【摘要】 利用Gleeble热模拟技术,保持第一道次焊接热循环参数(模拟第一道次焊接粗晶区组织)不变,并将第二道次峰值温度固定为800℃,研究了第二道次焊接热循环不同冷却速度(2.0、6.8和15.3℃/s)对X100管线钢临界再热粗晶区组织及冲击性能的影响。结果表明:冷速为6.8℃/s时的冲击性能最高,冲击吸收能量平均为84.9 J,而2.0℃/s和15.3℃/s冷速下冲击吸收能量较低,分别为40.3 J和65.8 J。微观组织分析表明,不同冷速下晶粒内部组织均为板条状贝氏体和粒状贝氏体,但是沿原奥氏体晶界分布的马氏体-奥氏体(M-A)组元的体积分数和分布状态有较大差别。冷速为15.3℃/s时,M-A组元沿晶界成链状连续分布,且体积分数较高(6.3%)。而2.0℃/s和6.8℃/s下形成的M-A组元的体积分数相近,分别为3.3%和3.7%,但2.0℃/s时形成的组织中存在较多大尺寸、尖角形的M-A组元,对韧性的危害更大。更多还原

【Abstract】 Influence of second pass thermal cycle cooling rate( 2. 0,6. 8,15. 3 ℃/s) on microstructure and impact toughness of intercritically reheated coarse grain heat-affected zone( ICCGHAZ) of X100 pipeline steel was studied by using Gleeble thermal simulation technique,with the parameters of first pass thermal cycle( to simulate the CGHAZ formed during the first pass welding) and the second peak temperature( 800 ℃) being fixed. The results show that with a cooling rate of 6. 8 ℃/s,the impact property is the highest and the impact absorbed energy is 84. 9 J. While at 2. 0 ℃/s and 15. 3 ℃/s,the impact absorbed energy is lower,being 40. 3 J and 65. 8 J,respectively.Microstructure analysis shows that under different cooling rates,the microstructure of ICCGHAZ is mainly consisted of upper bainite and a small fraction of granular bainite,however,the distribution of martensite-austenite( M-A) constituent along prior austenite grain boundaries has large difference. When the cooling rate is 15. 3 ℃/s,M-A constituent is continuously distributed along prior austenite grain boundaries with a high volume fraction of 6. 3%. In contrast,the volume fraction of M-A constituent formed under 2. 0 ℃/s and 6. 8 ℃/s is similar,being 3. 3% and 3. 7%,respectively. Whereas,the M-A constituent formed under 2. 0 ℃/s is larger in size and with sharp angle in the aspect of morphology,which is more detrimental to toughness.更多还原