加导致在 CGHAZ 中形成更细、更分散的马氏体 - 奥氏体 (M/A) 成分。因此，该CGHAZ 的冲击韧性得到了增强。这可归因于 CGHAZ 的微观结构细化，而这又归因于氮的增加。添加氮导致在 CGHAZ 中形成更细、更分散的马氏体-奥氏体 (M/A) 成分。因此，该CGHAZ 的冲击韧性得到了增强。这可归因于 CGHAZ 的微观结构细化，而这又归因于氮的增加。添加氮导致在 CGHAZ 中形成更细、更分散的马氏体-奥氏体 (M/A) 成分。因此，该CGHAZ 的冲击韧性得到了增强。这可归因于 CGHAZ 的微观结构细化，而这又归因于氮的增加。