This is the first of a two-parter in which ESAB’s Mick Andrews takes Andrew Pearce through the finer points of hardfacing, piercing and gouging. Sounds painful…
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Hardfacing is something of a mystery. It’s like driving round the farm on a foggy morning – all the familiar landmarks are there but somehow different, and you’re not necessarily sure that you’re looking at a profitable operation.
Still, this much is clear. Hardfacing is the business of laying down abrasion – and (maybe) impact-resistant metal on new or worn mechanical or soil-engaging parts, with the aim of extending service life.
The thick rod coat contains metal powder, so hardfacing consumables lay down more material than core wie diameter alone suggests. That is, the recovery rate is more than 100%.
Next time: Weave patterns for hardfacing and a look at gouging and piercing electrodes – handy things to take to the field.
More welding advice
The speed and ease of MIG/MAG welding suggests that’s the way to go. But hardfacing with MIG means using cored wires, and to get the required burn-off and fusion with these needs more current than single-phase sets can deliver.
So for most farms, the weapon of necessity is a manual metal arc (MMA) stick set. Depending on the rods you choose, even that may not be up to scratch, as Get set explains.
Matching electrode and job takes us back into the fog. Most repair and fabrication involves mild or low-alloy steels, so you can jog along quite happily with general-purpose rods; their forgiving composition handles surface contamination and minor variations in metal make-up.
But wear-resistant parts are made of sterner stuff. In the workshop it’s impossible to fathom their composition, so the repairer can’t properly match electrode and material in the way that industry can.
The wrong rod and/or technique can see expensive hard covering flaking off, and perhaps even the whole part cracking through – although with a little care neither should happen. To make sure it doesn’t, here’s the low-down on electrode selection and care, plant setting, pre- and post-heat treatment and welding technique.
First though, please take two cautions to heart – see Alerts.
Rod selection and care
Hardfacing rods can be formed as a tube packed with flux and powdered metal, or as a conventional coated stick. ESAB offers the latter.
Four ESAB electrodes cover farming’s needs:
1. OK 83.28 is a low-alloy rod designed for building up parts in metal-to-metal contact: gears, sprockets, clog clutches and so on. Hardness is 30 HRC, machinability is good. Min OCV 70V, AC or DC+ operation.
2. OK 83.50 is a low alloy, high carbon electrode for repair and of worn parts. Runs from small sets with low open circuit voltage. Resistant to abrasion and impact. Hardness is 50-60 I-IRC; can only be ground, not machined. Min OCV 45V, AC or DC+ operation
3. OK 84.78 contains chromium carbides and is for surfacing only. Ideal for very abrasive soils or corrosive conditions. High recovery – puts down a lot of metal for a given rod diameter. Hardness 59-63 HRC so can only be ground. Min OCV 50, AC or DC+ operation.
4. OK 84.84 is a very expensive, complex carbide-containing rod for surfacing only, suited to extremely abrasive soils where pressure on the part is high. Good for edges, unusual in giving high hardness for a single layer.
Hardness is 62 HRC, can only be ground. Min OCV 45V, AC or DC+ operation. Keep rod vertical to work while welding. Notes: Equivalent rods are available in other brands. HRC is a comparative hardness scale.
The electrodes above come vacuum-packed to keep them dry. Once opened and stored, all four types should be oven-baked before use, or water in the coating is likely to produce hydrogen, cracking the weld. RE-drying instructions are on the packet, along with info on welding current range, OCV requirement and so on.
ESAB’s hardfacing consumables come vacuum-packed. Plant setting and re-drying requirements are on the pack.
The harder the deposit, the less flexible and more brittle it is. If very hard material is laid directly over substantially softer metal, the top layer may crack on cooling and flake or spall off altogether, and the expensive hard metal is diluted by mixing with the softer stuff.
One way round cracking and spalling is to use a buffer or buttering layer between soft and hard metal, like the jam in a sandwich. ESAB’s OK 67.45 lays down the required tough, stress-absorbing buffer, while dilution can be kept down by welding relatively quickly, and by using minimum current and minimum weave to restrict melt and mix.
How do you know when to butter? This is formally defined according to parent material and impact level in service, but lacking accurate information on the former have to suck it and see.
The simple way is to hardface a few trial parts without buttering, and if the top coat stays put in work you’ll have the answer.
The more complicated – but much better -approach is to badger the maker of the part to be surfaced for info on its composition, than to ask an corrode supplier about the best technique and rods for the job.
Importantly and irrespective of buttering, at least two hardfacing layers are usually needed for the top one to show maximum hardness.
While not all hardfacing rods require it, pre-heating and slow cooling of the work make good insurance against cracking. Usually pre-heat is to a specific temperature, but in the rough-and-ready workshop it’s enough to warm the part evenly and thoroughly with a gas torch.
The aim is just to drive off any water, so don’t overdo it. After welding let the work cool slowly in air. Quenching is a sure way to produce cracks or worse.
ESAB’s hardfacing consumables come vacuum-packed. Plant setting and re-drying requirements are on the pack.
Nothing out of the ordinary here in rod angles, speed of travel, arc length and plant setting – just keep within the requirements laid out on the packet and weld as you would with a general-purpose rod.
Expect a fluffy arc punctuated by quiet spittings (much like cast iron or special-steel rods) with a lacy slag covering to follow. Watch your eyes with this, as bits can ping off spontaneously as the weld cools.
Hardfacing electrodes are designed to give a quick-freezing deposit which helps when working along edges, but paradoxically the weld pool tends to be wide.
This makes working away from the flat rather tricky; use the shortest arc, lowest current and fastest travel consistent with good fusion to control the pool. Overhead work is best avoided or left to owners of a thoroughly fireproof hat.
Use conventional arc length, travel speed and rod angles when handfacing. For overlapping passes, angles are roughly 60° from vertical, 45° from parent material. Weave patterns will be covered next time.
A VOLTAGE – the open circuit voltage or OCV – must exist between the electrode and work before the arc can strike. Simple stick units have one output terminal and generally offer 50V OCV. Others provide a second tine at up to 90V.
Stick welding electrodes always have a specific OCV requirement. General-purpose rods are usually happy strike and run at 50V, but specialist rods – including some hardfacing varieties – need higher voltage to strike cleanly and run with a stable arc.
So before buying consumables, ask the supplier for their OCV requirement and check that your set can deliver the goods. If it can’t the results will be poor.
DONT hardface I2-14% manganese steel. Often used for bucket teeth and other bits which have to put up with high impact, this material is very tough, but quickly turns brittle when re-heated and slow-cooled – so the heat from the hardfacing is very likely to crack to it. Structural steels with lower manganese content are fine.
High manganese steels are typically used in crushing and milling applications and, crucially, aren’t magnetic. Otherwise they’re light grey in colour and are usually castings, designed to be bolted on to avoid welding.
Sometimes they come with a warning label, and may have the letters ‘MN’ cast into them.
Now to fume. Hardfacing electrodes carry a lot of metallic elements in their flux coating – which is how even a small diameter rod manages to lay down a very substantial bead.
Consequently hardfacing fume contains much human-damaging heavy metal vapour, which won’t do you any good at all.
Ideally, use forced fume extraction. If that’s not possible, wear a specific welding respirator marked EN149:2001 (3M’s disposable 06920 mask is an example). Work in moving air and stay out of the main fume column.
Hardfacing releases more hazardous metal vapour than general repair work. If fume extraction is not possible, wear a purpose-designed welding respirator and stay out of the main fume column. Nuisance dust respirators will not protect.
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Welding is typically a process of joining two pieces of material using the heat generated by an electric arc and often a filler material to add and strengthen the resulting joint. However, the same basic technique can be used in other ways by adjusting a few parameters. A primary example is plasma cutting, which is largely the same as arc welding but with a controlled jet of gas used to melt and blow away material to cut rather than combine.
A similar adjustment of parameters leads to hardfacing. Some think of hardfacing as a complex and advanced technique that only the most experienced welding operators can pull off. Others just consider it an irritation and not worth the time and effort required to perform it. What is it, though, and how can you use the process? Let’s discuss.
What is Hardfacing and How Does it Work?
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Hardfacing is a process where you use the general concept of welding – specifically the deposition of material – to coat the outside of a base metal with a tougher, harder metal. This can make the resulting workpiece more durable, more resistant to abrasion, wear, and damage, and expand its longevity. Hardfacing is performed using specialized electrodes or filler rods but largely uses the same kind of arc welding process to melt those fillers onto the surface of the base material.
This isn’t quite the same as something like adhering a shell to the outside of a workpiece. Since the welding process is used, the surface of the base material is melted enough to combine with the filler material, resulting in a merger of the two. This creates a thick, dense layer between 1 and 10 mm, made of a highly bonded, wear-resistant alloy combining the base and filler metals.
Hardfacing improves the surface strength, ductility, wear resistance, corrosion resistance, and erosion resistance of the original workpiece. It can be performed on cast iron, copper, and nickel alloys, stainless steel, carbon steel, and manganese steel.
One key to successful hardfacing is minimizing heat. While you need enough surface melt to the base material to adhere to the hardfacing filler, you want as little mixing as possible because the base material will soften the added material and reduce the utility of the hardfacing. Therefore, knowing what material you’re hardfacing is critical so you can identify ideal temperatures.
What Are the Benefits of Hardfacing?
Hardfacing is a way to strengthen and extend the working life of metal parts that see a lot of wear, particularly surface wear. By hardfacing a worn part, additional lifespan can be drawn from the base workpiece, extending longevity and reducing the need to replace it; this saves money over the long run.
Hardfacing is commonly used in agricultural and mining situations and is frequently also an option for getting more useful life out of a part while a replacement is on order. In remote locations or for specialized parts that need lead time to be made and shipped, when the difference is between halted operations and continued operations, hardfacing can make the difference.
Overall, hard facing can be used to minimize the downtime spent replacing worn or broken parts, allows you to store fewer replacements on-site if you typically do so, and increases the average lifespan of those parts. In many cases, the lifespan of a working piece can be extended by up to 300% with dedicated hard facing, which can mean overall savings for the company of 25% to 75% in the cost of replacements.
Where is Hardfacing Often Used?
Hardfacing can be used in a wide range of different applications. Since it’s coating the outside of a workpiece, it’s generally used on pieces that have to resist impacts or abrasions over time.
In construction, an excavator’s plow is one common piece that has to endure an immense amount of impact and erosion damage. Heavy use of an excavator can wear it down, reducing the strength of the plot and even the workable dimensions of the machine. Hardfacing the plow strengthens it against this kind of damage.
In agriculture, the manufacture of sugar involves crushing sugarcane in a roller. Despite being a plant – which you might not think of as being able to damage metal parts – the sugarcane plant is quite strong and can give as good as it gets. These rollers can be hard-faced to help resist the damage of continually crushing sugar cane and extend the operating life of the machine.
Another common example from mining is the crusher that breaks up larger chunks of ore-bearing material for processing. There are a wide range of different designs for these machines, but many of them end up using plates of metal and heavy motors to crush rock. Rock, too, resists being crushed and will damage and abrade the crusher over time. Hardfacing the jaws of the crusher will help them resist that force and can be used as a repair to restore functionality to damaged jaws before they need to be fully replaced.
Are There Different Techniques for Hardfacing?
Yes. Hardfacing can be performed in two ways: overlay and build-up. These are roughly equivalent to enhancing existing materials and repairing damaged materials.
Imagine a workpiece with many gouges, scratches, abrasions, dings, scrapes, and other forms of damage from long use. The workpiece is worn and nearing the end of its lifespan. Such a piece can be restored with hard facing using the build-up technique. Build-up hardfacing entails using the welding process to deposit hardfacing material and spending additional time and care on the deeper gouges and abrasions to rebuild the working surface of the workpiece. A layer to smooth and even out the working surface is applied, and any finishing is performed.
Overlay hardfacing can be done on pieces that have been built up already using the previous technique or on brand-new or barely-worn pieces that need additional reinforcement to expand their lifespan. This technique simply uses repeated and iterative passes of hard facing to deposit a layer of material across the entire surface of the workpiece; no special care is necessary for repairs because no repairs are necessary. It’s simply a method of reinforcement.
How is Hardfacing Performed?
The step-by-step process of hard facing is relatively simple and similar to many other welding processes. The primary difference is that it takes place over the whole surface of a typically large workpiece rather than along a single seam or crack in the workpiece.
Step one is to clean the part. Since hard facing is typically used on working machines, these have likely built up grime, dirt, oils, greases, rust, and chemicals, all of which can inhibit the performance of a weld and cause inclusions, weaknesses, and faults in the resulting surface. A thorough cleaning is required to avoid cracking, warping, and damage to the workpiece. This process may even need to be performed on brand-new pieces, particularly if they’ve been painted or coated in rust-resistant chemicals.
Step two is to perform build-up hard facing on any deep gouges, abrasions, cracks, or other damage to the surface of the workpiece. Hardfacing requires that the surface be more or less the shape and form you want the finished piece to be, so any repairs you need to make should be made at this step in the process. This isn’t necessary for new pieces you’re reinforcing with hard facing, as there’s likely no damage to repair.
Step three is to “butter” the part. Buttering is the act of forming a thin buffer layer between the base material and the hardfacing material. It’s most commonly used in cases where the two materials are dissimilar and will have a hard time bonding with one another. By using an intermediary as a buffer layer, you can create more comprehensive bonds and reduce the chances of the final coating cracking or shrinking and causing problems.
The fourth and final step is to perform the actual hard facing. This is where you apply your coats of hardfacing material. This may be spotty and sporadic, or it may be comprehensive and can be anywhere from one to three coats for most situations.
One critical component of the actual hardfacing process is deciding on a hardfacing pattern. While a complete coat of cladding can be used, this is often unnecessary, depending on the purpose of the workpiece. Other patterns include:
Dots. A dot pattern involves using a series of regularly spaced dot-shaped welds to deposit the hardfacing material across the surface. This is typically used on machines that deal with larger rocks and aggregate; smaller material can fill the gaps between the raised dots, while the raised dots become the source of impact and are strengthened against it. Other types of impact are cushioned by the “dead bed” between the dots.
Stringers. Stringers are long, straight beads of welding, typically spaced some distance apart, between a quarter of an inch all the way up to 1.5 inches. This is typically chosen with beads that run parallel to the direction the material flows in use, so it doesn’t “catch” and cause more damage to the hard-faced material.
Waffles. A waffle, criss-cross, or herringbone process is perpendicular beads that leave small square pockets behind. Again, this is usually used for dealing with larger aggregate materials, where smaller materials and sand form a cushioning bed in between.
All of these patterns are ways to save time, energy, and material when hardfacing, so you don’t have to coat the entire working surface of a piece completely.
Hardfacing Frequently Asked Questions
What does successful hardfacing look like? Ironically, hard facing often looks visually like bad welds because it’s an uneven and rough build-up of material on the surface of the workpiece. In a way, it’s almost like more of a “brute force” approach to welding rather than more elegant seams and connections.
What materials can and can’t be hard-faced? Hardfacing is generally done on harder steels, like stainless, manganese, carbon, and alloy steels. It can also be performed on cast iron, nickel-base alloys, and copper-base alloys. Other base materials are often too soft to take hardfacing well or are not used in the kinds of applications where hardfacing is beneficial.
One of the greatest details of hardfacing is that it’s only applicable to high-wear pieces in heavy industry. It’s typically not used in cases where direct wear isn’t responsible for damage. That is, cases where the cause of damage is flexing stress or sheer stress are not going to benefit from hard facing.
What’s the best process for hard facing? Many forms of hard facing are performed using submerged arc welding. Another popular process is flux-core arc welding. However, any welding process can be used for hardfacing, up to and including plasma arc welding, laser welding, and even brazing.
What matters most is the heat control and deposition rates of the process you choose. Some processes have better deposition rates and can hardface a workpiece faster and more effectively. Others need more careful control to avoid overheating the area. At the end of the day, though, what matters most is that you pick a process you’re familiar with and can control well.
What is “wear” in the industry? Most often, wear is caused by abrasion with a material like rock or aggregate or by impact. Sometimes, wear can be defined as metal-to-metal abrasion, heat, or corrosion, but these are less common in the cases where hard facing is most beneficial. Additionally, many different kinds of wear can apply at once; using an excavator to plow can cause both abrasion and impact, for example.
How can you pick the best machine for hardfacing? The best machine for hardfacing is one that can handle long duty cycles with enough power to deposit material quickly and limit the heat-affected zone of the base material. As such, nearly any good welder can handle the process, but it can benefit more from a 220v machine over a 110v machine. Either way, there are many options you can explore to find the welder that best suits your needs. Our welding equipment rentals help you test and try out machines and, if you don’t like them, return and rent different machines.
Red-D-Arc, an Airgas company, rents and leases welders, welding positioners, welding-related equipment, and electric power generators – anywhere in the world. Our rental welders, positioners and specialty products have been engineered and built to provide Extreme-Duty™ performance and reliability in even the harshest environments, and are available through over 70 Red-D-Arc Service Centers, strategically located throughout the United States, Canada, the United Kingdom, France, and the Netherlands, as well as through strategic alliances in the Middle East, Spain, Italy, Croatia, and the Caribbean. From our rental fleet of over 60,000 welders, 3,700 weld positioners, and 3,700 electric-power generators, we can supply you with the equipment you need – where you need it – when you need it.
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