Cracking the Mystery: Choosing Filler Metals for Welding AR Plate
For any welding application, it is important to consider ways to make the process more efficient and more effective. Welding abrasion resistant plate, commonly known as AR plate, is no exception.Taking certain precautions and choosing the most appropriate filler metal for your application, whether it is repairing serviced equipment or fabricating a new part or structure requiring the protection of AR plate, is vital to ensuring your welding success.
AR Plate and Typical Applications
Typical AR plate products have numbers ranging from 200 to 500 in their name - AR 200, AR 400, AR 500, for example. These numbers typically designate the hardness of the material in Brinell (BHN), which can easily be converted into alternative hardness scales such as Rockwell B (HRB) or Rockwell C (HRC). Typically, the higher the hardness of the material, the more resistant it will be to abrasive wear. Therefore, the harder grades of AR plate such as AR 400 (~42 HRC), AR 450 (~46 HRC) and AR 500 (~50 HRC) are the most common. Plates can range in thickness from 1/2- to 2-plus inches in a variety of sizes (length and width) depending on manufacturer.
Because AR plate has such a high hardness (a 400 grade AR plate equals about 42 Rockwell C), heavy equipment manufacturers and job shop personnel rely on it to protect equipment from excessive wear. Typical applications include backhoe buckets and teeth, bulldozer blades, dump truck beds, ore and coal chutes, augers and aggregate conveyors.
Note: AR plate is designed to protect equipment against wear. Typically, AR plate should not be used in a structural or load bearing design. To ensure the best results, please review the application with the AR plate manufacturer.
Beyond the Filler Metal: What You Shold Know Before Making a Selection
Welding AR plate to itself or any structure with dissimilar and softer or lower strength steels poses particular challenges, the biggest of which is the potential for cracking in the weld metal or heat affected zone (HAZ) of the AR plate. Many factors can contribute to cracking, but some common causes include: rapid cooling, highly restrained joints, excessive hydrogen in the weld metal and filler metals that have limited resistance to cracking.
Pre-heating the base metal before welding is one important defense against rapid cooling and can help reduce hydrogen levels, both factors that can lead to cracking. The proper pre-heat temperature is determined by the material to be pre-heated and its thickness. (See Figure 1 for pre-heating recommendations for AR plate).
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| Figure 1 |
Joint design is another factor to consider before welding. If possible, do not locate the weld joint in a highly restrained area. A highly restrained joint is defined by the inability of the base material, weld metal, or overall weldment to expand and contract freely. Welding shorter, smaller fillet welds can also reduce heat input and overall residual stresses on the AR plate to help minimize cracking.
In addition to pre-heating and avoiding highly restrained joints, choosing a filler metal with the least amount of hydrogen content, as well as one that provides good toughness (high impact values) can reduce the potential for cracking.
Making the Filler Metal Choice
Choosing the right filler metal for welding AR plate to dissimilar steels is comparable to choosing one for other welding applications. The base metal to which you are welding to the AR plate will determine which filler metal is the most appropriate. Some of the most common ASTM grade base metals joined to AR plate include: A36, A572 GR50, A656 GR80 and A514 steels.
Your filler metal choice depends on the tensile strength of the base material being welding to the AR plate and whether you are repairing the plate or fabricating a new weldment. As a rule, choosing filler metals with lower tensile strengths and lower hydrogen will yield the best results, e.g. the least amount of potential for cracking (See figure 2 for filler metal recommendations).
Note: Different AR plate manufacturers recommend different tensile strengths for welding AR plate to a particular grade base metal. You should always check those recommendations before making your final filler metal selection.
Filler Metals for Repair
Stick Electrodes
To repair or replace AR plate on existing equipment, using a low hydrogen stick electrode with a basic slag system (an AWS E7018 rod, for example) can provide distinct advantages such as: excellent as-welded mechanical properties, high resistance to hydrogen pickup and the ability to weld through contaminants (light mud, rust, or oil) that can accumulate on serviced heavy equipment. More importantly, low hydrogen basic slag stick electrodes have good toughness properties to accommodate for the residual stress of welded AR plate-the welds have good resistance to cracking.
As with other welding applications, stick electrodes offer the benefit of portability for field repairs-they are lightweight and do not require shielding gas-and many welding operators feel comfortable using them.Disadvantages to using stick electrodes include: slag removal, frequent electrode changes, which make them inefficient for large AR plate repairs, and the potential for lower quality bead appearance.
Self-Shielded (Gasless) Flux Cored Wire
As with stick electrodes, self-shielded flux cored wires work well for repairing AR plate outdoors. They do not require shielding gas, which eliminates the need to haul gas tanks into the field. The main disadvantageof self-shielded flux cored wires is the lack of required impact properties (typical for classifications T-4, T-7, T-11) which increases the potential for cracking.
Gas-Shielded Flux Cored Wire
Gas-shielded flux cored wire offers the greatest versatility for welding AR plate to heavy equipment (it can be used for fabrication as well as repairs). T-5, basic slag gas-shielded flux cored wires are recommended due to their toughness, high resistance to hydrogen pickup and ability to weld through light rust and mill scale. These features improve the crack resistance of the filler metal.
Note that flux cored wire does produce slag, which will need to be removed if multiple passes are to be welded.
Filler Metals for Fabrication
Solid Wire
Solid wire, such as an ER70S-3 or ER70S-6 welded on A36 base metal, is best suited for welding AR plate onto a new heavy equipment structure indoors on clean materials. Advantages of solid wire include: lower purchase cost, lack of slag removal and nice bead appearance. Using solid wire also offers the advantage of familiarity: it is a more common filler metal with which operators often feel comfortable using.
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| Figure 2 |
Disadvantages include: limited de-oxidizers in the filler metal, required use of shielding gas and the potential for heavy spatter on dirty materials (rust, mill scale, etc).
Metal Cored Wire
Metal cored wires perform very well on clean materials and even light mill scale and rust and create little to no spatter. In instances of poor fit-up between the AR plate and the base metal, metal cored wire tends to bridge those gaps more efficiently than other filler metals. It also offers higher deposition rates than a solid wire to help increase production.
Most importantly, metal cored wire can increase travel speeds, which minimizes heat input that could lead to rapid cooling and, ultimately, cracking. Most metal cored wires also offer excellent toughness properties.
Gas-Shielded Flux Cored Wire
For welding AR plate to a new piece of heavy equipment, T-5 basic slag gas-shielded flux cored wires are recommended due to their toughness, ability to resist hydrogen pickup and capacity to weld over light rust and mill scale.
Note that flux cored wire does produce slag, which requires removal and can cause additional time and expenses for cleanup.
Piecing It All Together
In the end, choosing filler metals for welding AR plate is as much a matter of education as it is a matter of requirements. Considering your base metal and remembering to use lower tensile strength filler metals with high toughness and low hydrogen content is important. Applying proper pre-heat for the given material thickness and choosing an appropriate joint design is equally important.
In addition to the above factors, you have to determine your requirements or goals: do you simply want to get a piece of equipment back in service or do you want to weld AR plate on a new weldment and make it aesthetically pleasing?
Whichever the case may be, armed with some basic information, you can easily avoid cracks, not to mention time and frustration, when welding AR plate.