HARDFACING COMPLETE
Hardfacing is a technique that consists of depositing a hard layer to resist abrasion, erosion, scaling, high temperatures, cavitation and wear. Hardfacing is therefore a way to increase the lifetime of certain pieces in an economical manner. Building-up, on the other hand, is an operation to restore the dimensional form to a work piece.
The properties of the base metal chemical composition, melting point, coefficient of thermal expansion, microstructure, etc., influence the welding procedure. The main requirements that determine and limit the choice of the process are that it must minimize dilution while maintaining as high a deposition rate as possible. The procedure may call for preheating to a temperature specific to the alloy, if needed.
Some of our electrodes have a deposition rate greater than 200% which is an advantage for rebuilding and hardfacing large pieces that must be worked on site.
To facilitate the selection of a filler metal for a given use, we have classified our electrodes, according to their properties and their areas of application, into six different groups (see hardfacing 1 table).
Group 1: These have moderate abrasion resistance and excellent impact resistance ; some of them can be cold worked thereby increasing their abrasion resistance. They are machinable.
Group 2 : These are alloys with very good impact resistance and better wear resistance than the mild steels to which they are applied.
Group 3 : These are hypereutectic alloys containing a large amount of carbides (3 to 7% carbon). They have excellent abrasion resistance, moderate impact resistance, and can be used at rather high temperatures, depending on the product.
Group 4 : These are cobalt-based alloys. They are the most versatile. They resist heat, abrasion, corrosion, impact, spalling, oxidation, thermal shock, erosion and cavitation.
Group 5 : This type of coating is composed of tungsten carbides distributed in a steel, nickel or bronze matrix. They provide maximal abrasion resistance.
Group 6 : These are austenitic stainless steels used for their good erosion resistance and stability in corrosive environments.

Factors affecting the selection of filler metals
In choosing a filler metal, it is important to consider the application in order to determine the characteristic desired in the deposited metal. You should also take into account other variables you have to work with such as : composition of the base metal to be hardfaced or rebuilt, weld process available, and area where the welding will be done.
The following test presents the various factors affecting the choice of a proper filler metal. Also, to make it easier to compare the various Sodel filler products, table hardfacing 2, qualitatively illustrates their abrasion and impact resistance, hardness and maximum service temperature.
Hardness
The hardness of the deposited metal will particularly affect the machinability of the deposit. In some cases, the deposit reaches such a high hardness that machining is not even possible using conventional equipment. Contrary to general belief, it is not hardness alone that determines the degree of wear resistance of a hardfacing alloy. Microstructure also plays the most important role and is the basis of resistance against wear factors. The hardness of the deposited metal only reinforces this base. However, for a given microstructure, wear is greatly increased when the hardness of the coating is exceeded by that of the abrasive. The hardfacing 3, compares the hardness of certain minerals with the microconstituents of ferrous alloys.
Microstructure
-Bainitic build-up alloys (Sodel 320 and Wirotek 9320)
Bainitic alloys are used because they have excellent impact resistance. They absorb shocks well by deforming in an elastic and plastic manner. They are very easy to weld and have only a slight risk of cracking. These alloys are not designed to resist wear, but rather as a cushion layer prior to hardfacing the surface with an alloy having better abrasion resistance. They are also used for metal-to-metal wear in cases where it is preferable not to wear out the opposing piece.
-Martensitic alloys (Sodel 20, Sodel 22, Sodel 221, Sodel 243, Sodel 245)
Martensitic alloys show very high impact resistance and good abrasion resistance. An increase in abrasion resistance always results in a decrease of shock resistance, and these alloys are a compromise between these two constrains. They are primarily used to combat metal-to-metal wear and mechanical fatigue in pieces under dynamic stresses.

Here, for comparison purpose, Knoop – Rockwell C equivalences

-Austenitic alloys with manganese (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250)
Alloys containing 12 to 14% manganese are characterized by increased hardness under cold working. They are moderately abrasion resistant, but in the presence of shocks, their hardness increases along with their abrasion resistance. They are therefore used for pieces subject to severe shocks. They are also used as cushion layer prior to hardfacing to reduce dilution of the hard alloy and protect it from impacts. They must always be welded without preheating to eliminate any risk of embrittlement through carbon precipitation in the form of carbides on the edges of the grains.
-Alloys close to the austenite/carbide eutectic (Sodel 2024Plus and Wirotek 8210)
These alloys have excellent abrasion resistance and good impact resistance. They have high hardnesses and a carbon content of between 3 and 4%.
-Primary carbide and austenite/carbide eutectic alloys (Sodel 2023, Sodel 2045 and Wirotek 8240Plus, Wirotek 8245)
These alloys have a very high hardness and superior resistance to very severe abrasion. This high abrasion resistance results from the presence of primary carbides. To obtain these carbides, at least 4% carbon and 16% chromium are required. Impact resistance is moderate; it can be improved by making a cushion with a manganese austenitic alloy (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250)
-Cobalt based alloys (Sodel 1A / 1G, Sodel 6A / 6G, Sodel Turballoy)
These alloys are composed of cobalt-chromium-tungsten matrices containing complex carbides. This mix of microconstituents makes them resistant to abrasion, impact, corrosion, oxidation, spalling, erosion, cavitation and thermal shock. In addition, they retain their properties up to temperatures approaching 2000°F (1100°C) in non-continuous use. The value of their resistance varies from good to excellent depending on the property and the alloy.
-Tungsten carbide alloys (Sodel 229, Sodel 529, Sodel 2000)
These alloys differ principally in the size of the carbide particles and the nature of the matrices that hold them in place. These carbides provide maximal abrasion resistance. For its part, the matrix gives the deposit its resistance to high temperatures, impacts, corrosion, etc. Depending on its type (steel, bronze or nickel). To choose the appropriate product for your application, contact Sodel Technical Service.
-Austenitic stainless steels (Sodel 130, Sodel 131, Wirotek 3080, Wirotek 3090, Wirotek 3160)
As their name indicates, these alloys are stainless and therefore highly corrosion resistant. However, they have only weak abrasion resistance. The oxide film that protects them provides them with moderate erosion, cavitation and metal-to-metal wear resistance.
Abrasion
Abrasion resistance is the most sought-after property for hardfacing since you want to have the most resistant deposit possible to regenerate or maximize the lifetime of the piece or apparatus that is being hardfaced. There are several kinds of abrasion :
-Metal-to-Metal
Metal-to-Metal wear occurs when two pieces of metal slide, roll, strike or rub against each other. This causes fine particles to flake off and come between the two pieces in friction thus creating tiny scratches that multiply and end up by changing the shape or dimension of the pieces.
To counter rolling or striking when there is no risk of seizing, martensitic steels with a high elastic limit (Sodel 20, Sodel 22, Sodel 221) or manganese austenitic steels (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250), are used.
To counter rubbing without seizing, martensitic steels (Sodel 22, Sodel 221) or high-speed steels (Sodel 243, Sodel 245) are used.
If there is a risk of adhesion or seizing, one surface can be coated with an alloy having a hardness at least 200 Brinell less than the alloy applied to the other face. Alloy with a low friction coefficient such as a bronze alloy (Sodel 660FC) or aluminum bronze (Sodel 661) can also be deposited. In all cases where the pieces will be worked at high temperatures or in a corrosive environment, cobalt alloys are used (Sodel 1A / 1G, Sodel 6A / 6G).
-Erosion
Erosion wear is caused by the abrasion action of a fluid in motion. This fluid may be a gas or liquid, and the amount of wear increases when solid particles are in suspension in the fluid. The martensitic steels (Sodel 20, Sodel 22, Sodel 221, Sodel 243, Sodel 245) are a good choice to resist tangential erosion (particles impact at a low angle) when the flow rate is low (see figure hardfacing 1). For best results, if the severity of the wear increases, you can use chromium-alloyed cast irons (Sodel 2024Plus, Sodel 2023, Sodel 2045 and Wirotek 8210, Wirotek 8240Plus, Wirotek 8245) depending on the fineness of the abrasives or the temperature. Cobalt alloys (Sodel 1A / 1G, Sodel 6A / 6G) are primarily used for applications above 1200°F (650°C), or when there are risks of corrosion.
When the particle impact angle increases, impact resistance becomes the property of choice to resist to micro-spalling. Alloys that are too brittle must therefore be avoided. For assistance in choosing the appropriate product, contact Sodel Technical Service.
-Abrasion under stress
Abrasion through slippage due to low or moderate working stresses (see figure hardfacing 1) treated like tangential flow.
Abrasion through high working stresses (see figure hardfacing 1) can often be found in grinding operations. Alloys must have some compression resistance, shock resistance and, if the environment so demands, resistance to corrosion and high temperature.
Carbide-rich martensitic steels (Sodel 221, Sodel 243, Sodel 245) and chromium alloyed cast iron (Sodel 2024Plus, Sodel 2023, Sodel 2045 and Wirotek 8210, Wirotek 8240Plus, Wirotek 8245) respond well to crushing operations. If the shocks are severe, manganese austenitic steels (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250) are preferable.
Temperature and corrosion are criteria for choosing high-carbon cobalt alloys (Sodel 1A / 1G).
-Cavitation
Cavitation wear appears with liquids subject to wide and intense pressure variations. It occurs when tiny bubbles on the surface of the piece implode (explode inwardly) chipping particles of material from the surface. Depending on the temperature and nature of the liquid, you would choose cobalt alloys (Sodel 1A / 1G, Sodel 6A / 6G, Turballoy), some stainless steels (Sodel 130, Sodel 131 and Wirotek 3080, Wirotek 3160) or, for sea water, aluminum bronze (Sodel 661).
-Gouging
Gouging is a type of abrasion that results from severe impacts and deformation (see figure hardfacing 1). An example of this is the streaks forming on the bucket of a mechanical shovel used to move oversized rocks. The parts that are subject to impact are covered with manganese austenitic alloy (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250) and a layer of hardfacing (Sodel 2024Plus, Sodel 2023, Sodel 2045 and Wirotek 8210, Wirotek 8240Plus, Wirotek 8245) which are applied in a pattern adapted to the operation.

Impact resistance
Resistance to impacts or shocks requires a material that is able to absorb a substantial amount of energy in a very short time. The material absorbs the energy through elastic and plastic deformation ; if it is not capable of deforming it breaks or cracks. The bainitic structure (Sodel 320 and Wirotek 9320) and the manganese austenitic structure steels (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250) provide good impact resistance. They are able to deform under impact and they become harder under cold deformation as well. The surface receiving the impact is thereby virtually unaltered by the blows and the interior remains ductile to continue to absorb the shocks.
To a lesser extent, shocks can be absorbed elastically by alloys composed of martensite and secondary carbides (Sodel 20, Sodel 22, Sodel 221).
In some applications, hypereutectic alloys can be used (Sodel 2024Plus, Sodel 2023, Sodel 2045 and Wirotek 8210, Wirotek 8240Plus, Wirotek 8245) if they are well supported by a manganese austenitic alloy (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250).
High-temperature resistance
The mechanical properties of steel always decline as their service temperature increases. Structural stability is paramount for maintaining properties at high temperatures. The presence of secondary phases should be limited, and a low coefficient of thermal expansion is a plus. This is why it is very important to take into account the service temperature of the material when choosing a filler metal.
For temperatures above 1100°F (600°C), cobalt alloys will mainly be used (Sodel 1A / 1G, Sodel 6A / 6G). These electrodes are specially designed to maintain their properties at high temperatures. Some alloys other than the cobalts can withstand fairly high service temperatures; Sodel 2023 can go up to 900°F (480°C), Sodel 243 and Sodel 245 can go to 1050°F (550°C), and Sodel 2045 and Wirotek 8245 can withstand 1200°F (650°C).
Oxidation and corrosion resistance
For temperatures less than 1100°F (600°C) and only slightly corrosive environments, oxidation and corrosion can usually be prevented using products with a high enough chromium content (Sodel 2024Plus, Sodel 2023, Sodel 2045 and Wirotek 8210, Wirotek 8240Plus, Wirotek 8245). For more corrosive environments, austenitic stainless steels must be used (Sodel 130, Sodel 131 and Wirotek 3080, Wirotek 3160).
When temperatures exceed 1100°F (600°C), or when the environment is highly corrosive, it is essential to use cobalt alloys (Sodel 1A / 1G, Sodel 6A / 6G). These are the only ones to combine good mecanical properties with good corrosion and high temperature resistance.
Mechanical fatigue resistance
Mechanical fatigue is a reason for choosing materials with a high elastic limit such as martensitic steels (Sodel 20, Sodel 22, Sodel 221). Under certain conditions, chromium alloyed cast irons (Sodel 2024Plus, Sodel 2023, Sodel 2045 and Wirotek 8210, Wirotek 8240Plus, Wirotek 8245) in which a network of fine cracks forms upon cooling can be used. However, it is very important that these chromium alloyed cast irons are supported by a cushion layer of manganese austenitic steel (Sodel 324, Sodel 325 and Wirotek 9240, Wirotek 9250) to prevent the cracks from propagating into the base metal.
Dilution
Dilution is the percentage of filler metal that takes part in the fusion. The effect of filler metal dilution is to reduce its mechanical properties. For example, if you select an alloy for its carbides, too much dilution lowers the alloy content of the deposited metal and prevents carbide formation. The mechanical properties sought are thereby greatly reduced or even non-existent. To limit dilution we recommend :
-using a low-intensity welding current while ensuring that the base metal melts properly (good fusion);
-making small passes to increase the effectiveness of the deposit (if there is no risk of embrittlement of the heat affected zone due to overly-rapid cooling);
-depositing two layers of hardfacing filler metal to optimize the mechanical properties;
-rebuilding with an electrode with a chemical composition close to that of the hardfacing electrode (Sodel 325 and Wirotek 9250);
-and finally, if dilution cannot be reduced and you can only make one pass, we recommend using an alloy with a higher alloy content than necessary to counteract the dilution effect.
Welding thermal cycle
Welding thermal cycle (preheating and interpass temperature), depends on the material, its cracking tendency, its cross section, its condition and amount of restraint. The same weld thermal cycle such as the one for joining these materials can be used to a lower extent when the heat affected zone (HAZ) is only under compression stress.
Manganese austenitic steels and deposits of the same composition (Handfield, about 12% Mn or more) require a cold welding technique, 300°F (150°C) maximum, and no post-weld heat treatment to prevent the formation of carbides at the grain boundaries. Formation of such carbides can cause the heat affected zone to rupture and spalling of the hardfacing.
Chromium-manganese type austenitics will withstand up to 500°F (260°C) but no post-weld heat treatment. Austenitics such as the 18Cr-8Ni types are more stable and can be stress-relieved thermally, but cold welding technique is preferable to limit deformation.
Nickel-based alloys (Sodel 2000) are deposited cold as are cobalt alloys of an equivalent hardness (Sodel 1A / 1G, Sodel 6A / 6G).
For some applications, cobalt alloys are not allowed to have cracks. The welding thermal cycle must then be adapted to the amount of restraint and hardness of the filler metal. To select an adequate preheat temperature for your application, contact Sodel Technical Service.
Martensitic structures (Sodel 20,Sodel 22, Sodel 221, Sodel 243, Sodel 245) can be deposited between 400 and 775°F (200 and 400°C) depending on the hardness and amount of restraint.
Chromium-alloyed cast irons (Sodel 2024Plus, Sodel 2023, Sodel 2045 and Wirotek 8210, Wirotek 8240Plus, Wirotek 8245) are only crack-free in the 775 to 1300°F (400 to 700°C) range, depending on the grade and restraint. However, shrinkage cracks have little influence on the service performance since it reduces deformations and residual stresses. It is better to make quick passes to keep the interpass temperature between 80 and 300°F to produce transverse cracks about every centimeter. Preheating is less favorable because cracks that are farther apart and deeper have higher tendency to propagate into the underlying metal. In addition, shear forces at the base of the weld deposit increase the risk of spalling.
Whatever the type of deposit used, absence of cracking usually requires that the weld thermal cycle be maintained throughout the welding operation. Cooling can be retarded by using a thermal cover. Sometimes, stress-relief / tempering heat treatment is required. If so, it is done immediately after welding or after a controlled intermediate cooldown until the temperature required for martensite formation is achieved.
Postheating
When the piece is subject to dynamic loading in service, especially fatigue mode, stress relief is beneficial but care should be taken not to lower the hardness excessively.
With some exceptions, the deposited metal has in its as welded condition, the properties required for the application. Apart from the previously-mentioned heat treatments, it is sometimes necessary to harden the part to provide it with the necessary strength in the areas that were not hardfaced.
Beyond about 40 HRC, it is difficult to hard-face a hardened part. It is often better to weld it in its annealed state and harden it later at a temperature and in an environment appropriate to the deposited metal. De pending on the circumstances, the deposited metal may: not be affected, soften, harden or spall if the hardening is too severe. It is also possible to deposit a cusion layer with a specialized electrode designed for hard-to-weld steels (Sodel 330, Sodel 333, Sodel 335); this deposit will act as a transition and limit risks of spalling.
Method of applying coating
It is not always necessary to hard-face completely the surface subject to wear. Sometimes it is enough to apply the hardfacing alloy in a predetermined pattern depending on the wear mode. For example, the teeth of a bucket must be hard-faced on the side that is more exposed to wear by various types of abrasion. If both sides of a tooth are hard-faced, it will wear out from the point.

The direction of bead deposition depends a lot on the usage. If the work is done in sand for the most part, the beads are deposited transversely on the teeth and inside the bucket about every 25 mm. If working in rock, the beads must be positioned longitudinally to allow stones to slide along the beads. Make the beads diagonally for multi-purpose use.

Quantity of filler metal needed for rebuilding or hardfacing
To find the weight of filler metal needed to build-up a part, we must :
1-Taking the dimension in centimeter, we shall find, with the help of figure hardfacing 2, the volume of metal, in cubic centimeter, needed to build-up the part. If the part is made of different shapes, we shall find the individual volume of each one and add them.
Consider a supplement to the volume needed for the loss due to machining.
2-Then multiply the volume by the factor found in table hardfacing 4, for the filler metal used, to obtain the weight in kilogram.
3-We suggest to add 10% to the weight for the losses and calculation errors by multiplying the weight by 1,1.



1-Volume calculation.
2 X π X 60 cm X 180 cm X (2,5 cm + 0,5 cm for machining) =
2 X π X 60 cm X 180 cm X 3 cm =
2 X 3,14159 X 32400 cm3 =
Volume to rebuild = 203575 cm3
2-Multiplication by the factor found in table hardfacing 4.
203575 cm3 X 0,01263 = 2571 kg of filler metal
3-Add 10%
2571 kg X 1,1 = 2828 kg
Conclusion :
2828 kg of Sodel 324 will be used to rebuild this part.
PRACTICAL TIPS FOR REBUILDING OR HARDFACING
1-If possible, always know the base metal to be welded.
2-Determine the mechanical properties sought for the working conditions.
3-Never assume a mechanical property on the basis of another mechanical property. One alloy can have a higher hardness than another and still have a lower tensile strength and lower abrasion resistance. Never forget that it is the microstructure that plays the most important role in wear resistance.
4-To quickly determine the abrasion resistance of an alloy quickly, carbon content is the most important element.
5-In general, the chromium concentration will increase the corrosion resistance of an alloy.
6-For a very high hardness and superior abrasion resistance, use electrodes containing at least 4% carbon and 16% chromium (Sodel 2023, Sodel 2045 and Wirotek 8240PLUS, Wirotek 8245).
7-The filler metal used for hardfacing must be compatible with the base metal or the piece to be hard-faced. On the other hand, you must remember that it is the hardfacing alloy that provides the mechanical properties you are looking for.
8-Never make more than two or three passes with a hardfacing electrode because the mechanical properties could increase dramatically and cause other problems such as cracking, scaling or lack of ductility.
9-Always minimize dilution with the base metal to maintain the mechanical properties. However, you must always be sure to have good base metal fusion.
10-To help reduce the dilution rate, weld using direct current (DC- / DCEN) when the product permits.
11-Observing the wear surface will enable you to evaluate the wear mechanism. Consult Sodel Technical Service for assistance in choosing the right filler product.
12-The mechanical properties of a filler metal are not the same in practice as in theory. When tested in a laboratory, the dilution rate with the base metal is 0% ; therefore no lowering of the properties occurs through dilution.
13-When a high dilution rate cannot be avoided (like deposit in a single pass), compensate by using filler products with alloy concentration higher than required.
14-To rebuild a manganese austenitic steel, use a manganese steel. Manganese steels can be removed with a torch; stainless steels can only be removed using a chamfering electrode such as Sodel 512Plus.
15-Niobium, titanium, vanadium and tungsten carbides are superior to chromium carbides for resisting abrasion by fine particles or hig temperatures.
16-Excessive preheat and interpass temperatures will cause a lowering of mechanical properties and make it more difficult to remove slag.
17-Keep your arc short when welding for better transfer and to reduce the risk of porosities.
18-Wide passes can affect the mechanical properties and alloy constituents because of the excessive heating they produce.
19-It is usually possible to use a 100% CO2 type shielding gas with open arc flux cored wires (Wirotek wires). This can reduce the amount of spattering, but you must be sure not to over protect the weld pool; this could cause porosities.