核电用316LN不锈钢在不同温度下的形变行为和机理
发布时间：2019-07-08 11:06
【摘要】：中国核电的发展路线以压水堆为主,技术处在二：代,接近第三代。国际上所有核电站对安全性都有着严格的要求,且由于核电用材料服役环境复杂,其在选材上有着苛刻的条件。316LN不锈钢具有优良的耐腐蚀性及综合力学性能,是第三代压水堆一回路主管道和堆内构件的首选材料。本论文通过对相关文献的调研,结合实际生产的需求,从以下几个方面对核电用316LN不锈钢进行了研究。 首先,对核电用316LN不锈钢的锻材进行了热压缩试验,通过热压缩应力-应变曲线计算出热激活能,建立了本构方程,并绘制了热加工图,直观地表明了热加工参数优先选择能量耗散率较高的[区域。同时,通过显微组织分析,得到了高温压缩形变过程中的动态再结晶规律。 其次,对316LN不锈钢的锻材和轧材从室温到1000℃范围内进行了拉伸试验。通过对应力-应变曲线和硬化速率-应变曲线的分析,以及对断口形貌和断口附近的显微硬度和组织的观察分析,得到了不同温度下拉伸形变的特点和机制。 在600℃以下温度拉伸时,锻材和轧材的硬化速率-应变曲线均可分为段：平稳段、下降段和塑性失稳段。锻材初始组织中的高密度位错使得动态回复速度加快,从而导致了锻材的硬化-应变曲线平稳段中无明显的上升部分。锻材的屈服强度明显高于轧材,这是由于锻材初始组织中的高密度位错促进了材料的动态回复,但还不足以消除初始组织对拉伸性能的影响。在此温度段拉伸形变机制以滑移和孪晶为主,随着温度的升高,位错交滑移逐渐增多。 在700℃拉伸时,其硬化速率-应变曲线可以分为两段：下降段和塑性失稳段。600℃至700℃拉伸时,氮、碳原子的扩散速率与位错运动速率相近,对位错形成反复“钉轧”作用,使得锻材和轧材均出现了动态应变时效现象,引起了硬化速率-应变曲线锯齿波状的波动,锻材在700℃时的波动现象最为明显。轧材700℃拉伸时由于位错交滑移导致试样中出现了大量的位错塞积,而锻材则出现位错网。位错运动机制的变化造成了,700℃时拉伸形变硬化行为的明显不同和形变组织的较大差异。 800℃C以上伸时,锻材和轧材硬化速率-应变曲线也可分为三段：快速下降段、平稳段、塑性失稳段。锻材原始组织中的亚晶和高密度位错对1000℃时拉伸行为已没有太大的影响。在此温度段的软化机制有高温组织多边形化和动态再结晶两种,锻材中大量的亚晶和高密度位错,使其具有更多的再结晶核心,从而导致其具有较短的快速下降阶段。轧材在900℃,锻材在950℃发生完全再结晶。 最后,对316LN不锈钢的锻材和轧材在350℃和600℃下不同应力下500-2000小时进行了预蠕变试验。通过对预蠕变试验后的试样进行性能测试及显微分析,得到了性能和组织变化的规律。 在预蠕变过程中,温度越高,时间越长,氮原子迁移偏聚越明显。元素的扩散偏聚对材料的组织和性能产生如下影响：造成基体层错能的提高,从而使扩展位错变窄；氮和铬的扩散迁移在600℃保温2000小时后形成了短程有序的铬氮原子团,使得试样中出现了位错对；试样显微硬度上升；部分晶界出现了宽化,晶界处的硬度明显要高于晶内；在氮原子的迁移以及长时间受力下造成的位错变化的共同作用下,轧材的屈服强度有明显的上升。 锻材初始组织中的大量亚晶和高密度位错使预蠕变后的性能和组织产生了影响。高密度位错在预蠕变初期的回复作用使得锻材在预蠕变500小时后显微硬度上升幅度明显低于轧材；亚晶界在预蠕变过程中发生了分解迁移,随着时间延长,有的亚晶界因分解迁移变薄直至消失,这种分解使得亚晶界在高温下易于滑动,但同时使得试样中不同方向运动的位错增多,这些位错相遇时相互反应能够产生位错网。在350℃／20MPa预蠕变500小时的试样出现了完整的近似四边形位错网,600℃／120MPa预蠕变500小时的试样则出现了近似六边形的波浪状位错网。位错网是一个较为稳定的结构,能够延缓蠕变的发生。随着预蠕变时间的延长,由于位错的持续运动,这些位错网孔的直径逐渐变小直至消失。
文内图片：
图片说明：(丨4钢热加工图的各种应用…I
[Abstract]:The development route of China's nuclear power is based on the PWR, and the technology is in the second generation, which is close to the third generation. All the nuclear power stations in the world have strict requirements for safety, and because of the complex service environment of nuclear power materials, it has harsh conditions in material selection. The 316LN stainless steel has excellent corrosion resistance and comprehensive mechanical properties. And is the preferred material of the third generation pressurized water reactor primary pipeline and the inner member of the reactor. Based on the investigation of the relevant literature and the demand of practical production, the 316LN stainless steel for nuclear power has been studied from the following aspects. In the first place, the thermal compression test is carried out on the forged material of the 316LN stainless steel for nuclear power, the thermal activation energy is calculated by the thermal compression stress-strain curve, the constitutive equation is established, and the hot working diagram is drawn, which shows that the preferential energy dissipation rate of the hot working parameter is higher[area And the dynamic recrystallization rule in the process of high-temperature compression deformation is obtained through the analysis of the micro-structure. Law. Second, the forged and rolled materials of 316LN stainless steel were pulled from room temperature to 1000 鈩，
本文编号：2511545
文内图片：
图片说明：(丨4钢热加工图的各种应用…I
[Abstract]:The development route of China's nuclear power is based on the PWR, and the technology is in the second generation, which is close to the third generation. All the nuclear power stations in the world have strict requirements for safety, and because of the complex service environment of nuclear power materials, it has harsh conditions in material selection. The 316LN stainless steel has excellent corrosion resistance and comprehensive mechanical properties. And is the preferred material of the third generation pressurized water reactor primary pipeline and the inner member of the reactor. Based on the investigation of the relevant literature and the demand of practical production, the 316LN stainless steel for nuclear power has been studied from the following aspects. In the first place, the thermal compression test is carried out on the forged material of the 316LN stainless steel for nuclear power, the thermal activation energy is calculated by the thermal compression stress-strain curve, the constitutive equation is established, and the hot working diagram is drawn, which shows that the preferential energy dissipation rate of the hot working parameter is higher[area And the dynamic recrystallization rule in the process of high-temperature compression deformation is obtained through the analysis of the micro-structure. Law. Second, the forged and rolled materials of 316LN stainless steel were pulled from room temperature to 1000 鈩，
本文编号：2511545
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