实测了核电转子用25Cr2Ni4MoV钢的高温应力-应变曲线和热物性参数, 基于 ABAQUS软件建立了锻造过程孔洞闭合的有限元模型, 模拟了不同温度和变形量下的孔洞闭合行为. 研究发现, 典型的孔洞闭合过程分为3个阶段, 即闭合速率减小-增加-再次减小. 模拟结果表明, 900-1200℃时孔洞几乎在同一压下率(约25%)下闭合, 即孔洞闭合对变形温度不敏感. 在模拟结果的基础上, 进一步设计了孔洞闭合后焊合过程的物理模拟实验, 研究了恒应变速率(0.01 s-1)下压下率(25%-45%)和变形温度(900-1200℃)对闭合孔洞焊合过程的影响. 焊合界面的拉伸实验结果表明, 较高的温度和闭合后持续的塑性变形能极大地促进闭合界面的焊合, 当变形温度大于1000℃, 压下率为35\%时, 闭合界面结合强度可达基体强度, 孔洞实现完全焊合; 当温度降至900℃时, 孔洞需45\%的压下率才能完全焊合. 最后, 基于拉伸断口的形貌, 对影响孔洞焊合的因素进行了讨论.
Based on the measured stress-strain curves and thermo-physical data of 25Cr2Ni4MoV steel, a FEM model of void closure in heavy forging process was established through ABAQUS software. The void closure behaviors under different hot plasticity conditions have been investigated. The FEM results showed three distinct stages during the void closure. The voids with the same position in a cylindrical specimen close up at a similar height reduction ratio (ΔH/H0) around 25\% at different temperatures, which indicates that the void closure is not sensitive to the deformation temperature. On basis of the FEM results, a physical-simulated experiment for void bonding process has been performed through compression tests on a hollow cylindrical specimens, with deformation temperatures ranging from 900 ℃ to 1200 ℃, ΔH/H0 from 25\% to 45\% and a constant strain rate 0.01 s-1. The experimental results have shown that the ΔH/H0 for the void completely bonded at 1200, 1100 and 1000℃ are all about 35%, but increases to 45\% when the deformation temperature decreased to 900℃, which confirms that void bonding is a diffusion controlled process. Through the experimental results, it can be further demonstrated the high temperature combined with severe deformation can enhance the ability of atoms transition and decrease the micro-gap between contacted surfaces. Finally, the influencing factors on the bonding efficiency were investigated through SEM observation on the fractured surface of the tensile specimen with internal closed void.
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