Metal magnetic memory (MMM) testing is an advanced and nondestructive testing method based on magneto-mechanical effects. This technique can be used to assess defects based on MMM signals (MMMS). However, a thorough understanding of the impact that crack depth, working load, and heat treatment have on residual magnetic field variations (which can in turn affect defect assessment) has not yet been established in the literature. This report presents MMMS testing results of buried welding cracks under different applied loads, as well as before and after heat treatment, in order to analyse the impact of such factors on MMMS data. The results show that the MMMS is significantly affected by the depth at which a given crack is buried in a material, any load applied to the specimen, and the type of heat treatment employed. Therefore, the above factors should be considered when evaluating defects to avoid the inappropriate assessment of such defects.