Wear can occur in several ways. While there are many specialized categories, most hardfacing decisions begin by identifying the most common wear mechanisms. Approximate shares of total wear are often described as follows:
In real operating environments, components usually experience more than one wear condition at the same time. A bucket tooth used in mining, for example, may be exposed to both abrasion and impact. The dominant condition can change depending on whether the tooth is working in soft material, hard rock, or mixed service. That operating profile helps determine the best hardfacing welding product. Because wear conditions can be difficult to diagnose, selecting a hardfacing alloy may require field testing, application review, and adjustment based on actual service results.
Carbon steels and low-alloy steels containing less than 1% carbon are commonly hardfaced. Higher-carbon alloys may need a buffer layer before the wear-resistant overlay is applied.
Materials that can often be hardfaced include:
Hardfacing alloys are often discussed by metallurgical family because each family responds differently to abrasion, impact, heat, corrosion, and metal-to-metal contact. The following categories are commonly used when comparing hardfacing options:
Some hardfacing alloys are designed to develop visible check cracks as they cool. This behavior is common with many chromium carbide deposits and is not necessarily a defect. Other alloy families, including many austenitic and martensitic deposits, should not crack when applied with the correct welding procedure.
Check cracking is a pattern of cracks often seen in metal carbide hardfacing deposits. The cracks usually run across the weld bead rather than along it and may be spaced roughly 3/8 inch to 2 inches apart. They form as the weld metal contracts during cooling and relieves internal stress.
In a sound application, check cracks extend through the overlay but stop at the base metal. If the base material is hard, brittle, or crack-sensitive, a softer and tougher buffer layer can be used to help stop crack propagation. Austenitic buffer deposits are often used for this purpose.
Chromium carbide hardfacing generally refers to iron-based alloys with high chromium content, typically above 18%, and high carbon content, typically above 3%. These elements combine to form hard chromium carbides that improve abrasion resistance. Chromium carbide overlays often develop stress-relieving check cracks about every 1/2 inch and can also offer favorable slip characteristics because of their low coefficient of friction.
As chromium and carbon levels increase, abrasion resistance generally improves, with carbon having the strongest influence. Typical hardness values range from 40 HRC to 65 HRC. Some formulations include additional carbide- or boride-forming elements for improved wear resistance at elevated temperatures. Many chromium carbide products are limited to two or three layers.
Complex carbide overlays are typically chromium carbide deposits enhanced with elements such as columbium, molybdenum, tungsten, vanadium, or a combination of these additions. These elements can form their own carbides or combine with chromium carbides, increasing overall abrasion resistance. Complex carbide alloys are commonly selected for severe abrasion, high-temperature wear, or both.
Hardness alone is not a reliable predictor of field performance. A martensitic alloy and a chromium carbide alloy may both measure about 58 HRC, yet perform very differently under the same abrasive conditions. Microstructure is usually a better indicator of expected wear resistance, although that information is not always available to the end
user.
Hardness comparisons are most useful when the products being compared are within the same alloy family. For example, a 55 HRC martensitic deposit will usually resist abrasion better than a 35 HRC martensitic deposit. That same comparison may not apply across austenitic or carbide-based alloys. For application-specific selection, consult the hardfacing product manufacturer or a qualified welding specialist.
Wear testing depends on the wear mechanism being evaluated. For abrasive wear, one widely used method is the ASTM G65 Dry Sand/Rubber Wheel test. In this test, the sample is weighed before and after exposure, and the result is typically reported as weight loss or volume loss.
During the test, a specimen is pressed against a rotating rubber wheel under a controlled load for a set number of revolutions. A carefully sized sand flows between the wheel and the specimen to simulate abrasion. The resulting data is used as a comparative guide when selecting hardfacing materials.
In plasma transferred arc welding, hardfacing applications typically aim for low penetration and low dilution. Pure argon or argon-hydrogen blends are commonly used to help achieve those results.
At minimum, parts should generally be brought to room temperature before welding. Higher preheat and interpass temperatures may be required depending on the chemistry of the base metal and the specific hardfacing product being applied.
Cobalt-based hardfacing alloys contain multiple carbide types and are often selected for severe abrasion at elevated temperatures. They may also provide corrosion resistance in certain service environments. Deposit hardness commonly ranges from 25 HRC to 55 HRC, and work-hardening versions are available.
Nickel-based hardfacing alloys may contain chromium borides for abrasion resistance. They are often considered when the application involves abrasion along with high temperature, corrosive atmospheres, or both.
Layer limits are most common with carbide-based products such as chromium carbide and tungsten carbide. Martensitic and austenitic hardfacing products can often be applied in additional layers unless the manufacturer specifies a limit.
Because metal carbide deposits are comparatively brittle, repeated layers can increase internal stress. Stress may concentrate at the roots of check cracks until separation or spalling occurs between the base metal, buffer layer, and hardfacing deposit.
Buildup and buffer alloys are used to restore badly worn components to their required dimensions or to prepare the surface for a harder wear-resistant overlay. These alloys often resemble the base material in composition or mechanical behavior. When the final hardfacing layer is prone to check cracking, a tough manganese-style buffer can help blunt the cracks and reduce the chance that they will penetrate into the base metal.
Yes. Cast iron can be rebuilt or hardfaced, but preheat and interpass temperature control are important. Nickel and nickel-iron welding products are commonly used for cast iron buildup because they are not significantly affected by the carbon content of the base metal and remain ductile. Multiple layers can be applied. If added wear protection is required, a metal carbide overlay may be placed over the nickel or nickel-iron buildup. This hardfacing FAQ provides a practical starting point for evaluating wear mechanisms, base metals, overlay alloys, PTA hardfacing, and repair strategies. For critical applications, consult the hardfacing consumable manufacturer or a qualified welding specialist to confirm product selection and procedure requirements.
Many steel and stainless-based alloys can receive a weld overlay, including manganese-based and non-magnetic materials.
Porosity can occur when gas becomes trapped in the weld. Common causes include contamination or moisture in the weld area, base metal, filler metal, shielding gas, or surrounding atmosphere. Oil, dirt, grease, cutting fluids, damp flux, moisture on the base metal, and atmospheric humidity can all contribute to porous weld deposits. When a welding process uses external shielding gas, porosity may result from incorrect gas flow, poor gas quality, leaks or defects in the torch, gun, or hose, or inadequate shielding of the weld pool. Welding technique can also affect porosity. Torch, gun, or electrode angle, excessive arc length, long electrode extension, and travel speed that is too fast can all increase the risk of porosity. Plasma transferred arc welding, or PTA welding, uses the heat of a constricted arc between an electrode and the workpiece to create a metallurgically bonded overlay. In PTA welding, a shielded arc is established between a non-consumable tungsten electrode and the torch body. The arc heats an inert gas, typically argon, into plasma. Metal powder is then metered under positive argon pressure into the molten pool on the workpiece surface. The torch may travel over the workpiece on a side-beam carriage, the workpiece may rotate or move under the torch, or both motions may be combined to create the overlay. PTA deposits are fully dense and metallurgically bonded to the base component. One important advantage of PTA hardfacing is dilution control. PTA can produce dilution as low as about 5%, compared with roughly 20% to 25% in many MIG or TIG hardfacing processes, helping the overlay retain its intended properties even in a single pass.
Wear can occur in several ways. While there are many specialized categories, most hardfacing decisions begin by identifying the most common wear mechanisms. Approximate shares of total wear are often described as follows:
In real operating environments, components usually experience more than one wear condition at the same time. A bucket tooth used in mining, for example, may be exposed to both abrasion and impact. The dominant condition can change depending on whether the tooth is working in soft material, hard rock, or mixed service. That operating profile helps determine the best hardfacing welding product. Because wear conditions can be difficult to diagnose, selecting a hardfacing alloy may require field testing, application review, and adjustment based on actual service results.
Carbon steels and low-alloy steels containing less than 1% carbon are commonly hardfaced. Higher-carbon alloys may need a buffer layer before the wear-resistant overlay is applied.
Materials that can often be hardfaced include:
Hardfacing alloys are often discussed by metallurgical family because each family responds differently to abrasion, impact, heat, corrosion, and metal-to-metal contact. The following categories are commonly used when comparing hardfacing options:
Some hardfacing alloys are designed to develop visible check cracks as they cool. This behavior is common with many chromium carbide deposits and is not necessarily a defect. Other alloy families, including many austenitic and martensitic deposits, should not crack when applied with the correct welding procedure.
Check cracking is a pattern of cracks often seen in metal carbide hardfacing deposits. The cracks usually run across the weld bead rather than along it and may be spaced roughly 3/8 inch to 2 inches apart. They form as the weld metal contracts during cooling and relieves internal stress.
In a sound application, check cracks extend through the overlay but stop at the base metal. If the base material is hard, brittle, or crack-sensitive, a softer and tougher buffer layer can be used to help stop crack propagation. Austenitic buffer deposits are often used for this purpose.
Chromium carbide hardfacing generally refers to iron-based alloys with high chromium content, typically above 18%, and high carbon content, typically above 3%. These elements combine to form hard chromium carbides that improve abrasion resistance. Chromium carbide overlays often develop stress-relieving check cracks about every 1/2 inch and can also offer favorable slip characteristics because of their low coefficient of friction.
As chromium and carbon levels increase, abrasion resistance generally improves, with carbon having the strongest influence. Typical hardness values range from 40 HRC to 65 HRC. Some formulations include additional carbide- or boride-forming elements for improved wear resistance at elevated temperatures. Many chromium carbide products are limited to two or three layers.
Complex carbide overlays are typically chromium carbide deposits enhanced with elements such as columbium, molybdenum, tungsten, vanadium, or a combination of these additions. These elements can form their own carbides or combine with chromium carbides, increasing overall abrasion resistance. Complex carbide alloys are commonly selected for severe abrasion, high-temperature wear, or both.
Hardness alone is not a reliable predictor of field performance. A martensitic alloy and a chromium carbide alloy may both measure about 58 HRC, yet perform very differently under the same abrasive conditions. Microstructure is usually a better indicator of expected wear resistance, although that information is not always available to the end
user.
Hardness comparisons are most useful when the products being compared are within the same alloy family. For example, a 55 HRC martensitic deposit will usually resist abrasion better than a 35 HRC martensitic deposit. That same comparison may not apply across austenitic or carbide-based alloys. For application-specific selection, consult the hardfacing product manufacturer or a qualified welding specialist.
Wear testing depends on the wear mechanism being evaluated. For abrasive wear, one widely used method is the ASTM G65 Dry Sand/Rubber Wheel test. In this test, the sample is weighed before and after exposure, and the result is typically reported as weight loss or volume loss.
During the test, a specimen is pressed against a rotating rubber wheel under a controlled load for a set number of revolutions. A carefully sized sand flows between the wheel and the specimen to simulate abrasion. The resulting data is used as a comparative guide when selecting hardfacing materials.
In plasma transferred arc welding, hardfacing applications typically aim for low penetration and low dilution. Pure argon or argon-hydrogen blends are commonly used to help achieve those results.
At minimum, parts should generally be brought to room temperature before welding. Higher preheat and interpass temperatures may be required depending on the chemistry of the base metal and the specific hardfacing product being applied.
Cobalt-based hardfacing alloys contain multiple carbide types and are often selected for severe abrasion at elevated temperatures. They may also provide corrosion resistance in certain service environments. Deposit hardness commonly ranges from 25 HRC to 55 HRC, and work-hardening versions are available.
Nickel-based hardfacing alloys may contain chromium borides for abrasion resistance. They are often considered when the application involves abrasion along with high temperature, corrosive atmospheres, or both.
Layer limits are most common with carbide-based products such as chromium carbide and tungsten carbide. Martensitic and austenitic hardfacing products can often be applied in additional layers unless the manufacturer specifies a limit.
Because metal carbide deposits are comparatively brittle, repeated layers can increase internal stress. Stress may concentrate at the roots of check cracks until separation or spalling occurs between the base metal, buffer layer, and hardfacing deposit.
Buildup and buffer alloys are used to restore badly worn components to their required dimensions or to prepare the surface for a harder wear-resistant overlay. These alloys often resemble the base material in composition or mechanical behavior. When the final hardfacing layer is prone to check cracking, a tough manganese-style buffer can help blunt the cracks and reduce the chance that they will penetrate into the base metal.
Yes. Cast iron can be rebuilt or hardfaced, but preheat and interpass temperature control are important. Nickel and nickel-iron welding products are commonly used for cast iron buildup because they are not significantly affected by the carbon content of the base metal and remain ductile. Multiple layers can be applied. If added wear protection is required, a metal carbide overlay may be placed over the nickel or nickel-iron buildup. This hardfacing FAQ provides a practical starting point for evaluating wear mechanisms, base metals, overlay alloys, PTA hardfacing, and repair strategies. For critical applications, consult the hardfacing consumable manufacturer or a qualified welding specialist to confirm product selection and procedure requirements.
Many steel and stainless-based alloys can receive a weld overlay, including manganese-based and non-magnetic materials.
Porosity can occur when gas becomes trapped in the weld. Common causes include contamination or moisture in the weld area, base metal, filler metal, shielding gas, or surrounding atmosphere. Oil, dirt, grease, cutting fluids, damp flux, moisture on the base metal, and atmospheric humidity can all contribute to porous weld deposits. When a welding process uses external shielding gas, porosity may result from incorrect gas flow, poor gas quality, leaks or defects in the torch, gun, or hose, or inadequate shielding of the weld pool. Welding technique can also affect porosity. Torch, gun, or electrode angle, excessive arc length, long electrode extension, and travel speed that is too fast can all increase the risk of porosity. Plasma transferred arc welding, or PTA welding, uses the heat of a constricted arc between an electrode and the workpiece to create a metallurgically bonded overlay. In PTA welding, a shielded arc is established between a non-consumable tungsten electrode and the torch body. The arc heats an inert gas, typically argon, into plasma. Metal powder is then metered under positive argon pressure into the molten pool on the workpiece surface. The torch may travel over the workpiece on a side-beam carriage, the workpiece may rotate or move under the torch, or both motions may be combined to create the overlay. PTA deposits are fully dense and metallurgically bonded to the base component. One important advantage of PTA hardfacing is dilution control. PTA can produce dilution as low as about 5%, compared with roughly 20% to 25% in many MIG or TIG hardfacing processes, helping the overlay retain its intended properties even in a single pass.
Metal parts often fail their intended use not because they fracture, but because they wear, which causes them to lose dimension and functionality. Hard-facing, also known as hard-surfacing, is the application of buildup or wear-resistant weld metals to a part’s surface by means of welding or joining.
It depends on the hard-facing alloy. Many chromium carbide alloys check-crack when cooled to moderate temperatures; this is normal. Others, such as the austenitic and martensitic families, don’t crack when applied with proper welding procedures.
Complex carbides generally are associated with the chromium carbide deposits that have additions of columbium, molybdenum, tungsten, or vanadium. The addition of these elements and carbon form their own carbides and/or combine with the present chromium carbides to increase the alloy’s overall abrasion resistance. They can have all of these elements or just one or two. They are used for severe-abrasion or high-heat applications.
No, this isn’t a good idea. A martensitic alloy and a chromium carbide alloy can have the same hardness, let’s say 58 HRC, and perform vastly different under the same abrasive conditions. The metallurgical micro-structure is a better measuring stick, but that isn’t always available.
The only time hardness can be used to predict wear is when the alloys being evaluated are within the same family. For example, in the martensitic family, a 55 HRC alloy will have better abrasion resistance than a 35 HRC alloy. This may or may not be the case in either the austenitic or metal carbide families. Again, you have to consider the micro-structure. You should consult with the manufacturer for recommendations.
It depends on the type of wear involved, but in the case of abrasive wear—by far the most predominant wear mechanism—the ASTM Intl. G65 Dry Sand Rubber Wheel Test is used extensively. This essentially is a test in which the sample is weighed before and after the test, and the result usually is expressed in grams of weight loss or volume loss.
A sample is held against a spinning rubber wheel with a known force for a number of revolutions. A specific type of sand, which is sized carefully, is trickled down between the sample and rubber wheel. This simulates pure abrasion, and the numbers are used as guidelines in material selection.
Low penetration and dilution are the major objectives in hard-facing, so pure argon and mixtures of argon with hydrogen generally will produce the desired result.
As a rule, you should bring all parts at least to room temperature. You can select higher preheat and inter-pass temperatures based on the base metal chemistry and hard-facing product you’re using.
Cobalt alloys contain many types of carbides and are good for severe abrasion at high temperatures. They also have good corrosion resistance for some applications. Deposit hardness ranges from 25 HRC to 55 HRC. Work-hardening alloys also are available.
Nickel-base alloys can contain chromium borides that resist abrasion. They can be good particularly in corrosive atmospheres and high temperatures when abrasion is a problem.
Limited-layer products usually are in the metal carbide families, such as chromium carbide and tungsten carbide. You can apply martensitic and austenitic products in unlimited layers unless the manufacturer specifies otherwise.
The brittle nature of the metal carbides leads to check-cracking, and as multiple layers are applied, stress continues to build, concentrating at the root of the check cracks, until separation or spalling occurs between the parent metal or buffer and the hard-facing deposit.
These alloys often resemble the parent metal alloy and are applied to severely worn parts to bring them back to dimension or act as a buffer for subsequent layers of a more wear-resistant hard-facing deposit. If the hard-facing produces check cracks, then it’s wise to use a tough manganese product as the buffer to blunt and stop the check cracks from penetrating into the base metal
Yes, but you must take preheat and inter-pass temperatures into account. Nickel and nickel-iron products usually are suitable for rebuilding cast iron. These products aren’t affected by the carbon content of the parent metal and remain ductile. Multiple layers are possible. If further wear protection is required, metal carbide products can work well on top of the nickel or nickel-iron buildup.
These frequently asked questions only begin to address hard-facing. Hard-facing product manufacturers and specialists can contribute to a greater in-depth understanding of hard-facing and help assist you in product and process selection for your application
Almost any steel, or stainless based alloy can be over-layed, including manganese based or non-magnetic materials.
Wear can occur in several ways. While there are many specialized categories, most hardfacing decisions begin by identifying the most common wear mechanisms. Approximate shares of total wear are often described as follows:
In real operating environments, components usually experience more than one wear condition at the same time. A bucket tooth used in mining, for example, may be exposed to both abrasion and impact. The dominant condition can change depending on whether the tooth is working in soft material, hard rock, or mixed service. That operating profile helps determine the best hardfacing welding product. Because wear conditions can be difficult to diagnose, selecting a hardfacing alloy may require field testing, application review, and adjustment based on actual service results.
Carbon steels and low-alloy steels containing less than 1% carbon are commonly hardfaced. Higher-carbon alloys may need a buffer layer before the wear-resistant overlay is applied.
Materials that can often be hardfaced include:
Hardfacing alloys are often discussed by metallurgical family because each family responds differently to abrasion, impact, heat, corrosion, and metal-to-metal contact. The following categories are commonly used when comparing hardfacing options:
Some hardfacing alloys are designed to develop visible check cracks as they cool. This behavior is common with many chromium carbide deposits and is not necessarily a defect. Other alloy families, including many austenitic and martensitic deposits, should not crack when applied with the correct welding procedure.
Check cracking is a pattern of cracks often seen in metal carbide hardfacing deposits. The cracks usually run across the weld bead rather than along it and may be spaced roughly 3/8 inch to 2 inches apart. They form as the weld metal contracts during cooling and relieves internal stress.
In a sound application, check cracks extend through the overlay but stop at the base metal. If the base material is hard, brittle, or crack-sensitive, a softer and tougher buffer layer can be used to help stop crack propagation. Austenitic buffer deposits are often used for this purpose.
Chromium carbide hardfacing generally refers to iron-based alloys with high chromium content, typically above 18%, and high carbon content, typically above 3%. These elements combine to form hard chromium carbides that improve abrasion resistance. Chromium carbide overlays often develop stress-relieving check cracks about every 1/2 inch and can also offer favorable slip characteristics because of their low coefficient of friction.
As chromium and carbon levels increase, abrasion resistance generally improves, with carbon having the strongest influence. Typical hardness values range from 40 HRC to 65 HRC. Some formulations include additional carbide- or boride-forming elements for improved wear resistance at elevated temperatures. Many chromium carbide products are limited to two or three layers.
Complex carbide overlays are typically chromium carbide deposits enhanced with elements such as columbium, molybdenum, tungsten, vanadium, or a combination of these additions. These elements can form their own carbides or combine with chromium carbides, increasing overall abrasion resistance. Complex carbide alloys are commonly selected for severe abrasion, high-temperature wear, or both.
Hardness alone is not a reliable predictor of field performance. A martensitic alloy and a chromium carbide alloy may both measure about 58 HRC, yet perform very differently under the same abrasive conditions. Microstructure is usually a better indicator of expected wear resistance, although that information is not always available to the end
user.
Hardness comparisons are most useful when the products being compared are within the same alloy family. For example, a 55 HRC martensitic deposit will usually resist abrasion better than a 35 HRC martensitic deposit. That same comparison may not apply across austenitic or carbide-based alloys. For application-specific selection, consult the hardfacing product manufacturer or a qualified welding specialist.
Wear testing depends on the wear mechanism being evaluated. For abrasive wear, one widely used method is the ASTM G65 Dry Sand/Rubber Wheel test. In this test, the sample is weighed before and after exposure, and the result is typically reported as weight loss or volume loss.
During the test, a specimen is pressed against a rotating rubber wheel under a controlled load for a set number of revolutions. A carefully sized sand flows between the wheel and the specimen to simulate abrasion. The resulting data is used as a comparative guide when selecting hardfacing materials.
In plasma transferred arc welding, hardfacing applications typically aim for low penetration and low dilution. Pure argon or argon-hydrogen blends are commonly used to help achieve those results.
At minimum, parts should generally be brought to room temperature before welding. Higher preheat and interpass temperatures may be required depending on the chemistry of the base metal and the specific hardfacing product being applied.
Cobalt-based hardfacing alloys contain multiple carbide types and are often selected for severe abrasion at elevated temperatures. They may also provide corrosion resistance in certain service environments. Deposit hardness commonly ranges from 25 HRC to 55 HRC, and work-hardening versions are available.
Nickel-based hardfacing alloys may contain chromium borides for abrasion resistance. They are often considered when the application involves abrasion along with high temperature, corrosive atmospheres, or both.
Layer limits are most common with carbide-based products such as chromium carbide and tungsten carbide. Martensitic and austenitic hardfacing products can often be applied in additional layers unless the manufacturer specifies a limit.
Because metal carbide deposits are comparatively brittle, repeated layers can increase internal stress. Stress may concentrate at the roots of check cracks until separation or spalling occurs between the base metal, buffer layer, and hardfacing deposit.
Buildup and buffer alloys are used to restore badly worn components to their required dimensions or to prepare the surface for a harder wear-resistant overlay. These alloys often resemble the base material in composition or mechanical behavior. When the final hardfacing layer is prone to check cracking, a tough manganese-style buffer can help blunt the cracks and reduce the chance that they will penetrate into the base metal.
Yes. Cast iron can be rebuilt or hardfaced, but preheat and interpass temperature control are important. Nickel and nickel-iron welding products are commonly used for cast iron buildup because they are not significantly affected by the carbon content of the base metal and remain ductile. Multiple layers can be applied. If added wear protection is required, a metal carbide overlay may be placed over the nickel or nickel-iron buildup. This hardfacing FAQ provides a practical starting point for evaluating wear mechanisms, base metals, overlay alloys, PTA hardfacing, and repair strategies. For critical applications, consult the hardfacing consumable manufacturer or a qualified welding specialist to confirm product selection and procedure requirements.
Many steel and stainless-based alloys can receive a weld overlay, including manganese-based and non-magnetic materials.
Porosity can occur when gas becomes trapped in the weld. Common causes include contamination or moisture in the weld area, base metal, filler metal, shielding gas, or surrounding atmosphere. Oil, dirt, grease, cutting fluids, damp flux, moisture on the base metal, and atmospheric humidity can all contribute to porous weld deposits. When a welding process uses external shielding gas, porosity may result from incorrect gas flow, poor gas quality, leaks or defects in the torch, gun, or hose, or inadequate shielding of the weld pool. Welding technique can also affect porosity. Torch, gun, or electrode angle, excessive arc length, long electrode extension, and travel speed that is too fast can all increase the risk of porosity. Plasma transferred arc welding, or PTA welding, uses the heat of a constricted arc between an electrode and the workpiece to create a metallurgically bonded overlay. In PTA welding, a shielded arc is established between a non-consumable tungsten electrode and the torch body. The arc heats an inert gas, typically argon, into plasma. Metal powder is then metered under positive argon pressure into the molten pool on the workpiece surface. The torch may travel over the workpiece on a side-beam carriage, the workpiece may rotate or move under the torch, or both motions may be combined to create the overlay. PTA deposits are fully dense and metallurgically bonded to the base component. One important advantage of PTA hardfacing is dilution control. PTA can produce dilution as low as about 5%, compared with roughly 20% to 25% in many MIG or TIG hardfacing processes, helping the overlay retain its intended properties even in a single pass.
Hardfacing is a proven way to extend the service life of industrial components exposed to abrasion, impact, heat, corrosion, and metal-to-metal wear. This FAQ explains how wear-resistant weld overlays, PTA hardfacing, chromium carbide coatings, buildup alloys, and base-metal preparation work together to restore worn parts, reduce downtime, and improve equipment reliability.
Wear can occur in several ways. While there are many specialized categories, most hardfacing decisions begin by identifying the most common wear mechanisms. Approximate shares of total wear are often described as follows:
In real operating environments, components usually experience more than one wear condition at the same time. A bucket tooth used in mining, for example, may be exposed to both abrasion and impact. The dominant condition can change depending on whether the tooth is working in soft material, hard rock, or mixed service. That operating profile helps determine the best hardfacing welding product. Because wear conditions can be difficult to diagnose, selecting a hardfacing alloy may require field testing, application review, and adjustment based on actual service results.
Carbon steels and low-alloy steels containing less than 1% carbon are commonly hardfaced. Higher-carbon alloys may need a buffer layer before the wear-resistant overlay is applied.
Materials that can often be hardfaced include:
Hardfacing alloys are often discussed by metallurgical family because each family responds differently to abrasion, impact, heat, corrosion, and metal-to-metal contact. The following categories are commonly used when comparing hardfacing options:
Some hardfacing alloys are designed to develop visible check cracks as they cool. This behavior is common with many chromium carbide deposits and is not necessarily a defect. Other alloy families, including many austenitic and martensitic deposits, should not crack when applied with the correct welding procedure.
Check cracking is a pattern of cracks often seen in metal carbide hardfacing deposits. The cracks usually run across the weld bead rather than along it and may be spaced roughly 3/8 inch to 2 inches apart. They form as the weld metal contracts during cooling and relieves internal stress.
In a sound application, check cracks extend through the overlay but stop at the base metal. If the base material is hard, brittle, or crack-sensitive, a softer and tougher buffer layer can be used to help stop crack propagation. Austenitic buffer deposits are often used for this purpose.
Chromium carbide hardfacing generally refers to iron-based alloys with high chromium content, typically above 18%, and high carbon content, typically above 3%. These elements combine to form hard chromium carbides that improve abrasion resistance. Chromium carbide overlays often develop stress-relieving check cracks about every 1/2 inch and can also offer favorable slip characteristics because of their low coefficient of friction.
As chromium and carbon levels increase, abrasion resistance generally improves, with carbon having the strongest influence. Typical hardness values range from 40 HRC to 65 HRC. Some formulations include additional carbide- or boride-forming elements for improved wear resistance at elevated temperatures. Many chromium carbide products are limited to two or three layers.
Complex carbide overlays are typically chromium carbide deposits enhanced with elements such as columbium, molybdenum, tungsten, vanadium, or a combination of these additions. These elements can form their own carbides or combine with chromium carbides, increasing overall abrasion resistance. Complex carbide alloys are commonly selected for severe abrasion, high-temperature wear, or both.
Hardness alone is not a reliable predictor of field performance. A martensitic alloy and a chromium carbide alloy may both measure about 58 HRC, yet perform very differently under the same abrasive conditions. Microstructure is usually a better indicator of expected wear resistance, although that information is not always available to the end
user.
Hardness comparisons are most useful when the products being compared are within the same alloy family. For example, a 55 HRC martensitic deposit will usually resist abrasion better than a 35 HRC martensitic deposit. That same comparison may not apply across austenitic or carbide-based alloys. For application-specific selection, consult the hardfacing product manufacturer or a qualified welding specialist.
Wear testing depends on the wear mechanism being evaluated. For abrasive wear, one widely used method is the ASTM G65 Dry Sand/Rubber Wheel test. In this test, the sample is weighed before and after exposure, and the result is typically reported as weight loss or volume loss.
During the test, a specimen is pressed against a rotating rubber wheel under a controlled load for a set number of revolutions. A carefully sized sand flows between the wheel and the specimen to simulate abrasion. The resulting data is used as a comparative guide when selecting hardfacing materials.
In plasma transferred arc welding, hardfacing applications typically aim for low penetration and low dilution. Pure argon or argon-hydrogen blends are commonly used to help achieve those results.
At minimum, parts should generally be brought to room temperature before welding. Higher preheat and interpass temperatures may be required depending on the chemistry of the base metal and the specific hardfacing product being applied.
Cobalt-based hardfacing alloys contain multiple carbide types and are often selected for severe abrasion at elevated temperatures. They may also provide corrosion resistance in certain service environments. Deposit hardness commonly ranges from 25 HRC to 55 HRC, and work-hardening versions are available.
Nickel-based hardfacing alloys may contain chromium borides for abrasion resistance. They are often considered when the application involves abrasion along with high temperature, corrosive atmospheres, or both.
Layer limits are most common with carbide-based products such as chromium carbide and tungsten carbide. Martensitic and austenitic hardfacing products can often be applied in additional layers unless the manufacturer specifies a limit.
Because metal carbide deposits are comparatively brittle, repeated layers can increase internal stress. Stress may concentrate at the roots of check cracks until separation or spalling occurs between the base metal, buffer layer, and hardfacing deposit.
Buildup and buffer alloys are used to restore badly worn components to their required dimensions or to prepare the surface for a harder wear-resistant overlay. These alloys often resemble the base material in composition or mechanical behavior. When the final hardfacing layer is prone to check cracking, a tough manganese-style buffer can help blunt the cracks and reduce the chance that they will penetrate into the base metal.
Yes. Cast iron can be rebuilt or hardfaced, but preheat and interpass temperature control are important. Nickel and nickel-iron welding products are commonly used for cast iron buildup because they are not significantly affected by the carbon content of the base metal and remain ductile. Multiple layers can be applied. If added wear protection is required, a metal carbide overlay may be placed over the nickel or nickel-iron buildup. This hardfacing FAQ provides a practical starting point for evaluating wear mechanisms, base metals, overlay alloys, PTA hardfacing, and repair strategies. For critical applications, consult the hardfacing consumable manufacturer or a qualified welding specialist to confirm product selection and procedure requirements.
Many steel and stainless-based alloys can receive a weld overlay, including manganese-based and non-magnetic materials.
Porosity can occur when gas becomes trapped in the weld. Common causes include contamination or moisture in the weld area, base metal, filler metal, shielding gas, or surrounding atmosphere. Oil, dirt, grease, cutting fluids, damp flux, moisture on the base metal, and atmospheric humidity can all contribute to porous weld deposits. When a welding process uses external shielding gas, porosity may result from incorrect gas flow, poor gas quality, leaks or defects in the torch, gun, or hose, or inadequate shielding of the weld pool. Welding technique can also affect porosity. Torch, gun, or electrode angle, excessive arc length, long electrode extension, and travel speed that is too fast can all increase the risk of porosity. Plasma transferred arc welding, or PTA welding, uses the heat of a constricted arc between an electrode and the workpiece to create a metallurgically bonded overlay. In PTA welding, a shielded arc is established between a non-consumable tungsten electrode and the torch body. The arc heats an inert gas, typically argon, into plasma. Metal powder is then metered under positive argon pressure into the molten pool on the workpiece surface. The torch may travel over the workpiece on a side-beam carriage, the workpiece may rotate or move under the torch, or both motions may be combined to create the overlay. PTA deposits are fully dense and metallurgically bonded to the base component. One important advantage of PTA hardfacing is dilution control. PTA can produce dilution as low as about 5%, compared with roughly 20% to 25% in many MIG or TIG hardfacing processes, helping the overlay retain its intended properties even in a single pass.