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首页> 外文期刊>Materials Science and Engineering >Serrated yielding in an advanced stainless steel Fe-25Ni-20Cr (wt%)
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Serrated yielding in an advanced stainless steel Fe-25Ni-20Cr (wt%)

机译：在高级不锈钢Fe-25Ni-20Cr中的锯齿形屈服（wt％）

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摘要

Understanding serrated yielding behavior resulting from dynamic strain aging (DSA) is essential for design and safety considerations. In this work, uniaxial tensile tests were carried out at temperatures ranging from 298 to 1073 K and strain rates 10(-5) - 10(-3) s(-1) followed by microstructural examination of Fe-25Ni-20Cr (wt%) austenitic stainless steel (Alloy 709), a candidate structural material for Sodium-cooled Fast Reactors. Serrated yielding was found to occur in this alloy in two temperature regimes; low-temperature serrated flow (LT-SF) from 498 to 648 K and high-temperature serrated flow (HT-SF) from 648 to 973 K (depending on the strain rate) with activation energies of 103 +/- 13 kJ/mole and 204 +/- 11 kJ/mole respectively. The critical strain for the occurrence of serrations was found to increase with strain rate as an exponential function with exponent (m + beta) of 0.78 +/- 0.1 and 1.56 +/- 0.2 for the LT-SF and HT-SF regimes respectively. Based on the activation energies and m + 13 values, diffusion of interstitial atoms has been suggested to be responsible for serrated flow in the LT-SF regime while Cr atom migration was inferred to be responsible for DSA in the HT-SF regime. Manifestations of DSA in the Alloy 709 were observed including peaks and/or plateaus in flow stresses along with negative strain rate sensitivity at intermediate temperatures. However, no loss in ductility was observed within DSA regime attributed to the relatively high work hardening rate and strain-hardening exponent. The samples deformed in DSA regime showed planar substructure while equiaxed subgrains formed at higher temperatures. The fraction of low angle grain boundaries after deformation exhibited a valley at intermediate temperatures believed to be another manifestation of the DSA.
机译：了解动态应变时效（DSA）导致的锯齿状屈服行为对于设计和安全考虑至关重要。在这项工作中，在298至1073 K的温度和10（-5）-10（-3）s（-1）的应变速率下进行了单轴拉伸试验，然后对Fe-25Ni-20Cr（wt％ ）奥氏体不锈钢（合金709），是钠冷快堆的候选结构材料。发现该合金在两个温度范围内出现锯齿状屈服。活化温度为103 +/- 13 kJ / mole的低温锯齿状流（LT-SF）从498至648 K和高温锯齿状流（HT-SF）从648至973 K（取决于应变率）和204 +/- 11 kJ / mole。发现出现锯齿的临界应变随着应变速率的增加而增加，其中LT-SF和HT-SF机制的指数（m + beta）分别为0.78 +/- 0.1和1.56 +/- 0.2。根据活化能和m + 13值，已提出间隙原子的扩散是造成LT-SF模式锯齿状流动的原因，而铬原子的迁移则被认为是HT-SF模式中DSA的原因。在中间温度下，观察到合金709中DSA的表现，包括流动应力的峰值和/或平稳期以及负应变速率敏感性。然而，在DSA方案中未观察到延性损失，这归因于较高的加工硬化率和应变硬化指数。在DSA模式下变形的样品显示出平面亚结构，而在较高温度下形成了等轴亚晶。变形后低角度晶界的分数在中间温度下显示出谷，这被认为是DSA的另一种表现。

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