Advanced SA508-4N RPV steel samples, unadded, P-added, and P+Ce-added, are investigated on their hot ductility behavior. Hot tensile tests are carried out in the temperature range of 750 to 1000 °C through a Gleeble 1500D machine. It is demonstrated that the deformation temperatures of all the three steels are located in the austenite single-phase region. There is no ductility trough present for the P+Ce-added steel, but the unadded one exhibits a deep ductility trough. The reduction of area (RA) of the former is always higher than 75% and increases with rising temperature until reaching ~95% at 900 °C or above, whereas the lowest RA value of the latter is only ~50% at 850 °C. Microanalysis indicates that the grain boundary segregation of P and Ce takes place in the tested P+Ce-added steel. This may restrain the boundary sliding so as to improve the hot ductility behavior of the steel. Furthermore, the addition of P and Ce is able to facilitate the occurrence of the dynamic recrystallization (DR) of the steel, lowering the initial temperature of DR from ~900 to ~850 °C and thereby enhancing the hot ductility performance. Consequently, the combined addition of P and Ce can significantly improve the hot ductility of SA508-4N RPV steel, thereby improving its continuous casting performance and hot workability.

中文翻译：

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痕量杂质磷和稀土铈对SA508-4N RPV钢的高延展性

研究了未添加，P添加和P + Ce添加的高级SA508-4N RPV钢样品的热延性行为。通过Gleeble 1500D机器在750至1000°C的温度范围内进行热拉伸测试。结果表明，三种钢的变形温度均位于奥氏体单相区。添加P + Ce的钢不存在延性槽，但是未添加的钢则具有较深的延性槽。前者的面积减少率（RA）始终高于75％，并且随着温度的升高而增加，直到在900°C或更高温度下达到〜95％，而后者的最低RA值在850°C时仅为〜50％。 。显微分析表明，P和Ce的晶界偏析发生在测试的添加P + Ce的钢中。这可以限制边界滑动，从而改善钢的热延性行为。此外，P和Ce的添加能够促进钢的动态再结晶（DR）的发生，将DR的初始温度从〜900降低至〜850°C，从而提高热延展性能。因此，P和Ce的组合添加可以显着改善SA508-4N RPV钢的热延展性，从而改善其连续铸造性能和热加工性。