How can the uneven degree of graphitization of graphite electrodes lead to local overheating and abnormal wear?

Uneven graphitization of graphite electrodes directly causes local overheating and abnormal consumption through several mechanisms.

First, different degrees of graphitization lead to large differences in electrical resistivity. Well-graphitized regions have low resistivity, so current passes through them easily; poorly graphitized regions have noticeably higher resistivity. Inside the electrode, current tends to follow low-resistance paths, but the overall current is forced through the entire cross-section, so high-resistance regions heat up first because their Joule heating is significantly greater. This uneven temperature distribution makes local areas much hotter than the overall average temperature, forming hot spots.

Second, poorly graphitized regions have an incomplete crystal structure and lower thermal conductivity. Even if they generate the same amount of heat, these regions cannot conduct heat away in time, so heat accumulates locally and pushes the temperature even higher. The high temperature in turn causes further degradation of these regions, forming a positive feedback loop.

The direct consequence of local overheating is concentrated thermal stress. Regions with different degrees of graphitization have inconsistent thermal expansion coefficients and shrinkage behavior. The expansion of a high-temperature zone is constrained by the surrounding lower-temperature zones, generating considerable thermal stress. When the stress exceeds the mechanical strength of the material, microcracks form at the interfaces or at weak points. Once cracks appear, the effective conductive cross-section of the electrode is reduced, and current is forced more concentratedly through the remaining channels, further increasing the local current density and intensifying overheating.

In electric arc furnaces or submerged arc furnaces, the electrode tip is subjected to high-temperature arcs and melt corrosion. Poorly graphitized regions have poor oxidation resistance and are more likely to react with oxygen, slag, or molten metal at high temperatures, being preferentially oxidized or dissolved. At the same time, these regions have low mechanical strength and are prone to blocky spalling or slagging off under thermal stress and electromagnetic forces. After spalling, pits or notches form, the electrode shape becomes irregular, current distribution becomes even more disordered, and abnormal consumption spreads from a point to a larger area.

In addition, uneven graphitization makes problems at the electrode joint even more pronounced. The joint area itself has relatively high resistance. If the degree of graphitization near the joint is inconsistent, contact resistance and bulk resistance superimpose, causing faster local temperature rise and making the joint prone to loosening, oxidation, or even breakage, resulting in abnormal electrode consumption.

Overall, uneven graphitization first causes uneven current and temperature distribution, and then, through mechanisms such as thermal stress, oxidation, and mechanical spalling, converts local overheating into rapid local consumption. This ultimately manifests as surface pitting, spalling, joint damage, and a marked increase in electrode consumption per ton of steel.