What Is a Hard-Facing Weld?

What Is Hard Facing Welding?

Hard facing welding (also known as build-up or cladding welding) is a surface coating process that uses flame, arc, or plasma arc to create coatings on metal surfaces that are resistant to wear, corrosion, and high temperatures. This method is notable for its repair and surface strengthening capabilities and has become an important coating technology in industries where wear-resistant materials are widely used.

The composition and structure of the hardfacing coating layer directly affect the performance of the entire component. The alloys used for coating are classified into categories such as iron-based, nickel-based, cobalt-based, copper-based, or tungsten carbide.

Selection of Hard Facing Welding Consumables

Three key criteria are considered when selecting welding consumables:

1. Risk of cold cracking: Appropriate preheating and pass temperature must be determined.
2. Thermal compatibility: The thermal expansion properties of the base material and the cladding material must be compatible.
3. Interlayer compatibility: Compatibility between the interlayer and the filler layer is important.

Buffer Layer

The buffer layer creates a strong bond between the hard filler and the base material, preventing the propagation of stress-induced cracks. The properties of the buffer layer must be carefully selected to prevent cracks and delamination when there is significant incompatibility between the base material and the filler layer.

Types of Hard Filler Layers

1. Iron-Based Alloys: These are low-cost and can be alloyed with various elements to impart different properties. For example:
   • Pearlitic steel: It has low hardness and good impact resistance.
   • Austenitic steel: It has high impact toughness and corrosion resistance.
   • Martensitic steel: Offers high hardness and wear resistance.
   • Alloyed cast iron: Possesses high wear and heat resistance and is used in agricultural and mining machinery.
2. Cobalt-Based Alloys: Known as Stellite alloys, these provide hardness and corrosion resistance at high temperatures.
3. Nickel-Based Alloys: They have high resistance to wear, corrosion, and oxidation. For example, Hastelloy C-22 alloys are used on valve sealing surfaces in harsh environments.
4. Copper-Based Alloys: They offer high resistance to corrosion and cavitation but are used in environments below 200 °C.
5. Tungsten Carbide Alloys: They offer the highest wear resistance and are resistant to severe abrasive conditions. They are widely used in oil drilling, mining, and agricultural machinery.