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Vineet Shibe & Vikas Chawla / Mechanica Confab ISSN : 2320-2491
Vol. 2, No. 3, April-May 2013 111
ENHANCEMENT IN WEAR RESISTANCE BY
HARDFACING: A REVIEW
Vineet Shibe*, Vikas Chawla
1
*
Ph.D. Research Scholar, Department of Mechanical Engineering, Punjab Technical
University, Jalandhar, India
1
DAV College of Engineering and Technology, Kanina, District Mohindergarh, India
shibevineet@gmail.com, vikkydmt@gmail.com
Abstract
Many Industries face the problem of wear on components in service. Due to wear the
components need replacement, which costs money and causes downtime of the equipment.
Surfacing is a process of depositing a material layer over a base metal or substrate either to
improve surface characteristics like corrosion resistance, wear resistance, etc. or to get the
required size or dimension. The economic success of the hardfacing process depends on
selective application of hardfacing material and its chemical composition for a particular
application. Many studies revealed that carbon and chromium are the major elements which
are used in hardfacing alloys. It is found that the by varying the percentage of carbon and
chromium corrosion and wear resistance can be enhanced. In this paper an attempt has been
made to discuss the various types of wear, surface protection by hardfacing techniques,
Manual Metal Arc Welding (MMAW) process and applications of hardfacing.
Keywords: Wear, Hardfacing, Manual Metal Arc Welding (MMAW)
1. Introduction
In well-designed tribological systems, the removal of material is usually a very slow
process but it is very steady and continuous [1]. The modes or different types of wear are:
abrasion, erosion, corrosion, adhesion, impact and surface fatigue. The surface characteristics
of engineering materials have a significant effect on the serviceability and life of a
component thus cannot be neglected in design. Surface engineering can be defined as the
branch of science that deals with methods for achieving the desired surface requirements and
their behavior in service for engineering components. The surface of any component may be
selected on the basis of texture and color, but engineering components generally demand a lot
more than this. Engineering components must perform certain functions completely and
effectively, under various conditions in aggressive environments. Engineering environments
are normally complex, combining loading with chemical and physical degradation to the
surface of the component. Surface wear is a phenomenon, which effects how a component
will last in service. Surface coatings can help to deal with the circumstances such as
component working in an aggressive environment. In wear resistant components, as their
surface must perform many engineering functions in a variety of complex environments. The
behavior of a material is therefore greatly dependent on the surface of a material and the
Vineet Shibe & Vikas Chawla / Mechanica Confab ISSN : 2320-2491
Vol. 2, No. 3, April-May 2013 112
environment under which the material must operate. The surface of these components may
require treatment to enhance the surface characteristics. Surface modification techniques such
as hardfacing and surface coating may be used enhance the wear resistance. In this paper
surface protection by hardfacing techniques, Manual Metal Arc Welding (MMAW) process
and applications of hardfacing are discussed.
2. Wear
Wear is a process of removal of material from one or both of two solid surfaces in
solid state contact, occurring when two solid surfaces are in sliding or rolling motion together
[4]. The deterioration of surfaces is a very real problem in many industries. Wear is the result
of impact, erosion, metal-to-metal contact, abrasion, oxidation, and corrosion, or a
combination of these. Figure 1 shows the five main categories of wear and the specific wear
mechanisms that occur in each category [14].
Figure 1. Flow Chart of Various Wear Mechanisms
2.1. Abrasion
Abrasion is the wearing away of surfaces by rubbing, grinding, or other types of
friction. It usually occurs when a hard material is used on a softer material. It is a scraping or
grinding wear that rubs away metal surfaces. It is usually caused by the scouring action of
sand, gravel, slag, earth, and other gritty material.
Vineet Shibe & Vikas Chawla / Mechanica Confab ISSN : 2320-2491
Vol. 2, No. 3, April-May 2013 113
Figure 2. Abrasion Mechanism
2.2. Erosion
Erosion is the wearing away or destruction of metals and other materials by the
abrasive action of water, steam or slurries that carry abrasive materials. Pump parts are
subject to this type of wear. The impingement of solid particles, or small drops of liquid or
gas often cause what is known as erosion of materials and components. As shown in Figure
3 the erosion mechanism is simple. Solid particle erosion is a result of the impact of a solid
particle A, with the solid surface B, resulting in part of the surface B been removed.
Cavitation erosion occurs when a solid and a fluid are in relative motion, due to the fluid
becoming unstable and bubbling up and imploding against the surface of the solid.
2.3. Adhesive Wear
It is often called galling or scuffing, where interfacial adhesive junctions lock together
as two surfaces slide across each other under pressure. As normal pressure is applied, local
pressure at the asperities become extremely high. Often the yield stress is exceeded, and the
asperities deform plastically until the real area of contact has increased sufficiently to support
the applied load, as shown in Figure 4. In the absence of lubricants, asperities cold-weld
together or else junctions shear and form new junctions. This wear mechanism not only
destroys the sliding surfaces, but the generation of wear particles which cause cavitation and
can lead to the failure of the component. An adequate supply of lubricant resolves the
adhesive wear problem occurring between two sliding surfaces.
2.4. Surface Fatigue
When mechanical machinery move in periodical motion, stresses to the metal surfaces
occur, often leading to the fatigue of a material. All repeating stresses in a rolling or sliding
contact can give rise to fatigue failure. These effects are mainly based on the action of
stresses in or below the surfaces, without the need of direct physical contact of the surfaces
under consideration. When two surfaces slide across each other, the maximum shear stress
lies some distance below the surface, causing micro cracks, which lead to failure of the
Vineet Shibe & Vikas Chawla / Mechanica Confab ISSN : 2320-2491
Vol. 2, No. 3, April-May 2013 114
component. These cracks initiate from the point where the shear stress is maximum and
propagate to the surface as shown in Figure 5.
Figure 3. Schematic of Erosive Wear
Figure 4. Schematic of Generation of Wear Particle as a result of Adhesive Wear
Figure 5. Schematic of Fatigue Wear
Vineet Shibe & Vikas Chawla / Mechanica Confab ISSN : 2320-2491
Vol. 2, No. 3, April-May 2013 115
2.5. Corrosion
The dynamic interaction between the environment and mating material surfaces play a
significant role, whereas the wear due to abrasion, adhesion and fatigue can be explained in
terms of stress interactions and deformation properties of the mating surfaces. In corrosive
wear firstly the connecting surfaces react with the environment and reaction products are
formed on the surface asperities. Attrition of the reaction products then occurs as a result of
crack formation, and/or abrasion, in the contact interactions of the materials. This process
results in increased reactivity of the asperities due to increased temperature and changes in
the asperity mechanical properties.
3. Surface Protection by Surface Modification Techniques
Serviceable engineering components not only rely on their bulk material properties but
also on the design and characteristics of their surface [14]. Although considerable attention
has already been paid by the researchers to develop modern techniques to prevent and control
the problems resulting from wear; still there is a need for further research to reduce the losses
incurred. These wear and corrosion related problems can be minimized mainly by following
two methods [13]:
• By using high cost wear resistant alloys/metals better than the existing low cost ones.
• By improving the wear resistance of the existing metals and alloys by applying certain
modifications to the surface.
Individuals and industry tend to focus on the wearing surface that has the greatest impact
on their own economic situation. As the wear is a surface phenomenon and occurs mostly at
outer/mating surfaces, therefore it is more appropriate and economical to use the latter
method of making surface modifications than using the former one which will not only
involve very high cost of the operation but also involve longer time as compared to the
second technique. To this end; a host of surface modification techniques can be used such as
hardfacing by welding or thermal spraying in which a layer of strong and hard alloys is fused
onto the surface of the component for improving its wear resistance [15].
4. Hardfacing
Surface modification techniques are used to enhance the service life of several
engineering components. Surfacing is one of such technique, wherein a superior material is
deposited over industrial components, by welding, to enhance surface characteristics.
Material loss due to wear in various industries is significantly high. All these components
face the problem of wear, before put into service, are given a surface hardening treatment or a
protective coating with wear resistant materials of various types, depending upon its service
conditions. After a period of service these components will get reduced in size because of
wear and can no longer be used. So these components either have to be rebuilt or rejected.
Rebuilding of these components to the required size by welding can save the cost
tremendously. Surfacing is a cost effective and proven method of depositing protective
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coating. The effect of surfacing on component life and performance will depend upon the
surfacing material and the application process.
Hardfacing is one of the versatile techniques that can produce the hard and wear
resistant surface layer of various metals and alloys on metallic substrate. It not only helps
them withstand wear, but also helps to prevent corrosion and high temperature oxidation [16].
Hardfacing is a commonly employed method to improve surface properties of agricultural
tools, components for mining operation, soil preparation equipments and others. An alloy is
homogeneously deposited onto the surface of a soft material (usually low or medium carbon
steels) by welding with the purpose of increasing hardness and wear resistance without
significant loss in ductility and toughness of the substrate [5]. The hardfacing technique has
in the mean time grown into a well-accepted industrial technology. Due to continuous rise in
the cost of materials as well as increased material requirements, the hardfacing has been into
prominence in the last few decades. Manual Metal Arc Welding (MMAW) process is
commonly selected for hardfacing applications, as it is highly versatile and most economical
[12].
5. Hardfacing Deposition Techniques
The various types of hardfacing deposition techniques are as under:
• Thermal Spraying
• Cladding
• Welding
5.1. Thermal Spraying
These processes are preferred for applications requiring thin, hard coatings applied
with minimal thermal distortion of the work piece and with good process control. These
processes are most commonly use the coating material in the powder form, and almost
any material capable of being melted without decomposition, vaporization, sublimation, or
dissociation can be thermally sprayed.
5.2. Cladding
These processes are used to bond bulk materials in foil, sheet or plate form to the
substrate to provide triboligical properties. The cladding processes are used either where
coatings by thermal spraying and welding cannot be applied or for applications which require
surfaces with bulk like properties. Since relatively thick sheets can be readily clad to
substrate, increased wear protection may be possible compared to thermal spraying and
welding. If the coating material is available in sheet form, then cladding may be cheaper
alternative to surface protection. It is difficult to clad parts having complex shapes and
extremely large sizes.
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5.3. Welding
Welding is preferred for applications requiring dense relatively thick coatings (due to
extremely deposition rates) with high bond strength. Welding coatings can be applied to
substrate which can withstand high temperatures (typically 7900 C). Welding processes most
commonly use the coating material in the rod or wire form. Thus, materials that can be easily
cast in rods or drawn into wires are commonly deposited. In Arc Welding the substrate and
the coating material must be electrically conductive. Welding processes are most commonly
used to deposit primarily various metals and alloys on metallic substrates.
Hardfacing by arc welding is performed using all of the common processes and
equipment. From the arc welding group, Manual Metal Arc Welding (MMAW), or stick
welding is the most common and versatile process, although it does not provide the highest
deposition rate. The rate of dilution depends on materials and on the welder’s skill.
Submerged Arc Welding can provide a much higher deposition rate if the conditions are
correct for uninterrupted alloy deposition of hardfacing filler wire. The limitations are that
dilution tends to be higher unless speed is kept as high as possible, and that the process is not
readily adapted to field conditions. GMAW, or MIG, where shielding is provided only by
inert gas, is readily applicable but only for those fillers supplied in wire form, and usefully
complements the range of applications of the preceding process.
6. Hardfacing Processes
There are various processes for hardfacing. They can be grouped in the following
ways [11]:
6.1. Hardfacing by Arc Welding
Shielded Metal Arc Welding [Amado et al., (2008)], Flux Cored Arc Welding
[Coronado et al., (2009)], Submerged Arc Welding [Chang et al., (2003)].
6.2. Hardfacing by gas welding
Deposition by Oxy-Acetylene Gas Welding [Buchely et al., (2005)].
6.3. Hardfacing by combination of arc and gas
Tungsten Inert Gas Welding [Kashani et al., (2007)], Gas Metal Arc Welding [Fouilland et
al., (2009)].
6.4. Powder Spraying
Flame Spraying [Navas et al., (2006)], High Velocity Oxy-Fuel Process [Lin et al.,
(2006)], Electric Arc Spraying [Buchanan, (2009)], Plasma Transferred Arc [Oliveira et al.,
(2002)] etc.
6.5. Laser hardfacing
Laser hardfacing (Laser Cladding) [Ming et al., (1998)].
Vineet Shibe & Vikas Chawla / Mechanica Confab ISSN : 2320-2491
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7. Hardfacing alloys
Different types of hard-facing alloys are available and they fall into four general
categories [11]:
• Low-alloy iron-base alloys
• High-alloy iron-base alloys,
• The cobalt-base and nickel-base alloys
• Tungsten carbide materials
8. Base Materials
Almost 85% of the metal produced and used is steel. The term steel encompasses many types
of metals made principally of iron. The various types of steels used in the industry for making
different components for different applications are grouped into the following types [11]:
• Low-Carbon Steels and Low-alloy Steels
• Medium-Carbon Steels
• High-Carbon Steels
• Other steels are Low-Nickel Chrome Steels, Low-Manganese Steels, Low-Alloy
Chromium Steels and the electric furnace steels
9. Manual Metal Arc Welding (MMAW)
Welding with stick electrodes is called Manual Metal Arc Welding (MMAW). In this
process heat required for fusion is generated by the electric arc formed between a metallic
electrode and the base metal. The electrode is consumed in the arc and provides the filler
metal on the substrate. The extremely high arc temperature of over 5000°C permits it to
supply a large amount of heat.
Figure 6. Manual Metal Arc Welding (MMAW) Process
Vineet Shibe & Vikas Chawla / Mechanica Confab ISSN : 2320-2491
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Among the arc processes, manual metal arc welding is the most common, versatile,
inexpensive one, and has advantages in areas of restricted access and accounts for over 60%
of the total welding in advance countries and over 90% of the total welding in India.
9.1 Merits of MMAW process over other welding processes used for Hardfacing
• Flexible
• Inexpensive
• Can used in areas of restricted access
• Ideal for repairs
• All position welding is possible
• Most common and versatile.
9.2 Demerits of MMAW process used for Hardfacing
• The major disadvantage of the MMAW process used for hard facing is the high
degree of the skill required for the welder.
• Relatively low productivity in terms of rate of metal deposition.
10. Benefits of Hardfacing
• Most Versatile: Hard facing is the most versatile process to improve the life of the
worn out component.
• Best chosen: Hard facing is the best chosen process these days for reducing the cost
of replacement.
• Reduces downtime: Hard facing reduces downtime because parts last longer and
fewer shutdowns are required to replace them.
• Any steel material: Hard facing can be done on any steel material using wide
variety of welding processes.
• Desired property: Different alloying elements can be introduced into the base metal
in the form of weld consumables to achieve any desired property like hardness, wear
resistance, abrasive resistance, crack resistance etc.
• Longer service life: Fewer replacements of parts are needed when parts are hard
faced.
• Higher productivity: Upon improving wear life, this contributes to the equipment
working and producing more per hour. This increases the productivity and profits.
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• Less downtime: Greater availability of machine, a longer service life means that you
will spend less time replacing the tips. This contributes to a reduction in operating
costs.
• Reduced cost: As wear resistance and hardness are the required at surface, one can
deposit the superior material on the substrate to enhance the surface characteristics at
less cost.
11. Some Industrial Applications of Hardfacing
• Agriculture: Plowshare points, Soil-tamper points, Harrower teeth, Tiller blades,
Canadian plowshare points, Blade components of silo feeding equipment.
• Automotive: Trucks, automobiles, highway construction and agricultural vehicles,
cam actuators and shafts, Exhaust manifolds, Pumps, Mufflers, Brakes, Clutches,
Cones, Synchronizers, Valve heads and stems, Inlet and exhaust seats, Eccentrics,
Eccentric shafts, Rods, Rockers.
• Building construction: Brick moulds, Wear plates, Mixing machine blades, Fuller
screws, Crushing cylinders, Punches and dies for ceramic materials.
• Chemical: Pump shafts and sleeves, Rotating joints, Valves, Mixer blades,
Homogenizer blades, Agitator blades, Moulds, Shearing equipment.
• Food Processing: Extruder screws for vegetables oils, Grain mill equipments, Corn
and sugar cane cutting equipments, Archimedean screws.
• Glass & Ceramics: Moulds, Screws, Mixing blades, Kneader blades, Agitator
blades, Shearing equipment.
• Leather goods
• Cutting tools and equipment
• Metal Working: Shear blades, Conveyor rollers, Surface cleaning rollers,
Straightening rollers, Draw die equipment, Moulds, Cast iron and galvanized pipe
production.
• Mining Ore: Crusher blades, Power-shovel teeth, Conveyor chains, Agglomeration
grilles, Scraper blades, Cut-off blades, Coke oven supports, Blast-furnace hoppers,
Pump sleeves and conduits, Filters, Elevator conveyor belts.
• Naval works: Rod ends, Blower turbines, Piston rods, Transmission shafts, Screw
shafts.
• Paper: Roll cylinders for continuous machines, Drying cylinders, Mixers, Heaving
plates, Pressure bars.
• Petroleum: Blowers and ventilators, Pumps, Heat exchangers, Rods.
• Power generation: Turbines, Joints.
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• Public works: Steam shovel teeth and edges, Excavator teeth, Bulldozer blades and
teeth, Dredge rollers, Tractor rollers and track links, Rubber Tire moulds, Mixers.
• Shop Machinery: Tool machinery, Carriage guides, Mandrels and spindles, Tail
stocks, Bushings.
• Steel & Foundry: Ventilator and blower parts, Coke wagons, Blower nozzles, Feed
rollers, Gaskets, Speed reducer, Ore and earth handling equipment, De-flashing dies,
Shear blades, Punches, Forging moulds and punches, Sheet metal conveyor guide,
Smooth-faced rollers.
• Textiles: Filament guides, Diagonal cutter, Rollers, Heating plates, Cloth puller.
12. Conclusion
Surfacing by hardfacing is an economical tool which can be used to increase the
service life of the components used in various types of industries. The economic success of
the hardfacing process depends on selective application of hardfacing material and its
chemical composition for a particular application. Effort should be made for the right
selection of surfacing materials and the process to achieve the full advantage of hardfacing.
Carbon and chromium are the major elements which are used in hardfacing alloys. It is found
that less percentage of carbon and high percentage of chromium will enhance corrosion
resistance whereas the high percentage of carbon and chromium will increase wear resistance
as well as hardness.
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