Can I Use 7018 For Hardfacing?

Hardfacing is a process of depositing wear-resistant, corrosion-resistant or high-temperature-resistant coatings on metal surfaces through welding technology. It is widely used in mining machinery, cement equipment, metallurgical rollers and other fields. Recently, users have raised the question of "whether E 7018 welding rods can be used for hardfacing welding". This article combines scientific research data with industrial practice to conduct an in-depth analysis of this issue.

E7018 is a low-hydrogen potassium type welding rod, known for its high toughness, crack resistance and medium strength, and is commonly used for structural steel welding (such as bridges and buildings). Its core characteristics include:

• Chemical composition: Contains 5.4% manganese (Mn), mainly iron (Fe) based alloy.
• Mechanical properties: tensile strength 510-590 MPa, yield strength 430-510 MPa, elongation 24%-36%.

• Welding process: only supports short-circuit metal transfer mode, suitable for flat welding and vertical welding

 However, the core requirements of hardfacing welding are high hardness (usually requiring HRC 50 or above) and wear resistance, which requires carbides (such as Cr7C3, TiC) or martensite structure. The hardness of 7018 welding rod (about 29.5 HB after welding) is much lower than that of special hardfacing welding materials (such as EDZCr-C series welding rods, which can reach HRC 55-56).

• Hardfacing requires high carbon and high chromium alloys (such as Cr13, Cr20-35%) to form carbides. 7018 electrodes lack such elements and cannot generate sufficient wear-resistant phases (such as Cr7C3).
• Although the manganese content of 7018 can improve toughness, manganese oxides (MnO, Mn3O4) are easily brittle at high temperatures, reducing wear resistance.

• Hardfacing requires controlling the dilution rate (base material melting ratio) to maintain coating performance. 7018 electrodes are mostly used for deep penetration welding, and the dilution rate is high (>20%), which may weaken the hardness of the cladding layer.
• Specialized hardfacing welding materials (such as flux-cored wires) suppress cracks by adjusting current and preheating temperature (such as 150-300℃), while 7018 electrodes are not optimized for such parameters.

• Temporary repair: 7018 can be used for emergency repairs with low wear loads (such as slightly worn steel structures), but the wear life is short.
• Not applicable to high-demand scenarios: For parts such as mining crusher hammers and cement vertical mill rollers that need to withstand impact and abrasive wear, special welding materials containing carbide hard phases must be used.

• Cr13 stainless steel welding wire: After adding Mo and Ni, the hardness of the surfacing layer reaches HRC 50-53, and the high-temperature wear resistance is improved by 30%.
• Fe-based flux-cored welding wire: Contains Cr20-35%, C4-6%, forming (Cr,Fe)7C3 carbide, and the wear resistance is 3-8 times that of the base material.
• Cobalt-based alloy (Stellite 12): The hardness reaches 700 HV after laser surfacing, which is suitable for high-temperature sliding wear environment.

If 7018 needs to be used temporarily, it is recommended:

• Post-heat treatment: Tempering at 450-500℃ can slightly increase the hardness.
• Multi-layer surfacing: Reduce the impact of dilution rate, but the interlayer temperature needs to be controlled to prevent cracking.

• Give priority to special welding materials: such as EDZCr-C series, HYDCrMo welding wire, etc., which are designed to take into account hardness (HRC 50+) and crack resistance.
• Process optimization: Use submerged arc welding or laser surfacing, control heat input to reduce base material dilution.
• Safety protection: 7018 welding rod contains manganese, and ventilation should be strengthened during welding to avoid exposure to manganese fumes. 

Although E 7018 welding rods perform well in structural welding, their composition and performance are difficult to meet the high hardness and high wear resistance requirements of hardfacing. In industrial repair, it is recommended to use special welding materials containing carbide-forming elements (Cr, Mo, Nb), and select laser surfacing or submerged arc welding processes according to working conditions to achieve long-term wear protection.