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Mar 29, 2017

Hardfacing Frequently asked questions

Hardfacing Frequently asked questions

At first glance, hardfacing can be confusing and troublesome; in reality, it isn't. Understanding some of the basics about hardfacing can go a long way toward instilling confidence in your hardfacing product selection.
The following 19 answers to frequently asked questions may help you select hardfacing products that are most appropriate for your application.

1. What is hardfacing?

Metal parts often fail their intended use not because they fracture, but because they wear, which causes them to lose dimension and functionality. Hardfacing, also known as hardsurfacing, is the application of buildup or wear-resistant weld metals to a part's surface by means of welding or joining.

2. What base metals can be hardfaced?

Carbon and low-alloy steels with carbon contents of less than 1 percent can be hardfaced. High-carbon alloys may require a special buffer layer.
The following base metals can be hardfaced:
  • Stainless steels
  • Manganese steels
  • Cast irons and steels
  • Nickel-base alloys
  • Copper-base alloys

3. What is the most popular procedure used to apply hardfacing?

In order of popularity, the following procedures can be used:
  • Flux cored arc welding (FCAW)
  • Gas metal arc welding (GMAW)
  • Shielded metal arc welding (SMAW)
  • Submerged arc welding (SAW)
  • Gas tungsten arc welding (GTAW)
  • Oxyfuel welding (OFW) or oxyacetylene welding
  • Plasma transferred arc welding, laser welding, thermal spray, and brazing
FCAW and GMAW may be interchangeable or the same in terms of popularity. However, the trend is toward use of semiautomatic and automatic welding procedures.
ProcedureDeposition Rate (lbs./hr.)
FCAW8 to 25
GMAW5 to 12
SMAW3 to 5
SAW8 to 25
GTAW3 to 5
OFW5 to 10
Figure 1 

4. With so many welding processes available, which ones are the most economical?

Many factors affect the economics of hardfacing, but a major one is the deposition rate. Figure 1shows the estimated deposition rate for each process.

5. Wear is such an all-encompassing term. Can it be broken down into more manageable categories?

Yes. Many different categories of wear exist—too many to cover in one article—but the most typical modes of wear are as follows (percentages are estimates of total wear):
  • Abrasion—40 percent
  • Impact—25 percent
  • Metallic (metal to metal)—10 percent
  • Heat—5 percent
  • Corrosion—5 percent
  • Other—5 percent
Most worn parts don't fail from a single mode of wear, such as impact, but from a combination of modes, such as abrasion and impact. For example, a mining bucket tooth usually is subjected to abrasion and impact, and depending on what type of material is mined (soft or hard rock), one mode may be more dominant than another. This will dictate the welding product used.
Determining the wear mode can be challenging and may require trial and error when you select hardfacing products.

6. Is there a convenient way to categorize the many alloys when determining which hardfacing to use?

Yes. Iron-base alloys can be divided into three main categories:
  • Martensitic. This includes all hardenable steels with Rockwell hardness from 20 to 65. This group, similar to tool steel, hardens upon cooling. They are good for metal-to-metal and abrasive wear. They also can withstand a great deal of impact.
  • Austenitic. Austenitic alloys include work-hardening steels, such as manganese and stainless. This group generally is soft when it's welded and hardens only after the weld metal is worked. They have good impact properties and moderate abrasion resistance. The stainless steel family is good for corrosion resistance.
  • Metal carbide. These alloys contain large amounts of metal carbides in a soft, tough matrix and are good for severe-abrasion applications. The alloys that contain large amounts of chromium and carbon are known as the chromium carbide family and are closer to a cast iron or white iron. Their hardnesses are from 40 HRC to 65 HRC. Alloys that contain large amounts of tungsten and carbon belong to the tungsten carbide family. Some contain small amounts of chromium and boron that form borides and are good for severe-abrasion applications.

7. Many hardfacing alloys crack. Is this normal?

It depends on the hardfacing 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.
Figure 2
Caption here.

8. What is check-cracking?

Check-cracking, or checking as it's sometimes called, occurs in the metal carbide families and can be seen as cracks that are perpendicular to the bead length (see Figure 2). They generally occur from 3/8 to 2 inches apart and are the result of high stresses induced by the contraction of weld metal as it cools.
The cracks propagate through the thickness of the weld bead and stop at the parent metal, as long as it's not brittle. In cases in which the parent metal is hard or brittle, you should select a buffer layer of a softer, tougher weld metal. The austenitic family is a good choice for a buffer deposit.

9. What is chromium carbide hardfacing?

Generally, these are iron-base alloys that contain high amounts of chromium (greater than 18 percent) and carbon (greater than 3 percent). These elements form hard carbides (chromium carbides) that resist abrasion. The deposits frequently check-crack about every 1/2 in., which helps relieve stress from welding. Their low friction coefficient also makes them desirable in applications that require material with good slip.
Generally speaking, the abrasion resistance increases as the amount of carbon and chromium increases, although carbon has the most influence. Hardness values range from 40 HRC to 65 HRC. They also can contain other elements that can form other carbides or borides that help increase wear resistance in high-temperature applications. These alloys are limited to two or three layers.

10. What are complex carbides?

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.

11. Can hardness values be used to predict abrasion resistance?

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 microstructure 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 microstructure. You should consult with the manufacturer for recommendations.
Figure 3
ASTM G65 Test Apparatus

12. If hardness is unreliable, then how is wear measured?

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 (seeFigure 3).

13. What type of gas is used in GMAW hardfacing?

Low penetration and dilution are the major objectives in hardfacing, so pure argon and mixtures of argon with oxygen or carbon dioxide generally will produce the desired result. You also can use pure carbon dioxide, but you'll get more spatter than you would with an argon mixture.

14. What is a ball, or globular, transfer, and why is it important?

Welding wires produce either a spray transfer or a globular (ball) transfer of molten metal across the welding arc. Spray transfer is a dispersion of fine molten metal drops and can be characterized as a smooth-sounding transfer. These wires are desirable in joining applications in which you require good penetration.
Ball transfer wires disperse larger molten metal drops, or balls. This type of transfer promotes low penetration and dilution, suitable for hardfacing. It has a noisier arc that produces an audible crackling sound and generally has a higher spatter level than spray transfer wires. Welding parameters such as electrical stickout, gas (if any), amperage, and voltage can affect the size of the ball and its transfer. Gasless, or open arc, wires all have a globular or ball transfer.

15. Must parts be preheated before hardfacing?

As a rule, you should bring all parts at least to room temperature. You can select higher preheat and interpass temperatures based on the base metal chemistry and hardfacing product you're using.
Manganese and some stainless steels and similar hardfacing products require no preheating, and welding temperatures should be kept as low as possible. Other steels usually require proper preheat and interpass temperatures. You should consult the manufacturer for the best combination to prevent cracking and spalling.

16. When is a cobalt or nickel hardfacing alloy used?

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.

17. Why are some hardfacing products limited to two or three layers?

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 hardfacing deposit.

18. What is meant by a buildup or buffer alloy?

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 hardfacing deposit. If the hardfacing 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.

19. Can cast iron be hardfaced?

Yes, but you must take preheat and interpass 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 hardfacing. Hardfacing product manufacturers and specialists can contribute to a greater in-depth understanding of hardfacing and help assist you in product and process selection for your application

Source: thefabricator.com

Jan 24, 2017

Happy Lunar New Year 2017 - Notification of TET Holidays

On the occasion of Vietnam Tet holidays Bao Chi Corp. wish our customers a New year Luckiness- Prosperity, health and success, We thank a lots your trust and cooperation for Bao Chi during the past.

For your proactivities in business, We would like to stay informed about the Dinh Dau Tet 2017 of our Company as follows:

Days offFrom 25/01/2017 to end on 05/02/2017
On 06/02/2017 working normally.

We wish you please arrange delivery – receiving time, ordering so that we can deliver before or after the Tet holidays period to ensure the operation of your business.

Bao Chi Corp thank your cooperation and supports.

We wish more and more Happiness, Good health and Prosperity
To you, Your family,Your Staff and Office associates


Jun 18, 2016

Trends of Hardfacing

1. General

Hardfacing is applied in cases where the surface of engine parts is being subject to abrasion by wear, corrosion or heat. According to the definition hardfacing is applied when the surface is going to be damaged by wear due to hard minerals. 

This happens in all domains of mechanical processing, where processes are realised at room temperature or increased temperatures, such as in crushing, conveying, mixing and separating in the field of mining, steel and iron industry, cement industry, coal power plants, overground and underground working, recycling and environmental protection.
In chemical industry it is applied in areas of sharp mineral dressing.
The objective of hardfacing according to DIN 50320 is to surface a layer onto the basebody, which is most beneficially resisting to the wear-causing mineral.

The meaning of hardsurfacing did significantly increase in the course of the last 10 years, as standstills do become more and more expensive for big factories, due to increased wages and salaries, but also for reasons of networking. Layers of between 2 mm and 200 mm thickness can be produced by application of the different hardfacing procedures, whereas the fusion-efficiency rate can vary between 0,5 and 50 kg/hour, with fusion penetrations of between 0,5 mm and 10 mm.

The welding procedures can be differentiated by the intensity of mixture with the base body, which is usually increasing along with an increasing fusion efficieny rate.
Nearly all kinds of weldable materials can be hardfaced and mostly all types of known wear- resistant metals in combination can be used as hardfacing materials.
Ceramic materials, which can only be coated by spraying-on thin layers, cannot be hardfaced.

2. Trends for Welding
2.1 Stick Electrodes and Filler wires 

Stick electrodes will be further used, before all for reparation in built-in condition, as they can be processed not only in tub position. Anyhow, their low fusion-efficiency rate, which results in costs of more than 50 Euro per kg, is a disadvantage.

Filler wires can be regarded as an absolutely necessary welding process, with regard to a consumption per buyer of more than 1 ton of material per year.
The fusion penetration per burner is usually between 3 – 6 kg per hour, so that the costs per kg welding material are decreased to an amount of about 20 Euro per kg.

But this processing can almost only be easily used in tub position. This means, that the engine parts to be protected have to be moved accordingly, so that welding in built-in condition is often impossible.
The results of fusion efficiencies of the latest developments in the sector of filler wires where up to 15 kg per hour, so that the costs per kg welding material decreased to 10 – 15 Euro per kg.
It is most important for tubular-wire welding that removal by suction is made very carefully. 

2.2 Plasmapowder-Hardfacing 

Plasmapowder-hardfacing made a triumphant march through hardfacing of valves for the motor car industry. A mechanical hardsurfacing at permanent operation was achieved, with very slight mixtures and good surface qualities, so that the material consumption was only half compared to the demand for continuous casting sticks as used before.

This procedure is also qualified for tungsten carbides, which are not added into the metal arc, but behind it, in order to have them gently inserted into the melt, without their dissolution, what is a second advantage. Thus a higher rate of tungsten carbides is achieved, which means a significantly better resistance to abrasive minerals compared to usual chromium carbides.
This processing, as a special procedure, is widely applied at Rheinbraun, but also for processing of oil sands and in oil mining. The trend for this area has not yet become obvious.

2.3 Submerged hardfacing

Submerged welding processes
 give us the chance of achieving fully mechanically even higher fusion efficiencies, compared to tubular-wire welding with open metal-arc, which often do achieve between 8 – 10 kg. 

But when applying this process, using wire or band, it is nearly impossible to produce high-quality hardfacings. Therefore this process, within the scope of hardfacing, is meant for big construction parts, such as cones of blast furnaces, but also for regenerating of earth shifting units, especially in the Far East, whereas in Europe it seems to be more economic to use new parts, which are scrapped after their wear reserve has been exhausted.

Hardfacing is a wage-intensive process, which is only to be applied, where operation costs in Western European countries, where wages costs are high, can really be decreased by applying this technology, or when operativeness cannot be guaranteed in another way. 

4 Application of prefabricated hardfaced plates
Instead of hardfacing the part by own production, semifinished hardfaced products are more and more used.
These polyburner-technology plates with a high fusion-efficiency rate can be produced much more economically than having them manufactured by own production.
Constuction parts, such as hoppers, chutes, screens, tubes, fans, separators or others, can be manufactures by plasma-cutting and forming of such plates.

3. Trends for Welding Fillers
3.1 Increased Application of titanium-carbide containing martensitic alloys
The main application of hardsurfacing was formerly the use of martensitic alloys with 400 – 600 Brinell, but nowadays such material contain titanium-carbide fortifications, although the removal of slag is quite difficult when using such addings. Especially when using these materials, or those where niobium is added to martensitic alloys, the application is recommended for wear problems of so-called high- pressure rollers in a wide range. 

3.2 Use of highly-chromium containing materials with higher carbon contents then those of filler wires
Compared to formerly used hardfacing materials as filler wires, normally of the alloy group 10 with 4,5% C and 30% Cr, there is a clear trend towards higher alloyed filler wires to be seen, as only when using these filler wires as a second and third layer a significantly longer lifetime will be achieved.
In general such materials do contain 5,5% C, 20% Cr and 7% niobium, at higher temperatures they do also contain molybdenum and tungsten. In a certain range these materials can also be applied for higher temperatures up to ca. 750° C, but they will lose their wear-resistance at higher temperatures due to transformation of the matrix.

3.3 Tungsten-carbide containing hardfacings
In former times such materials were only used in oil- mining due to reasons of costs, whereas their application did meanwhile considerably increase, not only for stick electrodes, but also for filler wires and PTA- welding and special-welding procedures, as the lifetime is significantly higher, whereas the wages costs are the same. did meanwhile considerably increase, not only for stick electrodes, but also for filler wires and PTA- welding and special-welding procedures, as the lifetime is significantly higher, whereas the wages costs are the same.
But meanwhile there is a clear trend towards iron- containing materials, which are, as a consequence, cheaper.

4. Trends for Applications
4.1 Hardfacing of Strips and Disks for Coal- and Cement-Crushing
Application for Vertical Roller Mills in Cement Plant

Generally such strips do consist of materials which are known from the literature as being unweldable, having a high carbon-, chromium- or nickel-content.
Anyhow this is the second-largest application worldwide for hardfacing with chromium-containing hardfacing materials. Compared to casting materials, the achieved lifetime is twice or three times longer and the grinding result is much better for a long period of time.
In the same way the disk, on which the strip rolls, can thus be regenerated and the lifetime extended.

4.2 Sinter-crusher stars with cobalt-base alloys and inserted mixed carbides
Sinter crushers are a considerable wear problem in each iron and steel work worldwide. Generally their lifetime in hardfaced condition is about 2-4 months. Actually tests are made, in order to find out if the use of tungsten-chromium carbides can increase lifetime significantly, which are promising.
But with regard to bar frames (the counter-part) it already became obvious that with such materials a longer lifetime is not achieved, due to even higher temperatures.

4.3 Use of hardfaced Plates as semifinished Products
The main trend and most important application for hardfacing worldwide is the production of hardfaced plates in standard sizes, of which parts ready to be installed are being manufactured. Processes according to drawings of parts to be manufactured can be made of such hardfaced plates, using plasma- burners or water-jet.
Even complicated equipments can be made by cold- work, like some examples show. The cheap production of the semi-finished products is mainly interesting, whereas the welding mechanization is most important. This can be achieved by using special procedures with an extremely intensive fusion efficiency rate per burner, or by combining many burners, e.g. up to 10 burners for filler-wire weldings.
Wear Plate Producing
5. Trends as a Result of Environmental Protection Prescriptions
The environmental protection is a very important trend for hardfacing, which will cause much more problems in the future than it did the last 100 years. Steams are emerging whilst hardfacing, which are not that dangerous, as they do nearly not contain hexavalent chromium. The size of dust particles is dangerous, so that a good suction during work shall be ensured.
In addition, there are new trends coming up with regard to valuation of danger of nickel and manganese, which will probably afford high investments with regard to the suction of such welding-steams within the next 10 years.
For that reason we assume that in the future there will be a concentration of orders in less locations, where an excellent suction is guaranteed, or where in fully- enclosed cabins, supported by robots, the main hardfacing work will be done.

6. Summary
Hardfacing is a modern procedure, which nowadays is mainly applied for bigger construction parts, in order to extend the lifetime, instead of using massive solutions, such as castings. This “added value” makes the parts more valuable, and the demand for it will be constant, as the standstill of concatenated machines will become more and more expensive. 

Jun 17, 2016

Welding For Repair and Surfacing

Abstract:  Repair welding and surfacing are both considered in the field of maintenance welding and are covered together since they are both done by the same welders. Often it is extremely difficult to separate what is considered repair welding from maintenance welding, and surfacing can be included in both situations. The same basic factors apply to both weld repair and surfacing. Repaired parts may be more serviceable than the original part, since they can be reinforced and the weaknesses of the original part corrected. It is often more economical to weld repair since the delay in obtaining the replacement part could be excessive and the cost of the new part would normally exceed the cost of repairing the damaged part.

Seeking Regional Distributor - Australia, South Africa, South East Asia

We currently are looking for the partners who are invested in Wear Plate / Wear Parts selling. These partners should be the Engineering/Fabrication companies & serving in some heavy industries, such as: Cement, Mining, Quarry etc.

We specially are focusing on some strategy countries / regions: Australia, South Africa, Japan & South East Asia Countries. If you are interested in working with us! Please kindly contact us for further discussion!

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