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金属学报  2017, Vol. 53 Issue (7): 778-788    DOI: 10.11900/0412.1961.2016.00521
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FB2马氏体耐热钢在焊接热作用下奥氏体相变过程研究
李克俭1,蔡志鹏1,2,3(),吴瑶4,潘际銮1
1 清华大学机械工程系 北京 100084
2 清华大学摩擦学国家重点实验室 北京 100084
3 先进核能协同创新中心 北京 100084
4 清华大学天津高端装备研究院 天津 300304
Research on Austenite Transformation of FB2 Heat-Resistant Steel During Welding Heating Process
Kejian LI1,Zhipeng CAI1,2,3(),Yao WU4,Jiluan PAN1
1 Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
2 State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
3 Collaborative Innovation Center of Advanced Nuclear Energy Technology, Beijing 100084, China
4 Tsinghua University Research Institute for Advanced Equipment, Tianjin 300304, China
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摘要: 

借助光学显微镜、扫描电镜分析对比了FB2马氏体耐热钢在焊接热模拟前后的组织状态,认为FB2钢在快速加热条件(≥100 ℃/s)下的奥氏体相变是切变型的,表现出奥氏体记忆效应;而在慢速加热条件(≤5 ℃/s)下其奥氏体相变是扩散型的,该过程是受原子短程扩散控制的,并且无奥氏体记忆效应发生。FB2钢在焊接过程中特殊的相变过程是其焊接热影响区呈现出“无粗晶区”的主要原因。结合已有的文献报道,初步提出了B元素改变FB2钢在加热过程中奥氏体相变类型的机理模型,进一步发展了现有的研究结果。

关键词 FB2钢焊接切变型相变奥氏体记忆效应B元素    
Abstract

The improvement of steam parameters in fossil power plants requires the development of new kinds of 9% Cr martensitic heat-resistant steels, among which FB2 steel is a 100×10-6 (mass fraction) boron-containing steel and mainly used for manufacturing components with thick walls operating at high temperatures above 600 ℃. In the alloy system of martensitic heat-resistant steels, boron plays an important role in suppressing type IV crack of weld joints by the formation of heat affected zone (HAZ) with no fine grains in the normalized and intercritical zones, where there exhibit fine grains in conventional 9%Cr heat-resistant steels with no boron such as P91 steel. In this work, the formation process of HAZ in FB2 steel was investigated. The microstructures before and after thermal simulation were compared using OM and SEM. It was concluded that the austenization of FB2 steel at rapid heating rates (≥100 ℃/s) took place by shear mechanism, demonstrating austenite memory effect; while at slow heating rates (≤5 ℃/s), the austenization was by atom short range diffusion mechanism, without austenite memory effect. The special phase transformation of austenization is the main cause for the formation of HAZ with no coarsened grain in the overheated zone. Based on the previous results reported by other researchers, a preliminary model was proposed to describe how boron atoms change the austenite transformation type of FB2 steel during heating process, which developed the previous ideas about the phenomenon.

Key wordsFB2 steel    welding    martensitic transformation    austenite memory effect    boron
收稿日期: 2016-11-21      出版日期: 2017-02-27
基金资助:上海市科学技术委员会科研计划项目No.13DZ1101502和清华大学摩擦学国家重点实验室自主项目No.SKLT2015A02

引用本文:

李克俭,蔡志鹏,吴瑶,潘际銮. FB2马氏体耐热钢在焊接热作用下奥氏体相变过程研究[J]. 金属学报, 2017, 53(7): 778-788.
Kejian LI,Zhipeng CAI,Yao WU,Jiluan PAN. Research on Austenite Transformation of FB2 Heat-Resistant Steel During Welding Heating Process. Acta Metall, 2017, 53(7): 778-788.

链接本文:

http://www.ams.org.cn/CN/10.11900/0412.1961.2016.00521      或      http://www.ams.org.cn/CN/Y2017/V53/I7/778

图1  焊接接头垂直于焊缝纵向的截面图和取样示意图
Rh / (℃s-1) tH / s Tp / ℃
960 1000 1250
1 0.5 × ×
5 0.5 × ×
100 0.5
30 ×
表1  热模拟实验的热循环参数
图2  FB2钢焊接HAZ的OM像
图3  不同热模拟条件下试样的膨胀量随温度(T)变化曲线
图4  FB2钢在热模拟前后的OM像
图5  FB2钢在不同条件热模拟并回火后的OM像
图6  FB2钢同一位置在Rh=100 ℃/s、tH=0.5 s、Tp=1000 ℃热模拟前后的SEM像
图7  FB2钢在Rh=100 ℃/s、tH=0.5 s、Tp=1000 ℃热模拟后的SEM像
图8  FB2钢在不同条件热模拟并回火后的OM像
图 9  FB2钢在Rh=100 ℃/s、Tp=1000 ℃、tH=30 s条件下的奥氏体化过程
图10  高温LSCM观察FB2钢在5 ℃/s加热速率下的形貌变化
图11  马氏体、α-Fe以及γ-Fe的自由焓与温度的关系
Tp / ℃ Rh / (℃s-1) Dislocation density in alstenite Ms / ℃
960 100 +++++ 391
1000 100 ++++ 381
1000 5 +++ 373
1000 1 ++ 364
1250 100 + 326
表2  FB2钢在不同加热条件下奥氏体的位错密度与对应的Ms
图12  FB2钢在加热过程中2个特定时刻的表面形貌
图13  不同受热条件下B原子在晶格内部的分布情况示意图
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