To investigate the effect of M/A island on impact properties of inter-critical heat affected zone(ICHAZ)in T24 steel welding joint

subcritical normalizing on the T24 steel was carried out at different temperatures

and several tests such as scanning electron microscope(SEM)

transmission electron microscope(TEM)

Vickers hardness test and impact experiments were performed.The results show that

hard and brittle M/A islands distributed in the grain boundary of ICHAZ in the T24 steel suffered subcritical normalizing at different temperatures.With an increase in the normalizing temperature

the amounts and size of the M/A islands increased significantly and the impact absorbed energy decreased linearly.Under the impact load action

the M/A islands which located in grain boundaries could become crack sources easily due to the three dimensional stresses concentration.The impact fracture mechanism of the material changed from quasi-cleavage to cleavage as the relative amounts and size of the M/A islands increased.