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Edgar López-Martínez,Octavio Vázquez-Gómez,Héctor Javier Vergara-Hernández,Sergio Serna,Bernardo Campillo 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6
The microhardness and nanohardness of the welding zone of two experimental HSLA steels were determined. The first steel has a microstructure of martensite and bainite, and the second one has a microstructure of quasipolygonalferrite and acicular ferrite. In the bainitic - martensitic steel, softening of the heat affected zone wasobserved. This softening can be attributed to: the formation of polygonal ferrite in the recrystallization subzone,the formation of quasi-polygonal ferrite and the tempering of martensite in the intercritical subzone, andthe tempering of martensite in the subcritical subzone. Besides the softening, with nanoindentation technique, hardeningwas observed at the position where the peak temperature reached the critical temperature Ac1, which canbe attributed to a phenomenon of secondary hardening by precipitation of carbides of alloying elements. In theferritic steel, a softening phenomenon did not appear since there was no martensite in its initial microstructure. Finally, it was noted that both polygonal ferrite and the bainite have similar behavior and nanohardness, thiscoincidence can be attributed to the effect of grain boundary.