Hard-facing is a welding technique used to apply a layer of wear-resistant material to a metal surface. The deposit protects the metal underneath from abrasion, impact, erosion and other forms of wear, and it can extend the life of a component in mining, agriculture, construction or manufacturing by a large multiple.
Carbides are compounds of carbon and a metal element — tungsten, chromium or titanium among them. They are exceptionally hard and wear resistant, which is what makes them ideal for hard-facing. When electrodes or wires with a high carbide content are used, the deposit contains significant amounts of these carbides, distributed evenly through the weld metal, and the result is a strong, wear-resistant surface.
How carbides enhance hard-facing
Hardness and wear resistance. Carbides are inherently harder than the surrounding metal matrix, which gives exceptional resistance to abrasion and erosion. The harder the carbide, the greater the wear resistance.
Impact resistance. While hard, some carbides are also tough, meaning they can take an impact without fracturing. That matters wherever the hard-faced surface is subject to repeated blows.
Friction reduction. Certain carbides, chromium carbides among them, have a low coefficient of friction and so reduce the wear caused by sliding contact. Bearings and sliding wear plates benefit.
High-temperature performance. Some carbides — tungsten carbides in particular — retain their hardness and wear resistance at elevated temperature, which suits them to hot wear applications such as kiln liners and furnace components.
Types of carbide in hard-facing
- Primary carbides form during solidification of the weld metal and are typically large and blocky. Chromium carbides and titanium carbides are examples.
- Secondary carbides form during cooling after solidification and are usually smaller and more finely dispersed. Vanadium and molybdenum carbides are examples.
- Complex carbides contain more than one metal element — chromium-molybdenum carbides, for instance — and offer a combination of properties.
The presence of carbides improves the hardness, abrasion resistance and overall durability of the weld, which suits these materials to heavy wear: mining equipment, agricultural implements, oil drilling tools, industrial machinery. Carbide formation also improves mechanical properties such as toughness and impact resistance, which matters where the welded part sees impact or high stress.
Choosing the right carbide
The ideal carbide depends on the specific wear conditions and on the properties wanted in the deposit. Four things are worth weighing:
- Wear type — different carbides excel in different conditions: abrasion, impact, erosion.
- Temperature — choose carbides that hold their properties at the operating temperature.
- Matrix compatibility — the carbide has to be compatible with the surrounding metal matrix, or the deposit will crack or delaminate.
- Cost — some carbides are considerably more expensive than others. Balance cost against the performance actually required.
Carbide formation is a critical part of hard-facing electrodes and wires, because it directly influences the performance and longevity of the deposit and, through it, the lifespan of the component. Understanding the role of carbides and choosing the right hard-facing materials is what achieves proper wear protection in demanding industrial environments. With the right carbide content and careful control of the welding process, welders can produce durable welds matched to the requirements of each application.