The influences of post-welding heat treatment on the microstructures and properties of dissimilar steel friction stir welded joints for China low activation martensitic(CLAM) and 316L stainless steels have been investigated. It is found that the microstructure hardening tendency of the hardened martensite in the nugget of joint is obviously reduced by the post-welding heat treatment (PWHT)

and which promotes the carbide to be precipitated again and transformed into a low carbon α phase. The weak site of the high temperature mechanical properties for dissimilar steel welded joint is transformed from the base metal to the further softening heat affected zone. The static recovery occurs in the nugget of 316L steel

and the property is slightly decreased. With the increase of post welding temperature

the phenomenon of interfacial carbon migration is intensified around the bonding-interface

the softened ferrite zone is formed around the interface at the side of CLAM steel and the chromium-rich carbide is formed around the interface at the side of 316L steel. When using the process of heating to 740℃ and holding for 2 hours

the dissimilar steel friction stir welded joint can obtain good strength and toughness matching

and the high temperature tensile strength reaches 97.5% of the welding state joint.