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International Conference on Advancements and Futuristic Trends in Mechanical and Materials Engineering (October 5-7, 2012)

Punjab Technical University, Jalandhar-Kapurthala Highway, Kapurthala, Punjab-144601 (INDIA) 42

A REVIEW PAPER ON HARDFACING

*Vineet Shibe,

1Vikas Chawla

*Ph.D. Research Scholar, Deptt. of Mech. Engg., Punjab Technical University, Jalandhar, India.

2Bhai Maha Singh College of Engineering, Muktsar, Punjab, India.

[email protected], [email protected]

ABSTRACT 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. Different modes of wear are abrasion, impact, metallic, heat, corrosion etc. Mostly the worn out components fail due to combination of modes of wear, such as

abrasion and impact etc. Wear can be reduced either in the form of using a new wear resistant material or by

improving the wear resistance of the existing material by addition of any wear resistant alloying element etc. Many

methods to reduce wear are in practice. In the last years hardfacing processes have been developed and used for

most of the wear resistant applications. Research is carried out for studying the wear characterization, as the basic

aim of hardfacing is to improve or extend the life of various components used across the industry owing to the high

cost of replacement of original part. In this paper an attempt has been made to review few hardfacing processes,

base materials used, the current research being done and the advantages of hardfacing.

Key Words: Hardfacing, Wear resistance, Welding, Shield manual arc welding (SMAW) process

1. Introduction

Degradation of materials by wear results in very

high losses in several industries such as agricultural,

automobiles, constructional, metal working etc.

Individuals and industry tend to focus on the wearing surface that has the greatest impact on their own

economic situation. Wear is a surface phenomenon

and occurs mostly at outer surfaces. Every part that is

moving in service will be subject to wear at the

contact point with other parts. The consequence of

this wear is that the parts need to be replaced, which

costs money and causes downtime on the equipment.

Common Methods to control wear are hardfacing, use

of surface coatings and lubrication. Hardfacing is the

application of build-up of deposits of specialized

alloys by means of welding process to resist abrasion,

corrosion, high temperature, or impact. Surface coating may be defined as a layer of material, formed

naturally or deposited artificially on the surface of an

object made of another material, with an aim of

obtaining required technical or decorative properties.

Lubrication is done to separate the sliding/mating

surfaces with a lubricating film.

Surface Engineering is 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

characteristics of engineering materials have a significant effect on the serviceability and life of a

component thus cannot be neglected in design.

Hardfacing is a surface modification technique

used to rebuild the surface of a work piece and is the

most common process to improve the wear resistance

of the components. It is a technique in which a

superior material is deposited on the substrate having

a sufficient mechanical strength but of less cost and to

achieve the desired properties in an economical way.

Such an alloy may be deposited on the surface, an

edge, or merely the point of a part subject to wear.

Welding is a key technology to fulfil these

requirements and to apply hardfacing alloys [1].

Hardfacing may be applied to a new part during its

production, or it may be used to restore a worn-down surface. Hard-facing increases the service life of a part

and there by extend the lifetime of machinery

equipment efficiently [1].

In the last years hardfacing became an issue of

intense development related to wear resistant

applications. Economic success of this process

depends on selective application of hardfacing

material & its chemical composition.

2. Welding Processes Used for Hardfacing

The different welding processes used for

hardfacing are Arc Welding, Gas Welding,

combination of Arc and Gas Welding, etc. Mostly

MMAW process is used for hardfacing because it is

the most common and versatile process. It has low

cost of equipment, portable, inexpensive; flexible in

use, ideal for repair and all position welding can be

performed easily.

The different welding processes used for

Hardfacing can be classified as under:



Hardfacing by Arc Welding Shielded Metal Arc Welding [2], Flux Cored Arc Welding [3], Submerged Arc Welding [4].

Hardfacing by Gas Welding Deposition by Oxy-Acetylene Gas Welding [5].

Hardfacing by combination of Arc and Gas Welding Tungsten Inert Gas Welding [6], Gas Metal Arc

Welding [7].

Powder Spraying Flame Spraying [8], High Velocity Oxy-Fuel Process

[9], Electric Arc Spraying, Plasma Transferred Arc

[10], etc.

Laser Hardfacing or Cladding [11].

The various factors that should be considered for

selecting of the most suitable welding process for a

given job and application are: Base metal (substrate)

composition, Nature of Work to be hardfaced,

Function of the component, Size and shape of

component, Accessibility of welding equipment, State

of repair of worn component and Number of same or

similar items to be hardfaced, etc.

3. Types of Hardfacing Alloys

The different hard-facing alloys available can be

classified as under:

Low alloy iron-base alloys

High alloy iron-base alloys

The cobalt-base and nickel-base alloys Tungsten carbide materials

Low alloy iron-base alloys Materials containing up to 12% alloy components,

usually chromium [12], molybdenum [13], and

manganese [14].

High alloy iron-base alloys Materials with 12-50% alloy content, in addition to

the chromium found in all iron- base hard-facing

alloys, some of these alloys may also contain nickel [15] or cobalt [7].

The cobalt-base [7] and nickel-base alloys [15] Contain relatively small amounts of iron (1.3 to

12.5%). Of these, the most costly, but also the most

versatile, are the cobalt-chromium-tungsten alloys

[16]. All the cobalt- base and nickel-base alloys have

high resistance to corrosion and oxidation; they

possess low coefficients of friction, making them

especially suitable for applications involving metal-to-

metal wear; and they are almost always selected for applications involving temperatures of 5500C or

higher. The cobalt-base alloys retain much of their

original hardness at red heat (8000C).

Tungsten carbide materials [17] Tungsten carbide is one of the hardest materials

available for industrial use. It cannot be melted by any

flame and is also rather brittle. For hard-facing

purposes, it is crushed and applied in conjunction with

a binding metal.

4. Types of Base Materials

The base or substrate material on which

hardfacing alloys are deposited by different welding

processes is steel. Steel comprises of different types of

metals and is made principally of iron. The various

types of steels used in the industry for making

different components or parts for different

applications are classified in to the following types:

Low Carbon Steels and Low alloy Steels

Medium Carbon Steels

High Carbon Steels

Other steels

Low Carbon Steels and Low alloy Steels: These steels include those in the AISI series C-1008

to C-1020 [18]. Carbon ranges from 0.10 to 0.25%,

manganese ranges from 0.25 to 1.5%, phosphorous is

0.4% maximum, and sulfur is 0.5% maximum. Steels

in this range are most widely used for industrial fabrication and construction. These steels can be

easily welded with any of the arc, gas, and resistance

welding processes. These steels include the low-

manganese steels, the low-to-medium nickel steels,

the low nickel-chromium steels, the molybdenum

steels, the chromium-molybdenum steels, and the

nickel-chromium-molybdenum steels. These alloys

are included in AISI series 2315, 2515, and 2517.

Carbon ranges from 0.12-0.30%, manganese from

0.40-0.60%, silicon from 0.20-0.45% & nickel from

3.25-5.25%.

Medium Carbon Steels: These steels include those in the AISI series C-1025

to C-1050 [19]. The composition is similar to low-

carbon steels, except that the carbon ranges from 0.25

to 0.50% and manganese from 0.60 to 1.65%.

Medium carbon steels are readily weld able provided

some precautions are observed. These steels can be

easily welded with any welding processes discussed

above.



High Carbon Steels:

These steels include those in the AISI series from C-

1050 to C-1095[20]. The composition is similar to medium-carbon steels, except that carbon ranges from

0.30 to 1.00%. Special precautions must be taken

when welding steels in these classes. These steels can

be easily welded with any of the processes discussed

above.

Other steels: These are Low Nickel Chrome Steels (AISI 3120,

3135, 3140, 3310, and 3316), Low Manganese Steels

(AISI 1320, 1330, 1335, 1340, and 1345), Low Alloy

Chromium Steels (AISI 5015 to 5160) and the electric

furnace steels 50100, 51100, and 52100) which can be welded without special precautions when carbon is at

low end of the range.

5. Hardfacing Applications

Hard facing technique is widely used in

Agriculture: Plowshare points, Soil-tamper points,

Harrower teeth, Tiller blades; Automotive: Trucks,

automobiles, highway construction and agricultural

vehicles, cam actuators and shafts, Exhaust

manifolds, Pumps, Mufflers, Brakes, Clutches, Cones;

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; Food processing: Extruder screws

for vegetables oils, Grain mill equipments, Corn and sugar cane cutting equipments; Glass & Ceramics:

Moulds, Screws, Mixing blades, Agitator blades;

Leather goods; Cutting tools and equipment;

Metal Working: Shear blades, Conveyor rollers,

Surface cleaning rollers, Straightening rollers, Draw

die equipment, Moulds; Mining Ore: Crusher blades,

Power-shovel teeth, Conveyor chains, Scraper blades,

Cut-off blades; Naval works: Rod ends, Blower

turbines, Piston rods, Transmission shafts, Screw

shafts; Paper: Roll cylinders for continuous

machines, Drying cylinders, Mixers; Petroleum: Blowers and ventilators, Pumps, Heat exchangers;

Power generation: Turbines; Public works:

Steam shovel teeth and edges, Excavator teeth,

Bulldozer blades and teeth, Dredge rollers, Tractor

rollers; Rubber Tire moulds; 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; Textiles: Filament guides, Diagonal cutter, Rollers, Heating plates.

6. Results and Discussion from Current Research

Current Research on hardfacing focuses on using

various hardfacing/ welding techniques, different weld consumables and different base materials. Most

of the research is carried out in studying the wear

characterization, as the basic aim of hardfacing is to

extend the service life of components used in the

industry owing to the high cost of replacement of

original component.

The different hardfacing layers produced by

shield manual arc welding (SMAW) process with a

bare electrode coated with fluxes and to which

different measures of ferrotitanium (Fe–Ti),

ferrovanadium (Fe–V), ferromolybdenum (Fe–Mo)

and graphite had been added showed good resistance to cracking and wear when the amounts of graphite,

Fe–Ti, Fe–V and Fe–Mo were controlled within a

range of 8–10%, 12–15%, 10–12% and 2–4%,

respectively [21]. The coated tubular electrodes

presented a favorable performance in comparison to

the conventional coated electrode, making possible to

reach lower dilutions yet keeping the same deposition

rates. These results encourage further researches

aiming the exploitation of this fabrication conception

of SMAW electrodes [2]. FCAW welds presented

higher abrasive wear resistance than the SMAW deposits [3]. Fe-based hardfacing alloys containing

molybdenum compound have been deposited on AISI

1020 steel substrates by shield manual arc welding

(SMAW) process. The hardfacing layer with good

cracking resistance and wear resistance could be

obtained when the amounts of Fe–Mo was controlled

within a range of 3–4 wt. %. The improvement of

hardness and wear resistance of the hardfacing layers

attributed to the formation of Mo2C carbide and the

solution strengthening of Mo [13].

Gas welding is often a convenient and relatively

inexpensive method of applying wear-resistant surface coatings [22]. In the analysis of microstructure and

properties of TiC particles reinforced Fe-based surface

composite coatings produced by gas tungsten arc

welding (GTAW), the results showed that in situ

synthesized TiC particle reinforced composite

coatings can be achieved under suitable welding

parameters. The wear resistance of multi-layers

composite coatings is about three to four times higher

than that of 1045 steel substrate [23].

A series of high chromium Fe–Cr–C hardfacing

alloys were produced by gas tungsten arc welding

(GTAW). Chromium and graphite alloy fillers were

used to deposit coatings on ASTM A36 steel

substrates. X-ray diffraction analysis and

microstructure characteristics showed Cr–Fe solid

solution (α), (Cr,Fe)23C6 and trace amounts of

(Cr,Fe)7C3. Massive (Cr,Fe)23C6 contain (Cr,Fe)7C3

in the center, and causes high hardness value up to



HRC 70 [24]. A series of high carbon Fe–Cr–C

hardfacing alloys were produced by gas tungsten arc

welding (GTAW). Chromium and graphite alloy fillers were used to deposit hardfacing alloys on

ASTM A36 steel substrates. Depending on the four

different graphite additions in these alloy fillers, this

research produced hypereutectic microstructures of

Fe–Cr phase and (Cr,Fe)7C3 carbides on hard-facing

alloys. The microstructural results indicated that

primary (Cr,Fe)7C3 carbides and eutectic colonies of

[Cr–Fe+(Cr,Fe)7C3] existed in hardfacing alloys.

With increasing the C contents of the hardfacing

alloys, the fraction of primary (Cr,Fe)7C3 carbides

increased and their size decreased. The hardness of

hardfacing alloys increased with fraction of primary (Cr.Fe)7C3 carbides [25].

The FE-based hardfacing alloy has excellent wear

resistance, excellent cavitation erosion resistance, and

excellent corrosion resistance, thereby being

substituted for a cobalt-based satellite alloy, which

has been used for the hardfacing of a nuclear power

plant valve. When the provided Fe-based hardfacing

alloy is used for the hardfacing of the nuclear power

plant valve, inexpensive Fe can be substituted for

expensive Co and radiation fields formed by 58Co

and 60Co radioactive isotopes can be efficiently

reduced [26].

7. Conclusions

Hardfacing is a low cost, most versatile method

of depositing wear resistant surfaces on components

to extend their life and it provides the following benefits: Longer service life, higher productivity, less

downtime - greater availability of machine and

reduced cost.

Hardfacing improves the life of the worn out

component and reduces the cost of replacement. It

reduces downtime by extending the service life and

hence few shutdowns are required to replace them.

Hardfacing can be done on any steel material

using a suitable welding technique for a given job and

application. Different alloying elements can be

deposited on the substrate or base metal to achieve the desired properties such as hardness, wear resistance,

abrasive resistance and impact resistance etc.

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