Abstract: Cracking propagation and fracture morphology characteristics in the fusion zone of HQ130 high strength steel are studied by means of "the y-slit test", microscope and SEM. Experimental test indicated that welding crack commonly produced in the partially-melted zone at about 20μm-60μm from the melting line and propagated parallel to the fusion zone or turned into the weld metal. Crack propagation conducts alternatively between the weld zone and the partially-molten zone, and is not strictly to rupture at W/F boundary surface. Controlling weld heat input (≤20kJ/cm) may avoid forming coarse lath martensite or upper bainite nearby the fusion zone, and welding crack can be effectively prevented.

Key words: Fracture morphology, Fusion zone, HQ130 high strength steel, Micro-cracking