Effect of Heat Treatment on Microstructure and Properties of 9Ni Steel Welded Joint
The deterioration mechanism of plastic toughness of welded joints of 9Ni steel for cargo shipsat low temperature was clarified.After manual arc welding,the effect of heat treatment on the microstructure and properties of 9Ni steel welded joint was studied.The results show that after QT heat treatment,the reversion austenite in the joint heat affected zone is generally dispersed around the grain boundaries,and there is also a trend of precipitation at the martensitic lath boundaries,but the content is very small compared with the grain boundary distribution.Compared with QT heat treatment,after QLT process,the amount of reversed austenite in the heat affected zone of the joint increases greatly,and the grains are dispersed in various grain boundaries and smaller.The structure of the fusion zone is finer,more dispersed,the lath martensite is more obvious,and the directivity is better.The impact absorption energy of the joint weld increases more,and QLT can improve the low temperature toughness of the weld more.The impact fractures under the two heat treatment processes are typical dimple fractures.
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