THE STRESS CORROSION CRACKING OF 7021 MARAGING STEEL(18Ni)WELDED JOINT

The stress corrosion behavior of 7021 maraging steel (18Ni) welded joint in 3.5% NaC1 aqueous solution has been studied by means of specimens of TIG welded joint and synthetic heat affected zone.The results show that welding heat does not affect the fracture toughness but sharply weakens the resistance to SCC of the steel,when the peak temperature is about 1280℃.This phenomenon is thought to be caused by the segregation of alloying elements at grain boundaries and the grain growth during welding.The resistance to SCC can be increased by post-weld solid solution at 820℃,1h,and improved further by double solid solution treatment.And yei the triple water quench treatment at 900℃ gives the best results,creates a very fine grain size and changes SCC fracture mode from intergranular to ductile transgranular.However,the effect of post-weld treatment on K_Iscc of weld metal is different to that of HAZ.Single or double solid solution treatment decreases the K_Iscc of weld metal;only triple water quench treatment can get higher K_Iscc matching that of HAZ.