| For multi-wire submerged arc welding X80 pipe, the inner weld HAZ and the outer welding CGHAZ are the weakest part after welding. Microstructure change and the performance characteristics distribution of inner article CGHAZ welding and outside CGHAZ were as focus of the research.In SYSWELE software, X80 database and plate butt welding model in conformity with the practical requirements of welding were established. Got four different heat source inner welding of multi-wire submerged arc welding and four different heat source of outside corresponding welding zone suitable for the experimental materials. The thermal cycle curve and corresponding regional organization composition change curve of the inside and ouside welding in different areas were got.SH-CCT curve was established. When the cooling rate of X80 pipeline steel is greater than or equal to 70 ℃/s, there is martensite in the shift organization.When the cooling rate is less than 50 ℃ /s, change organization containing acicular bainite, granular bainite, upper bainite and lower bainite and so on. During continuous cooling, in X80 part of carbon-rich austenite change into martensite and others until cooled to room temperature in the form of retained austenite, that is M- A island.Transformation product contains martensite. The greater the cooling rate, the faster the speed of shear martensite, the greater the width of lath martensite.In the weld heat-affected zone of coarse grain area, when the external weld thermal cycle’s peak temperature is at the time of(α + γ) two-phase region range, X80 pipeline steel toughness is minimal, significantly lower than the base metal; hardness is maximal significantly higher than the female materials. It is proved that IICGHAZ show embrittlement and hardening significantly. In the outside weld heat-affected zone of coarse grain area, while in the welding thermal cycle peak solder temperature is lower than the Ac1 temperature namely ESCGHAZ, microstructure and performance are worst. |
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