MICROSTRUCTURAL CHARACTERS AND TOUGHNESS OF DIFFERENT SUB–REGIONS IN THE WELDING HEAT AFFECTED ZONE OF LOW CARBON BAINITIC STEEL
MICROSTRUCTURAL CHARACTERS AND TOUGHNESS OF DIFFERENT SUB–REGIONS IN THE WELDING HEAT AFFECTED ZONE OF LOW CARBON BAINITIC STEEL
复制标题
DOI：
10.3724/sp.j.1037.2011.00089
复制
发表时间：
2011-08
影响因子：
2.3
通讯作者：
Lan Liang-yun;Qiu Chunlin;Diao De-Wen;Li Can-Meng;Gao Xiuhua;L. Du
中科院分区：
文献类型：
--
作者：
Lan Liang-yun;Qiu Chunlin;Diao De-Wen;Li Can-Meng;Gao Xiuhua;L. Du
焊接热影响区(WHAZ)是公认的低碳贝氏体钢焊接接头韧性最差的区域。本文采用热力模拟装置模拟了低碳贝氏体钢焊接热影响区不同分区的焊接热循环过程。在仪器化落锤冲击试验机上结合示波器对模拟试件进行了韧性测试，并利用OM、SEM、TEM等手段观察了显微组织特征。 EBSD结果表明,当冷却时间(t_(8/5))为30 s时,各子区域的裂纹萌生能相近,其取值范围在40~70 J之间。而细晶热影响区(FGHAZ)由于冲击载荷-时间曲线包含较宽的裂纹延性扩展阶段和裂纹脆性扩展阶段,因而表现出优异的止裂性能。热影响区(CGHAZ)明显恶化。随着冷却时间的增加,各子区域的裂纹萌生能和裂纹扩展能均下降,其中CGHAZ的裂纹萌生能和FGHAZ的裂纹扩展能显着下降。不同冷却速率下,M-A组元形貌和尺寸的变化是裂纹萌生能恶化的主要原因。裂纹扩展能方面,FGHAZ由于大角度晶粒密度高,具有良好的抗裂纹扩展能力。因此，其裂纹扩展能远优于其他子区域。 ICHAZ中有效晶粒尺寸不均匀，随着冷却速度的降低，铁素体晶粒长大，裂纹扩展能降低；CGHAZ中原奥氏体晶粒粗化，大角度晶界密度大幅下降，导致裂纹扩展能降低。
It is generally recognized that welding heat affected zone(WHAZ) is the poorest toughness region in the welded joint of low carbon bainitic steels.The thermomechanical simulator was employed to simulate the welding thermal cycle processes of different sub-regions in WHAZ of low carbon bainitic steel in this work.The toughness of simulated specimens were tested on the instrumented drop weight impact tester with oscilloscope,and miscrostructure features were observed by means of OM,SEM,TEM and EBSD.The results showed that when cooling time(t_(8/5)) was 30 s,the crack initiation energy of various sub-regions was similar,and the range of their values was between 40 and 70 J.However,fine grained heat affected zone(FGHAZ) exhibited excellent crack arrest properties because the impact load-time curve included wide crack ductile propagation and crack brittle propagation stages.By contrast,the crack propagation energy of intercritical heat affected zone (ICHAZ) and coarse grained heat affected zone(CGHAZ) obviously deteriorated.With the increase in cooling time,both crack initiation energy and crack propagation energy of various sub-regions decreased,in which the crack initiation energy of CGHAZ and the crack propagation energy of FGHAZ decreased notably.Under different cooling rates,the variation of morphology and size of M-A constituents was mainly responsible for the deterioration of crack initiation energy.As for crack propagation energy,the FGHAZ had a good resistance to crack propagation due to high density of high angle grain boundary.Therefore,its crack propagation energy was far superior to other sub-regions. There was uneven effective grain size in the ICHAZ and ferrite grain grew with the decease in cooling rate,which decreased the crack propagation energy.In the CGHAZ,prior austenite grains coarsened and the density of high angle grain boundaries decreased greatly,which resulted in the decrease in crack propagation energy.