Effect of welding heat input on microstructural evolution, precipitation behavior and resultant properties of the simulated CGHAZ in high-N V-alloyed steel
Effect of welding heat input on microstructural evolution, precipitation behavior and resultant properties of the simulated CGHAZ in high-N V-alloyed steel
复制标题
焊接热输入对高氮 V 合金钢中模拟 CGHAZ 的显微组织演变、析出行为和最终性能的影响
DOI：
10.1016/j.matchar.2020.110201
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发表时间：
2020-04-01
影响因子：
4.7
通讯作者：
Xian, Shangtong
中科院分区：
文献类型：
--
作者：
Zhang, Jing;Xin, Wenbin;Xian, Shangtong
使用 Gleeble-1500D 热机械模拟器对高 N V 合金钢中模拟 CGHAZ 的显微组织演变、V(C,N) 析出和最终机械性能进行了比较研究，以从 800 ℃ 到 500 ℃ 的冷却时间 (t(8/5)) 为特征。金相分析表明，当t(8/5)从30 s增加到90 s时，主要组织由板条贝氏体转变为粒状贝氏体，然后在t(8/5)为180 s时转变为晶内铁素体。随着t(8/5)的增加，纳米级V(C,N)沉淀物变粗，同时数密度略有增加。此外，取向关系[001](α)//[1 (1) over bar0](v(C,N))降低了界面结构能(MC/α)并增强了铁素体基体中V(C,N)的析出。此外，由于显微组织、析出物和晶界的综合作用，显微硬度逐渐降低。冲击韧性先下降后上升，在t(8/5)为180 s时达到最佳值。此外，晶内铁素体尤其是针状铁素体的形成以及大角度晶界分数的增加可以完全弥补晶界铁素体含量增加以及粗化有效晶粒尺寸和析出物所造成的不利影响。此外，240 ppm的高氮含量加速了奥氏体区域V(C,N)的析出，亚微米V(C,N)析出物可以通过提供异质形核位点来促进晶内铁素体的形成，同时结合较高的焊接热输入导致的较大的原奥氏体晶粒尺寸。
The effect of welding heat input characterized by the cooling time taken from 800 degrees C to 500 degrees C (t(8/5)) on the microstructural evolution, V(C,N) precipitation and resultant mechanical properties of the simulated CGHAZ in high-N V-alloyed steel was comparatively investigated using a Gleeble-1500D thermomechanical simulator. Metallographic analysis indicated that the dominant microstructure transformed from lath bainite to granular bainite when t(8/5) increased from 30 s to 90 s and then changed to intragranular ferrite at t(8/5 )of 180 s. The nanoscale V(C,N) precipitates were coarsened as t(8/5) increased, coupled with a slightly increased number density. Furthermore, the orientation relationship [001](alpha)//[1 (1) over bar0](v(C,N)) reduced the interfacial structural energy (MC/alpha) and enhanced the V(C,N) precipitation in the ferrite matrix. Moreover, the microhardness progressively decreased due to the combined effect of microconstituents, precipitates and grain boundaries. The impact toughness first decreased and then increased, and the optimal value was obtained at t(8/5 )of 180 s. Furthermore, the formation of intragranular ferrite, especially acicular ferrite, and the increased fraction of high angle grain boundaries could completely remedy the detrimental effect caused by the increased content of grain boundary ferrite and the coarsened effective grain size and precipitates. In addition, the high nitrogen content of 240 ppm accelerated V(C,N) precipitation in the austenite region, and the submicron V(C,N) precipitates could promote the formation of intragranular ferrite by providing heterogeneous nucleation sites, in combination with the larger prior austenite grain size caused by higher welding heat input.