Effects of inclusions on microstructure and properties of heat-affected-zone for low-carbon steels

Abstract

The characteristics of inclusions in two types of low-carbon steels by different deoxidization methods have been investigated by using the welding thermal simulation, the optical microscopy and scanning electron microscopy. In addition, the effects of inclusions on microstructure and properties of heat-affected-zone were studied. The nucleation and growth of intragranular acicular ferrite was observed in situ by the laser scanning confocal microscopy. The distribution of Mn element near the inclusion was also analyzed by the auger electron spectroscopy. The results showed that the inclusions in Al killed steel are mainly aluminum oxides, manganese sulfide and titanium nitrides, and that the inclusions in Ti killed steel are mainly titanium oxide, manganese sulfide complex inclusion and single manganese sulfide. The auger electron spectroscopy showed that there is an Mn-depleted zone near the interface of TiO x /MnS complex inclusion in the size of 1–3 μm. It could be the effective nucleus of intragranular acicular ferrite which could divide the prior austenite grains, inhibit the growth of low-temperature microstructure, and refine the final microstructure, so as to improve the toughness of heat-affected-zone significantly.