AWS PRGHF

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The Practical

Reference Guide for

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REFERENCE GUIDE

fo

forr

HARDFACING

Compiled/Edited by

Lee G. Kvidahl

Manager

Manager, Welding and

, Welding and Manufacturing Engineering

Manufacturing Engineering

Ingalls Shipbuilding Operations

Northrop Grumman Corporation

This publication is designed to provide information in regard to the subject matter covered. It is made available

with the understanding that the publisher is

with the understanding that the publisher is not engaged in the rendering of professional advice. Reliance upon

not engaged in the rendering of professional advice. Reliance upon

the information contained in this document should not be undertaken without an independent verification of

its application for a particular use. The

its application for a particular use. The publisher is not responsible for loss or

publisher is not responsible for loss or damage resulting from use of t

damage resulting from use of this

his

publication. This document is not a consensus standard. Users should refer to the applicable standards for their

particular application.

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ii

Photocopy Rights

Authorization to photocopy items for internal, personal, or educational classroom use only, or the internal,

personal, or educational classroom use only of specific clients, is granted by the American Welding Society

(AWS) provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive,

Danvers, MA 01923, Tel: 978-750-8400; online: http://www.copyright.com

© 2002 by the American Welding Society. All rights reserved.

Printed in the United States of America.

EDITOR NOTES

The editor would like to thank the AWS Product Development Committee for sponsoring this publication. A

special thanks, also, to Dr. Ravi Menon, Stoody Co., Bowling Green, Kentucky (a Thermadyne company) for

his suggestions.

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Page No.

Basic Safety Precautions ... iv

Introduction...1

Hardfacing Applications ...1

Hardfacing Properties...2

Selection of Hardfacing Materials...2

Hardfacing Processes—the Effect of Welding Variables on Dilution...7

Other Publications Available from AWS ...15

LIST OF TABLES

Table

Page

No.

1 Common Surfacing Processes and Materials...1

2 High-Speed Steel Filler Metals...3

3 Austenitic Manganese Filler Metals ...3

4 Austenitic High Chromium Iron Filler Metals ...4

5 Cobalt Base Alloy Filler Metals ...5

6 Copper Base Alloy Filler Metals ...6

7 Nickel Chromium Boron Alloy Filler Metals...7

8 Tungsten Carbide Filler Metals...8

9 Shielded Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics ...9

10 Gas Tungsten Arc Process Variables—Independent Effects on Key Surfacing Characteristics...10

11 Gas Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics ...11

12 Submerged Arc Process Variables—Independent Effects on Key Surfacing Characteristics...12

LIST OF FIGURES

Figure

Page

No.

1 Different Impingement Angles ...8

2 Calculation of Base Metal Dilution...9

3 Effect of Travel Speed on Dilution (Other Conditions Unchanged) ...13

4 Basic Surfacing Oscillation Techniques and Bead Configurations...13

5 Uphill and Downhill Welding Flat Plate and Rotating Cylindrical Parts...14

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iv

BASIC SAFETY PRECAUTIONS

Burn Protection. Molten metal, sparks, slag, and hot work surfaces are produced by welding, cutting, and

allied processes. These can cause burns if precautionary measures are not used. Workers should wear

protec-tive clothing made of fire-resistant material. Pant cuffs, open pockets, or other places on clothing that can

catch and retain molten metal or sparks should not be worn. High-top shoes or leather leggings and

fire-resistant gloves should be worn. Pant legs should be worn over the outside of high-top shoes. Helmets or

hand shields that provide protection for the face, neck, and ears, and a head covering to protect the head

should be used. In addition, appropriate eye protection should be used.

Electrical Hazards. Electric shock can kill. However, it can be avoided. Live electrical parts should not be

touched. The manufacturer’s instructions and recommended safe practices should be read and understood.

Faulty installation, improper grounding, and incorrect operation and maintenance of electrical equipment are

all sources of danger.

All electrical equipment and the workpiece should be grounded. The workpiece lead is not a ground lead. It

is used only to complete the welding circuit. A separate connection is required to ground the workpiece. The

workpiece should not be mistaken for a ground connection.

Fumes and Gases.

Many welding, cutting, and allied processes produce fumes and gases which may be

harmful to health. Avoid breathing the air in the fume plume directly above the arc. Do not weld in a

con-fined area without a ventilation system. Use point-of-welding fume removal when welding galvanized steel,

zinc, lead, cadmium, chromium, manganese, brass, or bronze. Do not weld on piping or containers that have

held hazardous materials unless the containers have been inerted properly.

Compressed Gas Cylinders.

Keep caps on cylinders when not in use. Make sure that gas cylinders are

chained to a wall or other structural support. Do not weld on cylinders.

Radiation.

Arc welding may produce ultraviolet, infrared, or light radiation. Always wear protective

cloth-ing and eye protection to protect the skin and eyes from radiation. Shield others from light radiation from

your welding operation.

Ventilation During Welding. Five major factors govern the quantity of fume to which welders and welding

operators are exposed during welding:

(1) Dimensions of the space in which welding is done (with special regard to the height of the ceiling)

(2) Number of welders and welding operators working in that space

(3) Rate of evolution of fumes, gases, or dust, according to the materials and processes involved

(4) The proximity of the welder or welding operator to the fumes as they issue from the welding zone, and to

the gases and dusts in the space in which he is working

(5) The ventilation provided to the space in which the welding is done

Refer to the section entitled, “Ventilation” in American National Standard ANSI Z49.1, Safety in Welding,

Cutting, and Allied Processes for a discussion on the ventilation that is required during welding.

Special Precautions. In the following conditions when using thermal spraying:

(1) The main source of hazard during the thermal spraying operation is the intense heat produced by the

spray gun.

(2) The heat combines with other factors to produce additional secondary hazards. These include: dust and

mist; radiated light, infrared and ultraviolet; and high intensity noise.

(3) Grit blasting, performed for surface preparation, provides hazardous conditions: high velocity air and

grit stream, dust from blast impact, and loud noise.

Caution must be exercised in protective clothing, safety glasses and shoes, and eye and ear protection. AWS

recommends a personal copy of “Arc Welding Safely,” “Fire Safety in Welding and Cutting,” “Safety in

Weld-ing, Cutting and Allied Processes,” “Thermal Spray Manual,” “Arc Welding and Cutting Noise,” and “Lens

Shade Selector.” See Ordering Information under “Other Publications Available from AWS.”

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Introduction

Hardfacing is one category from the family of

surfac-ing processes. Surfacsurfac-ing is defined in AWS A3.0,

Standard Welding Terms and Definitions, as “The

appli-cation by welding, brazing, or thermal spraying, of a

layer, or layers, of material to a surface to obtain

desired properties or dimensions, as opposed to

making a joint.” The surfacing processes may be

grouped as surface cladding, buildup, buttering, and

hardfacing. These processes are defined as follows:

Cladding. A surfacing variation that deposits or

applies surfacing material usually to improve

corrosion or heat resistance.

Buildup. A surfacing variation in which surfacing

material is deposited to achieve the required

dimensions.

Buttering. A surfacing variation that deposits

sur-facing metal on one or more surfaces to provide

metallurgically compatible weld metal for the

subsequent completion of the weld.

Hardfacing. A surfacing variation in which

surfac-ing material is deposited to reduce wear. (A

non-standard term for hardfacing is hard surfacing.)

Hardfacing Applications

In hardfacing applications, a layer of surfacing

metal is applied to reduce wear by increasing the

resistance of a metal surface to abrasion, impact,

erosion, galling, or cavitation. As with cladding, the

strength of hardfacing is not considered in the

de-sign of the component (see Table 1).

In addition to the characteristics of the surfacing

material and base metal, other important

consider-ations when choosing hardfacing applicconsider-ations are:

(1) Geometry of the part to be surfaced

(2) Cost of the material and labor

(3) Techniques to prevent cracks in the surfacing or

application-generated cracks

(4) Techniques to minimize distortion from the

thermal stresses of welding

(5) Quality of the deposit

Table 1. Common Surfacing Processes and Materials

Process Mode of Application Surfacing Metal Forms Oxyfuel gas (OFW) Manual or semiautomatic Powder and bare cast and tubular rods Shielded metal arc (SMAW) Manual Covered electrodes, solid cast electrodes,

and tubular electrodes

Flux cored arc (FCAW) Semiautomatic or automatic Composite electrode of metallic sheath and powder core

Gas metal arc (GMAW) Semiautomatic or automatic Bare solid and tubular electrodes Submerged arc (SAW) Automatic Bare solid and tubular wires and strip Gas tungsten arc (GTAW) Manual or automatic Powder, bare solid and tubular wires, and

bare cast rods

Plasma arc (PAW) Automatic Powder and bare and tubular wires Thermal Spray Processes

Flame spraying (FLSP) Semiautomatic or automatic Powder and bare and tubular wires Plasma spraying (PSP) Semiautomatic or automatic Powder

Arc spraying (ASP) Semiautomatic or automatic Bare and tubular wires High-velocity flame Semiautomatic or automatic Powder

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2 AWS Practical Reference Guide Hardfacing

Hardfacing Properties

Properties of the hardfacing process are as follows:

Hardness

• Macrohardness (gross hardness)

• Microhardness (hardness of individual

constitu-ents in a heterogeneous structure)

• Hot hardness (resistance to the weakening effect

of service at elevated temperature during short

time loading)

• Creep resistance (resistance to plastic

deforma-tion when loaded at elevated temperatures for

relatively long periods of time)

Abrasion Resistance

• Under low stress (scratching wear)

• Under high stress (grinding)

• Under high stress and impact (gouging)

Impact Resistance

• Resistance to plastic deformation under repeated

impact loading (related to yield strength and

fatigue strength)

• Resistance to cracking under impact loading

(re-lated to ductility but including work-hardening

considerations)

Heat Resistance

• Resistance to tempering (softening with time at

temperature)

• Retention of strength when hot (including hot

hardness)

• Creep resistance (time factor added to hot

strength)

• Resistance to oxidation or corrosion by hot gases

Corrosion Resistance

Metal-to-Metal Resistance

• Friction coefficients (relative ease of sliding)

• Galling tendency (localized welding)

• Surface films (oxide layers)

• Lubricity (slipperiness)

• Plasticity (ability to deform)

Erosive Wear Resistance

• Under high-angle solid particle impingement

• Under low-angle solid particle impingement

• Under liquid droplet erosion

• Under cavitation conditions

Hardfacing Advantages

When compared with other surfacing processes,

hardfacing has the following advantages:

(1) Additional resistance to wear or corrosion

exactly where it is needed

(2) Ready application in the field

(3) Economical use of expensive alloys

(4) A hard surface layer to resist wear that is

sup-ported by a tough substrate to carry the load

Selection of Hardfacing Materials

Factors to be identified for selection of surfacing

materials (see Tables 2–8) includes:

• The type of abrasive to be encountered and its

characteristics (hardness, sharpness, particle

size, and toughness)

• The amount of impact to be encountered

• The amount of support provided to the deposit

• The levels of stress involved

• The nature of the stress (tensile, compression, or

shear)

• The operating temperature

• Other significant environmental conditions

Impact Resistance

Impact may be classified as light, medium, or heavy,

depending upon the result of the impact energy.

An example of a heavy impact application is a

hardfaced mill hammer. In light impact, kinetic

en-ergy is absorbed elastically. It is absorbed both

elas-tically and plaselas-tically in medium impact. In heavy

impact, the surface of even the strongest materials

must either deform or fracture.

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Table 2. High-Speed Steel Filler Metals

Properties Characteristics

Hardness The Rockwell hardness of the undiluted filler metals, in the as-welded condition, is in the range of C 55 to C 60. Hot Hardness At temperatures up to 1100°F (595°C), the deposited Rockwell hardness of C 60 falls off very slowly to

approximately C 47. At higher temperatures, it falls off more rapidly. At about 1200°F (650°C), the maxi-mum Rockwell hardness is about C 30.

Impact These filler metals can withstand only medium impact without cracking in the as-welded condition. After tempering, the impact resistance is increased appreciably.

Oxidation Resistance Because of high molybdenum content, these filler metals will oxidize readily. A non-oxidizing furnace atmosphere salt bath or borax coating should be used to prevent decarburization when heat treatments are required.

Corrosion Resistance The weld metal can withstand atmospheric corrosion, but it is not effective in providing resistance to liquid corrosion.

Abrasion The high stress abrasion resistance of the materials, as deposited and at room temperature, is much bet-ter than low carbon steel. However, they are not considered high abrasion resistance alloys. Resistance to deformation at elevated temperatures up to 1100°F (593°C) is their outstanding feature, and this may aid hot abrasion resistance.

Metal-to-Metal Wear Deposits are well suited for metal-to-metal wear, especially at elevated temperatures. They have a low coefficient of friction and the ability to take a high polish and retain their hardness at elevated tempera-tures. The compressive strength is very good and will fall or rise with the tempering temperature used. Mechanical Properties

in Compression

Deposits are well suited for metal-to-metal wear, especially at elevated temperatures. They have a low coefficient of friction and the ability to take a high polish and retain their hardness at elevated tempera-tures. The compressive strength is very good and will fall or rise with the tempering temperature used. Machinability After deposition, these materials often have to be annealed for machining operations. For machinability,

when thoroughly annealed, they are rated at 65—as compared to 1% carbon tool steel, which has a rating of 100. Full hardness can be regained by heat treating procedures.

Identification In the hardened or as deposited condition, these materials are highly magnetic. When spark tested, they give off a very small, thin stream of sparks approximately 60 in. (1500 mm) long. Close to the grinding wheel, the spark is red; at the end, it is straw color.

Table 3. Austenitic Manganese Filler Metals

Hardness The normal hardness of these weld deposits is 170 to 230 BHN. This may be misleading as these materi-als work harden readily to 450 to 550 BHN.

Hot Hardness Reheating above 500°F to 600°F (250°C to 315°C) may cause serious embrittlement.

Impact These materials, as deposited, are considered the outstanding engineering material for heavy impact service.

Oxidation Resistance These materials are similar to ordinary carbon steels in this respect and are not resistant to oxidation. Corrosion Resistance These materials are similar to ordinary carbon steels in this respect and are not resistant to corrosion. Abrasion Resistance to high and low stress abrasion is moderate against hard abrasives like quartz.

Metal-to-Metal Wear Metal-to-metal wear resistance is frequently excellent. The yield strength in compression is low, but any compressive deformation rapidly raises it until plastic flow ceases. This behavior is an asset in hammer-ing, pounding and bumping wear situations.

Mechanical Properties in Compression

Metal-to-metal wear resistance is frequently excellent. The yield strength in compression is low, but any compressive deformation rapidly raises it until plastic flow ceases. This behavior is an asset in hammer-ing, pounding and bumping wear situations.

Machinability Machining is very difficult with ordinary tools and equipment; finished surfaces are usually ground. Identification A clean ground surface is substantially non-magnetic and grinding sparks are plentiful in contrast to the

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Austenitic steels containing 11% to 20% manganese are

commonly used for resisting heavy impact due to their

work-hardening characteristics. Certain low-carbon

co- balt and nickel alloys also are excellent for impact

resis-tance. Other choices for impact resistance include

pearlitic steels and martensitic steels. In general, the

im-pact resistance of martensitic steels is inferior to that of

manganese-containing austenitic or pearlitic steels, but

the abrasion resistance of martensitic steels is better.

Heat Resistance

In general, resistance to thermal fatigue increases

with increasing thermal conductivity, ultimate

ten-sile strength, elongation at rupture, and Young’s

modulus. Resistance to thermal fatigue decreases

with increasing coefficient of expansion.

Martensi-tic stainless steels containing 5% to 12% chromium

are often used for resistance to thermal fatigue.

Table 4. Austenitic High Chromium Iron Filler Metals

Hardness The as-welded hardness for these materials, when deposited with an oxyfuel process will vary with the carbon content. As dilution is not expected in normal oxyfuel welding applications, the principle variable in carbon pick-up is flame adjustment. The average Rockwell hardness can be from C 51 to C 62.

Hot Hardness Hardness for these materials falls slowly with increasing temperatures up to about 800°F to 900°F (425°C to 480°C), thereafter, it falls rapidly and also becomes strongly affected by creep. However, the loss of hardness due to tempering is negligible in comparison with many martensitic alloys. Very little is known about the resistance of these alloys to thermal shock and thermal fatigue. Impact These deposits may withstand very light impact without cracking but cracks will form readily if blows

produce plastic deformation. These filler metals seldom are used under conditions of medium impact and they are generally considered unsuitable for heavy impact.

Oxidation Resistance The high chromium content of these materials confers excellent oxidation resistance up to 1800°F (980°C), and they can be considered for hot wear applications in which their hot plasticity is not objectionable.

Corrosion Resistance The matrix chromium content is comparatively low and thus, not very effective in providing resis-tance to liquid corrosion. These deposits will rust in moist air and are not stainless, but are more stable than ordinary iron and steel.

Abrasion The resistance to low stress abrasion is outstanding and is related to the volume of the hard car-bides. As stress on the abrasion increases, their performance declines. As deposited, the materials are only mediocre under high stress grinding abrasion, and are not advantageous for such service. Metal-to-Metal Wear Low stress abrasion produces a good polish on these filler metals, with a resulting low coefficient of friction. where the polish is produced by metal-to-metal wear, performance is also good. Resis-tance to galling is considered better than for ordinary hardened steel because tempering from fric-tional heat is negligible. Austenite alone is prone to gall, and its presence may lead to unfavorable performance. Also, the hard carbides can stand in relief through wear of the austenite, and can cut or cause excessive wear upon a mating surface. Therefore, metal-to-metal service should be approached cautiously.

In compression, these materials are expected to have a yield strength of between 80,000 and 140,000 psi (551 to 965 MPa) with an ultimate strength ranging from 150,000 psi to 180,000 psi (1034 MPa to 1930 MPa). They will show about one percent elastic deformation and tolerate from 0.5% to 3% additional plastic deformation before failure at the ultimate strength. Like other cast irons, the tensile strength is low; therefore, tension should be avoided in designs for their use. Machinab ility These deposits are considered commerci ally unmachinable with cutting tools, and they are also

very difficult to grind.

Identification The filler metals frequently can be identified by certain characteristics: (1) brittleness of the cast welding rod; (2) nonmagnetic behavior; (3) a very dull, lifeless spark that is short and produced with difficulty; and (4) sometimes the presence of fine needle-like Cr7C3 crystals on a fracture section. A spot test for cobalt will distinguish it from the somewhat similar CoCr-C filler metals. The mag-netic permeability is about 1.03 with a magnetizing force of 24 oersteds.

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An example of failure due to thermal fatigue is “fire

cracking” in continuous casting rolls in steel mills.

Metal-to-Metal Wear Resistance

The wear that results from metal-to metal contact is

due primarily to galling, i.e., the localized welding

of mating surfaces with subsequent ripping apart of

these welds. This in turn leaves a roughened

sur-face and produces additional wear. Resistance to

galling is greatly influenced by the type and

stabil-ity of oxide that is present on the surface. Tough

adherent films are desirable, because a ruptured

metal oxide film can become trapped and act as an

abrasive.

Subsurface fatigue is another mechanism leading to

metal-to-metal wear. In addition to the nature of the

surface oxide, materials that work harden or have

low stacking-fault energy offer good resistance to

Table 5. Cobalt Base Alloy Filler Metals

Hardness The usual hardness ranges for these alloys are dependent upon the specific alloy selected. For example, CoCr-A may range from C 38-47 when welded with the oxyfuel process and from C 23-47 when an arc welding process is used. Similarly, CoCr-B can range from C 45 to 49 with oxyfuel and from C 34 to 47 with arc welding, and alloy CoCr-C may range from C 48 to 58 with oxyfuel and C 43 to 58 with arc welding processes. The cobalt base alloys are exceptions to the norm in that although they exhibit lower hardness while hot, they return to approximately their original hardness upon cooling and can be considered immune to tempering.

Hot Hardness Elevated temperature strength and hardness are outstanding properties of CoCr filler metals. These materials are generally considered superior to other surfacing alloys where these properties are required above 1200°F (650°C). Additionally, at temperatures above 1000°F to 1200°F (540°C to 650°C), weld deposits of these filler metals have greater resistance to creep than other available surfacing alloys for which data is available. This distinction, and their hardness at 1200°F (650°C) and above, are the primary reasons for their selection for use in many applications.

Impact Resistance to flow under impact increases with carbon content in CoCr filler metals. CoCr-C weld deposits are quite brittle and crack readily when impact flow does occur. CoCr-A deposits, while easily deformed, can withstand some plastic flow under compression before cracking.

Oxidation Resistance The presence of more than 25% chromium in CoCr filler metals promotes the formation of a thin, tightly adherent protective scale under oxidizing conditions. Scaling resistance to combustion products of internal combustion engines is also generally adequate, even in the presence of lead compounds.

Corrosion Resistance CoCr filler metals are considered to be “stainless” and are frequently useful where abrasion and corrosion are involved. They can be considered corrosion resistant in the less severe media, in foods, and in air; and they even may have good resistance in some corrosives. However, an appli-cation that involves corrosion should be confirmed by a field test.

Abrasion Carbon content has much to do with the response of CoCr filler metals to abrasion. At 1% carbon (CoCr-A), the performance is inferior to that of carbon steel; at 2.5% carbon (CoCr-C), the resis-tance to high stress grinding abrasion is good.

Metal-to-Metal Wear The CoCr filler metals are well suited for metal-to-metal wear because of their ability to take a high polish and their low coefficient of friction.

The compressive yield strength ranges from 64 to 76 ksi (441 to 524 MPa) for CoCr-A and 85 ksi to 110 ksi (586 MPa to 758 MPa) for CoCr-C. The ultimate compressive strength similarly ranges from 150 ksi to 230 ksi (1034 MPa to 1586 MPa) for CoCr-A and 250 ksi to 270 ksi (1724 MPa to 1861 MPa) for CoCr-C.

Machinability None of the deposits from CoCr filler metals are easily machinable, and the difficulty increases along with the increased carbon content.

Identification These materials usually may be distinguished by their relative hardness and brittleness. They are nonmagnetic. A spark test may be used to differentiate them from austenitic manganese steel. However, the austenitic chromium irons are so similar that an acid test may be required to differen-tiate between these materials.

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metal-to-metal wear. Low stacking-fault energy

oc-curs in face-centered cubic alloys when there is great

separation between adjacent partial dislocations,

and it is a condition that favors a high rate of strain

hardening, a desirable characteristic.

The material selection obviously depends on the

mating metal. Commonly used alloys for galling

re-sistance contain carbides of such elements as

tung-sten, chromium, molybdenum, or vanadium in a

cobalt matrix, nickel alloys, tool steels, and

austen-itic manganese steels also are used.

Erosive Wear Resistance

In situations of solid-particle impingement,

hard-facing alloys with high carbide content are

gener-ally recommended for low-angle impingement (less

than 15°). Those with low carbide content or other

precipitates are preferred for high-angle

impinge-ment (greater than 80°). Figure 1 illustrates different

impingement angles.

Cobalt alloys are typically used for liquid droplet

erosion and cavitation resistance due to their

inher-ent properties in work hardening and fatigue

Table 6. Copper Base Alloy Filler Metals

Hardness Deposit hardness will vary with the welding process used and the manner in which the metal is deposited. For example, deposits made with the gas metal arc or gas tungsten arc processes will be higher in hardness than deposits made with the oxyfuel or shielded metal arc welding pro-cesses. This is because lower losses of aluminum, tin, silicon, and zinc are encountered in the remelting process due to better shielding from oxidation.

Hot Hardness The copper base alloy filler materials are not recommended for use at elevated temperatures. Impact The impact resistance of CuAl-A2 deposits will be the highest of the copper base alloy

classifica-tions. As the aluminum content increases, impact resistance decreases markedly. CuSi weld deposits have good impact properties. The CuSn filler metals, as deposited, have low impact values due to the coarse grain structures and the lower strength inherent in these alloys. The CuZn-E deposits have very low impact values.

Oxidation Resistance Deposits of the CuAl filler metals form a protective oxide coating upon exposure to the atmosphere. Oxidation resistance of the CuSi deposit is fair, while that of CuSn filler metals is comparable to that of pure copper.

Corrosion Resistance Copper base alloys are used rather extensively to surface areas subjected to corrosion from vari-ous acids, mild alkalies, and salt water. The only exception is filler metal of the CuZn-E classifica-tion. Filler metals producing deposits of higher hardness, that is, 120 to 200 BHN (3000 kg load), may be used to surface areas subjected to corrosive action as well as erosion from liquid flow. Abrasion None of the copper base alloy deposits are recommended for use where severe abrasion is

encountered in service.

Metal-to-Metal Wear The CuAl filler metals producing deposits of highest hardness, 130 BHN to 390 BHN (3000 kg load) are used to overlay surfaces subjected to excessive wear from metal-to-metal contact. All of the copper base alloy filler metals are used to deposit overlays and inlays for bearing surfaces, with the exception of the CuSi filler metals. Silicon bronzes are considered poor bearing alloys. Slight poros-ity in the deposit is sometimes acceptable for bearing service. In fact, CuZn-E, which is a leaded bronze, was designed to produce a porous deposit in order to retain oil, primarily for additional lubrication purposes in the overlay of locomotive journal boxes.

Deposits of the CuAl filler metals have high elastic limits and ultimate strengths in compression ranging from 25,000 psi to 65,000 psi (172 MPa to 448 MPa) and 120,000 psi to 171,000 psi (827 MPa to 1174 MPa), respectively. The elastic limit of CuSi deposits is approximately 22,000 psi (152 MPa) with an ultimate strength in compression of 60,000 psi (414 MPa). The CuZn deposits will have an elastic limit of 11,000 psi (76 MPa) and an ultimate strength of 32,000 psi (221 MPa). The mechanical properties of the leaded bronzes, CuZn-E, are very low in compression, with an elastic limit of about 5000 psi (34 MPa) and an ultimate strength of 20,000 psi (138 MPa).

Machinability All of the copper base alloy deposits can be machined.

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strength and their ability to absorb stresses. Certain

iron-chromium-manganese alloys also have shown

excellent cavitation resistance.

Hardfacing Processes—

the Effect

of Welding Variables on Dilution

Most surfacing is performed by using one of the

consumable electrode arc welding processes.

Dilu-tion is the change in chemical composiDilu-tion of a

welding filler metal caused by the admixture of

the base metal or previous weld metal in the weld

bead. It is measured by the percentage of base

metal or previous weld metal in the weld bead

(see Figure 2).

Because of the importance of dilution, it is

neces-sary that the effect of each consumable electrode arc

welding variable be known. Many of the welding

variables that affect dilution, and therefore require

close control in surfacing, need not be controlled

when arc welding a joint (see Tables 9–12 and Figures

3 and 4).

Welding Variables Affecting Dilution

The welding variables are as follows:

Amperage

Increasing the amperage (current density) increases

dilution. The arc becomes stiffer and hotter,

pene-trating more deeply and melting more base metal.

Table 7. Nickel Chromium Boron Alloy Filler Metals

Hardness The hardness of these alloys may range from Rockwell C 24 to C 62. Deposits of NiCr filler metals work harden to a greater degree when considerable iron dilution is present (one layer arc weld) than when there is l ess iron dilution (two-layer arc weld).

Hot Hardness The hardness of the deposits wi ll soften at elevated temperatures. For example, an arc welded deposit of NiCr-A may be reduced from Rockwell C 30 to C 24 at 1000°F (540°C) while an arc welded deposit of NiCr-C may change from C 49 to C 39.

Impact Deposits of NiCr filler metal will withstand light impact fairly well. However, if the impact blows pro-duce plastic deformation, cracks are certain to appear in the NiCr-C weld metal and less likely to appear in the NiCr-A and NiCr-B deposits.

Oxidation Resistance NiCr deposits are oxidation-resistant up to 1800°F (980°C) because of their high nickel and chro-mium contents. However, the incipient fusion may occur near this temperature, and use of these filler metals above 1750°F (955°C) is not recommended.

Corrosion Resistance Deposits of NiCr filler metal are completely resistant to atmospheric, steam, salt water, and salt spray corrosion. They are also resistant to the milder acids and many common corrosive chemicals. However, if an application that involves corrosion is under consideration, general statements about corrosion should be confirmed by a field test.

Abrasion The high carbon classification of these alloys, NiCr-C, has excellent resistance to low stress scratching abrasion and is particularly valuable where such abrasion is combined with corrosion. Abrasion resistance is expected to decrease with decreasing carbon content. These filler metals are not recommended for high stress grinding abrasion.

Metal-to-Metal Wear NiCr deposits have excellent metal-to-metal wear resistance and acquire a high polish under wear-ing conditions. They are particularly resistant to gallwear-ing.

Information on these properties is not available.

Machinab ility Deposits of NiCr filler meta ls may be machined with tungsten carbide tools by using slow speeds, light feeds, and heavy tool shanks. NiCr filler metals also may be finished by grinding, using a soft to medium vitrified silicon carbide wheel.

Identification NiCr deposits are nonmagnetic. When spark teste d, they give off a short, dull, red spark without bursting. They have a higher fluidity and lower melting point than the cobalt base alloy filler metals.

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Polarity

Direct current electrode negative (DCEN) give less

penetration and therefore lower dilution than direct

current electrode positive (DCEP). Alternating

cur-rent gives dilution that is intermediate between

DCEN and DCEP.

Electrode Size

Smaller electrodes mean lower amperages, as a

rule, and therefore lower dilution. In gas metal arc

welding, for a given amperage, larger electrodes

(and lower current densities) mean lower dilution if

the larger electrodes result in spray transfer. With

other welding processes the results may vary.

Electrode Extension

A long electrode extension decreases dilution (for

consumable electrode processes) by increasing the

melting rate of the electrode (I

2

_{R heating) and}

dif-fusing the energy of the arc as it impinges on the

base metal. Conversely, a short electrode extension

increases dilution, within limits.

Travel Speed

A decrease in travel speed decreases the amount

of base metal melted and increases the amount of

Table 8. Tungsten Carbide Filler Metals

Hardness The hardness of the deposit is dependent upon the size of the carbide granules in the welding rod. For example, a hardness of Rockwell C 30 can be obtained for a deposit of 10 mesh particles and a hardness of C 60 can be obtained for a deposit of 100 mesh particles.

Hot Hardness The weld deposit retains its hardness up to 1000°F (540°C). Arc welded deposits exhibit better hot hardness than oxyfuel deposit.

Impact Both the carbide granules and the weld deposits are relatively brittle and vulnerable to sudden ten-sile stresses. They have high compressive strength and can withstand light impacts that do not pro-duce compression stress above the yield strength. Impact blows faster than 50 ft/s (15.2 m/s) should be avoided and the design should avoid tensile stress.

Oxidation Resistance Tungsten carbide has a low resistance to oxidation. Exposed granules of tungsten carbide will oxi-dize to form voluminous yellow tungsten oxide at temperatures above 1000°F (540°C).

Corrosion Resistance Though the granules may be resistant to many media, the matrix of the standardized tube welding rod is practically as vulnerable to rusting and corrosion as ordinary steel. These materials should not be selected if corrosion resistance is required.

Abrasion Weld deposits made from these materials are appropriate for resisting low stress scratching or high stress grinding abrasion. In either type, the matrix tends to abrade more rapidly, permitting the car-bides to stand in relief. Arc welds have behavior related to granule size and welding current, while oxyfuel gas process welds are usually higher in abrasion resistance and are more consistent. Metal-to-Metal Wear Tungsten carbide deposits are not applicable for conditions of metal-to-metal wear.

Deposits can be made by using high strength bonding alloys to give a deposit with high compres-sive strength; but the usual carbon steel binders give deposits that have a compression strength about the same as a high carbon steel deposit.

Machinability Tungsten carbide deposits are considered commercially unmachinable.

Identification Tungsten carbide particles have the following properties: (1) nonmagnetic; (2) high density; (3) insoluble in most acids; (4) readily form a yellow oxide when heated red hot in air; (5) high melting point (practically impossible to melt in an oxyacetylene flame); and (6) very hard and quite brittle.

Figure 1. Different Impingement Angles

HIGH ANGLE

LOW

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Figure 2. Calculation of Base Metal Dilution

Table 9. Shielded Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics

Variable Change of Variablea

Influence of Change on

Dilution Deposition Rate Deposit Thickness Polarity AC DCEP DCEN Intermediate High Low Intermediate Low High Intermediate Thin Thick Amperage High Low High Low High Low Thick Thin Technique Stringer Weave High Low No effect No effect Thick Thin Bead spacing Narrow

Wide Low High No effect No effect Thick Thin Electrode diameter Small

Large High Low High Low Thick Thin Arc length Long

Short Low High No effect No effect Thin Thick Travel speed Fast

Slow High Low No effect No effect Thin Thick Position Flat Uphill Downhill Horizontal Vertical-upb Vertical-upc 4 3 4 2–4 1 (Highest) 5 (Lowest) No effect No effect No effect No effect No effect No effect 4 3 4 1 (Thickest) 5 (Thinnest) 2 Notes:

a. This table assumes that only one variable at a time is changed. However, for acceptable surfacing conditions, a change in one variable may require a change in one or more other variables.

b. The arc directed on work (forehand welding).

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surfacing metal added, per unit time or distance;

thus it decreases dilution. This reduction in dilution

is brought about by the change in bead shape and

thickness and by the fact that the arc force is

expended on the weld pool rather than the base

metal.

Welding Position and Work Inclination

The position of welding in which the surfacing is

applied has an important bearing on the amount of

dilution obtained. Depending on the welding

posi-tion or work inclinaposi-tion, gravity will cause the pool

to run ahead of, remain under, or run behind the

arc. The more the pool stays ahead of or under the

arc, the less the penetration into the base metal and

the lower the dilution; thus, the pool acts as a

cush-ion, absorbing some of the arc energy before it can

impinge on the base metal. This absorption of arc

energy flattens and spreads the pool and also, the

weld bead. If the pool is too far ahead of the arc or

too thick, there will be insufficient melting of the

surface of the base metal and fusion will not take

place.

Table 10. Gas Tungsten Arc Process Variables—Independent Effects on Key Surfacing Characteristics

Dilution Deposition Deposit Thickness Current type AC DC Average Lower or higher Average Lower or higher Average Lower or higher Polarity DCEN DCEP High Low High Low Thick Thin Shielding gas Argon

Helium Lowest Highest Lowest Highest Thinnest Highest Amperage High Low High Low High Low Thick Thin Technique Stringer Weave High Low No effect No effect Thick Thin Bead spacing (pitch) Narrow

Wide Low High No effect No effect Thick Thin Electrode extension Short

Long No effect No effect No effect No effect No effect No effect Surfacing wire di ameter Small

Large High Low Low High Thin Thick Voltage High Low Low High No effect No effect Thin Thick Travel speed Fast

Slow High Low No effect No effect Thin Thick Position Flat Uphill Downhill Horizontal Vertical-upb Vertical-upc 4 3 4 2–4 1 (Highest) 5 (Lowest) No effect No effect No effect No effect No effect No effect 4 3 4 1 (Thickest) 5 (Thinnest) 2

Auxiliarywire(s) Low High Thicker Notes:

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The order of decreasing dilution for work position

is as follows:

(1) Vertical-up (highest dilution)

(2) Horizontal

(3) Flat with incline, uphill

(4) Flat with no incline

(5) Flat with incline, downhill (lowest dilution)

The ranking represents the typical case. With

spe-cialized procedures, the dilution obtained in a

given position can be significantly changed, with a

resultant change in the ranking.

Most surfacing is performed in the flat position.

Uphill or downhill welding can be achieved by

inclining the part to be surfaced or by placing the

arc off-center for rotating cylindrical parts (see

Figure 5).

Table 11. Gas Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics

Dilution Deposition Rate Deposit Thickness Polarity DCEP DCEN High Low Low High Thin Thick Shielding Gas Argon

Helium Carbon dioxide Lowest Highest Intermediate Lowest Highest Intermediate Thinnest Thickest Intermediate Arc Transfer Spray

Globular Short circuit Pulsed 1 (Highest) 3 4 (Lowest) 2 1 (Highest) 3 4 (Lowest) 2 1 (Thickest) 3 4 (Thinnest) 2 Amperage High Low High Low High Low Thick Thin Technique Stringer Weave High Low No effect No effect Thick Thin Bead Spacing Narrow

Wide Low High No effect No effect Thick Thin Electrode Extension Short

Long High Low Low High Thin Thick Electrode Diameter Small

Large High Low High Low Thick Thin Voltage High Low Low High No effect No effect Thin Thick Travel Speed Fast

Slow High Low No effect No effect Thin Thick Position Flat Uphill Downhill Horizontal Vertical-upb Vertical-upc 3 2 4 2–4 1 (Highest) 5 (Lowest) No effect No effect No effect No effect No effect No effect 4 3 4 1 (Thickest) 5 (Thinnest) 2

AuxiliaryWire(s) Low High Thicker Notes:

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Arc Shielding

The shielding medium, gas or flux, has a significant

affect on dilution. It influences the fluidity and

sur-face tension of the weld pool. These, in turn,

deter-mine the extent to which the weld metal will wet

the base metal and blend in along the edges of the

bead, forming a nicely shaped weld bead. The

shielding medium also has a significant effect on

the type of welding current that can be used. The

list below ranks, in general, the different shielding

media in order of decreasing dilution:

(1) Helium (highest dilution)

(2) Granular fluxes without alloy addition

(3) Carbon dioxide

(4) Argon

(5) Granular fluxes with alloy addition (lowest

dilution)

Auxiliary Surfacing Metal

The addition of surfacing metal, other than the

elec-trode, to the weld pool during surfacing can greatly

Table 12. Submerged Arc Process Variables—Independent Effects on Key Surfacing Characteristics

Influence of Change on Dilution Deposition Rate

Deposit Thickness Power supply and connection AC

DCEP DCEN Intermediate Highest Lowest Intermediate Lowest Highest Intermediate Thinnest Thickest Amperage High Low High Low High Low Thick Thin Technique Stringer Weave High Low No effect No effect Thick Thin Bead spacing Narrow

Wide Low High No effect No effect Thick Thin Electrode extension Short

Long High Low Low High Thin Thick Electrode diameter Small

Large High Low High Low Thick Thin Voltage High Low Low High No effect No effect Thin Thick Travel speed Fast

Slow High Low No effect No effect Thin Thick Position Flat Uphill Downhill Intermediate Highest Lowest No effect No effect No effect Intermediate Thickest Thinnest Process variations 1 electrode

1 electrode & surfacing wire 1 electrode & hot surfacing wire 2 wire series

2 wire series & cold wire Multiple wire

Strip electrode Hot and cold strip Powder addition 2 3 4 3 4 2 1 (Highest) 5 (Lowest) 4 5 (Lowest) 5 4 4 3 2 2 1 (Highest 3 5 (Thinnest) 4 4 4 3 2 3 1 (Thickest) 3

a. This table assumes that only one variable at a time is changed. The table indicates only general trends and does not cover questions of weldability or weld soundness. These factors may make it unwise to change only the indicated variable; the desired change in dilution, deposition rate, or deposit thickness may not be achieved.

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reduce dilution. The extra metal, added separately as

powder, wire, or strip or with the flux, reduces

dilu-tion by both increasing the total amount of surfacing

metal and reducing the amount of base metal that is

melted. This is accomplished by using some of the

arc energy to melt auxiliary surfacing metal instead

of the base metal. The greater the amount of

surfac-ing metal added, the lower the dilution (see Figure 6).

Figure 3. Effect of Travel Speed on Dilution

(Other Conditions Unchanged)

LOWEST DEPOSITION RATE HIGHEST DEPOSITION RATE

DECREASING TRAVEL SPEED (INCREASING BEAD THICKNESS)

I N C R E A S I N G D I L U T I O N

Figure 4. Basic Surfacing Oscillation

Techniques and Bead Configurations

STRINGER BEAD PENDULUM STRAIGHT LINE STRAIGHT LINE, CONSTANT VELOCITY

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Hardfacing

14 AWS Practical Reference Guide

Figure 5. Uphill and Downhill Welding Flat Plate and Rotating Cylindrical Parts

Figure 6. Map of Hardfacing Applications

C E N T E R L I N E C E N T E R L I N E OFF-CENTER DISTANCE ROTATION DIRECTION DIRECTION OF ROTATION OFF-CENTER DISTANCE

Uphill Welding

W E L D I N G D I R E C T I O N ANGLE OF INCLINATION C E N T E R L I N E C E N T E R L I N E OFF-CENTER DISTANCE ROTATION DIRECTION OFF-CENTER DISTANCE

Downhill Welding

W E L D I N G D I R E C T I O N ANGLE OF INCLINATION DIRECTION OF ROTATION

SEVERE ABRASIVE WEAR IMPACT AND ABRASIVE WEAR GOUGING AND IMPACT WEAR ROLLING AND SLIDING WEAR ALLOY, % C A R B O N , % EXTRA CARBIDE PREMIUM CARBIDE PRIMARY CARBIDE AND EUTECTIC NEAR EUTECTIC PRIMARY AUSTENITE PLUS EUTECTIC (CARBIDE & AUSTENITE) MARTENSITE

+ AUSTENITE _TENITIC AUS-Mn PREMIUM AUSTENITIC Cr + Mn MAR- TEN-SITE TOOL STEEL CASTER ROLLS BUILD UP 10.0 7.0 5.0 4.0 3.0 2.0 1.0 0.7 0.5 0.4 0.3 0.2 0.1 0 5 10 15 20 25 30 35

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Other Publications Available from AWS

Code

Document

A2.4

Standard Symbols for Welding, Brazing, and Nondestructive Examination

A3.0

Standard Welding Terms and Definitions

A5.various

Surfacing Alloy Series in AWS Filler Metal Specifications

TSM

Thermal Spray Manual

TSS

Thermal Spraying: Practice, Theory, and Application

UGFM-95

User’s Guide to Filler Metals

WHB-2.8

Welding Processes, Welding Handbook (2.8 or latest volume)

WHB-4.8

Materials and Applications, Part 2, Welding Handbook (2.8 or latest volume)

For ordering information, contact Global Engineering Documents, An Information Handling Services Group

Company, 15 Inverness Way East, Englewood, Colorado 80112-5776. Telephones: (800) 854-7179, (303) 397-7956;

FAX (303) 397-2740; E-Mail: [email protected]; Internet: www.global.ihs.com.

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