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金属学报  2020, Vol. 56 Issue (6): 874-884    DOI: 10.11900/0412.1961.2019.00310
  本期目录 | 过刊浏览 |
热变形后Ni-30%Fe模型合金中奥氏体的亚动态软化行为
陈文雄1,2, 胡宝佳1,2, 贾春妮1,2, 郑成武1,2(), 李殿中1,2
1.中国科学院金属研究所沈阳材料科学国家研究中心 沈阳 110016
2.中国科学技术大学材料科学与工程学院 沈阳 110016
Post-Dynamic Softening of Austenite in a Ni-30%Fe Model Alloy After Hot Deformation
CHEN Wenxiong1,2, HU Baojia1,2, JIA Chunni1,2, ZHENG Chengwu1,2(), LI Dianzhong1,2
1.Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2.School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
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摘要: 

利用Gleeble热力模拟、EBSD和TEM等方法,研究了Ni-30%Fe合金热变形后奥氏体的亚动态软化行为,分析了微观亚结构演化对奥氏体亚动态软化机制的影响。结果表明,亚结构恢复和亚动态再结晶是奥氏体亚动态软化的2种主要机制。当奥氏体内发生部分动态再结晶时,再结晶晶粒与变形基体间的储能差较大,热变形后保温过程的软化首先是通过亚动态再结晶进行;同时,变形基体内亚结构的恢复会逐渐降低变形基体内的形变储能,使晶界迁移速率降低而抑制亚动态再结晶的继续进行。而当奥氏体内动态再结晶发生完全时,在热变形后的保温过程中,再结晶晶粒内部因持续变形而形成的小角度亚结构会通过快速恢复而大量分解,形成不均匀的高密度位错会促进大角度晶界的局部迁移,从而促进晶粒的粗化,加速材料软化。

关键词 Ni-30%Fe模型合金热变形亚结构恢复亚动态再结晶奥氏体    
Abstract

Multi-pass processing is commonly used in hot working of steels. Dynamic recrystallization (DRX) occurs during hot deformation, while post-dynamic softening takes place during the inter-pass times and post-deformation annealing. Three different mechanisms are believed to be responsible for the post-dynamic softening stage. These are static recovery (SRV), static recrystallization (SRX), and post-dynamic recrystallization (P-DRX). Each of these mechanisms can change the microstructure of austenite (i.e. grain size and distribution). As a result, the post-dynamic softening behavior of austenite may play an important role in the microstructures and the final mechanical properties of the steel product. In this work, a Ni-30%Fe model alloy is used to study softening of austenite in post-deformation annealing after the hot deformation at 900 °C and strain rate 0.001 s-1. The microstructures in the annealed samples are carefully analyzed by EBSD in conjunction with TEM. The results show that P-DRX and sub-structural restoration are believed to be responsible for softening of the material after hot deformations. The P-DRX generally consumes deformed structures by the growth of the preformed nuclei of dynamic recrystallization. The sub-structural restoration in austenite usually takes place through the dislocation climb, leading to sub-boundary disintegrations and dislocation annihilations. When the sample is deformed to the peak strain, the deformation microstructure is composed of both recrystallized grains and deformed matrix. The large gradient of stored energy between the recrystallized grains and deformed matrix effectively promotes the strain-induced migration of the large-angle grain boundaries, which makes the P-DRX become the predominated post-dynamic softening mechanism during the post-deformation annealing. Meanwhile, the sub-boundaries within the deformed matrix gradually disintegrate through the restoration mechanism, which also contributes to the post-dynamic softening of austenite. On the other hand, the dislocation annihilation can result in a reduction of the stored energy within the deformation matrix, which inhibits the further migration of grain boundaries. In contrast, when the sample is deformed to the steady-state stage of the dynamic recrystallization, a fully recrystallized microstructure is obtained. The sub-structural restoration process of the fully recrystallized microstructure is much faster than that in the deformed matrix during the post-deformation annealing. It makes the sub-structural restoration become the predominated post-dynamic softening mechanism of this alloy in the steady-state condition. Furthermore, the disintegration of large numbers of sub-boundaries leads to an increase of the dislocation density in local region around the grain boundaries, which facilitates local migration of the high-angle grain boundaries and accelerates the softening of the material.

Key wordsNi-30%Fe austenitic model alloy    hot deformation    sub-structure restoration    post-dynamic recrystallization    austenite
收稿日期: 2019-09-20     
ZTFLH:  TG331  
基金资助:国家自然科学基金项目(51771192);国家自然科学基金项目(51371169);国家自然科学基金项目(51401214)
通讯作者: 郑成武     E-mail: cwzheng@imr.ac.cn
Corresponding author: ZHENG Chengwu     E-mail: cwzheng@imr.ac.cn
作者简介: 陈文雄,男,1991年生,博士生

引用本文:

陈文雄, 胡宝佳, 贾春妮, 郑成武, 李殿中. 热变形后Ni-30%Fe模型合金中奥氏体的亚动态软化行为[J]. 金属学报, 2020, 56(6): 874-884.
Wenxiong CHEN, Baojia HU, Chunni JIA, Chengwu ZHENG, Dianzhong LI. Post-Dynamic Softening of Austenite in a Ni-30%Fe Model Alloy After Hot Deformation. Acta Metall Sin, 2020, 56(6): 874-884.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2019.00310      或      https://www.ams.org.cn/CN/Y2020/V56/I6/874

图1  双道次热压缩实验工艺流程图
图2  材料亚动态软化分数测量方法示意图
图3  Ni-30%Fe合金在应变速率ε˙=0.001 s-1、温度T=900 ℃条件下等温热压缩变形时的应力-应变曲线(虚线)及初始应变分别为0.3和0.8条件下不同保温时间后第2道次压缩变形时的应力-应变曲线(实线)
图4  不同初始应变下Ni-30%Fe合金经过不同保温时间后的软化分数
图5  不同变形状态下Ni-30%Fe 合金微观组织的EBSD像、局部取向差分布图及取向差角度分布曲线
图6  Ni-30%Fe 合金在T=900 ℃、ε˙=0.001 s-1 条件下变形至应变ε=0.3后续保温不同时间过程中微观组织演变的EBSD像
图7  沿图6中直线L1、L2、L3和L4的取向差变化规律
图8  在T=900 ℃、ε˙=0.001 s-1 条件下变形至ε=0.3的Ni-30%Fe合金在后续保温不同时间过程中的TEM像
图9  Ni-30%Fe 合金在T=900 ℃、ε˙=0.001 s-1 条件下变形至ε=0.8后保温过程中微观组织演变的EBSD像
图10  沿图9中直线K1、K2、K3 和K4的取向差变化规律
图11  在T=900 ℃、ε˙=0.001 s-1 条件下变形至ε=0.8的Ni-30%Fe 合金在后续保温不同时间过程中的TEM像
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