Herein, several treatments, including modified quenching and tempering (QT) treatment, ultrafast cooling and tempering (UFC-T) treatment, and ultrafast cooling, intercritical quenching, and tempering (UFC-LT) treatment, are used to prepare low-Ni steels and compared with conventional QT treatment. All the three treatments enable low-Ni steel to achieve equivalent or better cryogenic toughness than 9% Ni steel. The toughening effect of modified QT treatment is better than that of UFC-T treatment, which is attributed to the increase in density of high-angle grain boundaries (HAGBs). For modified QT treatment, fine equiaxed prior austenite grains and weak variant selection of martensite transformation lead to higher density HAGBs. Although the coarse elongated prior austenite grains in UFC-T treatment are beneficial to Bain grouping and not conducive to matrix refinement, the intercritical quenching step in UFC-LT treatment further increases the density of HAGBs due to the jagged prior austenite grain boundaries (PAGBs) and fresh martensite formed along PAGBs. Therefore, UFC-LT treatment achieves high-density HAGBs and excellent cryogenic toughness similar to modified QT treatment. Due to the wider tempering temperature process window, UFC-LT treatment is the optimal process route for low-Ni liquefied natural gas tank steel.

中文翻译：

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低温韧性优异的低镍液化天然气罐钢的工艺路线

在这里，几种处理方法，包括改进的淬火和回火（QT）处理、超快冷和回火（UFC-T）处理以及超快冷、临界间淬火和回火（UFC-LT）处理，用于制备低镍钢。并与常规 QT 治疗进行比较。所有三种处理方法都使低镍钢达到与 9% Ni 钢相当或更好的低温韧性。改性QT处理的增韧效果优于UFC-T处理，这归因于高角度晶界（HAGBs）密度的增加。对于改良的 QT 处理，细小的等轴原始奥氏体晶粒和马氏体转变的弱变体选择导致更高密度的 HAGB。尽管 UFC-T 处理中粗细拉长的原奥氏体晶粒有利于贝恩组化而不利于基体细化，但由于锯齿状的原奥氏体晶界 (PAGB)，UFC-LT 处理中的临界间淬火步骤进一步增加了 HAGB 的密度和沿 PAGB 形成的新鲜马氏体。因此，UFC-LT 处理实现了类似于改良 QT 处理的高密度 HAGB 和优异的低温韧性。由于回火温度工艺窗口较宽，UFC-LT处理是低Ni液化天然气罐钢的最佳工艺路线。UFC-LT 处理可实现高密度 HAGB 和类似于改良 QT 处理的出色低温韧性。由于回火温度工艺窗口较宽，UFC-LT处理是低Ni液化天然气罐钢的最佳工艺路线。UFC-LT 处理可实现高密度 HAGB 和类似于改良 QT 处理的出色低温韧性。由于回火温度工艺窗口较宽，UFC-LT处理是低Ni液化天然气罐钢的最佳工艺路线。