The aim of this work was to investigate the effect of the carbides precipitated on the hardness and structure in the heat-affected zone of a Hadfield steel that has been used as broke stone tool during ten months and that have to be repaired by the welding process. The steel presents significant structural changes for the presence of the discontinuities in the heat-affected zone, that affect the hardness and the structure in comparison to the homogenized sample. The investigation is carried out with X-ray diffraction (XRD), microhardness Vickers, and Scanning Electron Microscopy (SEM) system. According to the XRD patters, the presence of Manganese carbides was identified. The identification of the types of carbides present in the steel structure allows us to say that it belongs to the Mn 23 C 6 and Mn 7 C 3 type.

In this paper, the influence of the cooling rate on the structural properties, hardness, and defect formations of the heat affected zone (HAZ) of Hadfield steels was studied. The chemical composition of the samples used in this study was determined using X-ray fluorescence. The microhardness was measured using the Vickers hardness test. X-ray diffraction was used to study the influence of the heat treatment on the crystalline quality of the austenitic grain. The X-ray FWHM of the samples was used to study the evolution of the crystalline quality. And finally, electronic microscopy images were used to study the evolution of defects, especially voids, microvoids, carbide precipitates, and microfractures caused by the cooling rates on the heat affected zone. The homogenized samples exhibited residual stress and lower crystalline quality. The results indicate that when the cooling rate decreases, the crystalline quality, grain hardness, and grain microhardness increases. The sample cooled in oil showed changes in void formation when compared to the homogenized sample. In the case of air cooling, there were increments in size of the voids and also microfissures and carbide precipitation. Finally, for the furnace-cooled sample, the existence of microfissures along with fractures was evident, and a significant carbide precipitation exhibiting different morphology was also observed in this case.