Non-metallic inclusions were inspected and graded under a 100x optical microscope. To further determine the source of inclusions within cracks, energy dispersive spectroscopy (EDS) was used for qualitative analysis of the defect composition. The analysis results showed that the inclusions within the cracks contained iron and oxygen elements, thus identifying them as iron oxide inclusions. Chemical composition analysis of ER70S-6 welding wire rods followed the internal control technical conditions for hot-rolled wire rods used in gas-shielded welding wire. The chemical composition of the failed wire rods was analyzed according to the standard measured results. From the above test results, it can be seen that the chemical composition and the type and size of inclusions in the failed wire rods meet the standard requirements. However, the presence of cracks and mixed crystal structure on the wire rod surface does not meet the requirements for the inclusion inspection results of the gas-shielded welding wire pull-out test material (sulfides) B (oxides) C (silicates) D (spherical oxides) Fine series Coarse series Fine series Coarse series Fine series Coarse series Fine series Coarse series 1.0-0.5-0.5-0.5- The ER70S-6 wire rod product inspection standard requires a smooth surface, free from defects such as cracks, folds, and inclusions. However, the failed wire rod had an uneven surface with cracks, and energy dispersive spectroscopy (EDS) analysis confirmed the presence of iron oxide inclusions within the cracks. These defects existed before the billet was heated. The cracks on the billet surface were oxidized under the high temperature and oxidizing atmosphere in the furnace, and the inability to fuse during rolling resulted in longitudinal cracks on the wire rod surface. These longitudinal cracks further complicate subsequent processing steps, deteriorate the uniform deformation performance of the welding wire during drawing, disrupt the continuity of the matrix, and cause microcracks to transform into macrocracks, eventually leading to further cracking as the wire is drawn. Furthermore, the wire rod has a uniform and fine grain structure, resulting in good overall performance and uniform deformation during drawing, meeting the drawing performance requirements for gas-shielded welding wire. The uneven grain size and mixed-grain phenomenon in the failed wire rod indicate a connection to the heating or cooling process of the steel, such as: ① excessively high heating temperature and prolonged heating time result in coarse austenite grains, which easily form a mixed-grain structure after cooling; ② excessively low heating temperature causes the billet to already exhibit mixed grains before entering the rolling mill, making it impossible to eliminate the mixed grain phenomenon during subsequent rolling; ③ mixed grains appear in the recrystallization zone of the austenite portion during rolling. Wire rods with mixed-grain structures exhibit inconsistent internal deformation during drawing, leading to decreased drawing performance.

In the study of lead-free solders, the study of intermetallic compounds in the microstructure is a fundamental project. Observation under bright field requires sample etching. However, the solder microstructure is very soft, and a deformation layer easily forms on the sample surface, usually resulting in poor etching effects. In this case, utilizing the slight differences in surface height caused by the differences in hardness properties between different compounds and the matrix, DIC (Differentiated Indication) technology can obtain better image results. Intermetallic compounds in lead-free solder. However, the application of DIC technology does not lower the requirements for sample preparation; on the contrary, it raises them, referring to the requirements for sample grinding and polishing techniques. Scratches are clearly visible under DIC technology. Defects in sample preparation are even more prominent at this time. In the center of the lead-free solder, a scratch at a 120° angle to a large compound is clearly identifiable at the location of the intermetallic compound.