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.
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.
What is hardfacing?
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.
Why hardfacing may be needed?
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
The savings from hardfacing
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.
What is hardfacing for? Some examples
Hardfacing is used for a wide range of applications, but we can highlight some examples.
Excavator plowshare
These parts suffer abrasion daily like any other construction equipment. The constant abrasion and erosion due to its daily outdoor heavy duty may significantly reduce the dimension and strength of the piece.
By hardfacing these parts, the total machinery lifespan can be extended many times, with a very reduced investment.
Sugar cane crusher roll
This part is constantly exerting pressure to mill the cane to extract the sugar to process. The sugar cane is a strong plant that can put these metal-made parts to the test.
Hardfacing is the usual procedure to extend the life of these parts, lowering production costs and downtime.
Mining crushing rolls
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.
What techniques and methods for hardfacing are there?
There are several techniques and methods for applying hardfacing. The one you should choose will depend on your equipment and needs. Let’s talk about the techniques first.
Techniques for applying hardfacing
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).
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:
Submerged Arc Welding (SAW)
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
Flux Cored Arc Welding (FCAW)
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.
Shielded Metal Arc Welding (SMAW)
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
Gas Metal Arc Welding (GMAW)
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
Gas Tungsten Arc Welding (GTAW)
When welding using GTAW or TIG an arc between a non-consumable electrode and the piece is produced. Around the area, a shielding gas is formed to protect the welding puddle. Even though the deposition rates of this process are low, there some advantages, like:
- Very flexible process because can be welded in every position and almost all metals
- Can be performed manually or automatically
- Leaves a clean-finished
The process to apply hardfacing
No matter what particular method you choose, there are some steps to carry out hardfacing the right way. These are:
- Clean the part: Take away any rust, grime, oil, grease, or gunk that the workpiece may have. If there is any previous hardfacing layer, take it out to avoid any cracking
- Build up: The part may have an indent caused by an impact. In that case, fill the space before applying layers. Some people know this step as rebuilding because the purpose is to restore the piece to its original dimensions.
- Buttering: This step is also known as a buffer layer. The objective is to overcome the possible incompatibility between the metal base and the final coating. By doing this, shrinkage cracks from the hardfacing to the base metal can be avoided.
- Hardfacing: Here is when the job is done. This consists of the addition of coating layers to the workpiece. Normally 3 layers are the most you can add but are unlimited when using certain materials.
Who may need hardfacing?
In short, hardfacing is the option for any company trying to save in parts or equipment with a high rate of abrasion or erosion. Some of the many industries in which hardfacing is quite popular or convenient are:
- Mining
- Sugarcane and food
- Steel
- Power
- Cement
- Petrochemical
- Construction
But this list does not pretend to be exclusive, so despite your industry not being there, chances are hardfacing may be an option for you.
So, if after reading this you have concluded that hardfacing is a must in your industry, a first step should be to find the appropriate equipment and consumables to carry it on. Count on us for this.
You are not alone in this
We, the people at Ifexport have been working with industrial processes, like hardfacing, since 1979. So, we can tell you one thing or two about it.
Helping our clients to implement hardfacing effectively is one of our goals. We can’t wait to apply our expertise to your workshop also.
