AR (abrasion-resistant) plate is quench-and-tempered steel designed for applications where abrasive wear destroys standard structural steel. Buckets, liners, chutes, crusher plates, dozer blades, and dump truck bodies use AR400 and AR500 to resist the grinding action of rock, sand, ore, and other abrasive materials. The quench-and-temper process gives AR plate its hardness, and welding partially reverses that process in the heat-affected zone. Your job is to make sound welds while minimizing the damage to the plate’s hardness.
AR400 (360-440 BHN, 38-47 HRC) is the workhorse grade for general wear applications. AR500 (470-540 BHN, 48-54 HRC) handles more severe abrasion but is harder to weld. Both use similar procedures with adjustments for the higher carbon equivalent of AR500.
AR Plate Properties
| Property | AR400 | AR450 | AR500 |
|---|---|---|---|
| Brinell Hardness | 360-440 BHN | 420-480 BHN | 470-540 BHN |
| Rockwell Hardness | 38-47 HRC | 43-50 HRC | 48-54 HRC |
| Tensile Strength | 180 ksi min | 200 ksi min | 230 ksi min |
| Carbon (typical) | 0.20-0.30% | 0.25-0.35% | 0.30-0.40% |
| Manganese (typical) | 1.00-1.60% | 1.00-1.60% | 1.00-1.60% |
| Carbon Equivalent (CE) | 0.45-0.55 | 0.50-0.60 | 0.55-0.70 |
The chemistry varies by manufacturer. SSAB (Hardox brand), Arcelor, JFE, and domestic mills all produce AR plate with slightly different compositions while meeting the same hardness specification. Always check the mill test report (MTR) for the actual carbon and carbon equivalent of the specific plate you’re welding. The CE drives preheat requirements.
Preheat Requirements
| Grade | Thickness Under 1" | Thickness 1" to 2" | Thickness Over 2" |
|---|---|---|---|
| AR400 (CE < 0.52) | 150-200F | 200-300F | 300-400F |
| AR400 (CE 0.52+) | 200-300F | 300-400F | 400F |
| AR450 | 200-300F | 300-400F | 400F |
| AR500 | 300-400F | 400F | 400-500F |
Interpass temperature maximum: 400F. Don’t exceed 400F between passes. Higher interpass temperatures extend the soft zone width by keeping more of the HAZ above the plate’s tempering temperature. The goal is to keep heat input localized and controlled.
Verify preheat with temperature crayons or contact thermocouples placed 3 inches from the weld on the side opposite the heat source.
Filler Metal Selection
The filler metal for AR plate welds doesn’t need to match the plate’s hardness. The weld attaches the AR plate to the structural frame. The wear surface is the plate itself, not the weld. Using a lower-strength, more ductile filler actually improves joint reliability because it reduces residual stress and cracking risk.
Standard Fillers
E7018 (stick): The default for AR plate. Low hydrogen, 70 ksi tensile, ductile deposit. Prequalified under most structural codes. Keep rods in an oven at 250-300F.
ER70S-6 (MIG): Standard solid wire with 75/25 Ar/CO2 or straight CO2. Inherently low hydrogen content (H4 or better). Good for production welding of wear plate liners.
ER70S-3 (MIG): Alternative to S-6 on clean, prepped AR plate. Fewer silica islands on multi-pass welds.
E71T-1 (flux-core, gas-shielded): High deposition rate for attaching large wear plate sections. The go-to for production shops doing excavator bucket rebuilds and liner installations. Must be H8 designation or better.
Higher-Strength Fillers
E8018-C1 (stick) / ER80S-D2 (MIG/TIG): Used when the weld must carry significant load or when the AR plate also serves a structural function. The 80 ksi deposit provides a closer strength match to the plate, but the higher residual stress means stricter preheat and hydrogen control.
E11018 and above: Rarely needed for AR plate attachment. These are used when the weld itself needs to be wear-resistant, which is a hardfacing application rather than a structural attachment.
| Application | Stick | MIG | Flux-Core |
|---|---|---|---|
| AR plate to mild steel frame | E7018 | ER70S-6 | E71T-1 |
| AR plate to AR plate | E7018 or E8018-C1 | ER70S-6 or ER80S-D2 | E71T-1 |
| AR plate to structural (load-bearing) | E8018-C1 | ER80S-D2 | E81T1-Ni1 |
| Hardfacing overlay on AR plate | CrC hardfacing electrode | CrC hardfacing wire | CrC flux-core wire |
HAZ Softening: The Unavoidable Tradeoff
Every weld on AR plate creates a softened zone in the HAZ. Understanding and minimizing this zone is the central challenge of AR plate welding.
What Causes the Soft Zone
AR plate achieves its hardness through quench-and-temper processing. The mill heats the plate above the austenitizing temperature (about 1550-1650F), quenches it (rapid cooling), then tempers it at a controlled temperature to achieve the target hardness. Tempering temperature for AR400 is typically 350-500F. For AR500, it’s even lower (250-400F).
During welding, the HAZ adjacent to the weld heats above the plate’s original tempering temperature. This re-tempers the quenched microstructure, reducing hardness. The higher the temperature (closer to the weld), the more softening occurs. The zone directly adjacent to the fusion line heats well above the austenitizing temperature and re-quenches on cooling, recovering some hardness, but the band beyond it (which heated to 500-1200F) gets progressively over-tempered.
HAZ Hardness Profile
| Zone | Peak Temperature | AR400 Hardness After Welding |
|---|---|---|
| Weld metal | Above melting (2700F+) | 200-250 BHN (E7018 deposit) |
| Coarse-grain HAZ | 2000-2700F | 380-450 BHN (re-quenched, may harden) |
| Fine-grain HAZ | 1600-2000F | 350-400 BHN (slight softening) |
| Intercritical HAZ | 1350-1600F | 280-350 BHN (significant softening) |
| Subcritical HAZ (soft zone) | 500-1350F | 250-300 BHN (maximum softening) |
| Unaffected base metal | Below 500F | 360-440 BHN (original hardness) |
The “soft zone” (subcritical HAZ) is 5-15 HRC softer than the base plate. On AR400, this band drops from ~400 BHN to ~280 BHN. The width of this band depends on heat input. More heat = wider soft zone.
Minimizing the Soft Zone
Use stringer beads. No weaving. Stringer beads concentrate heat in a narrow band. Weave beads spread heat across a wider area, expanding the soft zone.
Control interpass temperature. Stay below 400F between passes. Higher interpass temps keep a larger area above the tempering threshold, widening the soft zone.
Moderate amperage. Run at the minimum amperage for good fusion. Excess heat input widens the HAZ.
Fast travel speed. Within the range that maintains proper fusion and bead quality, faster is better on AR plate.
Minimize number of passes. Each pass re-heats the HAZ from the previous pass. Fewer passes = less cumulative thermal damage. Size the filler and joint to minimize the total pass count.
You can’t eliminate the soft zone. You can only minimize its width. On AR400 with controlled technique, the soft zone is typically 1/4 to 3/8 inch wide. With sloppy technique (high heat, weaving, high interpass), it can exceed 3/4 inch.
Joint Design for Wear Plates
Most AR plate installations involve welding wear plate liners onto structural steel frames. The joint design should:
Minimize constraints on the AR plate. Fillet welds on two or three sides (not all four) allow the plate to move slightly under thermal cycling and impact loading without cracking.
Position welds away from the wear surface. If the plate is being abraded from one face, weld on the opposite face so the weld and HAZ soft zone aren’t exposed to direct wear.
Use intermittent welds where possible. On long liner installations, intermittent fillet welds (4 inches on, 8 inches off, for example) provide adequate attachment while reducing total heat input and the extent of the softened zone. The plate between welds retains full hardness.
Plug welds for flat liner attachment. Holes drilled through the structural backing allow plug welds that hold the liner flat without edge welds. This keeps the wear face and its edges at full hardness.
| Joint Type | Application | Notes |
|---|---|---|
| Fillet (continuous) | Bucket lips, high-load edges | Maximum attachment, maximum soft zone |
| Fillet (intermittent) | Liner panels, chute sides | Reduced heat input, partial soft zone |
| Plug weld | Flat liner panels | Minimal edge damage, hidden welds |
| Butt (AR to AR) | Large plate fabrication | Full penetration, V-groove, higher preheat |
| Lap joint | Overlapping liners | Simple, limited strength |
Common AR Plate Welding Problems
Hydrogen cracking in the HAZ. Caused by insufficient preheat, high-hydrogen consumables, or moisture contamination. Cracks appear 24-48 hours after welding, typically in the coarse-grain HAZ adjacent to the fusion line. Prevention: preheat per chart, low-hydrogen consumables with proper storage, clean joint surfaces.
Excessive soft zone width. Caused by high heat input, weaving, high interpass temperature, or too many passes. Prevention: stringer beads, controlled interpass, moderate amperage, efficient pass count.
Plate distortion. AR plate is typically thin relative to its area (3/8 to 1 inch). Welding heat causes distortion just like any thin plate. Prevention: balanced welding sequence, alternating sides, proper clamping, skip welding.
Delamination at weld. On very hard grades (AR500+), the high residual stress at the weld can cause the plate to delaminate or spall adjacent to the HAZ. Prevention: higher preheat, ductile filler (E7018), controlled cooling, stress relief (1050-1100F) if specification allows.
Overheating the plate. Running excessively hot or allowing the plate to glow red destroys the quench-and-temper hardness far beyond the normal HAZ. If any area of AR plate glows visibly during welding, you’ve already lost significant hardness over a wide area. Keep heat input controlled and monitor with interpass temperature checks.
Cutting AR Plate
AR plate’s hardness makes cutting more difficult than standard structural steel. Plan your cutting method before starting fabrication.
Plasma cutting works well on AR plate up to 1-1/2 inch. The cut quality is comparable to mild steel. The HAZ from plasma cutting is narrow (typically 0.010-0.030 inch) and doesn’t significantly affect the plate’s bulk hardness.
Oxy-fuel cutting works but the high-carbon content requires a slower cut speed and sometimes a preheat pass (especially on AR500). The HAZ from oxy-fuel is wider than plasma and creates a hard zone at the cut edge that can crack during handling or welding. Consider grinding the cut edge before welding to remove the hardened layer.
Abrasive cutting (sawing or abrasive wheel) is possible but slow. Standard bi-metal band saw blades struggle with AR500. Carbide-tipped blades work better.
Shearing is limited to thinner gauges (typically under 3/8 inch for AR400). AR plate dulls shear blades faster than mild steel. Expect reduced blade life.
For hardfacing overlay techniques that add wear resistance beyond the base plate’s hardness, see the hardfacing guide.