The Practical Reference Guide for
THE PRACTICAL REFERENCE GUIDE for for HARDFACING
Compiled/Edited by
Lee G. Kvidahl Manager, Manager, Welding and 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 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 publisher is not responsible for loss or damage resulting from use of this t his publication. This document is not a consensus standard. Users should refer to the applicable standards for their particular application.
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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.
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.
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TABLE OF CONTENTS 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
1 2 3 4 5 6 7 8 9 10 11 12
Page No.
Common Surfacing Processes and Materials...............................................................................................1 High-Speed Steel Filler Metals.......................................................................................................................3 Austenitic Manganese Filler Metals ..............................................................................................................3 Austenitic High Chromium Iron Filler Metals ............................................................................................4 Cobalt Base Alloy Filler Metals ......................................................................................................................5 Copper Base Alloy Filler Metals ....................................................................................................................6 Nickel Chromium Boron Alloy Filler Metals...............................................................................................7 Tungsten Carbide Filler Metals......................................................................................................................8 Shielded Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics ........9 Gas Tungsten Arc Process Variables—Independent Effects on Key Surfacing Characteristics.........10 Gas Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics ...............11 Submerged Arc Process Variables—Independent Effects on Key Surfacing Characteristics.............12
LIST OF FIGURES Figure
1 2 3 4 5 6
Page No.
Different Impingement Angles ......................................................................................................................8 Calculation of Base Metal Dilution................................................................................................................9 Effect of Travel Speed on Dilution (Other Conditions Unchanged) ......................................................13 Basic Surfacing Oscillation Techniques and Bead Configurations.........................................................13 Uphill and Downhill Welding Flat Plate and Rotating Cylindrical Parts.............................................14 Map of Hardfacing Applications.................................................................................................................14
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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 protective 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 fireresistant 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 g round 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 confined 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 clothing 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 Welding, 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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Hardfacing
Introduction Hardfacing is one category from the family of surfacing processes. Surfacing is defined in AWS A3.0, Standard Welding Terms and Definitions, as “The application 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 surfacing 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 surfacing material is deposited to reduce wear. (A nonstandard 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 design of the component (see Table 1). In addition to the characteristics of the surfacing material and base metal, other important considerations when choosing hardfacing applications 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
AWS Practical Reference Guide 1
Hardfacing
Hardfacing Properties
Erosive Wear Resistance
Properties of the hardfacing process are as follows:
• Under high-angle solid particle impingement
Hardness
• Under low-angle solid particle impingement
• Macrohardness (gross hardness)
• Under liquid droplet erosion
• Microhardness (hardness of individual constituents in a heterogeneous structure)
• Under cavitation conditions
• Hot hardness (resistance to the weakening effect of service at elevated temperature during short time loading)
Hardfacing Advantages
• Creep resistance (resistance to plastic deformation when loaded at elevated temperatures for relatively long periods of time) Abrasion Resistance
• Under low stress (scratching wear) • Under high stress (grinding)
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 supported by a tough substrate to carry the load
• Under high stress and impact (gouging) Impact Resistance
Selection of Hardfacing Materials
• Resistance to plastic deformation under repeated impact loading (related to yield strength and fatigue strength)
Factors to be identified for selection of surfacing materials (see Tables 2–8) includes:
• Resistance to cracking under impact loading (related to ductility but including work-hardening considerations)
• The type of abrasive to be encountered and its characteristics (hardness, sharpness, particle size, and toughness)
Heat Resistance
• Resistance to tempering (softening with time at temperature)
• The amount of impact to be encountered • The amount of support provided to the deposit • The levels of stress involved
• Retention of strength when hot (including hot hardness)
• The nature of the stress (tensile, compression, or shear)
• Creep resistance (time factor added to hot strength)
• The operating temperature
• Resistance to oxidation or corrosion by hot gases
• Other significant environmental conditions
Corrosion Resistance
Impact Resistance
Metal-to-Metal Resistance
Impact may be classified as light, medium, or heavy, depending upon the result of the impact energy.
• Friction coefficients (relative ease of sliding) • Galling tendency (localized welding) • Surface films (oxide layers) • Lubricity (slipperiness) • Plasticity (ability to deform)
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AWS Practical Reference Guide
An example of a heavy impact application is a hardfaced mill hammer. In light impact, kinetic energy is absorbed elastically. It is absorbed both elastically and plastically in medium impact. In heavy impact, the surface of even the strongest materials must either deform or fracture.
Hardfacing
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 maximum 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 better 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 temperatures. 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 temperatures. 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 Properties
Characteristics
Hardness
The normal hardness of these weld deposits is 170 to 230 BHN. This may be misleading as these materials 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 hammering, 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 hammering, 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 non-magnetic stainless steels.
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Hardfacing
Table 4. Austenitic High Chromium Iron Filler Metals Properties
Characteristics
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 resistance 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 carbides. 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. Resistance to galling is considered better than for ordinary hardened steel because tempering from frictional 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.
Mechanical Properties in Compression
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 magnetic permeability is about 1.03 with a magnetizing force of 24 oersteds.
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 resistance. Other choices for impact resistance include pearlitic steels and martensitic steels. In general, the impact resistance of martensitic steels is inferior to that of manganese-containing austenitic or pearlitic steels, but the abrasion resistance of martensitic steels is better.
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AWS Practical Reference Guide
Heat Resistance In general, resistance to thermal fatigue increases with increasing thermal conductivity, ultimate tensile strength, elongation at rupture, and Young’s modulus. Resistance to thermal fatigue decreases with increasing coefficient of expansion. Martensitic stainless steels containing 5% to 12% chromium are often used for resistance to thermal fatigue.
Hardfacing
Table 5. Cobalt Base Alloy Filler Metals Properties
Characteristics
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 application 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 resistance 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.
Mechanical Properties in Compression
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 differentiate between these materials.
An example of failure due to thermal fatigue is “fire cracking” in continuous casting rolls in steel mills.
Metal-to-Metal Wear Resistance
face and produces additional wear. Resistance to galling is greatly influenced by the type and stability 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.
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-
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
AWS Practical Reference Guide 5
Hardfacing
Table 6. Copper Base Alloy Filler Metals Properties
Characteristics
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 processes. 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 classifications. 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 various acids, mild alkalies, and salt water. The only exception is filler metal of the CuZn-E classification. 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 porosity 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.
Mechanical Properties in Compression
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.
Identification
All of the copper base alloy deposits are nonmagnetic and non-sparking.
metal-to-metal wear. Low stacking-fault energy occurs 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 resistance contain carbides of such elements as tungsten, chromium, molybdenum, or vanadium in a cobalt matrix, nickel alloys, tool steels, and austenitic manganese steels also are used.
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AWS Practical Reference Guide
Erosive Wear Resistance In situations of solid-particle impingement, hardfacing alloys with high carbide content are generally recommended for low-angle impingement (less than 15°). Those with low carbide content or other precipitates are preferred for high-angle impingement (greater than 80°). Figure 1 illustrates different impingement angles. Cobalt alloys are typically used for liquid droplet erosion and cavitation resistance due to their inherent properties in work hardening and fatigue
Hardfacing
Table 7. Nickel Chromium Boron Alloy Filler Metals Properties
Characteristics
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 produce 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 chromium 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 wearing conditions. They are particularly resistant to galling.
Mechanical Properties in Compression
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.
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. Dilution is the change in chemical composition 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 necessary 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, penetrating more deeply and melting more base metal.
AWS Practical Reference Guide 7
Hardfacing
Table 8. Tungsten Carbide Filler Metals Properties
Characteristics
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 tensile stresses. They have high compressive strength and can withstand light impacts that do not produce 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 oxidize 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 carbides 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.
Mechanical Properties in Compression
Deposits can be made by using high strength bonding alloys to give a deposit with high compressive 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.
Electrode Size
HIGH ANGLE
LOW ANGLE
SURFACE
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
Figure 1. Different Impingement Angles
Polarity
Direct current electrode negative (DCEN) give less penetration and therefore lower dilution than direct current electrode positive (DCEP). Alternating current gives dilution that is intermediate between DCEN and DCEP.
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AWS Practical Reference Guide
A long electrode extension decreases dilution (for consumable electrode processes) by increasing the melting rate of the electrode (I 2R heating) and diffusing 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
Hardfacing
Figure 2. Calculation of Base Metal Dilution
Table 9. Shielded Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics Influence of Change on Variable
Change of Variablea
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-up b Vertical-up c
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). c. The arc directed on surfacing buildup (backhand welding).
AWS Practical Reference Guide 9
Hardfacing
Table 10. Gas Tungsten Arc Process Variables—Independent Effects on Key Surfacing Characteristics Influence of Change on Variable
Change of Variablea
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-up b Vertical-up c
4 3 4 2–4 1 (Highest) 5 (Lowest)
No No No No No No
4 3 4 1 (Thickest) 5 (Thinnest) 2
Low
High
Auxiliary wire(s)
effect effect effect effect effect effect
Thicker
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). c. The arc directed on surfacing buildup (backhand welding).
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-
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AWS Practical Reference Guide
tion or work inclination, 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 cushion, 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.
Hardfacing
Table 11. Gas Metal Arc Process Variables—Independent Effects on Key Surfacing Characteristics Influence of Change on Change of Variablea
Variable
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-up b Vertical-up c
3 2 4 2–4 1 (Highest) 5 (Lowest)
No No No No No No
4 3 4 1 (Thickest) 5 (Thinnest) 2
Low
High
Auxiliary Wire(s)
effect effect effect effect effect effect
Thicker
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). c. The arc directed on surfacing buildup (backhand welding).
The order of decreasing dilution for work position is as follows: (1) Vertical-up (highest dilution)
The ranking represents the typical case. With specialized procedures, the dilution obtained in a given position can be significantly changed, with a resultant change in the ranking.
(2) Horizontal (3) Flat with incline, uphill (4) Flat with no incline (5) Flat with incline, downhill (lowest dilution)
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).
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Hardfacing
Table 12. Submerged Arc Process Variables—Independent Effects on Key Surfacing Characteristics Influence of Change on
Change of Variablea
Variable
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.
Arc Shielding
The shielding medium, gas or flux, has a significant affect on dilution. It influences the fluidity and surface tension of the weld pool. These, in turn, determine 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:
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AWS Practical Reference Guide
(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 electrode, to the weld pool during surfacing can greatly
Hardfacing
LOWEST DEPOSITION RATE HIGHEST DEPOSITION RATE
STRINGER BEAD
N O I T U L I D G N I S A E R C N I
PENDULUM
STRAIGHT LINE
STRAIGHT LINE, CONSTANT VELOCITY
DECREASING TRAVEL SPEED (INCREASING BEAD THICKNESS)
Figure 3. Effect of Travel Speed on Dilution (Other Conditions Unchanged)
Figure 4. Basic Surfacing Oscillation Techniques and Bead Configurations
reduce dilution. The extra metal, added separately as powder, wire, or strip or with the flux, reduces dilution 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 surfacing metal added, the lower the dilution (see Figure 6).
AWS Practical Reference Guide
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Hardfacing
E N I L R E T N E C
E N I L R E T N E C
OFF-CENTER DISTANCE
ROTATION DIRECTION
T I O N R E C I D D I N G W E L
OFF-CENTER DISTANCE
DIRECTION OF ROTATION
ANGLE OF INCLINATION
Uphill Welding E N I L R E T N E C
E N I L R E T N E C
OFF-CENTER DISTANCE
ROTATION DIRECTION
T I O N R E C I D D I N G W E L
OFF-CENTER DISTANCE
DIRECTION OF ROTATION
ANGLE OF INCLINATION
Downhill Welding
Figure 5. Uphill and Downhill Welding Flat Plate and Rotating Cylindrical Parts
10.0 7.0
EXTRA CARBIDE PREMIUM CARBIDE
5.0
PRIMARY CARBIDE AND EUTECTIC
4.0
NEAR EUTECTIC
3.0 PRIMARY AUSTENITE PLUS EUTECTIC (CARBIDE & AUSTENITE)
% 2.0 , N O B R 1.0 A C 0.7
MARTENSITE + AUSTENITE MARTENSITE
0.5 0.4
AUSTENITIC Mn PREMIUM AUSTENITIC Cr + Mn
TOOL STEEL
0.3 0.2
CASTER ROLLS
BUILD UP
0.1 0
5
10
15
20
ALLOY, %
Figure 6. Map of Hardfacing Applications
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AWS Practical Reference Guide
25
30
35
SEVERE ABRASIVE WEAR IMPACT AND ABRASIVE WEAR GOUGING AND IMPACT WEAR ROLLING AND SLIDING WEAR
Hardfacing
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.
AWS Practical Reference Guide
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