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Frequently asked questions about hardfacing

Understanding what it is and how its used

By Bob Miller March 8, 2005 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 build-up 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 This robot is hardfacing an agricultural tool.

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. 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.


Deposition (lbs./hr.) 8 to 25 5 to 12 3 to 5 8 to 25 3 to 5 5 to 10


Yes. Many different categories of wear existtoo many to cover in one articlebut the most typical modes of wear are as follows (percentages are estimates of total wear):

Abrasion40 percent Impact25 percent Metallic (metal to metal)10 percent Heat5 percent Corrosion5 percent Other5 percent

Most worn parts don't fail from a single mode of wear, such as impact, but OFW 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 Figure 1 used. Determining the wear mode can be challenging and may require trial and

error when you select hardfacing products.



7. Many hardfacing alloys crack. Is this normal?


8. What is check-cracking?

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). Figure These elements form hard carbides (chromium carbides) that resist Caption here. 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. 2


10. What are complex carbides?


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



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 (see Figure 3).

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



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 Figure that produces an audible crackling sound and generally has a higher spatter level ASTM G65 Test Apparatus 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. 3

15. Must parts be preheated before hardfacing?


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.


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


19. Can cast iron be hardfaced?
