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首页> 外文期刊>Materials Science and Engineering >Interpretation of significant decrease in cryogenic-temperature Charpy impact toughness in a high manganese steel
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Interpretation of significant decrease in cryogenic-temperature Charpy impact toughness in a high manganese steel

机译：解释高锰钢的低温夏比冲击韧性显着降低

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The grain boundary segregation and precipitation and associated deformed microstructure under cryogenic-temperature and dynamic-loading conditions were systematically investigated by means of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and electron back-scattered diffraction (EBSD). The studied steels exhibit equiaxed grains with a similar grain size of 12.0–13.3 µm. The twinning and dislocation slip were observed as the main deformation modes under cryogenic-temperature and dynamic-loading conditions. However, the secondary twinning system is suppressed and plastic deformation by dislocation slip is small in the steel annealed at 800 °C for 3 h, leading to a significant decrease in Charpy impact toughness at − 196 °C. The HAADF-STEM results show that there are numerous (Cr,Mn)23C6-type carbides along grain boundaries and the Cr or C peaks have been detected at grain boundaries without (Cr,Mn)23C6-type carbides in the steel annealed at 800 °C for 3 h, whereas these carbides and Cr or C peaks were not observed in the steel annealed at 300 °C for 3 h. However, the Mn, P, S, Si and Cu peaks were not observed at grain boundaries in both steels by means of STEM-EDX. The critical shear twinning stress is high in the steel annealed at 800 °C for 3 h due to heavier grain boundary segregation. Meanwhile, the local stress concentration at grain boundaries may be relaxed because the crack may easily nucleate at grain boundaries whose cohesion is weakened by heavier grain boundary segregation or (Cr,Mn)23C6-type carbides/matrix interfaces whose bonding strength is relatively small. Therefore, the secondary twinning system is relatively hardly activated and plastic deformation by dislocation slip is relatively small for the steel annealed at 800 °C for 3 h.
机译：利用高角度环形暗场扫描透射电子显微镜（HAADF-STEM），透射电子显微镜（TEM），高分辨率TEM（HRTEM）和电子背散射衍射（EBSD）。所研究的钢具有等轴晶粒，晶粒尺寸类似，为12.0-13.3μm。孪晶和位错滑移是低温和动态载荷条件下的主要变形模式。但是，在800 C退火3 h的钢中，二次孪晶体系得到抑制，位错滑移引起的塑性变形很小，导致在-196 C下的夏比冲击韧性大大降低。 HAADF-STEM结果表明，在800℃退火的钢中，沿晶界存在大量（Cr，Mn）23C6型碳化物，并且在没有（Cr，Mn）23C6型碳化物的晶界处检测到Cr或C峰。在300°C退火3 h的钢中未观察到这些碳化物和Cr或C峰。然而，通过STEM-EDX，在两种钢的晶界都未观察到Mn，P，S，Si和Cu峰。由于较重的晶界偏析，在800 C退火3 h的钢中的临界剪切孪生应力很高。同时，由于裂纹可能在晶界容易形核，而该晶界由于较重的晶界偏析或结合强度相对较小的（Cr，Mn）23C6型碳化物/基体界面而减弱了内聚力，因此可以放松晶界处的局部应力集中。因此，对于在800 C退火3 h的钢，次级孪生系统很难激活，并且位错滑移引起的塑性变形也相对较小。

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