How to choose the right filler metals to weld AR plate
July 11, 2006
Before welding abrasion-resistant plate, it's important to take certain precautions and choose the most appropriate filler metal for your application and weld metal.
It's important to consider ways to make any welding process more efficient and 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 you're repairing service equipment or fabricating a new part or structure that requires the protection of AR plate—are vital to ensuring welding success.
Typical AR plate products are assigned numbers ranging from 200 to 500 in their name; AR 200, AR 400, and AR 500 are examples. These numbers designate the hardness of the material in Brinell (BHN), which can 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 (about 42 HRC), AR 450 (about 46 HRC), and AR 500 (about 50 HRC), are the most common. Plates can range in thickness from 1/2 inch to 2 in. and thicker and come in a variety of lengths and widths depending on the manufacturer.
Because AR plate has such a high hardness, heavy equipment manufacturers and job shops 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.
Keep in mind that AR plate is designed to protect equipment against wear; it shouldn't be used in a structural or load-bearing design. To ensure the best results, review your application with an AR plate manufacturer.
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 are rapid cooling, highly restrained joints, excessive hydrogen in the weld metal, and filler metals that have limited resistance to cracking.
Preheating the base metal before welding is an important defense against rapid cooling and can help reduce hydrogen levels; both are factors that can lead to cracking. The material to be preheated and its thickness determine the proper preheat temperature (see Figure 1).
Maximum interpass should not exceed 400oF
to ensure hardness is maintained.
Joint design is another consideration. If possible, don't 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 short, small fillet welds also can reduce heat input and overall residual stresses on the AR plate to help minimize cracking.
A filler metal with the least amount of hydrogen content—as well as one that provides good toughness (high impact value)—also helps reduce cracking potential.
Choosing the right filler metal for welding AR plate to dissimilar steels is much like choosing filler metal for other welding applications. The base metal you are welding the AR plate to will determine which filler metal is most appropriate. Common ASTM-grade base metals joined to AR plate are A36, A572 GR50, A656 GR80, and A514 steels.
Your filler metal choice will depend on the tensile strength of the base material being welded to the AR plate and whether you're repairing the plate or fabricating a new weldment. As a rule, filler metals with low tensile strengths and low hydrogen will yield the best results with the least amount of potential for cracking (see Figure 2).
Filler Metal Recommendations for Abrasion-resistant Plate.
Remember, different AR plate manufacturers recommend different tensile strengths for welding AR plate to a particular grade of base metal. Always check those recommendations before making your final filler metal selection.
Filler Metals for Repair. Three basic types of filler metals can be used to repair AR plate:
Filler Metals for Fabrication. As with repair, three main types of wire are suitable for fabricating AR plate:
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 low-tensile-strength filler metals with high toughness and low hydrogen content are important. Applying proper preheat for the given material thickness and choosing an appropriate joint design are equally important.
In addition to these factors, you must 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 its appearance appealing?
Whichever the case, if you're armed with basic information, you can avoid cracks—as well as time and frustration—when welding AR plate.
Keith Packard is product manager, tubular wire, at Hobart Brothers, 400 Trade Square, Troy, OH 45373, 937-332-4000, www.hobartbrothers.com.