hardfacing to increase wear resistance

National Conference on Advancements and Futuristic Trends in Mechanical and Materials Engineering (February 19-20, 2010)

Yadavindra College of Engineering, Punjabi University Guru Kashi Campus, Talwandi Sabo 90

IMPROVEMENT IN ABRASIVE WEAR RESISTANCE BY

HARDFACING: A REVIEW

A.K.Mangla1*, Sehijpal Singh

2, J.S. Grewal

2, Vikas Chawla

1

1 Mechanical Engineering Department, L.L.R.I.E.T., Moga-1442001, India.

2 Mechanical Engineering Department, G.N.D.E.C., Ludhiana-141003,India * Corresponding author. Phone: +91-9417341292 Fax: +91-1636-265319

Email: [email protected]

ABSTRACT

Wear is the major problem leading to replacement of engineering components in the

industry. For many years, welding technology has supplied an effective means of

protecting the surface of components. Surfacing is used to produce a composite material

i.e. base material that has good mechanical properties such as strength and toughness and

a surface coating that can withstand abrasion, corrosion and impact. 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. If a hard wear resistant material is deposited over a soft,

ductile material to improve wears resistance then it is called as hardfacing. It is a modern

procedure, which nowadays is mainly applied for bigger construction parts, in order to

extend the lifetime, instead of using massive solutions, such as castings. This“added

value” makes the parts more valuable. The economic success of the 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 majar elements

which are used in hardfacing alloys. The formation of chromium carbide enhance the

wear resistance and hardness. The varying percentage of C and Cr has different effects.

It is found that carbon less than 0.3% and high percentage of chromium will enhance

corrosion resistance but the high C and high chromium will increase wear resistance as

well as hardness.

1. Introduction

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 behaviour

in service for engineering components. The

surface of any component may be selected on the

basis of texture and colour, 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. An example of a component

working in an aggressive environment is a

cutting tool used in machining processes. The

tool experiences high loads, high speeds and

friction and, as a consequence, high

temperatures. These factors lead to surface wear

of the component. Surface coatings can help to

deal with these circumstances. Improving the

tool surface, not only improves the life of the

tool, but also improves the surface finish of the

machined part. In wear resistant components, as

their surface must perform many engineering

functions in a variety of complex environments.

The behaviour of a material is therefore greatly

dependent on the surface of a material and the

environment under which the material must

operate. The surface of these components may

require treatment, to enhance the surface

characteristics.



2. Wear 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. The effects of wear, which

are extremely expensive, can be repaired by

means of welding. Surfacing with specialized

welding filler metals using the normal welding

processes is used to replace worn metal with

metal that can provide more satisfactory wear

than the original. Hardfacing applies a coating

for the purpose of reducing wear or loss of

material by abrasion, impact, erosion, oxidation,

cavitations, etc. In order to properly select a hard

facing alloy for a specific requirement it is

necessary to understand the wear that has

occurred and what caused the metal

deterioration.

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.

The various types of wear can be categorized and

defined as follows:

.

Figure1.2, Abrasion

Figure 1.1, Flow chart of various wear mechanisms 2.2 Erosion It 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 1.3 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 1.4. 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

microcracks, which lead to failure of the

component. These cracks initiate from the point

where the shear stress is maximum, and

propagate to the surface as shown in figure 1.5.

Figure1.3, Schematic of erosive wear

Figure1.4, Schematic of generation of wear particle as

a result of adhesive wear

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 Many of the above types of wear occur in

combination with one another. It is wise to

Figure1.5, Schematic of fatigue wear

consider not only one factor, but to look for a

combination of factors that create the wear

problem in order to best determine the type of

hard facing material to apply. This is done by

studying the worn part, the job it does, how it

works with other parts of the equipment and the

environment in which it works. With these

factors in mind it is then possible to make a

hardfacing alloy selection. A variety of bulk

materials, (ferrous and non-ferrous metals,

alloys, ceramics and cermets), can be modified

by alloying, mixing, compositing, and coating to achieve adequate resistance to wear corrosion

and friction. Hardfacing techniques is discussed

in the current study.



3.1 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 rebuild 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 coating. The effect of surfacing on

component life and performance will depend

upon the surfacing material and the application

process. Hardfacing is used to deposit a wear

resistant material on either a worn component or

a new component, which is to be subjected to

wear in service. These coatings are also used to

provide protection from corrosion by oxidation

or sea water. “Hard” connotes durability rather

than the denotation. Since added service life is

the objective of hardfacing. The cost of replacing

components which become worn or damaged

during service has led to the development of a

wide range of techniques known as “hardfacing”,

which can restore the parts to a reusable

condition. Many such repairs have a longer life

than the original component because it is

possible to deposit coatings more resistant to

wear, impact, abrasion or corrosion than the

original material. As a result, hardfacing is now

widely used on many production components.

Hardfacing deposits are usually fairly thick

(2mm and upwards) and for some applications

intermediate sub-layers must be used to inhibit

metallurgical problems with the final deposit.

Electrodes and filler wires are available to give

varying degrees of wear, corrosion, or heat

resistance and can be applied to small discrete

areas such as valves and valve seats, or large

areas such as shaft bearing surfaces or complete

steel mill rolls. Hard facing is particularly

associated with the earth moving equipment,

cement ovens and rock crushing and processing

industries. Hard facing technique is described in

detail especially with regard to coating

deposition technologies, with MMAW process,

that used in the current study.

3.2 Hardfacing Deposition Techniques: (i) - Thermal Spraying

(ii) - Cladding

(iii)- Welding

(i) Thermal spraying 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.

(ii) Cladding 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 can

not 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 maybe cheaper

alternative to surface protection. It is difficult to

clad parts having complex shapes and extremely

large sizes.

(iii) Welding on the other hand, are 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 material

that can be easily cast in rods or drawn into wire

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. Of

the arc welding group, SMAW, 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.

3.4 MMAW or SMAW Welding with stick electrodes is called

Manual Metal Arc Welding(MMAW) or

Shielded Metal Arc Welding (SMAW). It is the

oldest and most versatile of the various arc

welding processes.An electric arc is maintained

between the end of a coated metal electrode and

the work piece. As molten metal droplets from

the electrode are transferred across the arc and

into the molten weld puddle, they are shielded

from the atmosphere by the gases produced from

the decomposition of the flux coating. The

molten slag floats to the top of the weld puddle

where it protects the weld metal from the

atmosphere during solidification. The slag must

be removed after depositing each weld run.

Hundreds of different varieties of electrodes are

produced, often containing alloys to add

durability, strength and ductility to the weld. The

process is mostly used for ferrous alloys in the

structural steelwork, shipbuilding and general

fabrication industries.Repair and maintenance is

another important application for MMA. Despite

the relative slowness of the process, because of

electrode changes and slag removal, it remains

one of the most flexible techniques and has

advantages in areas of restricted access.

3.4.1. Advantages of MMAW process used for hardfacing (i) Flexible

(ii) Low cost

(iii) Mobile

(iv) Ideal for repairs

In this process an arc is drawn between a

coated consumable electrode and the workpiece.

The metallic core-wire is melted by the arc and is

transferred to the weld-pool as molten drops. The

electrode coating also melts to form a gas shield

around the arc and the weld pool as well as a slag

on the surface of the weld-pool, thus protecting

the cooling weld-pool from the atmosphere. The

slag must be removed after each layer. Manual

Metal Arc welding is still a widely-used hard-

facing process. Due to the low cost of the

equipment, the low operating costs of the process

and the ease of transporting the equipment, this

flexible process is ideally suited to repair work.

3.4.2 Disadvantages of MMAW process used for hardfacing (i) The major disadvantage of the process is the

high degree of the skill required for the

welder.

(ii) Relatively low productivity in terms of rate

of metal deposition.

3.4.3 Benefits of Hardfacing Hardfacing is a low cost method of depositing

wear resistant surfaces on metal components to

extend service life. Although used primarily to

restore worn parts to usable condition,

hardfacing is also applied to new components

before being placed into service. In addition to

extending the life of new and worn components,

hardfacing provides the following benefits:

(i)- Longer service life- Fewer replacement

parts are needed when parts

are hardfaced with MIG Tungsten Carbide.

(ii)- Higher productivity- Upon improving wear

life with MIG-TC, this

contributes to the equipment working and

producing more per hour. This

increases the productivity and therefore your

profits.

(iii)- Less downtime- Greater availability of

machine- a longer

service life means that it will you will spend less

time replacing the tips. This

contributes to a reduction in total operating costs.

(iv)- 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.



Figure1.6,Principle of manual metal arc welding.

3.4.4 Hardfacing Applications There are many different items that could

potentially benefit from hardfacing on the farm.

They can basically be put into three "wear"

categories - abrasion, impact, and metal-to-

metal. Abrasion is one of the most common

wears you will see on a farm, in this category

falls all earth engaging implements such as

tractor buckets, blades, teeth, grain handling

products and feed mixers. Under the impact

heading you will find equipment used to pound

and smash such as crusher hammers. Metal-to-metal refers to wear from steel parts rolling or

sliding against each other. Metal-to-metal wear

occurs on such items as crane wheels, pulleys,

idlers on track-drives, gear teeth and shafts.

Although farmers use welding and hardfacing

techniques to rebuild old, worn-out components.

By hardfacing something that is new, it may

increase the overall life expectancy of that

product.

4. Conclusion

It is proved that surfacing is economical

tool which can be used to increase the service

life of the components used in various types of

industries. Effort should be made for the right

selection of surfacing materials and the process

to achieve the full advantage of hardfacing.

References

1. William R. Oates, Alexander M. Saitta,, Materials and

applications, Welding Handbook (8th edition), Volume 4, 420-435, American Welding Society, Miami, FL 33126.

2. Damian Kotecki, Hardfacing Benefits Maintenance and Repair Welding, Welding Journal, Nov 1992, p. 51-53..

3. O.O. Zollinger, J.E. Beckham, What to Know Before Selecting Hardfacing Electrodes, Welding Journal, Feb

1998, p. 39-43.

4. C.A.Mayer, How to Select Hardfacing Materials,

Welding Design & Fabrication, Oct 1982, p. 61-67.

5. Ravi Menon, New Developments in Hardfacing Alloys, Welding Journal, Feb 1996, p. 43-49.

6. Arulmani.R, Pandey sunil, Surfacing through Plasma Enhanced Shielded Metal Arc Welding, International

Welding Symposium, February 2003, Hyderabad, p. 61-68.

7. Ben Zahner, Hardfacing Alloys: Selection and

Application, Welding Design & Fabrication, Dec 1995,

p. 11-13.

8. K.G. Budinski, Hardfacing II- Consumables, Welding

Design & Fabrication, Aug 1986, p. 42-46.

9. R.Arulmani, Pandey Sunil, “Surfacing Applications – a

Review”, National Workshop on Welding Technology,

NWWT-2K3, April 25-26, SLIET, Longowal, p. 233-238..

10. R.S. Chandel, Hardfacing Consumables and Their

Characteristics for Mining and Mineral Processing Industry, Indian Welding Journal, Jan 2001, p. 26-34

11. D.N. Noble, Abrasive wear resistance of hardfacing weld

deposits, Metal Construction, Sept 1985, p. 605-611

12. D.J. Kotecki, J.S. Ogborn, Abrasion Resistance of Iron-

Based Hardfacing Alloys, Welding Journal, Aug 1995, p.

269s-278s.

13. http://steel.keytometals.com/Articles/Art157.htm

14. http://webpages.dcu.ie/~stokesjt/ThermalSpraying

/Book/Chapter1.pd

hardfacing to increase wear resistance

Documents