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金属学报  2017, Vol. 53 Issue (11): 1427-1444    DOI: 10.11900/0412.1961.2017.00145
  研究论文 本期目录 | 过刊浏览 |
焊缝金属解理断裂微观机理
陈剑虹1,2(), 曹睿1,2
1 兰州理工大学省部共建有色金属先进加工与再利用国家重点实验室 兰州 730050
2 兰州理工大学材料科学与工程学院 兰州 730050
Micromechanism of Cleavage Fracture of Weld Metals
Jianhong CHEN1,2(), Rui CAO1,2
1 State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metal, Department of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China
2 Department of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China
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摘要: 

本文为低合金高强钢的解理断裂提出了一个新的理论框架:解理断裂不仅决定下平台的冲击韧性,而且对过渡温度区的韧性也起决定性的作用,因为在这个温度区间韧性取决于先前产生的塑性裂纹扩展的长度,而解理断裂终止了塑性裂纹的扩展,从而决定其长度。解理断裂包含3个不间断的阶段:(1) 裂纹在第二相颗粒起裂成核;(2) 第二相裂纹穿过第二相颗粒和晶粒边界扩展;(3) 晶粒裂纹穿过晶粒边界扩展进入相邻晶粒。本理论框架对整个过程进行了诠释:解理断裂的临界事件是在裂纹形成过程中提供最大困难的阶段,它控制了解理断裂过程,并确认了最薄弱的微观组分及其临界尺寸,这个尺寸决定了微观解理断裂应力σf。在断裂过程研究中最为重要的就是揭示各种条件下断裂的临界事件。提出引发解理断裂的3个准则:(1) 裂纹起裂成核准则;(2) 防止裂纹核钝化准则;(3) 裂纹扩展准则。并由这3个准则形成了一个活性区,在活性区中应力和应变的综合作用可以引发解理断裂,这个活性区被用来建立断裂的统计模型。本研究利用这个新的理论框架进行了8%Ni钢焊缝的实例研究,以说明实验研究的结果。

关键词 解理断裂断裂过程临界事件断裂准则    
Abstract

Cleavage fracture is the most dangerous form of fracture. Cleavage fracture usually happens well before general yielding at low nominal fracture stress and strain. Cleavage fracture is often spurred by low temperature and determines the toughness in the lower shelf temperature region. This paper describes a new framework for the micromechanism of cleavage fracture of high strength low alloy (HSLA) steel weld metals. Cleavage fracture not only determines the impact toughness in the lower shelf but also plays a decisive role on the impact toughness in the transition temperature region. The toughness is determined by the extending length of a preceding fibrous crack which is terminated by cleavage fracture. Three non-stop successive stages, i.e. crack nucleation, propagation of a second phase particle-sized crack across the particle/grain boundary, propagation of a grain-sized crack across the grain/grain boundary are explained. The "critical event" of cleavage fracture is emphasized which offers the greatest difficulty during crack formation and controls the cleavage process. The critical event indicates the weakest microstructural component and its critical size which specifies the local cleavage fracture stress σf for cleavage fracture. In toughness-study it is paramount important to reveal the critical events for various test specimens. Three criteria for crack nucleation, for preventing crack nucleus from blunting and for crack propagation are testified. An active region specified by these criteria is suggested where the combined stress and strain are sufficient to trigger the cleavage fracture. It can be used in statistical analyses. A case study, using the new framework of micromechanism for analyzing toughness of 8%Ni steel welding metals is presented to analyze the experimental results.

Key wordscleavage fracture    fracture process    critical event    fracture criteria
收稿日期: 2017-04-24      出版日期: 2017-08-14
:  TG111  
基金资助:国家自然科学基金项目Nos.51675255和51761027
作者简介:

作者简介 陈剑虹,男,1937年生,教授

引用本文:

陈剑虹, 曹睿. 焊缝金属解理断裂微观机理[J]. 金属学报, 2017, 53(11): 1427-1444.
Jianhong CHEN, Rui CAO. Micromechanism of Cleavage Fracture of Weld Metals. Acta Metall, 2017, 53(11): 1427-1444.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2017.00145      或      http://www.ams.org.cn/CN/Y2017/V53/I11/1427

图1  解理裂纹形态[8]
图2  冲击韧性-温度转变曲线[8]
图3  微观断口形貌
图4  过渡温度区裂纹及断口微观形貌
图5  在不同温度下对不同热输入的焊接金属测定的总的冲击能量随延伸区宽度(SZW)和塑性裂纹长度(SCL)的变化,起裂能量随SZW 的变化及裂纹扩展能量随SCL的变化[11]
图6  缺口根部正应力σyy沿y方向的分布以及沿y方向分布的横向收缩示意图
图7  缺口及预裂纹前沿正应力的分布图
Material C Mn Si Mo S P Ti V B O N Fe
WCF62 0.06 1.36 0.23 0.21 0.009 0.02 - 0.03 0.0017 - - Bal.
16MnR 0.18 1.40 0.36 - 0.018 0.02 - - - - - Bal.
16Mn 0.14 1.37 0.32 0.014 0.02 - - - - - Bal.
Ti-B weld 0.06 1.45 0.48 - 0.020 0.01 0.03 - 0.0040 0.03 0.019 Bal.
C-Mn weld 0.07 1.24 0.28 - 0.020 0.01 0.03 - - 0.03 0.019 Bal.
表1  所使用材料的化学成分
图8  在-130 ℃断裂的C-Mn钢裂纹尖端张开位移(COD)试样的断口[8]
图9  解理断裂过程简图[8]
图10  确定裂纹起裂颗粒的程序
图11  几种起裂微观裂纹的图片[8]
图12  裂纹起裂机理的简略描述 [8]
图13  三向应力引发铁素体母体在M-A岛边界附近分层的典型例子[8]
图14  垂直于断口面的金相截面和断口附近的残留裂纹示意图[8]
图15  观察裂纹起裂区微观组织的金相截面和围绕裂纹起裂点的粗大晶粒区示意图[8]
图16  缺口试样中残留在晶粒内的裂纹、缺口试样中残留在贝氏体团内的裂纹和预裂纹试样中残留裂纹截留在第二相颗粒中[8]
图17  缺口试样中解理断裂起裂于粗大晶粒区[8]
图18  测得焊缝金属的σf和晶粒尺寸分布直方图[8]
图19  测量微观解理断裂应力σf和临界塑性应变εpc的示意图[8]
图20  裂纹尖端前沿σyy的分布[8]
图21  三点弯曲(3PB)预裂纹试样在外加载荷为6.86 kN卸载时的结果[8]
图22  3PB预裂纹试样在外加载荷为9.80 kN卸载时的结果[8]
图23  3PB预裂纹试样在外加载荷为12.74 kN卸载时的结果[8]
图24  3个准则都满足的活性区(如阴影线所示)示意图,活性区宽度随外加载荷的变化以及断裂几率随外加载荷的变化(实线)和实测结果(圆圈点)[8]
图25  焊缝金属T5-21 和DM4-1的微观组织[8]
Material Mass fraction / % D σf Fb Cv(-50 ℃)
Ni Cr C Si+Mo+Mn+Cu+Nb+V Fe μm MPa % J
BM 7.58 0.60 0.08 1.77 Bal. 20 2705 42 177.3
T5-21 6.34 0.73 0.05 2.46 Bal. 30 61 163.0
DM4-1 3.09 0.69 0.06 2.71 Bal. 60 1591 74 24.5
表2  钢及焊缝金属成分和冲击韧性、微观参数及力学性能
图26  母材和DM4-1中的残留裂纹[8]
图27  随机测定的残留裂纹和贝氏体团尺寸[8]
图28  DM4-1和T5-21贝氏体团尺寸直方图[8]
图29  DM4-1和T5-21的EBSD图和晶粒取向直方图[8]
图30  DM4-1和T5-21贝氏体板条的宽度[20]
图31  起裂源位置的确定及缺口根部前沿的应力、应变和三向应力度分布
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