What is the process of hardfacing?

Some people have the idea that hardfacing is a complicated business, intended only for a small elite of welding pros. Other ones see hardfacing as a troublesome process that should be avoided.

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In reality, hardfacing is a special process that can be done with the only purpose of extending the service&#;s life of any equipment or surface. Now, if a metal part reaches a longer lifespan through hardfacing, more time can be used and fewer times will need to be replaced.

So, hardfacing is a good idea when there is a need for saving money. Even when hardfacing has several techniques to be done, it is not something too hard to understand. So, let&#;s get started by defining what hardfacing is.

Hardfacing is the process to apply a tougher material to a base metal, to make it more durable or extend its lifespan. This harder material is welded to the base metal by using specialized electrodes or filler rods.

They are meant to form very dense and thick layers (between 1 to 10 mm) above the base metal of wear-resistant material with high bond strength. The coating material can add ductility, hardness, corrosion resistance, and erosion resistance to the original part.

Other names given to hardfacing are hard surfacing, surface welding, and cladding. Among the base metals that can be hardfaced are the following ones:

• Cast Iron
• Copper-base Alloy
• Nickel-base Alloy
• Stainless Steel
• Manganese Steel
• Carbon and Alloy Steel

Many manufacturing equipment is made from low-alloy and higher carbon steel. Hobart&#;s filler metals are a complete solution whatever the base material.

Before starting any hardfacing process is needed to identify exactly what material is made the part of because this defines the pre-heat and post-heat temperature that should be applied.

These pre-heats and post-heat settings are even more important as the alloy percentage of the part content are higher.

All metal parts even with normal use will wear as time goes by. This may cause them to lose their functionality and as a result, the need for a new part.

In certain industrial applications, like in mining or agriculture, this may happen more frequently. Hardfacing can be an ideal option for any metal part that may wear for being used. In short, hardfacing can help to:

• Spend less downtime for replacing worn or broken components
• Store fewer spare parts to inventory, because they are not needed
• Longer equipment lifespan

Industrial equipment is intended to last for many years. So, many companies take some years to replace theirs.

Most of the time, hardfacing is applied to used rebuild machinery, but even new equipment can be hardfaced to make it more wear-resistant.

Hardfacing parts from equipment for many years can mean saving between 25-75% of the cost of replacement parts.

On recent equipment, hardfacing can help to extend up to 300% of the lifespan of the parts. Let&#;s see some examples.

Mining is an industry quite related to hardfacing. The material obtained from the mine should be crushed to be processed.

Even with being made of hard material, in a short time these rolls are worn down because they deal with strong minerals all day long. So, more than a possibility, hardfacing is a must for mining crushing rolls.

Hardfacing can be used to overlay, build-up, or both techniques at the same time. Each technique (or the combination of both) has a purpose.

The overlay is a technique used to avoid metal loss by adding a welded layer to the base. The build-up technique restores older equipment worn by abrasion or impact to its original dimensions by placing several weld layers (each one on top of the other).

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While the part is sound a combination of these hardfacing techniques can be used once and again. Some of the most common coating materials used for hardfacing are:

• Cobalt-based alloys (like stellite) for wear and corrosion resistance
• Copper-base alloys for rebuilding worn machinery parts
• Iron chromium alloys for high-stress abrasion
• Chromium carbide alloys
• Nickel-based alloys for metal-to-metal wear resistance
• Manganese steel for wear application
• Tungsten carbide for high-stress abrasion
• NOREM

The one you should use for your equipment can be defined by the base metal and the method of choice. There are many methods to apply hardfacing, like the following ones:

• Submerged Arc Welding (SAW)
• Flux Cored Arc Welding (FCAW)
• Shielded Metal Arc Welding (SMAW)
• Gas Metal Arc Welding (GMAW)
• Gas Tungsten Arc Welding (GTAW)
• Plasma Transferred Arc Welding (PTAW)
• Oxy-Fuel Welding (OFW)
• Electro Slag Welding (ESW)
• Open Arc Welding (OAW)
• Laser Cladding
• Cold Polymer Compounds
• Thermal Spraying

Let&#;s review some of the most popular ones:

In this process, a flux is used to unite protective gases and slag into the weld puddle. Before you start to weld on the workpiece a thin layer of flux should be added.

When welding, an arc is formed between the workpiece and the flux through a continuously fed wire electrode. The arc moves along the workpiece and excess flux can be recycled with a flux recovery system, filtered, and returned to the flux hopper.

This process, despite being carried out with not very portable equipment and being limited to some materials, has some pros, which are:

• Deep weld penetration
• Can be used indoors or outdoors
• Extremely high deposition rates

This process typically requires a constant voltage and a continuously-fed tubular electrode containing a flux.

This welding process is often chosen in construction applications because it is easily transportable and quick. Even when this process is not well-suited for all metals, have some advantages like:

• High deposition rate
• Can be used in all positions
• Excellent weld penetration

Another advantage of FCAW is that, besides being manual, it can be adapted as a semi-automatic or automatic arc welding process.

SMAW is a manual arc welding process carried out through a covered flux consumable metal electrode to shield the weld. This process is executed through an electric current that forms an arc between the coated electrode and the base metal.

When the weld is laid, the flux coating disintegrates and forms a shielding gas and a layer of slag which protects the weld until it cools. Even though deposition rates are typically lower than for other welding processes, have also advantages to take into account, like:

• Is the most portable of all welding processes
• Is well suited for a wide variety of commonly used metals and alloys
• Can be powered with gasoline or diesel which allow this process to be used in remote areas without electrical connections

GMAW, also known as MIG, is a process in which a consumable wire electrode and a shielding gas are fed through a welding gun. It can be a semi-automatic or automatic welding process. Whether the case, a constant voltage is most commonly used with this process.

MIG or GMAW is limited regarding flexibility because it cannot be used in overhead or vertical welding positions. Nevertheless, have some advantages like:

• Consumables are low cost and deposition rates are high
• Produce very little slag so there is a minimal post-weld cleaning

Hardfacing is a metalworking process where harder or tougher material is applied to a base metal. It is welded to the base material, and generally takes the form of specialized electrodes for arc welding or filler rod for oxyacetylene and gas tungsten arc welding. Powder metal alloys are used in plasma-transferred arc (PTA), also called powder plasma welding, and thermal spray processes like high-velocity oxygen fuel coating, plasma spray, spray and fuse, etc. Submerged arc welding, flux core arc welding (FCAW) and metal inert gas (MIG) / metal active gas (MAG) use continuously fed wire varying in diameter depending on the process and current. The strip cladding process uses strips from 50 mm wide to 125 mm with a thickness of 0.5mm. Open arc welding uses a continuously fed tubular electrode which may or may not contain flux.

Hardfacing may be applied to a new part during production to increase its wear resistance, or it may be used to restore a worn-down surface. Hardfacing by arc welding is a surfacing operation to extend the service life of industrial components, preemptively on new components, or as part of a maintenance program.[citation needed] The result of significant savings in machine down time and production costs has meant that this process has been adopted across many industries such as steel, cement, mining, petrochemical, power, sugar cane and food. According to the results of an experimental study, the shielded metal arc welding and the gas metal arc welding hardfacing processes were effective in reducing the wear on the mouldboard ploughshare. With the shielded metal arc welding and gas metal arc welding hardfacing processes, the life span of the ploughshare was increased approximately 2 times.[1]

Extensive work in research has resulted in the development of a wide range of alloys and welding procedures. The optimum alloy selection is made considering the component service conditions and feedback of the service performance.

For each industrial application and wear phenomena, there is a welding electrode to provide wear resistance.

Hardfacing can be deposited by various welding methods:

• Shielded metal arc welding
• Gas metal arc welding, including both gas-shielded and open arc welding
• Oxyfuel welding
• Submerged arc welding
• Electroslag welding
• Plasma arc welding, also called powder plasma welding
• Thermal spraying
• Cold polymer compounds
• Laser cladding
• Hardpaint

Commonly applied materials include cobalt-based alloys (such as Stellite), nickel-based alloys, chromium carbide alloys and NOREM. Hardfacing is sometimes followed by hot stamping to refinish the part or add color or instructional information to the part. Foils or films can be used for a metallic look or other protection.[citation needed]

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See also

• Case-hardening