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Home > News > Hardfacing Chromium Carbide Overlay CCO Plate

Hardfacing Chromium Carbide Overlay CCO Plate

Hardfacing is a cost-effective way to minimize wear and increase service life in industrial parts and equipment. At first glance, hardfacing can be confusing and troublesome, but it`s really not once you know the facts.

The following answers to frequently asked questions may help you understand the basics of the technology so you can select the 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 by abrasion, impact, or metal-to-metal contact, which causes them to lose dimension and functionality. Hardfacing, also known as hard surfacing, is the application of a buildup or wear-resistant weld metal onto a part`s surface by means of welding to extend the life of the part. The weld metal may be applied as a solid surface or in a pattern, such as a waffle, herringbone, or dot pattern.

Hardfacing is becoming increasingly important for many industries to protect equipment that is exposed to wear and abrasion. Extending the life of wear parts can save you thousands of dollars and improve productivity. Hardfacing can be used to recondition parts that have already been exposed to wear and have lost their useful life, or it can be used in the manufacture of new parts to improve their life before they are put into service. The three main types of hardfacing applications are:

Buildup or rebuilding.

Hardfacing or overlay.

Combination buildup and overlay.

2. What Base Metals Can Be Hardfaced?
Carbon and low-alloy steels with carbon contents of less than 1 percent can be hardfaced. Medium carbon and low-alloy steels are very common, since they provide higher strength than mild steels and better abrasion resistance. High-carbon alloys may require a special buffer layer. The following base metals can be hardfaced: stainless steel, manganese steel, carbon and alloy steels, cast iron, nickel-based alloys, and copper-based alloys.

Carbon and low-alloy steels are strongly magnetic and can easily be distinguished from austenitic manganese steel, which is nonmagnetic. Many low-alloy and higher-carbon steels are used for manufacturing equipment and spare parts, especially equipment that requires higher strength and abrasion resistance. They are not easily differentiated but should be identified to determine the proper preheat and post-heat temperature.

As the alloy content increases, the need for preheat and postheat becomes more critical. For example, steel made from 4130 generally requires a preheat of 400 degrees F. Steel used for rails is typically higher carbon and requires a minimum preheat of 600 to 700 degrees F. Manganese steel does not require preheat. In fact, steps should be taken to keep the base metal heat below 500 degrees F.

3. Which Welding Processes Are Most Popular for Applying Hardfacing?
In order of popularity, the following welding processes are used to apply hardfacing:

Flux-cored arc welding (FCAW) with open-arc or gas-shielded hardfacing wire

Gas metal arc welding (GMAW) with gas-shielded wire

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 spray and fuse

The current trend is toward the use of semiautomatic and automatic welding processes using FCAW and GMAW, which are about the same in terms of popularity. GMAW using either a solid wire or metal-cored welding wire requires a gas shield, whereas FCAW employs welding wires that are used open-arc or gasless, as well as with a gas shield. SMAW with flux-coated electrodes is still very popular, especially for field on-site hardfacing applications, because the equipment is inexpensive and portable.

Consider the following factors when selecting a welding process:

Welding equipment availability, including size of power source

Use of stick electrode or semiautomatic wire

Availability of hardfacing consumables

Size of welding consumable

Use of gas-shielded wire, open-arc wire, or submerged-arc wire

Operator skill available

Welding location-indoors or outdoors

Component size and shape, and the area to be hardfaced

Thickness of deposit

Deposition rate

Welding position

Machining requirements

Desired finish

Component preparation for previously hardfaced parts

Preheat and postweld treatments (temper/slow cool/air cool)

4. Which Welding Processes Are the Most Economical?
Many factors affect the economics of hardfacing, but a major factor is the deposition rate. Figure 1 shows the estimated deposition rate for each welding process.
5. What Are the Categories of Wear?
Following are the three most common types of wear:

Abrasive wear, which makes up 40 to 50 percent of all wear cases, occurs when materials such as grain, soil or sand, coal, or minerals slide across a metal surface. Abrasive wear can be divided into gouging abrasion, high-stress grinding abrasion, and low-stress scratching abrasion.

Impact wear (20 percent) occurs when an object is struck by another object, such as a crusher part or a railcar wheel rolling over a manganese crossing, resulting in material flaking off or spalling.

Adhesive wear (metal to metal) (15 percent) occurs when two metallic surfaces slide against each other under pressure, creating a micro-welding condition from frictional heat. It generally occurs in nonlubricated or dry conditions.

Heat and corrosion are two other types of wear, each of which make up about 5 percent of all cases.

Most worn parts don`t fail from a single type of wear, such as impact, but from a combination, such as abrasion and impact. For example, a mining bucket tooth usually is subjected to both abrasion and impact, although one type might be more dominant than the other. The type of wear dictates which hardface welding product is used. Determining the wear mode and understanding the environment to which the part is exposed are crucial to choosing the most suitable hardfacing alloy for the application.

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