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利用Gleeble-1500模拟不同热输入的单道次焊接热循环过程,通过光学显微镜(OM)、扫描电镜(SEM)及电子背散射衍射(EBSD)对高Nb X80管线钢焊接热影响区中的粗晶区(CGHAZ)显微组织、马/奥组元(M/A)形态和分布以及原奥氏体晶粒粗化情况进行研究.结果表明:高Nb X80管线钢的焊接热输入应不高于30 kJ/cm,虽然在高Nb钢中,原奥氏体晶粒的平均尺寸不会随热输入增加过于粗大,但当热输入高于40 kJ/cm时,会使得原奥氏体晶粒内粒状贝氏体的晶体取向选择过于单一,大角晶界(≥15°)密度明显降低,有效晶粒尺寸较大,M/A组元也由于热输入过大而明显粗化.上述原因使高Nb X80管线钢在大于40 kJ/cm热输入条件下热影响区粗晶区韧性明显恶化.
The Gleeble-1500 was used to simulate the heat cycle of single heat pass welding with different heat input. The coarse heat-affected zone (HAZ) of high Nb X80 pipeline steel was analyzed by optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) (CGHAZ) microstructure, the morphology and distribution of M / A and the austenite grain coarsening.The results show that the welding heat input of high Nb X80 pipeline steel should not be high At 30 kJ / cm, although the average prior austenite grain size in high Nb steels does not increase too coarse with heat input, when the heat input is above 40 kJ / cm, the original austenite grain The grain orientation of intragranular granular bainite is too single, the density of large angle grain boundaries (≥15 °) is obviously decreased, the effective grain size is larger, and the M / A component is obviously roughened due to the excessive heat input. So that the toughness of the coarse grain zone in the heat affected zone of the high Nb X80 pipeline steel under the heat input condition of more than 40 kJ / cm is obviously deteriorated.